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Relationship of Mesiodistal Tooth Size to Extraction Rate and Post-Treatment Changes in the Class II Division 1 Malocclusion

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Title:
Relationship of Mesiodistal Tooth Size to Extraction Rate and Post-Treatment Changes in the Class II Division 1 Malocclusion
Creator:
REED, JUDDSON ROBERTS ( Author, Primary )
Copyright Date:
2008

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Subjects / Keywords:
Average linear density ( jstor )
Crowding ( jstor )
Dental models ( jstor )
Headgear ( jstor )
Malocclusion ( jstor )
Orthodontics ( jstor )
Orthods ( jstor )
Overbite ( jstor )
Sex linked differences ( jstor )
Teeth ( jstor )

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University of Florida
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Copyright Juddson Roberts Reed. Permission granted to University of Florida to digitize and display this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
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RELATIONSHIP OF MESIODISTAL TOOTH SIZE TO EXTRACTION RATE AND
POST-TREATMENT CHANGES IN THE CLASS II DIVISION 1 MALOCCLUSION















By

JUDDSON ROBERTS REED


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTERS OF SCIENCE

UNIVERSITY OF FLORIDA


2006

































Copyright 2006

by

Juddson Roberts Reed
















TABLE OF CONTENTS

page

L IS T O F T A B L E S .......... .... .... .... .. .. ......... ................................................ .. iv

LIST OF FIGURES .............. ... ................................ ......... ..v

ABSTRACT .............. .................. .......... .............. vi

CHAPTER

1 IN TR O D U C TIO N ......................................................................... .... .. ........

2 MATERIAL AND METHODS................................................... ............... 3

S am p le .......................................................................... . 3
M eth od s ........................................................................... . 3
D ata A naly sis ............................................... 4

3 R E SU L T S ................................................................ .6

4 D ISC U SSIO N ..................................................... 12

5 C O N C L U SIO N S ................................................................16

L IST O F R E FE R E N C E S ............................................................................... 17

B IO G R A PH IC A L SK E T C H ........................................................................................ 20
















LIST OF TABLES

Table page

3-1. M ean tooth w idth (values in m m .).................................................... ....................7

3-2. Tooth width and initial PAR by sex ........................................ ....................... 7

3-3. Percent of subjects with extractions by treatment group, sex, and DC7 molar
c la ss sev e rity ..............................................................................................................9
















LIST OF FIGURES


Figure page

3-1. Mean combined 2-2 tooth width by sex for extraction and nonextraction subjects .10

3-2. Change from DCF in mean PAR score and components for extraction and
nonextraction groups ...................................................... ................ ........... 11















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

RELATIONSHIP OF MESIODISTAL TOOTH SIZE TO EXTRACTION RATE AND
POST-TREATMENT CHANGES IN THE CLASS II DIVISION 1 MALOCCLUSION

By

Juddson Roberts Reed

May 2006

Chair: Timothy T. Wheeler
Major Department: Orthodontics

Mesiodistal tooth size has been implicated in untreated crowding and post-

treatment alignment change. The purpose of this study was to determine if tooth size is

related to malocclusion severity, extraction frequency, and post-treatment change in a

group of class II division 1 subjects treated as part of a 2-phase randomized controlled

clinical trial at the University of Florida. Included subjects were those who began the

study and had initial Peer Assessment Rating (PAR) scores (n=257) and who completed

the study and had final PAR scores (n=204). Tooth width was measured on dental casts

at the completion of treatment or at the time point closest to completion of treatment, and

extracted teeth were noted from the casts. It was shown that males had significantly

larger teeth. Initial PAR and molar class severity did not differ by sex, but tooth size was

significantly correlated in males with initial overjet (R=0.23 [upper 2-2], 0.16 [combined

2-2]) and PAR score (R=0.28 [upper 2-2], 0.18 [combined 2-2]). Tooth size had

significant correlations with lower anterior alignment for females (R=0.20 [upper 2-2],









0.27 [lower 2-2], 0.23 [combined 2-2]). Tooth size was not related to initial molar class

severity. More males were treated with second phase extractions with the majority of

extractions done in the upper arch. Females only showed significant differences in tooth

size when comparing extraction and non-extraction subjects, suggesting that females

received extractions for excess tooth mass or protrusion, and males received extractions

for classification purposes. There were no differences in post-treatment PAR score

change between extraction and non-extraction subjects.














CHAPTER 1
INTRODUCTION

Tooth size, along with available arch length and desired ultimate tooth position, is

part of the important space analysis during orthodontic diagnosis and treatment planning.

Tooth size has been studied throughout the history of orthodontics to explain pre- and

post-treatment crowding, differences in classification, and even for extraction guidelines.

A few studies have shown that larger teeth are associated with crowding.1'2

However other studies found no association between tooth size and crowding3 while

others will claim that tooth size and arch dimension have equal contributions.4 Many

authors5-10 have found males to have larger teeth than females, and ethnic tooth size

differences have been shown.9 The size of the crowns of teeth have been shown to be

linked to heredity through twin studies."1

Skeletal and dental classification have been shown to influence tooth size and

Bolton's discrepancies, class III subjects having greater differences between maxillary

and mandibular tooth size than class I and class II, which did not differ.9'12-14

Incisor shape as defined as the ratio between mesiodistal and faciolingual

dimensions15 and contact point to cervical area mesiodistal width16 are the major

determinants in lower anterior crowding of untreated arches. However, other studies

have failed to show correlation between incisor shape and crowding and have suggested

that mesiodistal width alone correlates to crowding. 17,1

Gilmore and Little19 examined the relationship between mandibular incisor

dimensions and arch alignment in 164 class I and II cases 10 years after completion of









treatment. They found a weak positive correlation between incisor dimension and

crowding. Glenn et al.20 evaluated 28 nonextraction treated cases 8 years post-retention

and found no association between mesiodistal or faciolingual incisor dimension and

pretreatment or post-treatment incisor crowding.

Multiple scoring systems have been utilized to assign quantitative descriptors to

treatment results such as Little's irregularity index21 and the PAR index.22 Birkeland et

al.23 found that pre-treatment PAR score was a good predictor for post-treatment PAR

score and long term outcome. Pavlow24 found that post-treatment PAR score and PAR

score change is not related to Phase I treatment type in a group of class II subjects treated

during a prospective clinical trial.

Given the contradiction in the literature about tooth size and crowding, we sought

to examine if this relationship existed for class II subjects. In addition, we wanted to

determine if sexual dimorphism in tooth size existed in our cohort. Finally, we wanted to

evaluate whether tooth size related to extraction rate and PAR changes during retention.














CHAPTER 2
MATERIAL AND METHODS

Sample

This study included a sample of individuals with Class II malocclusion who

participated in a prospective randomized controlled trial at the University of Florida. The

design of this study was published by Keeling et al.25 in 1998.

Methods

Tooth measurements were done on stone casts with digital calipers by one

examiner [JRR]. The mesiodistal width was measured and recorded at the contact point

for maxillary and mandibular incisors, canines, and premolars, bilaterally. Stone models

have been validated for accurate measurement by Gilmore and Little,19 and bilateral

measurements are advocated by Ballard26 due to his documentation of right-left tooth size

discrepancies. A digital caliper was oriented parallel to the occlusal plane of the teeth

and the vestibular surface of the model as per the method standardized by Moorrees and

Reed.27

Measurements were done on final models. In the case of extraction treatment, the

size of any extracted tooth was taken from models at an appropriate previous time point if

available; the teeth that were extracted were noted for use in analysis. If the final models

were not of good diagnostic value (fractured or distorted) measurements were done on

the next available retention models. Of the 312 subjects who began the study's first

phase, 257 had tooth measurements and initial PAR scores available for analysis. For

subjects who may not have completed the study, models at the latest time point available









were measured. Dental casts of diagnostic value were available for 204 of the 208

subjects who completed the study.

The measurements were summed for each subject as summed upper and lower 2nd

premolar to 2nd premolar (5-5) and summed upper and lower lateral and central incisors

(2-2) for data analysis.

Initial molar class (mild, bilateral one-half cusp; moderate, 1 side three-fourths

cusp; severe, 1 side full cusp) was used to grade the severity of the class II

malocclusion.28

Peer assessment rating (PAR) scores were used to assess post-treatment stability.

The American weighted, raw unweighted, and component (upper and lower alignment,

overjet, and overbite) scores were used as stability variables. To quantify post-treatment

stability, the difference between PAR scores and components at DCF and DCR was

calculated as ([PAR score change] = [PAR score @ DCR1,2,3...] [PAR score @

DCF]).

Data Analysis

To determine examiner reliability, tooth width of ten randomly chosen subjects'

casts was measured twice two weeks apart. For each tooth measured, the difference

between the two measurement time points was averaged among the ten subjects. Mean

difference ranged from 0.10mm for the lower right canine to 0.20 for upper right lateral

incisor.

Chi-square test was used to compare the number of individuals with and without

extractions by phase I treatment group, sex, and initial molar class severity.

Combined tooth width between male and females and between extraction and

non-extraction subjects was compared with a 2 sample t-test.






5


Wilcoxon rank sum was used to compare combined tooth size and PAR score at

DC1 by sex. It was also used to compare PAR score components and PAR score

component change between extraction and non-extraction subjects.

Pearson correlation coefficients were used to examine the correlation between

tooth size and DC 1 PAR score and components.

ANOVA was used to determine significant differences between DC1 molar class

severity groups due to tooth size.














CHAPTER 3
RESULTS

There were 257 study participants who had available tooth width data and initial

PAR. There were more males (n=156) than females (n=101), but there were nearly equal

numbers in each of the three phase I groups (bionator n=93; observation n=78; headgear

n=86). The majority of the subjects had a high initial molar class severity (n= 18), with

less in the low (n=62) and mild (n=86) categories. The majority of the subjects were

White (n=238), with less Black (n=4), other (n=2) and Hispanic (n=13) subjects.

Table 3-1 shows the mean tooth width for this sample. The smallest tooth was the

mandibular central incisor (5.28mm) and the largest was the maxillary central incisor

(8.69mm). The greatest standard deviation was noted for the maxillary left lateral

incisor.

Table 3-2 depicts the mean 2-2 tooth size and DC1 PAR scores by sex. Males had

significantly greater combined 2-2 tooth width for the maxillary and mandibular arches

independently and together. However, there were no significant differences by sex for

weighted PAR score at DC1. For females, the correlation coefficient between tooth size

and DC1 PAR score and components were significant between upper 2-2 (R=0.20), lower

2-2 (R=0.27), and combined 2-2 (R=0.23) width for lower anterior alignment only at

p<0.05. For males there was no significant correlation between tooth size and lower

incisor alignment. However, males showed significant correlations for the following

combinations: weighted PAR and upper 2-2 (R=0.28) and combined 2-2 (R=0.18); raw

par and upper 2-2 (R=0.22); and overjet and upper 2-2 (R=0.23) and combined 2-2









(R=0.16), all at p<0.05. There were no other significant correlations between tooth size

and PAR scores and components (data not shown).


Table 3-1. Mean tooth width (values in mm.)
Tooth Number N Mean Std Dev Minimum Maximum
UR5 247 6.65 0.50 5.34 9.77
UR4 248 6.90 0.44 5.42 8.86
UR3 241 7.82 0.47 6.54 9.31
UR2 255 6.63 0.54 5.16 8.31
UR1 257 8.65 0.55 6.36 10.05
UL1 257 8.69 0.56 7.20 10.85
UL2 257 6.67 0.59 5.09 8.89
UL3 240 7.79 0.48 6.57 9.05
UL4 248 6.91 0.42 5.79 8.71
UL5 245 6.65 0.64 5.43 10.93

LL5 240 7.16 0.53 5.84 9.09
LL4 250 7.03 0.47 5.78 8.87
LL3 248 6.79 0.42 5.71 8.87
LL2 257 5.84 0.42 4.90 7.09
LL1 257 5.29 0.34 4.25 6.13
LR1 256 5.28 0.39 4.33 8.89
LR2 257 5.84 0.36 4.97 6.90
LR3 248 6.74 0.45 5.27 8.25
LR4 251 6.98 0.51 5.25 8.69
LR5 243 7.07 0.51 5.74 8.68


Tooth number is given in Palmer notation
left; LR lower right)


(UR, upper right; UL, uppe


r left; LL, lower


Table 3-2. Tooth width and initial PAR by sex
Male (n=156)
Mean SE
Upper 2-2, mm. 30.93 0.16
Lower 2-2, mm. 22.47 0.10
Combined 2-2, mm. 53.41 0.23


Female (n=101)
Mean SE
30.05 0.19
21.86 0.13
51.91 0.31


Weighted PAR
2 sample t-test used


21.13 0.51


20.57


0.63


0.49


There were no significant tooth size differences between DC 1 molar class severity


groups for males and females (data not shown).


p-value
0.0004
0.0002
<0.0001









Table 3-3 shows subjects treated with extractions in any arch who completed the

class II study and had casts available for measurement (n=204). Note that the values for

upper arch extractions represent any subjects treated with upper extractions including

those who may have been treated with lower extractions (this is true for the lower

extraction data as well). Although there were no significant sex differences between the

number of subjects treated by nonextraction and extraction, more males were treated with

extractions, and the difference was nearly significant (p=0.053 in both arches, p=0.0710

in the upper arch). There was a significantly greater number of subjects in the phase I

observation group treated by extractions in any (upper or lower) arch and the upper arch

alone, but not for subjects treated with lower arch extractions. A similar pattern of

significance was seen when subjects were grouped by DC7 molar class severity.

Figure 3-1 shows the combined 5-5 and 2-2 tooth width by sex and extraction for

class II study participants who finished the second phase of treatment and for whom

values for all 20 anterior teeth were available (n=169). Males had significantly larger

teeth than females (p < .001). Subjects treated with extractions had more combined tooth

width than those treated without extractions, though the difference is significant only for

females (p < .05).

The change in mean PAR scores and components from final to recall time points is

shown in Figure 3-2. The subjects represented are those who completed the study and

who had models scored by the PAR index. The number of subjects that were recalled

decreased as the interval from treatment completion increased. Also, not all subjects

were recalled at every year for retention. Therefore, the number of subjects not only

decreases in the later retention time points, but the subject pool is different at each









retention time point. There were no significant differences between extraction and

nonextraction groups at any data collection point for change in mean weighted or raw

PAR, upper anterior alignment, and overjet. The nonextraction group had a significantly

greater mean lower anterior alignment score change at DCR6. The nonextraction group

also had a significantly greater mean overbite score change at DCR3.

Table 3-3. Percent of subjects with extractions by treatment group, sex, and DC7 molar
class severity
Nonextraction Extraction
Percent (n) Upper arch Lower arch Both arches p
Total
(n=204) 81% (166) 19% (38) 5%(11) 19% (38)

Sex
Male 77% (94) 23% (28) 7% (8) 23% (28) n.s.
Female 88% (72) 12% (10) 4% (3) 12% (10) n.s.

Phase I treatment
group
Bionator 89% (59) 11% (7) 3% (2) 11% (7) < 0.05
Observation 72% (48) 28% (19) 9% (6) 28% (19) < 0.05
Headgear 83% (59) 17% (12) 4% (3) 17% (12) < 0.05

Initial molar class severity
High 74% (73) 26% (26) 4% (4) 26% (26) < 0.05
Low 90% (43) 10% (5) 2% (1) 10% (5) < 0.05
Mild 88% (50) 12% (7) 11% (6) 12% (7) < 0.05
Extraction Upper Arch = any subject with extractions in upper arch.


Extraction Lower Arch
Extraction Both Arches
Chi-square test used.


any subject with extractions in the lower arch.
=any subject with extractions in either arch.







10



5s 00 N Male Female
57 0oo Nonextraction 75 62
E 560 Extraction 25 7
56 00 All Subjects 100 69
55s00oo
S5400
530 Nonextraction
52 Extraction

51 00oo All Patients

Male Female

Figure 3-1. Mean combined 2-2 tooth width by sex for extraction and nonextraction
subjects (with standard error).
2 sample t-test used. *Significant difference male v. female p < .001. tSignificant
difference (extraction v. nonextraction) p < .05.













2b. Change in raw PAR score from DCF


2d. Change in lower anterior alignment from DCF


* ~ I


-- Nonextraction
........ Extraction
R1 R2 R3 R4 R5 R6 R7 R8
N (Nonext) 121 96 63 46 41 40 21 14
N (Ext) 29 16 11 7 9 10 2 2


Figure 3-2. Change from DCF in mean PAR score and components for extraction and
nonextraction groups (with standard error). 2a, weighted PAR; 2b, raw PAR; 2c, upper
anterior alignment; 2d, lower anterior alignment; 2e, overjet; 2f, overbite.
Wilcoxon rank sum test used. *Significant (extraction v. nonextraction) at p < .05.


2a Change in weighted PAR score from DCF


2c Change in antenor upper alignment from F


2e change n overjet from DCF


2f Change in overbite rom DCF














CHAPTER 4
DISCUSSION

Previous retrospective studies examined tooth size differences by comparing

crowded and non-crowded dentitions.1'2 This study, while retrospective, utilizes a subject

pool treated as part of a prospective randomized controlled clinical trial.25 Phase I

treatment was determined by randomization, while phase II treatment plan was

determined by using a collaborative treatment plan by sending phase II records to

multiple practitioners across the country.29 It should be noted that the extraction

frequency represented here is a result of model analysis and represents actual treatment

rather than the collaborative treatment plan.

Our investigation of tooth size in Class II subjects had a similar outcome as

previously reported studies5-10 with respect to sex differences. Our findings showed that

males had approximately 3.4 mm greater tooth mass for the 20 anterior teeth and 1.3 to

1.5mm greater tooth mass for the 8 anterior teeth. Molar class severity and DC 1 PAR

score did not differ by sex, suggesting that tooth size may not influence these measures.

We were not able to confirm the findings of Lavelle9 in regards to ethnic differences in

tooth size due to the predominately white sample in this study.

There were differences between males and females in regards to the pattern of

correlation between initial PAR components and tooth size. Anterior tooth size in males

significantly correlated with overjet and weighted PAR. The significant correlation in

females was with lower anterior alignment. The suggestion is that larger teeth in class II

children is manifested differently for boys than girls, such that boys show their arch









length discrepancy with overjet, and girls with lower crowding. The correlation between

lower incisor size and lower anterior alignment (R=0.27, females) is similar to the

correlation between incisor size and Little's irregularity index reported for treated and

untreated cases by Smith et al.18 and to that reported by Gilmore and Little19 for post-

retention cases. However, correlations in the range or R=0.30 are of questionable clinical

value.

While there were no significant differences in the number of males and females

requiring second phase extractions, the trend was that more males (28) than females (10)

had extractions, suggesting that the greater tooth mass may be related to more males

being treated with extractions.

Comparing nonextraction and extraction subjects showed that subjects treated with

extractions had significantly greater mean tooth mass for the 5-5 and 2-2 measurements.

This comparison alone would suggest that subjects with larger teeth had more crowding

and that our findings agree with those of Doris et al.1 and Norderval et al.2 However,

only 11 of the 38 extraction subjects had extractions in both arches. With the majority of

extractions being done in the upper arch, the suggestion is that the majority of extractions

were done for classification and maxillary anterior retraction rather than for crowding.

Furthermore, extraction frequency also showed significant differences with respect

to DC7 molar class severity, with 26.3% of severe class II subjects having extractions and

11.4% of low and mild class IIs having extractions. This is also suggestive that phase II

extraction decision is heavily influenced by the overall requirement for attaining a

desirable finishing classification.









The influence of phase I treatment on the frequency of extractions was significant.

Those with bionator or headgear phase I treatment had significantly fewer extractions

(13.9%) than the phase I observation group (28.4%). The suggestion is that phase I

treatment cuts the likelihood of having extractions during phase II treatment in half. A

similar study done at the University of North Carolina30 found an extraction rate of

approximately 17% in the observation group, 15% in the headgear group, and 38% in the

bionator group. They noted that the difference in extraction rate approached but was not

statistically significant.

The extraction rates for this study do not reflect the previously reported consensus

treatment plans29 as our extraction frequency was determined by looking at post-

treatment casts rather than the treatment plan. Therefore, these rates, while showing

interesting trends, should be interpreted with caution as they represent the treatment

preferences of a few practitioners.

There was a significantly greater difference in tooth size between extraction groups

for females, but not for males. With more males overall requiring extractions, less

difference in tooth size between extraction and nonextraction subjects is due to a majority

of subjects having extractions for classification purposes rather than for crowding.

Post DCF PAR score and component change did not show any trends in statistical

significance when comparing extraction and nonextraction groups. A possible

explanation for this is that there is no difference in relapse between extraction and

nonextraction subjects. However, different methods of retention were used for these

subjects, including removable Hawleys and fixed retention. One might feel that fixed

retention would prevent alignment changes. Efforts are being made to group these






15


subjects by retention type to analyze relapse. However, this could be difficult due to the

comparison of PAR values of subjects with fixed retention to those with Hawley retainers

due to the variable compliance with Hawley retainers. Additionally, the impact of third

molar status has not been examined.














CHAPTER 5
CONCLUSIONS

In summary, males had significantly larger teeth than females. Initial PAR score

and molar classification did not differ between males and females. For males, initial

weighted PAR score and overjet correlated with upper and combined upper and lower

anterior tooth size, while in females showed correlation between lower anterior alignment

and all measures of anterior tooth size. Tooth size was not related to initial molar class

severity.

During the second phase of treatment, there was a trend for more male subjects

being treated with extractions during the second phase of treatment. The majority of

extractions were done in the upper arch, with very few subjects having extractions in the

lower arch. The difference in tooth width for females treated with extractions compared

to females treated without extractions was much greater than the same difference for

males. There were significant differences in the number of subjects receiving extractions

when grouped by phase I treatment group and by DC7 molar class severity, with the

observation group and the severe class IIs having more extractions. There were few

significant differences between extraction groups with respect to PAR and component

scores at the end of treatment and throughout the retention period















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29. Aiosa, LSA. The effect of early class II bionator and headgear therapies on phase II
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BIOGRAPHICAL SKETCH

Juddson Reed received his BA in chemistry from Wake Forest University in 1999.

He received a DMD in 2003 and a Certificate in Orthodontics and Master of Science in

dental sciences in 2006 from the University of Florida College of Dentistry.




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RELATIONSHIP OF MESIODISTAL TOOT H SIZE TO EXTRACTION RATE AND POST-TREATMENT CHANGES IN THE CLASS II DIVISION 1 MALOCCLUSION By JUDDSON ROBERTS REED A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF SCIENCE UNIVERSITY OF FLORIDA 2006

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Copyright 2006 by Juddson Roberts Reed

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TABLE OF CONTENTS page LIST OF TABLES .............................................................................................................iv LIST OF FIGURES .............................................................................................................v ABSTRACT .......................................................................................................................vi CHAPTER 1 INTRODUCTION........................................................................................................1 2 MATERIAL AND METHODS....................................................................................3 Sample..........................................................................................................................3 Methods........................................................................................................................3 Data Analysis................................................................................................................4 3 RESULTS.....................................................................................................................6 4 DISCUSSION.............................................................................................................12 5 CONCLUSIONS........................................................................................................16 LIST OF REFERENCES...................................................................................................17 BIOGRAPHICAL SKETCH.............................................................................................20 iii

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LIST OF TABLES Table page 3-1. Mean tooth width (values in mm.)..............................................................................7 3-2. Tooth width and initial PAR by sex...........................................................................7 3-3. Percent of subjects with extractions by treatment group, sex, and DC7 molar class severity..............................................................................................................9 iv

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LIST OF FIGURES Figure page 3-1. Mean combined 2-2 tooth width by sex for extraction and nonextraction subjects.10 3-2. Change from DCF in mean PAR score and components for extraction and nonextraction groups................................................................................................11 v

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science RELATIONSHIP OF MESIODISTAL TOOTH SIZE TO EXTRACTION RATE AND POST-TREATMENT CHANGES IN THE CLASS II DIVISION 1 MALOCCLUSION By Juddson Roberts Reed May 2006 Chair: Timothy T. Wheeler Major Department: Orthodontics Mesiodistal tooth size has been implicated in untreated crowding and post-treatment alignment change. The purpose of this study was to determine if tooth size is related to malocclusion severity, extraction frequency, and post-treatment change in a group of class II division 1 subjects treated as part of a 2-phase randomized controlled clinical trial at the University of Florida. Included subjects were those who began the study and had initial Peer Assessment Rating (PAR) scores (n=257) and who completed the study and had final PAR scores (n=204). Tooth width was measured on dental casts at the completion of treatment or at the time point closest to completion of treatment, and extracted teeth were noted from the casts. It was shown that males had significantly larger teeth. Initial PAR and molar class severity did not differ by sex, but tooth size was significantly correlated in males with initial overjet (R=0.23 [upper 2-2], 0.16 [combined 2-2]) and PAR score (R=0.28 [upper 2-2], 0.18 [combined 2-2]). Tooth size had significant correlations with lower anterior alignment for females (R=0.20 [upper 2-2], vi

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0.27 [lower 2-2], 0.23 [combined 2-2]). Tooth size was not related to initial molar class severity. More males were treated with second phase extractions with the majority of extractions done in the upper arch. Females only showed significant differences in tooth size when comparing extraction and non-extraction subjects, suggesting that females received extractions for excess tooth mass or protrusion, and males received extractions for classification purposes. There were no differences in post-treatment PAR score change between extraction and non-extraction subjects. vii

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CHAPTER 1 INTRODUCTION Tooth size, along with available arch length and desired ultimate tooth position, is part of the important space analysis during orthodontic diagnosis and treatment planning. Tooth size has been studied throughout the history of orthodontics to explain preand post-treatment crowding, differences in classification, and even for extraction guidelines. A few studies have shown that larger teeth are associated with crowding. 1,2 However other studies found no association between tooth size and crowding 3 while others will claim that tooth size and arch dimension have equal contributions. 4 Many authors 5-10 have found males to have larger teeth than females, and ethnic tooth size differences have been shown. 9 The size of the crowns of teeth have been shown to be linked to heredity through twin studies. 11 Skeletal and dental classification have been shown to influence tooth size and Boltons discrepancies, class III subjects having greater differences between maxillary and mandibular tooth size than class I and class II, which did not differ. 9,12-14 Incisor shape as defined as the ratio between mesiodistal and faciolingual dimensions 15 and contact point to cervical area mesiodistal width 16 are the major determinants in lower anterior crowding of untreated arches. However, other studies have failed to show correlation between incisor shape and crowding and have suggested that mesiodistal width alone correlates to crowding. 17,18 Gilmore and Little 19 examined the relationship between mandibular incisor dimensions and arch alignment in 164 class I and II cases 10 years after completion of 1

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2 treatment. They found a weak positive correlation between incisor dimension and crowding. Glenn et al. 20 evaluated 28 nonextraction treated cases 8 years post-retention and found no association between mesiodistal or faciolingual incisor dimension and pretreatment or post-treatment incisor crowding. Multiple scoring systems have been utilized to assign quantitative descriptors to treatment results such as Littles irregularity index 21 and the PAR index. 22 Birkeland et al. 23 found that pre-treatment PAR score was a good predictor for post-treatment PAR score and long term outcome. Pavlow 24 found that post-treatment PAR score and PAR score change is not related to Phase I treatment type in a group of class II subjects treated during a prospective clinical trial. Given the contradiction in the literature about tooth size and crowding, we sought to examine if this relationship existed for class II subjects. In addition, we wanted to determine if sexual dimorphism in tooth size existed in our cohort. Finally, we wanted to evaluate whether tooth size related to extraction rate and PAR changes during retention.

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CHAPTER 2 MATERIAL AND METHODS Sample This study included a sample of individuals with Class II malocclusion who participated in a prospective randomized controlled trial at the University of Florida. The design of this study was published by Keeling et al. 25 in 1998. Methods Tooth measurements were done on stone casts with digital calipers by one examiner [JRR]. The mesiodistal width was measured and recorded at the contact point for maxillary and mandibular incisors, canines, and premolars, bilaterally. Stone models have been validated for accurate measurement by Gilmore and Little, 19 and bilateral measurements are advocated by Ballard 26 due to his documentation of right-left tooth size discrepancies. A digital caliper was oriented parallel to the occlusal plane of the teeth and the vestibular surface of the model as per the method standardized by Moorrees and Reed. 27 Measurements were done on final models. In the case of extraction treatment, the size of any extracted tooth was taken from models at an appropriate previous time point if available; the teeth that were extracted were noted for use in analysis. If the final models were not of good diagnostic value (fractured or distorted) measurements were done on the next available retention models. Of the 312 subjects who began the studys first phase, 257 had tooth measurements and initial PAR scores available for analysis. For subjects who may not have completed the study, models at the latest time point available 3

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4 were measured. Dental casts of diagnostic value were available for 204 of the 208 subjects who completed the study. The measurements were summed for each subject as summed upper and lower 2 nd premolar to 2 nd premolar (5-5) and summed upper and lower lateral and central incisors (2-2) for data analysis. Initial molar class (mild, bilateral one-half cusp; moderate, 1 side three-fourths cusp; severe, 1 side full cusp) was used to grade the severity of the class II malocclusion. 28 Peer assessment rating (PAR) scores were used to assess post-treatment stability. The American weighted, raw unweighted, and component (upper and lower alignment, overjet, and overbite) scores were used as stability variables. To quantify post-treatment stability, the difference between PAR scores and components at DCF and DCR was calculated as ([PAR score change] = [PAR score @ DCR1,2,3] [PAR score @ DCF]). Data Analysis To determine examiner reliability, tooth width of ten randomly chosen subjects casts was measured twice two weeks apart. For each tooth measured, the difference between the two measurement time points was averaged among the ten subjects. Mean difference ranged from 0.10mm for the lower right canine to 0.20 for upper right lateral incisor. Chi-square test was used to compare the number of individuals with and without extractions by phase I treatment group, sex, and initial molar class severity. Combined tooth width between male and females and between extraction and non-extraction subjects was compared with a 2 sample t-test.

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5 Wilcoxon rank sum was used to compare combined tooth size and PAR score at DC1 by sex. It was also used to compare PAR score components and PAR score component change between extraction and non-extraction subjects. Pearson correlation coefficients were used to examine the correlation between tooth size and DC1 PAR score and components. ANOVA was used to determine significant differences between DC1 molar class severity groups due to tooth size.

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CHAPTER 3 RESULTS There were 257 study participants who had available tooth width data and initial PAR. There were more males (n=156) than females (n=101), but there were nearly equal numbers in each of the three phase I groups (bionator n=93; observation n=78; headgear n=86). The majority of the subjects had a high initial molar class severity (n=118), with less in the low (n=62) and mild (n=86) categories. The majority of the subjects were White (n=238), with less Black (n=4), other (n=2) and Hispanic (n=13) subjects. Table 3-1 shows the mean tooth width for this sample. The smallest tooth was the mandibular central incisor (5.28mm) and the largest was the maxillary central incisor (8.69mm). The greatest standard deviation was noted for the maxillary left lateral incisor. Table 3-2 depicts the mean 2-2 tooth size and DC1 PAR scores by sex. Males had significantly greater combined 2-2 tooth width for the maxillary and mandibular arches independently and together. However, there were no significant differences by sex for weighted PAR score at DC1. For females, the correlation coefficient between tooth size and DC1 PAR score and components were significant between upper 2-2 (R=0.20), lower 2-2 (R=0.27), and combined 2-2 (R=0.23) width for lower anterior alignment only at p<0.05. For males there was no significant correlation between tooth size and lower incisor alignment. However, males showed significant correlations for the following combinations: weighted PAR and upper 2-2 (R=0.28) and combined 2-2 (R=0.18); raw par and upper 2-2 (R=0.22); and overjet and upper 2-2 (R=0.23) and combined 2-2 6

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7 (R=0.16), all at p<0.05. There were no other significant correlations between tooth size and PAR scores and components (data not shown). Table 3-1. Mean tooth width (values in mm.) Tooth Number N Mean Std Dev Minimum Maximum UR5 247 6.65 0.50 5.34 9.77 UR4 248 6.90 0.44 5.42 8.86 UR3 241 7.82 0.47 6.54 9.31 UR2 255 6.63 0.54 5.16 8.31 UR1 257 8.65 0.55 6.36 10.05 UL1 257 8.69 0.56 7.20 10.85 UL2 257 6.67 0.59 5.09 8.89 UL3 240 7.79 0.48 6.57 9.05 UL4 248 6.91 0.42 5.79 8.71 UL5 245 6.65 0.64 5.43 10.93 LL5 240 7.16 0.53 5.84 9.09 LL4 250 7.03 0.47 5.78 8.87 LL3 248 6.79 0.42 5.71 8.87 LL2 257 5.84 0.42 4.90 7.09 LL1 257 5.29 0.34 4.25 6.13 LR1 256 5.28 0.39 4.33 8.89 LR2 257 5.84 0.36 4.97 6.90 LR3 248 6.74 0.45 5.27 8.25 LR4 251 6.98 0.51 5.25 8.69 LR5 243 7.07 0.51 5.74 8.68 Tooth number is given in Palmer notation (UR, upper right; UL, upper left; LL, lower left; LR lower right) Table 3-2. Tooth width and initial PAR by sex Male (n=156) Female (n=101) Mean SE Mean SE p-value Upper 2-2, mm. 30.93 0.16 30.05 0.19 0.0004 Lower 2-2, mm. 22.47 0.10 21.86 0.13 0.0002 Combined 2-2, mm. 53.41 0.23 51.91 0.31 <0.0001 Weighted PAR 21.13 0.51 20.57 0.63 0.49 2 sample t-test used There were no significant tooth size differences between DC1 molar class severity groups for males and females (data not shown).

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8 Table 3-3 shows subjects treated with extractions in any arch who completed the class II study and had casts available for measurement (n=204). Note that the values for upper arch extractions represent any subjects treated with upper extractions including those who may have been treated with lower extractions (this is true for the lower extraction data as well). Although there were no significant sex differences between the number of subjects treated by nonextraction and extraction, more males were treated with extractions, and the difference was nearly significant (p=0.053 in both arches, p=0.0710 in the upper arch). There was a significantly greater number of subjects in the phase I observation group treated by extractions in any (upper or lower) arch and the upper arch alone, but not for subjects treated with lower arch extractions. A similar pattern of significance was seen when subjects were grouped by DC7 molar class severity. Figure 3-1 shows the combined 5-5 and 2-2 tooth width by sex and extraction for class II study participants who finished the second phase of treatment and for whom values for all 20 anterior teeth were available (n=169). Males had significantly larger teeth than females (p < .001). Subjects treated with extractions had more combined tooth width than those treated without extractions, though the difference is significant only for females (p < .05). The change in mean PAR scores and components from final to recall time points is shown in Figure 3-2. The subjects represented are those who completed the study and who had models scored by the PAR index. The number of subjects that were recalled decreased as the interval from treatment completion increased. Also, not all subjects were recalled at every year for retention. Therefore, the number of subjects not only decreases in the later retention time points, but the subject pool is different at each

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9 retention time point. There were no significant differences between extraction and nonextraction groups at any data collection point for change in mean weighted or raw PAR, upper anterior alignment, and overjet. The nonextraction group had a significantly greater mean lower anterior alignment score change at DCR6. The nonextraction group also had a significantly greater mean overbite score change at DCR3. Table 3-3. Percent of subjects with extractions by treatment group, sex, and DC7 molar class severity Nonextraction Extraction Percent (n) Upper arch Lower arch Both arches p Total (n=204) 81% (166) 19% (38) 5%(11) 19% (38) Sex Male 77% (94) 23% (28) 7% (8) 23% (28) n.s. Female 88% (72) 12% (10) 4% (3) 12% (10) n.s. Phase I treatment group Bionator 89% (59) 11% (7) 3% (2) 11% (7) < 0.05 Observation 72% (48) 28% (19) 9% (6) 28% (19) < 0.05 Headgear 83% (59) 17% (12) 4% (3) 17% (12) < 0.05 Initial molar class severity High 74% (73) 26% (26) 4% (4) 26% (26) < 0.05 Low 90% (43) 10% (5) 2% (1) 10% (5) < 0.05 Mild 88% (50) 12% (7) 11% (6) 12% (7) < 0.05 Extraction Upper Arch = any subject with extractions in upper arch. Extraction Lower Arch = any subject with extractions in the lower arch. Extraction Both Arches = any subject with extractions in either arch. Chi-square test used.

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10 50.0051.0052.0053.0054.0055.0056.0057.0058.00MaleFemaleCombined 2-2 width, m m N Male Female Nonextraction 75 62 Extraction 25 7 All Subjects 100 69 Nonextraction Extraction All Patients Figure 3-1. Mean combined 2-2 tooth width by sex for extraction and nonextraction subjects (with standard error). 2 sample t-test used. *Significant difference male v. female p < .001. Significant difference (extraction v. nonextraction) p < .05.

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11 2a. Change in weighted PAR score from DCF0.001.002.003.004.005.006.007.008.00R1R2R3R4R5R6R7R8Weighted PAR 2b. Change in raw PAR score from DCF0.000.501.001.502.002.503.003.50R1R2R3R4R5R6R7R8Component PAR 2c. Change in anterior upper alignment from DCF0.000.200.400.600.801.001.20R1R2R3R4R5R6R7R8Upper anterior alignment 2d. Change in lower anterior alignment from DCF-0.500.000.501.001.502.00R1R2R3R4R5R6R7R8Lower anterior alignment* 2e. Change in overjet from DCF0.000.100.200.300.400.500.600.700.80R1R2R3R4R5R6R7R8Overjet 2f. Change in overbite from DCF-0.200.000.200.400.600.801.001.20R1R2R3R4R5R6R7R8Overbite* Nonextraction Extraction R1 R2 R3 R4 R5 R6 R7 R8 N (Nonext) 121 96 63 46 41 40 21 14 N (Ext) 29 16 11 7 9 10 2 2 Figure 3-2. Change from DCF in mean PAR score and components for extraction and nonextraction groups (with standard error). 2a, weighted PAR; 2b, raw PAR; 2c, upper anterior alignment; 2d, lower anterior alignment; 2e, overjet; 2f, overbite. Wilcoxon rank sum test used. *Significant (extraction v. nonextraction) at p < .05.

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CHAPTER 4 DISCUSSION Previous retrospective studies examined tooth size differences by comparing crowded and non-crowded dentitions. 1,2 This study, while retrospective, utilizes a subject pool treated as part of a prospective randomized controlled clinical trial. 25 Phase I treatment was determined by randomization, while phase II treatment plan was determined by using a collaborative treatment plan by sending phase II records to multiple practitioners across the country. 29 It should be noted that the extraction frequency represented here is a result of model analysis and represents actual treatment rather than the collaborative treatment plan. Our investigation of tooth size in Class II subjects had a similar outcome as previously reported studies 5-10 with respect to sex differences. Our findings showed that males had approximately 3.4 mm greater tooth mass for the 20 anterior teeth and 1.3 to 1.5mm greater tooth mass for the 8 anterior teeth. Molar class severity and DC1 PAR score did not differ by sex, suggesting that tooth size may not influence these measures. We were not able to confirm the findings of Lavelle 9 in regards to ethnic differences in tooth size due to the predominately white sample in this study. There were differences between males and females in regards to the pattern of correlation between initial PAR components and tooth size. Anterior tooth size in males significantly correlated with overjet and weighted PAR. The significant correlation in females was with lower anterior alignment. The suggestion is that larger teeth in class II children is manifested differently for boys than girls, such that boys show their arch 12

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13 length discrepancy with overjet, and girls with lower crowding. The correlation between lower incisor size and lower anterior alignment (R=0.27, females) is similar to the correlation between incisor size and Littles irregularity index reported for treated and untreated cases by Smith et al. 18 and to that reported by Gilmore and Little 19 for post-retention cases. However, correlations in the range or R=0.30 are of questionable clinical value. While there were no significant differences in the number of males and females requiring second phase extractions, the trend was that more males (28) than females (10) had extractions, suggesting that the greater tooth mass may be related to more males being treated with extractions. Comparing nonextraction and extraction subjects showed that subjects treated with extractions had significantly greater mean tooth mass for the 5-5 and 2-2 measurements. This comparison alone would suggest that subjects with larger teeth had more crowding and that our findings agree with those of Doris et al. 1 and Norderval et al. 2 However, only 11 of the 38 extraction subjects had extractions in both arches. With the majority of extractions being done in the upper arch, the suggestion is that the majority of extractions were done for classification and maxillary anterior retraction rather than for crowding. Furthermore, extraction frequency also showed significant differences with respect to DC7 molar class severity, with 26.3% of severe class II subjects having extractions and 11.4% of low and mild class IIs having extractions. This is also suggestive that phase II extraction decision is heavily influenced by the overall requirement for attaining a desirable finishing classification.

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14 The influence of phase I treatment on the frequency of extractions was significant. Those with bionator or headgear phase I treatment had significantly fewer extractions (13.9%) than the phase I observation group (28.4%). The suggestion is that phase I treatment cuts the likelihood of having extractions during phase II treatment in half. A similar study done at the University of North Carolina 30 found an extraction rate of approximately 17% in the observation group, 15% in the headgear group, and 38% in the bionator group. They noted that the difference in extraction rate approached but was not statistically significant. The extraction rates for this study do not reflect the previously reported consensus treatment plans 29 as our extraction frequency was determined by looking at post-treatment casts rather than the treatment plan. Therefore, these rates, while showing interesting trends, should be interpreted with caution as they represent the treatment preferences of a few practitioners. There was a significantly greater difference in tooth size between extraction groups for females, but not for males. With more males overall requiring extractions, less difference in tooth size between extraction and nonextraction subjects is due to a majority of subjects having extractions for classification purposes rather than for crowding. Post DCF PAR score and component change did not show any trends in statistical significance when comparing extraction and nonextraction groups. A possible explanation for this is that there is no difference in relapse between extraction and nonextraction subjects. However, different methods of retention were used for these subjects, including removable Hawleys and fixed retention. One might feel that fixed retention would prevent alignment changes. Efforts are being made to group these

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15 subjects by retention type to analyze relapse. However, this could be difficult due to the comparison of PAR values of subjects with fixed retention to those with Hawley retainers due to the variable compliance with Hawley retainers. Additionally, the impact of third molar status has not been examined.

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CHAPTER 5 CONCLUSIONS In summary, males had significantly larger teeth than females. Initial PAR score and molar classification did not differ between males and females. For males, initial weighted PAR score and overjet correlated with upper and combined upper and lower anterior tooth size, while in females showed correlation between lower anterior alignment and all measures of anterior tooth size. Tooth size was not related to initial molar class severity. During the second phase of treatment, there was a trend for more male subjects being treated with extractions during the second phase of treatment. The majority of extractions were done in the upper arch, with very few subjects having extractions in the lower arch. The difference in tooth width for females treated with extractions compared to females treated without extractions was much greater than the same difference for males. There were significant differences in the number of subjects receiving extractions when grouped by phase I treatment group and by DC7 molar class severity, with the observation group and the severe class IIs having more extractions. There were few significant differences between extraction groups with respect to PAR and component scores at the end of treatment and throughout the retention period 16

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LIST OF REFERENCES 1. Doris JM, Bernard BW, Kuftinec MM. A biometric study of tooth size and dental crowding. Am J Orthod 1981;79:326-336. 2. Norderval K, Wisth PJ, Boe OE. Mandibular anterior crowding in relation to tooth size and craniofacial morphology. Scand J Dent Res 1975;83:267-273. 3. Howe RP, NcNamara JA, OConner KA. An examination of dental crowding and its relationship to tooth size and arch dimension. Am J Orthod 1983;83:363-373. 4. Lundstrm A. The aetiology of crowding of the teeth (based on studies of twins and on morphological investigations) and its bearing on orthodontic treatment (expansion or extraction). Eur Orthod Soc Trans 1951;176-191. 5. Morrees CFA. The dentition of the growing child. Harvard University Press, Cambridge 1959:79-86. 6. Garn SM, Lewis AB, Kerewski RK. Sex difference in tooth size. J Dent Res 1964;43:306. 7. Beresford JS. Tooth size and class distinction. Dent Pract 1969;20: 113-120. 8. Sanin C and Savara BS. An analysis of permanent mesiodistal crown size. Am J Orthod 1971;59:488-500. 9. Lavelle CLB. Maxillary and mandibular tooth size in different racial groups and in different occlusal categories. Am J Orthod 1972;61:29-37. 10. Bishara SE, Khadavi P, Jakobsen JR. Changes in tooth sizearch length relationships from the deciduous to the permanent dentition: A longitudinal study. Am J Orthod 1995;108:607-613. 11. Osborne RH, Horowitz SL, DeGeorge FV. Genetic variations in tooth dimensions; a twin study of permanent anterior teeth. Am J Human Gen 1958;10:350-359. 12. Sperry TP, Worms FW, Isaacson RJ, Speidel TM. Tooth size discrepancy in mandibular prognathism. Am J Orthod 1977;72:183-190. 13. Araujo E and Souki M. Bolton anterior tooth size discrepancies among different malocclusion groups. Am J Orthod 2003;73:307-313. 17

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18 14. Ayra BS, Savara BS, Thomas D, Clarkson Q. Relation of sex and occlusion to mesiodistal tooth size. Am J Orthod 1974;66:479-486. 15. Peck S and Peck H. Crown dimensions and mandibular incisor alignment. Angle Orthod 1972;42:148-153. 16. Rhee SH and Nahm DS. Triangular-shaped incisor crowns and crowding. Am J Orthod 2000;118:624-628. 17. Shah AA, Elcock C, Brook AH. Incisor crown shape and crowding. Am J Orthod 2003;123:562-567. 18. Smith RJ, Davidson WM, Gipe DP. Incisor shape and incisor crowding: a re-evaluation of the Peck and Peck ratio. Am J Orthod 1982;82:231-235. 19. Gilmore CA and Little RM. Mandibular incisor dimensions and crowding. Am J Orthod 1984;86:493-501. 20. Glenn G, Sinclair PM, Alexander RG. Nonextraction orthodontic therapy: Post-treatment dental and skeletal stability. Am J Orthod 1987;92:321-328. 21. Little RM. The irregularity index: a quantitative score of mandibular anterior alignment. Am J Orthod 1975;68:554-563. 22. Richmond S, Shaw WC, Roberts CT, Andrews M. The development of the PAR index (Peer Assessment Rating): reliability and validity. Eur J Orthod. 1992;14:180-7. 23. Birkeland K, Furevik J, Boe OE, Wisth PJ. Evaluation of treatment and post-treatment changes by the PAR index. Eur J Orthod 1997;19:279-288. 24. Pavlow SP. Effect of early treatment on stability of occlusion in patients with a class II malocclusion [Master of Science]: University of Florida, 2005. 25. Keeling SD, Wheeler TT, King GJ, Garvan CW, Cohen DA, Cabassa S, McGorray SP, Taylor MG. Anterioposterior skeletal and dental changes after early Class II treatment with bionators and headgear. Am J Orthod Dentofacial Orthop 1998;113:40-50. 26. Ballard ML. Asymmetry in tooth size: A factor in the etiology, diagnosis and treatment of malocclusion. Angle Orthod 1944;11:143-150. 27. Moorrees CFA and Reed RB. Biometrics of crowding and spacing of the teeth in the mandible. Am J Phys Anthropol 1954;12: 77-88. 28. Wheeler TT, McGorray SP, Dolce C, Taylor MG, King GJ. Effectiveness of early treatment of Class II malocclusion. Am J Orthod 2002;12:9-17.

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19 29. Aiosa, LSA. The effect of early class II bionator and headgear therapies on phase II treatment needs [Master of Science]: University of Florida, 1995. 30. Tulloch JFC, Proffit WR, Phillips C. Outcomes in a 2-phase randomized clinical trial of early Class II treatment. Am J Orthod 2004;125:657-67.

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BIOGRAPHICAL SKETCH Juddson Reed received his BA in chemistry from Wake Forest University in 1999. He received a DMD in 2003 and a Certificate in Orthodontics and Master of Science in dental sciences in 2006 from the University of Florida College of Dentistry. 20