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.

1

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.

2

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

i

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.

ii

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.

iii

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

iv

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

v

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

vi

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

1

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.

3

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

4

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

5

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

6

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

7

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

8

Figure 2.1: Discrepancy Index Instructions Form from the Case Report Work File on the

ABO website.12

9

Figure 2.2: Discrepancy Index Worksheet from the Case Report Work File on the ABO

website.12

10

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

12

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

13

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

14

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