the relationship between american board of orthodontics
TRANSCRIPT
THE RELATIONSHIP BETWEEN AMERICAN BOARD OF ORTHODONTICS
PRETREATMENT DENTAL CAST DISCREPANCY INDEX
SCORES AND POSTTREATMENT DENTAL CAST
OBJECTIVE GRADING SYSTEM SCORES
David Leaver Cameron, D.M.D.
An Abstract Presented to the Faculty of the Graduate School of Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of Master of Science in Dentistry
2010
ABSTRACT
Purpose: The purpose of this study was to investigate the correlation between the
American Board of Orthodontics (ABO) pretreatment dental cast Discrepancy Index (DI)
and the posttreatment Objective Grading System (OGS) scores. The relationships among
overall scores and individual components were investigated as well as the correlations
with treatment times.
Materials and Methods: The ABO’s DI was used to measure 165 dental cast cases that
were finished in 2007-2008 at the Saint Louis University Center for Advanced Education
Orthodontic clinic. No cephalograms or panoramic radiographs were measured. The
cases were divided into three pretreatment groups of low, medium and high DI.
Furthermore, the cases were additionally grouped into three posttreatment groups of
“Passing,” “Undetermined,” and “Failing.” ANOVA, Pearson correlation coefficients and
multiple regression analyses were performed.
Results: The low DI group and the high DI group had a significant difference of 4.2
points in the overall posttreatment OGS score. Three posttreatment components of the
OGS, buccolingual inclination, occlusal contacts and occlusal relationship were the
highest contributors to this difference in posttreatment scores. The three posttreatment
OGS group showed no differences in their pretreatment DI scores. However,
pretreatment lingual posterior crossbite was a significant 0.54 points lower in the
“Undetermined” group than in the “Failing” group. Treatment time was 4.56 months
longer for the high DI group when compared to the low DI group. No difference was
found in treatment time among the three OGS groups. No correlations were of reportable
strengths.
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Conclusions: Low complexity cases may have a better treatment outcome than high
complexity cases as measured by the ABO’s OGS Those components with the greatest
contribution to the poorer outcomes are buccolingual inclination, occlusal contacts and
occlusal relationship. Low complexity cases may finish in less time than high complexity
cases.
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THE RELATIONSHIP BETWEEN AMERICAN BOARD OF ORTHODONTICS
PRETREATMENT DENTAL CAST DISCREPANCY INDEX
SCORES AND POSTTREATMENT DENTAL CAST
OBJECTIVE GRADING SYSTEM SCORES
David Leaver Cameron, D.M.D.
A Thesis Presented to the Faculty of the Graduate School of Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of Master of Science in Dentistry
2010
COMMITTEE IN CHARGE OF CANDIDACY: Professor Eustaquio Araujo, Chairperson and Advisor Associate Clinical Professor Donald R. Oliver Assistant Clinical Professor Patrick F. Foley
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DEDICATION
I would like to dedicate this work to my loving wife and children. They give my
life meaning, fill me with joy and motivate me to be my best. It is only through their love
and my wife’s never-ending support that I have reached this culminating point of my
academic endeavors. Thank you Katie for all that you have done to help me accomplish
all of my goals.
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ACKNOWLEDGEMENTS
I would like to thank Dr. Eustaquio Araujo, my mentor and committee chair, for
all of his guidance through this process and my other committee members, Dr. Donald
Oliver and Dr. Patrick Foley, for all of their help with this work. Thank you to Dr. Heidi
Israel for her help with the statistical analyses and to Dr. Vance Dykhouse for his help
with the calibration process. I also need to thank the entire faculty, staff and
administration who have played a role in my acceptance to this program and in my
orthodontic education. Special appreciation goes to my parents, siblings and in-laws who
have always encouraged me as well as to Drs. Robert and Scott Leaver and their families
for their help and support through the years.
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TABLE OF CONTENTS List of Tables …….……………...………………………………………………….…… v
List of Figures……....…………………………………………………………………….vi
CHAPTER 1: INTRODUCTION ……………………………………………………….. 1 CHAPTER 2: REVIEW OF THE LITERATURE
The ABO Discrepancy Index ………………………….………………………... 4 The ABO Objective Grading System ...………………………………………...............12
Correlation between Discrepancy Index and Objective Grading System ….........25 References ……………………………...………………………………………... 27 CHAPTER 3: JOURNAL ARTICLE
Abstract …………………………………………………………………………..29 Introduction ……………………………….…………………….………………..31 Materials and Methods …………………………………………………………...33 Results ………………………………………………………………………........36 Discussion ……………………………………………………………………….. 40 Conclusions ………………………………………………………..…………….. 44 References ……………………………………………………………………….. 45
Appendix…………..…...……………………………………………………………..… 47 Vita Auctoris……....……………………………………………………………………..54
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LIST OF TABLES Table 3.1: Discrepancy Index Components by Objective Grading System Group……49 Table 3.2: Objective Grading System Components by Discrepancy Index Group……50 Table 3.3: Discrepancy Index Components by Objective Grading System Group……51 Table 3.4: Objective Grading System Components by Objective Grading System
Group………………………………………………………………………..52 Table 3.5: Treatment Times By Discrepancy Index and Objective Grading System
Groups………………………………………………………………………53 Table 3.6: Objective Grading System Group Frequency by Discrepancy Index Group…...53
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LIST OF FIGURES
Figure 2.1: Discrepancy Index Instructions Form ……………………………..………. 9 Figure 2.2: Discrepancy Index Worksheet ……………………………………………. 10 Figure 2.3: ABO Measuring Gauge and Instructions………...……………………….. 14 Figure 2.4: Objective Grading System Instruction Form..……………………………….. 23 Figure 2.5: Objective Grading System Scoresheet…………………………………….24
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CHAPTER 1: INTRODUCTION
Since its inception in 1929, the American Board of Orthodontics (ABO) has had
as part of its objectives to “elevate the standards of the practice of orthodontia; to
familiarize the public with its aims and ideals; to protect the public against irresponsible
and unqualified practitioners.” In order to accomplish this, the ABO established national
standards of orthodontics through a certifying process. Over the years, the ABO has made
various changes to the examination process in an attempt to create a fairer and more
objective system for assessing the treatment rendered on the board cases being
presented.1,2 A letter by Albert Ketcham, a key initiator of the establishment of the ABO,
set the stage for the continual changes required to maintain an effective examination. His
letter stated, “We must adapt our examination to the applicant, try to discover if he is
safe, whether he has the technical skill and scientific knowledge . . . A complete and
perfect plan for our examinations cannot be worked out except through long experience
in giving examinations to men of varied training, caliber and experience.”3 It is clear that
Dr. Ketcham understood the importance of continually reassessing the examination
process to improve upon it.
Beginning in 1940, certification requirements included a thesis, five case reports
and a set of casts with appliances on them. In 1967, case categories were introduced that
specified the type of cases that were required to be presented and the thesis requirement
was replaced by a written examination in 1978. Over the following 20 years, the criteria
for the cases have varied as the ABO has tried to improve the examination. Two systems,
in particular, have developed from these changes and are currently being used by the
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ABO to assess the pretreatment complexity and the posttreatment results of the clinical
examination board cases. These two systems, the Discrepancy Index (DI) and the
Objective Grading System (OGS) have been used by the ABO since 1998.3,4
Currently, the DI is used by the ABO to determine whether pretreatment cases are
complex enough to be considered for the certification process. The OGS is utilized in
determining whether cases presented by orthodontists during the certification process
have posttreatment results that are considered to be passing or failing. While the DI is
used to determine whether pretreatment cases are complex enough to be considered for
the certification process, it is not referenced when scoring the posttreatment results.5
Thus, the complexity of the case pretreatment is not taken into consideration when
scoring the posttreatment results. This study is important to determine whether the
pretreatment Discrepancy Index should be considered when scoring the posttreatment
results. In other words, if a case has a higher pretreatment case complexity, it may be
expected to have a poorer quality posttreatment outcome because of the complexities
inherent to the case. There have been various studies performed recently that center
around the ABO certification process, but none that have taken this approach to
investigating the factor of the Discrepancy Index in scoring the posttreatment results
directly with the OGS.6-10 While there have been some general trends related to DI and
the OGS discovered in previous studies these results have been conflicting and the nature
of the relationship, if any, has not been described in detail. It may also be helpful to
practitioners if they knew of a correlation so that they could assess an expected
posttreatment outcome based upon the pretreatment case complexity.
2
The purpose of this study is to determine if there is a relationship between the
pretreatment dental cast Discrepancy Index scores and the posttreatment dental cast
Objective Grading System scores used in the certification process by the ABO. The
question to be answered is: Does a higher pretreatment Discrepancy Index result in a
higher posttreatment ABO objective grading system score? Length of treatment will also
be measured for all cases to determine if there is a significant difference in length of
treatment times among various groups of case complexity or quality of treatment
outcome.
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CHAPTER 2: REVIEW OF THE LITERATURE
The ABO Discrepancy Index (DI)
Orthodontic indices have been used for many years to evaluate the complexity of
a patient's malocclusion and to determine the need for treatment. These indices generally
have a threshold that is set in order to determine the priority for treatment needs. The
ABO’s purpose was to find a method of evaluating the level of complexity of cases
submitted for the clinical examination, not to determine treatment need. To resolve this,
the ABO formed a committee to develop their own index to serve their needs of
evaluating case complexity using a quantifiable, objective list of certain characteristics of
malocclusion.11
The DI was first developed in 1998 by eight ABO directors and six former
directors who were acting as consultants to the ABO. During the clinical examination of
1999, 100 cases were scored using DI by two directors. This data was used to form the
initial pilot study of the DI. The results of the pilot study were reviewed and discussed by
committee and the DI was modified. Additional field tests were performed during the
2000 through 2003 examinations and every case that was submitted those years was
scored for DI by all directors and examiners of the ABO. Examinees were also asked to
score certain cases in 2002 and all of their cases in 2003 as part of the field testing.
Additional modifications were made to the DI based on the results of these
supplementary field tests and was made an official alternative for ABO case submission
in 2004. It was originally available as an alternative to the previous categories of cases
that the ABO had set forth and was to be used for 3 years followed by a reevaluation of
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the system and further consideration of how the DI could be factored into the overall
decision of case acceptability and completeness of treatment. It was set at a DI of 25 and
above for 2 cases, a DI of 16 and above for 6 cases and a DI of 7 and above for 2 cases.11
Then in 2005, more changes to the DI system were put into place and the
acceptance requirements were adjusted to 3 cases of DI of 10 and above and 3 cases of 20
and above. An objective of this study is to determine if the DI should be considered as a
weighted factor in assessing the posttreatment outcome using the OGS.1,5
The ABO has made a point of clarifying that the index be called the Discrepancy
Index and not the difficulty index because the system was developed to measure the
inherent complexity of the case, not the degree of difficulty. It is important to note the
elusive nature of difficulty as it invites subjectivity and personal perception. For example,
some conditions that are considered difficult by some orthodontists may be considered
fairly easy to treat by other orthodontists based on individual treatment philosophies,
differences in appliances or training. Thus, the ABO chose specific characteristics of
malocclusion that can be quantified and assessed in a more objective manner.11
There are currently 12 target areas that are assessed in the DI including overjet,
overbite, anterior openbite, lateral openbite, crowding, occlusion, lingual posterior
crossbite, buccal posterior crossbite, ANB angle, IMPA, SN-GoGn and an “Other”
category. The “Other” category allows points to be given for other conditions that may
contribute to case complexity such as generalized spacing of > 4mm, a diastema of >
2mm, ankylosis, transposition, etc.12
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The following measurement parameters and DI work form (Figures 2.1 and 2.2)
are taken directly from the ABO website’s Clinical Examination Case Report Work
File.12
1) Occlusion is determined by placing the backs of the bases of the pre-treatment
dental casts on a flat surface with the upper and lower cast pushed together in
occlusion. All measurements that involve both arches must be made from this
position.12
2) Overjet - A measurement between two opposing incisor teeth with the greatest
overjet that is:
measured from the facial surface of the most lingual tooth (maxilla or mandible) to the middle of the incisal edge of the more facially positioned tooth (maxilla or mandible). For overjet of 0 – 0.9 mm (edge-to-edge), 1 point is scored; for overjet of 1 to 3 mm, no points are scored; for 3.1 – 5 mm, 2 points are scored; for 5.1 – 7 mm, 3 points are scored; for 7.1 – 9 mm, 4 points are scored and if over 9 mm, 5 points are scored. If there is a negative overjet (anterior crossbite), the score is recorded as 1 point per millimeter per anterior tooth in crossbite.12
3) Overbite –
For overbites up to 3 mm, no points are scored. If the overbite is between 3.1 to 5 mm, 2 points are scored; if between 5.1 to 7 mm, 3 points are scored. 5 points are scored if the lower incisors are impinging on the palatal tissues and/or 100% overbite.12
4) Anterior open bite –
For each anterior tooth (canine to canine) that is in an edge-to-edge relationship (overbite = 0), 1 point is scored per tooth. For each additional full millimeter of open bite, 1 point is scored for each maxillary tooth involved. No points are scored for any anterior tooth that is simply blocked out of the arch or not fully erupted.12
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5) Lateral open bite –
For each maxillary tooth (from the first premolar to third molar) in an open bite relationship with the lower arch, 2 points are scored per mm of open bite for each tooth.12
6) Crowding –
When scoring, measure the most crowded arch circumference (only one arch) between the first molars. From 0 to 1 mm, 0 points are scored; from 1.1 to 3 mm, one point is scored; from 3.1 – 5 mm, 2 points are scored; from 5.1 – 7 mm, 4 points are scored. If the crowding is greater than 7 mm, 7 points are scored.12
7) Occlusion - The Angle classification is used for scoring occlusion.
If the mesiobuccal cusp of the maxillary first molar occludes with the buccal groove of the mandibular first molar or anywhere between the buccal groove and the mesiobuccal or distobuccal cusps, no points are scored. If the mesiobuccal cusp of the maxillary first molar occludes with the mesiobuccal (Class II end-to-end) or distobuccal (Class III end-to-end) cusps of the mandibular first molar, then 2 points per side are scored. If the relationship is a full Class II or III, then 4 points per side are scored. If the relationship is greater or beyond Class II or III, then 1 additional point per mm is scored. Each side should be scored individually and included in the point accumulation for this category.12
8) Lingual posterior crossbite –
For each maxillary posterior tooth where the maxillary buccal cusp is lingual to the buccal cusp tip of the opposing mandibular tooth (from the first premolar to the third molar), 1 point is scored.12
9) Buccal posterior crossbite –
For each maxillary posterior tooth (from the first premolar to the third molar) in complete buccal crossbite, 2 points are scored.12
10) Cephalometrics –
If the ANB angle is >6° or <-2°, then 4 points are scored. An additional point is scored for each degree above 6° or below -2°. If the SN-MP angle is between 27° and 37°, zero points are scored. If the SN-MP angle is 38° or greater, then 2 points are scored for each degree above 37°. If the SN-MP
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angle is 26° or less, then 1 point is scored for each degree below 27°. If the Lower Incisor to MP angle is 99° or greater, then 1 point is scored for each degree above 98°.12
11) Other – “Supernumerary teeth” are given “1 point for each extra tooth.” “Missing
teeth” are each given “1 point per tooth.” “Ankylosis of permanent teeth,”
“anomalous morphology of tooth size and shape (e.g. peg lateral incisor),”
“impaction of teeth (except third molars),” and “congenitally missing teeth” are
all given “2 points per tooth.” A “midline discrepancy” of 3 mm or more is given
2 points. A “maxillary central diastema” of 2 mm or more is given 2 points.
Generalized spacing of 4 mm or more is given 2 points per arch. “Tooth
transposition” is given “2 points for each event.” “Skeletal asymmetry” that is
“treated nonsurgically” is given “3 points.” “Additional treatment complexities”
as described by the examinee are given “2 points each.”12
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Figure 2.1: Discrepancy Index Instructions Form from the Case Report Work File on the
ABO website.12
9
In 2001, the ABO began discussing the possibility of allowing recent graduates to
take the certification clinical exam using cases that were treated during their residency
program. As a result of this discussion, 16 orthodontic programs were invited and agreed
to participate in a pilot study that would evaluate the treatment outcomes of cases treated
by residents. Part of this pilot study also investigated the level of case complexity found
within the sample of resident-treated cases. Eight hundred and fifty-seven cases were
submitted and evaluated. One of the questions posed was: Were the cases submitted by
the orthodontic residents sufficiently complex to qualify for the current ABO clinical
examination? The pilot study concluded that residents’ cases were sufficiently complex
to qualify for the ABO clinical examination. This finding supports the use of resident
cases in assessing DI and that it can be representative of orthodontic cases in private
practice as well.13
Various other studies have been conducted to assess the reliability of the DI. Most
of these studies are all in agreement that the DI can be a reliable instrument to assess the
pretreatment case complexity once the measurer has undergone training in its proper
use.6,8,10,14
A recent study was the first to be published that established the DI score as a
predictor of treatment duration. It was determined that a 1-unit increase in the DI score
increased treatment duration by 0.1 month. An objective of this current study will be to
compare the results of this sample to see if there is a similar finding and to see if there is
a correlation with treatment outcomes and treatment duration.10
11
The ABO Objective Grading System
Over the past 80 years, the ABO has continued to strive for the objectives that
were established at its inception. That is, to achieve the highest standards of excellence in
clinical orthodontics. Soon after its organization, the ABO began certifying orthodontists
via a case report examination that was intended to assess the candidate’s knowledge of
clinical orthodontics and the quality of the candidate’s clinical abilities. Over the years
the types and quantities of case reports have evolved.
Before the 1990s, 15 case reports were required with records made before
treatment, immediately after treatment, and at least 2 years after removal of orthodontic
appliance. These requirements were later modified in order to encourage greater
participation. Through the early part of 2000, the candidate was required to display 10
case reports from specific categories of malocclusions. These reports were only required
to include records made before and immediately after orthodontic treatment. These case
reports were presented to the board and they were assessed in a more subjective manner
as to the overall quality of the finished treatment. Seeing a need for a more quantitative
and objective manner of assessing the cases, the ABO began to investigate various
indices.4
A former index that had been developed in 1987 and that was commonly used
was the Peer Assessment Rating index. The PAR index is a malocclusion index that
measures the same parameters in pretreatment and posttreatment. There are 7 criteria of
the PAR: tooth alignment, buccal segment relationship, overjet, overbite, and midline. As
the same things are measured both pretreatment and posttreatment, it reflects primarily on
the therapeutic improvement of the patient’s malocclusion, but doesn’t necessarily
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describe the quality of finish in all three planes (first, second and third order) of
occlusion. The ABO wanted a system that measured several other criteria that would
describe the quality of finished treatment and not just the therapeutic improvement of
those 7 criteria. Therefore, the ABO formed a committee in 1994 to oversee the
development of a new measuring index.15
After conducting four field tests over a period of 5 years, the ABO published its
Objective Grading System for dental casts and panoramic radiographs in the American
Journal of Orthodontics and Dentofacial Orthopedics in November 1998.15 In 1999,
measuring gauges and instructions (Figures 2.3, 2.4 and 2.5) were also sent to candidates
to enable them to grade their own treatment results before presenting them for the ABO
clinical examination. This would allow the candidates to know whether the quality of the
result could meet the standard that had been established by the Board. The Board
continues to reevaluate its testing methods and has created a Calibration Committee that
will oversee the implementation and modification of this Objective Grading System in
the future.4
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A - This portion of the gauge is in 1 mm increments and is used to measure discrepancies in alignment, overjet, occlusal contact, interproximal contact, and occlusal relationships. The width of the gauge is 0.5 mm.
B - This portion of the gauge has steps measuring 1 mm in height and is used to determine discrepancies in mandibular posterior buccolingual inclination.
C - This portion of the gauge has steps measuring 1 mm in height and is used to
determine discrepancies in marginal ridges. D - This portion of the gauge has steps measuring 1 mm in height and is used to
determine discrepancies in maxillary posterior buccolingual inclination.
Figure 2.3: ABO Measuring Gauge and Instructions from the Grading System Casts-
Radiographs file on the ABO website.16
According to the June 2008 version of the ABO Grading System for Dental
Casts and Panoramic Radiographs, the following criteria should be evaluated and scored
on the OGS as found on their website (Figures 2.4 and 2.5):16
1) Usually, alignment is a primary “objective of any orthodontic treatment plan,”
specifically to address most patients’ concerns of having malaligned teeth.
Therefore, it is included as an assessment criterion in the OGS. “In the anterior
region, the incisal edges and lingual surfaces of the maxillary anterior teeth and
the incisal edges and labial surfaces of the mandibular anterior teeth were chosen
to assess anterior alignment.” According to the ABO, these are functioning areas
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of these teeth and they also influence esthetics if they are not arranged in proper
relationship. In the maxillary posterior region, the mesiodistal central groove of
the premolars and molars is used to assess sufficient alignment. In the mandibular
arch, the buccal cusps of the premolars and molars are used to assess proper
alignment. The ABO saw these areas as being easily identifiable points on the
teeth that represent the functioning areas of the posterior teeth. According to the
four field tests, the most commonly malaligned teeth were the maxillary and
mandibular lateral incisors and second molars, which accounted for nearly 80% of
the mistakes.16
If all teeth are in alignment, or within 0.50 mm of proper alignment, no
points are scored. If any of the contact points is 0.50 mm to 1 mm deviated from
proper alignment, 1 point shall be scored for the tooth that is out of alignment. If
adjacent teeth are out of alignment, then 1 point should be scored for each tooth.
If the discrepancy in alignment of a tooth at the contact point is greater than 1
mm, then 2 points shall be scored for that tooth. A maximum of 2 points shall be
scored for any tooth. 16
2) Marginal ridges can be representative of “proper vertical positioning of the
posterior teeth.” According to the ABO, “patients with no restorations, minimal
attrition, and no periodontal bone loss, the marginal ridges of adjacent teeth
should be at the same level.”
If the marginal ridges are at the same relative height, the cementoenamel junctions should be at the same level. In a periodontally healthy individual, this will result in flat bone level between adjacent teeth. In addition, if marginal ridges are at the same height, it will be easier to establish proper occlusal contacts, since some marginal ridges provide contact areas for opposing cusps. 16
15
“The most common mistakes in marginal ridge alignment” found in the “four
field tests” occurred between the maxillary first and second molars. “The second
most common” discrepancy “was between the mandibular first and second
molars.” 16
In both maxillary and mandibular arches, marginal ridges of adjacent
posterior teeth shall be at the same level, or within 0.50 mm of the same level.
The canine-premolar contact and the distal of the lower 1st premolar should not
be included in scoring. If adjacent marginal ridges have a discrepancy of 0.50 to 1
mm, then 1 point is scored for that interproximal contact. If the marginal ridge
discrepancy is greater than 1 mm, then 2 points shall be scored for that
interproximal contact. No more than 2 points should be scored for any contact
point. For measuring purposes, the marginal ridge will be defined as the most
occlusal point that is within 1 mm of the contact at the occlusal surface of
adjacent teeth. 16
3) “Buccolingual inclination is used to assess the buccolingual angulation of the
posterior teeth.”16 To assist in achieving “proper occlusion in maximum
intercuspation and” avoiding “balancing interferences,” the difference in heights
of the buccal and lingual cusps of the maxillary and mandibular molars and
premolars should be minimized. In past field tests, significant problems were
observed in the buccolingual inclination of the maxillary and mandibular second
molars.16
A special step gauge (Figure 2.3) is used to assess the relationship between
the heights of the buccal and lingual cusps of posterior teeth. The step gauge is
16
extended between the occlusal surfaces of the right and left posterior teeth. When
positioned in this manner, the straight edge should contact the buccal cusps of
contralateral mandibular premolars and molars and the lingual cusps of
contralateral maxillary premolars and molars. In the mandibular arch, the lingual
cusps should be within 1 mm of the surface of the straight edge. In the maxillary
arch, the buccal cusps should be within 1 mm of the surface of the straight edge.
The mandibular 1st premolars are not scored. If the mandibular lingual cusps or
maxillary buccal cusps are more than 1 mm, but less than 2 mm from the straight
edge surface, 1 point shall be scored for that tooth. If the discrepancy is greater
than 2 mm, then 2 points are scored for that tooth. No more than 2 points shall be
scored for any tooth. 16
4) “Occlusal relationship is used to assess the anteroposterior” relationship between
the “maxillary and mandibular posterior teeth.” Results of previous field tests
conducted by the ABO have shown that the most verifiable method of scoring this
criterion is to use Angle’s relationship.
Therefore, the buccal cusps of the maxillary molars, premolars, and canines must align within 1 mm of the interproximal embrasures of the mandibular posterior teeth. The mesiobuccal cusp of the maxillary first molar must align within 1 mm of the buccal groove of the mandibular first molar. 16 If the maxillary buccal cusps deviate between 1 and 2 mm from the
aforementioned reference points, then 1 point is scored for that maxillary tooth. If
the buccal cusps of the maxillary premolars or molars deviate by more than 2 mm
from the ideal position, then 2 points are scored for each maxillary tooth that
deviates. A maximum of 2 points is scored for each maxillary tooth.
17
In certain cases, the posterior occlusion may be finished in either an Angle
Class II or Class III relationship, depending upon the extractions performed in the
maxillary or mandibular arches. In a Class II situation, the buccal cusp of the
maxillary first molar should align with the embrasure or interproximal contact
between the mandibular second premolar and first molar. The buccal cusp of the
maxillary second molar should align with the embrasure or interproximal contact
between the mandibular first and second molars. If the case is finished in a Class
III relationship, the buccal cusp of the maxillary second premolar should align
with the buccal groove of the mandibular first molar and the teeth distal to the
maxillary second premolar and mandibular first molar are adjusted accordingly. 16
5) “Occlusal contacts are measured to assess the occlusion of the opposing posterior
teeth.” “The functioning cusps are used to assess the adequacy of this criterion;
i.e., the buccal cusps of the mandibular molars and premolars, and the lingual
cusps of the maxillary molars and premolars.” If a cusp is small or diminutive, it
is not scored. In past field tests, the most common area of inadequate contact has
been between maxillary and mandibular second molars.
If the functioning cusps of each arch are in contact with the opposing arch,
no points are scored. Again, neither diminutive distolingual cusps of the maxillary
1st and 2nd molars, nor lingual cusps of the mandibular first premolars are scored.
If a cusp is out of contact with the opposing arch by a distance of 1 mm or less,
then 1 point is scored for that tooth. If the cusp is out of contact by a distance of
greater than 1 mm, then 2 points are scored for that tooth. A maximum of 2 points
are scored for each tooth that is out of contact. 16
18
6) Overjet describes the “transverse relationship of the opposing posterior teeth, and
the anteroposterior relationship of the anterior teeth. In the posterior” segments,
“the mandibular buccal cusps and maxillary lingual cusps are used to determine
the proper position within the fossae of the opposing arch.” If the proper overjet
has been established, then the buccal cusps of the mandibular molars and
premolars will contact in the center of the occlusal surfaces, buccolingually, of the
maxillary premolars and molars. In the anterior region, the mandibular incisal
edges should be in contact with the lingual surfaces of the maxillary anterior
teeth. The common mistakes in overjet have occurred between the maxillary and
mandibular incisors and second molars, in previous field tests.
If the proper relationship exists, no points are scored. If the mandibular
buccal cusps deviate 1 mm or less from the center of the opposing tooth, 1 point is
scored for that tooth. If the mandibular buccal cusps deviate more than 1 mm
from the center of the opposing tooth, two points are scored for that tooth. If the
mandibular canines or incisors are not contacting lingual surfaces of the maxillary
canines and incisors, and the distance is 1 mm or less, then 1 point is scored for
each maxillary tooth. If the discrepancy is greater than 1 mm, then 2 points are
scored for each maxillary tooth. No more than 2 points are scored for any tooth.16
7) Interproximal contacts are evaluated to verify that all spaces have been closed
within the dental arch. Spaces that remain “between teeth after orthodontic
therapy are not only unesthetic, but can lead to food impaction.” Field tests in the
past have shown that “spacing is generally not a major problem with ABO cases.”
The maxillary and mandibular dental casts are viewed from an occlusal
19
perspective. The mesial and distal surfaces of the teeth should be in contact with
one another. If 0.50 mm or less interproximal space exists, then no points are
scored. If 0.50 to 1 mm of interproximal space exists between two adjacent teeth,
then 1 point is scored for that interproximal contact. If more than 1 mm of space
is present between two teeth, then 2 points are scored for that interproximal
contact. No more than 2 points are scored for any contact that deviates from the
ideal. 16
8) “Root angulation is used to assess how well the roots of the teeth have been
positioned relative to one another.” The relative angulation of the roots of the
maxillary and mandibular teeth is assessed using the panoramic radiograph.
Although this is not ideal due to distortion, it gives a reasonably good assessment
of root position and the ABO does acknowledge the distortion that frequently
occurs within panoramic radiographs. Therefore, the Board has recommended the
following: Omit scoring the canine relationship with the adjacent tooth root when
using a final panoramic radiograph.
In general, the roots of the maxillary and mandibular teeth should be
parallel to one another and oriented perpendicular to the occlusal plane. If this
situation exists, then no points are scored. If a root is angled to the mesial or distal
and is close to, but not touching, the adjacent tooth root, then 1 point is scored for
each discrepancy. If the root is angled to the mesial or distal and is contacting the
adjacent tooth root, then 2 points are scored for that tooth. . In previous field tests,
the common mistakes in root angulation occurred in the maxillary lateral incisors,
canines, second premolars, and mandibular first premolars.16
20
Both subjective and objective methods of scoring the dental casts and panoramic
radiographs were used by the ABO Directors during the 1997 and 1998 field tests. Based
upon a comparison of these two methods, a passing score was established. The ABO
established that a case report that scores more than 30 points will generally fail. A case
report that scores less than 20 points will generally pass that portion of the clinical
examination. It is important to note, however, that this score only represents a part of the
overall score for each case report. The quality of the records, the treatment plan, and the
objectives for positioning of the maxilla, mandible, maxillary dentition, mandibular
dentition, and soft tissue facial profile are also carefully scrutinized.15
There are various studies that have shown that the OGS, similar to the DI, can
serve as a reliable index if the measurer has been trained sufficiently in its use. For
example, several studies have shown an error of less than + 5% and correlations of r =.92,
.94, .97, .99, for intrajudge reliability.6,8,14,17 Two studies were conducted to determine,
specifically, the improvement in reliability that can be obtained through training.
Murakami et al. showed that doctors who used the OGS, for the first time, before
receiving training had an intrajudge correlation of r = .33. After a single training session,
the intrajudge correlation increased to r = .55 and after a second training session
improved to .75.18 Lieber et al. showed similar results with doctors receiving training and
obtaining an intrajudge correlation of .77. Verbal discussions with Board members
revealed that intrajudge reliability is roughly r = .85, although the Board has never
published any papers indicating this in writing. The lower intrajudge correlation
compared to the ABO verbally-reported reliability was attributed to the OGS being
21
dependent on landmark identification and measurements that are made landmark-to-
landmark.7
Additional studies have been conducted to determine if resident-treated cases
meet the criteria that the ABO has established for being a passing case. A pilot study
done by the ABO in 2006, showed that 90% of the resident-treated cases sample passed
the clinical examination while 85% of the cases submitted by practicing orthodontists
passed. There was a statistically significant difference between the average scores of the
two groups, but the difference was 1.97 points. When considering that scores less than 30
typically pass the examination, the committee stated that the 1.97 point difference was
irrelevant and that although there was a point difference, the resident-treated cases were
still acceptable as passing, and were considered to be so 90% of the time in the sample.19
Their conclusions were supported by a study by Cook et al. in 2005, who found that there
was no significant difference in the overall OGS score between cases treated by residents
and cases treated by private practitioners. It can be concluded that, in general, the quality
of treatment outcome when measuring with the OGS is essentially the same between
resident-treated cases and private practitioners.20
22
Figure 2.4: Objective Grading System instruction form the Case Report Work File on the
ABO website.12
23
Figure 2.5: Objective Grading System score sheet form the Case Report Work File on the
ABO website.12
24
Correlation between Discrepancy Index and Objective Grading System
Understanding if there is a correlation or not between these two indices could be
very helpful to the practitioner of orthodontics. If a positive correlation were to be found,
and the incremental amount of predictability was known, the practitioner could estimate
the quality of treatment outcomes as measured by the OGS. For example, if it is
determined that a 1-point increase in DI produces a 0.5-point increase in OGS, the
clinician could create an estimated pottreatment OGS score and could use that in
consideration of the treatment objectives and expectations. Of course, this would be
based on the average, and would therefore be subject to individual variation.
Furthermore, it may be something that the ABO could use when assessing the quality of
treatment outcomes. The DI could become a weighted factor in determining whether the
case was of passing quality or not and the OGS score could be used on a sliding-scale
method in relation to the pretreatment DI.
Several recent studies have investigated the possibility of a correlation between
the DI and the OGS. Some of these studies have been carried out at the same institution
with opposing results. Campbell et al studied 382 cases that were treated between 1998
and 2003 and found a positive correlation of r = 0.2 between DI and OGS, specifically in
more complex cases. Although this is a weak correlation, the study concluded that
complex malocclusions were challenging to finish well.14 These findings were supported
by another study by Pulfer et al. Seven hundred and sixteen patients that were treated
between 1998 and 2004 were studied and a weak, positive correlation was found of
r = .17. Conclusions from their study were that DI and OGS were correlated for “the most
severe malocclusions, but only a weak positive association is seen for all patients
25
treated,” and that “DI [is an] important indicator for estimating the difficulty expected in
achieving an optimal result.”8
A third study from the same institution as the previous two studies showed
opposing results. A sample of 455 patients treated between 2004 and 2006 were studied
primarily to determine factors of treatment duration as well as the relationship between
treatment duration and the quality of treatment outcomes. These results showed that, “the
initial DI scores were not significantly related to the final OGS score. Although patients
with DI > 20 required more time to treat, a similar OGS outcome was achieved compared
with less severe cases (DI <20).”10
Similar to these studies with conflicting results, this study will investigate the
correlation between DI and OGS. If a positive correlation is found, the incremental
association will be determined. Additionally, treatment duration and its relation to DI and
OGS will also be investigated.
26
References
1. Riolo ML, Owens J, Dykhouse VJ, Moffitt AH, Grubb JE, Greco PM, English JD, Briss BS, Cangialosi TJ. A change in the certification process by the American Board of Orthodontics. Am J Orthod Dentofacial Orthop 2005;127:278-281. 2. Owens J, Dykhouse VJ, Moffitt AH, Grubb JE, Greco PM, English JD, Briss BS, Jamieson SA, Riolo ML. The new American Board of Orthodontics certification process: Further clarification. Am J Orthod Dentofacial Orthop 2005;128:541-544. 3. Cangialosi TJ, Riolo ML, Owens SE, Dykhouse VJ, Moffitt AH, Grubb JE, Greco PM, English JD, James RD. The American Board of Orthodontics and specialty certification: the first 50 years. Am J Orthod Dentofacial Orthop 2004;126:3-6. 4. Vaden JL, Kokich VG. American Board of Orthodontics: Past, present, and future. Am J Orthod Dentofacial Orthop 2000;117:530-532. 5. Dykhouse VJ, Moffitt AH, Grubb JE, Greco PM, English JD, Briss BS, Jamieson SA, Kastrop MC, Owens J. ABO initial certification examination: Official announcement of criteria. Am J Orthod Dentofacial Orthop 2006;130:662-665. 6. Deguchi T, Honjo T, Fukunaga T, Miyawaki S, Roberts WE, Takano-Yamamoto T. Clinical assessment of orthodontic outcomes with the peer assessment rating, discrepancy index, objective grading system, and comprehensive clinical assessment. Am J Orthod Dentofacial Orthop 2005;127:434-443. 7. Lieber WS, Carlson SK, Baumrind S, Poulton DR. Clinical use of the ABO-Scoring Index: reliability and subtraction frequency. Angle Orthod 2003;73:556-564. 8. Pulfer RM, Drake CT, Maupome G, Eckert GJ, Roberts WE. The association of malocclusion complexity and orthodontic treatment outcomes. Angle Orthod 2009;79:468-472. 9. Campbell CL, Roberts WE, Hartsfield Jr JK, Qi R. Treatment outcomes in a graduate orthodontic clinic for cases defined by the American Board of Orthodontics malocclusion categories. Am J Orthod Dentofacial Orthop 2007;132:822-829. 10. Vu CQ, Roberts WE, Hartsfield Jr JK, Ofner S. Treatment complexity index for assessing the relationship of treatment duration and outcomes in a graduate orthodontics clinic. Am J Orthod Dentofacial Orthop 2008;133:9.e1-9.e13. 11. Cangialosi TJ, Riolo ML, Owens SE, Dykhouse VJ, Moffitt AH, Grubb JE, Greco PM, English JD, James RD. The ABO discrepancy index: a measure of case complexity. Am J Orthod Dentofacial Orthop 2004;125:270-278.
27
12. Case Report Work File.pdf (application/pdf Object). Available at: http://www.americanboardortho.com/professionals/downloads/Case%20Report%20Work%20File.pdf [Accessed July 29, 2009]. 13. Riolo ML, Owens J, Dykhouse VJ, Moffitt AH, Grubb JE, Greco PM, English JD, Briss BS, Cangialosi TJ. ABO resident clinical outcomes study: Case complexity as measured by the discrepancy index. Am J Orthod Dentofacial Orthop 2005;127:161-163. 14. Campbell CL, Roberts WE, Hartsfield Jr JK, Qi R. Treatment outcomes in a graduate orthodontic clinic for cases defined by the American Board of Orthodontics malocclusion categories. Am J Orthod Dentofacial Orthop 2007;132:822-829. 15. Casko JS, Vaden JL, Kokich VG, Damone J, James R, Cangialosi TJ, Riolo ML, Owens J, Bills ED. Objective grading system for dental casts and panoramic radiographs. Am J Orthod Dentofacial Orthop 1998;114:589-599. 16. Grading System Casts-Radiographs.pdf (application/pdf Object). Available at: http://www.americanboardortho.com/professionals/downloads/Grading%20System%20Casts-Radiographs.pdf [Accessed July 29, 2009]. 17. Knierim K, Roberts WE, Hartsfield J. Assessing treatment outcomes for a graduate orthodontics program: Follow-up study for the classes of 2001-2003. Am J Orthod Dentofacial Orthop 2006;130:648.e1-648.e11. 18. Murakami K, Deguchi T, Hashimoto T, Imai M, Miyawaki S, Takano-Yamamoto T. Need for training sessions for orthodontists in the use of the American Board of Orthodontics objective grading system. Am J Orthod Dentofacial Orthop 2007;132:427.e1-427.e6. 19. Dykhouse VJ, Moffitt AH, Grubb JE, Greco PM, English JD, Briss BS, Jamieson SA, Kastrop MC, Owens J. A report of the ABO Resident Clinical Outcome Study (the pilot study). Am J Orthod Dentofacial Orthop 2006;130:656-661. 20. Cook DR, Harris EF, Vaden JL. Comparison of university and private-practice orthodontic treatment outcomes with the American Board of Orthodontics objective grading system. Am J Orthod Dentofacial Orthop 2005;127:707-712.
28
CHAPTER 3: JOURNAL ARTICLE
Abstract
Purpose: The purpose of this study was to investigate the correlation between the
American Board of Orthodontics (ABO) pretreatment dental cast Discrepancy Index (DI)
and the posttreatment Objective Grading System (OGS) scores. The relationships among
overall scores and individual components were investigated as well as the correlations
with treatment times.
Materials and Methods: The ABO’s DI was used to measure 165 dental cast cases that
were finished in 2007-2008 at the Saint Louis University Center for Advanced Education
Orthodontic clinic. No cephalograms or panoramic radiographs were measured. The
cases were divided into three pretreatment groups of low, medium and high DI.
Furthermore, the cases were additionally grouped into three posttreatment groups of
“Passing,” “Undetermined,” and “Failing.” ANOVA, Pearson correlation coefficients and
multiple regression analyses were performed.
Results: The low DI group and the high DI group had a significant difference of 4.2
points in the overall posttreatment OGS score. Three posttreatment components of the
OGS, buccolingual inclination, occlusal contacts and occlusal relationship were the
highest contributors to this difference in posttreatment scores. The three posttreatment
OGS groups showed no differences in their pretreatment DI scores. However,
pretreatment lingual posterior crossbite was a significant 0.54 points lower in the
“Undetermined” group than in the “Failing” group. Treatment time was 4.56 months
longer for the high DI group when compared to the low DI group. No difference was
29
found in treatment time among the three OGS groups. No correlations were of reportable
strengths.
Conclusions: Low complexity cases may have a better treatment outcome than high
complexity cases as measured by the ABO’s OGS. Those components with the greatest
contribution to the poorer outcomes are buccolingual inclination, occlusal contacts and
occlusal relationship. Low complexity cases may finish in less time than high complexity
cases.
30
Introduction
The American Board of Orthodontics (ABO) has had as part of its objectives to
“elevate the standards of the practice of orthodontia; to familiarize the public with its
aims and ideals; to protect the public against irresponsible and unqualified practitioners”
since its inception in 1929. A certifying process was established by the ABO in order to
help achieve these objectives. Over time, the ABO has made various changes to the
examination process in an attempt to create a fairer and more objective system for
assessing the treatment rendered on the board cases being presented.1,2 A key initiator of
the establishment of the ABO, Albert Ketcham, wrote a letter that set the stage for the
continual changes required to maintain an effective examination. His letter stated, “We
must adapt our examination to the applicant, try to discover if he is safe, whether he has
the technical skill and scientific knowledge. . . A complete and perfect plan for our
examinations cannot be worked out except through long experience in giving
examinations to men of varied training, caliber and experience.”3 Dr. Ketcham clearly
understood the importance of continually reassessing the examination process to improve
upon it.
As early as 1940, certification requirements included a thesis, five case reports
and a set of casts with appliances on them. Then in 1967, case categories were introduced
that specified the type of cases that were required to be presented and the thesis
requirement was replaced by a written examination in 1978. Over the following 20 years,
the criteria for the cases have varied as the ABO has tried to adapt to their examinees.
Two systems, in particular, have developed from these changes and are currently being
used exclusively by the ABO to assess the pretreatment complexity and the posttreatment
31
results of the clinical examination board cases. These two systems, the Discrepancy Index
(DI) and the Objective Grading System (OGS) have been used by the ABO since 1998.3,4
The DI is currently being used by the ABO to determine whether pretreatment
cases are complex enough to be considered for the certification process. The OGS is
utilized in determining whether cases presented by orthodontists during the certification
process have posttreatment results that are considered to be passing or failing. The DI is
used to determine whether pretreatment cases are complex enough to be considered for
the certification process, however it is not referenced when scoring the posttreatment
results.5 Thus, the complexity of the case pretreatment is not objectively taken into
consideration when scoring the posttreatment results. This study is important to
determine whether the pretreatment Discrepancy Index should be considered when
scoring the posttreatment results. In other words, if a case has a higher pretreatment case
complexity, it may be expected to have a poorer quality posttreatment outcome because
of the complexities inherent to the case. There have been various studies performed
recently that center around the ABO certification process, but none that have taken this
approach to investigating the factor of the Discrepancy Index in scoring the posttreatment
results directly with the OGS.6-10 While there have been some general trends related to
DI and the OGS that have been discovered in previous studies, these results have been
conflicting and the nature of the relationship, if any, has not been described in detail. It
would also be helpful to practitioners if they knew of a correlation so that they could
assess an expected posttreatment outcome based upon the pretreatment case complexity.
The purpose of this study is to determine if there is a relationship between the
pretreatment dental cast Discrepancy Index scores and the posttreatment dental cast
32
objective grading system scores used in the certification process by the ABO. The
question to be answered is: Does a higher pretreatment Discrepancy Index result in a
higher posttreatment ABO objective grading system score? Length of treatment will also
be measured for all cases to determine if there is a significant difference in length of
treatment times among various groups of case complexity as well as treatment outcomes.
Materials and Methods
The principal investigator was initially trained in the ABO Discrepancy Index
(DI) and Objective Grading System (OGS) using the ABO board preparation CD ROM
from October 2000 as well as the online tutorial using the ABO gauge (Fig. 2.3).11 To
further train and calibrate the principal investigator, 10 cases that were started and
finished at Saint Louis University’s Center for Advanced Dental Education were selected
and graded by a past ABO president who is currently a board examiner. Only those
measurements made from dental casts were used for the Discrepancy Index and the
Objective Grading System. All cephalometric and panoramic radiograph components
were excluded from the measurements for this study. The principal investigator blindly
graded the same 10 cases and the scores were reviewed and compared with the scores of
the board examiner and a tutorial session was provided to discuss the reason for the
discrepancies. This process was repeated for any areas of discrepancy greater than 2
points until the principal investigator’s scores were within 2 points of the board
examiners, an agreement on the reasons for the deductions was achieved and calibration
confirmed.
33
It was determined by statistical power analysis that it would be necessary to have
three groups of 55 subjects in each group of low, medium and high case complexity as
measured by the Discrepancy Index to achieve a power of 0.82. The sample groups were
taken from sequential cases that were completed at the Saint Louis University graduate
orthodontic clinic from 2007-2008. Block randomization entry was used to fill the quota
of 55 cases for each group from sequential finishes based on pretreatment dental casts
that met the inclusion and exclusion criteria that were predetermined. Any cases requiring
jaw surgery were excluded as well as any models that had any amount of damage that
would hinder accurate measurements. Early debonds as indicated in the patients’ charts,
and cases that were treated with Phase 1 or transferred more than once were also
excluded. Cases that had any deciduous teeth present or missing permanent teeth on the
dental casts were excluded to avoid confusion of the amount of crowding or spacing or
possible missing teeth, which would affect the Discrepancy Index score.
Once all inclusion and exclusion were met, charts were reviewed and treatment
duration in months was recorded. There was no consideration of inclusion or exclusion
based on the posttreatment records and therefore cases were not subject to selection bias.
The ABO measuring gauge (Fig. 2.3) was used to measure the pretreatment
models for all 165 cases with the ABO Discrepancy Index instructions (Fig. 2.1) and
form (Fig. 2.2). Posttreatment models for all 165 cases were then measured with the ABO
measuring gauge using the ABO Objective Grading System instructions (Fig. 2.4) and
form (Fig. 2.5). All measurements were input into Excel and the 165 cases were sorted
into three groups based on the Discrepancy Index score.
34
The low Discrepancy Index group consisted of cases that scored <7, the medium
Discrepancy Index group consisted of cases that scored 8-16, and the high Discrepancy
Index group consisted of cases that scored >17. These groupings were determined based
on the ABO’s classification of case difficulty. Currently, the ABO requires 3 cases with a
Discrepancy Index of >10 and 3 cases with a Discrepancy Index of >20. Because this
study did not include radiographic components in the Discrepancy Index, the groups were
adjusted down from <10, 10-19 and >20 based on two recent studies that showed that the
radiographic components of the Discrepancy Index contributed an average of 4.7-5.4
points.8,10
Additionally, the cases were grouped together based on their posttreatment
Objective Grading System score into three groups of “Passing,” “Undetermined,” and
“Failing.” These grouping were based on the ABO’s experience that cases with a score
less than 20 generally pass and cases with scores greater than 30 generally fail. The
undetermined scores of 20-30 are scrutinized further and it is later determined by an
additional board examiner based on things such as the quality of the records and the
treatment plan, the positions of the maxilla, mandible and the dentition, and the facial
profile.12 It must be noted that this study did not include the parameter of root angulation
for the Objective Grading System. Root angulation has been shown to contribute an
additional 2.0-3.5 points, on average, to each case.6,10,13 Therefore, the statistical
analyses were broken down according to the following OGS groupings: “Passing” score
of <17 points, “Undetermined” score of 17-27, “Failing” score of >27.
For intraexaminer reliability of the principal investigator, 18 cases were
remeasured and an intraclass correlation coefficient test was performed as a replication
35
error procedure. The intraclass correlation coefficient for Discrepancy Index and
Objective Grading System measurements were 0.98 and 0.91, respectively.
The data was analyzed using ANOVA, Pearson correlation coefficient and
multiple regression tests with SPSS software. The level of significance was
predetermined at the level of p<.05.
Results
A) Discrepancy Index
The 165 cases that were measured were grouped into three groups as low
Discrepancy Index (DI <7), medium Discrepancy Index (DI 8-16) and high Discrepancy
Index (DI >17). These groups were then evaluated for descriptive characteristics and the
three groups were compared using statistical analyses of ANOVA.
The low Discrepancy Index group had a mean DI score of 5.5 and a mean OGS
score of 22.5. The medium Discrepancy Index group had a mean DI score of 12.4 and a
mean OGS score of 25.1. The high Discrepancy Index group had a mean DI score of 21.5
and a mean OGS score of 26.7.
All three groups were shown to be statistically different in their overall DI score
as well as some individual components. Overjet, crowding and occlusion were different
among all three groups. Overbite, lateral open bite and buccal posterior crossbite were
different between the low and high DI groups. Anterior open bite and lingual posterior
crossbite were significantly higher in the high group when compared to both the low and
medium group. The group of components in the “other” category of DI showed no
difference between the three groups (Table 3.1, Appendix). These differences are to be
36
expected, but are important in showing that the three DI groups are in fact different
overall as well as for individual components. This is most important when considering
the results of the analyses of the OGS components between the three DI groups.
The ANOVA showed that there was no significant difference in the posttreatment
OGS between the low Discrepancy Index group and the medium Discrepancy Index
group or between the medium Discrepancy Index group and the high Discrepancy Index
group. However, there was a significant difference of 4.2 points in the posttreatment OGS
between the low Discrepancy Index group and the high Discrepancy Index group at the
level of p< 0.03.
When the 7 individual factors of the posttreatment OGS score were analyzed, 3
components were found to be significantly different between the low Discrepancy Index
group and the high Discrepancy Index group. Buccolingual inclination was significantly
higher for the high Discrepancy Index group with a mean difference of 1.8 points
(p=0.003). Occlusal contacts were also significantly higher for the high Discrepancy
Index group with a mean difference of 1.3 points (p=0.008). Furthermore, occlusal
relationships were significantly higher for the high Discrepancy Index group with a mean
difference of 1.5 points (p=0.004) (Table 3.2, Appendix).
B) Objective Grading System
The 165 cases that were measured were also grouped into the following three
Objective Grading System groupings: “Passing” score of <17 points, “Undetermined”
score of 17-27, “Failing” score of >27. These groups were then evaluated for descriptive
characteristics and the three groups compared using statistical analyses of ANOVA.
37
The “Passing” group had a mean DI score of 10.70 and a mean OGS score of
12.10. The “Undetermined” group had a mean DI score of 13.11 and a mean OGS score
of 21.79. The “Failing” group had a mean DI score of 13.95 and a mean OGS score of
34.29.
There was no significant difference between the three OGS groups in their overall
DI score, but there was for one of the DI components. Lingual posterior crossbite showed
a statistically significant difference of 0.54 points between the “Undetermined” and
“Failing” OGS groups (Table 3.3, Appendix).
The ANOVA showed that there were significant differences in the OGS scores
between the three OGS groups. These differences were found between all three groups
for the overall OGS score, alignment, marginal ridges, buccolingual inclination and
occlusal contacts. Overjet was shown to be significantly different between “Failing” and
both “Passing” and “Undetermined,” but not between “Passing” and “Undetermined.”
Occlusal relationship was found to be significant between “Passing” and “Failing,” and
the OGS category of interproximal contacts showed no difference between any of the
groups (Table 3.4, Appendix). As with the individual components and the overall DI
scores and the DI groups, these differences are to be expected and are important in
showing that the three OGS groups are in fact different overall as well as for individual
components. This is important when comparing the DI components between the three
OGS groups.
To test for the strength of correlation between individual components of the
pretreatment DI and the posttreatment OGS, Pearson correlation coefficient tests and
multiple regression analyses were conducted. Although there were a few components that
38
were statistically significant, the strength of the relationship was so low that it does not
warrant reporting. For instance, the strongest relationship was r=0.27, thus there were no
relationships to show correlation or predictive qualities of any of the individual
components.
C) Treatment time
The low Discrepancy Index group had a mean treatment time of 19.6 months. The
medium Discrepancy Index group and high Discrepancy Index group had mean treatment
times of 22.3 months and 24.2 months, respectively.
The ANOVA did show a significant difference of 4.56 months longer treatment
time in the high Discrepancy Index group when compared to the low Discrepancy Index
group (p = 0.001). There was no significant difference between the medium Discrepancy
Index group and either of the other two DI groups (Table 3.5, Appendix).
The three OGS groups were also compared using ANOVA. The “Passing” group
had a mean treatment time of 21.15, the “Undetermined” group had a mean treatment
time of 22.60 and the “Failing” OGS group had a mean treatment time of 21.45.
However, there were no significant differences between any of the OGS groups for
treatment time (Table 3.5, Appendix).
Pearson correlation coefficient and multiple regression analyses were performed
for the overall Discrepancy Index scores as well as the individual components of the
pretreatment Discrepancy Index to determine if there was any significant correlation
between the overall DI score and the length of treatment as well as any single component
of pretreatment complexity and length of treatment. The overall DI score did show a
39
significant correlation at the p=0.01 level. However, the strength of the correlation was
only r=0.29 which is not strong enough to justify reporting. Furthermore, no individual
component showed a significant difference at a correlation worth reporting.
Additionally, the Pearson correlation coefficient and multiple regression analyses
were performed to determine if any relationship exists between the treatment duration
and the posttreatment Objective Grading System scores. Similar to the pretreatment DI
scores, there were no reportable significant correlations between the posttreatment OGS
and treatment time.
Discussion
The purpose of this study was to determine if there is a relationship between the
pretreatment dental cast Discrepancy Index scores and the posttreatment dental cast
Objective Grading System scores used in the certification process by the American Board
of Orthodontics. The question to be answered was: Does a higher pretreatment
Discrepancy Index result in a higher posttreatment ABO Objective Grading System
score? In other words, does a more complex case pretreatment result in a poorer
treatment outcome as determined by the ABO Objective Grading System?
The statistical analyses showed that there was a statistical difference in the
posttreatment Objective Grading System scores between the low Discrepancy Index
group and the high Discrepancy Index group. The mean difference was 4.2 points.
Individual posttreatment Objective Grading System components that were statistically
significant between the groups were buccolingual inclination, occlusal contacts and
occlusal relationships. It is interesting to note that these three criteria only involve the
40
posterior teeth and buccal occlusion. Previous studies have shown similar findings that
show that occlusal contacts and buccolinugal inclination were the two most common
problems on dental cast evaluations using the OGS.14, 15 This may be due to records being
taken the day of appliance removal without time to settle. A study by Nett et al.,16
showed significant improvement in occlusal contacts over time after debond.
According to the OGS groupings in this study, most cases that score >27 on the
posttreatment OGS would likely fail the boards.12 Based on this point allocation, with 27
being the highest number of points that one would want to receive, the mean difference
between the low and high DI groups of 4.2 points represents nearly 16% of the total
allowable passing score. It is important, however, to understand that the low Discrepancy
Index group would not qualify for the ABO examination because the cases must have a
DI score of at least 10.1,5 The two groups that do represent potentially qualifying
pretreatment DI board cases, the medium and high DI groups, showed no significant
difference. This supports the ABO’s rationale for selecting the two case categories of
< 10 and < 20 and expecting both groups to score similarly on the Objective Grading
System without having to take into consideration the pretreatment DI score.
Overall, 12% of the total sample was in the “Passing” group, 55% was in the
“Undetermined” group and 33% was in the “Failing” group. It is important to note
however, that these cases were selected from consecutively finished cases without any
consideration for the posttreatment results. This is different than those practitioners who
would be hand picking based on the results to present to the board, thus introducing a
selection bias. A study done by Cook17 analyzed 115 sequentially finished cases from
nine board certified orthodontists. Cook’s study had similar results of 18% of the cases
41
passed, 47% were undetermined and 35% failed. Similarly, Deguchi et al.6 found that a
consecutively finished sample from Indiana University had 14% in the “Passing” group,
33% in the “Undetermined” group and 53% in the “Failing” group. Additionally,
Deguchi et al. found that a random sample from Okayama University had 14% in the
“Passing” group, 31% in the “Undetermined” group and 55% in the “Failing” group.
To analyze whether there was a difference in the number of “Passing” cases,
“Undetermined” cases and “Failing” cases between the three DI groups, an ANOVA was
performed on the frequencies of these occurrences between the three groups. As shown in
Table 3.6, there was no significant difference in the number of cases that were considered
“Passing,” “Undetermined,” or “Failing,” among the three DI groups.
Treatment time was shown to be significantly higher for the high DI group than
the low DI group, which signifies that a complex case with a DI of >17 will take an
average of 4.6 months longer than a case with a DI of <7. However, there were no
individual factors that had a correlation strong enough to be of “predictive” value for
treatment time (Table 3.5, Appendix).
One of the objectives of this study was to determine if there are any correlations
among any of the factors involved that may provide some “predictive” value for
practitioners. For example, a study done by Campbell et al.18 stated that for every 1 point
increase in the DI, the OGS increased by 0.23 + 0.06 points. As indicated in the results,
the current study showed no correlations or multiple regressions that were statistically
significant with a correlation strength that is worth reporting. The greatest strength of
correlation for any of the relationships was r=0.29. With r2=0.08, that only explains 8%
of the variability, which provides no “predictive” value.
42
It is important to note that the components are different for each scoring system
and that they don’t necessarily measure the same things. Consequently, not all of the DI
components may be measured with the OGS, so objectively measuring the improvement
or outcome of a given case becomes more difficult. For example, overbite, is not a
component of the OGS, even though it is measured three times with the DI. There were
only a few significant differences that are worth noting when analyzing these measuring
systems. The posttreatment OGS components of buccolinugal inclination, occlusal
contacts, and occlusal relationship contributed most of points to the 4.2 point difference
of the overall OGS scores among the three DI groups (Table 3.2, Appendix). When
comparing the three OGS groups, the only pretreatment DI component that was
significantly different was lingual posterior crossbite with a mean difference of 0.54
points between the “Undetermined” and “Failing” groups.
Overall, there were no correlations with reportable strengths, although there were
some statistically significant positive correlations. This could be due to the multifactorial
contributions to reaching a posttreatment outcome. Many factors such as patient
cooperation with auxiliaries, appliance breakage and inherent limitations of the
pretreatment malocclusion, may have an effect on the correlations. This may help explain
the difference in treatment outcomes among the three pretreatment DI groups. Two out of
the three main contributing components of the OGS, occlusal contacts and occlusal
relationship, often depend on the patient for correction. For example, to correct for lack
of occlusal contacts and poor occlusal relationships (Class II or Class III) it is usually
required that patients wear elastics. Due to the fact that the high complexity cases take an
additional 4.56 months to finish, patients may begin to burn out and decrease compliance.
43
Additionally, high DI cases had a pretreatment occlusion (Class II or Class III) that was
3.86 points higher which would require more correction of the anteroposterior buccal
occlusion.
Conclusions
Based on this study, it can not be concluded that certain specific pretreatment
components will have an affect on the posttreatment outcome. However, it can be
concluded that cases with a pretreatment dental cast DI score of < 7 will have a
posttreatment dental cast OGS score 4.2 points lower than cases with a pretreatment
dental cast DI of > 17. It can also be concluded that buccolingual inclination, occlusal
contacts and occlusal relationships have the greatest contribution to this 4.2 points
difference.
In addition to a difference in treatment outcomes as measured by the OGS, cases
that have a pretreatment dental cast DI score of < 7 will finish 4.56 months sooner than a
case with a pretreatment dental cast DI score of >17.
44
References
1. Riolo ML, Owens J, Dykhouse VJ, Moffitt AH, Grubb JE, Greco PM, English JD, Briss BS, Cangialosi TJ. A change in the certification process by the American Board of Orthodontics. Am J Orthod Dentofacial Orthop 2005;127:278-281. 1. Owens J, Dykhouse VJ, Moffitt AH, Grubb JE, Greco PM, English JD, Briss BS, Jamieson SA, Riolo ML. The new American Board of Orthodontics certification process: Further clarification. Am J Orthod Dentofacial Orthop 2005;128:541-544. 3. Cangialosi TJ, Riolo ML, Owens SE, Dykhouse VJ, Moffitt AH, Grubb JE, Greco PM, English JD, James RD. The American board of orthodontics and specialty certification: the first 50 years. Am J Orthod Dentofacial Orthop 2004;126:3-6. 4. Vaden JL, Kokich VG. American Board of Orthodontics: Past, present, and future. Am J Orthod Dentofacial Orthop 2000;117:530-532. 5. Dykhouse VJ, Moffitt AH, Grubb JE, Greco PM, English JD, Briss BS, Jamieson SA, Kastrop MC, Owens J. ABO initial certification examination: Official announcement of criteria. Am J Orthod Dentofacial Orthop 2006;130:662-665. 6. Deguchi T, Honjo T, Fukunaga T, Miyawaki S, Roberts WE, Takano-Yamamoto T. Clinical assessment of orthodontic outcomes with the peer assessment rating, discrepancy index, objective grading system, and comprehensive clinical assessment. Am J Orthod Dentofacial Orthop 2005;127:434-443. 7. Lieber WS, Carlson SK, Baumrind S, Poulton DR. Clinical use of the ABO-Scoring Index: reliability and subtraction frequency. Angle Orthod 2003;73:556-564. 8. Pulfer RM, Drake CT, Maupome G, Eckert GJ, Roberts WE. The association of malocclusion complexity and orthodontic treatment outcomes. Angle Orthod 2009;79:468-472. 9. Campbell CL, Roberts WE, Hartsfield Jr JK, Qi R. Treatment outcomes in a graduate orthodontic clinic for cases defined by the American Board of Orthodontics malocclusion categories. Am J Orthod Dentofacial Orthop 2007;132:822-829. 10. Vu CQ, Roberts WE, Hartsfield Jr JK, Ofner S. Treatment complexity index for assessing the relationship of treatment duration and outcomes in a graduate orthodontics clinic. Am J Orthod Dentofacial Orthop 2008;133:9.e1-9.e13. 11. Grading System Casts-Radiographs.pdf (application/pdf Object). Available at: http://www.americanboardortho.com/professionals/downloads/Grading%20System%20Casts-Radiographs.pdf [Accessed July 29, 2009].
45
12. Casko JS, Vaden JL, Kokich VG, Damone J, James R, Cangialosi TJ, Riolo ML, Owens J, Bills ED. Objective grading system for dental casts and panoramic radiographs. Am J Orthod Dentofacial Orthop 1998;114:589-599. 13. Yang-Powers LC, Sadowsky C, Rosenstein S, BeGole EA. Treatment outcome in a graduate orthodontic clinic using the American Board of Orthodontics grading system. Am J Orthod Dentofacial Orthop 2002;122:451-455. 14. Knierim K, Roberts WE, Hartsfield J. Assessing treatment outcomes for a graduate orthodontics program: Follow-up study for the classes of 2001-2003. Am J Orthod Dentofacial Orthop 2006;130:648.e1-648.e11. 15. Pinskaya YB, Hsieh T, Roberts WE, Hartsfield J. Comprehensive clinical evaluation as an outcome assessment for a graduate orthodontics program. Am J Orthod Dentofacial Orthop 2004;126:533-543. 16. Nett BC, Huang GJ. Long-term posttreatment changes measured by the American Board of Orthodontics objective grading system. Am J Orthod Dentofacial Orthop 2005;127:444-450. 17. Cook MK. Evaluation of Board-certified orthodontist’s sequential finished cases with the ABO objective grading system [thesis]. Saint Louis: Saint Louis University; 2003. 18. Campbell CL, Roberts WE, Hartsfield Jr JK, Qi R. Treatment outcomes in a graduate orthodontic clinic for cases defined by the American Board of Orthodontics malocclusion categories. Am J Orthod Dentofacial Orthop 2007;132:822-829.
46
APPENDIX
Table 3.1. Discrepancy Index Components by Discrepancy Index Group
Mean Median SD Min. Max. Sig.
Overjet Low DI (<7 ) 1.35*† 2.00 1.14 0.00 4.00
Med. DI (8-16 ) 2.56*◊ 2.00 1.41 0.00 7.00
High DI (>17 ) 4.18†◊ 4.00 2.61 0.00 13.00
p<.01*
p=.00†
p=.00◊
Overbite Low DI (<7 ) 0.98† 0.00 1.06 0.00 3.00
Med. DI (8-16 ) 1.64 2.00 1.58 0.00 5.00
High DI (>17 ) 1.93† 2.00 2.12 0.00 5.00
p<.01†
Low DI (<7 ) 0.20† 0.00 0.68 0.00 4.00 Anterior open bite Med. DI (8-16 ) 0.71◊ 0.00 1.66 0.00 9.00
High DI (>17 ) 4.04†◊ 0.00 6.98 0.00 28.00
p=.00†
p=.00◊
Low DI (<7 ) 0.00† 0.00 0.00 0.00 0.00 Lateral open bite Med. DI (8-16 ) 0.22 0.00 0.74 0.00 4.00
High DI (>17 ) 0.75† 0.00 2.24 0.00 12.00
p<.02†
Crowding Low DI (<7 ) 1.35*† 1.00 1.32 0.00 4.00
Med. DI (8-16 ) 2.96*◊ 2.00 2.33 0.00 7.00
High DI (>17 ) 4.02†◊ 4.00 2.70 0.00 7.00
p=.00*
p=.00†
p<.04◊
Occlusion Low DI (<7 ) 0.36*† 0.00 0.95 0.00 4.00
Med. DI (8-16 ) 2.51*◊ 2.00 2.53 0.00 8.00
High DI (>17 ) 4.22†◊ 4.00 3.02 0.00 10.00
p<.01*
p=.00†
p=.00◊
Low DI (<7 ) 0.05† 0.00 0.23 0.00 1.00
Med. DI (8-16 ) 0.42◊ 0.00 1.17 0.00 6.00
Lingual posterior crossbite
High DI (>17 ) 1.02†◊ 0.00 1.68 0.00 6.00
p=.00†
p<.03◊
Low DI (<7 ) 0.04† 0.00 0.27 0.00 2.00
Med. DI (8-16 ) 0.18 0.00 0.70 0.00 4.00
Buccal posterior crossbite
High DI (>17 ) 0.44† 0.00 1.20 0.00 6.00
p<.04†
Other Low DI (<7 ) 1.13 0.00 1.84 0.00 6.00
Med. DI (8-16 ) 1.18 0.00 2.20 0.00 10.00
High DI (>17 ) 0.87 0.00 1.26 0.00 4.00
Total DI Low DI (<7 ) 5.45*† 6.00 2.01 1.00 8.00
Med. DI (8-16 ) 12.38*◊ 12.00 2.31 9.00 16.00
High DI (>17 ) 21.45†◊ 20.00 5.04 17.00 43.00
p=.00*
p=.00†
p=.00◊
* Statistically significant difference at p<.05 Low DI vs. Med. DI † Statistically significant difference at p<.05 Low DI vs. High DI ◊ Statistically significant difference at p<.05 Med. DI vs. High DI
47
Table 3.2. Objective Grading System Components by Discrepancy Index Group
Mean Median SD Min. Max. Sig.
Alignment Low DI (<7 ) 8.49 8.00 3.56 0.00 18.00
Med. DI (8-16 ) 8.16 7.00 3.79 1.00 19.00
High DI (>17 ) 8.13 7.00 3.89 3.00 19.00
Low DI (<7 ) 4.41 4.00 2.47 0.00 11.00 Marginal ridges
Med. DI (8-16 ) 4.93 4.00 2.62 0.00 12.00
High DI (>17 ) 4.65 4.00 3.07 0.00 17.00
Low DI (<7 ) 4.42† 4.00 2.29 0.00 9.00
Med. DI (8-16 ) 5.58 5.00 2.88 1.00 14.00 Buccolingual inclination
High DI (>17 ) 6.22† 6.00 2.94 0.00 14.00
p<.01†
Overjet Low DI (<7 ) 2.24 2.00 2.34 0.00 10.00
Med. DI (8-16 ) 2.25 1.00 2.81 0.00 14.00
High DI (>17 ) 1.93 1.00 2.06 0.00 10.00
Low DI (<7 ) 1.36† 1.00 1.89 0.00 7.00 Occlusal contacts
Med. DI (8-16 ) 2.04 2.00 1.93 0.00 8.00
High DI (>17 ) 2.65† 2.00 2.56 0.00 11.00
p<.01†
Low DI (<7 ) 1.29† 1.00 1.90 0.00 11.00 Occlusal relationship
Med. DI (8-16 ) 1.80 1.00 2.14 0.00 8.00
High DI (>17 ) 2.76† 2.00 2.86 0.00 12.00
p<.01†
Low DI (<7 ) 0.33 0.00 0.82 0.00 4.00 Interproximal contacts
Med. DI (8-16 ) 0.29 0.00 0.63 0.00 2.00
High DI (>17 ) 0.40 0.00 1.16 0.00 7.00
Total OGS Low DI (<7 ) 22.55† 23.00 7.41 7.00 40.00 Med. DI (8-16 ) 25.05 25.00 8.50 10.00 45.00 High DI (>17 ) 26.75† 24.00 9.12 9.00 48.00
p<.03†
† Statistically significant difference at p<.05 Low DI vs. High DI
48
Table 3.3. Discrepancy Index Components by Objective Grading System Group
Mean Median SD Min. Max. Sig.
Overjet "Passing" OGS (<17) 2.25 2.00 1.48 0.00 5.00
"Undetermined" OGS (17-27) 2.74 2.00 2.27 0.00 13.00
"Failing" OGS (>27) 2.78 3.00 2.21 0.00 10.00
Overbite "Passing" OGS (<17) 1.80 2.00 1.70 0.00 5.00
"Undetermined" OGS (17-27) 1.56 2.00 1.70 0.00 5.00
"Failing" OGS (>27) 1.35 0.00 1.67 0.00 5.00
"Passing" OGS (<17) 0.20 0.00 0.62 0.00 2.00 Anterior open bite "Undetermined" OGS (17-27) 2.08 0.00 5.42 0.00 28.00
"Failing" OGS (>27) 1.47 0.00 3.33 0.00 17.00
"Passing" OGS (<17) 0.00 0.00 0.00 0.00 0.00 Lateral open bite "Undetermined" OGS (17-27) 0.16 0.00 0.81 0.00 6.00
"Failing" OGS (>27) 0.71 0.00 2.13 0.00 12.00
Crowding "Passing" OGS (<17) 2.35 1.50 2.13 0.00 7.00
"Undetermined" OGS (17-27) 2.71 2.00 2.56 0.00 7.00
"Failing" OGS (>27) 3.04 2.00 2.37 0.00 7.00
Occlusion "Passing" OGS (<17) 2.00 0.00 2.90 0.00 8.00
"Undetermined" OGS (17-27) 2.27 0.00 2.83 0.00 8.00
"Failing" OGS (>27) 2.65 2.00 2.78 0.00 10.00
"Passing" OGS (<17) 0.20 0.00 0.70 0.00 3.00
"Undetermined" OGS (17-27) 0.33* 0.00 0.94 0.00 6.00
Lingual posterior crossbite
"Failing" OGS (>27) 0.87* 0.00 1.70 0.00 6.00
p<.04
"Passing" OGS (<17) 0.50 0.00 1.10 0.00 4.00
"Undetermined" OGS (17-27) 0.22 0.00 0.92 0.00 6.00
Buccal posterior crossbite
"Failing" OGS (>27) 0.11 0.00 0.46 0.00 2.00
Other "Passing" OGS (<17) 1.40 0.00 2.60 0.00 10.00
"Undetermined" OGS (17-27) 1.04 0.00 1.68 0.00 6.00
"Failing" OGS (>27) 0.96 0.00 1.67 0.00 6.00
Total DI "Passing" OGS (<17) 10.70 10.00 5.68 3.00 21.00
"Undetermined" OGS (17-27) 13.11 12.00 7.61 1.00 43.00
"Failing" OGS (>27) 13.95 13.00 7.50 1.00 35.00
*Statistically significant difference at p<.04
49
Table 3.4. Objective Grading System Components by Objective Grading System Group
Mean Median SD Min. Max. Sig.
Alignment "Pass" OGS (<17) 4.45*† 4.00 2.48 0.00 10.00
"Undetermined" OGS (17-27) 7.62*◊ 8.00 2.75 1.00 13.00
"Fail" OGS (>27) 10.7†◊ 10.00 3.95 5.00 19.00
p=.00*
p=.00†
p=.00◊
"Pass" OGS (<17) 2.35*† 2.50 1.27 0.00 4.00 Marginal
ridges "Undetermined" OGS (17-27) 4.09*◊ 4.00 1.96 0.00 10.00
"Fail" OGS (>27) 6.45†◊ 6.00 3.13 0.00 17.00
p=.01*
p=.00†
p=.00◊
"Pass" OGS (<17) 2.85*† 3.00 1.57 0.00 6.00 "Undetermined" OGS (17-27) 4.92*◊ 4.00 2.37 0.00 11.00
Bucco-lingual inclination
"Fail" OGS (>27) 7.13†◊ 7.00 2.82 1.00 14.00
p<.01*
p=.00†
p=.00◊
Overjet "Pass" OGS (<17) 0.85† 0.50 1.14 0.00 4.00
"Undetermined" OGS (17-27) 1.63◊ 1.00 1.81 0.00 10.00
"Fail" OGS (>27) 3.44†◊ 3.00 3.02 0.00 14.00
p=.00†
p=.00◊
"Pass" OGS (<17) 0.20*† 0.00 0.52 0.00 2.00 Occlusal
contacts "Undetermined" OGS (17-27) 1.48*◊ 1.00 1.52 0.00 6.00
"Fail" OGS (>27) 3.56†◊ 4.00 2.59 0.00 11.00
p=.02*
p=.00†
p=.00◊
"Pass" OGS (<17) 1.25 1.00 2.00 0.00 8.00 Occlusal
relationship "Undetermined" OGS (17-27) 1.67◊ 1.00 1.97 0.00 11.00
"Fail" OGS (>27) 2.67◊ 2.00 2.98 0.00 12.00
p<.05◊
"Pass" OGS (<17) 0.15 0.00 0.37 0.00 1.00 Interproximal
contacts "Undetermined" OGS (17-27) 0.38 0.00 0.86 0.00 4.00
"Fail" OGS (>27) 0.35 0.00 1.08 0.00 7.00
Total OGS "Pass" OGS (<17) 12.10*† 13.00 2.17 7.00 16.00
"Undetermined" OGS (17-27) 21.79*◊ 22.00 3.25 17.00 29.00
"Fail" OGS (>27) 34.29†◊ 32.00 5.82 28.00 48.00
p=.00*
p=.00†
p=.00◊
* Statistically significant difference at p<.05 “Pass” OGS vs. “Undetermined” OGS † Statistically significant difference at p<.05 “Pass” OGS vs. “Fail” OGS ◊ Statistically significant difference at p<.05 “Undetermined” OGS vs. “Fail” OGS
50
Table 3.5. Treatment Times by Discrepancy Index and Objective Grading System Groups
Treatment time (in months)
n Mean Median SD Min. Max. Sig.
Low DI (<7) 55 19.62* 19.00 6.24 8.00 45.00
Med. DI (8-16) 55 22.33 23.00 5.61 9.00 39.00
High DI (>17) 55 24.18* 24.00 7.14 11.00 45.00
p<.01
"Passing" OGS (<17) 20 21.15 21.00 5.83 12.00 39.00
"Undetermined" OGS (17-27) 90 22.60 23.00 6.83 8.00 45.00
"Failing" OGS (>27) 55 21.45 22.00 6.49 11.00 43.00
*Statistically significant difference at p<.01
Table 3.6. Objective Grading System Group Frequency by Discrepancy Index Group
Frequency of occurrence (% of total)
"Passing" (OGS <17
points)
"Undetermined" (OGS 17-27
points)
"Failing" (OGS >27 points)
Low DI group (<7 points) 16% 55% 29%
Med. DI group (8-16 points) 14% 53% 33%
High DI group (>17 points) 6% 56% 38%
Total sample 12% 55% 33%
51
VITA AUCTORIS
David Cameron was born on November 29, 1977 in Las Vegas, NV. He attended
Brigham Young University in Provo, UT for his undergraduate studies where he studied
visual arts. He later attended dental school at University of Nevada at Las Vegas in his
hometown and earned his DMD degree in 2007. During his final year of dental school, he
was accepted to pursue his Masters of Science degree in orthodontics at Saint Louis
University’s Center for Advanced Dental Education. Upon graduating from Saint Louis
University, he will enter the private practice of orthodontics in Denver, CO.
52