an assessment and comparison of third molar … · page i an assessment and comparison of third...

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AN ASSESSMENT AND COMPARISON OF THIRD MOLAR DEVELOPMENT IN RELATION

TO CHRONOLOGICAL AGE IN A WESTERN AUSTRALIAN AND A SOUTH INDIAN

POPULATION

Geetha Govindaiah Varadanayakanahally

Centre for Forensic Science

University of Western Australia

This thesis is presented in partial fulfilment of the requirements for the

Master of Forensic Science

2011

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Dedication

I would like to dedicate this research to my husband, Harish and my parents without whose continuous support this all would have not been possible.

“Everything is achievable, the more you want it, sooner you will get it“ Author unknown

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Declaration

I declare that the research presented in this thesis, for the Master of Forensic Science at the University of Western Australia, is my own work. The results of the work have not been submitted for assessment, in full or part, within any other tertiary institute, except where due acknowledgement has been made in the text.

…………………………………………………

Geetha Govindaiah Varadanayakanahally

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Abstract

In a forensic investigation the estimation of age at death is an important step

towards the identification of unknown human skeletal remains. An accurate

estimation of age will significantly narrow the field of possible matching

identities. In order to achieve this, there are many skeletal methods available to

the forensic odontologist and anthropologist, including assessment of skeletal

and dental maturation (in the juvenile age range). However, the rate of skeletal

maturation can be affected by environmental factors that include poor nutrition

and illness. Dental development, however, is under strict genetic control and is

strongly correlated to chronological age. This makes teeth a reliable age marker

for assessment in forensic investigations.

There are many published methods for evaluating and quantifying dental

maturation in order to estimate personal age. One of the more widely applied

methods was first described in 1973 by Demirjian and Goldstein, who studied

French-Canadian children. The present study applies a modification of that

method to statistically quantify the timing of third molar mineralization in a

Western Australian and South Indian population. The primary aim is to evaluate

how accurately age can be estimated using the third molars, to assess ethnic

differences in mineralization rates, and to formulate population specific

standards for age estimation using this tooth. Comparisons between sexes,

upper and lower arches and side differences (within and between populations)

are made to provide statistically usable reference data of mineralization rates in

the third molars specific to Western Australia and South India. In addition, the

degree of third molar agenesis is assessed in both populations.

The sample comprises 561 conventionally taken orthopanthomographs (OPG’s)

representing 312 Western Australian (173 males and 139 females aged between

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7 to 30 years) and 249 South Indian (124 males and 125 females aged between

(10 to 30 years) individuals. Mineralization status was assessed in each third

molar according to the eight stage (A – H) tooth classification system proposed

by Demirjian et al. (1973). Descriptive statistics, including the mean age and

standard deviation for individual third molar mineralization stages, are

presented for each population. Comparisons between sexes, upper and lower

arches, and left-right sides were statistically quantified using the Mann –

Whitney U test. All statistical analysis was performed using the SPSS software

18.00 package (SPSS Inc. Chicago, IL).

In the Western Australian population it was found that in males the upper third

molars complete development (stage H) by 23.47 years and the lowers by 23.06

years. In females the upper third molars are fully formed by 23.55 years and the

lowers by 24.62 years. In the South Indian population, the upper and lower third

molars complete development by 23.57 and 24.40 years respectively in the male

sample. In females the upper and lower third molars complete development by

23.45 and 24.10 years respectively.

Overall comparisons of third molar maturity between males and females in the

Western Australian population showed that the former generally achieved

maturity earlier than the latter; by approximately 7 to 11 months. In the South

Indian population, male dental development occurred earlier, by approximately

10 to 13 months. Mineralization of the upper (maxillary) third molars in both

populations occurred earlier than the mandibular dentition except for the

Western Australian males which showed the reversal. There were no significant

bilateral differences in the timing of third molar mineralization in either

population. It was found that Western Australian males and females generally

achieved third molar maturity earlier than the South Indians (by approximately

10 to 20 months). An important outcome of this research is a series of statistics

useful for predicting dental age in both populations.

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Regarding the frequency of missing individual third molars, the upper right

third molar were found to be the most commonly missing tooth in the Western

Australian (40.4%) and South Indian (22.5%) population. As this variability in

third molar development is mostly related to population differences, these

findings should be taken into account in forensic examinations when assessing

the viability of using this tooth.

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Acknowledgements

This project has become a dream come true for me as many goals were set and

achieved. I was blessed with the support, guidance of many people in life.

Though it will not be enough to express my gratitude on words to all those

people who helped me, I would still like to take this opportunity to thank them.

Professional Acknowledgement

First and foremost, I would like to thank the University of Western Australia for

offering me an ideal environment to continue my intellectual journey and

challenge myself everyday.

Dr. Daniel Franklin, my supervisor, I can never thank him enough for his

guidance, inspiration and patience to get the best out throughout the entire

research. I would also like to thank my co-supervisor Dr. Peter Mack for his

continued support and guidance.

The Centre for Forensic Science (CFS)

Thank you to the Centre for Forensic Science for providing me an wonderful

experience. My extended gratitude to Professor Ian Dadour (Director, Forensic

Entomologist, CFS) for providing admittance to the forensic science program. As

well thanks to Alexandra Knight (Administrative Assistant, CFS) for her patience

in answering numerous queries and e-mails.

Princes Margaret Hospital for Children

I would like to express my gratitude to all those who have offered me their time

while collecting numerous data for my research. Firstly Princes Margaret

Hospital for providing the Western Australian sample (OPG’s), The Ramaiah

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institute and KLE institute of Dental Sciences, Bangalore, India for providing the

South Indian sample. Thank you all.

Personal Acknowledgement

I would like to thank my husband Harish, and my family as they form the

backbone and origin of my happiness. Their love and support without any

complaint or regret has enabled me to complete this project. Also my heartfelt

gratitude to Professor Anil Sukumaran and Dr. Girish Kumar for helping hands

in this project. Thank you all again as I am deeply indebted.

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Table of Contents

Chapter One

Introduction ......................................................................................................................... 1

1.1. Background to the study .......................................................................................... 1

1.2. The importance and significance of population specific standards ......... 3

1.3. Aims of the project ..................................................................................................... 4

1.4. Sources of material .................................................................................................... 6

1.5. Thesis format ............................................................................................................... 6

Chapter Two

Dental Anatomy, Histology and Nomenclature ........................................................ 7

2.1. Introduction ................................................................................................................. 7

2.2. The Dentition ............................................................................................................... 7

2.2.1.Primary dentition ..........................................................................................................7

2.2.2.Permanent dentition ....................................................................................................8

2.3. Dentition periods ........................................................................................................ 9

2.3.1.Primary dentition period ...........................................................................................9

2.3.2.Mixed dentition period ............................................................................................ 10

2.3.3.Permanent dentition period .................................................................................. 10

2.4. Tooth numbering systems .................................................................................... 11

2.4.1.Universal numbering system ................................................................................. 11

2.4.2.The Zsigmondy/Palmer Notation System ........................................................ 12

2.4.3.Federation Dentaire International (FDI) .......................................................... 12

2.5. General dental anatomy terminology .............................................................. 13

2.5.1.Divisions of the tooth ................................................................................................ 13

2.5.2.Tissues of the tooth ................................................................................................... 14

2.6. Dental Nomenclature ............................................................................................. 15

2.7. The development and eruption of the teeth .................................................. 16

2.7.1.Stages of tooth development ................................................................................. 16

2.7.2.Eruption ......................................................................................................................... 17

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2.8. The anatomy of the primary dentition............................................................. 19

2.8.1.The primary maxillary dentition: ........................................................................ 19

2.8.2.The primary mandibular dentition: .................................................................... 21

2.8.3.Importance of the primary teeth: ........................................................................ 21

2.8.4.Morphological differences between the primary and the permanent teeth ........................................................................................................................................... 21

2.9. The anatomy of the permanent third molars ................................................ 22

2.9.1.An overview of the maxillary third molars ...................................................... 22

2.9.2.The morphology of the maxillary third molar ................................................ 23

2.9.3.Clinical consideration of the maxillary third molars .................................... 26

2.9.4.An overview of the mandibular third molars .................................................. 26

2.9.5.The morphology of the mandibular third molars ......................................... 27

2.9.6.Clinical considerations of the Mandibular third molars ............................. 28

2.9.7.Absence of the third molars ................................................................................... 29

2.9.7.1.Human molecular genetics: .......................................................................... 30

2.10. Histology of the dental tissues ......................................................................... 30

2.10.1.Enamel ......................................................................................................................... 31

2.10.2.Dentin ........................................................................................................................... 32

2.10.3.Dental pulp ................................................................................................................. 34

Chapter Three

Literature Review ............................................................................................................ 35

3.1. Introduction .............................................................................................................. 35

3.2. Dental age estimation ............................................................................................ 36

3.3. Dental age estimation methods .......................................................................... 37

3.3.1.Moorrees et al. (1963) .............................................................................................. 38

3.3.2.Demirjian et al. (1973) ............................................................................................. 38

3.3.3.Ubelaker (1999) ......................................................................................................... 40

3.3.4.Willems et al. (2001) ................................................................................................ 40

3.4. Dental age estimation using the third molars ............................................... 41

3.4.1.Mincer et al. (1993) ................................................................................................... 41

3.4.2.Chaillet et al. (2004) .................................................................................................. 42

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3.4.3.Arany et al. (2004) ..................................................................................................... 42

3.4.4.Prieto et al. (2005) ..................................................................................................... 43

3.4.5.Olze et al. (2006) ........................................................................................................ 43

3.4.6.Zeng et al. (2010) ....................................................................................................... 44

3.5. Brief review of other methods ............................................................................ 45

3.5.1.Gleiser and Hunt (1955) .......................................................................................... 45

3.5.2.Gustafson and Koch (1974) .................................................................................... 46

3.5.3.Harris and Nortje (1984) ........................................................................................ 46

3.5.4.Kullman et al. (1992) ................................................................................................ 46

3.6. Australian Research ............................................................................................... 46

3.6.1.Farah et al. (1999) ..................................................................................................... 46

3.6.2.McKenna (2002) ......................................................................................................... 47

3.6.3.Flood (2007) ................................................................................................................ 47

3.6.4.Blenkin and Evans (2011) ...................................................................................... 48

3.7. Indian research: ....................................................................................................... 48

3.7.1.Koshy and Tandon (1998) ...................................................................................... 48

3.7.2.Prabhakar et al. (2002) ............................................................................................ 49

3.7.3.Hegde and Sood (2002) ........................................................................................... 49

3.7.4.Rai et al. (2009)........................................................................................................... 50

3.8. Summary ..................................................................................................................... 50

Chapter Four

Materials and Methods .................................................................................................. 51

4.1. Materials ..................................................................................................................... 51

4.1.1.Population ..................................................................................................................... 54

4.1.2.Orthopantomographs (OPGs) ............................................................................... 54

4.2. Methods ....................................................................................................................... 55

4.2.1.Introduction ................................................................................................................. 55

4.2.2.Data Collection ............................................................................................................ 55

4.2.2.1.Demirjian et al. (1973) stage descriptions .............................................. 56

4.2.2.2.Criterion for allocation of stages ................................................................. 58

4.2.2.3.Assessment of intra-observer error .......................................................... 59

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4.2.3.Data Analysis ............................................................................................................... 60

4.2.3.1.Statistical analyses ........................................................................................... 60

Chapter Five

Results ................................................................................................................................. 62

5.1. Introduction .............................................................................................................. 62

5.2. Assessment of Intra-observer error ................................................................. 62

5.3. Descriptive statistics: Western Australian population .............................. 62

5.3.1.Upper Right Third Molar ......................................................................................... 63

5.3.2.Upper Left Third Molar ............................................................................................ 64

5.3.3.Lower right third molar ........................................................................................... 66

5.3.4.Lower left third molar .............................................................................................. 67

5.3.5.Overall development of all four third molars in males and females ...... 69

5.4. Comparative statistics: comparison of age of attainment of developmental stages A – H between the upper (maxillary) and lower (mandibular) third molars. .......................................................................................... 70

5.5. Comparative statistics: comparison of age of attainment of developmental stages A – H between the right and left third molars. .......... 71

5.6. Descriptive statistics: South Indian population ............................................ 73

5.6.1.Upper Right Third Molar ......................................................................................... 73

5.6.2.Upper Left Third Molar ............................................................................................ 74

5.6.3.Lower right third molar ........................................................................................... 76

5.6.4.Lower left third molar .............................................................................................. 78

5.6.5.Overall development of all four third molars in males and females ...... 79

5.7. Comparative statistics: comparison of age of attainment of developmental stages A – H between the upper (Maxillary) and lower (Mandibular) third molars ........................................................................................... 80

5.8. Comparative statistics: comparison of age of attainment of developmental stages (A – H) between the right and left third molars ....... 82

5.9. Comparative statistics: Comparison of age of attainment of developmental stages A – H for the upper (Maxillary) and lower (Mandibular) third molars between Western Australian and South Indian males and females ........................................................................................................... 83

5.9.1.Upper Third Molars (Male) .................................................................................... 84

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5.9.2.Lower Third Molars (Male) .................................................................................... 86

5.9.3.Upper third molars (Female) ................................................................................ 88

5.9.4.Lower third molars (Female) ................................................................................ 89

5.10. Absence of the third molars in the Western Australian and South Indian sample ................................................................................................................... 91

Chapter Six

Discussion and Conclusions ......................................................................................... 92

6.1. Introduction .............................................................................................................. 92

6.2. Developmental age range, sex differences and population variability of the third molars ............................................................................................................... 93

6.2.1.Overall developmental age range of the third molars in the Western Australian and South Indian populations .................................................................... 94

6.2.2.Overall sex differences in the third molar development in the Western Australian and South Indian population. ..................................................................... 94

6.2.3.Comparisons of third molar development between Western Australian and South Indian individuals............................................................................................ 95

6.2.4.Comparisons of third molar development to other populations ............. 96

6.3. Jaw differences in third molar development in a Western Australian and a South Indian sample ........................................................................................... 99

6.4. Bilateral variation in third molar development within Western Australian and South Indian individuals .............................................................. 100

6.5. Absence of the third molars ............................................................................... 101

6.6. Forensic importance of the third molars ...................................................... 102

6.7. Potential limitations of the present study .................................................... 103

6.8. Recommendation for future research ............................................................ 104

6.9. Conclusions .............................................................................................................. 104

References ........................................................................................................................ 106

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List of Tables:

Table 2.1: Sequence of chronology of tooth eruption of the primary dentition

(Avery, 1992).

Table 2.2: Sequence of chronology of tooth eruption of the permanent dentition

(Avery, 1992).

Table: 2.3: The development and eruption sequence of the Maxillary third

molars (Wheeler, 2003)

Table 2.4: The development and eruption sequence of the Mandibular third

molars (Wheeler, 2003)

Table 3.1: Description of the Demirjian et al. (1973) dental developmental stages

(A – H).

Table 4.1: Age and sex distribution of the Western Australian population.

Table 4.2: Age and sex distribution of the South Indian population.

Table 4.3: Interpretation of Kappa Value (from Landis and Koch 1997).

Table 5.1: Kappa values, indicating levels of agreement.

Table 5.2: Descriptive values (including mean and standard deviation) of stages

A - H for the upper right third molar in males and females.


A - H for the upper left third molar in males and females.


A - H for the lower right third molar in males and females.


A - H for the lower left third molar in males and females.

Table 5.6: Overall descriptive values (including mean, standard deviation and

significance) of stages A- H for all four third molars in males and females.

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Table 5.7: Comparative values (including mean, standard deviation and

significance values) for the age of attainment of developmental stages (A – H) for

the upper and lower third molar.


significance values) for the age of attainment of the developmental stages (A- H)

for the right and left third molars.


A - H for the upper right third molar in males and females.

Table 5.10: Descriptive values (including mean and standard deviation) of

stages A - H for the upper left third molar in males and females.


stages A - H for the lower right third molar in males and females.


stages A - H for the lower left third molar in males and females.

Table 5.13: Overall descriptive values (including mean, standard deviation and

significance) of stages A- H for all four third molars in males and females.


significance values) for the age of attainment of the developmental stages (A –

H) for the upper and lower third molars.


significance values) for the age of attainment of the developmental stages (A –

H) for the right and left third molars.


significance values) for the age of attainment of developmental stages A - H for

the upper third molars in Western Australian and South Indian males



the lower third molars in Western Australian and South Indian males

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the upper third molars for Western Australian and South Indian females



the lower third molars in Western Australian and South Indian females

Table 5.20: Percentage of missing all four third molars in different age groups

Table 5.21: Percentage of missing individual third molars in Western Australian

and South Indian Sample

Table 6.1: Mean age (in years) of attainment of Demirjian et al. (1973) stages (A,

D and H) in several populations for males and females.

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List of Figures:

Figure 2.1: Occlusal view of the primary dentition along with types of teeth

(from Thomas et al. 2006).

Figure 2.2: Occlusal views of permanent dentition along with types of teeth

numbered using universal dental numbering system (from Thomas et al. 2006).

Figure 2.3: Dentition Stages (from Fuller and Denehy, 1984).

Figure 2.4: Tissues of the tooth (from Short and Levin-Goldstein, 2002).

Figure 2.5: Illustration and definition of dental Nomenclature (from Wheeler,

2003)

Figure 2.6: The deciduous dentition – facial view (from Woelfel and Scheid,

1997)

Figure 2.7: Various views of the Maxillary third molar (from Thomas et al. 2006).

Figure 2.8: Crown form of the Maxillary right third molar (from Thomas et al.

2006).

Figure 2.9: Various views of the Mandibular right third molar (from Thomas et

al. 2006).

Figure 2.10: Diagramatic representation of rods in enamel (from Orban, 1976).

Figure 2.11: Composite diagram of a human tooth in cross-section illustrating

the different types of dentin (from Nanci, 2008).

Figure 2.12: Coronal section of a molar showing the dental pulp zones (from

Orban, 1976).

Figure 4.1: Age and sex distribution of the Western Australian population.

Figure 4.2: Age and sex distribution of the South Indian population.

Figure 4.3a-h: Stage A-H of the Demirjian et al. (1973) method.

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Figure 5.1: Illustration of mean age of attainment of Demirjian et al. (1973)

stages for the upper right third molar in males and females.


stages for the upper left third molar in males and females.


stages for the lower right third molar in males and females.


stages for the lower left third molar in males and females.


stages for the males and females.

Figure 5.6: Mean age of attainment of Demirjian et al. (1973) stages (A – H) for

the upper and lower third molars

Figure 5.7: Mean age of attainment of (A – H) Demirjian et al. (1973) stages for

the right and left third molars.





Figure 5.10: Illustration of mean ages of attainment of Demirjian et al. (1973)


Figure 5.11: Illustration of mean age of attainment of Demirjian stages for the

lower left third molar in males and females.




the upper and lower third molars.

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the right and left third molars.

Figure 5.15: Mean age of attainment of Demirjian et al. (1973) stages (A – H) in

the Upper third molar in males for Western Australia and South India.


the lower third molar in males for Western Australia and South India.


the upper third molar in females for Western Australian and South India


the lower third molar in females for Western Australia and South India.

Chapter One

Introduction

1.1. Background to the study

Forensic odontology, also known as forensic dentistry, is the application of

dentistry for criminal justice purposes. It involves the proper collection,

handling, examination, and evaluation of dental evidence (Neville et al. 2002).

That evidence can then be used in criminal investigation and to identify human

remains.

The estimation of age at death is an important step towards the identification of

human remains and has a long tradition in the field of forensic sciences. Forensic

age estimation has been beneficial in assisting authorities in narrowing the

search of possible matches for unknown victims, especially in the identification

of mass disaster victims (Herschaft et al. 2006). Age estimation of living

individuals is also an important current focus of forensic research, especially in

multicultural societies where legal and illegal immigration is increasing and

documentary evidence of age may be lacking (Bosmans et al. 2005).

Depending on the stage of the life cycle (eg: juvenile or adult), specific methods

are available for age estimation. Franklin (2010: 1-2) states that “It is well-

documented that age estimation is usually most accurate in individuals still

growing; in mature individuals however, most standards generally rely on the

highly variable degeneration of bones (e.g. pubic symphysis; sacro-iliac joint;

sternal rib ends). The latter characteristics are more influenced by

environmental factors, as opposed to the more predictable and well-

documented developmental markers characteristic of juveniles (e.g. dental

development; skeletal growth and maturation)”.

Dental emergence and mineralization are the main characteristics assessed for

forensic age estimation in children and young adults (Olze et al. 2003). Tooth

development is strongly correlated with chronological age, as the teeth

consistently develop in relation to age (even under conditions of chronic illness

and nutritional deficiency), which indicates that the process is under strict

genetic control (Cardoso, 2007). This makes the teeth a reliable age marker to

use in forensic anthropology and odontology. However, the reliability of age

estimates based on dental development is not uniform from birth to adulthood.

After the age of 14 years, when most of the teeth are in the process of

completing apical closure (Kullman et al. 1992), dental age estimation becomes

less accurate. The only teeth still forming after that age are the third molars,

which are highly variable in their pattern of formation and the age of complete

mineralization varies widely (Kullman et al. 1992, Bolanos et al. 2003). A further

limitation is that this tooth is often congenitally absent. For example, Thompson

et al. (1974) summarized published research on a variety of populations and

found that the proportion of subjects with one to four missing third molars

ranged from 9 to 35%. This issue is discussed further in Chapter Two.

The teeth are the most durable element of the human skeleton and their

structures provide an inherent resistance to erosion, deterioration, and fire long

after death. The teeth, although resistant to most physical trauma, can become

brittle and fragile when subjected to temperatures over 600°C (Karkhanis and

Franklin, 2010). The teeth demonstrate a variety of morphologies and varied

conditions of wear, trauma, disease, and professional manipulation. Thus an

approximate age and useful indications of probable sex, ethnicity, occupation,

personal habits, medical history, and environment can often be revealed

through the analysis of teeth (Rogers, 1988).

Dental techniques that use progressive morphological changes have proven to

be the most accurate methods for estimating age in infants, children and

adolescents (Senn and Stimson, 2010). Several methods for evaluating and

quantifying dental development have been performed in order to establish

dental age standards. One of the most widely applied of those methods was first

described in 1973 and was based on French-Canadian children (Demirjian et al.

1973). That method evaluates the development of seven mandibular teeth from

panaromic radiographs (OPG) and outlines a technique for calculating dental

age. Since then, numerous studies have been undertaken for other populations,

which have demonstrated considerable variability in dental development and

maturation.

The focus of the present study is to evaluate how accurately age can be

estimated using the third molar and to formulate population specific standards

for a Western Australian and a South Indian population. Other issues including

congenital variability are also considered (see section 1.3; page 5). This study

will collect statistically quantified reference data relating to the mineralization

status of the third molars specific to Western Australian and South Indian

populations.

1.2. The importance and significance of population specific

standards

As shown by Nystrom et al. (1986) and Olze et al. (2003) the timing of attaining

dental maturity varies between different population groups. In particular, the

development of the third molars show remarkable diversity, as well as different

frequencies of agenesis (congenital absence) among different ethnic groups

(Clow, 1984; Uzamis et al. 2000). Thus appropriate quantitative methods and

population specific standards should be applied when estimating dental age for

forensic purposes (Liversidge et al. 2003). Age estimation using a population

specific standard will obviously provide the greatest accuracy. At present there

are no Western Australian and South Indian population specific standards for

estimating age from third molar dental development. This study therefore will

use the Demirjian et al. (1973) eight stage (A-H) dental development system to

assess the third molars of Western Australian and South Indian individuals,

which will provide specific reference data for forensic application in those

populations. The specific aims of this project are detailed below.

1.3. Aims of the project

1. To evaluate the applicability of the Demirjian et al. (1973) method

of age estimation to third molar development in a Western Australian

and a South Indian population:

The Demirjian et al. (1973) method of age estimation has been widely used

for dental age estimation in different populations. However, to-date no

previous research has assessed the accuracy of using the individual third

molars to estimate age using this system. This study therefore, will focus

upon evaluating the applicability of the Demirjian et al. (1973) method to all

four third molars in a Western Australian and a South Indian population. The

primary aim of this study is to establish age estimation standards which can

be applied to both populations for estimating the age of an individual by

assessing the development of their third molars.

2. To evaluate ethnic differences in the mineralization rate of the third

molar:

Olze et al. (2003) demonstrated clear ethnic differences in the chronology of

third molar mineralization between Asian and European populations. In

order to maximize the accuracy of age estimation, it is important that such

findings are considered when examining individuals from different ethnic

groups. The increasing volume of Indian immigrants and students settling in

Australia, in the broader context of globalization, has led to a need for

development of population specific age assessment standards. Since there is

no such study on either the Australian or Indian populations, the present

research will establish any differences in the chronology of third molar

mineralization. The outcome of this study can then provide reference data

for age estimation of unidentified deceased individuals, in addition to

forensic age estimation in living persons. Results will also be evaluated in a

broader global context (e.g: published data on other populations).

3. To evaluate if any statistically significant sex differences exist in the

timing of mineralization of the third molar in both Western Australian

and South Indian individuals:

It is of at-most importance for forensic investigators to know the variation in

age estimation accuracy between males and females, as this determines

whether the sex of unknown remains must be known prior to applying any

age estimation standard. This study will therefore, examine the accuracy of

age estimation using Demirjian et al. (1973) method as applied to both sexes.

The rate of error for the individual sexes will then be compared with

previous studies and interpreted in the context of suitability for forensic use.

4. To evaluate the variability in the development and eruption of the

third molars:

For forensic purposes the reliability and adequate precision of age

estimation using the third molars is crucially important. The main limitation

of this study is the remarkable biological variability in the formation of third

molars compared to all other permanent teeth. Differences in the

developmental pattern and mineralization of this particular tooth vary

widely. Discrepancies have also been observed between the development of

the maxillary (upper) and the mandibular (lower) third molars (Garn et al.

1963). Furthermore Saito (1936) reported earlier mineralization and

emergence on the right side than on the left in the mandibular third molars.

Accordingly, this study will evaluate and compare the development and

emergence of the maxillary and mandibular third molars, and also consider

left and right side differences.

5. To evaluate the frequency of absence of the third molars:

There is a high frequency of, and large variations in, the prevalence of third

molar absence. Garn et al. (1963) demonstrated between 10 - 20% agenesis

of this tooth in white American and European individuals older than 14

years of age. More recent studies have presented variable estimates, ranging

from 7 to 10% to as high as 32.4% (Llarena and Nuno, 1990). Although this

variability may mostly relate to population differences, other factors, such as

sex, age, and degree of dental maturation of the individuals play a major role

(Bolanos et al. 2003). This issue is discussed further in Chapter Two.

1.4. Sources of material

The OPG’s (orthopantomographs) examined in this project were taken as part of

routine therapeutic scans. OPGs are full mouth x-rays that show all the upper

and lower teeth, including teeth that are unerupted. The OPGs from Southern

India were obtained from diagnostic and radiography centres in Bangalore,

India in accordance with established ethical guidelines. The OPGs from Western

Australia were obtained through the Picture Archive and Communication

System (PACS) from medical practices of various Western Australian hospitals

(e.g. Charles Gairdner; Royal Perth) following established ethical guidelines.

Ethics approval to undertake this project was granted by the Human Research

Ethics Committee, of the University of Western Australia (Reference no.

RA/4/1/4158).

1.5. Thesis format

The thesis is presented in six chapters. The first chapter is the introduction and

outlines the aims of the project and sources of data. The second chapter

concerns general dental anatomy, dental development, eruption sequences,

mineralization and shedding of teeth. Chapter Three reviews the literature on

dental age estimation methods. The fourth chapter outlines the materials and

methods; followed by Chapter Five which outlines the results. The final chapter

provides a discussion of the results and the final conclusions.

Chapter Two

Dental Anatomy, Histology and Nomenclature

2.1. Introduction

Dental anatomy is the study of the morphology of the various teeth in the human

dentitions and knowledge of how their shape, form, structure, colour, and

function relate to each other, both in the same dental arch, and to the teeth in

the opposing arch. Thus the study of dental anatomy provides one of the basic

components of the skills needed to practice all aspects of dentistry (Wheeler,

2003). This chapter presents an overview of tooth morphology, development,

classification and nomenclature of the human dentition. This is then followed by

a general outline of the deciduous and permanent dental development rates.

2.2. The Dentition

The term ‘dentition’ refers to all of the teeth in the upper jaw (maxilla) and the

lower jaw (mandible) bones. Accordingly, the upper teeth are known as

‘maxillary’, and together form an arch shape known as the maxillary arch. In

contrast, the lower teeth are ‘mandibular’ and they collectively form the

mandibular arch. Humans have two dentitions throughout life: one during

childhood, known as the primary dentition; and one for most (or all) of

adulthood, which is the permanent dentition (Woelfel and Scheid, 1997).

2.2.1. Primary Dentition

The first set of teeth in the mouth is the primary or deciduous dentition, which

begins to form prenatally about 6 weeks in utero, and is completed postnatally

at approximately 3 years of age. The first teeth in this dentition appear in the

oral cavity at approximately 6 months of age; the last primary teeth generally

emerge at 28(±4 months) years of age. The deciduous dentition remains intact

until the child is about 6 years of age (Wheeler, 2003). There are only 20 teeth in

the primary dentition; 10 each in the maxillary and mandibular arches. This

dentition is also known as the deciduous dentition, referring to the fact that

these teeth are eventually shed or exfoliated by 12 to 13 years of age, having

being replaced by the permanent dentition. The complete primary dentition has

five teeth in each quadrant as shown in Figure 2.1. The two front teeth in each

quadrant are the central and lateral incisor, followed posteriorly by one canine,

then a first and second primary molar (Woelfel and Scheid, 1997).

Figure 2.1: Occlusal view of the primary dentition along with types of teeth

(from Thomas et al. 2006).

2.2.2. Permanent dentition

The permanent dentition is also known as the succedaneous dentition; it

succeeds the primary dentition. It is composed of 32 teeth: 16 each in the

maxillary and mandibular arches. The complete dentition has eight teeth in each

quadrant as shown in Figure 2.2. The two front teeth in a quadrant are the

central and lateral incisors, followed by one canine, a first and second premolar,

then the first, second, and third molars. Between 6 and 6 years of age, the first

permanent tooth (the mandibular first molar) erupts posterior to the second

deciduous molar. No deciduous tooth has exfoliated to provide space for this

permanent tooth; the mandible has increased in length so that there is now

space for an additional tooth (Short and Levin-Goldstein, 2002).

Figure 2.2: Occlusal views of permanent dentition along with types of teeth

numbered using universal dental numbering system (from Thomas et al.

2006).

2.3. Dentition periods

Although there are two dentitions, there are three dentitions periods (see Figure

2.3) because the two dentitions overlap; this overlap is known as the ‘mixed’

dentition period (see below).

2.3.1. Primary dentition period

The primary dentition period is the first of the three periods. It begins with the

eruption of the primary mandibular central incisors, generally at around 6

months of age, and is completed with the eruption of the second molar at around

3 years of age. Only the primary teeth are present during this time. This period

usually ends with the eruption of the permanent mandibular first molar. The jaw

bones are beginning to grow during this period to accommodate the larger

permanent teeth.

2.3.2. Mixed dentition period

The mixed dentition period follows the primary dentition period and occurs

between approximately 6 to 12 years of age. Both the primary and permanent

teeth are present during this transitional stage. In this period the shedding of

both the primary teeth and the eruption of the permanent teeth occurs. This

period thus begins with eruption of the first permanent tooth, a permanent

mandibular first molar and usually ends at around age 12, with the exfoliation of

the last deciduous tooth, normally the maxillary canine (Fuller and Denehy,

1984).

Figure 2.3: Dentition Stages (from Fuller and Denehy, 1984).

2.3.3. Permanent dentition period

The permanent dentition period is the last of the three. This period begins with

the shedding of the last primary tooth (canine or molar) at around 12 years of

age. This period includes the eruption of all the permanent teeth, except for

those teeth that are congenitally missing or impacted and cannot erupt (usually

the third molars). The permanent teeth are usually the only teeth present during

this period. Growth of the jawbones is not very noticeable as it slows and then

eventually stops (Thomas et al. 2006).

2.4. Dental numbering systems

Recording and storing accurate dental records is an important task in any dental

practice. To do so expeditiously, it is necessary to adopt a type of code or

numbering system for teeth. Uniformity in the methodology for maintaining

dental records is thus essential so that they are understandable to all dental

practitioners (Woelfel and Scheid, 1997). Several tooth numbering systems are

in use globally.

2.4.1. Universal numbering system

This system was first suggested by Parreidt in 1882 and was officially adopted

by the American Dental Association (ADA) in 1975. It is accepted by third party

providers and is endorsed by the American Society of Forensic Odontology. In

this system, the primary teeth are designated in a consecutive arrangement by

using capital letters (A through T) starting with the maxillary right second

molar, moving clockwise, and ending with the mandibular right second

molar(Avery 1992).

The Universal System notation for the entire primary dentition is as follows:

A B C D E F G H I J

T S R Q P O N M L K

In this system the permanent dentition are numbered from 1 through 32. The

maxillary teeth are numbered from 1 through 16, beginning with the right third

molar. The mandibular teeth are numbered from 17 through 32, beginning with

the mandibular left third molar, as shown below (Wheeler, 2003). For example,

the right maxillary first molar is designated as 3, the left maxillary central

incisor as 9 and right mandibular first molar as 30.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17

2.4.2. The Zsigmondy/Palmer Notation System

This system was introduced by Adolph Zsigmondy of Vienna in 1861 and then

modified for the primary dentition in 1874 (Wheeler, 2003). The system utilizes

simple brackets to represent the four quadrants of the dentition as if you are

facing the patient: ┘is upper right. └ is upper left, ┐is lower right, and┌ lower

left (Woelfel and Scheid, 1997). For example left maxillary central incisor is

designated as └A and the right mandibular second molar as E┐.

The primary dentition is as follows:

E D C B A A B C D E

E D C B A A B C D E

The permanent dentition is a four quadrant symbolic system, in which

beginning with the central incisors, the teeth are numbered 1 through 8 in each

arch. For example the maxillary right first molar is designated 6┐ and the

maxillary left central incisor as └1.

8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8

8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8

2.4.3. Federation Dentaire International (FDI)

The two digit system proposed by the FDI (for both the primary and permanent

dentitions) has been adopted by the World Health Organization (WHO) and

accepted by other organizations such as the International Association of Dental

Research (IADR) (Wheeler, 2003). In this system the first digit denotes the

dentition, arch and side; the second digit denotes the tooth (1 to 8 for

permanent and 1 to 5 for deciduous teeth). The first of the two digits used in this

system are designated as follows.

1. Permanent dentition, maxillary, right side

2. Permanent dentition, maxillary, left side

3. Permanent dentition, mandibular, left side

4. Permanent dentition, mandibular, right side

5. Deciduous dentition, maxillary, right side

6. Deciduous dentition, maxillary, left side

7. Deciduous dentition, mandibular, left side

8. Deciduous dentition, mandibular, right side

The FDI system of tooth notation for primary teeth is as follows:

55 54 53 52 51 61 62 63 64 65

85 84 83 82 81 71 72 73 74 75

The FDI system of tooth notation for permanent teeth is as follows, for example

the permanent upper right central incisor is designated as 11 (pronounced as

“one – one”, not “eleven”).

18 17 16 15 14 13 12 11 21 22 23 24 25 26 27 28

48 47 46 45 44 43 42 41 31 32 33 34 35 36 37 38

2.5. General dental anatomy terminology

A brief definition and description of the various anatomical features of a normal

tooth and its supporting structures are discussed below.

2.5.1. Divisions of the tooth

Each tooth consists of a crown and one or more roots. The crown is that portion

of the tooth which is normally visible in the mouth and covered with enamel.

The teeth have differently shaped crowns, each adapted to perform a specific

function. The roots located in the bone are not normally visible and are covered

with cementum. The roots stabilize or support the teeth from the pressures of

mastication (Short and Levin-Goldstein 2002; Fuller and Denehy 1984). Portions

of the crown and roots of a tooth can also be defined in more specific ways. The

anatomical crown is that portion covered by enamel which remains mostly

constant throughout the life of the tooth. The clinical crown is the portion of the

anatomical crown that is visible and not covered by the gingiva. Similarly, the

anatomical root is the portion of the root covered by cementum. The clinical

root of a tooth is the portion of the anatomical root that is visible, subject to

variability over time, again related to ginvival recession.

2.5.2. Tissues of the tooth

There are four tissues of a tooth: enamel; dentin; cementum; and pulp (as shown

in Figure 2.4). The crown of the tooth is covered with enamel which is the

hardest tissue in the body. Enamel is made up of 96% inorganic and 4% organic

matter and water. Dentin is the hard yellowish tissue underlying the enamel and

cementum that constitutes the bulk of the tooth. Dentin is not normally visible

except on a dental radiograph, a sectioned tooth, or on a badly worn (attrition)

tooth. Dentin is made up of 70% inorganic and 30% organic matter and water.

Cementum is the dull-yellow layer of hard, bone like tissue which covers the

dentin of the anatomical root.

The pulp is the soft tissue found in the centre part of the tooth. It contains the

nutrient supply in the form of blood vessels and nerves. The pulp cavity is the

internal cavity (surrounded by dentine), which contains the pulp. The pulp

cavity consists of the pulp canal, which is the portion of the pulp cavity that is

located in the root of the tooth while the pulp chamber is that portion which is

found in the anatomical crown of the tooth (Woelfel and Scheid 1997; Thomas et

al. 2006).

Figure 2.4: Tissues of the tooth (from Short and Levin-Goldstein, 2002).

2.6. Dental Nomenclature

The teeth in the maxillary arch of the upper jaw bone are the maxillary teeth.

The teeth in the mandibular arch of the lower jaw bone are the mandibular

teeth. Each dental arch has a midline; an imaginary vertical plane that divides

the arch into two approximately equal halves (right and left). Thus each dental

arch can be divided into two quadrants, with four quadrants in the entire oral

cavity; the maxillary right and left quadrant, the mandibular right and left

quadrant. Teeth can also be described according to their position in each dental

arch in relation to the midline. The incisiors and canines are considered anterior

teeth; in contrast the premolars and molars are considered posterior teeth

because they are away from the midline (Wheeler, 2003).

Each tooth has five surfaces: mesial; distal; facial; lingual; and occlusal (see

Figure 2.5). The surface closest to the midline is the mesial surface and away

from the midline is the distal surface. Tooth surfaces closest to the facial surface

are considered the facial surface. Those facial tooth surfaces closest to the lips

are termed labial, close to the inner cheek the surface is termed buccal. Those

tooth surfaces closest to the tongue are the lingual surfaces and those closest to

the palate are the palatal surfaces. The masticatory surface is the chewing

surface on the superior surface of the crown. This is the incisal surface for

anterior teeth and the occlusal surface for the posterior teeth (Wheeler, 2003).

Figure 2.5: Illustration and definition of dental Nomenclature (from

Wheeler, 2003).

2.7. The development and eruption of the teeth

The knowledge of the development and emergence of the teeth into the oral

cavity is not only applicable to clinical practice, but in forensics, bioarchaeology

and paleoanthropology. Tooth development is initiated by the interaction of the

oral epithelial cells with the underlying mesenchymal cells. From this

interaction, a total of 20 primary and 32 permanent teeth normally develop.

Each developing tooth grows as an anatomically distinct unit and the

fundamental developmental process is similar for all teeth (Avery, 1992). Each

tooth develops through successive bud, cap and bell stages. The various stages

of tooth development and eruption are summarized below.

2.7.1. Stages of tooth development

Although tooth formation is a continuous process, it is characterized by a series

of easily distinguishable stages known as the bud, cap and bell stages. These

stages are defined according to the shape of the epithelial enamel organ segment

of the developing tooth. During these early stages the tooth germs grow and

expand, and the cells that are to form the hard tissues of the teeth then

differentiate. The bud (or the first) stage is the rounded localized growth of the

epithelial cells of the enamel organ. This happens at about six weeks of post-

conception. During this stage the 20 tooth buds begin to appear segmentally in

the dental lamina in the approximate location of the corresponding primary

teeth (Fuller and Denehy, 1984).

As further development takes place, the generally round form of the bud gains a

concave surface. The basal portion invaginates, and the structure thus formed

gives the appearance of a cap, and hence this phase is termed the cap stage. This

stage consists of an enamel organ, dental papilla, and dental follicle (Fuller and

Denehy, 1984).

As the concavity in the basal area of the cap continues to deepen, the

development of the tooth enters the bell stage. At this stage the enamel organ

has differentiated and the tooth’s crown is identifiable. During this time most of

the dentin and enamel of the crown is laid down. After this stage, when enamel

and dentine deposition have formed, the bell stage is regarded as ending and the

root development stage begins.

After the crowns and roots of these teeth form and mineralize, the supporting

tissues of the teeth, cementum, periodontal ligament, and alveolar bone begin to

form. Subsequently, the completed tooth crown erupts into the oral cavity. Root

formation and cementogenesis then proceed until a functional tooth and its

supporting apparatus are fully developed (Avery, 1992).

2.7.2. Eruption

Tooth eruption is the process by which the developing teeth emerge through the

bone and soft tissue of the jaws, and the overlying mucosa, to enter the oral

cavity, contact teeth of the opposing arch, and function in mastication. The

movements related to tooth eruption begin during crown formation and require

adjustments relative to the forming bony crypt. This is termed the pre-eruptive

phase. Tooth eruption is also involved in the initiation of root development and

continues until the emergence of the teeth into the oral cavity; this is the pre-

functional eruptive phase. The teeth continue to erupt until they reach occlusal

or incisal contact. They then undergo functional eruptive movements, which

include compensation for jaw growth and occlusal wear of the enamel. This

stage is known as the functional eruptive phase. Eruption is actually a

continuous process, ending only with the loss of the tooth. The teeth differ

extensively in their eruptive schedules as shown in Tables 2.1 and 2.2 (Avery,

1992).

Table 2.1: Sequence of chronology of tooth eruption of the primary

dentition (Avery, 1992).

Table 2.2: Sequence of chronology of tooth eruption of the permanent

dentition (Avery, 1992).

The eruption process can be divided into active and passive eruption. Active

eruption is whereby the crown of the tooth first moves from within the jaw into

the oral cavity, a process that continues until the tooth meets its antagonist in

the opposite jaw. Active eruption begins when the crown of the tooth is

complete and a portion of the root has started to form. Once active eruption is

complete, other factors that occur during life, such as normal attrition or trauma

can cause breakdown on the periodontium. This can then result in exposure of

cementum, wearing of enamel, or gingival recession. The increase in the length

of the clinical crown caused by gingival recession is referred to as passive

eruption (Wheeler, 2003).

2.8. The anatomy of the primary dentition

The primary (or deciduous) dentition consists of 20 teeth; 10 each in the

maxillary and mandibular arches. There are five teeth in each quadrant; a

central and lateral incisor, canine, first and second molar. There are no

premolars in the primary dentition.

The primary teeth emerge in children between the ages of 6 months and 2 years.

At around age 6, these teeth are gradually replaced by the permanent dentition.

The primary teeth actually function in the mouth for an average of 8 and 7.6

years respectively for the maxillary and mandibular teeth. The primary teeth

perform vital functions such as effective mastication, formulation of clear

speech, and maintaining a normal facial appearance. The primary teeth also help

in maintaining space and arch continuity for the eruption of the permanent

dentition (Woelfel and Scheid, 1997).

2.8.1. The primary maxillary dentition:

Arch and side determination of primary teeth is based on the anatomical

differences, which are briefly elaborated below and is illustrated in Figure 2.6.

i) Incisors: the labial crown is smooth with a straight incisal edge; there

are no mamelons. The crown is wide with a cingulam and marginal ridges

on the lingual.

ii) Canine: a broad cervical ridge causes the cervix to appear constricted.

The cusp tip is pointed, but short; the single root is long and slender.

iii) First Molar: the number of cusps varies from two to four. There is no

groove on the buccal surface to divide the cusps. The occlusal surface has

a central fossa and a mesial triangular fossa molars, and the bifurcation

of the two buccal roots begins almost apically to the cervix.

iv) Second Molar: the anatomy is the same as that of the permanent

maxillary first molar (see below). There are two buccal cusps divided by

a buccal groove and two lingual cusps with a cusp of tubercle or fifth cusp

groove, on the mesiolingual cusp. There are three roots; two buccal and

one lingual (Short and Levin-Goldstein, 2002).

Figure 2.6: The deciduous dentition – facial view (from Woelfel and

Scheid, 1997).

2.8.2. The primary mandibular dentition:

i) Incisors: both labial and lingual surfaces are smooth, although there is a

slight cingulam and marginal ridges on the lingual surface.

ii) Canines: the buccal surface has a pronounced cervical ridge. The lingual

surface has a cingulum and lingual ridges.

iii) First Molar: as with the maxillary first molar, there is no definite

anatomy. Usually there are two buccal cusps divided by a depression,

rather than a groove, and two lingual cusps. There are two roots; both are

long, slender and divergent. The occlusal surface has lingual groove and a

central groove that is crossed by the buccal groove.

iv) Second Molar: the anatomy is identical to that of the permanent

mandibular first molar. Grooves divide the three buccal and the two

lingual cusps. The occlusal groove pattern resembles the permanent

mandibular first molar. Although there may be more supplemental

grooves. There are two long, thin and divergent roots, which can be twice

as long as the crown (Woelfel and Scheid, 1997).

2.8.3. Importance of the primary teeth:

The form and function of the primary dentition are both important. Each

primary tooth has the same function as the permanent tooth that succeeds it,

and each maintains a position for its permanent tooth replacement. If a primary

tooth is prematurely lost, the permanent replacement may erupt too early or

emerge in an incorrect position. This may result in improper alignment and

malocclusion.

2.8.4. Morphological differences between the primary and the permanent

teeth

The morphological differences between the primary and permanent dentition

with respect to the crown form, root and the pulpal cavity are discussed below.

i) The primary teeth are generally smaller than their permanent

counterparts. This size discrepancy exists for crown and root portions of

both anterior and posterior teeth.

ii) The primary teeth are usually less pigmented and are whiter in

appearance than the permanent teeth.

iii) The crowns of the primary anterior teeth are larger mesiodistally in

comparison with the permanent teeth.

iv) The crowns of the primary teeth are more constricted at the cervix than

those of the permanent teeth.

v) The crowns of the primary teeth appear bulbous often having labial or

buccal cingula.

vi) The roots of the primary molars are much more flared or spread, than the

roots of the permanent molars. This flare creates additional space for the

permanent premolar crown to develop.

vii) The cervical ridges of the enamel of the anterior teeth are more

prominent.

viii) The layers of enamel and dentin in the crowns of primary teeth are

thinner when compared to the permanent teeth.

ix) The pulp cavity is relatively larger in the deciduous teeth. The mesial

pulp horns of the primary molars are especially large.

x) The primary teeth have more consistent shapes than the permanent

dentition.

xi) All of the primary second molars resemble the first permanent molar

(Woelfel and Scheid 1997; Wheeler 2003; Short and Levin-Goldstein

2002).

2.9. The anatomy of the permanent third molars

2.9.1. An overview of the maxillary third molars

The maxillary third molar is the eighth and last maxillary tooth to erupt from

from the midline; the sequence of eruption is shown in Table 2.3. If they erupt, it

is distal to the permanent maxillary second molars. This tooth has mesial

contact but not distal contact. The maxillary third molar often varies

considerably in size, contour, and relative position to other teeth. If well

developed, it often bears a resemblance to the maxillary second molar. The third

molar supplements the second molar in function, but the crown is smaller and

the roots are shorter, there is also often fusion of one or more roots. The third

molars show more variation in development than any other tooth in the

dentition (Wheeler, 2003).

Table: 2.3: The development and eruption sequence of the maxillary third

molar (Wheeler, 2003).

Stage Approximate Age

First evidence of mineralization 7 to 9 years

Enamel completed 12 to 16 years

Eruption 17 to 21 years

Root completed 18 to 21 years

2.9.2. The morphology of the maxillary third molar

The following describes the morphology of the maxillary third molar from

various aspects.

i) Buccal Aspect

The crown is shorter cervico-occlusally and narrower mesio-distally. The roots

are fused together (functioning as one large root), and are shorter cervico-

apically. The fused roots end in a taper at the apex. The mesial outline of the

roots have a more extreme slant to the distal root, giving the apices of the fused

roots a more distil relationship to the center of the crown (Figure 2.7).

Figure 2.7: Various views of the Maxillary third molar (from Thomas

et al. 2006).

ii) Lingual aspect

In addition to the differences mentioned above, there is just one large lingual

cusp and therefore no lingual groove (Figure 2.7).

iii) Mesial aspect

Aside from metrical differences, the main mesial feature is the taper of the fused

roots and a bifurcation in the region of the apical third of the root (Figure 2.7).

iv) Distal aspect

From this aspect most of the buccal surface of the crown is in view. Part of the

occlusal surface may be seen because of the angulation of the occlusal surface in

relation to the long axis of the root. The distance from the cervical line to the

marginal ridge is short (Figure 2.7).

v) Occlusal aspect

The occlusal aspect has a heart-shaped outline. The lingual cusp is large and well

developed. There is no disto-lingual cusp, which gives a semi-circular outline to

the tooth from one contact area to the other (Figure 2.7) (Wheeler, 2003).

vi) Crown form

The crown of the maxillary third molar is poorly developed compared with the

other maxillary molars. The tooth is composed of four developmental lobes.

There are two types of occlusal outlines for this tooth; the most common outline

is heart-shaped, similar to the maxillary second molar. Generally with this

outline the teeth has only three cusps; mesio-buccal, disto-buccal and mesio-

lingual. If a fourth cusp is present, the occlusal outline is a rhomboidal type, with

a small and non-functioning disto-lingual cusp (see Figure 2.8). No oblique ridge

is present. For both types of occlusal form, the disto-buccal cusp is much shorter

than the mesio-buccal cusp, which helps to distinguish the right maxillary third

molar from the left.

Figure 2.8: Crown form of maxillary right third molar (from Thomas et al.

2006)

vii) Root form

Like crown form, root numbers and morphology are extremely variable. There

are three roots which may be separated, but more commonly they are fused

most of their length, with the furcation extending only a short distance cervically

from the apices of the roots. This results in a long fused root trunk that is often

very crooked; the majority of the roots curve distally in their apical third

(Woelfel and Scheid, 1997).

2.9.3. Clinical consideration of the maxillary third molars

The permanent maxillary third molars may fail to erupt and remain impacted

within the alveolar bone. An impacted tooth is an unerupted or partially erupted

tooth that is positioned against another tooth, bone, or even soft tissue in such a

way that complete eruption is unlikely. This impaction usually occurs because

the maxilla is under-developed and space (or arch length) is insufficient to

accommodate these teeth. Surgical removable may be necessary if impacted

(Thomas et al. 2006).

2.9.4. An overview of the mandibular third molars

The mandibular third molar is the eighth and last mandibular tooth from the

midline. The development and eruption sequence is shown in Table 2.4. The

mandibular third molars vary considerably in different individuals and present

many anomalies both in form and position. This tooth supplements the second

molar in function and has an irregularly developed crown with undersized roots

that are more or less malformed. Occasionally, mandibular third molars are

present that are comparable in size and development to the mandibular first

molar.

Table 2.4: The development and eruption sequence of the mandibular

third molar (Wheeler, 2003).

Stage Approximate Age

First evidence of mineralization 8 to 10 years

Enamel completed 12 to 16 years

Eruption 17 to 21 years

Root completed 18 to 25 years

2.9.5. The morphology of the mandibular third molars

The following describes the morphology of the mandibular third molar from

various aspects.

i) Buccal aspect

The crown is about the same length cervico-occlusally but is narrower mesio-

distally. The roots are fused together (functioning as one large root) and they

are shorter cervico-apically. The fused roots divide sufficiently at the apex to

form two distinct apices. The outline mesially and distally of the fused roots

have a more extreme slant distally, which places the apices of the roots in a

more distal relationship to the centre of the crown (Figure 2.9).

Figure 2.9: Various views of the Mandibular right third molar (from

Thomas et al. 2006).

ii) Lingual aspect

There is no outstanding variation except for those mentioned above (see buccal

aspect).

iii) Mesial aspect

The distal root apex cannot be seen; the only variation in the morphology of this

tooth (from that of the second molar) are odontometric.

iv) Distal aspect

The outline of the distal aspect is quite similar to that of the second molar, which

makes allowances for a narrower crown bucco-lingually and shorter roots

(Figure 2.9).

v) Occlusal aspect

The crown is shorter mesio-distally and narrower bucco-lingually, the crown

tapers more distally, and the line angles are more rounded. A number of

supplemental grooves are evident occlusally (Figure 2.9).

vi) Crown form

The crown is more oval than rectangular; the two mesial cusps are larger than

the two distal cusps. The occlusal surface appears quite wrinkled, with an

irregular groove pattern. Usually numerous occlusal pits are present; if an

excess of these features exists the occlusal surface is described as crenulated.

vii) Root form

The mandibular third molar usually has two roots that are fused, irregularly

curved, and shorter than those of a mandibular second molar. The roots show a

marked distal inclination (Wheeler, 2003).

2.9.6. Clinical considerations of the Mandibular third molars

The permanent mandibular third molars may fail to erupt and remain impacted

within the surrounding alveolar bone, which occurs more frequently than in the

maxilla. This impaction typically occurs in 10% of the population, usually

because the mandible is underdeveloped and space or arch length is insufficient

to accommodate these teeth. Surgical removable may be necessary if they are

impacted or partially erupted (Wheeler, 2003).

2.9.7. Absence of the third molars

Absence of one or more third molars is common anomaly in human dental

development. Third molar absence has also been associated with a reduction in

the number of other teeth and structural variations (Garn et al. 1962). Attempts

were made to explain this deviation through evolutionary and anatomical

models, such as Butler’s field theory, odontogenic polarity, or Sofaer’s model of

compensatory tooth size interactions (Vastardis, 2000).

i) Butler’s theory (1939): this theory attempts to explain why certain

teeth fail to form. According to this hypothesis, the human dentition can

be divided into three morphologic fields: incisors; canines; and

premolars/molars. Within each of those fields, one “key” tooth is

presumed to be stable; the other teeth within this field become

progressively less stable. Considering each quadrant separately, for

example the key tooth in the molar/premolar field would be, the first

molar. This positions the second and third molars at the distal end and

the first and second premolars on its mesial end of the field. Based on

Butler’s theory, the third molar is predicted to be most variable in size

and shape.

ii) Evolutionary theory: in human evolution there has been a tendancy

towards reduction in jaw length and prognathism, mandibular canine

size and first molar cusp number, and increased third molar agenesis

(Kraus, 1964). The reduction in tooth number is concomitant with the

reduction in the size of the jaws in human evolution and is believed to be

a continuing evolutionary trend. These changes in dentition correlate to

functional adaptations; however it has been difficult to determine what

advantage to survival has been confirmed by a reduction in dental

structures. Kraus (1964) suggested that reductions of dental structures

are controlled by genes that produce other structural changes that are

advantageous to survival.

2.9.7.1. Human molecular genetics:

Identification of the underlying cause of a condition starts with the localization

of the defective gene in the human genome. Familial tooth agenesis can be the

result of a single dominant gene defect. This is a clearly recognizable well

defined and relatively common dental anomaly. However, a large family and an

accurate assessment of the phenotype are essential to perform genetic linkage

studies. The objective of these studies is to determine whether two genetic traits

are segregating independently (Vastardis, 2000). The two genetic traits are a

genetic marker (DNA polymorphism of known chromosomal location) and the

condition of interest (e.g familial tooth agenesis). Genes located close to each

other are passed together from parent to child (Ott, 1992). Therefore,

cosegregation of a phenotype, such as tooth agenesis and a particular known

marker, would suggest that these genetic traits lie close to each other, on the

same region of a chromosome, providing at the same time the locus for the

defective dental gene. Once the condition locus is identified in one family the

above step is designed to determine whether the same chromosomal location is

responsible for tooth agenesis in other families (Ott, 1992; Vastardis, 2000).

Vastardis (2000) applied the same strategy to an American family presenting

with autosomal dominant agenesis of the second premolar and third molars.

They were able to find out in which chromosome the abnormal dental gene was

located and concluded that a location on chromosome 4p is responsible for

tooth agenesis in that family.

2.10. Histology of the dental tissues

All teeth consist of acellular enamel that forms the outermost layer. This hard

tissue is supported by resilient dentin. The roots of the teeth are covered by

cementum. All the dental hard tissues have a distinctive microscopic structure

which can be analysed histologically. The following is a brief description of the

histology of enamel, dentin and cementum.

2.10.1. Enamel

Enamel is an epithelially derived protective covering (of variable thickness) over

the entire surface of the crown. During the eruptive phase the ameloblasts that

form the enamel are lost. This means that thereafter if the enamel is damaged

(e.g. due to caries, attrition, erosion) thereafter, it cannot be reformed. As a

compensatory mechanism, enamel has a complex structure with a high mineral

content, which makes it the hardest tissue in the human body.

i) Physical properties: enamel is composed of 96% inorganic mineral in

the form of hydroxyapatite and 4% organic material and water. The

hydroxyapatite is a crystalline calcium phosphate that is also found in

bone, dentin and cementum. Enamel is white to grayish-white in colour,

but appears slightly yellow because it is translucent. Enamel ranges in

thickness from a ‘knifelike edge’ at its cervical margin to about 2.0mm to

2.5 mm maximum thickness over the occlusal (or incisal) surfaces

(Avery, 1992).

ii) Structure of enamel: enamel is composed of rods that extend from their

site of origin to the outer surface of enamel. Each rod is formed by

ameloblasts; four ameloblasts form a part of each rod. In cross-section a

rod is keyhole-shaped with a head and a tail as shown in Figure 2.10. The

head of the rod is the broadest part; the tail is the elongated thinner part.

Each rod is filled with crystals. Rods are formed perpendicular to the

dentino-enamel junction and curve slightly towards the cusp tip (Orban,

1976).

Figure 2.10: Diagramatic representation of rods in enamel (from Orban,

1976).

2.10.2. Dentin

Dentin is the mineralized tissue that forms the bulk of the tooth. As a living

tissue it consists of specialized cells called odontoblasts and an intercellular

substance. Dentin is structurally unique due to the presence of closely packed

dentinal tubules. These tubules traverse the entire thickness of dentin and have

a wavy course (Nanci, 2008).

Head

Crystals

Tail

Figure 2.11: Composite diagram of a human tooth in cross-section

illustrating the different types of dentin (from Nanci, 2008).

i) Physical properties: dentin is yellowish in colour and is composed of

70% inorganic hydroxyapetite crystals, 20% organic collagen fibres

(along with small amounts of proteins) and 10% water. It is softer than

enamel but slightly harder than bone or cementum. Radiographically,

therefore, it is more radiolucent than enamel. Dentin is slightly elastic

which allows the impact of mastication to occur without fracturing the

enamel. This resilience is due to the presence of dentinal tubules

throughout its matrix (Avery, 1992).

ii) Types of dentin: dentin is composed of primary, secondary and tertiary

dentin as shown in Figure 2.11. Most dentin external to the pulp chamber

is primary (also known as circumpulpal) dentin. The outermost layer of

primary dentin is mantle dentin, secondary dentin develops after root

formation has been completed. Tertiary (or reparative) dentin is formed

in response to disease or trauma, which is formed by odontoblasts that

are directly affected by the stimuli (Nanci, 2008).

2.10.3. Dental pulp

Dental pulp is the soft connective tissue that supports the dentin. Each tooth has

coronal (crown) and radicular (root) pulp. It contains connective tissue, blood

vessels, nerves, and cells (such as odontoblasts and fibroblasts). The pulp has

several functions, including initiative, formative, protective, nutritive and

reparative (Nanci, 2008).

i) Histology of dental pulp: the centre of the pulp contains large veins and

arteries surrounded by fibroblasts and collagen fibres embedded in a

intercellular matrix. More peripherally, along the dentin in both the

coronal and radicular pulp, are the formative cells of the dentin termed

odontoblasts. Histologically three distinct zones can be identified in the

dental pulp as shown in Figure 2.12:

A. Odontogenic zone (Odontoblasts);

B. Cell free zone;

C. Cell rich zone.

Figure 2.12: Coronal section of a molar showing the dental pulp zones

(from Orban, 1976).

Chapter Three Literature Review

3.1. Introduction

Forensic age estimation is of considerable importance for the identification of

unknown individuals involved in fatal accidents, crimes, as well as in mass

disasters. In the case of living individuals who have no acceptable identification

documents, verification of chronological age is also required, in order to be

entitled to the appropriate civil rights and social benefits. A common role of a

forensic dentist, is therefore, the estimation of age in both deceased and living

persons (Willem et al. 2002).

The earliest attempts to use teeth as an indicator of age originated from England

in the early 19th century (Stavrianos and Metska, 2002). Until this time the

estimation of age was mostly based on the measurement of living height. In

1836, A.T. Thomson first demonstrated when the first permanent molars had

not erupted in children they were most likely less than seven years of age. He

thus established a rudimentary age estimation criterion for that tooth (Miles,

1963). The first scientific study was presented in 1837 by Edwin Saunders, in

which he claimed that the dentition is a more reliable characteristic than height

for the estimation of age (Kvaal, 2006). In 1872, Wedl made the first

observations of changes with age, such as degeneration, mineralization, pigment

deposits in the pulp tissue and reduction in the size of pulp cavity due to

deposits of new dentin layers in the permanent dentition. This was subsequently

followed by research that led to the development of various methods for dental

age estimation using both the developing or developed dentition (Stavrianos et

al. 2008 and see section 3.2).

Forensic age estimation of sub-adults (≤ 18.0 years of age) relies primarily on

the degree of dental maturity; skeletal maturation is more susceptible to

environmental factors (such as chronic illness and nutritional deficiency) and is

therefore less reliable (Cardoso, 2007). The developing dentition, especially

during childhood, represents a key developmental characteristic for age

assessment through radiographic evaluation of tooth mineralization or

macroscopic observation of tooth eruption patterns (Franklin, 2010). It is thus

not surprising that there are many dental standards and methods available in

the literature. This chapter reviews a selection of common methods appropriate

for dental age estimation in juveniles, in addition to a brief review of other

methodologies, including current Australian and South Indian studies, and the

importance of population specific data.

3.2. Dental age estimation

The teeth represent a useful biological marker for age estimation. Dental age can

be estimated by assessing the emergence and formation of the teeth. In the early

20th century, dental eruption (emergence) was one of the main developmental

markers used to estimate age (Demirjian et al. 1973); visual inspection of dental

eruption was the first and most common method for dental age estimation.

Dental eruption is, however, a process which progresses gradually over time and

the precise moment that a tooth reaches the occlusal plane is very difficult to

determine. Tooth eruption is a reliable age indicator when used alone, as it can

be influenced by individualistic factors such as the available space in the dental

arch, exfoliation of deciduous teeth, impaction and crowding of the permanent

teeth (Willems et al. 2001). Furthermore, eruption of the primary dentition is

generally complete by the age of two and half to three years and eruption of the

permanent dentition starts at six years of age when the first molar erupts. If

dental eruption is used as the criterion for age assessment, then strictly

speaking it cannot be applied correctly between the ages of two and half until six

years because no emergence occurs in this period. In contrast, dental

development is a much more uniform and continuous process, which is less

influenced by external factors such as malnutrition, disease and mental stress.

The dental development process is correlated with different morphological

crown and root developmental stages of mineralization that can be observed

radiographically. However, the reliability of estimating age from dental

development is not uniform from birth to adulthood. After the age of 14, at

which point most of the permanent teeth are already developed, age estimation

becomes less accurate. The only teeth developing at this stage are the third

molars and hence radiographic evaluation of mineralization of this tooth is

generally used to estimate age (Reppien et al. 2006). For adults (older than 21

years of age) their dental development is complete, therefore, dental age

estimation is typically based upon degenerative process, such as attrition, root

transparency, periodontitis and secondary dentine deposition.

3.3. Dental age estimation methods

There are various methods available for the estimation of age from the

developing dentition. The developmental process of the teeth correlates with

different morphological stages of mineralization that can be observed

radiographically, which means it is also possible to perform age estimation in

both living and unidentified deceased persons. The use of radiography is

characteristic of techniques for sub-adults (not skeletally mature; ≤ 18 years of

age) using composite visual image systems, where the morphologically distinct

stages of mineralization (which all teeth share) are observed and quantified. A

range of different classifications have been devised for evaluating tooth

mineralization: e.g. Gleiser and Hunt (1955); Nolla (1960); Liliequist and

Lundberg (1971); Gustafson and Kosh (1974); Harris and Nortje (1984); and

Kullman et al. (1992). Currently, amongst the most popular tooth formation

standards are those of Moorrees et al. (1963) and Demirjian et al. (1973). Both

systems utilize composite visual images (macroscopic and radiographic) of

developmental stages for individual teeth, from which sex specific age

estimations are formulated. Those two and a selection of other studies are

examined in more detail below.

3.3.1. Moorrees et al. (1963)

Moorrees et al. (1963) divided dental maturation of the permanent dentition

into 14 different stages, ranging from initial cusp formation to complete apical

closure. In their study the permanent maxillary incisors and all the mandibular

teeth were considered. The maxillary posterior teeth were not used because the

teeth were not clearly identifiable on their radiographs. The chronology of the

formation of the permanent mandibular posterior teeth, and the permanent

maxillary and mandibular incisors, was determined and presented in graphic

form by the authors. Specific reference tables were formulated for males and

females. For each tooth an estimation of chronological age can be made using

these tables based on the mineralization and stage of development of that

specific tooth. Anderson et al. (1976) further developed the Moorrees et al.

system to include the third molars. Saunders et al. (1993) states that Moorrees

method provides estimations of age with a standard deviation of 1.5 years.

3.3.2. Demirjian et al. (1973)

Demirjian et al. (1973) attempted to simplify the process of estimating age from

the developing dentition. They presented four distinct stages each for the crown

and the root (giving them a score of A – H). The authors did not number the

stages to avoid creating the impression that they are all of the same duration.

The sample analyzed included 1446 boys and 1482 girls (aged 3 to 17 years)

from a French-Canadian population. The analysis was restricted to the

radiological appearance of first seven teeth of the lower left quadrant (left

mandible). This study, however, did not consider third molar development.

The authors provided a written description and illustration of each stage (A-H)

as shown in Table 3.1. Based on statistical analysis they assigned a maturity

score for each developmental stage of each tooth and differentiated them for

boys and girls. The sum of those eight scores results in an overall dental

maturity score that is then used to make an estimation of chronological age. The

Demirjian stages are defined by changes in shape and do not depend on

speculative estimates of length. For this reason the authors’ classification are

considered more suitable than other tooth classification systems for dental age

estimation (Olze et al. 2006).

Table 3.1: Description of the Demirjian et al. (1973) dental developmental

stages (A – H).

Stage A

Cusp tip calcification, in the form of inverted cones, is

seen at the superior level of the crypt.

There is no fusion of these cones.

Stage B

Fusion of the calcified points is evident which gives a

regularly outlined upper surface of the tooth.

Stage C

Enamel formation of the upper surface of the tooth is

complete.

Dentine deposition is seen.

The pulp chamber has a curved outline.

Stage D

Crown formation is complete.

Pulp chamber assumes a triangular form.

Beginning of root formation is seen.

Stage E

Initial evidence of division of roots is seen.

This is in the form of a calcified point.

Root length is less than crown height.

Stage F

The region of division of roots is further calcified.

This gives a more definite and distinct shape to the

roots.

Here, the root length is more than or equal to crown

height.

Stage G

Root ends are still partially open.

Root canal walls are more or less parallel.

Stage H

The root ends are closed.

There is a uniform space between the tooth and the

bone.

Hagg and Matson (1985) examined 300 Swedish children aged 3.5 to 12.5 years

using the Demirjian et al. (1973) method (amongst others). Accuracy tests were

performed and the authors suggested that Demirjian et al. (1973) system has a

high degree of accuracy and precision, especially for younger age groups (3.5 to

6.5 years). They found, however, that it was less reliable for the older age group

(10.5 to 12.5 years). It is also frequently reported that the Demirjian et al.

(1973) system involves a significant overestimation of actual age (Willems et al.

2001; and see section 3.3.4).

3.3.3. Ubelaker (1999)

One of the more commonly applied dental ageing standards is the composite

visual “atlas” system of Ubelaker, based on data from Native American and

Caucasian individuals. This method provides schematic charts of tooth

formation and eruption suitable for individuals aged 5 months in utero through

to 35 years, with standard error rates ranging from ±2 months to 3 years. One of

the major drawbacks of the Ubelaker method is that it classifies each age group

with both the maxillary and mandibular dentition combined. Since upper and

lower teeth develop at different rates, it is difficult to determine the mean

developmental rate. Furthermore, this method does not consider sex-specific

variations in dental development.

3.3.4. Willems et al. (2001)

Willems et al. (2001) evaluated the accuracy of the Demirjian et al. (1973)

dental age system in a Belgian Caucasian population; they also aimed to adapt

the scoring system to avoid overestimations. The sample consisted of 2523

orthopantomograms (OPG’s) of 1265 boys (aged 1.8 to 18 years) and 1258 girls

(aged 2.1 to 18 years), of which 2116 (1029 boys and 1087 girls) were assessed

using the Demirjian et al. (1973) method. A second hold-out sample of 355

OPG’s were used to evaluate the accuracy of the original Demirjian et al. (1973)

and the adapted method. The Demirjian et al. (1973) method resulted in a

consistent overestimation of dental age for the first Belgian Caucasian sample;

on average 0.5 years for boys (mean: 0.4; standard deviation: 1.0) and 0.6 years

for girls (mean: 0.7; standard deviation: 1.0).

In order to try and avoid this overestimation, a new standard for boys and girls

with age scores expressed in years (specific to this population) were formulated.

Adding the overall maturity scores for the seven mandibular teeth directly gives

an estimate of dental age. The accuracy of the new standard was then tested on

the hold-out sample and compared to the accuracy of the original method when

applied to the same sample. The original method resulted in an overestimation

for boys by 0.5 years and girls by 0.6 years. The new adapted method resulted in

a smaller overestimation for boys and girls (0.1 and 0.2 years respectively). The

authors concluded that the adapted method resulted in more accurate dental

age estimations in this population, but it may not be as accurate in other

populations.

3.4. Dental age estimation using the third molars

The third molars are the most variable teeth in regards to their size, shape, and

formation. The third molars, however, are also the only teeth to complete their

formation after the onset of puberty; they exhibit an unusually long

developmental course lasting more than 10 years (approximately 8.5 to 20

years). This is a period when very few other skeletal markers of biological age

are available for assessment; hence mineralization of the third molars is

considered the main criterion for dental age estimation of adolescents and living

individuals without documentary evidence of birth (Olze et al. 2006).

Demirjian et al. (1973) did not specifically evaluate the development of the third

molars for age estimation, however, a number of other researchers have

assessed this tooth by modifying his eight stage (A-H) system. As the main focus

of the present study is to evaluate the accuracy of age estimation to third molars,

a selection of the most relevant studies are considered below.

3.4.1. Mincer et al. (1993)

Mincer et al. (1993) proposed a method to evaluate the mineralization of the

third molars in relation to chronological age. The rationale for using the third

molars was that all the other teeth have completed development by 14 to15

years of age. The development of this tooth, therefore, may be used to estimate

age in ‘older’ sub-adults. The sample consisted of 823 (54% females and 46%

males) individuals of different ethnicities (80% American Caucasian, 19%

African American and 1% unspecified). Since the African American sample size

was relatively small, the authors pooled the data for both sexes. The authors

adapted Demirjian et al’s. (1973) eight stage (A-H) tooth development

classification system to score third molar mineralization. The authors reported

that the maxillary third molars were fully developed by 20.2 years in American

Caucasian males; 20.6 years in American Caucasian females; and 20.4 years in

African Americans. Mandibular third molars were fully developed by 20.5 years

in Caucasian males; 20.9 years in Caucasian females; and 21.4 years in African

Americans. The authors concluded that males were ahead of females in third

molar root formation and eruption (by 4 months in American Caucasians).

3.4.2. Chaillet et al. (2004)

Chaillet et al. (2004) examined third molars in a French population to evaluate

the applicability of the Demirjian et al. (1973) method. The study consisted of

1031 individuals (561 females and 740 males) aged 2 to 18 years. They modified

the original method to include two additional stages of mineralization, thus

bringing the total number of stages to 10 for each tooth. Their study showed

that inclusion of third molars increased the reliability (from 10.2% to 4.2% of

error) and predicted accuracy by ± 2 years, as compared to the original

Demirjian et al. (1973) system.

3.4.3. Arany et al. (2004)

Arany et al. (2004) adapted the Demirjian et al. (1973) method to assess

mandibular and maxillary third molar maturity in 1289 Japanese juvenile

individuals aged 14 to 24 years. The aim of the study was to establish juvenile

forensic reference data on third molar development in that population. They

observed statistically significant differences in the maturity of the mandibular

and maxillary third molars and also between the sexes. Males attained root

development earlier (by 8 months) than females of the same age group.

Maxillary third molars showed more advanced calcification than the mandibular

third molars. The accuracy of age estimation based on this method was

calculated by averaging the differences between chronological and estimated

age. The mean difference was 1.6 years for both sexes with a standard deviation

of 1.2 years.

3.4.4. Prieto et al. (2005)

Prieto et al. (2005) assessed the estimation of chronological age based on third

molar development in a Spanish population by applying the eight stage (A–H)

method of Demirjian et al. (1973). The sample consisted of 1,054 OPG’s of

Spanish individuals of known chronological age (range 14–21 years) and sex

(462 male and 592 female). The results showed a stronger correlation to

chronological age for the males (0.54) compared to the females (0.45). Root

formation occurred earlier in stages E to G in the males; the mean difference

between chronological and estimated age was –0.10 years (±1.23 SD) for the left

third molar and –0.07 years (±1.22 SD) for the right third molar. No significant

bilateral differences were observed. The authors concluded that third molar

mineralisation took place earlier in their Spanish population, than published

data compared to French-Canadian (Demirjian et al. 1973), Scandinavian

(Kullman et al. 1992), American (Solari et al. 2002), German (Olze et al. 2003),

Japanese (Olze et al. 2003) and South African (Olze et al. 2003) population.

3.4.5. Olze et al. (2006)

Olze et al. (2006) conducted an extensive series of studies on third molar

mineralization by applying the Demirjian et al. (1973) method to a variety of

populations (German, Japanese and South African). Those studies are

considered below:

i) Olze et al. (2003) assessed the mineralization status of the third molars

in a Japanese and a German population. The aim of the study was to

gather statistically usable data relating to the mineralization rate of this

tooth in different ethnic groups. They examined the OPG’s of 1597

Japanese and 1434 German individuals aged between 12 and 26 years.

The results showed significant differences between stages D, E and F for

both populations. Japanese men and women reached stages D, E and F

approximately 2 to 3 years later than their German counterparts. It was

concluded that as they demonstrated statistically significant differences

between both populations, population specific reference data should be

used when assessing different ethnic groups, which will reduce the error

in forensic age estimation.

ii) Olze et al. (2006) examined third molar mineralization status in a South

African population. The study consisted of 595 OPG’s of 474 males and

121 females, aged 10 to 26 years. Statistically significant differences were

observed between the upper and the lower arch; lower third molars

developed 0.8 years earlier than the upper third molars. Significant sex

differences were found with regard to the age at which the lower left

third molar reached stage G; females reached this stage 1.5 years earlier.

No significant bilateral differences were observed. As previously noted,

this is in contrast to other studies, where the upper third molars, were

shown to develop earlier than the lower third molars, with males

developmentally ahead of females. Again it was concluded that

population specific standards should be used for the most accurate age

estimations.

3.4.6. Zeng et al. (2010)

Zeng et al. (2010) assessed the chronology of third molar mineralization by

applying the Demirjian et al. (1973) method to a Han population in southern

China. A total of 3100 OPG’s of individuals aged between 4.1 to 26.9 years were

examined. The authors concluded that regardless of sex, the chronological age of

third molar mineralization was bilaterally symmetrical. Third molar

mineralization in males was 5 to 9 months earlier than females. In comparison

with the Olze et al. (2008) study, the authors reported that dental development

of the Han population was 1 to 4.6 years earlier than that of a Japanese

population. According to the study of Olze et al. (2003), their German population

reached third molar stages D to G earlier (2 to 3 years) than their Japanese

sample. However, the Han (southern China and Japan) are of an Asian ethnicity;

it is confusing why there appears to be a significant difference in the third molar

mineralization age. The authors thus conclude that further study is required

among different ethnic groups.

3.5. Brief review of other methods

There are number of other tooth classification standards available for forensic

age estimation from the developing dentition: e.g. Gleiser and Hunt (1955);

Nolla (1960); Haavikko (1970); Liliequist and Lundberg (1971); Gustafson and

Kosh (1974); Harris and Nortje (1984); and Kullman et al. (1992). These

methods differ with regard to the number of stages, definition and illustration of

each stage.

3.5.1. Gleiser and Hunt (1955)

This method comprises seventeen different developmental stages of tooth

mineralization based on the fractions of future length of the crown or root. The

sample analysed included randomly selected lateral jaw radiographs of 25 boys

and 25 girls from Boston, USA. The stages are illustrated with accompanying

written descriptions. Olze et al. (2005) evaluated the mineralization status of the

third molar using common classification systems devised by Gleiser and Hunt

(1955) and Demirjian et al. (1973). The results for Gleiser and Hunt method

showed an intra-class coefficient of >0.95 and eta coefficient (correlation

between estimated age and true age) of 0.879. However Demirjian et al.’s

method showed the highest intra-class coefficient of >0.98 and eta coefficient of

0.883. The authors concluded that although accurate results were achieved by

the Gleiser and Hunt method, the Demirjian method was considered to be the

most accurate of the five methods they reviewed, as the stages are defined by

changes in form and do not depend on speculative estimates of length (Olze et al.

2005).

3.5.2. Gustafson and Koch (1974)

Gustafson and Koch (1974) proposed a four stage tooth development

calcification system based on actual tooth length. This system only has a written

description without any illustrations of the stages. This method showed an

intra-class coefficient of <0.90, eta coefficient of <0.8, and had higher intra and

inter-observer error than the method devised by Demirjian et al. (1973). The

lower accuracy of the Gustafson and Koch method is likely associated with fewer

tooth mineralization stages (Olze et al. 2005).

3.5.3. Harris and Nortje (1984)

Harris and Nortje (1984) developed a five stage written and diagrammatic tooth

classification system to estimate chronological age. The five stage system is

based on estimates of crown or root length. This classification system yielded

lower accuracy (intra-class coefficients of <0.90) than the system devised by

Demirjian et al. (1973) due to fewer stages, which results in a larger age interval

between stages. The flow-on effect of this is greater error in age estimation (Olze

et al. 2005).

3.5.4. Kullman et al. (1992)

Kullman et al. (1992) proposed a seven stage classification system based on

tooth length. This system included both a written and diagrammatic illustration

of the seven stages. Olze et al. (2005) reported that after the Demirjian et al.

(1973) method, the Kullman et al. method has the highest correlation between

actual age and estimated dental age (0.880).

3.6. Australian Research

3.6.1. Farah et al. (1999)

Farah et al. (1999) assessed dental maturity in children from Perth, Western

Australia, using the Demirjian et al. (1973) method. Their cross sectional study

included 1450 children (690 males and 760 females) aged 4.0 to 16.0 years.

They found that females of 5 to 7 years were more dentally advanced (by up to

12 months) than males of the same age group. There were no significant

differences between the age group of 7 to 8 years or beyond 12 years of age.

However, they did not include the third molar in their study and only considered

the four permanent mandibular teeth; specifically the lower first and second

premolars and the lower first and second molars. Their results indicated that

the probability of prediction of chronological age from estimated age using the

Demirjian et al. (1973) method was 51.7% for females and 56.4% for males. A

strong correlation between mean estimated age and actual age were observed

(R2 = 0.970 for males and R2= 0.975 for females). The authors concluded that the

Demirjian et al. (1973) eight stage system was convenient to use as well as

reproducible and can be applied to a Western Australian population.

3.6.2. McKenna et al. (2002)

McKenna et al. (2002) evaluated the accuracy of the Demirjian et al. (1973)

method in a sample of 615 (288 males and 327 females) South Australian sub-

adults aged 4.9 to 16.9 years. Their study involved scoring the teeth (from

OPG’s) in the left mandibular quadrant, with the exception of the third molars.

For any tooth missing on the left side the equivalent tooth on the right side was

used. The estimated and actual age were compared; only a small percentage of

individuals (34.7% of boys and 36.9% of girls) estimated and chronological age

was within 6 months. The South Australian sub-adults were found to be less

dentally mature in their earlier years, but more advanced after 15 years as

compared to the French-Canadian population originally considered by

Demirjian et al. (1973). McKenna concluded that the Demirjian et al. (1973)

method is not an accurate method for estimating dental age in South Australian

sub-adults.

3.6.3. Flood (2007)

Flood (2007) examined Western Australian sub-adults to evaluate the

applicability of three established dental development standards; Demirjian et al

(1973), Ubelaker (1987) and Mincer et al. (1993). A total of 225 randomly

selected OPGs were collected from a clinical database, comprising 119 females

and 106 males, aged 2.8 to 23.5 years. The results showed that the accuracy of

the Ubelaker method varied more than the other two methods. The estimation

of age for individuals older than 15 years indicated that all the three methods

under estimated chronological age by an average of 2 years (Ubelaker method);

16 months (Demirjian et al. method); and 4 months ( Mincer et al. method). On

the other hand estimation of age for individuals less than 15 years showed that

Mincer and Demirjian methods overestimated age by an average of 1.7 and 1.1

years respectively; the Ubelaker method underestimated age by 1.4 years. Flood

concluded that the Demirjian et al. (1973) and Mincer et al. (1993) methods

were more accurate than the Ubelaker (1987) method; the Demirjian et al.

(1973) method being more accurate for individuals under 15 years of age and

the Mincer et al. (1993) method for individuals older than 15 years of age.

3.6.4. Blenkin and Evans (2010)

Blenkin and Evans (2010) evaluated the applicability of the Demirjian et al.

(1973) method to a New South Wales (Sydney) population. The sample

consisted of 3261 OPG’s of 1623 females and 1038 males aged between 1 to 23

years. The Demirjian standards resulted in a consistent overestimation of

chronological age in children under the age of 14 years (by 0.61 years in males

and 0.42 years in females) and an underestimation of chronological age in

children over 14 years (by 2.18 years for both sexes). These results are

consistent with other Australian study of McKenna et al. (2002) and indicates

that the mean rate of dental development of the Australian samples are

significantly different to that of the French-Canadian population originally

considered by Demirjian et al. (1973).

3.7. Indian research:

3.7.1. Koshy and Tandon (1998)

Koshy and Tandon (1998) assessed the applicability of the Demirjian et al.

(1973) dental age system to South Indian sub-adults. A total 184 OPG’s (93

males and 91 females) of individuals aged 5 to 15 years were examined. Their

study involved scoring seven permanent teeth in the left mandibular quadrant

(with the exception of the third molars). An attempt was made to compile a

maturity standard for South Indian sub-adults. It was found that Demirjian et

al’s (1973) method overestimated age by 3.04 years in males and 2.82 years in

females. The comparison of estimated dental age with the actual age showed no

significant difference for males and females.

3.7.2. Prabhakar et al. (2002)

Prabhakar et al. (2002) evaluated the applicability of the Demirjian et al. (1973)

method to a Davangere (South India) population. The sample consisted of 151

OPG’s (78 males and 73 females) aged 6 to 15 years. Their study involved

scoring of seven permanent teeth in the left mandibular quadrant (again with

the exception of third molars). The developmental stage of each tooth was

converted into a maturity score, and summing the overall maturity score for the

seven mandibular teeth directly gives an estimate of dental age. A statistically

significant correlation between actual and dental age was reported (r = 0.94 in

males and r = 0.95 in females). Dental age was found to be overestimated by

±1.02 to 1.20 years and ±0.87 to 0.90 years in males and females respectively.

3.7.3. Hegde and Sood (2002)

Hegde and Sood (2002) evaluated the accuracy of the Demirjian et al. (1973)

dental age system in a Belgaum population in South India. The sample consisted

of 197 OPG’s of 94 males and 103 females of known chronological age (6 to 13

years). They assessed the development of all the left permanent mandibular

teeth, except for the third molars. They found a significant positive correlation

between estimated dental and chronological age for both sexes (r =0.985 for

males and r = 0.988 for females). They reported an overestimation of

chronological age by 0.14 years (51 days) for males and 0.04 years (15 days) for

females in their older age group (10 to 12 years). This study was in accordance

with Nanda and Chawla (1966) and Sapoka and Demirjian (1971), who reported

that dental development of French-Canadian sub-adults is closely correlated to

Lucknow (Indian) sub-adults. The authors thus concluded that their study

supports the use of Demirjian et al. (1973) method for age estimation in India in

particular to a Belgaum (South Indian) population.

3.7.4. Rai et al. (2009)

Rai et al. (2009) assessed the estimation of chronological age based on

mandibular third molar development in a North Indian population by applying

the eight stages (A–H) method of Demirjian et al. (1973). The authors examined

250 OPG’s of 124 males and 126 females aged between 7 to 26 years.

Statistically significant differences were observed in third molar development

with regard to the calcification of stage D (±4.33 SD for females and ±5.62 SD for

males) and stage G (±4.67 SD for females and ±4.46 SD for males). Their results

indicated that third-molar formation was attained earlier in females (by 6 to 21

months).

3.8. Summary

Although, the various dental age estimation studies described above yielded

high degrees of reliability, ethnic differences between various population groups

are found to affect prediction accuracy resulting in overestimation or

underestimation of chronological age. It appears to be generally accepted that

the method devised by Demirjian et al. (1973) is appropriate for evaluating third

molar mineralization for forensic age estimation. Further, after reviewing the

literature, the Demirjian et al. (1973) method has not been extensively applied

to the third molars in either a Western Australian or South Indian population. To

that end, this study will primarily focus on evaluating the accuracy of this

method and to provide population specific reference data for forensic

application in these populations.

Chapter Four

Materials and Methods

4.1. Materials

A total of 561 conventionally taken orthopantomographs (OPGs) of 312 Western

Australian (173 males and 139 females aged between 7 to 30 years) and 249

South Indian (124 males and 125 females aged between 7 to 30 years)

individuals were examined. The age and sex distribution of the samples for both

populations are shown in Tables 4.1 – 4.2 and Figures 4.1 - 4.2. The OPGs used in

this project were taken as part of routine therapeutic scans. OPGs are full mouth

x-rays that show all the upper and lower teeth, both erupted and unerupted (see

4.1.2 below). The OPGs from the Western Australian population were obtained

through the Picture Archive and Communication System (PACS) from medical

practices of various Western Australian hospitals (e.g. Charles Gardner; Royal

Perth) following established ethical guidelines. The OPGs from Southern India

were obtained from diagnostic and radiography centres in Bangalore, India, in

accordance with established ethical guidelines.

The OPGs were anonymised prior to receipt, thus ensuring patient

confidentiality. There was no actual contact with any patient nor were they

informed about any aspects of this project. The criteria for inclusion in the

sample were adequate OPG quality and no evidence of apparent pathology that

could affect the presence and development of the third molars. Ethics approval

to undertake this project was granted by the Human Research Ethics Committee,

of the University of Western Australia (Reference no. RA/4/1/4158).

Table 4.1: Age and sex distribution of the Western Australian population.

Age (years) Male Female Total

n % n % n % 7 10 3.21 7 2.24 17 5.45 8 12 3.85 8 2.56 20 6.41 9 8 2.56 6 1.92 14 4.49

10 12 3.85 9 2.88 21 6.73 11 9 2.88 13 4.17 22 7.05 12 18 5.77 12 3.85 30 9.62 13 6 1.92 4 1.28 10 3.21 14 8 2.56 7 2.24 15 4.81 15 5 1.60 8 2.56 13 4.17 16 12 3.85 10 3.21 22 7.05 17 8 2.56 8 2.56 16 5.13 18 6 1.92 5 1.60 11 3.53 19 10 3.21 10 3.21 20 6.41 20 4 1.28 3 0.96 7 2.24 21 3 0.96 7 2.24 10 3.21 22 10 3.21 5 1.60 15 4.81 23 5 1.60 4 1.28 9 2.88 24 5 1.60 0 0.00 5 1.60 25 7 2.24 3 0.96 10 3.21 26 2 0.64 2 0.64 4 1.28 27 3 0.96 1 0.32 4 1.28 28 4 1.28 1 0.32 5 1.60 29 4 1.28 2 0.64 6 1.92 30 2 0.64 4 1.28 6 1.92

Total 173 55.45 139 44.55 312 100

Figure 4.1: Age and sex distribution of the Western Australian population.

02468

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7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Num

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f ind

ivid

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(n)

Age

Total number of male and female individuals

Male

Female

Table 4.2: Age and sex distribution of the South Indian population.

Age (years) Male Female Total

n % n % n % 7 0 0.00 1 0.40 1 0.40 8 0 0.00 0 0.00 0 0.00 9 1 0.40 1 0.40 2 0.80

10 8 3.21 3 1.20 11 4.42 11 3 1.20 4 1.61 7 2.81 12 9 3.61 8 3.21 17 6.83 13 12 4.82 6 2.41 18 7.23 14 10 4.02 8 3.21 18 7.23 15 6 2.41 9 3.61 15 6.02 16 10 4.02 7 2.81 17 6.83 17 6 2.41 7 2.81 13 5.22 18 10 4.02 9 3.61 19 7.63 19 6 2.41 8 3.21 14 5.62 20 11 4.42 6 2.41 17 6.83 21 5 2.01 9 3.61 14 5.62 22 4 1.61 7 2.81 11 4.42 23 5 2.01 13 5.22 18 7.23 24 4 1.61 6 2.41 10 4.02 25 3 1.20 6 2.41 9 3.61 26 3 1.20 2 0.80 5 2.01 27 3 1.20 0 0.00 3 1.20 28 3 1.20 3 1.20 6 2.41 29 2 0.80 0 0.00 2 0.80 30 0 0.00 2 0.80 2 0.80

Total 124 49.80 125 50.20 249 100

Figure 4.2: Age and sex distribution of the South Indian population.

0

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6

8

10

12

14

7 8 9 101112131415161718192021222324252627282930

Num

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(n)

Age

Total number of male and female individuals

Male

Female

4.1.1. Population

The specific ethnicity was not known for any individual in either the Western

Australian or South Indian sample. The study sample comprises individuals of

various ethnic backgrounds (primarily caucasian) but overall it is representative

of a ‘typical’ Western Australian population (Franklin et al. 2011). However, for

the former sample, it is known that there are no participants of Australian

Aboriginal descent. Both male and female participants are assumed to be of

good general health with no evidence of pathology or trauma affecting the

dental structures being examined in this study.

4.1.2. Orthopantomographs (OPGs)

Orthopantomographs (also known as panoramic radiography or

pantomography) are extra oral radiographs that produce a single image of the

facial structures, including both the maxillary (upper) and mandibular (lower)

arches and their supporting structures (White and Pharaoh, 2000). Panoramic

radiography is often used as the initial survey film to help provide the required

clinical insight for diagnosis or to assist in determining the need for other

radiographs. These radiographs have inherent advantages and disadvantages, as

compared with other radiographic techniques (e.g: periapical, bite-wings, and

occlusal radiographs), which are discussed below.

i) Advantages: The principal advantage of panoramic images is their broad

coverage of the facial bones and teeth, which are clinically most useful for

diagnosing problems. These radiographs are especially useful in the

evaluation of trauma, tooth development (especially during mixed

dentition period 6 to 13 years), retained teeth or root tip and

developmental anomalies (e.g. peg-lateral; super numerary teeth). OPG’s

have a low patient radiation dose and panoramic images can be made

within a very short time (3 to 4 minutes). Furthermore, OPGs can be used

in patients who are unable to open their mouth (e.g: jaw bone fractures).

ii) Disadvantages: The main disadvantage of OPGs is that the image does

not display the fine anatomical details that are found in intra-oral

periapical radiographs. Visualization of fine anatomical details are

necessary for detecting small carious lesions and bone and gum diseases.

The other problem associated with these radiographs are uneven

magnification and geometric distortion; the presence of overlapping

structures, such as the cervical spine, can mask odontogenic lesions,

especially in the mandibular incisor region. However, despite these

disadvantages, OPGs are very useful for examination of the developing

dentition, thus OPGs were accordingly used to examine third molar

mineralization in the present study.

4.2. Methods

4.2.1. Introduction

In the present study third molar development was evaluated according to the

eight stage (A – H) tooth classification system proposed by Demirjian et al.

(1973). Although the authors did not consider the third molar in their study,

Arany et al. (2004) and Mincer et al. (1993) successfully adapted the Demirjian

et al. (1973) method to quantify third molar maturity (see Chapter Three). A

range of different classifications for evaluating tooth mineralization are

available in the literature (as discussed in Chapter Three), however the

Demirjian method defines stages by changes of shape, independent of

speculative estimations of lengths, therefore this method was considered the

most appropriate for the present study.

4.2.2. Data Collection

The stage of development and mineralization of all four third molars in each

OPG were examined and assessed according to the A-H stages described by

Demirjian et al. (1973). These stages are described in written and diagrammatic

form. The first four stages (A – D) encompass crown mineralization and the

second four stages (E – H) cover root formation and apical closure. After

allocation of a stage (A – H; “0” used to indicate a missing tooth) to each

individual third molar, the assigned stages are recorded on the data sheet for

that specific OPG along with sex and age.

4.2.2.1. Demirjian et al. (1973) stage descriptions

The authors provided a written description and illustration for stages A-H as

described below. Figures 4.3 (a-h) shows the developmental status of both

uniradicular and multiradicular teeth; from left to right – molars, premolars,

canines and incisors.

Stage descriptions

i) Stage A: In both uniradicular and multiradicular teeth, the initiation of

calcification is seen at the superior level of the crypt in the form of an

inverted cone or cones. There is no fusion of these calcified points (Figure

4.3a).

Figure 4.3a: Stage A of the Demirjian et al. (1973) method.

ii) Stage B: Fusion of the calcified points forms one or several cusps which

unite to give a regularly outlined occlusal surface (Figure 4.3b).

Figure 4.3b: Stage B of the Demirjian et al. (1973) method.

iii) Stage C

a. Enamel formation is complete at the occlusal surface. Its extension and

convergence towards the cervical region is evident;

b. The beginning of dentinal deposit is visible;

c. The outline of the pulp chamber has a curved shape at the occlusal

border (Figure 4.3c).

Figure 4.3c: Stage C of the Demirjian et al. (1973) method.

iv) Stage D

a. Crown formation is complete to the level of the cemento-enamel junction;

b. The superior border of the pulp chamber in the uniradicular teeth has a

definite curved form, being concave towards the cervical region. The

projection of the pulp horns (if present) results in outline shaped like an

umbrella top. In the molars the pulp chamber has a trapezoidal form;

c. Beginning of root formation is apparent in the form of a spicule (Figure

4.3d).

Figure 4.3d: Stage D of the Demirjian et al. (1973) method.

v) Stage E

Uniradicular teeth:

a. The walls of the pulp chamber now form straight lines, whose continuity

is broken by the presence of the pulp horn, which is larger than in the

previous stage;

b. The root length is less than crown height.

Multiradicular teeth:

a. Initial formation of the radicular bifurcation is evident in the form of

either a calcified point or a semi-lunar shape;

b. Root length is still less than crown height (Figure 4.3e).

Figure 4.3e: Stage E of the Demirjian et al. (1973) method.

vi) Stage F

Uniradicular teeth:

a. The walls of the pulp chamber now form a more or less isosceles triangle.

The apex ends in a funnel shape;

b. Root length is equal to or greater than crown height.

Multiradicular teeth:

a. The calcified region of the bifurcation has developed down further from

its semi-lunar stage to give the roots a more definite and distinct outline with

funnel shaped endings;

b. Root length is equal to or greater than crown height (Figure 4.3f).

Figure 4.3f: Stage F of the Demirjian et al. (1973) method.

vii) Stage G: The walls of the root canal are now parallel and the apical end is

still partially open- distal root in molars (Figure 4.3g).

Figure 4.3g: Stage G of the Demirjian et al. (1973) method.

viii) Stage H

a. The apical end of the root canal is completely closed (distal root on

molars);

b. The periodontal membrane has a uniform width around the root and the

apex (Figure 4.3h).

Figure 4.3h: Stage H of the Demirjian et al. (1973) method.

4.2.2.2. Criterion for allocation of stages

In assigning a developmental stage to a tooth Figure 4.3a-h are used in

conjuction with the written criteria as described above. Demirjian et al. (1973)

also provided a set of guidelines that should also be met in order to allocate a

stage to a tooth as described below:

i) If only one written criterion is provided, then this must be met for the stage

to be considered as reached;

ii) If two criteria are indicated, then it is sufficient if the first statement has been

met for the stage to be recorded as reached;

iii) If three criteria are indicated, the first two of them must be met for the stage

to be considered reached and documented.

At each stage, in addition to the criteria for that stage, the criteria for the

previous stage must be satisfied. In borderline cases the earlier stage is always

assigned.

4.2.2.3. Assessment of intra-observer error

A precision study was conducted to assess the degree of intra-observer error.

This involved scoring all four third molars of 50 randomly selected OPGs and

then re-analysing them approximately three months after the initial analysis.

This time gap was left between the second assessment because it ensured a

minimal possibility of recalling results from the first assessment. The

significance of the level of agreement between the two assessments was

quantified using the Cohen’s Kappa test; the results are presented in Chapter

Five.

i) Cohen’s Kappa: The Kappa statistics provides a reliable indication of the

level of agreement between assessments. It takes into account the

proportion of times that two observed analyses are consistent and

negates the proportion of agreement between them that is chance-

expected. A high Kappa value indicates a high degree of consistency

between assessments therefore, implies a low level of intra-observer

error. According to Landis and Koch (1997) the following Kappa values

represent the respective degree of reliability. (Table 4.3).

Table 4.3: Interpretation of Kappa Value (from Landis and Koch, 1997).

Kappa Values Agreement <0 Less than chance agreement

0.01 – 0.20 Slight Agreement 0.21 – 0.40 Fair Agreement 0.41 – 0.60 Moderate Agreement 0.61 – 0.80 Substantial Agreement 0.81 – 0.99 Almost Perfect Agreement

4.2.3. Data Analysis

Following the allocation of a developmental stage to each third molar, an

average chronological age of attainment for the eight stages of dental

development is calculated; differences exhibited in development between the

upper and lower arches, bilateral and sex differences are also quantified.

Descriptive statistics are obtained by calculating the mean age, standard

deviation and range of age of attainment of each stage for both sexes. The

prevalence of third molars in the four quadrants is also determined in-order to

estimate the frequency of absence.

4.2.3.1. Statistical analyses

The statistical significance of variation between mean age of stage attainment

between both sexes, upper and lower arches and bilateral differences is tested

using the Mann-Whitney U test. All statistical analyses are performed using the

SPSS software package (SPSS 19.0 Inc., Chicago, IL).

i) Mann-Whitney U Test: Mann-Whitney U Test is used to evaluate the

differences between two independent groups on a continuous measure.

This test is a nonparametric alternative to a t-test, but instead of

comparing the means of the two groups, the Mann-Whitney test actually

compares medians by converting the scores on the continuous variable to

ranks across the two groups. Then the test evaluates whether the ranks

for the two groups differ significantly (Pallant, 2007).

To conduct the Mann-Whitney U test, each case must have scores on two

variables; the grouping variable and the test variable. The grouping

variable divides cases into two groups (or categories) and the test

variable assesses individuals on a variable with at least an ordinal scale

(Green and Salkind, 2008).

Chapter Five Results

5.1. Introduction

This chapter presents the descriptive statistics and statistical analyses of all four

third molars in both sexes for the Western Australian and South Indian

populations. The chapter first outlines the results of the intra-observer error

calculations and continues with the descriptive statistics and other statistical

analyses of the individual third molars in the Western Australian and South

Indian population.

5.2. Assessment of Intra-observer error

The results of the precision test between the two sets of repeat data are

summarized in Table 5.1. All of the Kappa values for each tooth range between

0.857 to 0.929 and thus indicate an “almost perfect agreement” between the

first and second assessment (see Chapter Four).

Table 5.1: Kappa values, indicating levels of agreement

Tooth Kappa Value 18 (UR) 0.928 28 (UL) 0.857 38(LL) 0.858 48(LR) 0.929

5.3. Descriptive statistics: Western Australian population

The descriptive statistics, including the mean, standard deviation and the range

of age of attainment of each stage (A- H) for all four third molars are presented

below.

5.3.1. Upper Right Third Molar

A summary of the descriptive statistics relating to the development of the upper

right third molar in males and females is shown in Table 5.2.


stages A - H for the upper right third molar in males and females.

Upper Right Third Molar (Western Australia) Demirjian

Stage Male Female Significance

N Mean SD Min Max N Mean SD Min Max Z value Stage A 8 9.12 1.55 7 12 9 9.33 0.86 8 10 0.544 NS Stage B 8 10.25 0.88 9 11 15 11.42 1.22 9 14 0.058 NS Stage C 14 12.21 0.80 11 14 12 11.83 1.11 10 14 0.286 NS Stage D 8 14.37 0.80 12 16 12 14.66 1.37 12 17 0.604 NS Stage E 6 15.00 1.09 13 16 8 15.12 1.55 12 17 0.685 NS Stage F 10 16.40 1.26 14 19 10 17.10 1.44 15 19 0.243 NS Stage G 8 19.50 2.77 17 25 6 19.83 0.98 19 21 0.359 NS Stage H 44 23.44 3.62 18 30 13 23.23 3.65 19 30 0.826 NS KEY: NS = Not Significant.

As shown in Table 5.2, the mean age of attainment of stage A for the upper right

third molar in males is 9.12 years and 9.33 years in females. The mean age of

crown completion (stage D) for this tooth is 14.37 years and 14.66 years in

males and females respectively, whereas the mean age of completion of

development (root apical closure - stage H) is 23.44 years in males and 23.23

years in females. There are no statistically significant differences in the mean

age of stage attainment between males and females (Table 5.2). The largest

standard deviation is for stage H (male 3.62; females 3.65). In males the smallest

standard deviation of 0.80 years is for stages C and D, whereas in females the

smallest standard deviation is for stage A (0.86 years).

It is evident that the mean age of attainment of developmental stages follows a

general trend of increasing age between each successive stage (A to H) in both

males and females (Figure 5.1). An average increase of 1.5 years was observed

from stages A to C and between stages E and F, whereas an average increase of

3.5 years was found between stages F and G and 4 years between G and H in

males. In females an average increase of 2.5 years was observed between stages

A and B, C and D, E and F, F and G and 3.4 years between stages G and H.



5.3.2. Upper Left Third Molar


left third molar in males and females is shown in Table 5.3.


stages A - H for the upper left third molar in males and females.

Upper Left Third Molar - Western Australia

Demirjian Stage

Male Female Significance N Mean SD Min Max N Mean SD Min Max Z value

Stage A 9 8.88 1.05 7 10 6 9.00 0.89 8 10 0.902 NS

Stage B 9 11.00 1.00 9 12 13 11.15 1.81 8 14 0.973 NS Stage C 14 12.50 1.28 11 16 14 12.28 1.72 11 16 0.289 NS Stage D 5 13.80 1.09 12 15 15 14.66 1.49 12 17 0.179 NS

Stage E 6 14.83 1.16 13 16 7 14.85 1.57 12 17 0.941 NS

Stage F 10 16.30 1.33 14 19 8 17.12 1.24 15 19 0.155 NS

Stage G 9 18.66 2.64 16 25 7 19.57 0.97 19 21 0.063 NS Stage H 46 23.47 3.60 17 30 14 23.85 3.37 19 30 0.725 NS

KEY: NS = Not Significant.

As shown in Table 5.3, the mean age of attainment of stage A for the upper right


0

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15

20

25

A B C D E F G H

Mea

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Yea

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Developmental Stage

Upper Right Third Molar (Western Australia)

Male Mean

Female Mean

crown completion (stage D) for this tooth is 13.80 years and 14.66 years in

males and females respectively, whereas the mean age of root apical closure

(stage H) is 23.47 years in males and 23.85 years in females. There are no

statistically significant differences in the average age of stage attainment

between males and females. The largest standard deviation (3.60 and 3.37

years) is for stage H in males and females respectively. In males the smallest

standard deviation was for stage B (1.00 years) and in females it is for stage A

(0.89 years).

Figure 5.2 shows that dental development follows a general trend of increasing

age between each successive stage (A to H) in males and females. An increase of

1.5 to 2.0 years was observed between each successive stages A to F and an

increase of 4.81 years for stages G to H in males. In females an average increase

of 1.0 to 2.5 years was observed between stages A to G, whereas an increase of

4.3 years was observed between stages G to H (Table 5.3).



0

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25

30

A B C D E F G H

Mea

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Yea

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Developmental Stage

Upper Left Third Molar (Western Australia)

Male Mean

Female Mean

5.3.3. Lower right third molar

A summary of the descriptive statistics relating to the development of the lower




Lower Right Third Molar (Western Australia)

Demirjian Stages

Male Female Significance

N Mean SD Min Max N Mean SD Min Max Z value

Stage A 18 9.11 1.40 7 12 12 10.08 1.67 8 14 0.108 NS

Stage B 15 11.66 1.04 10 13 11 10.81 1.25 9 13 0.077 NS

Stage C 14 13.00 1.24 12 15 17 13.00 2.34 8 17 0.902 NS

Stage D 2 14.50 2.12 13 16 4 15.55 1.29 14 17 0.481 NS

Stage E 4 15.25 0.95 14 16 10 16.00 1.82 12 18 0.279 NS

Stage F 7 16.42 1.27 14 18 3 18.33 3.05 15 21 0.298 NS

Stage G 8 19.12 3.04 16 25 13 19.07 1.49 16 21 0.556 NS

Stage H 38 23.07 3.46 18 29 14 24.57 2.82 21 30 0.114 NS KEY: NS = Not Significant.

As shown in Table 5.4, the mean age of attainment for stages A and B for the

lower right third molar in males is 9.11 and 11.66 years and in females it is

10.08 and 10.81 years. The mean age of crown completion (stage D) is 14.50

years for males and 15.55 years for females, whereas the mean age of root apical

closure (stage H) is 23.07 years and 24.57 years in males and females

respectively. There are no statistically significant differences in mean age of

attainment of stages A – H between males and females (Table 5.4). The smallest

standard deviation of 0.95 years was observed in stage E for males and for

females the smallest value was stage B at 1.25 years. The largest standard

deviation of 3.46 years and 3.05 years were observed for stage H and F in males

and females respectively.

Figure 5.3 clearly demonstrates that in both sexes the mean age of attainment of

developmental stages follows a general trend of increasing age between stages A

to H. In males an average increase of 1.5 to 2.5 years was observed between

each stages A to D and stages E and F and 4 years between stages G and H. In

females an increase of 2.5 years was observed between stages B to F and 5.5

years for stages G and H (Table 5.4; Figure 5.3).



5.3.4. Lower left third molar





Lower Left Third Molar (Western Australia) Demirjian

Stages Male Female Significance

N Mean SD Min Max N Mean SD Min Max Z value Stage A 18 9.22 1.59 7 13 11 10.09 1.75 8 14 0.134 NS

Stage B 15 11.53 0.99 10 13 12 10.83 1.26 9 13 0.135 NS

Stage C 14 12.92 1.32 11 15 19 13.47 2.50 8 17 0.468 NS

Stage D 1 13.00 N/A N/A N/A 3 15.00 1.00 14 16 0.180 NS

Stage E 7 15.42 0.78 14 16 8 16.00 2.00 12 18 0.283 NS

Stage F 7 16.57 1.27 14 18 6 17.83 2.71 15 21 0.417 NS

Stage G 5 17.60 1.14 16 19 10 18.90 1.52 16 21 0.070 NS

Stage H 41 23.04 3.53 17 29 15 24.66 3.39 19 30 0.120 NS KEY: N/A= Not Applicable; NS = Not Significant;

0

5

10

15

20

25

30

A B C D E F G H

Mea

n A

ge (

Yea

rs)

Developmental Stage

Lower Right Third Molar (Western Australia)

Male Mean

Female Mean

As shown in Table 5.5, the mean age of attainment of stage A for the lower left


crown completion (stage D) and root apical closure (stage H) for this tooth is

13.00 and 23.04 years in males and 15.00 and 24.66 years in females

respectively. There are no significant differences in the average age of stage

attainment for this tooth in both males and females. The largest standard

deviation of 3.53 years and 3.39 years were for stage H in males and females

respectively. The smallest standard deviation in males was 0.78 years for stage E

and 1.00 years for females in stage D (Table 5.5).

As shown in Figure 5.4 there is general increase in age between stages A – H in

males and females, with an average increase of 1.5 to 2.5 years for each stages

between A to C in males and an increase of 1.5 years between each stages B to D

in females.


stages for the lower left third molar in males and females.

0

5

10

15

20

25

30

A B C D E F G H

Mea

n A

ge (

Yea

rs)

Developmental Stage

Lower Left Third Molar (Western Australia)

Male Mean

Female Mean

5.3.5. Overall development of all four third molars in males and females

Mean weighted age of attainment of developmental stages for all four third

molars were combined for both the male and female sample. The overall mean

ages and standard deviations for the Demirjian stages are described in Table 5.6

and illustrated in Figure 5.5.

Table 5.6: Overall descriptive values (including mean, standard deviation

and significance) of stages A- H for all four third molars in males and

females.

Demirjian Stages

Male Third Molar Female Third Molar Significance N Mean SD N Mean SD Z value

Stage A 53 9.11 1.40 38 9.73 1.46 0.031* Stage B 47 11.25 1.09 51 11.01 1.44 0.310 NS Stage C 56 12.66 1.19 62 12.75 2.13 0.603 NS Stage D 16 14.12 1.25 34 14.79 1.36 0.083 NS Stage E 23 15.13 0.96 33 15.54 1.75 0.178 NS Stage F 34 16.41 1.23 27 17.40 1.86 0.032* Stage G 30 18.83 2.57 36 19.25 1.33 0.023* Stage H 169 23.28 3.53 56 24.10 3.27 0.105 NS

KEY: NS = Not Significant; *P<0.05



0

5

10

15

20

25

30

A B C D E F G H

Mea

n A

ge (

Yea

rs)

Developmental Stage

Male /Female (Western Australia)

Male Third Molar Mean

Female Third Molar Mean

From Table 5.6 it is evident that there are statistically significant differences in

the mean age of attainment of stages A, F and G between males and females

(P<0.05). On average, males attain these stages significantly earlier than females

(Stage A: 7 months, Stage F: 11 months, Stage G: 5 months). In all comparisons

except stage B, male dental development is slightly more advanced than it is for

the female sample (Table 5.6; Figure 5.5).

5.4. Comparative statistics: comparison of age of attainment of

developmental stages A – H between the upper (maxillary) and

lower (mandibular) third molars.

In this section the timing of the development of the upper and lower third

molars for both sexes are compared. The mean weighted developmental scores

of the upper right and left and the lower right and left third molars are

considered collectively. The results are shown in Table 5.7 and illustrated in

Figure 5.6.


significance values) for the age of attainment of developmental stages (A –

H) for the upper and lower third molar.

Demirjian Stages

Upper Third Molars Lower Third Molars Significance N Mean SD N Mean SD Z value

Stage A 32 9.09 1.08 59 9.52 1.61 0.383 NS Stage B 45 10.97 1.42 53 11.26 1.16 0.205 NS Stage C 54 12.22 1.26 64 13.12 1.98 0.005** Stage D 40 14.5 1.35 10 14.90 1.37 0.455 NS Stage E 27 14.96 1.31 29 15.75 1.55 0.037* Stage F 38 16.71 1.33 23 17.08 1.99 0.561 NS Stage G 29 19.33 2.08 36 18.83 1.90 0.383 NS Stage H 117 23.49 3.54 108 23.48 3.43 0.928 NS

KEY: NS = Not Significant; *P<0.05; **P<0.01

Figure 5.6: Mean age of attainment of Demirjian et al. (1973) stages (A – H)

for the upper and lower third molars

As shown in Table 5.7 it is evident that the upper third molars reach

developmental stages A to F earlier than lower third molars. The difference is

statistically significant difference for stages C and E ( both P<0.05). In stage G

the difference is reversed and for stage H the values are almost identical (Table

5.7; Figure 5.6).


developmental stages A – H between the right and left third

molars.

In this section comparison between the timing of the development of the right

and left third molars for both sexes are considered. Data corresponding to the

right third molars was obtained by calculating the mean weighted ages of the

developmental scores of the right upper and lower third molars and for the left

upper and lower third molars. The results of these comparisons are shown in

Table 5.8 and illustrated in Figure 5.7.

0

5

10

15

20

25

A B C D E F G H

Mea

n A

ge (

Yea

rs)

Developmental Stage

Upper/Lower Third Molar (Western Australia)

Upper Third Molar Mean

Lower Third Molar Mean


significance values) for the age of attainment of developmental stages (A-


Demirjian Stages

Right Third Molar Left Third Molar Significance N Mean SD N Mean SD z value

Stage A 47 9.40 1.43 44 9.34 1.49 0.710 NS Stage B 49 11.10 1.27 49 11.16 1.31 0.843 NS Stage C 57 12.56 1.60 61 12.85 1.86 0.568 NS Stage D 26 14.58 1.35 24 14.45 1.38 0.590 NS Stage E 28 15.42 1.50 28 15.32 1.49 0.735 NS Stage F 30 16.83 1.57 31 16.87 1.66 0.947 NS Stage G 35 19.31 2.12 31 18.77 1.82 0.285 NS Stage H 109 23.44 3.46 116 23.52 3.51 0.834 NS

KEY: NS = Not Significant;

Figure 5.7: Mean age of attainment of (A – H) Demirjian et al. (1973) stages

for the right and left third molars.

Table 5.8 shows that there are no significant differences between the timing of

development of right and left third molars. The largest difference is only 6

months (Stage G) between the right and the left side (Table 5.8; Figure 5.7).

0

5

10

15

20

25

A B C D E F G H

Mea

n A

ge (

Yea

rs)

Developmental Stage

Right/left Third Molar (Western Australia)

RightThird Molar Mean

Left Third Molar Mean

5.6. Descriptive statistics: South Indian population

The descriptive statistics, including mean, standard deviation and the range of

age of attainment of each stage (A- H) for all four third molars are presented

below.

5.6.1. Upper Right Third Molar




stages A - H for the upper right third molar in males and females.

Upper Right Third Molar – South India Demirjian


N Mean SD Min Max N Mean SD Min Max Z value Stage A 1 10 N/A N/A N/A 1 7 N/A N/A N/A 0.317 NS Stage B 3 10.66 1.52 9 12 7 12.28 1.70 10 14 0.166 NS Stage C 20 12.15 1.56 10 15 8 12.62 1.40 11 15 0.533 NS Stage D 13 13.92 1.75 10 16 14 13.85 1.61 11 16 0.863 NS Stage E 9 15.33 0.86 14 16 7 16.42 1.13 15 18 0.062 NS Stage F 10 17.60 1.17 16 20 5 18.60 2.70 16 23 0.567 NS Stage G 18 19.33 1.90 14 23 14 19.78 1.96 17 23 0.756 NS Stage H 27 24.11 3.30 18 29 36 23.25 3.01 18 30 0.219 NS KEY: NS = Not Significant; N/A = Not Applicable;

As shown in Table 5.9, the age of attainment of stage A for the upper right third

molar in males is 10 years and 7 years in females. The mean age of crown

completion (stage D) for this tooth is 13.92 years and 13.85 years in males and

females respectively, whereas the mean age of completion of development (root

apical closure - stage H) is 24.11 years in males and 23.25 years in females.

There are no statistically significant differences in the average age of stage

attainment between males and females. The largest standard deviation is for

stage H (male 3.30 years; female 3.01 years) and the smallest is for stage E (male

0.86; female 1.13 years).

It is evident from Figure 5.8 that the mean age of attainment of developmental

stages follows a general trend of increasing age between stages (A to H) in both

males and females. In males an average increase of 1.5 to 2.0 years was

observed between each stages B to G, whereas an increase of 4.5 years was

observed between stages G and H. In females an average increase of 2.5 years

was observed between each stages D to F and 3.4 years between stages G and H.



5.6.2. Upper Left Third Molar



0

5

10

15

20

25

30

A B C D E F G H

Mea

n A

ge (

year

s)

Developmental Stage

Upper Right Third Molar (South India)

Male Mean

Female Mean

Table 5.10: Descriptive values (including mean and standard deviation) of stages A - H for the upper left third molar in males and females.

Upper Left Third Molar - South India Demirjian

Stages Male Female Significance

N Mean SD Min Max N Mean SD Min Max z value Stage A 2 9.50 0.70 9 10 3 10.33 2.88 7 12 0.554 NS Stage B 4 12.25 1.25 11 14 2 10.00 N/A 10 10 0.057 NS Stage C 17 12.11 1.53 10 15 12 13.16 1.64 11 16 0.124 NS Stage D 18 13.66 1.78 10 16 14 13.92 1.43 11 16 0.684 NS Stage E 8 15.75 0.88 14 17 7 16.14 0.89 15 17 0.421 NS Stage F 7 17.42 0.97 16 19 9 19.00 2.44 16 23 0.142 NS Stage G 13 19.23 1.42 17 22 16 19.62 1.74 17 23 0.559 NS Stage H 34 23.14 3.71 18 29 32 23.68 2.87 19 30 0.652 NS


As shown in Table 5.10, the mean age of attainment of stage A for the upper left

third molar in males is 9.50 years and 10.33 years in females. In males the mean

age of crown completion (stage D) and root apical closure (stage H) for this

tooth is 13.66 and 23.14 years respectively, whereas in females it is 13.92 years

(stage D) and 23.68 years (stage H). There are no statistically significant

differences in the average age of stage attainment between both sexes. The

largest standard deviation of 3.71 and 2.88 years was for stage H and A in males

and females respectively. The smallest standard deviation was for stage A (0.70

years) in males and stage E (0.89 years) in females.

Figure 5.9 shows that the development of this tooth follows a general trend of

increasing age between each successive stage in both males and females. An

increase of 2.75 years was observed between stages A to B and 3.91 years for

stages G to H in males. In females an average increase of 3.16 years was

observed between stages B to C and 4 years for stages G to H (Table 5.10).



5.6.3. Lower right third molar





Lower Right Third Molar – (South India)

Demirjian Stages

Male Female Significance


Stage A 2 10.00 1.41 9 11 3 10.33 2.88 7 12 0.554 NS Stage B 7 11.85 1.57 10 14 5 10.80 0.83 10 12 0.242NS Stage C 18 12.16 1.50 10 14 16 13.25 1.23 11 15 0.060 NS Stage D 11 13.45 1.12 12 15 7 14.71 1.38 13 17 0.082 NS Stage E 12 15.58 0.66 14 16 11 17.45 2.94 15 23 0.093 NS Stage F 9 17.88 1.26 16 20 6 17.66 2.06 15 21 0.669 NS Stage G 22 19.22 1.54 17 23 21 19.90 1.92 17 24 0.258 NS Stage H 25 24.84 2.73 20 29 29 24.10 2.71 19 30 0.249 NS


0

5

10

15

20

25

A B C D E F G H

Mea

n A

ge (

year

s)

Developmental Stage

Upper Left Third Molar (South India)

Male Mean

Female Mean

Table 5.11 shows that the mean age of attainment of stage A for the lower right

third molar is 10.00 and 10.33 years in males and females respectively. The

mean age of attainment of stages D and H for this tooth in males is 13.45 and

24.84 years and in females it is 14.71 and 24.10 years respectively. There are no

statistically significant differences in the mean age of attainment of any stage

between males and females (Table 5.11). The smallest standard deviation of

0.66 years was observed in stage E for males and 0.83 years in stage B for

females. The largest standard deviation of 2.73 years and 2.94 years were

observed for stages H and E in males and females respectively.

Figure 5.10 clearly demonstrates that the mean age of attainment of

developmental stages follows a general trend of increasing age between stages

in both sexes. An average increase of 1 to 2.5 years was observed between each

successive stages A to G in both males and females. An increase of 5.62 years and

4.20 years was observed between stages G and H in males and females

respectively (Table 5.11; Figure 5.10).

Figure 5.10: Illustration of mean ages of attainment of Demirjian et al.

(1973) stages for the lower right third molar in males and females.

0

5

10

15

20

25

30

A B C D E F G H

Mea

n A

ge (

year

s)

Developmental Stage

Lower Right Third Molar (South India)

Male Mean

Female Mean

5.6.4. Lower left third molar





Lower Left Third Molar - South India Demirjian


N Mean SD Min Max N Mean SD Min Max z value Stage A 2 9.50 0.70 9 10 3 10.33 2.88 7 12 0.554 NS Stage B 5 12.00 1.00 11 13 6 11.00 0.89 10 12 0.129 NS Stage C 20 12.45 1.43 10 14 16 13.87 1.36 12 16 0.013 * Stage D 10 13.70 1.15 12 15 9 14.00 1.41 11 16 0.553 NS Stage E 11 15.63 0.67 14 16 9 16.77 1.85 15 21 0.103 NS Stage F 10 17.80 1.22 16 20 9 19.44 2.74 17 23 0.237 NS Stage G 17 19.29 1.61 17 23 20 19.80 1.85 17 24 0.392 NS Stage H 31 23.58 3.98 19 29 28 24.10 2.80 19 30 0.861 NS

KEY: N= No data; NS = Not Significant.

Table 5.12 shows that the mean age of attainment of stage A for the lower left

third molar in males is 9.50 and 10.33 years in females. The only statistically

significant difference between males and females is for stage C (Z = 0.013;

P<0.05). On average males attain this stage significantly earlier than females (by

17 months). The mean age of crown completion (stage D) and root apical closure

(stage H) for this tooth is 13.70 and 23.58 years in males and 14.00 and 24.10

years in females. The largest standard deviation of 3.98 and 2.88 years is for

stages H and A in males and females respectively. The smallest standard

deviation in males is 0.67 years for stage E and 0.89 years for females (stage B).

Figure 5.11 shows that the development of this tooth follows a general trend of

increasing age between stages in both sexes. In males an average increase of 1 to

2.5 years is observed from stages A to G and 4.29 years for stages G and H. In

females an increase of 0.5 to 2.5 years is observed between each stages A to G

and 4.30 years for stages G and H.

Figure 5.11: Illustration of mean age of attainment of Demirjian et al.

(1973) stages for the lower left third molar in males and females.

5.6.5. Overall development of all four third molars in males and females

The mean weighted age of attainment of developmental stages for all four third

molars were combined for both the male and female sample. The overall mean

ages and standard deviations for the Demirjian et al. (1973) stages are described

in Table 5.13 and illustrated in Figure 5.12.

Table 5.13: Overall descriptive values (including mean, standard deviation

and significance) of stages A- H for all four third molars in males and

females.

Demirjian Stages

Male Third Molar Female Third Molar Significance N Mean SD N Mean SD Z value

Stage A 7 9.71 0.75 10 10.00 2.58 0.480 NS Stage B 19 11.78 1.35 20 11.30 1.38 0.206 NS Stage C 75 12.22 1.48 52 13.32 1.42 0.001 *** Stage D 52 13.69 1.52 44 14.04 1.46 0.239 NS Stage E 40 15.57 0.74 34 16.79 2.02 0.002 ** Stage F 36 17.69 1.14 29 18.79 2.46 0.121 NS Stage G 70 19.27 1.60 71 19.78 1.83 0.148 NS Stage H 117 23.84 3.52 125 23.75 2.85 0.403 NS

KEY: NS = Not Significant; **P <0.01; ***P<0.001

0

5

10

15

20

25

30

A B C D E F G H

Mea

n A

ge (

year

s)

Developmental Stage

Lower Left Third Molar (South India)

Male Mean

Female Mean

Figure 5.12: Illustration of mean age of attainment of Demirjian et al.

(1973) stages for the males and females.

From Table 5.13 it is evident that there are statistically significant differences in

the mean age of attainment of stages C and E between males and females

(P<0.001; P<0.01). On average, males attain these stages significantly earlier

than females (Stage C: 13 months; Stage E: 14 months). In all comparisons

(except for stages B and H) male third molars development is slightly more

advanced than the female sample (Table 5.13; Figure 5.12).


developmental stages A – H between the upper (Maxillary) and

lower (Mandibular) third molars

In this section the timing of the development of the upper and lower third

molars for both sexes are compared. The mean weighted developmental scores

of the upper right and left, and the lower right and left, third molars are

0

5

10

15

20

25

30

A B C D E F G H

Mea

n A

ge (

year

s)

Developmenatal Stage

Male / Female - (South India)

Male Third Molar Mean

Female Third Molar Mean

considered collectively. The results are outlined in Table 5.14 and illustrated in

Figure 5.13.


significance values) for the age of attainment of the developmental stages

(A – H) for the upper and lower third molars.

Demirjian Stages

Upper Third Molars

Lower Third Molars Significance

N Mean SD N Mean SD z value Stage A 7 9.57 2.07 10 10.10 2.02 0.614NS Stage B 16 11.68 1.62 23 11.43 1.19 0.630 NS Stage C 57 12.42 1.56 70 12.08 1.51 0.063 NS Stage D 59 13.83 1.62 37 13.89 1.28 0.847 NS Stage E 31 15.87 0.99 43 16.32 1.89 0.739 NS Stage F 31 18.12 1.91 34 18.23 1.95 0.781 NS Stage G 61 19.49 1.75 80 19.56 1.73 0.937 NS Stage H 129 23.51 3.22 113 24.12 3.12 0.106 NS


Figure 5.13: Mean age of attainment of Demirjian et al. (1973) stages (A –

H) for the upper and lower third molars.

As shown in Table 5.14, it is evident that the upper third molars (except for

stage B and C) attain the developmental stages slightly earlier than the lower

0

5

10

15

20

25

30

A B C D E F G H

Mea

n A

ge (

year

s)

Developmental Stage

Upper/Lower Third Molar (South India)

Upper Third Molar Mean

Lower Third Molar Mean

third molars. There are no statistically differences in the mean age of attainment

of any stage between the upper and lower third molars (Table 5.14, Figure 5.13).


developmental stages (A – H) between the right and left third

molars

In this section comparisons between the timing of the development of the right

and left third molars for both sexes are made. Data corresponding to the right

third molars is obtained by calculating the mean weighted ages of the

developmental scores of the right upper and lower third molars and for the left

upper and lower third molars. The results of these comparisons are shown in



significance values) for the age of attainment of the developmental stages

(A – H) for the right and left third molars.

Demirjian Stages

Right Third Molars Left Third Molars Significance N Mean SD N Mean SD z value

Stage A 7 9.71 2.13 10 10.00 2.00 0.762 NS Stage B 22 11.59 1.53 17 11.47 1.17 0.851 NS Stage C 62 12.50 1.49 65 12.84 1.60 0.274 NS Stage D 45 13.91 1.51 51 13.80 1.48 0.848 NS Stage E 39 16.20 1.88 35 16.05 1.21 0.746 NS Stage F 30 17.86 1.65 35 18.45 2.10 0.312 NS Stage G 75 19.54 1.81 66 19.51 1.66 0.854 NS Stage H 117 24.00 2.97 125 23.60 3.37 0.455 NS




Table 5.15 shows that there are no statistically significant differences between

the timing of development of the right and left third molars. However, the right

third molars reach developmental stages A, C, F and H earlier than the left side;

the left third molars reach the developmental stages B, D, E and G slightly earlier

than the right side. The largest of all these differences, however, is only 7

months (stage F) (Table 5.15; Figure 5.14).

5.9. Comparative statistics: Comparison of age of attainment of

developmental stages A – H for the upper (Maxillary) and lower

(Mandibular) third molars between Western Australian and

South Indian males and females

This section compares the timing of the development of the upper and lower

third molars in Western Australian and South Indian individuals. Data related to

the upper and lower third molars is obtained by calculating the mean weighted

ages of the developmental scores of the upper right and left, and lower right and

0

5

10

15

20

25

30

A B C D E F G H

Mea

n A

ge (

year

s)

Developmental Stage

Right/left Third Molar (South India)

RightThird Molar Mean

Left Third Molar Mean

left, third molars in both sexes in each population. This was performed to reduce

the amount of comparisons required and is justified by the fact that of no

statistically significant evidence of bilateral variation was found in either

population (see above).

5.9.1. Upper Third Molars (Male)

A summary of the comparative statistics relating to the development of the

upper third molar in the Western Australian and South Indian males is shown in

Table 5.16 and Figure 5.15.


significance values) for the age of attainment of developmental stages A - H

for the upper third molars in Western Australian and South Indian males

Upper Third Molars (Male) Demirjian

Stage Western Australia South India Significance

N Mean SD Min Max N Mean SD Min Max Z value Stage A 17 9.00 1.27 7 12 3 9.66 0.57 9 10 NS Stage B 17 10.64 0.99 9 12 7 11.57 1.51 9 14 NS Stage C 28 12.35 1.06 11 16 37 12.13 1.53 10 15 NS Stage D 13 14.15 1.21 12 16 31 13.77 1.74 10 16 NS Stage E 12 14.91 1.08 13 16 17 15.52 0.87 14 17 NS Stage F 20 16.35 1.26 14 19 17 17.52 1.06 16 20 0.003** Stage G 17 19.05 2.65 16 25 31 19.29 1.69 14 23 NS Stage H 90 23.47 3.59 17 30 61 23.57 3.54 18 29 NS KEY: NS = Not Significant; **P<0.01.


H) in the Upper third molar in males for Western Australia and South

India.

Table 5.16 shows that the mean age of attainment of stage A, for the upper third

molars in the Western Australian and South Indian males, is 9.00 and 9.66 years

respectively. The mean age of crown completion (stage D) is 14.15 years for the

Western Australian males and 13.77 years for the South Indian males. The mean

age of completion of development (root apical closure - stage H) is 23.47 and

23.57 years for Western Australian and South Indian males respectively. The

only statistically significant difference between the populations is for stage F

(P<0.01; Z = 0.003). On an average Western Australian males attain this stage

14 months earlier than the South Indian males (Table 5.16; Figure 5.15). The

largest standard deviation is for stage H (Western Australia: 3.59 years; South

Indian: 3.54 years) and the smallest standard deviation is for stage B (0.99

years) for Western Australian males and stage A (0.57 years) for South Indian

males.

0

5

10

15

20

25

Stage A Stage B Stage C Stage D Stage E Stage F Stage G Stage H

Mea

n A

ge (

Yea

rs)

Developmental Stage

Upper Third Molars - (Male)

WA Mean

SI Mean

It is evident from Figure 5.15 that the upper third molars development of

Western Australian males is slightly more advanced (by 7 to 14 months) than

the South Indian males, except for (stage D).

5.9.2. Lower Third Molars (Male)


lower third molars of Western Australian and South Indian males is shown in


Table 5.17: Comparative values (including mean, standard deviation and significance values) for the age of attainment of developmental stages A - H for the lower third molars in Western Australian and South Indian males

Lower Third Molars (Male) Demirjian


N Mean SD Min Max N Mean SD Min Max z value Stage A 36 9.16 1.48 7 13 4 9.75 0.95 9 11 NS Stage B 30 11.60 1.00 10 13 13 11.76 1.36 10 14 NS Stage C 28 12.96 1.26 11 15 38 12.31 1.45 10 14 NS Stage D 3 14.00 1.73 13 16 21 13.57 1.12 12 15 NS Stage E 11 15.36 0.80 14 16 23 15.60 0.65 14 16 NS Stage F 14 16.50 1.22 14 18 19 17.84 1.21 16 20 0.008** Stage G 13 18.53 2.53 16 25 39 19.25 1.55 17 23 NS Stage H 79 23.06 3.48 17 29 55 24.40 2.96 18 29 0.020*

KEY: NS = Not Significant; *P<0.05; **P <0.001.


H) in the lower third molar in males for Western Australia and South India.

As shown in Table 5.17, the mean age of attainment of stage A for the lower

third molars in Western Australian males is 9.16 years and 9.75 years in South

Indian males respectively. The mean age of crown completion (stage D) is 14.00

and 13.57 years for the Western Australian and South Indian males respectively.

It is evident that there are statistically significant difference in the mean age of

attainment of stages F and H between the two populations (P<0.001; Z = 0.008,

P<0.05; Z = 0.020). On average Western Australian males attain these stages

significantly earlier than South Indian males (stage F: 16 months; stage H: 16

months). The largest standard deviation of 3.48 and 2.96 years was for stage H,

and the smallest standard deviation of 0.80 and 0.65 years was for stage E, in

both populations.

Figure 5.16 clearly illustrates that in all comparisons (except for stages C and D)

the upper third molars development of Western Australian males is slightly

more advanced (by 8 to 16 months) than the South Indian population.

0

5

10

15

20

25

30


Mea

n A

ge (

Yea

rs)

Developmental Stages

Lower Third Molars - Male

WA Mean

SI Mean

5.9.3. Upper third molars (Female)


upper third molars of Western Australian and South Indian females is shown in


Table 5.18: Comparative values (including mean, standard deviation and significance values) for the age of attainment of developmental stages A - H for the upper third molars for Western Australian and South Indian females

Upper Third Molars (Female)

Demirjian Stage

Western Australia South India Significance


Stage A 15 9.20 0.86 8 10 4 9.50 2.88 7 12 NS Stage B 28 11.17 1.61 8 14 9 11.77 1.78 10 14 NS Stage C 26 12.07 1.46 10 16 20 12.95 1.53 11 16 0.031* Stage D 27 14.66 1.41 12 17 28 13.89 1.49 11 16 NS Stage E 15 15.00 1.51 12 17 14 16.28 0.99 15 18 0.017* Stage F 18 17.11 1.32 15 19 14 18.85 2.44 16 23 0.038* Stage G 13 19.69 0.94 19 21 30 19.70 1.82 17 23 NS Stage H 27 23.55 3.45 19 30 68 23.45 2.93 18 30 NS

KEY: NS = Not Significant; *P<0.05


H) in the upper third molar in females for Western Australian and South

India

0

5

10

15

20

25


Mea

n A

ge (

Yea

rs)

Developmental Stage

Upper Third Molars (Female)

WA Mean

SI Mean

From Table 5.18, it is evident that there are statistically significant differences in

the mean age of attainment of stages C, E and F for the upper third molars

(P<0.05). On average, Western Australian females attain these stages

significantly earlier than South Indian females (stage C: 10 months; stage E: 15

months; stage F: 20 months). The smallest standard deviation of 0.86 years was

observed in stage A in the Western Australian females and 0.99 years for stage E

in the South Indian females. The largest standard deviation of 3.45 and 2.93

years were observed for stages H in both population.

Figure 5.17 clearly demonstrates that upper third molar development of

Western Australian females is slightly more advanced (by 10 to 20 months) than

the South Indian females, except for stage D which shows the reversal.

5.9.4. Lower third molars (Female)

A summary of the comparative statistics relating to the timing of development of

the lower third molars in Western Australian and South Indian females is shown

in Table 5.19 and illustrated in Figure 5.18.


significance values) for the age of attainment of developmental stages A - H

for the lower third molars in Western Australian and South Indian females

Lower Third Molars ( female) Demirjian


N Mean SD Min Max N Mean SD Min Max z value Stage A 23 10.08 1.67 8 14 6 10.33 2.58 7 12 NS Stage B 23 10.82 1.23 9 13 11 10.90 0.83 10 12 NS Stage C 36 13.25 2.40 8 17 32 13.56 1.31 11 16 NS Stage D 7 15.28 1.11 14 17 16 14.31 1.40 11 17 NS Stage E 18 16.00 1.84 12 18 20 17.15 2.47 15 23 NS Stage F 9 18.00 2.64 15 21 15 18.73 2.57 15 23 NS Stage G 23 19.00 1.47 16 21 41 19.85 1.86 17 24 NS Stage H 29 24.62 3.07 19 30 57 24.10 2.73 19 30 NS



H) in the lower third molar in females for Western Australia and South

India.

Table 5.19 shows that the mean age of attainment of stage A for the lower third

molars is 10.08 and 10.33 years, for the Western Australian and South Indian

females respectively. The mean age of crown completion (stage D) is 15.28 years

for the Western Australian females, and 14.31 years for the South Indian

females. The mean age of completion of development (stage H) is 24.62 and

24.10 years in Western Australian and South Indian females respectively. There

are no statistically significant differences between the mean age of development

of these teeth between the Western Australian and South Indian females. The

largest difference however, is 13 months (stage E) in which Western Australian

females are ahead of South Indian females. The largest standard deviation of

3.07 and 2.73 years was observed for stage H in both populations. The smallest

standard deviation of 1.11 years was observed in stages D in the Western

Australian females and 0.83 years for stage B in the South Indian females.

0

5

10

15

20

25

30


Mea

n A

ge (

Yea

rs)

Developmental Stage

Lower Third Molars (Female)

WA Mean

SI Mean

5.10. Absence of the third molars in the Western Australian and

South Indian sample

This section outlines the assessment of frequency of missing third molars (both

congenitally absent and/or extracted) in each population. The main aim here is

to simply evaluate how frequently this tooth is unavailable for forensic analysis

in both populations; the data is shown in Table 5.20. Sex differences in the

frequency of missing third molars are not considered at this stage.

Table 5.20: Frequency of missing individual third molars (combined sex)

in the Western Australian and South Indian population.

Western Australia South India Tooth Absent (n) Percentage (%) Absent (n) Percentage (%)

Upper Right Third Molar

126/312 40.4 56/249 22.5

Upper Left Third Molar 120/312 38.5 51/249 20.5

Lower Right Third Molar

122/312 39.1 44/249 17.7

Lower Left Third Molar

120/312 38.5 43/249 17.3

From Table 5.20 it is evident that within the Western Australian sample the

upper right third molar (40.4 %) is the most frequently missing, closely followed

by the lower right third molar (39.1%). In the South Indian sample the upper

right third molar (22.5%) is the most frequently missing, followed by the upper

left third molar (20.5%). The frequency of missing third molars is consistently

higher in the Western Australian sample by almost twice (Table 5.20).

Chapter Six Discussion and Conclusions

6.1. Introduction

Dental age can be estimated by assessing the emergence and mineralization

status of the teeth in the juvenile age range. However, the reliability of

estimating age from dental development is not uniform from birth to adulthood.

After the age of 14, when most of the permanent teeth are fully formed, the third

molars are the only teeth still developing. Radiographic assessment of the

development of the third molars is, therefore, a characteristic technique for age

estimation of sub-adults (individuals who are not skeletally mature; ≤ 18 years).

In the literature, a range of different classification systems for evaluating tooth

mineralization are available: e.g. (Gleiser and Hunt (1955); Nolla (1960);

Moorrees et al. (1963); Liliequist and Lundberg (1971); Demirjian et al. (1973);

Gustafson and Kosh (1974); Harris and Nortje (1984); and Kullman et al. (1992).

All of these methods differ with regard to the number of developmental stages

and their definitions. The Demirjian et al. (1973) tooth mineralization stages

however, are defined by changes in shape and do not depend on speculative

estimates of length.

As discussed in Chapter Three, Demirjian et al. (1973) presented a visual and

descriptive system of four distinct stages each for the crown and the root (A –

H). Olze et al. (2005), Dhanjal et al. (2006) and Hagg and Matson (1985)

subsequently tested the applicability of the Demirjian et al. (1973) method and

the authors concluded that it has a high degree of accuracy and precision, both

for intra and inter-examiner agreement and also in the correlation between

estimated and actual age. It is important to note however, that the timing of

attaining dental maturity varies between different ethnic groups (Nystrom et al.

1986; Tompkins 1996 and Olze et al. 2003). In consideration of the important

requirement for population specific standards, this study applied a modification

of the Demirjian et al. (1973) dental development classification system to the

third molars in individuals drawn from Western Australian and South Indian

populations.

The primary aims of the present study were to evaluate how accurately age can

be estimated using the third molars, and to evaluate population differences in

the timing of mineralization. The main aim is to formulate population specific

age estimation standards for both groups. This is the first study to apply the

Demirjian et al. (1973) method exclusively to third molar development in both

populations. The results of this study are discussed below, including overall

comparisons between sexes, upper and lower arches and side differences

(within and between populations). The congenital variability exhibited by the

third molars is then discussed, followed by the limitations of the study, future

research and conclusions.

6.2. Developmental age range, sex differences and population

variability of the third molars

The combined data from the four third molars are considered for both sexes in

each population. This was performed (instead of discussing the results

pertaining to each individual tooth) to reduce the amount of comparisons and is

justified in light of finding no strong evidence of statistically significant

differences in the mean age of attainment of any developmental stages (see

Chapter 5). Meaningful landmarks in third molar development, such as initiation

(Stage A) and completion of development (Stage H), are considered as they are

of forensic importance (e.g: ascertaining if a individual is at the age of criminal

responsibility). In addition, the mean age and the developmental age range of

these two stages are considered for both sexes in each population.

6.2.1. Overall developmental age range of the third molars in the Western

Australian and South Indian populations

In the Western Australian population the male third molars are slightly more

developmentally advanced than that of the female. The mean age of initiation of

development (Stage A) was 9.11 years (range 7 – 13 years) and 9.73 years

(range 8 – 14 years) in males and females respectively (see Table 5.6). The mean

age of completion of development (Stage H) was 23.28 years (range 18 – 30

years) and 24.10 years (range 19 - 30 years) in males and females respectively.

For all Western Australian individuals, fully developed third molars (Stage H)

thus occurred at no younger than 17 years of age in males and 18 years in

females. Furthermore, only 1.15% (2/173) of males actually reached Stage H by

17 years. Bassed et al. (2011) and Meinl et al. (2007) similarly found that there

were very few (not quantified) Australian individuals displaying root

completion of the mandibular third molar in males less than 18 years of age.

In the South Indian population, male third molars are slightly more dentally

advanced than the female. The mean age of initiation (Stage A) was 9.71 years

(range 9 – 11 years) in males and 10.00 years (range 7 – 12 years) in females.

Whereas the mean age of completion of development (Stage H) was 23.84 years

(range 18 - 29 years) and 23.75 years (18 – 30 years) in males and females

respectively (see Table 5.13). For all South Indian individuals, fully developed

third molars (Stage H) thus occurred at no younger than 18 years of age in both

sexes.

6.2.2. Overall sex differences in the third molar development in the

Western Australian and South Indian population.

With regard to sex-specific variation in the timing of third molar development,

statistically significant sex differences were observed in the mean age of

attainment of Stages A, F and G in Western Australian males and females. On

average males attain these stages 5 to 11 months earlier than females (see Table

5.6). In the South Indian population, statistically significant differences were

observed in the mean age of attainment of Stages C and E between both sexes.

On average males attain these stages significantly earlier than the females (13 to

14 months) (see Table 5.13).

It is clearly evident that in both populations males are slightly more advanced

with respect to the timing of third molar development. This is consistent with

previous research in a Japanese population which showed that third molar

formation in males was more than six months advanced in stages E, F and G

(Arany et al. 2004). The results of the present study also accords with research

in other ethnic groups: e.g: Gunst et al. (2003 - Belgian Caucasians); Solari et al.

(2002 - American Hispanics); Kullman et al. (1992 – Scandinavians); Zeng et al.

(2010 - Southern Chinese); and Olze et al. (2008 – German).

Bassed et al. (2011) assessed mandibular third molar development in an

Australian (Victorian) sample and also concluded that males are more advanced

than females. The Western Australian studies conducted by Flood (2007) and

Farah et al. (1999) found that females are more dentally advanced than males

during the initial developmental stages (A – D) and males are more advanced

during the later stages (F – H). However, these studies applied the Demirjian et

al. (1973) method for all permanent teeth except the third molars. Rai et al.

(2009) evaluated mandibular third molar development in a North Indian

population and concluded that female dental development is slightly more

advanced (by 6 to 21 months). The findings of the latter study are obviously not

consistent with the present and numerous other studies, which showed the

reverse. This demonstrates, however, the need for future research in Indian

populations to explore if this is an issue with regard to formulating local

reference databases for dental age estimation.

6.2.3. Comparisons of third molar development between Western

Australian and South Indian individuals

In considering the dental developmental data overall, it is evident that there was

a statistically significant difference in the mean age of attainment of stages F and

H. On average Western Australian males attain these stages earlier than the

South Indian males, by 14 to 16 months (Tables 5.16, 5-17). However, with

respect to the crown mineralization and completion (stages C and D), the

reverse relationship was found; on average South Indian males attain these

stages slightly earlier; stage C (2 - 7 months); stage D (5 months) with no

statistically significant difference.

In considering the development of the upper third molars the Western

Australian females attain stages C (10 months); E (15 months); F (20 months)

significantly earlier than the South Indian females There were no statistically

significant differences in the timing of dental development of the lower third

molars, however the largest difference was 13 months for attainment of stage E,

with the Western Australian females being more dentally advanced than the

South Indians.

It is evident from the results of this study that in all comparisons (except for

crown mineralization - stages C and D) third molar development in the Western

Australian population is slightly more advanced than the South Indian

population by 7 to 11 months. Olze et al. (2003) concluded that population

specific standards enhance the accuracy of forensic age estimation based on

third molar mineralization as the timing of tooth mineralization varies in

different populations. This issue is discussed in more detail below.

6.2.4. Comparisons of third molar development to other populations

A comparison of the mean age of attainment of landmark tooth formation stages,

(including initiation stage A, crown completion Stage D, and root completion

stage H) in several ethnic groups is presented in Table 6.1. Where data for

individual third molars was presented, the weighted mean was calculated to

give a single comparative value for each stage in each population.

Table 6.1: Mean age (in years) of attainment of Demirjian et al. (1973) stages (A, D

and H) in several populations for males and females.

Key: N/D – No Data.

Demirjian et al.

(1973) Stage

Mincer et al. (1993)

Solari et al. (2002)

Olze et al. (2003)

Olze et al. (2003)

Arany et al. (2004)

Prieto et al.

(2005)

Olze et al.

(2006)

Orhan et al.

(2007)

Sisman et al.

(2007)

Rai et al. (2009)

Kasper et al. (2009)

Zeng et al.

(2010)

Bassed et al. (2011)

Present Study

Present Study

Sex American Caucasian

American Hispanic Japanese Germany Japanese Spanish South

Africa Turkish Turkish North India

African -American Chinese Melbourne

- Australia Western Australia

South India

A M N/D N/D N/D N/D N/D N/D N/D N/D N/D 11.51 N/D 10.05 N/D 9.11 9.71

F N/D N/D N/D N/D N/D N/D N/D N/D N/D 11.93 N/D 10.28 N/D 9.73 10.00

D M 15.05 15.04 18.25 16.45 15.60 15.06 13.07 14.65 12.90 13.00 13.06 13.55 16.40 14.12 13.69

F 16.00 15.65 18.67 15.65 16.00 15.11 13.09 15.22 13.60 14.79 13.45 13.80 16.65 14.79 14.04

H M 20.35 20.35 22.52 22.62 21.52 19.73 22.08 20.10 22.10 23.34 18.07 22.74 22.00 23.28 23.84

F 20.75 21.25 22.35 22.87 21.75 19.63 22.37 20.00 22.66 23.58 19.04 23.35 22.08 24.10 23.75

It is evident from Table 6.1 that the mean age of initiation (Stage A) of

development of third molars in Western Australian and South Indian individuals

is slightly less than the Chinese and North Indian population by 4 to 28 months.

The mean age of crown completion (Stage D) for both populations in the present

study occurs earlier than the Turkish, Spanish, Japanese, German and American

populations (by 11 to 48 months). Whereas, the mean age of completion of

development (Stage H) in the Western Australian and South Indian males and

females is less advanced compared to other populations (by 6 to 52 months).

Overall, the timing of third molar development of both populations in the

present study is closest to the North Indian and Southern Chinese populations.

This may be related to the diversity in the ethnic mix in the Australian

population and geographic closeness. There are many Indian and Chinese

individuals living in Western Australia; many of the comparative populations,

however are possibly more homogenous (e.g: Spanish, Turkish, Japanese)

compared to the heterogeneous Australian population.

It is evident from the literature that ethnicity influences the timing of tooth

mineralization. Gorgani et al. (1990) examined 229 African-American and 221

American-Caucacian individuals aged between 6 to 14 years. The authors

concluded that in the African-American population third molar crown

mineralization (stage C) was completed one year earlier than the American-

Caucasian group. Harris and McKee (1990) examined 655 American-Caucasians

and 355 African-Americans aged 3.5 to 13 years and concluded that African-

Americans reached stages A to H of third molar mineralization one year earlier

than American-Caucasians. However, differences in the timing of attaining the

later stages of development (F – H) were minimal. This trend for the same

population was confirmed by Mincer et al. (1993) who found no significant

differences with regard to the chronology of third molar mineralization. Olze et

al. (2003) compared the mineralization status of the third molar in a Japanese

and German population. They found significant differences between stages D, E

and F in both populations; Japanese males and females reached those stages

approximately 2 to 3 years later than German males and females.

The aforementioned population variation in the timing of dental development

may be related to tooth jaw size differences between ethnic groups. Stringer et

al. (1990) proposed that the timing of mineralization and eruption of teeth is

influenced by the tooth and jaw size relationship. They reported that African

individuals, who have larger jaws and well spaced teeth, were more dentally

advanced than other ethnic groups. Further, Byers et al. (1997) and Merz et al.

(1991) examined African-American, American-Caucasian and Native American

individuals; they concluded that the African-Americans had a larger jaw to tooth

size and were more dentally advanced than the other two populations.

6.3. Jaw differences in third molar development in a Western

Australian and a South Indian sample

In the Western Australian population the upper (maxillary) third molars reach

developmental stages A to F earlier than the lower (mandibular) third molars.

However, with regard to the individual developmental stages, the only stages

that had a statistically significant difference were C and E. On average the upper

third molars develop slightly earlier than the lower third molars (stage C: 10

months; stage E: 9 months) (see Table 5.7).

The South Indian population follows the same trend; upper third molar (except

stages B and C) were more dentally advanced than the lowers by 1 to 7 months.

However, no statistically significant differences in the mean age of attainment of

individual developmental stages between the upper and lower third molars

were found in this population (see Table 5.14)

Sisman et al. (2007) and Orhan et al. (2007) evaluated third molar development

in a Turkish population and both reported that the upper third molars

developed earlier than the lower third molars; the difference, however was not

statistically significant. This observation was consistent with Kullman et al.

(1992) for Scandinavian and Solari et al. (2002) for Hispanic individuals. Those

authors applied the Demirjian et al. (1973) method and demonstrated that

upper third molars were slightly advanced compared to the lower jaw. Arany et

al. (2004) assessed the mineralization status of third molars in a Japanese

population and concluded that the upper third molars were more advanced (not

quantified) than the lower. Olze et al. (2004) and Prieto et al. (2005) evaluated

the chronological age of third molar mineralization in a Japanese and Spanish

population respectively. The authors concluded that no statistically significant

differences exist between the timing of mineralization of the upper and lower

third molars. Olze et al. (2006) demonstrated statistically significant differences

between the timing of development of upper and lower third molars

development in a South African population; the lower third molars developed

0.8 years earlier than the upper molars. The result of Olze et al. (2006) study is

obviously different compared to the present and other studies. This again

highlights the importance of population specific standards for accurate dental

age estimation.

6.4. Bilateral variation in third molar development within

Western Australian and South Indian individuals

No statistically significant bilateral differences between the age of attainment of

any stage in both populations were found in the Western Australian population

the right third molars reached developmental stages B, C, F and H slightly earlier

than the left side; the largest difference, however, was only 6 months (stage G -

see Table 5.8). In the South Indian population, the right third molars reached

developmental stages A, C, F slightly earlier than the left side; the largest

difference is only 7 months (stage F - see Table 5.15).

Olze et al. (2006) assessed the chronology of third molar mineralization by

applying the Demirjian et al. (1973) method to a South African population; no

statistically significant bilateral differences were observed. Olze et al. (2004)

and Arany et al. (2004) demonstrated no statistically significant bilateral

differences in a Japanese population. Orhan et al. (2007) and Sisman et al.

(2007) concluded that no statistically significant bilateral difference were

present in a Turkish population. Prieto et al. (2005) evaluated the mandibular

third molars in a Spanish population and concluded that no significant

differences existed in the timing of development of the right and left sides.

Levesque and Demirjian (1981) also reported no significant bilateral differences

in a French–Canadian population. Zeng et al. (2010) in their Chinese study

concluded that, regardless of sex, the chronological age of third molar

mineralization was symmetrical for the right and left sides. Thus the results of

the present study are in accordance with the results of previous research on a

variety of different ethnic groups.

6.5. Absence of the third molars

The third molars are the teeth with the highest degree of variability associated

with morphology, absence and age of eruption (Demirjian et al. 1973; Prieto et

al. 2005). These teeth also exhibit a wide range of morphological variations and

frequencies with which the formative organs fail to develop, resulting in

complete absence of one or more third molars (Nanda, 1954). In addition this is

the tooth that is most often extracted in adults either due to a lack of space to

erupt (impacted) or due to dental therapeutic (orthodontic) procedures. Hence,

another aim of this study was to quantify the variability in the third molars in

relation to the degree of absence (missing) in both populations. Establishing

whether the teeth were congenitally missing or extracted could not be reliably

ascertained, so they were simply scored as ‘missing’.

The upper right third molar were found to be the most commonly missing tooth

in the Western Australian (40.4%) and South Indian (22.5%) populations. It is

possible to posit that the higher degree of absence of this tooth within the

Western Australian sample, as compared to South Indian individuals, may be

related to the higher extraction rate of third molars in this population. In

comparison to other studies, Nanda (1954) also reported that upper right third

molar was most frequently missing in their American population. However Garn

(1963) reported that mandibular (lower) third molars were most frequently

missing in their American- Caucasian population.

This study demonstrates that there is a relatively high frequency of missing

third molars in the Western Australian sample, which potentially limits the

applicability of age estimation using the third molars. This issue requires further

elucidation, especially with regard to how frequently all third molars are

missing (see section 6.8, page 104).

6.6. Forensic importance of the third molars

In recent years age estimation of living individuals has received increasing

attention largely because the accurate estimation of age is essential in cases

involving persons without valid identification documents. The age of criminal

responsibility varies according to a specific jurisdiction, but it is usually ≥ 18

years for adult law. Age estimation for children up to the age of 14 – 15 years

can be reliably estimated using dental and skeletal developments (see Chapter

One). At 14 years of age all of the permanent teeth (except the third molars)

have normally erupted and completed root formation. The third molars,

therefore are of considerable importance when attempting to assess whether an

Individual is at an age of criminal responsibility.

Demirjian et al. (1973)’s tooth developmental stage A signifies the initiation of

development. This stage marks the first developmental stage which appears in

the form of an inverted cone (or cones) depending on if it is a single or multi-

rooted tooth. Third molar crypts may appear as early as the 5th year and as late

as 14th year of life (Banks, 1934). In both populations in the present study

initiation occurred no earlier than 7 years of age. Demirjian et al. (1973)’s

developmental stage H is of specific importance in forensic age estimation as it

is a useful developmental marker to answer the question whether an individual

is legally an adult. This stage marks the last stage of tooth development, which is

easily recognizable in the form of a fully mineralized tooth with apex closure.

Thus, the probability for an individual being older or younger than 18 years can

be determined. In the Western Australian population, for male individuals with

fully developed third molars (stage H) they are at least 17 years of age and if

females they are at least 18 years of age older. In the South Indian population,

individuals with fully developed third molars (stage H) are at least 18 years of

age (or older) irrespective of sex.

A major focus of recent forensic research is the importance of population

specific reference data to arrive at the most accurate age estimation. It is evident

from numerous other studies that the timing of the mineralization of the third

molars is population specific and does not occur at the same age in all

populations (see above and Chapter Three). The present study, therefore, has

shown the importance of, and provided, population specific standards for dental

age estimation in Western Australian and South Indian individuals. These data

can be used for forensic age estimation of unknown individuals in both

populations and thus fill a gap in existing knowledge.

6.7. Potential limitations of the present study

1. Sample size: a potential limitation concerns the size of the sample

examined in this study. A total of 561 conventionally taken OPGs of 312

Western Australian and 249 South Indian individuals were examined.

Although the sample size is relatively large, it would be desirable to use

an even larger sample (500 to 1000 each) to represent the wider

community as a whole in both the Western Australian and South Indian

populations.

2. Technological limitations: Superposition and distortion of anatomical

structures in the orthopantomographs (OPG’s) at the maxillary

tuberosity level can lead to poor visualization of the maxillary third

molars, especially until its entire occlusal surface is mineralized. There

are limits to the possibility of radiographic diagnosis, which may

produce errors in the frequency of agenesis and in the rate of third

molar mineralization, thus increasing the magnitude of error in age

estimation from the dentition (Bolanos et al. 2003). This potential

limitation, however, applies to any study utilizing dental OPG’s.

6.8. Recommendation for future research

This thesis was a preliminary study which applied the Demirjian et al. (1973)

tooth developmental method to third molar mineralization in a Western

Australian and South Indian population. Nystrom et al. (1986), Tompkins et al.

(1996) and Olze et al. (2003) demonstrated that the timing of attaining dental

maturity varies between different population groups and dental age estimation

is more accurate when population specific standards are applied. To that end

the present study has provided population specific and comparable reference

data of third molar development for forensic application in both populations. As

the sample (OPG’s) evaluated in the study was small as compared to the other

studies (500-1000), it is recommended that more samples be acquired to

expand these population specific reference databases. It is also recommended

that this preliminary study evaluating the frequency of missing third molars be

expanded to consider the frequency of total absence of the third molars; this will

provide a more holistic insight into just how often methods based on the third

molars are unable to be applied. In addition, it was shown that Rai et al. (2009)

suggested that females are slightly more dentally advanced than males in a

North Indian population (see Table 6.1; page 67). However, that finding is

obviously not consistent with the present and numerous other studies. This

demonstrates the need for further research on Indian populations to evaluate if

this is an issue with regard to formulating local reference databases for dental

age estimation.

6.9. Conclusions

• The present study provides reference data for the timing of initiation (stage

A) through to completion (stage H) of third molar mineralization in a

Western Australian and South Indian population. It can be concluded that for

those individuals with completed root formation (apex closure), Western

Australian females will be at least 18 years of age and males will have a 99%

certainty of being 18 years of age or older. In the South Indian population,

both males and females will be at least 18 years or older.

• The Western Australian and South Indian individuals assessed in this study

complete third molar development later compared to other populations

(American-Caucasians, African-Americans, German, Turkish, Spanish, and

South African). The timing of third molar development of both populations

studied here is closest to North Indian and Southern Chinese populations.

• Males achieve third molar maturity slightly earlier than females in the

Western Australian (5 to 11 months) and South Indian populations (13 to 14

months).

• The upper (maxillary) third molars develop earlier (7 to 10 months) than the

lower (mandibular) third molar in both populations.

• There are no statistically significant bilateral differences in Western

Australian and South Indian population.

• Regarding the frequency of missing individual third molars, the upper right

third molar were found to be the most commonly missing tooth in the

Western Australian (40.4%) and South Indian (22.5%) populations.

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