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INTERNATIONAL DENTAL JOURNAL OF STUDENTS RESEARCH| January 2015 | Volume 2| Issue 4

29

CASE STUDY

The Inter-arch anterior tooth size discrepancy in different malocclusion groups

Dr. Jamshaid Ali Imran1,2

, Dr. Ambreen Afzal3

Dr. Zeeshan Sheikh4,5,6

Dr. Sahar Jamshaid Ali7

1Resident

Department of Orthodontics

Karachi Medical and Dental College/Altamash

Institute of Dental Science, Karachi, PAKISTAN

2Senior Registrar

Ziauddin College of Dentistry

Ziauddin University, Karachi, PAKISTAN

3Professor & Head

Department of Orthodontics

Altamash Institute of Dental Science

Karachi, PAKISTAN

4PhD Scholar

Faculty of Dentistry, Biomedical Sciences

McGill University, Montreal, Quebec, CANADA

5Post-Doctoral Fellow

Faculty of Dentistry, Matrix Dynamics Group,

University of Toronto, Ontario, CANADA

6Associate Professor

Department of Material Sciences & Preclinical

Dentistry, Altamash Institute of Dental Medicine

Karachi, PAKISTAN

7Private Dental Practitioner

Corresponding Author

Dr. Jamshaid Ali Imran

E mail: [email protected]

Phone: +1 647 4701537

Access this Article Online

Abstract Objectives: The present study was aimed to

investigate the correlation between anterior tooth

size discrepancies and Angles class I, II, and III

malocclusions and to assess their prevalence in the

Pakistani population from the metropolitan city,

Karachi.

Study design: A Cross sectional, comparative

study.

Place and duration of study: Out-patient

department (OPD) of Orthodontics division at

Karachi Medical and Dental College. Six months.

Subjects and methodology: Total 90 subjects.

(Angles class I: 30, Angles class II: 30 and

Angles class III: 30) with an age range of 15-25

years were included n the study. Equal distribution

of male and female subjects was maintained. The

comparison of male and female subjects was done

regardless of body height and weight. Non-

probability, purposive type of sampling technique

was done for data collection. The mesiodistal tooth

width was measured from first molar to first molar

on 90 mandibular and 90 maxillary plaster models

with a vernier caliper. Analysis of variance was

used to compare the mean Bolton anterior tooth

size ratios as function of Angle classification and

gender. Statistical differences were determined at

the 95% Confidence level (P < 0.05).

RESULTS: When Comparing mean anterior ratio

of class I (mean=79.8), class II (mean =79.9) and

class III (mean =85) in 90 casts, significant

difference were found among all three

classification (P=0.008).The results showed that

significant difference found in mean anterior ratio

when comparing different malocclusion groups.

Significant difference was found in females when

comparing mean anterior ratio among males and

females in class III malocclusion group. When

multiple comparison was done of anterior ratios

between malocclusion groups there was no

significant difference found between class I and II

while class III malocclusion group was

significantly different from class I and class II

(P=0.007).

Conclusions: Significant difference found in mean

anterior ratio when comparing different

malocclusion groups. Subjects with an Angle class

III malocclusion had a significant greater

probability of tooth size discrepancies than those

with class I and class II malocclusions.

Key words: Tooth size discrepancy; Bolton

analysis; Bolton ratio; Tooth size analysis;

malocclusion.

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30

Introduction The presence of a tooth size discrepancy [TSD]

prevents the achievement of an ideal occlusion. A

high percentage of finishing phase difficulties

arises because of tooth size imbalance that could

have been detected and considered during initial

diagnosis and treatment planning. In some

situations, tooth size discrepancy is not observed at

the initial examination and could result in poor

contacts, spacing, crowding, and an abnormal

overjet and overbite.

The etiology of malocclusion can be broadly

categorized under either hereditary, environmental,

or a combination of both factors.1Exploring the

etiology of malocclusion is imperative for selecting

the most appropriate treatment approach as well as

the most appropriate retention device.1,2

Crowding

and spacing are considered the most common

manifestations of malocclusion3

and can occur as a

result of either a shortage of the space required for

tooth alignment or an excess of available space.

The tooth size measurements of Wheeler4also are

frequently used. As significant tooth size

discrepancies prevent an ideal occlusion being

produced at the end of orthodontic treatment, the

absence of a TSD is the seventh key for an ideal

occlusion.5

On a clinical level, mesiodistal tooth width is

correlated to the arch alignment and large teeth are

associated with crowded dental arches.6-8

Patients

with inter arch tooth size discrepancies require

either removal (e.g. interdental stripping) or

addition (e.g. composite buildups or porcelain

veneers) of tooth structure to open or close spaces

in the opposite arch, it is important to determine the

amount and location of a tooth size discrepancy

before starting treatment.9Bolton developed a

method of analyzing the mesiodistal tooth size ratio

between maxillary and mandibular teeth.10

Among patients undergoing orthodontic treatment,

the prevalence of an overall TSD has varied from

4% 11%.11

Anterior TSDs, however, have

prevalence between 17% and 31% among

orthodontic patients.12

The anterior tooth size ratio

was higher for Hispanics (80.5%) than for Black

people (79.3%). Despite these findings, Othman

and Harradine13

noted that the trend to larger

overall tooth size ratios in Black populations is

unlikely to be clinically relevant. Significant

discrepancies in the overall and anterior tooth size

ratios have been found in Japanese, Iranian-Azari,

Spanish, and Brazilian subjects.14-17

Much work has been done internationally, however

no study has been done in our population to set the

norms for mesiodistal crown dimension and

interarch tooth size ratios. Study of these lines

would greatly improve the quality of orthodontic

finish in our population and lead to a more sound

understanding of one of the most complex variables

affecting orthodontic malocclusion. Trends have

been identified in the prevalence of TSDs among

the malocclusion groups. TSDs are more common

in Class II division 1 malocclusions and in Class III

malocclusions.18-21

The purpose of the study is to set a baseline data to

encourage the research of this region to carry out

more research on this subject in Pakistani

population. The objective of the current study was

to determine any difference in intermaxillary tooth

size discrepancies represented by anterior ratios

when comparing Class I, Class II and Class III

cases in a Pakistani population. Study of these lines

would greatly improve the quality of orthodontic

finish in our population and lead to a more sound

understanding of one of the most complex variables

affecting orthodontic malocclusion.

Materials and Methods The data for this study was obtained from the

records of the Karachi Medical & Dental College,

Dept of Orthodontics. Considering that tooth size is

not related to age, the sample selection procedure

was based on dental age and the presence of a

permanent dentition defined by the presence of all

teeth at least from first molar to first molar. The

subjects were randomly selected and assigned to

three malocclusion groups according to the Angle

classification classes I, II, and III. Total 90 subjects

(30 pairs of Angles Class I, 30 pairs of Class II

and 30 pairs of Class III malocclusion). Sampling

Technique was Non-Probability, purposive type.

The selection criteria adopted were anterior

permanent teeth erupted in the upper and lower

arches; good-quality study casts; absence of tooth

deformity; no record of restoration or stripping of

incisor and canine teeth age range of 15 to 25 years

of age. Exclusion criteria were: Patients exhibiting

incisal or cuspal attrition, fractures of teeth or

ectopically erupted teeth, patients with anomalies

of tooth size (e.g. microdontia, macrodontia; peg

laterals etc), patients with anomalies of tooth

number (e.g. hyperdontia, hypodontia, cases of

fusion of teeth and gemination), patients with

history of previous orthodontic treatment, patients

with craniofacial syndrome or anomalies.

A stainless steel Boley Gauge vernier caliper

(Odontomed2011, product ref # 16140) was used to

measure the mesiodistal width to the nearest 0.1

mm. The width of each tooth was measured from

its mesial contact point to its distal contact point at

its greatest interproximal distance. Bolton anterior

(canine to the canine) ratios were calculated with

the following formulae:

Sum mandibular 6 X 100 = anterior ratio (%)

Sum maxillary 6

Statistical analysis was performed on data using the

software: IBMSPSS

(v. 20, IBM SPSS Inc.,

Chicago, IL). For all continuous variables including

age and malocclusion, mean (X) and standard

deviation (SD), values were calculated for each


31

measurement. To compare the means of anterior

ratio in different malocclusion groups analysis of

variance (ANOVA) statistical significance level

was taken at 0.05.

Results Out of 90 cast, 30 pairs of angle class 1, 30 pairs of

angle class II and 30 pairs of angle class III. The

age distribution is 15-25 where 55% are between

15-19 years, 43% in between 20-24 years and rest

are above 24 year as shown in fig 1. When

comparing mean anterior ratio of class I (mean

=79.8), class II (mean = 79.9) and class III (mean =

85) in 90 casts, significant difference were found

among all three classification (p=0.008) as shown

in table 1.When multiple comparison was done of

anterior ratios between malocclusion groups there

was no significant difference found between class I

and class II. The class III malocclusion group was

significantly different from class I and class II (p =

0.007) as shown in table 2.

Table 1. Comparison of means of anterior ratio in different

malocclusion groups (n=90).

Classes Range Mean SD 95%

CI

P-

value*

I

(n=30) 69 89.9 79.8 4.97

77.9 -

81.6

0.008 II

(n=30)

68.5 -

105.19 79.9 7.04

77.2 -

82.5

III

(n=30)

66.6 -

107.7 85 9.1

81.6 -

88.46

*By applying ANOVA (Analysis of Variance).

Class-I = The triangular ridge of the mesiobuccal

cusp of the maxillary first permanent molar

articulates in the buccal groove of the mandibular

first molar.

Class-II=The mesial groove of the mandibular first

permanent molar articulates posteriorly to the

mesiobuccal cusp of the maxillary first permanent

molar.

Class III= The mesial groove of the mandibular

first permanent molar articulates anteriorly to the


molar.

Table 2. Multiple comparisons of anterior ratio between

different malocclusion groups.

*By LSD test (used t-test to perform all pair wise comparisons) * Class-III is significantly different from class I and II

Class-I = The triangular ridge of the mesiobuccal

cusp of the maxillary first permanent molar

articulates in the buccal groove of the mandibular

first molar.

Class-II= The mesial groove of the mandibular first

permanent molar articulates posteriorly to the


molar.

CLASS III= The mesial groove of the mandibular

first permanent molar articulates anteriorly to the


molar.

Figure 1.Age distribution of patients (n = 90)

Age in Years (Mid values)

26.024.022.020.018.016.0

Nu

mb

er

of

Pati

en

ts

30

20

10

0

1313

22

19

22

Mean SD = 17.32 3.94 (years)

Range = 15 25 Years

Figure 2.Boley Gauge Vernier Caliper, stainless steel

(Odontomed2011, product ref # 16140)

Classes P-Values

Class-I and Class-II 0.977

Class-III and Class-I 0.007*

Class-III and Class-II 0.007*


32

Discussion A tooth-size discrepancy is defined as a lack of

harmony between the mesiodistal widths of

individual teeth or groups of teeth when related to

their functional counterparts of the opposing arch.

Any discrepancy will result in either spacing in 1

arch or a compromise in functional relationships.

To achieve good occlusion with the correct

overbite and overjet, the maxillary and mandibular

teeth must be proportional in size to each other.22

Tooth size discrepancies are considered an

important variable especially in the anterior

segment. Lavelle23

stated that although tooth size

and proportion have an important role in

malocclusion. Genetic influences have been

considered important in the determination of tooth

dimensions, and the first reports were related to

clinical observations within families. Studies on

twins, however, helped in understanding the

genetic contribution of tooth size in that a greater

tooth size correlation was found in monozygotic

twins.24,25

Other investigators de-emphasized the

genetic contribution and described the

determination of tooth size as multifactorial, with

the environment playing an important role.26

Teratogenic and nutritional factors have been

associated with the mechanism of tooth

formation.26

Space limitations and nutrition have

been described as important in the development of

a healthy tooth germ and have been related to

alterations in number, shape and form of permanent

teeth.26

Although it is widely accepted that both

genetic and environmental variables affect tooth

development, it is virtually impossible to identify

and describe the role each of these variables play in

the determination of tooth size.

Several studies were published describing the

importance of a correct tooth size proportion

between the upper and lower arches. Lundstrm27

studied the relationship between the mandibular

and the maxillary anterior sum and named it the

anterior index. For an ideal overbite, the optimal

ratio was found to be from 73% to 85%, with a

mean of 79%.

Bolton10,28

evaluated 55 cases with excellent

occlusion. After considering tooth sizes from

canine to canine in the maxillary and mandibular

arches, Bolton established an ideal anterior ratio

with a mean value of 77.2% and standard deviation

(SD) of 1.65%. It would be very difficult to obtain

an excellent occlusion in the finishing phase of

treatment without a correct mesiodistal tooth size

ratio. Orthodontists should be concerned with tooth

size discrepancies because of the high incidence in

orthodontic patient populations. Bolton10,28

reported

tooth size discrepancies greater than 1 SD in 29%

of the patients studied in his private practice, and

Richardson and Malhotra29

reported similar

discrepancies in 33.7% of their patients. Crosby

and Alexander30

stated that a tooth size discrepancy

had to be greater than 2 SD, e.g., two to three mm

of deviation, to influence the course of orthodontic

treatment. In studies involving 109 individuals,

22.9% showed anterior ratios that significantly

deviated from the Bolton analysis mean (greater

than 2 SD).

Sassouni31

was the first to report that individuals

with a Class III facial type and deficient maxillary

growth showed a greater prevalence of alterations

in shape of the anterior teeth as well as a greater

incidence of agenesis. In more recent articles, other

variables such as incisor inclinations,32

upper-

incisor thickness,33,34

and arch form33,35

have been

described as important to consider in achieving

optimal occlusion relationships. Efforts have been

made to adapt the Bolton analysis to these

variations. Cua-Benward et al36

studied the

prevalence of missing teeth in different

malocclusion groups, relating their findings to

Mosss functional matrix concept. They found a

greater prevalence of tooth deformities in the

maxilla in Class III individuals, whereas they found

more tooth deformities in the mandible in Class II

individuals. Hashim HA37

evaluated mesiodistal

crown width in different malocclusion groups

(class I, class II and class III) and found no

statistical difference between them. Discrepancies

in tooth size should be known at the initial

diagnosis and treatment planning stages if perfect

results in orthodontic finishing are to be achieved.

Tooth size discrepancies are considered an

important variable, especially in the anterior

segment. Araujo and Souki38

reported that the mean

anterior tooth size discrepancy for Angle Class III

subjects was significantly greater than that for

Class I and Class II Subjects.

A comparative study between Jordanians, Iraqi,

Yemenites, and Caucasians reported that

Jordanians and Iraqi had larger teeth than the other

populations.39

The later study, however, did not

discuss the differences in tooth size between

different malocclusions. Correct tooth size

relationship between maxillary and mandibular

teeth is an important factor to achieve a proper

occlusal interdigitation during the final stages of

orthodontic treatment.10,40

The importance of correct

tooth size proportions between the upper and lower

arches has been demonstrated. Neff 40

developed an

anterior coefficient, which was a proportion for the

width dimension of the teeth. A ratio of 1.20 1.22

when the maxillary mesio-distal sum was divided

by the mandibular mesio-distal sum would result in

an optimal overbite. Several methods have been

described to evaluate interarch tooth size

relationship such as Neffs anterior coefficient40,41

and Boltons ratios for the six anterior teeth and the

overall ratio for the 12 teeth.10,28

Many factors such as heredity, growth of the bone,

eruption and inclination of the teeth, external

influences, function, and ethnic background would


33

affect the size and shape of the dental arches.42-

45However, Gilmore and Little

46 found that,

although there was a tendency for incisors with a

greater mesiodistal dimension to be associated with

crowding, the association was so weak that

reduction of the widths of incisors to fit a specific

range cannot be expected to produce a stable

alignment. Theories proposed to explain the cause

of dental crowding vary widely, embracing

concepts of evolution, heredity, and environmental

effects.

In a more recent study, Santoro et al47

reinforced

the findings of Crosby and Alexander30

observing

that 28% of 54 Dominican Americans presented a

discrepancy greater than 2 SD. Lavelle23

studied

160 subjects for anterior tooth sizes and showed a

tendency for Angle Class III individuals to present

smaller upper teeth compared with subjects

classified as Class II or I. Moreover, Lavelle23

stated that teeth in the lower arch are larger in Class

III than in Classes II and I, with the inference that a

Bolton discrepancy is greater in Class III cases than

in the other malocclusion groups. In this study, the

mesiodistal tooth size and Bolton ratio were

compared in Class I, Class II and Class III in a

Pakistani sample.

In our study anterior ratio showed tendency

towards large Bolton ratio in class III malocclusion

group which is most similar to the studies done in

Chinese population.48,49

The difference in the results

between this study and the other investigations

might be attributed to the sample size, method of

analysis and large standard deviation found in this

study.Crosby and Alexander 30

also compared the

tooth size ratios among different malocclusion

groups, as in this study. They found that there were

no significant differences among Class I, Class II

division 1, Class II division 2, and Class II surgery

groups. This study also found no significant

difference between these groups. In this study we

compared the tooth size ratios among Angles class

I, class II and class III malocclusion groups and

found significant difference in mean anterior ratios

of class III malocclusion group.

Crosby and Alexander 30

also compared the tooth

size ratios among different malocclusion groups but

did not included class III malocclusion group, as in

the current study. They found that there was no

significant difference among Class I; Class II,

division 1; Class II, division 2; and Class II surgery

groups. In the present study, three malocclusion

groups were compared, and no statistically

significant difference was found among them in

overall ratio and statistical difference in anterior

ratio. For patients with Class III malocclusion, the

present findings were in accordance with Nie and

Lin48

and Lavelle.23

The subjects in the present investigation all had

malocclusions sufficiently severe to warrant

treatment and it is possible that this is contributed

to the larger percentage of tooth size discrepancies,

especially in the anterior region. This could be

explained by the fact that anterior teeth, especially

the incisors, have a much greater incidence of tooth

size deviations, that is, the greatest variables in

mesiodistal tooth width occur in the anterior region.

The findings that individuals with a Class III

malocclusion have a significantly greater mean

anterior ratio than the other groups may confirm the

results of Lavelle23

that Class III individuals have

disproportionately smaller maxillary teeth than

Class I and Class II subjects. However, a small size

of the maxillary teeth was not found in the present

study. Therefore, the Bolton discrepancy in the

Class III sample must either be attributed to an

increase in the width of the anterior mandibular

teeth or the accumulation of minor discrepancies of

individual teeth.

The results obtained by Nie and Lin48

using

Angles classification as a variable in analyzing

360 Chinese individuals for tooth size

discrepancies are in agreement with the present

findings that Class III patients demonstrate a

greater tooth size discrepancy when compared with

Class II and I patients. Crosby and Alexander30

tried to verify the presence of a tooth size

discrepancy in 109 patients divided into four

malocclusion groups, but not including Class III

subjects. They compared the average of the anterior

and overall Bolton indices but did not find any

statistical difference in the incidence of the tooth

size discrepancy among the groups (Class I, Class

II divisions 1 and 2, and surgical Class II). Some of

the findings in the present investigation were

similar to their results with respect to the absence

of statistically significant differences when

comparing Class I and Class II malocclusion

groups. Since they did not include subjects with a

Class III malocclusion in their investigation, they

could not find any difference between normal

occlusion and malocclusion groups coinciding with

the Bolton indices, while in the present study, a

large part of the differences in the Bolton indices

were attributed to the presence of a Class III

malocclusion.

Several authors50

proposed new methods to study

tooth size discrepancies. However, these proposals

need to be tested in clinical studies and, for now,

the Bolton analysis prevails as an efficacious

clinical tool for appraising various relationships of

upper to lower dentitions. The high prevalence of

anterior TSDs in Irish orthodontic population51

suggests that a tooth size analysis should be

conducted at the treatment planning stage. Where

significant TSDs are detected, this is normally

accommodated by the reduction or augmentation of

tooth tissue.

Further studies are needed to clarify whether a

correlation exists between increased mandibular

growths (as in Class III malocclusions) with


34

increased mesiodistal dimensions of lower anterior

teeth. The possible interaction of genetic factors

could determine mandibular size while affecting

the mesiodistal dimensions of lower mandibular

teeth in the same way.

Conclusion Subjects with an Angle Class III malocclusion had

a significantly greater probability of tooth size

discrepancies than those with Class I and Class II

malocclusions.The mean anterior tooth size

discrepancy for Angle Class III individuals was

significantly greater than that in Class II and Class

I malocclusion.The Orthodontist who is aware of

these possible discrepancies will be better prepared

to diagnose and plan treatment with a more

accurate certainty for patients of varied population

mix. These conclusions could greatly influence

clinical decision making and further studies should

be undertaken in this field.

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