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A comparison of extraction rates in two-phase versus one-phase class II malocclusion patients

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A comparison of extraction rates in two-phase versus one-phase class II malocclusion patients

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A COMPARISON OF EXTRACTION RATES IN TWO-PHASE VERSUS ONE-

PHASE CLASS II MALOCCLUSION PATIENTS

by

April Jalene Lee

____________________________________________________________________

A Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(CRANIOFACIAL BIOLOGY)

May 2008

Copyright 2008 April Jalene Lee
ii
Dedication
To my family for all their love and support.
Yu-Sun Lee, PhD
Ya-Wen Lee
Elaine Sulene Lee

iii
Acknowledgements
A special thank you to:
Dr. Glenn Sameshima
Dr. Nile Sorenson
Brian Chen

iv
Table of Contents
Dedication ii
Acknowledgements iii
List of Tables v
List of Figures vi
Abstract vii
Chapter 1: Introduction 1
Chapter 2: Review of Literature 4
Chapter 3: Hypothesis 23
Chapter 4: Materials and Methods 27
Chapter 5: Results 33
Chapter 6: Discussion 45
Chapter 7: Assumptions 56
Chapter 8: Limitations 57
Chapter 9: Summary 58
Chapter 10: Conclusions 59
Bibliography 64
v
List of Tables
TABLE 1: Inclusion Criteria for Previous Early vs. Late Class II Studies 9
TABLE 2: Early Two-Phase and Late Single Phase Extraction Frequency 30
TABLE 3: Male vs. Female Frequency 30
TABLE 4: Headgear Frequency 31
TABLE 5: Cephalometric Measurements 31
TABLE 6: Early vs. Late Treatment Extraction Data 33
TABLE 7: Early vs. Late Group Treatment Times 34
TABLE 8a: Cephalometric Measures at Various Time-points among the
Early Treatment Group 37

TABLE 8b: Cephalometric Measures at Various Time-points among the
Late Treatment Group 38

TABLE 9: Changes in Cephalometric Measures between Treatment
Groups, Stratified by Extraction Status 39

TABLE 10: Average Molar Severity Score among the Early Treatment
Group at Baseline and at the Start of Phase 2 Treatment 41

TABLE 11: Comparison of Headgear Therapy in Single Late Phase
Treatment Group 42

TABLE 12: Sex-Specific Mean Ages in Early and Late Treatment Groups 44
TABLE 13: Comparison of Gender Specific Total Treatment Time by
Treatment Group 44

TABLE 14: Differences in Average Total Treatment Time in Patients
Receiving Extractions vs. No Extractions 45

vi
List of Figures
FIGURE 1: Design of UNC Clinical Trial 11
FIGURE 2: Design of University of Florida Clinical Trial 14
FIGURE 3: Our Study’s Selection Process 28
FIGURE 4: Bar Graph of the Proportions of Patients with Tooth
Extractions by Treatment Group 33

FIGURE 5: Box Plots of Differences between Treatment Times
by Treatment Groups 35

FIGURE 6: Bar Graph Depicting the Mean Molar Severity Scores
At Baseline and at the Start of Phase 2 Treatment 41

FIGURE 7: Bar Graph Comparing the Percent of Patients Receiving
Tooth Extractions in Single Phase Treatment Group 43

vii
Abstract
Introduction: Although the pros and cons of early two-phase treatment to correct
Class II malocclusions have been examined, there is no study to date relating early
growth modification techniques to final extraction rates and tooth position outcomes.
Methods: Patients (n=61; age 6-17) were evaluated from a private orthodontic
practice in Southern California; 41 patients were treated in a single phase, and 20
patients in two-phases. Full records were examined to compare (1) extraction rates
in the permanent dentition and (2) final cephalometric numbers. Results: There was
a 20% rate of premolar extraction in the two-phase group versus a 43.90% extraction
rate in the single phase group (p=0.07). Final cephalometric numbers showed a
significant difference in IMPA (p=0.05) with more flaring in the early treatment
group, and no differences in ANB change. Conclusion: Early orthodontic
intervention of Class II malocclusion resulted in reduced rates of premolar
extractions with similar skeletal outcomes.
1
Chapter 1: Introduction
There has long been a debate over what is the most effective and efficient
treatment timing for children with Class II malocclusions. As Class II malocclusions
are found in nearly one out of every four children aged 10 to 12 studies aimed at
procuring a definitive solution to this age old question are always in vogue.
1

Historically, Class II patients are difficult to treat due to the unpredictable
nature of lower jaw growth. Class II patients tend to be deficient in horizontal
mandibular jaw growth and often times tend to grow in a downward and backward
rotating manner.
2,3,4,5
Since Class II patients have skeletal discrepancies which can
be improved with early growth modification treatments, the question faced by most
orthodontists is not whether to treat, but when to treat. One approach is to treat early,
prior to adolescence in order to maintain primary space and manipulate skeletal
growth. This early intervention helps to facilitate a simpler second phase of treatment
later in adolescence. Another approach to resolving Class II malocclusions is by
camouflaging skeletal defects in the permanent dentition with various extraction
patterns. Finally, it is also possible to combine orthodontics and orthognathic
surgery in the permanent dentition to ideally position the dentition and the skeleton
within the facial complex upon growth completion.
Advocates of early intervention claim that an early first phase care
facilitates an easier and more efficient second phase by decreasing the likelihood of
extractions and orthognathic surgery.
6
Other added benefits often cited by early
treatment advocates also include: decreased trauma to incisors, increased cooperation
2
with extraoral appliances, and positive psychosocial effects.
6,7,8,9,10,11
Opponents to
early treatment claim that early skeletal benefits gained during the first phase
treatment are evened out in the final outcome, and that patients gain similar skeletal
and dental treatment outcomes delivered in a more timely and monetarily efficient
manner from a single phase treatment during adolescence.
12,13,14,15,16,17,18,19,20,21

To date, there has been no consensus as to what the optimum time for Class
II treatment would be. Most orthodontists rely on their own clinical judgment in
determining the severity of a presenting malocclusion and instinct drives their
decision on when to begin treatment. Several major studies undertaken in recent
years aimed at analyzing treatment outcomes between single and two-phase
treatments have heavily favored a late single phase treatment.
13,15,17,18

In these prospective studies, early two phase treatment did not result in
substantial benefit to the patient. Statistically significant findings in all of these
studies included: increased treatment time, increased monetary investment, and
similar ABO and PAR scores in final cast evaluations. However, several studies
found differences in numbers of extractions that bordered on significance, and none
of them evaluated the final cephalometric outcomes between those early treatment
non-extraction cases and final tooth positions.
13,15,16,17,18,19,21
If a causal relationship
could be drawn between early treatment and reduction of premolar extractions, as
well as improved or equal skeletal and dental outcomes in these non-extraction cases,
the benefit of retaining all permanent teeth could be adequate motivation for some
patients to embark upon early treatment therapy.
3
To test the hypothesis that two-phase treatment benefits patient outcomes in
terms of extraction rates in the permanent dentition and final cephalometric
outcomes we investigated dental and skeletal outcomes of 500 consecutively treated
cases patients in a private practice in Southern California, 61 of which met all
inclusion criteria were retained in our final study. Full orthodontic records were
analyzed, and final outcomes were compared between single phase and two-phase
treatment groups.

Purpose of the study
• Compare premolar extraction rates between early two-phase treatment
patients versus late single phase treatment patients
• Compare final skeletal and dental incisor positions between early two-phase
and late single phase treatment groups

4
Chapter 2: Review of the Literature
Concepts of Early Treatment
The concept of early treatment has always been one of contention. Over the
past several decades the pendulum has swung widely between favoring early
intervention and favoring a single late phase of treatment. The objective of
orthodontists practicing early phase treatment is achieving Class I molar
relationships and decreasing overjet sometime between the ages of 8-11.
22
A
simpler second phase of treatment is then usually executed during the adolescent
years (ages 12-15) in order to fine tune the details of occlusion.
Supporters of the early treatment philosophy maintain that there are several
advantages to obtaining Class I molar relationship in the early mixed dentition that
are later diminished if not altogether lost if applied during adolescence. The first of
which is the ability to modify the patients skeletal growth by utilizing functional
appliances and extra oral devices such as headgear. Many studies have reported
findings that while the tissues of the craniofacial complex are amenable to change in
both young and adult animals, that greater rates and magnitudes of change were
achieved in younger animals.
23, 24,25,26,27
Secondly, proponents of early treatment
believe that greater patient compliance is obtained from younger patients who are
still psychologically hardwired to please adult authority figures. Several studies
aimed at examining compliance with orthodontic appliances have indeed found a
correlation between pre-adolescents and increased rates of compliance.
28,29,30
While
other studies have not found this relationship to be true, most clinicians have often
5
noted in their own practice experience that compliance is often higher among
younger patients.
31, 32, 33

Several treatment modalities are favored by orthodontists when attempting to
achieve the early treatment goals of Class I molar occlusion and decreased overjet.
With an objective of bringing about a more harmonious balance to the facial skeleton
in early treatment, the most common appliances to effect such a change have been a
combination of headgear, functional appliances, and fixed brackets. However, the
effects on the skeleton and dentition of headgear and functional appliances are
variable.

Functional Appliances: Effect and Efficacy
There is a wide variety of functional appliances utilized in the modern
orthodontic office. Frankel’s, Activators, Bionators, and Twin Blocks are just some
of the appliances which have been designed to reposition the mandible forward and
restrict maxillary growth in an effort to encourage more balanced skeletal growth
pattern. Animal studies conducted to evaluate the effectiveness of such mandibular
repositioning by studying condylar remodeling have shown a significant amount of
responsive mandibular growth.
23,24,25,34,35,36,37
Studies in human trials evaluating the
Frankel and activator therapy have also shown increases in mandibular growth,
though in smaller increments than those shown in the previously mentioned animal
studies.
38,39,40,41,42
Others would argue that it is difficult to determine whether the
amount of “additional” growth stimulated by these appliances are the result of the
6
appliance itself, or simply an expression of the natural growth potential of the given
individual.
43, 44
Indeed many studies have shown that much of the changes affected
by functional appliances are largely dentoalveolar and only mildly attributed to true
skeletal change.
44, 45,46,47,48
However, there is good consensus on the ability of
functional appliances to restrict forward growth of the maxilla.
41,42,45,49
So while,
many clinicians have had much success in obtaining Class I molar relationships with
functional appliances, the jury is still out as to how much of the correction is natural
potential expression and how much is effected dentoalveolar compensation and/or
true skeletal change.

Headgear: Effect and Efficacy
Headgear has been a part of the orthodontic armamentarium for almost as
long as orthodontics has been a recognized specialty. There is photographic
evidence of extraoral forces being applied to the maxilla as early as the late 1800s.
Headgear was reintroduced during the 1940s and became widely used in Class II
treatment protocols.
50
Over time many orthodontists have come to consider
headgear almost as integral to patient care as wires or brackets. Animal and human
clinical studies have shown the effectiveness of headgear in restricting maxillary
horizontal growth by placing extraoral posterior traction on the maxillary complex.
This in turn yields beneficial results when trying to obtain Class II correction.
26,27,51,52,53,54,55

7
The amount Class II correction gained by orthopedic change versus
dentoalveolar compensation has also been examined by several researchers.
Gianelly and Poulton both found that the orthopedic change observed in cases treated
with headgear was only about 20-30%.
56, 57
Headgear was also noted to have higher
effectiveness in correcting Class II malocclusions when it was compared to
functional appliances such as the bionator or Frankel regulator.
19,14
Regardless of
the relative agreement or disagreement between studies concerning functional
appliances or headgear the greater question at hand is whether the clinician has the
ability to maintain the changes in growth or molar occlusion from the first phase of
treatment to the final outcome.

Class II Malocclusion Studies
In order to thoroughly investigate the outcomes of Class II malocclusions
treated with early treatment the U.S. National Institutes of Health funded select
prospective randomized clinical trials in response to the 1987 World Health
Organizations request for more information on the subject. The subsequent studies
were conducted at the University of Florida, the University of North Carolina,
University of Pennsylvania, and the University of Michigan. Each study sought to
more clearly define the potential benefits of early treatment when compared to late
single phase treatment of Class II malocclusions. All studies were completed
independently of one another with no collaboration among the principle investigators.
8
Each of the studies were designed to determine whether early treatment in
mixed dentition followed by a second phase of treatment in the permanent dentition
demonstrated superior results to a single phase of treatment in the permanent
dentition. Subsequently, efforts were made by each investigator to analyze the
perceived benefits of early treatment, and also to analyze possible risks or burdens to
this type of treatment. All studies included an experimental group which included
those treated with a two-phase approach as well as a control group who were
observed initially and treated in a single phase during adolescence. The particulars
of the inclusion criteria were varied slightly between all the aforementioned studies,
and will be discussed in detail separately below.

9
Table 1: Inclusion Criteria for Previous Early vs. Late Class II Studies
North Carolina Florida Pennsylvania Michigan USC
Overjet > 7 mm > 0 mm > 3 mm ---- ≥ 4mm
Overbite ---- > 0 mm ---- ----
----
Molars ----
Bilateral > ½
cusp Class II
If one side < ½
cusp, the other
side > ½ cusp
Class II
Bilateral Class
II
No unilateral
Class I

Bilateral
Class II,
Division I >
½ cusp
Class II molar
relationship
of any degree
(excluding
bilateral Class
I)
Teeth
All permanent
incisors & first
molars erupted
All permanent teeth
(excluding third
molars) developing
as seen on panorex
Fully erupted
permanent first
molars
< 3 permanent
cuspids/bicuspids
---- ----
Ph1: ≥ 5
primary teeth
or < 20
permanent
teeth

Ph 2: ≤ 4
primary teeth
or ≥20
permanent
teeth
Cephalometric
criteria
1 yr prepeak-height
velocity as judged
from the hand/wrist
radiograph
---- ANB > 4.5° ----

ANB ≥ 5º
SN-GoGn ---- ---- ---- ----
SN-GoGn ≥
37º or
FMA ≥ 30˚
Age ---- ---- 7-12.5/13 years 7-14 years
Start of Ph2:
boys < 14.5
y.o. & girls <
13.5 y.o.
# of treating
orthodontists
1 for Phase 1
4 for Phase 2
4 for Phase 1
1 for Phase 2
---- 1
3 for Phase 1
3 for Phase 2
Other ---- ---- ----
Initial non-
extraction
treatment
plan
----

The University of North Carolina
The University of North Carolina prospective study was designed to address
specific questions regarding the optimal timing for the treatment of preadolescent
10
patients with Class II malocclusions. They sought to prove whether it was possible
to change growth, and does growth modification in the early phase of treatment
make a difference in the long term outcomes of the case.
17
The study was conducted
by Drs. Proffit and Tulloch between 1988 and 2001 included children who exhibited
a minimum of 7mm of overjet with no upper limit, and who have had no previous
orthodontic space maintenance or habit appliance therapy. All patients were still in
the mixed dentition and were at least 1 year before their peak height velocity.
17, 18

Patients who had obvious facial asymmetries or vertical mandibular plane angles
greater than 2 standard deviations outside published norms were excluded. Phase 1
lasted 15 months and all patients were treated by a single supervising faculty, though
in phase 2 four faculty members were each assigned their own randomized groups
and were allowed to treat the remaining malocclusion as each saw fit.
18

11

Figure 1: Design of UNC Clinical Trial

Children with overjet > 7mm
Randomized
(Stratified on gender)
Phase 1
Observation Functional Appliance Headgear
15 months = Phase 1
(Single doctor treatment protocol)
Re-randomization
(Stratified on gender and phase 1 group)
Phase 2
Dr. A Dr. B Dr. C Dr. D
Comprehensive Treatment
(Doctor determines their own treatment plan)
12
The results from the first phase of treatment demonstrated favorable growth
changes in about 75% of those in the headgear and bionator groups as compared to
their control counterparts. The headgear group demonstrated a restriction in the
forward movement of the maxilla and the functional appliance group showed an
increase in the mandibular length as well as an increase in chin projection compared
to the observation group.
17,18,58,59

Premolar extraction rates in the 1990’s for all patients attending the
University of North Carolina’s orthodontic clinic was about 30%.
17
Amongst those
patients included in the Class II study the extraction rate was found to be slightly less
than that number in all three treatment groups. The bionator group had the highest
number of extractions followed by the control group, and finally the combination
headgear group demonstrated the least amount of extractions in the permanent
dentition. However these slight differences in the absolute numbers of teeth
extracted amongst the three groups during the adolescent phase of treatment was not
statistically significant. Additionally, the functional appliance group was shown to
have approximately three degrees more proclination of the lower incisors than the
control or headgear groups during phase I and showed the greatest variability in
lower incisor angulation.
16, 17

At the end of the second phase of treatment gains obtained by the early
treatment group in terms of skeletal change, alignment, final occlusion, and length of
treatment were not sustained.
16,18,59,60
Final PAR (Peer Assessment Rating System)
scores for the early treatment experimental and control late treatment groups were
13
also found to be the same. The prevalence of convex facial profiles in final
outcomes also did not show differences amongst the different treatment groups.
18, 60

Therefore, the North Carolina study concluded that early treatment was unable to
provide any advantages in the final treatment outcome. This was seen to be true
regardless of the severity of the initial problem, and in fact early treatment protocols
were no more effective and less efficient than their single phase counterparts.

The University of Florida
Another prospective, longitudinal, randomized control trial study on Class II
malocclusions was undertaken at the University of Florida by Drs. Wheeler and
Keeling. Their inclusion criteria varied from the North Carolina study because rather
than selecting based upon overjet, inclusion was based upon a molar class II
classification of at least a bilateral half step or a greater than half step Class II molar
unilaterally. Patients could not have had more than three permanent premolars or
canines erupted, and while there were no upper limits in terms of SN mandibular
plane angles (unlike UNC), positive overbites and overjets were required. The
decision to select patients based upon molar classification allowed for treatment of
Class II division II malocclusions that would not have qualified for the North
Carolina study.
19

Phase I treatment lasted either 24 months or upon obtaining molar class I
correction, whichever came first. Patients initial Class II malocclusion was classified
based upon a scale of severity as follows: mild (bilateral half-step Class II molars),
14
moderate (unilateral three-quarter step Class II molar), or severe (bilateral full step
Class II molars). All patients were divided either into a bionator, headgear with
posterior bite plane, or observation group for phase 1. Cervical pull or high pull
headgear was given depending on whether the mandibular plane angle was above or
below 40˚.
61
Results of treatment were also analyzed based upon sex and race (%
non white), recall between phase 1 and 2 was in 6 month intervals, and all patients
were followed three years post treatment to examine stability.

Figure 2: Design of University of Florida Clinical Trial

Children with Class II molars (minimum bilateral ½ step)
Randomization
Observation Headgear/ Biteplane Bionator
Phase 1
24 months = Phase 1
Fixed Appliances
(4 doctors rotate seeing all patients)
Phase 2
15

Results of the Florida study showed significant (P=.001) changes following
early treatment amongst all groups where Class I molar goals were achieved in 83%
of the bionator group, 100% of the headgear group, and 14% of the observation
group. Multivariate analysis suggested that headgear may be superior to bionators in
achieving a class II correction during early treatment.
19
It was also noted that a
combined skeletal and dental effect in the headgear and bionator groups enhanced
mandibular growth on average of 0.5- 0.75mm per year during phase 1 treatment
without any detectable relapse in skeletal changes a year after the end of active
treatment, whereas the dental correction did show a significant relapse.
19
Initial
molar class severity was also found to be associated with success levels in phase 1.
Success of molar correction in the observation group was achieved in 30% of those
with mild initial molar class severity, in 10% with moderate initial molar class
severity, and in 3% of those with severe initial molar class severity (P=.007). For
those who received treatment with bionator or headgear in phase 1 success was seen
in 65%, 49%, and 29% for mild, moderate, and severe molar class groups,
respectively (P=.001). Race was also observed to be a factor in treatment success
(P=.039) with success in 69% (11 of 16) of the nonwhite subjects compared with
42% (64 of 153) of the white subjects.
19

Following phase II of treatment no differences were found with respect to
initial PAR or final PAR among the three treatment protocols. Early treatment
groups were found to have lower PAR scores entering phase 2 of treatment, but this
16
was not translated to the completion of phase 2.
62
Subjects of the study were
followed for three years post treatment to examine treatment effects on stability, and
again no significant differences were detected between the early and late treatment
groups.
When extraction rates were examined, 20% of the observations, 12% of the
headgear/biteplane, and 8% of the bionator groups had some premolars extracted
(p=0.07).
63
Therefore, premolar extractions were found to be almost twice as likely
in the phase 1 observation group as in the headgear group, and nearly three times as
likely as the bionator group. Statistically speaking a correlation between first phase
therapy and growth modification does seem to reduce rates of premolar extraction in
the second phase.
The University of Florida study noted that two phase early treatments
concluded about 6 months faster than those who were treated in a single phase. This
was different than the UNC study which detected only a slight reduction in treatment
length following first phase. The authors in Florida noted however that timing
differences may be due to a 24 month phase 1 length versus UNC’s 15month
protocol. Florida’s study also had four treating orthodontists who oversaw the
treatment of all patients in order to help control for proficiency of treatment times
between different operators.
21
Conclusions drawn from the Florida study were that
early treatment yielded no superior skeletal or dental benefits in the final outcome,
and did not affect the stability of the overall treated case.
19, 21,61,62,64

17
The University of Michigan
This retrospective study examined the benefits of a 2-stage bionator/edgewise
regimen in comparison to the more conventional 1-stage edgewise alternative in non-
extraction patients. Discriminate analysis identified two sub-samples of patients who
were relatively similar before treatment and thus equally susceptible to the two
treatments. Based on each patient’s discriminate score, the extreme 25% were
subsequently discarded, leaving a central 75% that were similar at the outset and thus
relatively free of susceptibility bias. The Michigan study did not have any
cephalometric criteria relating the maxillary-mandibular position or angle of the
mandibular plane as part of their selection criteria. Also with the extremes of the
sample population discarded, some of the most severe Class II malocclusions were
not treated in this study.
The conclusions of this study showed that despite a slight post-treatment
difference in age, the two groups underwent skeletal changes that left them
essentially indistinguishable at the end of treatment. In both groups, skeletal changes
were largely responsible for molar and overjet corrections that were found to be
nearly identical in the two groups. Thus, early functional appliance treatment
conferred no obvious, measurable benefits on the central 75%.
65, 66

The University of Pennsylvania
The University of Pennsylvania conducted a prospective randomized clinical
trial evaluating early treatment of Class II division I malocclusions in pre-pubertal
18
children with support by the National Institute of Dental Research. The two
principle aims of this study were to compare extraoral traction and functional
appliance therapy in the early correction of distocclusion of molars, and to establish
whether treatment in early to mid-childhood is necessary or whether intervention in
late childhood is timely enough to correct the malocclusion.
13, 14

Enrollment criteria included: Class II division I malocclusion of any severity,
a minimum ANB angle of 4.5, between 7 and 12.5/13 years of age, no prior
orthodontic treatment, and expected residential stability of 3 years. Early treatment
protocols were undertaken either with a headgear or a Frankel functional regulator.
Dental casts were taken every 2 months and evaluated for occlusal changes, and
cephalometric radiographs were taken annually.
14

Results from phase 1 indicated that both headgear and Frankel’s function
regulator were effective in correcting the malocclusion. However, while both
appliances seem to have a similar effect on mandibular length, the appliances tended
to affect the position of the jaws in a differential manner. Headgear had a distal
effect on the maxilla and the first molars, but not the maxillary incisors. The Frankel
regulator restrained the growth of the maxilla resulting in a retroclination of the
maxillary incisors, and encouraged a more forward position of the mandible with
proclination of the mandibular incisors.
13, 14, 15

Conclusions from this study indicate that while appliances seemed to
generate differential growth between the jaws in an early phase of treatment, single
19
phase treatment in late childhood was shown to be as effective on treatment
outcomes as those who were treated in mid-childhood.
14

The University of Southern California
A retrospective master’s thesis study on early treatment of high angle Class II
malocclusions was conducted by two former residents of the University of Southern
California. The study examined patient charts in from the offices of three ABO
diplomats in Seattle, Los Angeles, and Vancouver. Cephalometric inclusion criteria
included an ANB ≥ 5º and either SN-GoGn ≥ 37º or FMA ≥ 30º. Dental inclusion
criteria included an overjet ≥ 4mm, and a Class II molar relationship of any degree.
First phase orthodontic therapy was initiated in children with a minimum of 5
primary teeth still present or less than 20 of the possible 24 teeth (central and lateral
incisors, canines, first and second premolars, and first molars) clinically visible.
Treatment during phase 1 involved attempted growth modification via headgear,
functional appliance, or both.
Following completion of phase 1 therapy, patients were either discontinued
from active treatment or they continued directly into a second phase of full appliance
treatment. Phase 2 treatment begin for boys who were < 14.5 years of age and for
girls who were <13.5 years of age to allow for growth potential during this phase of
treatment. Dental requirements for beginning phase 2 meant that fewer than 4
primary teeth were present or at least 20 out of the possible 24 permanent teeth were
20
clinically visible. Those patients treated in a single phase had the same guidelines as
those in the two-phase treatment group.
Conclusions drawn from this study showed that prior to, and following
completion of treatment the early and late treatment groups were skeletally similar
with regard to the nature and degree of anterior-posterior and vertical relationships.
Dental relationships found statistically significant (p<0.05) differences between pre-
and post-treatment incisor inclinations (interincisal angle) and the relationship
between lower incisors to the mandibular plane (IMPA). Late treatment groups had
more proclined lower incisors and more compensation when relating upper to lower
incisors, hence a smaller interincisal angle. There were no significant differences
with respect to initial PAR, final PAR, or percentage PAR reduction following
treatment amongst the early and late treatment groups. With respect to extraction
rates, while the early treatment group tended to have fewer total extractions in the
permanent dentition, this difference was not found to be statistically significant
(P=.17). Finally, treatment duration for the early treatment group was significantly
longer than for the late treatment group.
67

The Cochrane Review
The Cochrane Library completed a systematic review of the efficacy of 2-
phase treatment when initiated in patients between the ages of 7 and 9 years to
correct Class II malocclusions. The authors searched every electronic database
available, and hand searched key international orthodontic journals with no
21
restriction for language, for randomized or controlled clinical trial studies. Criteria
of these studies were treatment to correct prominent maxillary front teeth. Subjects
were children or adolescents, aged 16 or younger, whose first phase treatment
included interventions by various fixed or removable appliances or headgear, with an
untreated control group for comparison.
68
Expected outcomes examined included:
correction of prominent maxillary teeth, skeletal relationships of the two jaws, self
esteem, incidence of injury to maxillary incisors, patient satisfaction, and the overall
number of appointments required to complete treatment. Eight trials were eventually
included, with data from 592 patients who had Class II division I malocclusions.
18,
61,69,70,71,72,73,74

Like all of the studies previously mentioned in this section significant
differences were found in the final overjet and ANB angle after phase I. Headgear
was found to have a small but significant effect on the reduction of overjet, and a
large effect on the reduction of ANB angle. Both headgear and functional appliances
had similar positive outcomes when comparing differences in overjet, final ANB
angle, and PAR score. However, this review of the literature showed that following
the end of phase II treatment no significant differences in overjet, final ANB, or PAR
scores were detected between children who had early treatment and those who had
not received early treatment.
The final conclusions of this paper included a recommendation to clinicians
to not feel pressured to begin treatment before 10 years of age due to the findings
about similar skeletal and dental outcomes. However, the authors did not completely
22
discount early treatment in select patients for treatment of arch length problems,
functional crossbites, accidental fracture of front teeth, and the opportunity to
enhance a child’s self-esteem.
68
23
Chapter 3: Hypothesis
Research Hypothesis
1. That there is a statistically significant difference in premolar extraction rates
in the early treatment group versus the single late phase treatment group.
2. That there is a statistical difference between the early versus late treatment
group in terms of both total treatment time and treatment time spent in fixed
appliances.
3. There is a statistical difference when comparing the following cephalometric
measurements:
Within the Early Treatment Group
a) Initial values versus those observed at the End of phase 1 treatment
b) End of phase 2 values versus Initial values
c) End of phase 2 values versus End of phase 1 values
Within the Late Treatment Group
a) Initial versus Final values
Early treatment group versus Late treatment group
a) Comparing changes from Initial to Final values and determining
significant differences between the two groups
4. There is a statistically significant differences seen in cephalometric
measurements when controlling for extractions:
a) Early treatment extraction versus Late treatment extraction patients.
24
b) Early treatment non-extraction versus Late treatment non-extraction
patients.
5. There is a statistically significant correlation seen in the early treatment group
comparing initial molar severity scores to molar severity scores at the
beginning of phase 2, with decreased molar severity scores at the start of
phase 2.
6. There is a statistically significant correlation between patients who used
headgear in the single late phase treatment group showing greater
improvement in ANB angle and fewer extractions than those who did not
receive headgear treatment.

Secondary Hypothesis
1. There is a significant difference between treatment duration and gender with
females completing orthodontic treatment faster than males.
2. There is a significant difference between males and females regarding age at
onset of treatment, with females beginning early phase 1 treatment sooner
than males.
3. There is a significant difference between treatment duration and treatment
modality, with non-extraction treatments completing orthodontic treatment
faster than extraction treatments.

25
Null Hypothesis
Null Hypotheses
1. That there is no statistically significant difference in premolar extraction rates
in the early treatment group versus the single late phase treatment group.
2. That there is no statistical difference between the early versus late treatment
group in terms of both total treatment time and treatment time spent in fixed
appliances.
3. That there is no statistical difference when comparing the following
cephalometric measurements:
Within the Early Treatment Group
a) Initial values versus those observed at the End of phase 1 treatment
b) End of phase 2 values versus Initial values
c) End of phase 2 values versus End of phase 1 values
Within the Late Treatment Group
a) Initial values versus Final values
Early treatment group versus Late treatment group
a) Comparing changes from Initial to Final values and determining
significant differences between the two groups
4. There is no statistically significant difference seen in cephalometric
measurements when controlling for extractions:
a) Early treatment extraction versus Late treatment extraction patients.
26
b) Early treatment non-extraction versus Late treatment non-extraction
patients.
5. There is no statistically significant correlation seen in the early treatment
group comparing initial molar severity scores to molar severity scores at the
beginning of phase 2, with decreased molar severity scores at the start of
phase 2.
6. There is no statistically significant correlation between patients who used
headgear in the single late phase treatment group showing greater
improvement in ANB angle and fewer extractions than those who did not
receive headgear treatment.

Secondary Null Hypotheses
1. There is no significant difference between treatment duration and gender with
females completing orthodontic treatment faster than males.
2. There is no significant difference between males and females regarding age at
onset of treatment, with females beginning early phase 1 treatment sooner
than males.
3. There is no significant difference between treatment duration and treatment
modality, with non-extraction treatments completing orthodontic treatment
faster than extraction treatments.
27
Chapter 4: Materials and Methods
Subject Screening and Inclusion Criteria
In order to identify Class II subjects suitable for this study, 500 consecutively
treated patient charts were examined in the private office an American Board of
Orthodontics Diplomate and Angle Society member in Orange County, CA. Our
efforts centered upon selecting subjects who presented with Class II malocclusions
who were subsequently treated with one- or two-phase treatments immediately upon
diagnosis regardless of timing of presentation. Therefore selection bias was
minimized.
The following inclusion criteria was constructed to ensure that the patients
studied were skeletally and dentally Class 2 prior to treatment. Criteria for the first
screening were as follows: All patient models taken from February 1998 to August
2001 were consecutively examined for the presence of a Class 2 malocclusion.
Models were initially examined for a minimum of quarter-cusp molar classification.
Patients with overbulked restorations or crowns were excluded, as were patients who
had previous interceptive space maintenance care. At the end of this initial screening
205 patients were found to be potentially suitable and were examined further with
more stringent requirements.
A second screening of the remaining 205 patients was done with the criteria
of a minimum quarter step Class 2 molar, complete records (including all x-rays,
photos, models), and no missing teeth other than third molars. 99 patients passed
through this second round of screening.
28
In the final round of selection, each of the remaining 99 patient charts were
examined and those with a minimum of a bilateral half-step or unilateral three-
quarter step Class 2 molar, with a positive overbite and overjet, no ankylosed teeth,
and no treatments requiring orthognathic surgery were retained for our study. 61
patients were accepted into our final study. No limits were set regarding starting
mandibular plane angles, nor number of permanent teeth erupted into the oral cavity.

Figure 3: Our Study’s Selection Process

Examined 500 Consecutively Treated Cases
Selection of Cases with Minimum of ¼ Cusp Class II Molars
(No Over-bulked Restorations or Previous Space Maintenance Therapy)
205 Patients Thru Round 1
Full Records with No Missing Teeth (other than third molars)
99 Patients Thru Round 2
Minimum Bilateral ½ Step Molar Class 2, Positive OB & OJ, No
Ankylosed Teeth, No Treatments Requiring Surgery
61 Patients Accepted into Study
29
Case Selection for the Early Two-Phase Treatment Group
Pre- treatment inclusion criteria for the two-stage treatment group included:
1) molar Class II relationship with a minimum of bilateral half-step or unilateral
three-quarter step classification, 2) no missing or ankylosed teeth, and 3) full records
and models at each phase of treatment. A minimum overjet was not established for
inclusion in the study otherwise many Class II division II patients would have been
excluded.
Treatment during the first phase of orthodontic therapy involved attempted
growth modification by headgear. Patients in this category still had primary C’s, D’s,
and E’s at the onset of the first phase of treatment. Following phase I treatment,
patients were on periodic recall for a period of time leading up to full appliance
therapy. In the interim some patients were given retainers, others had maxillary or
mandibular space maintainers, while others had no interim appliance at all. All
patients who completed a first phase treatment also completed a second phase during
adolescence.

Case Selection for the Single-Phase Treatment Group
Guidelines for case selection of the one-phase treatment group were similar
to the two-phase treatment group. Patients included in this treatment group either
presented for consultation during adolescence, or elected to only have single phase
treatment due to finances.
30
The main difference distinguishing this group was that most had all
permanent teeth up to the first molars erupted, or had only E’s remaining in the oral
cavity at the beginning of treatment.

Patient Sample, Distribution, and Extraction Rate
A total of 61 patients were included in this study. 20 patients were treated in
two-phase treatment, whereas 41 patients were treated as single-phase treatments.
Within the two-phase treatment group 4 of 20 patients were treated with extractions,
whereas within the single-phase treatment group 18 of 41 patients were treated via
extraction therapy. Extraction is defined as removing any premolars to facilitate
orthodontic treatment. A Pearson’s Chi-Square Test was used to test the hypothesis
that early two phase treatment results in fewer extractions than late one phase
treatment in a Class II patient. Significance was set at p≤0.05.
Table 2: Early Two-Phase and Late Single Phase Extraction Frequency
Overall Extraction Non-Extraction
Early 2-Phase 20 4 (20%) 16 (80%)
Late Single Phase 41 18 (44%) 23 (56%)
Total Patients 61 22 39

Table 3: Male vs. Female Frequency

Overall Early Two-Phase Late Single Phase
Male 21 (34%) 7 (35%) 14 (34%)
Female 40 (66%) 13 (65%) 27 (66%)
Total Patients 61 20 41
31
Table 4: Headgear Frequency
Overall Early Two-Phase Late Single Phase
Headgear 33 (54%) 20 (100%) 13 (32%)
No Headgear 28 (46%) 0 (0%) 28 (68%)
Total Patients 61 20 41

Cephalometric Landmarks and Measurements
All lateral cephalometric films obtained from the charts were scanned with
150 dpi of resolution using an Epson Expression 1680 (Epson, US) and each image
was saved as a JPEG format. Each initial, mid-, and final lateral cephalometric film
was then digitally traced by a single trained operator using Dolphin Imaging 10.5
Premium software (Dolphin Imaging Company, USA). All measurements and
statistics were made based upon these new data points. Eleven angular, linear, and
proportional measurements were determined for each patient at each time point of
treatment (initial, mid, and final) as shown in Table 5. Additionally, 10 randomly
chosen lateral cephalograms were retraced to check intra-examiner measurement
error.
Table 5: Cephalometric Measurements
AP-Maxilla Vertical Skeletal
SNA (º) FMA (MP-FH) (º)
AP-Mandible Dental Relationship
SNB (º) Inter-incisal Angle (U1-L1) (º)
Maxilla to Mandible Upper Incisor Inclination
ANB (º) U1-NA (º)
Lower Incisor U1-NA (mm)
L1-NB (º) Chin Projection
L1-NB (mm) Pog-NB (mm)
IMPA (L1-MP) (º)

32
Statistical Methods
Since our sample size was relatively small (n=61), we used the Wilcoxon
signed rank test to compare the differences of a continuous variable between groups
(e.g. early treatment vs. late treatment). Pearson's chi-square tests were used to
detect differences in categorical outcome variables between groups. The one-sample
t-test was used to test if the change in molarity severity scores was different from
zero (i.e. no change). Means, standard deviations, and p-values were reported. All
analyses were conducted using Stata 10 (College Station, TX, USA).

Institutional Review Board (IRB) Approval
The proposal to undertake this study was approved by the IRB in August 9,
2007. USC UPIRB # UP-07-00212

33
Chapter 5: Results

Premolar Extraction Rates in Early vs. Late Treatment Groups (Table 6)
The early two-phase treatment group demonstrated a 20% overall extraction
rate with 4 out of 20 patients receiving premolar extractions. The late single phase
treatment group demonstrated a 44% extraction rate with 18 out of 41 treated
patients receiving premolar extractions. These percentage differences in extraction
rates between the early and late treatment groups were a close but not statistically
significant value of p=0.05.
Table 6: Early vs. Late Treatment Extraction Data

Extraction Early 2-Phase Tx Late Single Tx
Yes 4 18
No 16 23
Pearson Chi-squared = 3.33, p=0.07

Figure 4: Bar graph of the Proportions of Patients with Tooth Extractions
by Treatment Group (1 = Early two-phase, 2 = Late single phase)

0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1 2
Treatment group
Proportion with extractions

34
Early vs. Late Group Treatment Times (Table 7)
Total treatment time for the early two-phase treatment group was 35.75 ±4.38
months as compared to 28.41 ±4.81 months (p<0.01) in the late single phase
treatment group. The seven months longer on average that the early two-phase
treatment group spent in treatment overall is understandable since the early group
underwent an additional first phase of care which lasted on average 13.40 ±2.30
months. When comparing phase 2 treatment times, the early two-phase treatment
group spent less time in fully bonded fixed appliances, only 22.35 ±4.49 months
versus the late single phase treatment group which spent 28.41±4.81 months in fixed
appliances (p <0.01). Thus, the two-phase treatment group spent a longer time
overall in treatment, but 6 months less time in braces than the late single phase
treatment group.

Table 7: Early vs. Late Group Treatment Times

Early Two-Phase
Tx
Late Single Phase
Tx
p-value
Total treatment
time (months)
35.75 ± 4.38 28.41 ± 4.81 <0.01
Phase 2 treatment
time (months)
22.35 ± 4.49 28.41 ± 4.81 <0.01
35
Figure 5: Box plots of Differences between Treatment Times by Treatment Groups
A)
20 25 30 35 40 45
Total Treatment Time
1 2

B)
15 20 25 30 35 40
Phase 2 Treatment Time
1 2

X-axis is the treatment group (1=single late phase, 2=early two-phase treatment).
(A) Differences in total treatment time in months (p<0.01). (B) Differences in phase 2
treatment time in months (p<0.01).

Early Treatment Cephalometric Data (Table 8a)
Cephalometric values were fairly similar when comparing the early two-
phase treatment group end of phase 1 values to its initial values. Significant findings
was noted in the two-phase treatment group where ANB was decreased following
phase 1 treatment (initial= 6.89˚, end of phase 1= 4.74˚, p=0.03).
When comparisons were drawn between cephalometric measurements for the
two-phase treatment group at the end of phase 2 compared to initial values statistical
36
significance was detected in IMPA, ANB, U1NA(mm), L1NB(mm), L1NB (deg),
PogNB, and in interincisal angle. Lower incisors (IMPA) proclined from 88.61˚ to
97.16˚ (p=0.03), ANB was reduced from 6.89˚ to 3.22˚ (p<0.01), both upper and
lower incisors moved forward and flared, which accounts for the decrease observed
in interincisal angle from 123.9˚ to 118.68˚ (p=0.05). Pogonion had also moved
forward from1.07mm to 2.63mm by the end of phase 2 (p<0.01).
A statistically significant difference was detected in PogNB measurements
when comparing end of phase 2 cephalometric values to end of phase 1 values (end
of phase 1=1.31mm, end of phase 2= 2.63mm, p<0.01). Increases in IMPA values
(92.34˚ to 97.16˚) and flaring in the lower incisors, L1NB (26.02˚ to 30.38˚) was also
observed to have close to significant findings, p=0.07 and p=0.06 respectively.

Late Treatment Cephalometric Data (Table 8b)
When comparing start and end cephalometric values within the late single
phase treatment group significant changes were observed for SNA, ANB, U1NA
(deg), PogNB, and interincisal angle. Following treatment the maxillary movement
was restricted (SNA initial = 83.54˚, final =80.78˚, p<0.01) that logically would lead
to a significant decrease in the relationship between the maxilla to the mandible
(ANB initial = 4.54˚, final = 2.17˚, p<0.01). The upper incisors flared a few degrees
(U1NA initial =22.14˚, final =28.06˚, p<0.01), which led to a reduction in the
interincisal angle (initial =127.22˚, final = 121.76˚, p <0.01). Pogonion was also
observed to move forward (initial= 1.34mm, final= 2.87mm, p<0.01).
37
Early vs. Late Treatment for Cumulative Sample (Table 8)
Of all recorded cephalometric measurements only IMPA was found to be
statistically significant when comparisons were drawn between early two-phase and
late single treatment groups. IMPA was seen to increase in both the two-phase and
single phase groups (p=0.03 and p=0.09, respectively), however the increase in the
early treatment group was significantly greater (p=0.05).
SNB and ANB closely approached significance (p = 0.07 and p=0.12,
respectively) with better Class II skeletal correction achieved in the two-phase
treatment group. SNB increased from 78.02˚ to 79.04˚, and ANB decreased from
6.89˚ to 3.22˚ in the two-phase treatment group. In the single phase treatment group
SNB decreased from 78.99˚ to 78.66˚, and ANB decreased from 4.54˚ to 2.17˚.

Table 8a: Cephalometric Measures at Various Time-points Among the Early
Treatment Group

Initial values End of Phase 1 p
a
End of Phase
2
p
a
p
b

IMPA 88.61 ± 9.41 92.34 ± 7.17 0.81 97.16 ±6.71 0.03 0.07
ANB 6.89 ± 3.00 4.74 ± 3.26 0.03 3.22 ± 2.34 <0.01 0.19
U1NA
(mm)
3.22 ± 2.88 4.83 ± 2.72 0.14 5.15 ± 2.30 0.05 0.48
U1NA
(deg)
24.07 ± 7.16 26.02 ± 5.48 0.42 27.74 ± 3.74 0.14 0.34
L1NB
(mm)
4.81 ± 2.06 5.34 ± 2.13 0.53 6.36 ± 1.93 0.03 0.13
L1NB
(deg)
25.14 ±5.10 26.02 ±6.54 0.65 30.38 ± 5.21 <0.01 0.06
SNA 84.91 ± 6.46 83.61 ± 6.73 0.28 82.25 ± 4.63 0.12 0.74
SNB 78.02 ± 4.71 75.53 ± 6.57 0.45 79.04 ± 3.65 0.24 0.62
POGNB
(mm)
1.07 ± 1.53 1.31 ± 1.24 0.48 2.63 ± 1.23 <0.01 <0.01
IntAng 123.90 ± 9.21 123.22 ± 7.84 0.77 118.68 ±7.21 0.05 0.11
FMA 29.32 ± 4.79 31.30 ± 4.85 0.20 30.84 ± 5.63 0.40 0.70

38
Table 8b: Cephalometric Measures at Various Time-points Among
the Late Treatment Group

a) Wilcoxon p-value compared to initial values as reference.
b) Wilcoxon p-value comparing end of Phase 2 to those at the end of Phase 1
c) Wilcoxon signed rank test p-values comparing the amount of change (i.e. Difference between
"end of Phase 2" and initial values) in cephalometric measures in early vs. late treatment groups.

Cephalometric Measurements Early vs. Late Stratified by Extraction (Table 9)
An analysis of cephalometric measurements comparing the early two-phase
extraction group to the late single phase extraction group, and the early two-phase
non-extraction group to the late single phase non-extraction group was done to try
and extrapolate whether differences existed in cephalometric outcomes when the
groups were stratified by extraction. Interestingly enough, none of the measurements
approached statistically significant values. The change in measurements (final
values-initial values) seemed to be similar for all groups compared in table 9 below.

Initial values Final values p
a
p
c

IMPA 94.22 ± 6.45 96.21 ± 5.80 0.09 0.05
ANB 4.54 ± 2.02 2.17 ± 2.12 <0.01 0.12
U1NA
(mm)
3.59 ± 2.94 4.85 ± 3.03 0.09 0.55
U1NA
(deg)
22.14 ±6.79 28.06 ±7.09 <0.01 0.18
L1NB
(mm)
4.61 ±2.09 5.23 ± 1.76 0.15 0.16
L1NB
(deg)
26.10 ±6.03 28.05 ± 4.79 0.11 0.22
SNA 83.54 ± 4.21 80.78 ± 4.41 <0.01 0.98
SNB 78.99 ±3.73 78.66 ±4.21 0.61 0.07
POGNB
(mm)
1.34 ±1.63 2.87 ± 1.93 <0.01 0.89
IntAng 127.22 ± 9.51 121.76 ± 7.72 0.01 0.76
FMA 27.48 ± 6.24 28.50 ± 7.29 0.46 0.35
39
Table 9: Changes in Cephalometric Measures between Treatment Groups,
Stratified by Extraction Status

EXTRACTION NO EXTRACTION
Early Tx (n=4) Late Tx (n=18) Early Tx (n=16) Late Tx (n=23)

Initial
value
Final
value
Initial
value
Final
value
P
Initial
value
Final
value
Initial
value
Final
value
P
IMPA 95.48
± 3.86
97.78
±
6.95
92.32
± 5.14
93.04
± 4.72
0.61 86.89 ±
21.41
97.01
± 6.88
95.70
± 7.08
98.69
± 5.42
0.12
ANB 7.90 ±
4.84
4.53
±
3.75
4.87 ±
1.66
2.47 ±
1.94
0.59 6.64 ±
2.53
2.89 ±
1.88
4.29 ±
2.27
1.87 ±
2.23
0.20
U1NA
(mm)
2.63 ±
4.83
3.20
±
2.39
3.68 ±
2.91
4.12 ±
3.12
0.86 3.36 ±
2.40
5.64 ±
2.06
3.52 ±
3.02
5.43 ±
2.89
0.82
U1NA
(deg)
22.38
±12.61
24.50
±
2.09
21.72
± 6.98
25.51
± 6.61
0.61 24.49 ±
5.68
28.54
± 3.66
22.47
± 6.78
30.05
± 6.94
0.11
L1NB
(mm)
5.75
±1.87
6.28
±
2.87
5.09 ±
2.17
5.26 ±
1.86
0.77 4.58 ±
2.09
6.38 ±
1.75
4.24 ±
2.00
5.22 ±
1.72
0.14
L1NB
(deg)
27.85
± 3.94
29.65
±
6.42
26.17
± 2.17
26.66
± 4.75
0.61 24.46 ±
5.24
30.56
± 5.10
26.06
± 5.56
29.15
± 4.64
0.19
SNA 87.63
± 9.49
84.15
±
7.81
83.22
± 4.59
79.47
± 4.50
0.86 84.23 ±
5.69
81.77
± 3.71
83.78
± 3.98
81.80
± 4.14
0.68
SNB 79.78
± 5.11
79.65
±
4.25
78.36
± 3.72
77.01
± 3.49
0.31 77.58 ±
4.67
78.89
± 3.62
79.49
± 3.74
79.95
± 4.34
0.23
POGN
B (mm)
-0.85
± 1.69
2.63
±
2.14
1.16 ±
2.07
3.23 ±
2.27
0.22 1.54 ±
1.09
2.63 ±
1.00
1.49 ±
1.23
2.59 ±
1.61
0.94
Int Ang

121.88
±
11.84
121.3
0 ±
10.61
127.2
6 ±
10.20
125.3
8 ±
7.19
0.73 124.41
± 8.84
118.0
2 ±
6.41
127.1
9 ±
9.18
118.9
3 ±
7.03
0.98
FMA 31.40
± 5.82
31.65
±
8.28
31.00
± 5.96
32.33
± 6.01
0.73 28.80 ±
4.57
30.64
± 5.12
24.72
± 5.02
25.49
± 6.86
0.26
Wilcoxon signed rank test p-value comparing differences between the changes in the cephalometric
measures (final value – initial value) between the early vs. late treatment groups

40
Molar Severity Scores in Early Treatment Group: (Table 10)
Molar severity scores were calculated on a ¼ cusp increment scale. Initial
and start of phase 2 models were examined individually and right and left molar
severity scores were recorded separately at each time point. A value of 0 was
assigned for a Class I molar relationship, whereas 0.25 for a ¼ cusp, 0.5 for ½ step,
0.75 for ¾ step, and 1 for a complete molar Class II relationship. Severity scores
were then averaged for each time point (initial= 0.69 ±0.23, start of phase 2= 0.13 ±
0.27) and significance change was detected between the two time points (p<0.01) via
the Wilcoxon signed rank test which was used to accommodate for the small sample
size. The results indicate that initial molar severity scores averaged to be almost a ¾
step Class II molar classification, however with interceptive headgear therapy during
phase 1, molar severity scores were reduced to ¼ cusp molar Class II relationships at
the start of phase 2.
Assuming that all patients were treated to a Class I molar relationship at the
end of phase 1 care, 30% of the early treatment group demonstrated some degree of
relapse in their molar corrections during the interim time between end of phase 1 and
start of phase 2 care. However, we were unable to verify that all patients attained
Class I molar correction during phase 1, as end of phase 1 treatment models were not
taken. The phase 1 treatment philosophy in this private practice allowed for an
average of one year in phase 1 care to attempt Class II molar correction with
headgear, at the end of which time appliances were debanded whether Class I molars
were obtained or not. These maximum time limits to phase 1 care were also
41
enforced in the UNC and University of Florida studies. As orthodontic practices will
never be able to achieve 100% compliance with appliance therapy, these maximum
phase 1 treatment time protocols are the necessary reality in efficient daily practice.
Therefore, it is highly likely that our percentage rate of “relapse” of phase 1 molar
correction is overestimated.

Table 10: Average Molar Severity Score among the Early Treatment Group at
Baseline and at the Start of Phase 2 Treatment

Average molar
severity score at
Baseline
Average molar
severity score at
start of Phase 2 Tx
Average change in molar
severity score (Baseline –
start of phase 2)
p
0.69 ± 0.23 0.13 ± 0.27 0.56 ± 0.35 <0.01
One-sample t-test p-value of the average change in molar severity score
Note: 30% of patients in early treatment group relapsed to some degree.

Figure 6: Bar graph depicting the mean molar severity scores at baseline and at
the start of phase 2 treatment (p<0.01)

0
0.4
0.8
1.2
1 2
Baseline Start of phase 2 Tx
Molar severity score

42
Headgear Effect on the Late Treatment Group: (Table 11)
A Wilcoxon signed rank test was conducted on the late single phase
treatment group to detect whether or not patients who used headgear in this group
had significantly improved ANB or fewer extractions than those who did not receive
headgear therapy. Both headgear and no headgear patients showed a significant
improvement in ANB change (headgear group change= 2.44˚, p=0.01, no headgear
group change= 2.47˚, p<0.01). However when the groups were compared to one
another there was no significant difference in overall ANB outcome (p=0.96).
Regarding extraction rates, the patients treated with headgear had a 23.1%
premolar extraction rate versus 53.6% extraction rate seen in the no headgear group.
P value was 0.10, which indicates that there may be an association between headgear
therapy in the late single phase treatment and reduced rates of extraction had our
sample size had been larger.

Table 11: Comparison of Headgear Therapy in the Single Late Phase
Treatment Group

Headgear No Headgear
Initial Final Change p
a
Initial Final Change p
a

p
b

ANB 4.75 ±
2.37
2.31 ±
1.88
2.44 ±
2.01
0.01 4.45 ±
1.88
2.10 ±
2.26
2.47 ±
1.88
<0.01 0.96
% with
extractio
ns
23.1% (3 of 13 patients) 53.6% (15 of 28 patients) 0.10
a) Wilcoxon signed rank test p-value comparing initial to the final ANB value stratified by headgear use.
b) Wilcoxon signed rank test p-value comparing the change in ANB values in headgear users vs. non-headgear
users.
Chi square test exact p-value reported for difference in % with extractions between headgear users and non-
headgear users.

43

Figure 7: Bar graph comparing the percent of patient receiving tooth extractions
in single phase treatment group

0
10
20
30
40
50
60
1 2
Treatment group
Percent with extractions

1= Single phase treatment group treated with headgear
2= Single phase treatment group treated without headgear

Male vs. Female Average Age at Onset of Treatment: (Table 12)
Early two-phase treatment was begun at an earlier age than late single phase
treatment. Males in general began early first phase treatment later (9.85 ± 1.01 years
in comparison to their female counterparts (8.74 ± 0.85 years) and this difference
was found to statistically significant (p<0.01). These results are to be expected since
early first phase treatment is targeted at modifying skeletal growth prior to
adolescence with a target range in age between 8-10 years old, and females in
general are more skeletally and dentally advanced than males who are the same age.
44
In the late single phase treatment group, males began treatment (11.58 ±3.26
years) on average earlier than the females (12.37 ±1.45 years), but the range of age at
the start of male single phase treatment was much broader than the females. The
slightly younger and broader range in age at start for males in the late single phase
treatment group may be a function of our limited sample size.

Table 12: Sex Specific Mean Ages in Early and Late Treatment Groups

Early Two-phase Tx Late Single phase Tx P
Male 9.85 ± 1.01 yrs 11.58 ± 3.26 yrs <0.01
Female 8.74 ± 0.85 yrs 12.37 ± 1.45 yrs <0.01
Wilcoxon signed rank test p-value

Male vs. Female Total Treatment Time by Early vs. Late Groups (Table 13)
In comparing treatment times stratified upon gender, we found that males and
females spent the same amount of time in treatment regardless of their experimental
treatment groups. Males actually treated out in slightly less time than females, 0.28
months less on average in the early two-phase group, and 0.42 months less on
average in the late single phase group. These slight differences in treatment times
were not found to be statistically significant at p=0.81 and p=0.78 respectively.

Table 13: Comparison of Gender Specific Total Treatment Time by Treatment
Group

Early Two-phase Tx time
(months)
Late Single Phase Tx time
(months)
Female 35.85 ± 4.54 28.56 ± 4.81
Male 35.57 ± 4.39 28.14 ± 4.96
P 0.81 0.78
Wilcoxon signed rank test p-value.

45
Extraction vs. Non-extraction Total Treatment Times (Table 14)
When examining overall treatment times comparing duration of extraction
therapy to non-extraction therapy a slightly shorter treatment time was observed in
the extraction group. This difference was roughly half a month reduction in average
treatment time in the extraction group which was not statistically significant.

Table 14: Differences in Average Total Treatment Time in Patients Receiving
Extractions vs. Non-extractions

Extraction
(n=22)
Non Extraction
(n=39)
p
Total Tx time
(months)
30.64 ± 5.86 31.14 ± 5.78 0.79
Wilcoxon signed rank test p-value.
46
Chapter 6: Discussion

Overall
The purpose of this study was to compare premolar extraction rates in Class
II patients who were treated with early two-phase treatment protocols versus late
single phase treatment protocols in a sample patient population gathered from the
office of a diplomate of the American Board of Orthodontics. We tested the
hypothesis that treating Class II patients in two phases produced reduced rates of
premolar extractions as well as superior skeletal and dental treatment outcomes
compared to treating in a single phase. The findings of this study demonstrate
differences in treatment outcomes of early two-phase Class II care that may aide the
clinician in evaluating start times for class II patients in private practice.
All patients were included in our study based upon similar presentations of
molar Class II relationships and our two-phase treatment cases included active
growth modification with headgear in phase one. All patients included were
consecutively treated by a single ABO diplomate orthodontist in a normal private
practice setting, mixed with other patients, and were not subject to any special care
related to this study. The use of cases drawn from a single clinician who treated all
patients with the same treatment philosophy served to minimize clinician bias that is
evident in other previously published studies.

47
Extraction Rate
Investigation of differences in premolar extraction rates between early two-
phase and late single phase treatment groups yielded dramatic percentage differences
in each group (Table 6). The two-phase treatment group demonstrated a 20% overall
extraction rate (4 out of 20 patients), whereas the single phase treatment group
demonstrated a 44% extraction rate (18 out of 41 patients). The p value determined
by the Pearson Chi-squared test was shown to be p=0.07 which narrowly misses the
traditional cut-off value of p<0.05 that is utilized for measuring statistical
significance. However, considering that the difference in p value between 0.07 and
0.05 is relatively small, we should not discount our findings as insignificant. This
difference indicates only a 2% increase in the likelihood of a false positive
correlation for the samples being measured. Indeed, as our sample size was limited
and effects on p value increase with decreasing sample size, it is very likely that a
relationship between early treatment leads to fewer premolar extractions in the
second phase of care does exist.
The Florida study observed that of 261 subjects, 20% of the observation, 12%
of the headgear/biteplane, and 8% of the bionator groups had some premolars
extracted (p=0.07).
63
The relative percentages and p value regarding extraction rates
in the observation and headgear groups in Wheeler study is similar to our findings,
with almost a 2 to 1 likelihood of extraction in the observation group. Therefore, the
Florida study whose sample size was much greater than our own confirms our
48
finding of a correlation existing between phase 1 interceptive care and reduced rates
of premolar extraction in the second phase.
The UNC study observed that after removing surgical option patients, the
control sample had a 28% extraction rate, whereas the early treatment group had a
35% and 17% extraction rate for the functional appliance and headgear groups
respectively. However, they did not find this difference to be statistically significant.
An interesting aside noted in the UNC study was that the control group had the
surgical option discussed most frequently (20 out of 52 patients) as compared to the
early treatment groups who were treated with functional appliances (5 out of 45
patients) and headgear (9 out of 50). Proffit’s group stated that the preliminary data
from this trial suggested that early treatment might influence both the rate of
extraction and the need for orthognathic surgery.
17

The USC retrospective study concluded that there was a tendency toward
greater non-extraction treatment in the early two-phase treatment group. When
calculated as a percentage of the total patient sample the early two-phase treatment
group had a 37.5% extraction rate compared to 50% extraction rate in the late single
phase treatment group (p=0.17).
67

Overall, our study mimics the general trends observed in previous studies
who noted increased extraction rates in late single phase treatment protocols. Further
investigation with larger sample size may more clearly delineate this probable
connection between early two-phase treatment and reduced premolar extractions.

49
Treatment Time
Evaluation of total treatment time between early two-phase and late single
phase treatment groups showed that the early treatment group took on average 7
extra months to complete treatment (Table 7). Total treatment time for the early two-
phase treatment group was shown to be 35.75 ±4.38 months as compared to the
28.41 ±4.81 months (p<0.01) in the late single phase group. When comparing
second phase treatment times, the time spent in fully bonded appliances, the early
two-phase treatment group treated faster, in only 22.35 ± 4.49 months versus the late
single phase treatment group which spent 28.41±4.81 months in fixed appliances
(p<0.01). Therefore we can conclude that the early two-phase treatment group spent
a longer time overall in treatment, however in phase 2 they actually spent 6 months
less time in braces as compared to the late single phase treatment group.
These results paint a very different picture when compared to previous
studies examining treatment time. Proffit found early treatment tended to be less
efficient as it produced only a slight reduction in the average time a child is in fixed
appliances during a second stage of treatment.
18, 58
Recorded phase 2 treatment times
demonstrated a median of 34.5 months treatment time in the control group, versus
the functional group who averaged 25.5 months, and the headgear group who
averaged 30.1 months (p=0.03).
18
Increased treatment times in the UNC trial is
likely to be attributed to the presence of multiple operators (residents and faculty)
treating their patient sample. Each of the four supervising orthodontists were
allowed to determine their own treatment plans, bracket systems, and archwire
50
sequences for their assigned cohort of patients, which lead to a broad range in
treatment time existing from one faculty member to another. For example, in the
single late phase treatment group, median treatment times ranged from 28-48 months
among the four orthodontists.
17, 18, 58
the presence of multiple operators’ likely
accounts for the increased treatment times which led them to conclude that early
two-phase treatment yielded no benefits in reduction of overall treatment times.
Comparatively, researchers at the University of Florida discovered that
patients with phase 1 treatment completed phase 2 care about 6 months faster than
those treated in a single phase. When they compared total treatment time for phases 1
and 2 combined, early two-phase treatments were found to take significantly longer
to treat than the single late phase approach. The Florida group recognized that a
possible flaw that may have affected these conclusions was that their protocol
allowed for a maximum of 24 months for phase 1 treatment regardless of
cooperation.
12
Additionally, like Proffit, Wheeler’s study also included four different
orthodontic faculty overseeing care for study participants.
12
In comparison, our study
averaged only 13.40 ±2.30 months spent in phase 1 achieving Class I molars, and
only involved one treating orthodontist.
Therefore, our findings in the early treatment group which included 6 months
reduced treatment times in phase 2, and an increase of only 7 months in overall
treatment time are likely more reflective of treatment times experienced
orthodontists can expect to see in their private practices than those previously
reported in institutional studies.
51
PAR Scoring
Many studies examining Class II early treatment outcomes rely on PAR
scoring for evaluation of final occlusions. However, PAR scores are limited in that
they only evaluate upper and lower incisor alignment in relationship to one another.
Indeed, PAR scoring allows leniency in grading poor finishes because it does not
scrutinize inappropriate inclinations of teeth, orthodontic treatments involving
inappropriate expansion, and discrepancy in contact point displacements within the
buccal segments.
The studies conducted at UNC, University of Florida, and USC all discovered
similar PAR scores between the two groups at the end of phase 2 treatment. Proffit
indicated in his discussion following their prospective study of early Class II
malocclusions that, “it is also possible for two patients to have the same PAR score
with different relationships of tooth to basal bone. Although this possibility poses a
special problem in the comparison of the outcome of treatment across groups of
children who have sustained more-or-less successful growth modification during
early treatment, the distribution of PAR scores (both percentages and categories) do
not seem different for the children who had early treatment than for those who did
not.”
17
For this reason we choose not to evaluate PAR scoring in the finishes of our
Class II treated case, and choose instead to compare cephalometric measurements
which would be a better indicator of skeletal and dental relationships in the final
occlusion.

52
Cephalometric Measurements
Cephalometric values recorded for the early treatment group showed a
significant reduction in ANB from an initial value of 6.89˚ to 3.22˚ (p=0.03) at the
end of phase 2 (Table 8a). This reflects a categorical change in these patients who
presented initially with moderate Class II skeletal relationships converting to a
normal Class I skeletal relationship at the end of orthodontic treatment. Lower
incisors were observed moving forward and proclining at all cephalometric time-
points recorded during treatment with IMPA increasing on average by 8.55˚, p=0.03
(Table 8a).
Skeletal changes in the late single phase treatment group was similar to those
seen in the early two-phase treatment group, with an ANB reduction from a mild
class II relationship of 4.54˚ to a Class I relationship of 2.17˚ (p<0.01) at the end of
orthodontic care (Table 8b). The single phase treatment group also experienced
proclination in the lower incisors, though to a lesser degree than experienced by the
two-phase treatment group (two-phase =88.61˚ to 97.16˚, single phase=94.22˚ to
96.21˚, p=0.05).
Proffit’s study had a mean initial ANB angle of 6.2˚, similar to the mean
initial ANB angle of 6.89˚ in our study.
17
Both the UNC and Florida studies
concluded that statistically speaking, final skeletal ANB changes were similar
regardless of early or late treatment protocols, which agreed with our study’s
findings.
19,58,59,76
However, it is interesting to note that with only a mean difference
of less than 1˚ in final IMPA and ANB measurements separating the early two-phase
53
and late single phase treatment groups, as well as less than two degrees in
proclination and 1mm difference in upper and lower incisor positioning which is
nearly negligible, that early two-phase patients were able to avoid extraction therapy
in much greater percentages than their single late phase counterparts. This would
then indicate that final skeletal and dental outcomes were found to be similar
amongst the two groups, but that the early two-phase treatment group was able to
achieve this similarity in skeletal and dental outcomes with non-extraction therapy.
This indicates that a clear benefit exists in treating patients presenting with Class II
malocclusions with an early first phase of skeletal growth modification.

Molar Class Severity
When we analyzed the change in molar class severity in the early treatment
group from the initial time-point to the beginning of phase 2 we discovered that there
was a significant reduction in Class II molar severity (Table 10). Our findings
demonstrated a greater than ½ step molar class II correction during phase 1 therapy
involving headgear use, which was largely retained at the start of phase 2.
Wheeler’s study followed changes in molar class severity as well and utilized
categories of mild (bilateral ½ cusp), moderate (1 side ¾ cusp), and severe (1 side
full cusp) to denote levels of Class II molar severity. Percentage of treatment goal
achieved was calculated based upon the number of ¼ cusp units of change required
to achieve a bilateral Class I molar relationship. Median values for percentage of
54
goal achieved during phase 1 ranged from 75-100% in the early functional/headgear
group versus the 15% in the observation group.
19

The Florida study considered successful phase 1 treatment as correction of
malocclusion to a ¼ cusp Class II molar relationship.
19
Therefore, in comparison to
our findings; it would seem that interceptive care with headgear produced a
considerable improvement in mean molar severity scores that can be directly
attributed to growth modification in early phase 1 care. Proffit explained that in
Class II populations of European origin, there is about a 30% chance in untreated
children of a favorable change in Class II jaw relationship, with approximately 50%
of no change and 15% of the condition worsening. He also stated that headgear and
functional appliances appeared to have between 70-80% chance of producing a
favorable or highly favorable change with early treatment.
58
Therefore, even with
consideration given to our estimated 30% rate of relapse to an average score
equivalent to ¼ cusp molar Class II at the start of phase 2, this result would still be
considered phase 1 success by Wheeler’s study standards and falls directly in line
with Proffit’s expectations of dental molar change when growth modifications are
applied to a sample patient population.

Headgear Use in the Late Single Phase Treatment Group
Analysis of headgear use in the late single phase treatment group showed
similar changes in ANB over the given treatment period. However, when the sample
of headgear patients were compared to non-headgear users it was shown that the
55
non-headgear patients were almost twice as likely to experience extraction therapy
than their headgear wearing counterparts, 53.6% versus 23.1% respectively (Table
11).
Wheeler noted that in their study headgear was utilized much more frequently
during phase 2 in the observation group (42%) than in the headgear (15%) or
bionator (23%) groups (p=0.0001).
63
The Florida study also concluded that through
multivariate analysis that headgear may be superior to the bionator in achieving
Class II correction during early treatment.
19
Perhaps this increased efficiency with
headgear use contributes to the decreased need for camouflage treatment resulting in
reduced premolar extractions.

Gender and Mean Treatment Age
Gender analysis revealed that 34% of patients in our late single phase
treatment group were male in comparison to 35% of patients who were male in our
early two-phase treatment group (Table 3). Males were found to begin treatment on
average 1.11 years later than females in the early two-phase treatment group, but
began single late phase treatment on average 0.79 years earlier on average than
females (Table 12). As females began their peak skeletal growth spurt on average
two years earlier than their male counterparts and are often more dentally advanced
75
, average earlier start ages for females in the early treatment group were expected
and confirmed in this study.
56
In Proffit’s study, 58% of their patients were male, in the mixed dentition,
and had a mean age of 9.9 years at the start of treatment.
17
In Wheeler’s study 61%
of the patients were male, and the average age of all patients starting their study was
9.6 ±0.8 years.
61
In comparison to these previous studies who took into account
skeletal age and measured peak height velocity growth prior to starting treatment,
our average start ages for males and females fall within similar ranges and so are
likely within the target range for growth modification even though hand-wrist films
were not taken in our patient sample.

Gender Specific Treatment Times
In both the early two-phase and late single phase treatment overall treatment
times for males and females were found to be very similar. The less than half a
month longer average treatment times observed in females in both the two-phase and
single phase treatment groups was not found to be statistically significant, p=0.81
and p=0.78 respectively (Table 13). This is despite the noted tendency for girls to
have higher levels of compliance with headgear wear.
19
Fagin and Yang also noted
in their findings that females began treatment at a younger age than their male
counterparts, but that there was no significant differences in overall treatment time.
67
This seemingly discredits the belief that females complete treatment faster due to
higher levels of compliance.

57
Extraction versus Non-extraction Treatment Times
Many hold the belief that extraction therapy is more complicated and
involved and therefore requires more time in fixed appliances. However, when we
examined the averaged treatment times for all non-extraction and extraction patients,
the extraction patients actually completed treatment on average a half a month faster
than their non-extraction counterparts (Table 14). This slight difference in average
treatment time was not found to be statistically significant (p=0.79).
58
Chapter 7: Assumptions

There were several assumptions made in this study. Firstly, that the patient
population in the private practice examined is representative of the patient population
elsewhere in the United States. Secondly, that all measurements made were accurate
and reproducible. Thirdly, and finally, that there were no external variables to distort
the relationship between receipt of treatment and the outcome variables.

59
Chapter 8: Limitations

There were several potential limitations to this study. Firstly, that there was no
selection bias involved since there were a limited number of patient records in the
practice’s archives that met study inclusion criteria, it is possible that this patient
population does not represent the population at large. Secondly, that patient
selection was random, again since patients who obtain treatment in this private office
may not represent the orthodontic population at large. Thirdly, our measurements
were subjected to human error. And finally, we cannot know whether compliance
amongst patients was equal within and between the experimental groups.
60
Chapter 9: Summary

Several previous studies have found only slight variances in premolar
extraction rates, and no differences in skeletal and dental outcomes in patients who
underwent early Class II treatment. This study sought to determine whether
examining patients treated in a private practice, real world setting would yield
different outcomes than previously published institutional studies. Our results
demonstrated significant findings in regards to reduced rates of premolar extractions
in patients treated with headgear in early phase 1 treatment as well as reduced rates
of extractions in the late single phase treatment group who received headgear therapy.
Cephalometric analysis of skeletal and dental outcomes showed similar final skeletal
and dental positioning between the two treatment groups, confirming previous
findings found university studies. Thus, we were able to show that while skeletal
and dental outcomes were similar between early two-phase and late single phase
treatment groups, that the early two-phase treatment group patients experienced far
fewer extractions confirming the success of phase 1 growth modification. Treatment
times were also shown to be minimally increased in the two-phase early treatment
group, and in fact, the early treatment group was shown to be in fully bonded
appliances for six months less than their late treatment group counterparts. Thus, the
argument can be supported that early treatment does in fact yield significant benefits
for patients who place value on retaining their permanent teeth.

61
Chapter 10: Conclusions

1. Comparisons in premolar extraction rates demonstrated close but statistically
insignificance at a p=0.07 level with the early treatment group (20%)
undergoing fewer extractions than the single late phase treatment group
(44%).
2. Treatment time comparisons demonstrated a significantly longer overall
treatment time in the early treatment group as compared to the late treatment
group, 35.75 months and 28.41 months respectively (p<0.01). However, a
significantly less amount of time was spent in braces by the early treatment
group than the late treatment group in the second phase, 22.35 months and
28.41 months respectively (p<0.01).
3. Statistical differences were found during cephalometric analysis of the
following:
Within the Early Treatment Group
a. When comparing end of phase 1 treatment to initial measurements
statistical significance was detected in ANB change which decreased
following phase 1 treatment (initial= 6.89˚, end of phase 1= 4.74˚)
p=0.03.
b. When comparing end of phase 2 measurements to initial values
statistical significance was detected in increases in IMPA (88.61˚ to
97.16˚, p=0.03), reduction in ANB (6.89˚ to 3.22˚, p<0.01), forward
and flaring of both upper and lower incisors, a decrease in interincisal
62
angle (123.9˚ to 118.68˚, p=0.05), and forward movement of
Pogonion (1.07mm to 2.63 mm, p<0.01).
c. When comparing end of phase 2 values to end of phase 1
measurement changes, statistical significance was detected in PogNB
measurements with Pogonion moving forward (1.31mm to 2.63 mm,
p<0.01).
Within the Late Treatment Group
a. When comparing initial to final values statistical significance was
detected in a reduction in SNA (83.54˚ to 80.78˚, p<0.01), ANB
(4.54˚ to 2.17˚, p<0.01), interincisal angle (127.22˚ to 121.76˚,
p<0.01), and increases in U1NA (22.14˚ to 28.06˚, p<0.01), and
PogNB (1.34mm to 2.87mm, p<0.01).
Early versus Late Treatment Groups
a. When comparing initial to final values statistical significance was
detected only in IMPA which increased in both treatment groups
(p*=0.03 and p*=0.09, respectively), however the increase in the
early treatment group was significantly greater (p***=0.05).
4. When comparing cephalometric changes stratified by extraction or non-
extraction status:
a. Early extraction patients and late extraction group patients
demonstrated no statistically significant differences in cephalometric
change outcomes.
63
b. There were also no statistically significant differences in
cephalometric change outcomes between early non-extraction group
patients and late non-extraction group patients.
5. When comparing molar severity scores, a statistically significant change was
detected between initial (0.69) and start of phase 2 (0.13) scores, p<0.01.
6. There was a significant difference in extraction rates when headgear was
utilized in late single phase treatment (23.1% versus 53.6%, p=0.01), but no
statistically significant difference in ANB change whether or not headgear
was used (p=0.96).
7. No statistical significance was detected when comparing treatment duration
and gender, as both sexes finished treatment in the same amount of time.
8. There was a statistically significant difference detected in age of onset of
early phase 1 care with females staring treatment 1.11 years sooner than
males.
9. No statistical significance was detected when comparing treatment duration
and treatment modality, both non-extraction and extraction therapies required
the same amount of treatment time.

64
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Abstract (if available)

Abstract Introduction: Although the pros and cons of early two-phase treatment to correct Class II malocclusions have been examined, there is no study to date relating early growth modification techniques to final extraction rates and tooth position outcomes. Methods: Patients (n=61

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Asset Metadata

Creator Lee, April Jalene (author)

Core Title A comparison of extraction rates in two-phase versus one-phase class II malocclusion patients

School School of Dentistry

Degree Master of Science

Degree Program Craniofacial Biology

Degree Conferral Date 2008-05

Publication Date 04/15/2008

Defense Date 03/10/2008

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag class II,extraction rates,malocclusion,OAI-PMH Harvest

Language English

Advisor Sameshima, Glenn T. (committee chair), Moon, Holly (committee member), Paine, Michael (committee member)

Creator Email aprillee@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-m1122

Unique identifier UC1305797

Identifier etd-Lee-20080415 (filename),usctheses-m40 (legacy collection record id),usctheses-c127-51913 (legacy record id),usctheses-m1122 (legacy record id)

Legacy Identifier etd-Lee-20080415.pdf

Dmrecord 51913

Document Type Thesis

Rights Lee, April Jalene

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Repository Name Libraries, University of Southern California

Repository Location Los Angeles, California

Repository Email cisadmin@lib.usc.edu