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Comparison of premolar extraction rates between one-phase and two-phase class II malocclusion
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Comparison of premolar extraction rates between one-phase and two-phase class II malocclusion
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Content
COMPARISON OF PREMOLAR EXTRACTION RATES BETWEEN ONE-PHASE
AND TWO-PHASE CLASS II MALOCCLUSION
by
Lindsey Hambleton MacFarlane
________________________________________________________________________
A Thesis Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fufillment of the
Requirements for the Degree
MASTER OF SCIENCE
(CRANIOFACIAL BIOLOGY)
May 2011
Copyright 2011 Lindsey Hambleton MacFarlane
ii
Dedication
To my family for all their love and support.
Mark MacFarlane
Cindy Hambleton
Robert Hambleton, D.D.S
iii
Acknowledgements
A special thank you to:
Dr. Glenn Sameshima
Dr. Ronald Garibaldi
iv
Table of Contents
Dedication ii
Acknowledgements iii
List of Tables vi
List of Figures viii
Abstract ix
Chapter 1: Introduction 1
Chapter 2: Literature Review 4
Functional Appliance 5
The Headgear 6
Self Esteem 7
Class II Malocclusion Studies 8
University of Florida Study 10
University of North Carolina Study 12
University of Pennsylvania 15
The Cochrane Review 16
The United Kingdom Studies 17
The University of Southern California Studies, Fagin and Yang 19
The University of Southern California Study, Lee 20
The University of Southern California Study, Fields 21
Chapter 3: Hypothesis 24
Chapter 4: Materials and Methods 26
Subject Screening and Inclusion Criteria 26
Two-Phase Treatment Group-Case Selection 28
Single Phase Treatment Group-Case Selection 29
Patient Sample, Distribution, and Premolar Extraction Rate 29
Cephalometric Tracings and Measurements 30
Statistical Methods 31
Institutional Review Board Approval 31
Chapter 5: Results 32
Premolar Extraction Rates 32
Cephalometric Measurements 33
Molar Severity 39
v
Headgear 40
Treatment Time 41
Age and Gender 42
Chapter 6: Discussion 44
Overall 44
Premolar Extraction Rates 45
Treatment Time 47
Cephalometric Measurements 49
Molar Severity 51
Headgear Use 52
Age and Gender 53
Chapter 7: Conclusions 55
Chapter 8: Limitations 58
Chapter 9: Summary 59
Bibliography 60
vi
List of Tables
TABLE 1: Inclusion Criteria for Previous Class II Studies 9
TABLE 2: Extraction Rates in Single- and Two-Phase Treatment Groups 30
TABLE 3: Frequency of Males versus Females in Our Study 30
TABLE 4: Frequency of Headgear Use in Treatment 30
TABLE 5: Cephalometric Measurements 31
TABLE 6: Extraction Rates in Single-versus Two-Phase Treatment Groups 32
TABLE 7: Comparison of Cephalometric Measurements at Initial, Middle,
and Final Time Points for Two-Phase Treatment Group 34
TABLE 8: Comparison of Cephalometric Measurements at Initial
and Final Time Points for Single-Phase Treatment Group 34
TABLE 9: Comparison of Change in Cephalometric Measurements
Between Single and Two-Phase Treatment Groups 35
TABLE 10: Comparison of Cephalometric Measures at Initial and
Final Time Points in Extraction Cases 36
TABLE 11: Comparison of Cephalometric Measurements at Initial
and Final Time Points in Non-Extraction Cases 36
TABLE 12: : Comparison of Cephalometric Measurements at Initial
and Final Time Points Between Single- and Two-Phase
Treatment Groups 37
TABLE 13: Definition of Molar Severity Score 40
TABLE 14: Molar Severity 40
TABLE 15: Change in ANB With and Without Headgear 40
TABLE 16: Total Treatment Time in Single- versus Two-Phase
Treatment Groups 41
vii
TABLE 17: Total Treatment Time in Extraction versus
Non-Extraction Cases 42
TABLE 18: Total Treatment Time in Male versus Female Subjects 42
TABLE 19: Sex Specific Mean Ages in Single- versus Two-Phase
Treatment Groups 43
viii
List of Figures
FIGURE 1: Design of University of Florida Study 10
FIGURE 2: Design of University of North Carolina Study 14
FIGURE 3: Design of Our Study 28
FIGURE 4: Bar Graph of Patients with Tooth Extractions 33
FIGURE 5: Initial and Final ANB for Single-Phase and Two-Phase 38
FIGURE 6: Final ANB Angles for Single-Phase and Two-Phase 39
FIGURE 7: Bar Graph Depicting Extractions with Headgear or
No-Headgear in Single-Phase 41
ix
Abstract
Introduction: The pros and cons of early two-phase treatment of Class II malocclusion
have been examined recently. This study examines how growth modification will affect
premolar extraction rates as well as final cephalometric outcomes.
Methods: Patients (n=46; ages 7-17) from a private practice of an American Board of
Orthodontics diplomat in Southern California were evaluated. 27 patients were treated in
a single-phase, and 19 were treated in two-phases. Full records of each patient were
examined to compare premolar extraction rates in the permanent dentitions and resulting
cephalometric measurements in single- and two-phase treatment groups.
Results: Out of the 27 patients undergoing single-phase treatment, 13 out of 27 (48.1%)
required premolar extractions. 6 out of the 19 (31.6%) two-phase treatment patients
needed extractions. Extraction rate between the two groups proved not to be significant.
(p=0.261) Final cephalometric changes show no significant changes between the two
groups.
Conclusions: Early orthodontic intervention in Class II malocclusion does not provide
reduced rates in premolar extraction and does not affect cephalometric outcomes.
1
Chapter 1: Introduction
The timing of Class II treatment in orthodontics has been a longtime debate. The
question raised is whether to treat children early in a two-phase treatment plan or wait
until they are adolescence and complete a single-phase treatment plan. Early intervention
as the standard has wavered over the course of orthodontic history. Now many
orthodontists rely on his expertise, past experiences and instinct to make the decision
regarding timing. As 1 out of every 4 children between the ages of 10 and 12 maintains
Class II maloclussion
1
, the proper timing of treatment of Class II malocclusion is of great
importance to the orthodontic community.
Class II patients have notoriously been difficult to treat due to the irregular nature
of lower jaw growth. The following may be present in a Class II malocclusion: deficiency
in the mandible, excess in the maxilla, or both. Patients with Class II malocclusion tend
to have horizontal deficiency, which cause the mandible to rotate downward and
backward.
2,3,4,5
. Early intervention has allowed the orthodontist to alter the growth in
preadolescent years, but the decision remains in the orthodontist’s hands. There are three
options for treating Class II malocclusion. Firstly, there is a two-phase treatment by
which there is an early intervention phase and a later, adolescent phase. The first phase of
treatment allows limited orthodontic goals to be achieved, namely a Class I molar, incisor
alignment, decreasing overbite and overjet, growth modification using various compliant-
dependent appliances, and psychosocial advantages. The second phase completes the
final detailing and finishing of orthodontic treatment. The second option entails a single-
2
phase treatment that achieves all the specific orthodontic goals during adolescent years.
However, growth modification cannot be achieved during this stage and often times,
dental compensation is used to disguise skeletal discrepancies (i.e. extractions of
premolars). Finally, orthognathic surgery can be completed to achieve the most optimal
skeletal and dental orthodontic positions. Surgery can only be completed after growth has
ceased and is a very invasive procedure.
Advocates for early treatment believe that the first phase of treatment allows for a
more efficient and easier second phase, therefore decreasing the chances of premolar
extraction and orthognathic surgery.
6
Other benefits for the two-phase treatment include
the following: increased cooperation with extraoral appliances, decreased risk of injury to
upper incisors, and greater psychosocial effects.
6,7,8,9,10,11
On the other hand, the
orthodontists who advocate for a single-phase treatment believe that the first phase does
not prove any better final outcome nor does it have any more efficient skeletal and dental
outcome. Additionally, the single phase provides a more effective monetary option in
many orthodontists’ viewpoints.
12
Due to the fact that most orthodontists have relied upon their own expertise to
determine what the best Class II treatment, the World Health Organization realized a
need for a study concerning the proper timing of Class II malocclusion. These
prospective randomized clinical trials were funded by the National Institutes of Health
and proved that early two-phase treatment was not a benefit for patients. The only
statistically significant findings in this study were as follows: similar ABO and PAR
scores in cast evaluation increased treatment timing and increased monetary investment.
3
No significant findings were discovered in final ANB, overjet and PAR scores. These
findings all suggested that there is no advantage to two-phase treatment
13
and this
sparked a fury of debate among the orthodontic community.
Several of the studies did, indeed, find that number of premolar extractions
amongst the two groups did border on significance, however none of the studies
thoroughly investigated the cephalometric findings between the initial and final
outcomes.
14, 15,16,17,18,19,20
Cephalometric analysis provides an accurate account of
skeletodental features and is used commonly in treatment planning and diagnosis in
orthodontics. Therefore, if a relationship could be established between early treatment
and decreased number of premolar extractions, then the benefit for a two-phase treatment
could be determined.
This study aims to examine how growth modification in the two-phase treatment
allows for a reduction in premolar extraction rates and more ideal final cephalometric
outcomes than the single-phase treatment. To investigate this hypothesis, 450
consecutively treated cases from a private practice in Southern California were examined.
46 fit the inclusion criteria and were retained for the study. The purpose of the study was
two-fold: 1. Compare premolar extraction rates among two-phase and single-phase
treatment 2. Compare final and initial cephalometric outcomes in the two-phase versus
the single-phase treatment.
4
Chapter 2: Literature Review
There has been much debate as to the treatment of class II malocclusion in
orthodontics. The debate remains to stand whether to treat patients early, using a two-
phase technique or to wait and treat children later, implementing a one-phase technique.
Various studies have investigated the benefits of either single-phase or two-phase
treatment, but the question still remains. Recently, most studies have found that a single-
phase treatment during adolescent ages have proven to be a more efficient approach.
16, 17,
18, 20, 21,22,23,24
Specifically, these studies state that two-phase treatment provides the same
outcome as one-phase treatment. However, advocates for the two-phase treatment defend
that establishing a class I molar relationship early in treatment allows for a simpler
second stage of treatment. Therein lies the question: does the first phase of a two-phase
treatment simplify the second phase rather than doing a single one-phase treatment? More
importantly, does a first phase of a single-phase treatment allow for less premolar
extractions and does it impact the changes in the cephalometric values?
Many advocates believe that starting orthodontic and/or orthopedic treatment
earlier rather than waiting until later allows a more effective and efficient treatment plan.
Firstly, many authors believe that the tissues are easily altered at a young age. Secondly,
it is believed that pre-adolescent children are more compliant than adolescent children.
Animal models have shown that the use of functional appliances
25,26,27
and extra-oral
forces
28
can affect growth in adults and young animals. The studies found greater change
in younger animals. This effect seems to be due to bones being less mineralized as well
5
as ligaments and sutures being more cellular.
29,30
Therefore, the growing tissues are more
malleable and responsive to external forces. Clinicians have also tested this hypothesis on
humans. Brodie et al found that orthopedic change is best when the growth is active
31
with the greatest change can be discovered at the beginning of adolescent growth.
32,33
Many early treatment appliances necessitate the cooperation of the patients.
Several studies found that cooperation is best during the preadolescent age. Several
studies indicated a relationship between preadolescent age and cooperation, namely those
children who did well in school.
34,35,36
Younger patients still yearn for pleasing adult
figures, whereas, teenagers tend to rebel. On the other hand, some studies found no
relationship at all.
37,38
Different treatment modalities are preferred by orthodontist to achieve the goals
of early treatment, namely decreasing overjet and establishing Class I molar. The
different modalities used include use of a combination of headgear, functional appliances,
and fixed appliances. All of these modalities are used to achieve facial balance, however,
the varying skeletal and dental effects are inconsistent.
The Functional Appliance
A variety of functional appliances are available for use within the orthodontic
office. Activators, Frankel’s, Bionators and Twin Block appliances are only a few
functional appliances that position the mandible more forward, thereby stimulating
mandibular growth. Animal studies have been conducted that demonstrate the
effectiveness of repositioning the mandible, thereby stimulating mandibular growth.
25, 26,
6
39, 40, 41
Human studies using Frankel’s and activators have confirmed these findings to a
lesser degree as well.
42, 43,44, 45, 46
In addition to the orthopedic changes produced by the
functional appliances, there are also dentoalveloar changes. Namely, the lower incisors
are proclined through the use of some functional appliances and help reduce overjet.
47, 48,
49, 50, 51,
52
O’Brien et al found that early treatment with a twin-block appliance both
decreased overjet and helps decrease the severity of malocclusion.
52
O’Brien et al also
investigated the difference between using the Herbst or the Twin-block appliance for
early treatment.
53
He found that he received better patient cooperation and less failure-to-
complete treatment when using the Herbst appliance. 12.9% of patients using the Herbst
had failure-to-complete, whereas, 33.6% of patients using the Twin-block did not
complete the treatment. There is also evidence that the functional appliances restrict
maxillary growth.
44, 46, 48
Although there are advocates that functional appliances mainly
affect dentoalveloar change, there are still opponents who question whether the growth is
due to natural growth and how much is true skeletal change and/or dentoalveolar
changes.
The Headgear
The headgear has been a widely used extra-oral appliance by orthodontists since
the 1800s. Many orthodontists now believe that the headgear is an added necessity to
accompany fixed brackets to help correct Class II malocclusion. Animal studies show
that posterior extra-oral forces can benefit Class II treatment by restricting the horizontal
7
growth of the maxilla.
28, 53, 54, 55, 56
Some studies believe that the headgear can also affect
mandibular remodeling even though it is only connected to the maxilla.
57
The headgear cannot only produce orthopedic effects, but also dentoalveolar
effects. At this point, the amount of dentoalveolar change created by a headgear is
debatable. Poulton’s study found that orthopedic change in his case was about 20-30%
58
,
thereby crediting most of the change to dentoalveolar change. Gianelly also confirmed
these findings.
59
The major change attributed to the use of a headgear is intrusion and
distalization of the maxillary molar, helping to correct Class II malocclusion.
60, 61, 62, 63
Self-Esteem
Self-esteem and an individual’s notion of attractiveness have been studied
worldwide. Studies have demonstrated a correlation between malocclusion and
psychosocial stigmas.
9, 10, 64, 65
Shaw et al discovered this correlation to be extremely
apparent in the pre-adolescent years. In this study, 531 children between the ages of 9
and 13 were interviewed. It was found that teasing about teeth was the fourth most
common cause of teasing. MacGregor also investigated malocclusion and teasing. He
found that children’s malocclusion also magnifies one’s anxiety.
8
Moreover, the children
with milder forms of malocclusion maintained higher anxiety than those with worse
malocclusion because those with greater deformity found a way to deal with the anxiety it
provoked. O’Brien et al further examined self-esteem and the use of twin-block
appliances in early treatment. He concluded that self-esteem did increase and children
8
had a more positive childhood experience.
66
Therefore, it would seem helpful to correct
malocclusion at an early age to avoid psychosocial stigmas and unnecessary anxiety.
Class II Malocclusion Studies
The National Institute of Dental and Craniofacial Research (NIDCR) funded a
prospective randomized clinical trial to investigate the treatment of Class II malocclusion
in 1987 and these studies truly spurred on treatment questions. Conducted by the
University of Florida and University of North Carolina, they hoped to establish a protocol
for proper timing of Class II malocclusion. The schools sought to determine whether
growth modification would affect the outcome as well as subsequent treatment. Each
study maintained a control group (those treated in a single phase) and an experimental
group treated in two-phases.
NIDCR also funded a study at the University of Pennsylvania comparing the use
of headgear and functional appliances for Class II treatment. However, this study did not
have a control group. Therefore, a more recent study has been carried out in the United
Kingdom examining Class II treatment using functional appliances, headgear treatment,
as well as a control group.
In an effort to minimize the bias discovered at a teaching institution, the
University of Southern California studies used private practices across the United States
to determine the efficiency of early two-phase or later single-phase treatment. Fagin and
Yang compared the outcomes of early two-phase versus late single-phase treatment of
moderate-to-high angle Class II patients. Both Lee and Fields (in separate studies)
9
evaluated the number of premolar extraction rates in early two-phase versus single-phase
class II patients.
All of these studies will be described in detail below.
Table 1: Inclusion Criteria for previous class II studies
10
The University of Florida Study
Drs. Wheeler and Keeling implemented a prospective, longitudinal randomized
study at the University of Florida. The University of Florida implemented a plan as
follows: Firstly, the patient must possess a Class II molar relationship (minimum bilateral
½ step or greater than ½ step unilaterally). Patients needed to have positive overbite and
overjet. There was no upper limit on the SN mandibular plane angle. Finally, patients
could not have more than three permanent premolars or canines erupted.
Figure 1: Design of University of Florida study
11
Phase I treatment at the UFA lasted 24 months of until Class I molar was
achieved, whichever approached first. To judge initial severity of Class II molar
occlusion, the following scale was used: mild (bilateral half-step Class II molar),
moderate (unilateral three-quarter step Class II molar) or severe (bilateral full step Class
II molar.)
The patients were then divided into three subgroups, namely an observation
group, a group treated with a bionator and a group treated with a headgear/biteplane.
Those who had a functional appliance or headgear underwent a first phase of treatment.
Depending upon the SN mandibular plane angle (either above or below 40), either
cervical pull or high pull headgear was used. Patients were also examined based upon
race and sex during this study. Each group was treated and analyzed by four doctors at
the University of Florida. After phase 1, recall patients were seen every six months in
between phase 1 and phase 2.
The University of Florida showed significant results following early treatment
amongst all three groups. At the end of treatment, class I molar was achieved in 83% of
the bionator group, 100% of the headgear group and 14% of the observation group. The
headgear group demonstrated a greater correction of Class II correction during early
treatment according to multivariate analysis. Furthermore, the skeletal and dental effects
in the headgear and bionator groups improved mandibular growth 0.5-0.75 mm per year
during the first phase of treatment and no relapse were detected one year after treatment.
Molar correction was achieved in 30% of those starting with mild molar severity, 10%
with moderate severity and 3% with severity. (p=0.007). With the use of the bionator or
12
headgear in phase 1, success was even greater. 65% with mild initial molar severity, 49%
with moderate molar severity and 29% with severe molar severity. (p=0.001).
After the second phase was completed, there were no significant findings with
respect to initial PAR or final PAR amongst the three groups. The patients were
examined for three years post treatment for effects on stability. Once again, there were no
significant differences discovered between the early and late treatment groups.
When examining extraction rates, the three groups were significant. 20% of the
observation group, 8% of the bionator group, and 12% of the bionator group had
premolars extracted (p=0.07). Therefore, premolar extractions were twice as likely in the
phase 1 observation group as they were with headgear group and almost three times as
likely with the bionator group.
The University of Florida found that the two-phase treatment group finished about
6 months earlier than those patients treated in one phase. This may be due to the 24
month first phase, which allowed for a faster second phase. Furthermore, four supervising
orthodontist oversaw the treatment of all patients in this institution. The University of
Florida concluded that early treatment provided no advantage (both skeletally and
dentally) than the later, single-phase treatment.
19, 20, 67, 22, 68
The University of North Carolina Study
Drs. Tulloch and Proffit sought to examine specific questions regarding the
optimal timing of Class II treatment. From 1998 to 2001, the study was conducted at the
University of North Carolina. Patients needed an overjet of greater than 7mm rather than
13
University of Florida’s molar classification. Patients were not allowed to have received
any previous orthodontic habit appliance therapy or space maintenance. Additionally, if
their SN mandibular plan angle was greater than 2 standard deviations away from the
norm or they had obvious facial asymmetries, they were excluded. Although University
of Florida could not have more than three permanent teeth or canines erupted, UNC’s
patients were all in mixed dentition and were at least one year before their peak height
velocity.
Subjects were then divided into the following: observation group, functional
appliance group and headgear group. University of North Carolina chose to only use
combi-headgears whereas UFA used both cervical pull and high pull headgears as
needed. Additionally in phase 1, one supervising faculty treated all the patients.
However, in phase 2, the patients were divided randomly and four supervising faculty
members oversaw the treatment of the patients.
14
Figure 2: Design of University of North Carolina Study
At the end of the first phase, there were considerable changes found in the
headgear or bionator groups when compared to the observation group. 75% of the
headgear or bionator group showed positive results. The headgear seemed to restrict the
growth of the maxilla while the functional appliance group showed an increase in
mandibular length and greater chin projection.
17,18, 24, 69
About 30% of all patients attending the UNC clinic received extractions, whereas
those participating in the study were found to be slightly less.
17
The combination
15
headgear group demonstrated the least number of extractions, followed by the
observation group. The bionator group had the most number of premolar extractions and
showed three degrees more proclination of the lower incisors that the other groups during
phase 1.
16
The results following phase 2 showed no advantage in regards to skeletal change,
final occlusion, alignment and length of treatment.
16, 17, 18, 21
PAR scores were the same
amongst the early treatment and late treatment group. In conclusion, the University of
North Carolina saw no benefit to early treatment. Regardless of the severity of the initial
malocclusion, early treatment did not prove to have any advantage.
The University of Pennsylvania
A prospective randomized clinical trial was performed at the University of
Pennsylvania. This study sought to evaluate early treatment of the Class II malocclusions
in pre-adolescent children. Specifically, the purpose of this study was to compare the use
of extraoral traction and functional appliances to distalize molars at an early age and to
determine if early childhood treatment is necessary.
70, 15
Inclusion criteria for this study is as follows: Class II division I malocclusion, no
prior orthodontic treatment, minimum ANB of 4.5 degrees, ages 7-12.5/13, and expected
residential stability for 3 years. Patients were then treated with either a headgear or a
Frankel appliance. Every two months dental casts were taken and evaluated for any
dental changes.
16
The results demonstrated that the headgear and Frankel appliance did correct
malocclusion. The headgear seemed to distalize the molars and restrict growth of the
maxilla whereas the Frankel appliance restricted the growth of the maxilla and allowed
the mandible to grow forward while proclining the lower incisors.
70,14,15
In conclusion, both appliances allowed differential growth to occur during the
early phase of two-phase treatment. However, treatment in later childhood was shown to
be as effective as those treated in early to mid-childhood.
70
The Cochrane Review
The Cochrane Review study entitled, “Orthodontic treatment for prominent upper
front teeth in children” was completed regarding the efficiency of two-phase treatment.
Children who had received initial orthodontic care during the ages of 7 to 9 were
evaluated for the correction of class II malocclusion. What sets this study apart is that the
Cochrane library searched all databases with no restriction on language or controlled or
randomized clinical trials.
The aim of this treatment was correction of prominent maxillary incisors. Patients
ages 16 years or younger were included in this study. Inclusion criteria stated these
patients must have completed early orthodontic intervention whereby fixed or removable
appliances with headgear were used. For comparison, a control group was used.
Eight trials fit the criteria with a total of 592 patients who had received Class II treatment.
17, 67, 53, 52, 71, 72, 73, 74
ANB and final overjet were found to be significant after completion of phase 1.
Headgear did reduce the ANB angle greatly and a significant effect on the amount of
17
overjet. When comparing final ANB, PAR score and final overjet, the headgear and
functional appliance had similar results. No significant difference was demonstrated
among the final ANB, PAR score or final overjet after completion of phase 2 in those
patients who had received early orthodontic treatment or later treatment.
In conclusion, the Cochrane review did not recommend beginning treatment prior
to age 10. Early treatment was advised for selected patient with functional crossbites,
accidental fracture of front teeth, and as means to increase self-esteem.
75
The United Kingdom Studies
Dr. O’Brien investigated the effectiveness of the early orthodontic treatment with
the Twin-Block appliance in a two-part study. The first part of his study observed the
skeletal and dental effects of the Twin-Block on Class II, division 1 malocclusion,
whereas, the second part looked into the psychosocial effects.
For the first study, fourteen hospital-based orthodontists in the United Kingdom
oversaw the orthodontic treatment. O’Brien believed the United States studies (namely
UNC and UFA studies) were not credible to the “real world” because they were carried
out at learning institutions. Therefore, he chose to use hospital-based orthodontists.
Patients chosen for this study needed a minimum of 7mm overjet, no craniofacial
abnormalities, pre peak height velocity as determined by a cervical spine analysis, and an
eagerness to participate. 174 children, aged 8 to 10 years old, were randomly assigned to
receive treatment using Twin-Block therapy or an observation group. A patient was
considered noncompliant if there was less than 10% change in overjet after 6 months.
52
18
14 of the children in the treatment group did not complete treatment with the Twin-Block
appliance, either due to compliance or lack of response.
O’Brien concluded that early intervention with the Twin-Block appliance reduced
dental overjet, severity of malocclusion, and molar discrepancies. Most of this change
was due to dental change (41%), whereas skeletal change only accounted for 27% of the
change. As calculated by Pancherz variables, there were considerable similarities
amongst the Twin-Block treatment group and the observation group. Pancherz
cephalometric analysis is a certain type of orthodontic analysis that uses the occlusal
plane and its perpendicular line running through sella to evaluate change in a patient.
76
This data supports the findings of both the University of North Carolina and the
University of Florida studies.
In his second part of the study, O’Brien investigates the psychosocial effects of
treatment with a Twin-Block appliance in Class II, division 1 malocclusion. One of the
aims of early Class II treatment is to improve the psychosocial environment for the
children. Therefore, the main purpose of this study aimed to determine whether features
of malocclusion, sex and socioeconomic status in fact influence self-esteem and social
experiences of the children. The second aim of the study is whether children have
realistic expectations of the benefit of early treatment.
176 children participated in the study and received a Twin-Block or participated
in the control group. Data was collected at the initial visit and then at 15 months after
treatment. The Piers-Harris Children’s Self Concept Scale was completed by the children
at the beginning of treatment and then again at 15 months.
66
19
The results discovered that children with early orthodontic treatment described
higher feelings of self-esteem and a more positive childhood experience. However,
according to the study, the patients who wanted orthodontic treatment had a higher
normal range of self-esteem from the beginning. The self-esteem scores from the
questionnaires used in the study supported this notion.
66
In conclusion, it was discovered that treatment with the Twin-Block appliance
does improve self-esteem among patients.
The University of Southern California Studies, Fagin and Yang
Two former residents from the University of Southern California completed a
retrospective master’s thesis about the early treatment of high angle Class II malocclusion
patients. Patient’s records were collected from three different offices of ABO diplomats
in Los Angeles, Vancouver, and Seattle.
The inclusion criteria for this study was a minimum of 4mm overjet, Class II
molar relationship of any kind, ANB greater than 5 and either Sn-GoGn greater than 37
degrees or FMA greater than 30 degrees. Patients were randomly grouped into a headgear
group, functional appliance group or an observation group. After completing of Phase 1,
patients either continued directly into phase 2 or active treatment was discontinued.
Phase 2 treatment began if at least 20 out of 24 possible permanent teeth were clinically
visible in the mouth. Patients beginning with a single-later phase also adhered to these
phase 2 regulations.
20
The results determined that early and later treatment groups were similar with
regards to vertical relationships and antero-posterior relationships. The difference
between the pre and post-treatment IMPA angle was statistically significant. (p<0.05)
Initial PAR, final PAR or PAR change was not significant among the early or later
treatment groups. Treatment time was significantly longer for the early treatment group
than the later treatment group. Finally, the early treatment group had fewer extractions,
but this was not statistically significant (p=.17)
77
The University of Southern California Study, Lee
Lee from the University of Southern California examined whether patients treated
in a private practice would produce similar results to the findings of the University of
North Carolina and the University of Florida studies.
79
Patients were evaluated in the
private office of an American Board of Orthodontics Diplomate in Yorba Linda, CA.
The study was aimed at discovering whether or not Class II patients treated in two-phases
would have less premolar extractions than those patients treated in a single-phase.
Patients included in this study needed a minimum of a bilateral half-step or
unilateral three-quarter step Class II molar, positive overbite and overjet, no ankylosed
teeth and no treatment plan for orthognathic surgery. 61 patients fit this criteria and were
analyzed for this study.
Lee discovered that those Class II patients who wore a headgear in the early first
phase of treatment were less likely to have premolar extractions. Additionally, the use of
the headgear allowed reduced number of premolar extractions to be conducted in the
21
single-phase patients as well. Although the numbers were not statistically significant,
23.1 % of patients treated with a headgear had premolar extractions versus 53.6% of
patients without a headgear who experienced extractions. Cephalometric analysis of
skeletal and dental results proved to not be significant, thereby confirming the findings
from UNC and UFA. There were far fewer premolar extractions completed in the early
two-phase patients, however, it was not statistically significant. (p=0.07).
The University of Southern California Study, Fields
Fields from the University of Southern California sought to investigate the
difference between single-phase and two-phase treatment at a private office in Southern
California
79
. Fields also sought to compare the premolar extraction rates in Class II
patients in single- vs. two-phase treatment. (Single- phase treatment seemed to have more
premolar extractions as noted by Dolce et al.)
The study used 98 consecutively treated cases, 63 in single-phase and 35 in two-
phases. The study was conducted at an ABO diplomat’s office in Yorba Linda, CA where
one private orthodontist oversaw the treatment of all cases.
The study conducted by the University of Southern California resident concluded
that there were more premolar extractions if patients waited for treatment in a single-
adolescent phase treatment. Moreover, the premolar extraction rates were approximately
double to that of the two-phase treatment group, which was statistically significant
(p=0.01). These results were similar to the findings at the University of Florida study,
however, the University of Florida had a much larger sample size (208). Of those
22
patients treated in a single-phase at the University of Florida, 20% required premolar
extractions. Within the growth modification group, 8% of the bionator group and 12% of
the headgear/biteplane group required premolar extractions.
The USC resident found that changes in cephalometric measurements were not
significant between single- or two-phase treatments.
79
This correlated with the findings
from the University of Florida and the University of North Carolina studies. Specifically,
investigating the ANB change resulted in no statistical significance amongst the two
groups. Furthermore, there was no statistical change noted in the IMPA (incisor
mandibular plane angle).
The USC study also investigated the molar severity after the first phase of
treatment. Due to the limitations at the private office, this was difficult to assess. This
particular orthodontist only treated the first phase for 12-13 months, even if Class I molar
was not achieved. Finally, two-phase treatment time took approximately six months
longer than one-phase treatment. Additionally, these two-phase patients spent seven
months less in fixed appliances.
The findings of this study strongly oppose those reported by the University of
Florida and the University of North Carolina. Similar to the finding by King et al, it was
discovered that two-phase treatment groups experienced an increased total treatment time
and a slight reduction in the second phase. This longer treatment time may be due to the
fact that universities have more than one supervising faculty and using various bracket
systems and archwires. The University of Southern California study used only one
private office with one private orthodontist overseeing all cases. Additionally, those
23
patients treated with premolar extractions in the USC study actually completed treatment
one month earlier than non-extraction cases.
24
Chapter 3: Hypothesis
1. There is a statistically significant difference in premolar extraction rates between
single-phase and two-phase treatment
2. There is a statistically significant difference in cephalometric outcomes between
single-phase and two-phase treatment groups
a. Single phase
i. Compare initial and final cephalometric outcomes
b. Two-phase
i. Compare initial and end of first phase cephalometric outcomes
ii. Compare end of first phase and final cephalometric outcomes
iii. Compare initial and final cephalometric outcomes
3. That there is statistically significant differences in comparing cephalometric
outcomes to extraction rates
a. Compare single and two-phase treatment extraction patients
b. Compare single and two-phase nonextraction patients
4. There is statistically significant reduction in molar severity for two-phase
treatment when comparing initial molar severity and molar severity at the
beginning of Phase 2.
5. There is a statistically significant difference in total treatment time and time spent
wearing appliances between single and two-phase treatment groups.
25
6. There is a statistically significant correlation between those patients wearing
headgear in a single-phase and a more ideal ANB and fewer extractions than
those who did not wear a headgear.
Secondary Hypothesis
1. There is a statistically significant difference between length of treatment time and
gender, with females finishing orthodontic treatment faster than males.
2. There is a statistically significant difference between age of patient at start of
treatment with females beginning treatment at an earlier age than males
3. There is a statistically significant difference between length of treatment and
treatment modality, with non-extraction cases finishing faster than extraction
cases.
26
Chapter 4: Materials and Methods
Subject Screening and Inclusion Criteria
The source materials for this retrospective study were collected from a private
practice of an American Board of Orthodontics (ABO) Diplomate in Covina, CA. This
particular orthodontist has been practicing for twenty-five years using the .018 appliance.
450 consecutively treated cases were screened for Class II malocclusions that were either
treated in two-phase or single-phase treatment regardless of the age upon presentation.
This particular orthodontist aimed to perfect cephalometric numbers to Class I norms and
improve the patient’s profile with his treatment.
To ensure that patients were truly skeletally and dentally class II prior to the start
of treatment, strict inclusion criteria was assembled. Screenings were conducted in two
different rounds. Inclusion criteria were as follows: all patient models were examined
from January 1998 to December 2004 to detect Class II malocclusion. A minimum of
bilateral quarter-step Class II was maintained. Those patients under the age of 16 years
who presented with Class II malocclusion with at least unilateral quarter-step Class II
malocclusion were examined. Patients with abnormally contoured restorations were
excluded as well as those patients who had previous space maintenance therapy. The
initial screening resulted in 205 patients who would undergo the second round of
screening.
The second round of inclusion criteria were as follows: a minimum of bilateral
half-step or unilateral three-quarter step Class II molar classification, full permanent
27
dentition with the exception of third molars, positive overbite, positive overjet and
complete orthodontic records. Complete orthodontic records included initial and final
lateral cephalometric radiographs, photographs, and orthodontic models. Patients who
had ankylosed teeth and surgical treatment plan were excluded. No limit was established
regarding mandibular plane angles nor the number of teeth erupted into the oral cavity.
Following the second round of screening, there were 46 patients remaining for the study.
28
Figure 3: Design of our study
Two-Phase Treatment Group-Case Selection
The inclusion criteria for the two-phase treatment group were as follows:
minimum bilateral half step or unilateral three-quarter step Class II molar classification,
positive overbite, positive overjet. Patients excluded from the study were those with
missing teeth (other than third molars), ankylosed teeth, and patients with any surgical
treatment plan.
29
The first phase of this treatment was completed using a headgear with a 2x4
appliance or a headgear with a biteplane in this particular office where the study was
conducted. Headgear growth modification was used from 12-15 months or until Class I
molar classification was achieved. After completing the first phase of treatment, patients
were given a retainer or no appliance at the discretion of the orthodontist.
Single-Phase Treatment Group-Case Selection
Selection for the single-phase treatment group was the exact same as the two-
phase treatment group. The single-phase patients presented at a later age (usually
adolescence) and usually only had E’s remaining in the oral cavity when treatment began.
Headgears were used to correct mild-moderate Class II malocclusions.
Patient Sample, Distribution, and Premolar Extraction Rate
Of the 46 patients completed Class II treatment, 27 were completed in a single-
phase, whereas, 19 were completed in two-phase treatment. Out of the 27 patients
undergoing single-phase treatment, 13 (48.1%) required premolar extractions. 6 (31.6%)
patients out of the 19 two-phase treatment patients needed extractions. Extractions were
mostly needed to help correct crowding and decrease IMPA in this practice.
30
Table 2: Extraction Rates in Single- and Two-Phase Treatment Groups
Table 3: Frequency of Males versus Female in Single or Two-Phase Treatment
Table 4: Frequency of Headgear Use in Treatment
Total Single-Phase Two-Phase
Headgear 33 14 19
No Headgear 13 13 0
Cephalometric Tracings and Measurements
All lateral cephalometric radiographs (initial, progress, and final) were scanned
using an Epson Expression (Epson, US) at 300 dpi resolution. Dolphin Imaging 10.5
Premium software (Dolphin Imaging Company, US) was then used to trace each
radiograph. The cephalometric measurements and statistics were computed using the
digitized tracings. To evaluate linear, angular and proportional changes, eleven different
cephalometric measurements were used (see Table 5). For the single-phase treatment
group, initial and final cephalometric tracings were analyzed. Two-phase treatment
groups had three respective cephalometric tracings (initial, progress, and final).
Total Extract Nonextract
1 Phase 27 13 14
2 Phase 19 6 13
Total 46 19 27
Total Single Phase Two Phase
Male 25 11 14
Female 21 16 5
31
Table 5: Cephalometric Measurements
A-P Maxilla SNA
A-P Mandible SNB
Maxilla to Mandible ANB
Lower Incisor L1-NB, L1-NB (mm)
Vertical (Skeletal) FMA (MP-FH)
Dental Relationship Interincisal Angle (U1-L1)
Upper Incisor
U1-NA, U1-NA (mm)
Chin Projection
Pog-NB (mm)
Statistical Methods
To evaluate the difference in extraction rates between the single-phase and two-
phase treatment groups, the Pearson chi squared test was used. The sample size of the
two-phase extraction patients was small, therefore, the Wilcoxon signed rank test was
used to calculate a change in a continuous variable for the group (i.e. change in ANB for
single-phase patients). The Mann-Whitney-Wilcoxon U-test was used to detect changes
of a continuous variable between different groups (i.e. ANB change between single-and
two-phase treatment groups). The following descriptive statistics for each were reported:
means, standard deviations, and p-value.. Significance was established at alpha ≤ 0.05 for
Pearson chi squared test and p≤ 0.01 for all other statistical analyses.
Institutional Review Board Approval
The proposal to undertake this investigation was approved by the Institutional Review
Board (IRB) on July 8, 2010. USC UPIRB # UP-10-00199
32
Chapter 5: Results
Premolar Extraction Rates
The two-phase treatment group showed a 31.6% overall extraction rate with 6 out
of the 19 patients receiving extractions. The single-phase treatment group revealed a 48%
extraction rate with 13 out of 27 patients receiving extractions. The difference in
extraction rates between the single- and two-phase treatment groups was found to not be
significant as Table 6 shows below (p=0.261). The p-value is 0.261 as measured by the
Pearson Chi Squared test. Figure 4 shows the difference in extractions between the
single-phase and two-phase treatment groups.
Table 6:Extraction Rates in Single-versus Two-Phase Treatment Groups (Chi-Squared
Contingency Table)
Total Extract NonExtract p
1 Phase 27 13 (48.1%) 14(51.9%) 0.261
2 Phase 19 6(31.6%) 13(68.4%)
Total 46 19 27
33
Figure 4: Bar Graph of Patients with Tooth Extractions
Cephalometric Measurements
Similar cephalometric measurements were demonstrated when analyzing early
two-phase treatment. Overall, there was no statistical significance found when examining
the difference in the cephalometric measurements as shown by Table 7. The exception is
PogNB mm during the middle to final of two-phase treatment when compared the initial
to final time points in two-phase treatment. From the middle to final time point of two-
phase treatment, PogNB mm changed from 2.4 to 3.7 (p ≤0.01) and from the initial to
final points of two phase, PogNB mm changed from 1.9 to 3.7 (p≤ 0.01).
Table 8 examined the changes among initial and final time point for single-phase
treatment group. Most of the cephalometric numbers were found to be similar, with the
exception of SNA, ANB, and Pog NBmm. The Wilcoxon signed rank test was used. SNA
Single Phase Two Phase
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Proportion with Extractions
Treatment Group
Extractions by Single or Two Phase Treatment Group
34
decreased from 82.3 to 80.7 (p≤ 0.01), ANB decreased from 5.0 to 4.2 (p≤ 0.01), and
PogNBmm increased from 1.2 to 2.3 (p≤ 0.01).
Table 7: Comparison of Cephalometric Measurements at Initial, Middle, and Final Time
Points for Two-Phase Treatment Group
Initial Middle p
1
Final p
2
p
3
SNA 82.9+/-4.2 82.1+/-3.5 0.112 81.6+/-3.4 0.389 0.027
SNB 77.0+/-3.4 76.9+/-3.6 0.625 77.1+/-3.7 0.539 0.781
ANB 5.9+/-2.6 5.3+/-2.6 0.063 4.5+/-2.6 0.135 <0.01
U1NAmm 4.9+/-2.6 4.2+/-2.4 0.300 4.4+/-1.5 0.585 0.407
U1NAdeg 19.2+/-7.2 17.4+/-5.6 0.469 19.7+/-5.7 0.184 0.952
L1NBmm 6.1+/-3.2 6.1+/-3.1 0.901 9.9+/-9.3 0.022 0.028
L1NBdeg 26.1+/-10.9 26.6+/-6.7 0.913 28.2+/-10.1 0.334 0.220
PogNBmm 1.9+/-1.7 2.4+/-2.0 0.152 3.7+/-2.5 <0.01 <0.01
IntAng 127.5+/-13.3 131.3+/-9.3 0.227 124.9+/-8.7 0.051 0.571
FMA 24.8+/-5.0 25.9+/-5.2 0.135 26.7+/-7.3 0.643 0.156
IMPA 97.7+/-8.6 96.9+/-7.1 0.722 101.0+/-8.3 0.037 0.139
p-values computed using Wilcoxon signed rank test
p1-initial to middle
p2-middle to final
p3-initial to final
Table 8: Comparison of Cephalometric Measurements at Initial and Final Time Points for
Single-Phase Treatment Group
1 Phase - Extract/Non-Extract
Initial Final p
SNA 82.3+/-3.5 80.7+/-3.3 <0.01
SNB 77.0+/-3.0 76.4+/-2.7 0.115
ANB 5.0+/-2.0 4.2+/-2.2 <0.01
U1NAmm 5.8+/-2.8 4.0+/-2.0 0.033
U1NAdeg 20.8+/-7.4 18.1+/-5.9 0.146
L1NBmm 7.1+/-2.9 7.0+/-2.1 0.882
L1NBdeg 30.4+/-7.1 29.6+/-4.5 0.232
PogNBmm 1.2+/-1.5 2.3+/-1.6 <0.01
IntAng 123.0+/-11.2 128.1+/-6.1 0.133
FMA 28.7+/-6.0 29.4+/-5.7 0.753
IMPA 97.2+/-6.9 94.7+/-14.6 0.597
p-value computed using Wilcoxon signed rank test
35
Table 9 shows there were no significant changes in cephalometric measurements
between the single- and two-phase treatment groups (either initial to final or middle to
final). There was a significant difference between the changes for one-phase as
compared to the change between initial to middle of two-phase treatment. The Mann-
Wilcoxon U-test was used.
Table 9: Comparison of Change in Cephalometric Measurements Between Single and
Two-Phase Treatment Groups
p (1/2) p 1/2(f-m) p 1/2(m-i)
SNA 0.553 0.075 <0.01
SNB 0.218 0.133 <0.01
ANB 0.160 0.779 <0.01
U1NAmm 0.402 0.042 <0.01
U1NAdeg 0.326 0.058 <0.01
L1NBmm 0.053 0.023 <0.01
L1NBdeg 0.108 0.184 <0.01
PogNBmm 0.081 0.591 <0.01
IntAng 0.082 0.012 <0.01
FMA 0.428 0.902 <0.01
IMPA 0.170 0.071 <0.01
p-value computed using Mann-Whitney-Wilcoxon U-test
p
1
: compare single-phase initial-final to two-phase initial-final
p
2
: compare single-phase initial-final to two-phase middle-final
Cephalometric measurements were similar between single-phase and two-phase
treatment within the Extraction or Non-Extraction groups as indicated by Table 10 and 11
below. The Mann-Whitney-Wilcoxon-U test was used to determine any difference
between the final and initial values for the single- and two-phase treatment groups.
36
Table 10: Comparison of Cephalometric Measures at Initial and Final Time Points in
Extraction Cases
Single-Phase
Two-Phase
Initial Final Initial Final p
SNA 82.2+/-3.6 81.0+/-3.5 82.4+/-3.7 81.9+/-3.2 0.272
SNB 77.0+/-2.6 76.6+/-3.1 77.5+/-3.7 77.8+/-3.8 0.421
ANB 5.2+/-2.2 4.4+/-2.2 4.9+/-1.6 4.1+/-2.3 0.770
U1NAmm 5.2+/-3.4 4.5+/-1.7 5.6+/-2.7 4.6+/-1.4 0.451
U1NAdeg 17.4+/-7.9 19.0+/-5.9 20.6+/-7.2 20.3+/-5.4 0.497
L1NBmm 6.4+/-2.6 7.3+/-2.2 5.7+/-3.4 11.1+/-11.1 0.225
L1NBdeg 28.6+/-5.9 30.8+/-5.0 24.5+/-12.5 25.9+/-10.5 0.942
PogNBmm 1.6+/-1.8 2.2+/-1.6 2.2+/-1.6 3.9+/-2.5 0.068
IntAng 128.0+/-8.8 125.9+/-6.4 127.9+/-14.5 125.5+/-9.1 0.808
FMA 27.5+/-6.4 28.1+/-5.6 24.0+/-5.5 25.1+/-7.5 0.961
IMPA 96.5+/-6.7 94.4+/-19.9 96.6+/-9.7 100.3+/-9.2 0.981
p-value computed using Mann-Whitney-Wilcoxon U-test
Table 11: Comparison of Cephalometric Measurements at Initial and Final Time Points in
Non-Extraction Cases
Single- Phase
Two-Phase
Initial Final Initial Final p
SNA 82.5+/-3.5 80.3+/-3.1 83.9+/-5.3 81.0+/-4.1 0.449
SNB 77.0+/-3.5 76.2+/-2.3 76.0+/-2.8 75.7+/-3.2 0.535
ANB 4.9+/-2.0 4.1+/-2.2 7.9+/-3.4 5.3+/-3.3 0.037
U1NAmm 6.5+/-1.8 3.5+/-2.2 3.3+/-1.6 4.0+/-1.9 0.030
U1NAdeg 24.6+/-4.8 17.0+/-6.0 16.2+/-6.7 18.3+/-6.7 0.061
L1NBmm 7.9+/-3.1 6.7+/-2.1 7.0+/-3.0 7.3+/-2.8 0.347
L1NBdeg 32.3+/-7.9 28.4+/-3.7 29.5+/-6.0 33.2+/-7.6 0.010
PogNBmm 0.8+/-1.0 2.5+/-1.7 1.2+/-1.7 3.3+/-2.6 0.381
IntAng 117.6+/-11.4 130.4+/-5.0 126.7+/-11.5 123.5+/-8.3 0.034
FMA 30.0+/-5.5 30.8+/-5.6 26.4+/-3.6 30.3+/-6.1 0.217
IMPA 97.9+/-7.3 95.0+/-6.0 100.0+/-5.7 102.3+/-6.4 0.049
p-value computed using Mann-Whitney-Wilcoxon U-test
Table 12 (below) compared the cephalometric measurements at the initial and
final time points between single and two-phase treatment groups. Almost all the
37
cephalometric numbers did not show significance with the exception of initial U1NA
degrees.
Table 12: Comparison of Cephalometric Measurements at Initial and Final Time Points
Between Single- and Two-Phase Treatment Groups
Initial Final
SNA 0.640 0.906
SNB 0.460 0.364
ANB 0.018 0.325
U1NAmm 0.030 0.719
U1NAdeg <0.01 0.991
L1NBmm 0.892 0.421
L1NBdeg 0.805 0.034
PogNBmm 0.862 0.516
IntAng 0.216 0.159
FMA 0.982 0.542
IMPA 0.673 0.863
p-value computed using Mann-Whitney-Wilcoxon U-test
The initial and final ANB angles for the single- or two-phase treatment groups
showed no significance as indicated by the box plots below (Figure 5 below). The single-
phase group with extractions has three outliers, which may have skewed the box plot.
However, it can be seen that ANB is decreasing amongst the groups.
38
Figure 5 : Initial and Final ANB angles for Single-Phase and Two-Phase
39
Figure 6: Final ANB angles for Single-Phase and Two-Phase
Molar Severity
Molar severity was scored based on ¼ cusp increments. A value of 0 was assigned
if the molar relationship was class 1, 0.25 if quarter-step, 0.5 if half step, and 1.0 if the
molar was full-step class II (Table 13). There is a significant change in molar relationship
from the initial point of the first phase of two-phase treatment to the start of the second
phase of treatment. Initially, it begins as 0.5 and then decreases to 0.0 (class I
relationship) by the beginning of the second phase (p<0.01).
40
Table 13: Definition of Molar Severity Score
Molar Class Severity Score
Class I 0.00
Quarter-Step Class II 0.25
Half-Step Class II 0.50
Full-Step Class II 1.00
Table 14: Molar Severity
Initial Start of Phase 2 Difference p
Score 0.5+/- 0.2 0.0 +/- 0.0 0.5 +/- 0.2 <0.01
Headgear
The use of the headgear did decrease the ANB angle as indicated by the change
from 5.6 to 4.4 (p<0.01) . However, the non-extraction headgear group did not show any
significant change. As indicated by Table 15, no significant difference was demonstrated
amongst the change in ANB between the headgear and non-headgear groups as shown by
the Mann-Whitney- Wilcoxon- U test. Figure 7 shows the bar graph depicting the number
of extractions found with our without the use of the headgear.
Table 15: Change in ANB With and Without Headgear
Headgear No Headgear
Initial Final p
a
Initial Final p
a
p
b
ANB 5.6+/-2.5
4.4+/-2.6 <0.01 4.9+/-1.8 4.2+/-1.8
0.026
0.026
Extraction
Rate
27.3%
9 of 33
76.9%
10 of 13
p
a
:p-value computed using Wilcoxon signed rank test
p
b
:p-value computed using Mann-Whitney-Wilcoxon U-test
41
Figure 7: Bar Graph Depicting Extractions with Headgear or No Headgear
Treatment Time
There is a significant difference between the treatment times in single versus two-
phase treatment groups. The total treatment time for single phase was 36.8, whereas two-
phase treatment lasted 53.9 months (Table 16). Treatment times between extraction and
the non-extraction groups proved to be very similar as indicated by Table 17. The
treatment time for the extraction group was 46.1 months, whereas the non-extraction
group was 42.3 months.
Table 16: Total Treatment Time in Single- versus Two-Phase Treatment Groups
Single-Phase Two-Phase p
Treatment during
adolescence
36.8+/-10.1 40.8+/-12.9 0.207
Total 36.8+/-10.1 53.9+/-12.3 <0.01
Headgear No Headgear
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Proportion with Extractions
Treatment Group
Extractions by Headgear or No Headgear
42
Table 17: Total Treatment Time in Extraction versus Non-Extraction Cases
Extract Non-Extract p
Total Time 46.1+/-15.7 42.3+/-12.5 0.390
When comparing the treatment time of males and females, the two groups were similar
(Table 18). Males and females undergoing single-phase treatment took about the same
amount of time with 36.8 months (p=0.857). Two-phase treatment seemed to take longer
in females (58.4months), whereas male treatment lasted 52.3 months(p=0.430).
Table 18: Total Treatment Time in Male versus Female Subjects
Single-Phase Two-Phase
Male 36.8+/-12.2 52.3+/-11.9
Female 36.8+/-9.3 58.4+/-13.7
P 0.857 0.430
Age and Gender
As shown in Table 18, there was no significant difference in ages between the
single- and two-phase treatment groups for the males and females. Males and females
tended to begin two-phase treatment about the same age. Single phase treatment started a
little later for males (12.4 +/- 2.0years old), whereas the females began earlier (11.9 +/-
1.4 years old). This is to be expected as growth modification is the aim of early treatment
and girls are skeletally and dentally more advanced than boys.
The later two-phase treatment began about the same age for males and females,
with males beginning at 10.7 +/-1.1 years old and females 10.6+/-1.5 years old. The
similar age for beginning the later two-phase treatment may be a result of our small
sample size.
43
Table 19: Sex Specific Mean Ages in Single- versus Two-Phase Treatment Groups
Single-Phase Two-Phase p
1
Male 12.4+/-2.0 10.7+/-1.1 0.032
Female 11.9+/-1.4 10.6+/-1.5 0.135
p
2
0.836 0.912
p-value computed using Mann-Whitney-Wilcoxon U-test
p
1
: Age between treatment modalities for a single gender
p
2
: Age between genders for a single treatment modality
44
Chapter 6: Discussion
Overall
This study was conducted in a private practice of a Diplomate of the American
Board of Orthodontics (ABO) in Southern California, aiming to compare premolar
extraction rates between Class II patients who were either treated with early two-phase
treatment or a later single-phase. The following hypotheses were investigated: 1. There is
a statistically significant difference in premolar extraction rates between single-phase and
two-phase treatment and 2. There is a statistically significant difference in cephalometric
outcomes between single-phase and two-phase treatment groups. The results of this study
may assist orthodontist’s in determining the appropriate timing for Class II treatment.
One orthodontist working under a single treatment philosophy completed the
cases examined for this study. 46 consecutively treated patients were selected as subjects
for our study. 27 were treated in a later single phase and 19 were treated in early two-
phase treatment. The first phase of the two-phase treatment philosophy involved use of a
headgear and biteplane in most cases or a headgear used in conjunction with a 2x4
appliance.
Previous studies conducted at a university had been completed and we were aware
that the results of a private practice may vary significantly from the university setting. In
a university setting, patients were subjected to resident class schedules and different
treatment philosophies. These two factors would alter the treatment time significantly. A
private practice setting was selected for this study to help eliminate these factors.
45
This study aimed to discover whether treating Class II patients in early two-phase
treatment would reduce the need for premolar extractions as well as provide more ideal
skeletal and dental outcomes as seen by the lateral cephalometric analysis. The
conclusion of this study found there was no difference in premolar extraction rates
whether or not early treatment was completed. Furthermore, cephalometric analysis
proved to be similar amongst the two treatment groups, while ANB and PogNB mm
value did border on significance.
Premolar Extraction Rates
Recent studies have shown that there is an increased premolar extraction rate if
the first phase of two-phase treatment is not completed
22, 78, 79
From our study, 46
subjects were examined. Out of these 46 patients, 48.1% (13 out of 27 subjects) from the
single-phase treatment group and 31.6% (6 out of 19 subjects) of the two-phase subjects
had extractions. This data revealed that single-phase treatment tended to have more
extractions, whereas two-phase treatment were likely to experience less extractions. The
p value determined by the Pearson Chi Squared test was p=0.261. Due to our limited
sample size, our p value may have been skewed. As the sample size decreased, p-values
tend to increase thereby altering our data.
The University of Florida found that extraction rates were increased in the single-
phase group as compared to the two-phase group. Out of 261 subjects, 20% of the
observation group, 12% of the headgear/biteplane group and 8% of the bionator group
experienced extractions. Although these results were not statistically significant, there
46
was a correlation found amongst the two groups.
19
This data seemed to be similar to our
findings.
The University of North Carolina found opposing results, that two-phase
treatment did not increase the need for extractions. For the single phase group, 27% of
the control group experienced extractions, whereas 35% of the functional group and 17%
of the headgear group underwent extractions.
16
It should be noted that surgical options
were discussed at the University of North Carolina. The surgical option was discussed
with 20 out of 52 patients in the control group, whereas the early two-phase treatment
groups were treated with a functional appliance or headgear. Interestingly enough,
Proffit’s group noted there may be a correlation between early treatment and rate of
premolar extraction and orthognathic surgery. Therefore, many patients may have chosen
the surgical option rather than having teeth extracted.
17
Fagin and Yang (USC) concluded that there was a tendency towards more non-
extraction treatment in the early two-phase treatment groups. 37.5% of the early two-
phase treatment patients had extractions, whereas there was a 50% extraction rate of the
later single-phase patients (p=0.017)
77
Lee (USC) , similar to Fagin and Yang, found that the early two-phase group
demonstrated 20% extraction rate, whereas the late single-phase group demonstrated
44%.
Fields (USC) seemed to discover similar findings of previous studies whereby
extraction rates were increased in later single-phase treatment groups. In her study, the
single-phase treatment group experienced a 49.2% extraction rate (31 of 63) whereas the
47
two-phase treatment group experienced a 22.9% extraction rate (8 of 35). There was
about 50% more extractions completed in the single-phase treatment as opposed to the
two-phase treatment. This demonstrated a significant p-value of 0.01
78, 79
Determining whether or not extraction rates are influenced by single- or two-
phase treatment is of the upmost importance to the orthodontic profession. Both the
University of Florida and University of North Carolina did not find statistical significance
in this regard.
16, 20, 69
While Fields discovered statistical significance with premolar
extractions, Fagin and Yang’s study as well as Lee’s study found a correlation that was
on the verge of statistical significance. Finally, our study did not find any statistical
significance in extraction rates amongst the two groups. There seems to be a correlation,
but no statistical significance.
Treatment Time
Examining the total treatment time between the single-phase and two-phase
patients showed that the two-phase treatment time was significantly longer. Total
treatment time for the later single-phase group was shown to be 36.8+/-10.1 months as
compared to the 53.9+/-12.3 months for the early two-phase treatment group. When
analyzing the second phase of treatment, the later single-phase group spent 36.8+/-10.1
months in treatment and the early two-phase treatment group spent 40.8+/-12.9 months in
treatment. It is important to note that there were several outliers in the treatment time of
the two-phase treatment. One patient took a total of eighty months while another took 72
months and many others lingered around the 60-month mark (this includes both the first
48
phase and the second phase of treatment). These outliers may have skewed the data for
the treatment time. We can conclude that early treatment was not more efficient in this
case.
These numbers show shockingly similar results to that of UNC and UF.
According to Proffit, early treatment was not as efficient as it only produced a slight
reduction in the second phase of treatment
16, 18
. In the UNC study, average treatment
time of the second phase was 34.5 months in the control group. The functional appliance
group demonstrated a median time of 25.5 months and the headgear group averaged 30.1
months. Due to the nature of a school atmosphere, the treatment time may have been
skewed. Dealing with resident schedules and vacations of the school may have also added
to the longer treatment time in this case. Additionally, the four supervising orthodontists
chose his own treatment plan, type of appliance and archwire sequence, leading to a wide
range of treatment times varying from one orthodontist to another.
The University of Florida study discovered that patients undergoing two-phase
treatment actually finished the second phase of treatment six months earlier than single-
phase patients. However, after comparing the total treatment time of single-phase to a
two-phase treatment, they discovered that early two-phase treatments did take much
longer to complete. A possible reason for elongation of treatment is the protocol of the
first phase of treatment. The University of Florida allowed a total of 24 months for the
first phase and was independent of cooperation
20
In addition, there were four treating
orthodontists overseeing the cases, which may have added to the treatment time.
49
Comparatively, Lee demonstrated that the early two-phase treatment group spent
a longer time in treatment overall. Early-two phase treatment took 35.75 +/-4.38 months
overall, whereas 28.41+/-4.81 months for the single phase group. When investigating the
time spent wearing appliances in the second phase treatment, the early two-phase group
spent 22.35+/-4.49 months to complete and the single-phase treatment group spent
28.41+/-4.81 months in treatment. Therefore, in phase 2 of their treatment the patients
actually spent six months less time in fixed appliances. Fields also showed that two-
phase treatment took approximately six months longer than later single-phase treatment.
Overall, single-phase lasted 30.76 +/- 6.24 months and two-phase 36.12 +/- 4.90. Similar
to Lee’s study, Fields showed that patients treated in two-phases demonstrated 7 months
less time in fixed appliances during the second phase. Single phase lasted 30.76 +/-6.24
months and the two-phase treatment group spent 23.46+/-4.66 months in treatment.
In conclusion, our treatment times seem to be extremely long when compared to
the UNC and University of Florida studies. Similar to the UF study, there is significance
when comparing the total treatment time of single-phase versus two-phase.
Cephalometric Measurements
Throughout the University of Florida, University of North Carolina studies, and
the USC study (Fagin and Yang) the Peer Assessment Rating (PAR) was used to analyze
the outcome of treatment. Originally, it was used to objectively assess the quality and
outcomes of treatment when studying rotations and occlusion. However, Tulloch found
that “it was possible for two dental outcomes to have the same PAR score with different
50
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 children who had
early treatment than for those who did not.”
17
As a result, cephalometric measurements
are an informative way to assess the relationship of the alveolus to the teeth to conclude
that the single and two-phase treatments are equal in outcome. Therefore, cephalometric
measurements were analyzed instead of PAR scoring.
Cephalometric values were assessed for the early treatment group demonstrating a
change from ANB of 5.9 to 4.5 at the end of treatment (Table 7), which was statistically
significant. The ANB change clearly indicates a change from a skeletal Class II to a near-
Class I. Similarly, PogNBmm showed a significant change in the two-phase treatment
group. Initially, PogNB mm measured 1.9mm and ended at 3.7mm (Table 7). Both
Field’s and Lee also found statistical significance when assessing the change of ANB in
the two-phase treatment group.
78, 79
Skeletal changes in the single-phase group did have some statistical significance
as well. ANB decreased from 5.0 to 4.2 (Table 8). This showed a tendency to change
from Class II to near-Class I. Similarly, SNA also decreased from 82.3 to 80.7 in the
single-phase patients (Table 8) and Pog NBmm increased from 1.2 to 2.3. Once again,
Field’s and Lee both demonstrated statistical significance when examining the ANB of
single-phase patients.
78, 79
51
After comparing the difference of cephalometric analysis between the two groups
(initial to final findings of early two-phase treatment and later single-phase treatment),
our study found no significant findings (Table 9). These results are consistent with Fields,
Lee, University of North Carolina, and University of Florida. Both the University of
Florida and University of North Carolina studies demonstrated that the ANB of their
patients did not change when comparing initial ANB to ANB at the end of treatment,
regardless of early or late treatment, which is consistent with our findings.
17,18,20
Molar Severity
Early phase treatment aimed to capitalize on growth modification to help correct a
skeletal and dental discrepancy. In this study, either a headgear used alongside a 2x4
appliance or the use of a headgear in conjunction with a biteplane were used to help
achieve the goal of Class I relationship at the end of the first phase. Our orthodontist
achieved a Class I relationship at the end of the first phase of treatment, regardless of the
length of time needed. Because of this decision, treatment time was definitely increased
in our patient pool. According to our findings (Table 14), there was significance with
regards to the end of the first phase of treatment.
University of Florida used different categories to denote the varying degrees of
Class II malocclusion. Mild (bilateral ½ cusp), moderate (unilateral ¾ cusp) and severe
(unilateral full step) molar classifications were implemented. To determine the type of
correction achieved, Wheeler utilized a quarter unit system to decide how much
correction was needed. UF found the median goal achieved during the first phase of two-
52
phase treatment ranged from 75-100% in the headgear/early functional group and 15% in
the observational group.
19
Furthermore, the University of Florida found that a successful
correction in the first phase to be a quarter-step Class II.
19
It is important to note that the capitalization of growth modification alongside the
use of a headgear can account for this change. Proffit noted that headgear and functional
appliances have about a 70-80% change of creating a favorable change with early
treatment.
76
Therefore, it would seem that growth modification might account for the
majority of our change in the first phase.
Lee also showed greater than ½ step Class II molar correction during the first
phase using a headgear, which was retained until the beginning of phase 2.
78,
Fields’
results were similar with a marked reduction in molar severity to less than half-cusp Class
II when compared to initial records in the two-phase treatment group.
79
The findings from
all of the studies proved to be similar to what our study showed.
Headgear Use
Our study discovered a significant difference between initial and final ANB for
those patients using a headgear. Beginning with an ANB of 5.6 and ending with 4.4, there
is statistical significance that the headgear does improve one’s skeletal relationship
(Table 15). Those not wearing a headgear did not experience any statistical change of
ANB, further indicating that growth modification does help achieve a better skeletal
relationship. When the extraction rate of headgear versus non-headgear group was
investigated, we found that the non-headgear group was almost three times as likely to
53
experience extractions. 76.9% of non-headgear group had extractions versus 27.3% of
headgear group (Table 15).
Wheeler found that headgear was used more frequently in the second phase of
treatment. Headgear was worn in 42% of the observation group, 15% of the headgear
group, 23% in the bionator group. Wheeler also discovered through multivariate analysis
that headgear may be superior to the bionator in achieving class II correction.
19
Additionally, using a headgear decreases the need for camouflage treatment and
therefore, less premolar extractions.
Lee and Fields showed that headgear use demonstrated similar changes with
ANB. When comparing the headgear group to the non-headgear group, they showed that
non-headgear patients were twice as likely to receive extractions.
78, 79
Age and Gender
Gender analysis revealed no statistically significant changes when examining the
mean age between males and females. Females began later single-phase treatment at
11.9+/-1.4 years and males tended to begin later (12.4+/-2.0 years). Since the male
growth spurt is two years later than the females, it is expected that females began
treatment at an earlier age.
Two-phase treatment for our study began at 10.7 +/-1.1 years and 10.6 +/-1.5
years for males and females, respectively. Although we did not take hand-wrist x-rays on
our patients to assess peak height velocity, our mean ages fall within range for growth
modification. UNC’s study began two-phase treatment for males at 9.9 years and UFA
54
began at 9.6 +/-0.8 years. Our findings seem to fall just outside of the range of those
studies.
55
Chapter 7: Conclusions
After completing this investigation, it can be determined that there is not
statistically significant advantage to single-phase versus two-phase Class II treatment.
The cephalometric measurements seem to be very similar, whether or not extractions are
completed. Furthermore, the skeletal and dental outcomes prove to be very similar.
The conclusions of this study are as follows:
1. The premolar extraction rate is not significant in the single-phase treatment
group when compared to the single-phase treatment group. Comparison of the
premolar extraction rates demonstrated that the early treatment group (31.6%)
receiving less extractions than the single-phase treatment group (48.1%)
2. The changes in the cephalometric measurements were not significant between
the single-phase or two-phase treatment groups. When comparing the time
points within the two-phase treatment or within the single-phase treatment,
there was significance.
Within the two-phase treatment group :
a. ANB decreased from 5.9° to 4.5° (p<0.01)
b. When comparing the initial time point of two-phase treatment to the
middle time point of two-phase treatment, PogNBmm increased from
1.9mm to 2.4mm, indicating that Pogonion moved forward. (p<0.01)
56
c. PogNBmm also increased significantly when comparing the initial
time point to the final time point in two-phase treatment. (initial=1.9
and final=3.7, p<0.01)
Within the single-phase treatment group:
a. SNA decreased from 82.3 to 80.7 (p<0.01)
b. ANB decreased from 5.0 to 4.2 (p<0.01)
c. PogNBmm increased from 1.2 to 2.3 (p<0.01)
3. The changes in cephalometric measurements were not significant between the
single- and two-phase extraction treatment groups or the non-extraction
groups.
4. There is a significant difference between treatment times associated with total
treatment time of single- and two-phase treatment groups. Overall, treatment
time for single-phase patients lasted 36.8 months, whereas two-phase
treatment lasted 53.9 months.
5. There is a significant difference between final and initial ANB for those
patients wearing a headgear. Initially, the headgear group presented with an
ANB of 5.6° and finished with an ANB of 4.4° (p<0.01)
Secondary Conclusions
1. There is no difference for the total treatment times between males and
females. Females did take longer in two-phase treatment (58.4 months) and
57
the duration of male treatment averaged 52.3 months, but this was not
significant.
2. There was no difference in ages for males and females between the treatment
groups. Males tended to start single-phase treatment at age 12.4 years while
females began treatment at an average age of 11.9 years.
58
Chapter 8: Limitations
Overall, there were few limitations to this study of importance. First and
foremost, the small sample size may have skewed the results. Gathering information from
a smaller Southern California orthodontic office may not be representative of the entire
population. Further investigation will be needed to assess this study.
Additionally, the compliance of patients was not accurately evaluated. Various
treatments may have taken a longer time due to the compliance factor of the patients.
Although compliance may be a difficult entity to investigate, it needs to be evaluated in
some regard, as it will significantly affect treatment time.
59
Chapter 9: Summary
Previous research about Class II treatment has attempted to clearly define the
proper timing of treatment, whether it is an early two-phase treatment or a later single-
phase. Previous residents at USC demonstrated that the findings from a private office
proved significantly different results from the previously published institutional studies,
namely University of North Carolina and University of Florida. Our data discovered that
Class II patients wearing a headgear were less likely to need premolar extractions. 27%
of those patients wearing a headgear did not have extractions, whereas 76% of those
patients not wearing a headgear needed extractions. Secondly, when comparing the
cephalometric analysis of two-phase treatment group to single-phase treatment groups,
there was no significant difference in the skeletal and dental outcomes, thereby validating
the results of previous institutional studies. Finally, there is no statistically significant
difference when comparing the premolar extraction rates of single-phase versus two-
phase treatment group.
60
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Abstract (if available)
Abstract
Introduction: The pros and cons of early two-phase treatment of Class II malocclusion have been examined recently. This study examines how growth modification will affect premolar extraction rates as well as final cephalometric outcomes.
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Asset Metadata
Creator
MacFarlane, Lindsey Hambleton
(author)
Core Title
Comparison of premolar extraction rates between one-phase and two-phase class II malocclusion
School
School of Dentistry
Degree
Master of Science
Degree Program
Craniofacial Biology
Degree Conferral Date
2011-05
Publication Date
03/09/2011
Defense Date
02/18/2011
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
extraction,OAI-PMH Harvest,premolar
Language
English
Contributor
Electronically uploaded by the author
(provenance)
Advisor
Sameshima, Glenn T. (
committee chair
), Moon, Holly (
committee member
), Paine, Michael (
committee member
)
Creator Email
lhambleton@gmail.com,lmacfarlane@yahoo.com
Permanent Link (DOI)
https://doi.org/10.25549/usctheses-m3686
Unique identifier
UC1460051
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etd-MacFarlane-4382 (filename),usctheses-m40 (legacy collection record id),usctheses-c127-441491 (legacy record id),usctheses-m3686 (legacy record id)
Legacy Identifier
etd-MacFarlane-4382.pdf
Dmrecord
441491
Document Type
Thesis
Rights
MacFarlane, Lindsey Hambleton
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
Tags
extraction
premolar