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EFFECTS OF EXTRACTION VS NON-EXTRACTION
ORTHODONTIC TREATMENT ON VERTICAL
SKELETAL AND DENTAL MEASUREMENTS
Vasileios Charalampakis, D.D.S.
An Abstract Presented to the Graduate Faculty of
Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2015
Abstract
Introduction: One of the most important steps in
orthodontic treatment planning is the extraction decision. The “wedge effect” hypothesizes that extracting
posterior teeth allows the mandible to hinge closed,
thereby allowing better vertical control. The objective
of the present study was to compare the different outcomes between patients treated non-extraction and patients treated with extractions, in order to assess the
validity of this concept. Subjects and Methods: Pre- and
post-treatment cephalograms of 191 normal, healthy subjects (67 treated without extractions, 61 treated with
four first premolar extractions and 63 treated with four
second premolar extractions) were obtained from the archive of the Center for Advanced Dental Education orthodontic clinic of Saint Louis University. Class I, Class
II and Class III subjects were similarly distributed
across the three groups. Tracings were superimposed according to Björk’s method for structural superimposition
and fiducial lines were drawn for the maxilla and mandible. A Cartesian system was used to measure vertical and
horizontal changes of ANS, upper first molar and central
incisor, Gonion, Menton, lower first molar and lower central incisor.
Overbite, as well as SN-GoMe, SN-FOP and
the angle between the maxillary and mandibular fiducial
lines was also measured. Because the different treatment
protocols resulted in significantly different treatment
times, analysis of covariance was performed to test for
different increments of change among the 3 groups while
controlling for the effect of treatment time. Results:
There was a statistically significant difference in horizontal displacement of upper first and lower first molars
between the 3 groups. The lower incisors showed significantly different amounts of extrusion for each group.
There were no statistically significant differences in
amounts of change in any of the other variables. Conclusions: The present study failed to produce evidence of
favorable vertical changes as a result of extractions.
Other than lower incisor vertical displacement, there was
no difference in magnitude of change in vertical measurements between the 3 groups.
EFFECTS OF EXTRACTION VS NON-EXTRACTION
ORTHODONTIC TREATMENT ON VERTICAL
SKELETAL AND DENTAL MEASUREMENTS
Vasileios Charalampakis, D.D.S.
A Thesis Presented to the Graduate Faculty of
Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2015
COMMITTEE IN CHARGE OF CANDIDACY:
Professor Rolf G. Behrents,
Chairperson and Advisor
Professor Emeritus Lysle E. Johnston Jr.
Professor Eustaquio A. Araujo
Associate Clinical Professor Donald R. Oliver
i
“For every complex problem there is an answer that is
clear, simple, and wrong.”
—Henry Louis Mencken
ii
DEDICATION
To my mother, the strongest person I have ever
met and a beacon of patience and bravery.
To my father, who taught me the value of humility, determination, hard work and perseverance.
To my teachers in Saint Louis University, who
honored me with the opportunity to learn from them.
To my loving partner Panagiota, who supported me
every step of the way. I am blessed to have you by my
side.
iii
ACKNOWLEDGEMENTS
The author acknowledges the following individuals
and expresses his sincere gratitude for their contributions:
Dr. Rolf G. Behrents, for his assistance in topic
selection, result interpretation and corrections;
Dr. Lysle E. Johnston Jr., for his assistance in
tracing cephalograms, suggestions regarding the methods
and statistical analysis and time spent on corrections;
Dr. Eustaquio A. Araujo, for his suggestions,
corrections and mentoring throughout the course of my
graduate education;
Dr. Donald R. Oliver, for his advice on this thesis and time spent on corrections;
Dr. Heidi Israel, for her patience and assistance
with the statistical analysis and result interpretation.
Finally, I would like to thank the rest of the
faculty for sharing their knowledge and experience, my
classmates for riding along in this journey, and the
staff at CADE for allowing us to focus on learning and
making me look forward to going to school every morning.
I am humbled and honored to have been part of such an incredible group of people.
iv
TABLE OF CONTENTS
LIST OF TABLES......................................... vi
LIST OF FIGURES....................................... vii
CHAPTER 1: REVIEW OF THE LITERATURE..................... 1
Introduction .................................. 1
The Vertical Dimension ...................... 2
Growth Pattern .............................. 2
The Wedge Hypothesis ........................ 4
The Extraction Decision ..................... 5
Clinical Studies .............................. 6
Overview ..................................... 19
Statement of Thesis .......................... 23
CHAPTER 2: JOURNAL ARTICLE............................. 28
Abstract ..................................... 28
Introduction ................................. 30
Subjects and Methods ......................... 32
Sample ..................................... 32
Cephalometric Analysis ..................... 33
Error Study ................................ 37
Statistical Analysis ....................... 37
Results ...................................... 39
ANCOVA ..................................... 45
Discussion ................................... 47
Limitations ................................ 47
The Wedge Hypothesis ....................... 49
Results Compared to Literature ............. 50
Overview and Future Research ............... 54
Conclusions .................................. 56
Literature Cited ............................. 57
Appendix............................................... 61
Vita Auctoris.......................................... 67
v
LIST OF TABLES
Table 1.1
Studies analyzing impact of extractions
on vertical measurements................ 17
Table 2.1
Distribution of patients by Angle
classification in each extraction group. 33
Table 2.2
Means and standard deviations for treatment time in days....................... 39
Table 2.3
Post-hoc analysis for treatment time
between groups.......................... 40
Table 2.4
Descriptive statistics pre-treatment.... 41
Table 2.5
Descriptive statistics post-treatment... 42
Table 2.6
Descriptive statistics for increments of
change.................................. 43
Table 2.7
Descriptive statistics for increments
of change adjusted for treatment time
according to ANCOVA...................
44
Results compared to similar studies...
53
Table 2.8
vi
LIST OF FIGURES
Figure 2.1
Figure 2.2
Figure A.1
Figure A.2
Figure A.3
Measurements based on maxillary superimposition............................
35
Measurements based on mandibular superimposition.........................
36
Upper first molar horizontal displacement..................................
62
Lower first molar horizontal displacement..................................
64
Lower incisor vertical displacement...
65
vii
CHAPTER 1: REVIEW OF THE LITERATURE
Introduction
Since the fathers of orthodontics laid the foundation of the specialty, the first practitioners engaged
in debates regarding solutions to common clinical problems, chief among which was addressing tooth space-arch
length discrepancies. Angle was an avid supporter of nonextraction treatment,1 whereas Tweed is widely considered
the pioneer of extraction treatment. The pendulum in the
extraction versus non-extraction approach has swung back
and forth numerous times since then, with ideas and
trends that were once popular lost in time, only to be
repackaged and presented anew. Therefore, it is important
to review the scientific literature in order, not only to
determine on which direction future research should focus, but also to guard against anachronistic arguments
and superseded theories.
Dealing with different types of malocclusion soon
gave rise to the need for a classification system that
would make diagnosis, communication and treatment planning more efficient and consistent. Angle’s nomenclature,
first published in the Dental Cosmos in 18992 has proven
to be a simple and powerful tool. As is often the price
of simplicity, however, it suffers from certain
1
limitations.3 For example, Angle’s classification strictly
refers to sagittal discrepancies, disregarding vertical
and transverse issues.
The Vertical Dimension
In 1964, Sassouni and Nanda4 proposed an analysis
that included eight skeletal open bite and eight skeletal
deep bite combinations to describe facial proportions,
introducing a system that took the vertical dimension into account. Sassouni5 further elaborated on this classification system in a paper published in 1969, describing
four “syndromes” of characteristics, skeletal deep bite,
skeletal open bite, skeletal Class II and skeletal Class
III. Schudy6 in 1964 introduced the terms hypo- and hyperdivergent.
Fields and coworkers7 argued there was a lack of
documentation in the scientific literature regarding the
morphological differences between long-, normal- and
short-faced patients. In their research, they found that
long-faced patients had greater anterior face height,
mandibular plane angles and mandibulopalatal plane angles.
Growth Pattern
It is important to know what one may expect from
normal growth in order to be able to assess the effects
2
of orthodontic and orthopedic interventions. In 1984,
Cangialosi8 described the skeletal features of patients
with anterior open bite. Comparing 60 open bite patients
(30 permanent and 30 mixed dentition) to 60 untreated
Class I normal subjects, he found significantly greater
SN-GoGn and gonial angles in the open bite group as well
as shorter posterior face height and greater anterior
face height. He reported significant differences in size,
but not proportions. Ratios and angles remained relatively constant between mixed and permanent dentition, which
suggests vertical problems do not self-correct as an individual ages. His study is important because it provides
useful information regarding changes that occur with
growth.
Surender Nanda9 examined a sample of 32 patients
between 3 and 18 years of age to determine patterns of
vertical development. Skeletal deep bite and open bite
subjects were selected based on lower face height (ANSMe) to total face height (N-Me) ratio. He reported significant differences between the two groups in anterior
total and anterior lower face height, whereas ramal
height showed no difference. His findings contrast those
of others4,
6
who reported significantly shorter ramal
height for open bite patients. Nanda concluded that vertical developmental patterns are determined at a very
3
young age, before the eruption of the first permanent molars, and the differences between the two groups increase
with time.
The Wedge Hypothesis
Schudy in 196810 argued that vertical growth affects all facial proportions and proposed treatment
strategies he believed prudent in order to minimize deleterious effects of unfavorable growth and reduce the
chance of relapse. He suggested that extractions may be
considered for better vertical control, even in cases
with sufficient space. Nasby and coworkers11 (1972) studied high and low angle patients. They believed that extractions allow the posterior teeth to drift mesially,
and this drift in turn produces forward rotation of the
mandible and a reduction in anterior facial height. They
concluded that extractions are indicated for high angle
patients but should be avoided for low angle individuals.
Along the same lines, Joondeph and Riedel12 advocated second premolar serial extraction in order to control overbite, due to a favorable mesial drift pattern.
Pearson13 discussed vertical control in hyperdivergent patients, advocating extraction of four first premolars and
vertical-pull chincup to close open bites prior to placement of fixed appliances. He offered several explanations
about the possible cause of the bite closure he observed,
4
among which was the mesial drift of the posterior teeth
“out of the wedge” which in turn allowed the mandible to
rotate forward and “hinge closed.”
The Extraction Decision
Clinicians may opt for different extraction patterns depending on each patient’s “needs.” Ketterhagen14
sought to investigate the decision making process involving the extraction of first versus second premolars.
Feeling a more scientific approach was necessary, he compared two groups of patients that had all four first premolars or all four second premolars extracted. Several
cephalometric measurements were examined (including mandibular plane angle) in an effort to identify what influenced the extraction decision. He found no difference between the two groups in terms of skeletal measurements,
but was able to identify soft tissue differences. Vertical control was not the primary criterion when selecting
an extraction pattern.
Yamaguchi and Nanda’s15 work was not specifically
focused on extraction patterns and vertical dimensions,
but certain conclusions can be drawn by analyzing their
data. They compared the effects of different types of
force application on 73 extraction and 48 non-extraction
patients. Interestingly, they reported larger lower anterior face height and smaller ramus height in the extrac5
tion group, suggesting that the vertical dimension was
perhaps an important factor in the extraction decision.
Controlling for mechanics and sex, they concluded that
vertical control of maxillary and mandibular molars is
necessary in order to prevent posterior rotation of the
mandible.
Clinical Studies
Several studies have directly approached the subject of extractions and vertical dimensions. Others focus
on different aspects of the extraction versus nonextraction dilemma, but pertinent information regarding
vertical changes can be found in their tables or discussion as well.
One of the first papers to examine the validity
of the wedge concept was Garlington and Logan’s16 study
(1990) based on a sample of 23 Class II, division 1 hyperdivergent patients (initial SN-GoGn greater than 38°)
who underwent enucleation of mandibular second premolars
followed by extraction of maxillary first premolars. Using Björk’s17 method of superimposition to measure preand post-treatment skeletal and dental changes, they compared their findings to those of Isaacson and co-workers18
and found a non-significant decrease of 0.8° in SN-GoGn
and a statistically significant reduction in lower face
height in the post-treatment group. They concluded that
6
treatment resulted in increased forward rotation of the
mandible, with possible compensatory maxillary growth offered as an explanation for failing to detect a significant difference in total face height.
Another study by Luecke and Johnston19 focused
mainly on the alleged retropositioning of the condyle
supposedly caused by extracting maxillary first premolars. It was published in 1992, when the debate regarding
the relationship between orthodontics and temporomandibular disorders was at its prime. They used Björk’s methods
of regional superimposition and measured growth and
treatment changes parallel to the mean functional occlusal plane.
To measure condylar displacement, a Cartesian
coordinate system was used where averaged Frankfort Horizontal served as the x-axis and a perpendicular through
SE point was the y-axis. Their sample showed forward displacement of the mandibular basal bone, and the FMA decreased by an average of 1°. Although not exclusively focused on the wedge effect, their findings seem to support
the concept.
In order to examine long-term changes after orthodontic treatment, Luppanapornlarp and Johnston20 recalled 62 Class II patients (33 extraction and 29 nonextraction) an average 15.3 years post-treatment. Again,
Björk’s regional superimposition technique was used in
7
the “pitchfork analysis” to evaluate growth and treatment
changes. Only y-axis change immediately post-treatment
was different. There were no long-term differences in
changes observed in any of the vertical measurements they
studied.
Anterior face height, defined as the distance between ANS-Menton, was the primary focus of Chua and
coworkers,21 who measured ANS-Me changes on a sample of
174 Class I and Class II patients. They examined the effects of growth, duration of treatment, extraction pattern and treatment mechanics. They used data from the
Michigan growth standards to normalize individual face
height measurements, in an attempt to adjust for the different effects of growth. No superimposition was done;
instead, pre- and post-treatment measurements were standardized and compared. A significant increase in ANSMenton was observed in the non-extraction group, whereas
in the extraction group no change could be detected. Thus
they noted that extractions alone may not be sufficient
to reduce lower anterior face height. The authors failed
to detect differences between the various treatment mechanics such as cervical headgear, intermaxillary elastics and tip-back bends. Another significant point was
that in the Class II group, clinicians tended to extract
more often in the patients with longer lower anterior
8
face height. They concluded that non-extraction treatment
increases ANS-Me and results in a clockwise rotation of
the mandible.
Aras22 examined a sample of open bite patients,
fifteen of which had first premolar extractions and seventeen had second premolar or first molar extractions. He
attempted to minimize the effects of growth by using a
hand-wrist radiographic method to select patients that
were past their peak growth velocity. First premolar extractions did not result in any significant mandibular
rotation; however, second premolar or first molar extractions produced a forward rotation of the mandible, therefore lending support to the wedge hypothesis.
Molar extractions were also studied by Hans and
coworkers23 (2006) who examined 30 patients who had undergone orthodontic treatment with first molar extractions,
31 patients with first premolar extractions, that were
then matched with two groups of untreated subjects from
the Bolton-Brush Growth Study based on age and gender.
They found that both treated groups showed no increase in
mandibular vertical height and concluded that both strategies were appropriate for vertical mandibular growth
control. The minimal impact that first molar extractions
had on overbite was labeled as “surprising.” Although
their findings seemingly support the wedge hypothesis, it
9
should be noted that the lack of a non-extraction treated
group does not allow comparisons to be drawn between the
two modalities.
Forward mandibular rotation and vertical control
is thoroughly discussed in a recent article published in
2013 by Bayirli and coworkers.24 A group of 36 patients
treated with four first premolar extractions and standard
edgewise treatment was compared to a matched group of untreated subjects from the Bolton-Brush Growth Study Center. Structural superimposition in the cranial base, maxilla and mandible were used to analyze dental and skeletal contributions to the overall measured changes as
measured by the so-called “pitchfork analysis” was performed. Anterior facial height, posterior facial height
and overbite showed significantly different changes compared to the control group, but FMA was not significantly
different. In the conclusions, the authors stress the importance of using structural superimposition to measure
rotation, since it cannot be inferred from surface landmarks alone, a point taken into consideration in the design of the present study,
Other authors, however, have reported similar
changes in vertical measurements in both extraction and
non-extraction groups, thereby contradicting the findings
of the previously summarized studies. For instance,
10
Klapper and coworkers25 examined dolichofacial and
brachyfacial groups that had undergone orthodontic treatment, either non-extraction or with four first premolar
extractions. They were unable to detect differences in
the facial axis change among the groups. Interestingly, a
positive correlation was reported between upper molar
displacement and facial axis change only in the nonextraction group, for both brachyfacial and dolichofacial
subjects.
Lin and coworkers26 approached the subject from a
slightly different perspective. They compared a group of
28 dolichofacial patients and 29 mesofacial patients,
matched for age; both groups were treated without extractions. This was done in order to examine the hypothesis
that non-extraction treatment would result in greater
vertical increase for the dolichofacial group. Cephalograms were taken pre- and post-treatment and 2 years after completion of orthodontic treatment. High-pull headgear was used for 12 dolichofacial and 6 mesofacial patients. No statistically significant changes were detected between the two groups, both of which showed similar
increases in facial height, from which the authors concluded that facial height depends more on genetics and
less on such environmental factors as orthodontics.
11
Hyperdivergent subjects (SN-GoGn angle of 36° or
greater) were studied by Cusimano and coworkers,27 who investigated the effects of four first premolar extractions
on patients averaging 11 years, 10 months of age at the
beginning of treatment. A “modified mandibular plane” using the mandibular canal and the internal lower border of
the symphysis was used to measure true matrix rotation.
They were unable to detect a reduction in vertical dimensions and argued that, although mesial molar movement
should cause a forward rotation of the mandible, this
movement is nullified by extrusion of the posterior
teeth. It was also concluded that the surface changes on
the lower border of the mandible were not significant to
the degree that GoGn would be rendered invalid.
In 1992, Paquette and coworkers28 studied longterm changes in 33 extraction and 30 non-extraction patients, an average 14.5 years after the completion of
treatment. They, too, used Björk’s structural superimposition methods to examine basal bone and tooth displacement and measure changes parallel to the mean functional
occlusal plane. There was no difference between the two
groups immediately post-treatment and the authors noted
that there was no correlation between treatment strategy
and overbite relapse. Interestingly, there were long-term
differences in FMA, S-Go, ANS-Me and N-Me, contrary to
12
the findings of Luppanapornlarp and Johnston.20 However,
any effects from mesial movement of the posterior teeth
on vertical dimensions should be measurable immediately
post-treatment. Therefore, the long-term difference between the two groups does not constitute solid evidence
for the wedge concept.
Staggers29 compared 38 Class I first premolar extraction and 45 Class I non-extraction cases at an average age of 14 years, 5 months. Pre- and post-treatment
lateral cephalograms were traced, then measured using a
digitization program (Dentofacial Planner version 5.3;
Dentofacial Software Inc., Toronto, Canada). Student’s ttests were used to compare the changes of eight variables
in the two groups, which showed no statistically significant differences. Mandibular plane angle increase, extrusion of upper and lower molars and anterior face height
increase were observed in both groups. Staggers concluded
that her findings do not support the notion of vertical
dimension reduction after extraction orthodontic treatment. It was argued that perhaps extractions have a different effect on Class II patients, who require more retraction of the posterior teeth.
This hypothesis was investigated by Kocadereli,30
who compared 40 Class I non-extraction to 40 Class I four
first premolar extraction cases. Cephalograms were
13
traced, digitized, and 6 linear and 8 angular measurements were obtained. Paired t-tests were used to evaluate
differences and the results showed no statistically significant differences between the two groups. In the discussion, it is hypothesized that, if anchorage is maintained and the extraction space is utilized to alleviate
anterior crowding, vertical dimension loss cannot happen.
Bishara and coworkers31 (1997) studied two groups
of Class II division 1 patients; 46 non-extraction, 45
patients that underwent first premolar extractions, and
35 matched untreated subjects from the Iowa Growth Study.
They examined lateral cephalograms and dental casts pretreatment, immediately post-treatment and two years posttreatment and used analysis of variance (ANOVA) and ttests to analyze the various effects. Although the main
focus was on soft-tissue profile changes, vertical measurements increased in both treatment groups. These changes were also observed two years later.
A study by Komolpis32 compared 32 patients treated
with four first premolar extractions with 48 second premolar extraction subjects. A significant between-groups
difference in linear measurements, such as ANS-Me, N-Me,
Ar-Go was reported. It was suggested that the greater
face height in the first premolar group at the end of
treatment was perhaps due to the excessive vertical
14
dimension they had pre-treatment. The two groups showed
no difference in bite closure as the mandibular plane angle remained constant. This study therefore did not support the wedge effect.
Long-term changes in patients treated with or
without extractions were examined by Stephens and coworkers.33 Forty patients, distributed evenly between the two
groups were analyzed pre- and post-treatment by way of a
coordinate system to measure cephalometric changes. Although this study was mainly focused on soft-tissue effects, it is noted that there were no significant differences between the two groups in terms of vertical and
horizontal displacement of the cephalometric landmarks.
Kim and coworkers34 tested the validity of the
wedge hypothesis by comparing hyperdivergent (defined as
SN-GoGn greater than 32°and FMA greater than 24°) Class I
patients, 27 of which were treated with first premolar
extractions and 27 were treated with second premolar extractions. The two groups were matched for crowding. No
extraoral appliances, elastics or expanders were used.
The maxilla was superimposed on ANS and palatal plane and
the structural method was used for the mandible. More mesial movement of maxillary and mandibular molars was evident in the second premolar group, but there were no dif-
15
ferences in angular and proportional dimensions. They
concluded that the wedge hypothesis seems invalid.
In 2010, Kumari and Fida35 compared 41 nonextraction and 40 first premolar extraction patients by
way of cephalograms and study casts. Interestingly, they
found initial facial height was greater for the extraction group, hinting that vertical dimension could be an
important criterion in the decision making process. Both
groups showed similar increases in vertical parameters
which were attributed to growth and the extrusive tendency of orthodontic treatment. The results of this study
therefore did not support the notion of vertical control
by extracting premolars.
The following year, Gkantidis and coworkers36 compared two groups of Class II division 1 hyperdivergent
patients (SN-GoGn greater than 32 degrees). A group of 29
patients was treated with four first premolar extractions
and high-pull headgear and a second group consisting of
28 patients was treated non-extraction with no vertical
control. They found no differences between the two groups
and concluded that there are limitations to the effects
of conventional orthodontics on skeletal pattern, imposed
by factors beyond our control such as neuromuscular balance and function.
16
An overview of the reviewed studies can be found
in Table 1.1.
Table 1.1. Studies analyzing impact of extractions on vertical measurements.
Author
Year
Groups
Björk’s method
Significant difference
Garlington &
1990
23 U4 L5
1991
48 non-ext
Yes
Logan16
Yamaguchi &
Nanda15
Luecke &
No
73 extraction*
1992
42 U4
Yes
1993
29 non-ext
Yes
Johnston19
Luppanapornlarp &
Johnston20
Chua et al.21
33 extraction*
1993
89 non-ext
No
85 extraction*
Aras22
2002
15 U4 L4
No
9 U5 L5
8 U6 L6
Hans et al.23
2006
56 untreated
Yes
45 U4 L4
30 U6 L6
Bayirli et al.24
2013
36 untreated
36 U4 L4
17
Yes
Table 1.1. Continued
Author
Year
Groups
Björk’s method
No significant difference
Klapper et al.25
1992
15 non-ext
No
15 U4 L4
Paguette et al.28
1992
30 non-ext
Yes
33 U4 L4
Cusimano et al.27
1993
37 U4 L4
Staggers29
1994
45 non-ext
No
Bishara et al.31
1997
35 untreated
No
Yes
46 non-ext
45 U4 L4
Komolpis32
1998
32 U4 L4
Yes
48 U5 L5
Kocadereli30
1999
40 non-ext
No
40 U4 L4
Stephens et al.33
2005
20 non-ext
No
20 extraction*
Kim et al.34
2005
27 U4 L4
No
27 U5 L5
Kumari & Fida35
2010
41 non-ext
No
40 U4 L4
Gkantidis et al.36 2011
28 non-ext
29 U4 L4
18
No
Table 1.1. Continued
Author
Year
Groups
Björk’s method
No significant difference
Lin et al.26
2012
57 non-ext
No
non-ext = non-extraction, U4 = upper first premolars, L4 = lower first premolars, U5 = upper second premolars, L5 = lower second premolars U6 = upper first molars, L6 = lower first molars
*extraction pattern not specified
Overview
After reviewing the literature, what becomes evident is a lack of consensus regarding the validity of the
wedge hypothesis and several weaknesses in the various
study designs and statistical methods. Most of the studies which used structural superimposition20,
23, 24, 27, 28, 32
reported significant differences between the extraction
and non-extraction groups, while most of the authors who
relied only on surface landmarks22,
25, 29, 30, 34, 35
concluded
both groups were similar at the end of treatment. Some
did not include a control group treated without extractions.16,
19, 22, 27, 32, 34
More importantly, none of the stud-
ies reviewed took treatment time into account, a factor
that, if significantly different between extraction and
19
non-extraction groups, raises the problem of differentiating between treatment effects and growth.
Chua and coworkers21 examined a large sample of
174 patients and reported a significant difference between non-extraction and four first premolar extraction
treatment, but did not utilize structural superimposition
and their study therefore is susceptible to the methodological shortcomings due to use of surface landmarks. The
same criticism applies to Staggers,29 who, contrary to the
previous group, reported similar increases in facial
height in both extraction and non-extraction patients.
Bishara and coworkers31 detected some differences in vertical measurements, but again structural superimposition
was not used and therefore caution must be employed when
interpreting these results. Kocadereli30 found similar
changes between the non-extraction and the extraction
groups, but he too relied on surface landmarks.
Aras’22 work differed in that he studied three
groups based on extraction pattern. He compared first
premolar, second premolar, and first molar extractions
and their effect on open bite malocclusions. If the wedge
hypothesis is true, then removing first molars should
produce a greater effect compared to premolars. Indeed,
he found that extracting first molars or second premolars
produced a relative reduction in vertical dimensions, but
20
he too can be criticized for relying on surface landmarks
and a relatively small sample size. Kim’s34 group found no
difference between first and second premolar extractions
and while they did use the structural method, they did
not compare their groups with a non-extraction control
group.
No significant difference was reported by Cusimano and coworkers27 between pre- and post-treatment measurements, but there was no control group and the statistical methods used are unclear. One of the most important
and well executed studies was the work of Hans’23 group,
who found minimal differences between first molar and
first premolar extractions. They had two untreated control groups matched for age and gender and used the
structural method to superimpose tracings.
Some interesting patterns emerge; only Bayirli
and coworkers24 found significant differences between nonextraction treatment and four first premolar extractions.
Kocadereli,30 Staggers,29 Kumari and Fida,35 Klapper and
coworkers,25 and Paquette and coworkers28 reported no differences. Perhaps first premolars are too far forward to
allow adequate molar protraction and produce a detectable
wedge effect.
Studies that included second premolar or first
molar extractions produced mixed results. Kim and cowork21
ers34 and Komolpis32 found no difference between first and
second premolar extractions. On the contrary, Aras22 and
Hans and coworkers23 concluded second premolar and first
molar extractions resulted in better vertical control.
Although this review is extensive, it is by no
means complete. For example, only studies published in
English were included. However, the conflicting results
and fundamental design flaws of some of the studies presented suffice to highlight the need for further research
in order to expand the current body of evidence. It is
worth pointing out once more that none of the reviewed
studies accounted for potential discrepancies in treatment time between extraction and non-extraction treatment.
Prospective, double-blind randomized control trials are the gold standard, but will never be available
due to obvious ethical and practical limitations in this
type of study. Therefore, the only reasonable alternative
for high quality evidence on this subject would be a meta
analysis of pooled data from several well designed retrospective and prospective longitudinal studies.
22
Statement of Thesis
The present study is an effort to contribute to
our knowledge on the effects of orthodontic treatment
with and without extractions, focusing on vertical skeletal and dental measurements. Björk’s37,
38
method of super-
imposition will be used in order to detect mandibular rotation without relying solely on surface landmarks. What
sets this study apart from the ones reviewed is the inclusion of a control group treated without extractions,
use of the structural method of superimposition, and the
use of analysis of covariance (ANCOVA) in order to control for disparities in treatment time.
Because the subjects studied are growing individuals, it is not easy to differentiate between changes
brought on by growth and treatment effects. Moreover, it
is reasonable to assume that as treatment time increases,
so do the effects of treatment and growth. Should treatment time differ significantly between the extraction and
non-extraction groups, the results may be skewed by this
discrepancy. These issues were not addressed by any of
the reviewed articles and a study designed accordingly
may provide more reliable answers.
23
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1. Angle EH. Treatment of Malocclusion of the Teeth. 7th
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2. Angle EH.
Cosmos.
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3. Rinchuse DJ, Rinchuse DJ. Ambiguities of Angle’s
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5. Sassouni V. A classification of skeletal facial
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Growth As Related To Function And Treatment. Angle
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7. Fields HW, Proffit WR, Nixon WL, Phillips C, Stanek E.
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8. Cangialosi TJ. Skeletal morphologic features of
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9. Nanda SK. Patterns of vertical growth in the face.
Am J Orthod Dentofac Orthop. 1988;93:103-16.
10. Schudy FF. The control of vertical overbite in
clinical orthodontics. Angle Orthod. 1968;38:1939.
11. Nasby JA, Isaacson RJ, Worms FW, Speidel TM.
Orthodontic extractions and the facial skeletal
pattern. Angle Orthod. 1972;42:116-22.
12. Joondeph DR, Riedel RA. Second premolar serial
extraction. Am J Orthod Dentofac Orthop.
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13. Pearson LE. Vertical control in treatment of
patients having backward-rotational growth
tendencies. Angle Orthod. 1978;48:132-40.
24
14. Ketterhagen DH. First premolar or second premolar
extractions: formula or clinical judgment? Angle
Orthod. 1979;49:190-8.
15. Yamaguchi K, Nanda RS. The effects of extraction and
nonextraction treatment on the mandibular position.
Am J Orthod Dentofac Orthop. 1991;100:443-52.
16. Garlington M, Logan LR. Vertical changes in high
mandibular plane cases following enucleation of
second premolars. Angle Orthod. 1990;60:263-7.
17. Björk A. Variations in the growth pattern of the
human mandible: longitudinal radiographic study by
the implant method. J Dent Research. 1963;42(1)Pt
2:400-11.
18. Isaacson JR, Isaacson RJ, Speidel TM, Worms FW.
Extreme variation in vertical facial growth and
associated variation in skeletal and dental
relations. Angle Orthod. 1971;41:219-29.
19. Luecke PE, III, Johnston LE, Jr. The effect of
maxillary first premolar extraction and incisor
retraction on mandibular position: testing the
central dogma of "functional orthodontics". Am J
Orthod Dentofac Orthop. 1992;101:4-12.
20. Luppanapornlarp S, Johnston LE, Jr. The effects of
premolar-extraction: a long-term comparison of
outcomes in "clear-cut" extraction and nonextraction
Class II patients. Angle Orthod. 1993;63:257-72.
21. Chua AL, Lim JY, Lubit EC. The effects of extraction
versus nonextraction orthodontic treatment on the
growth of the lower anterior face height. Am J
Orthod Dentofac Orthop. 1993;104:361-8.
22. Aras A. Vertical changes following orthodontic
extraction treatment in skeletal open bite subjects.
Eur J Orthod. 2002;24:407-16.
23. Hans MG, Groisser G, Damon C, Amberman D, Nelson S,
Palomo JM. Cephalometric changes in overbite and
vertical facial height after removal of 4 first
molars or first premolars. Am J Orthod Dentofac
Orthop. 2006;130:183-8.
24. Bayirli B, Vaden JL, Johnston LE, Jr. Original
article: Long-term mandibular skeletal and dental
effects of standard edgewise treatment. Am J Orthod
Dentofac Orthop. 2013;144:682-90.
25
25. Klapper L, Navarro SF, Bowman D, Pawlowski B. The
influence of extraction and nonextraction
orthodontic treatment on brachyfacial and
dolichofacial growth patterns. Am J Orthod Dentofac
Orthop. 1992;101:425-30.
26. Lin CH, Short LL, Banting DW. The effects of nonextraction orthodontic treatment on the vertical
dimension: a comparison of a dolichofacial and a
mesofacial group. Aus Orthod J. 2012;28:37-43.
27. Cusimano C, McLaughlin RP, Zernik JH. Effects of
first bicuspid extractions on facial height in highangle cases. J Clin Orthod. 1993;27:594-8.
28. Paquette DE, Beattie JR, Johnston LE, Jr. A longterm comparison of nonextraction and premolar
extraction edgewise therapy in "borderline" Class II
patients. Am J Orthod Dentofac Orthop. 1992;102:114.
29. Staggers JA. Vertical changes following first
premolar extractions. Am J Orthod Dentofac Orthop.
1994;105:19-24.
30. Kocadereli İ. The effect of first premolar
extraction on vertical dimension. Am J Orthod
Dentofac Orthop. 1999;116:41-5.
31. Bishara SE, Cummins DM, Zaher AR. Treatment and
posttreatment changes in patients with Class II,
division 1 malocclusion after extraction and
nonextraction treatment. Am J Orthod Dentofac
Orthop. 1997;111:18-27.
32. Komolpis R. Cephalometric comparison between first
premolar and second premolar extraction. Ann Arbor,
MI: University of Michigan; 1998.
33. Stephens CK, Boley JC, Behrents RG, Alexander RG,
Buschang PH. Long-term profile changes in extraction
and nonextraction patients. Am J Orthod Dentofac
Orthop. 2005;128:450-7.
34. Kim TK, Kim JT, Mah J, Yang WS, Baek SH. First or
second premolar extraction effects on facial
vertical dimension. Angle Orthod. 2005;75:177-82.
35. Kumari M, Fida M. Vertical facial and dental arch
dimensional changes in extraction vs. non-extraction
orthodontic treatment. J Coll Physicians Surg Pak.
2010;20:17-21.
26
36. Gkantidis N, Halazonetis DJ, Alexandropoulos E,
Haralabakis NB. Treatment strategies for patients
with hyperdivergent Class II Division 1
malocclusion: is vertical dimension affected? Am J
Orthod Dentofac Orthop. 2011;140:346-55.
37. Björk A, Skieller V. Normal and abnormal growth of
the mandible. A synthesis of longitudinal
cephalometric implant studies over a period of 25
years. Eur J Orthod. 1983;5:1-46.
38. Björk A, Skieller V. Postnatal growth and development
of the maxillary complex. Ann Arbor, MI: The
University of Michigan; 1976.
27
CHAPTER 2: JOURNAL ARTICLE
Abstract
Introduction: One of the most important steps in
orthodontic treatment planning is the extraction decision. The “wedge effect” hypothesizes that extracting
posterior teeth allows the mandible to hinge closed,
thereby allowing better vertical control. The objective
of the present study was to compare the different outcomes between patients treated non-extraction and patients treated with extractions, in order to assess the
validity of this concept. Subjects and Methods: Pre- and
post-treatment cephalograms of 191 normal, healthy subjects (67 treated without extractions, 61 treated with
four first premolar extractions and 63 treated with four
second premolar extractions) were obtained from the archive of the Center for Advanced Dental Education orthodontic clinic of Saint Louis University. Class I, Class
II and Class III subjects were similarly distributed
across the three groups. Tracings were superimposed according to Björk’s method for structural superimposition
and fiducial lines were drawn for the maxilla and mandible. A Cartesian system was used to measure vertical and
horizontal changes of ANS, upper first molar and central
incisor, Gonion, Menton, lower first molar and lower cen-
28
tral incisor.
Overbite, as well as SN-GoMe, SN-FOP and
the angle between the maxillary and mandibular fiducial
lines was also measured. Because the different treatment
protocols resulted in significantly different treatment
times, analysis of covariance was performed to test for
different increments of change among the 3 groups while
controlling for the effect of treatment time. Results:
There was a statistically significant difference in horizontal displacement of upper first and lower first molars
between the 3 groups. The lower incisors showed significantly different amounts of extrusion for each group.
There were no statistically significant differences in
amounts of change in any of the other variables. Conclusions: The present study failed to produce evidence of
favorable vertical changes as a result of extractions.
Other than lower incisor vertical displacement, there was
no difference in magnitude of change in vertical measurements between the 3 groups.
29
Introduction
The issue of vertical control has been a subject
of discussion for several decades, since Sassouni and
Nanda1 introduced their analysis. Schudy2 argued in 1968
that extractions may be considered for better vertical
control, even in cases with sufficient space. Nasby and
coworkers3 suggested that using the extraction space to
move the posterior teeth forward allows the mandible to
rotate closed therefore reducing anterior facial height.
Pearson4 examined a group of hyperdivergent patients
treated with first premolar extractions and attributed
the bite closure he observed to the mesial drift of the
posterior teeth “out of the wedge,” and so the wedge hypothesis was born.
As a concept, it had a sound geometric basis and
could be the key to some of the most challenging malocclusions. Logic, however, can sometimes be truth’s biggest enemy. Several investigators have examined the validity of this theory, but the review of the literature
reveals a lack of consensus and conflicting results that
seem to grow from technical differences. Some authors report significant differences between extraction and nonextraction orthodontic treatment,5-11 while others failed
to detect significant differences.12-25
30
The gold standard in assessing changes brought on
by growth and treatment is the fruit of Björk’s26-28 implant study, which identified structures that were stable
enough to use for superimposition. Despite the fact that
Björk’s study predates most of the reviewed articles, not
all the authors opted to use the structural method for
their own research, instead exposing their analysis to
the limitations of relying on surface landmarks.
If the wedge hypothesis is true, it may be difficult to validate by comparing first and second premolar
extractions alone because their antero-posterior position
is similar and may only produce minimal differences in
bite closure. A sample including a first or second molar
extraction group may be more useful in that regard, but
given the scarcity of such cases it was not possible to
obtain for this study. A non-extraction group is necessary in both scenarios in order to draw any meaningful
conclusions regarding the benefits of extractions in
terms of better vertical control.
Finally, treatment time is an important factor
that must be accounted for when trying to interpret any
observed changes. It is reasonable to assume that as
treatment time increases, so do the effects of treatment
and growth. Should treatment time differ significantly
between the extraction and non-extraction groups, results
31
may be difficult to compare and selecting the appropriate
statistical analysis is of utmost importance.
The present study is an effort to address some of
the abovementioned shortcomings in methods and design in
order to provide more reliable answers and contribute to
the existing body of evidence.
Subjects and Methods
Sample
For the present retrospective study, the records
of 191 patients were obtained from the archive of the
Center for Advanced Dental Education of Saint Louis University in Saint Louis, Missouri. The sample consisted of
67 patients treated without extractions (labeled “nonextraction” in tables and figures, mean age 13.18±2.51
years), 61 patients treated with four first premolar extractions (labeled “4s” in tables and figures, mean age
13.86±4.05 years) and 63 patients treated with four second premolar extractions (labeled “5s” in tables and figures, mean age 14.05±4.13 years). Inclusion criteria were
availability of pre- and post-treatment lateral cephalograms of sufficient quality and extraction patterns that
fell in one of the aforementioned categories. Patients
that underwent orthognathic surgery and patients with
craniofacial syndromes or missing teeth (other than third
32
molars) were excluded from the study. Patients with congenitally missing second premolars were included if the
primary second molars were still present at the beginning
of treatment.
Table 2.1. Distribution of patients by Angle
classification in each extraction group.
Non-extraction
4s
5s
Class I
47
40
41
Class II
19
21
20
Class III
1
1
1
Cephalometric Analysis
Pre- and post-treatment lateral cephalograms were
hand traced on 0.003” acetate by the principal investigator (V.C.) according to the guidance of a co-worker
(L.E.J.) who subsequently checked a subset of series. In
order to ensure consistency and reliability, tracings for
each subject were done side by side. Bilateral structures
were traced by bisecting the distance between the two
outlines. Arbitrary maxillary and mandibular fiducial
lines were drawn on one tracing, then transferred to the
other using Bjork’s29 method of structural superimposition. Figure 2.1 shows the anatomical structures and
landmarks traced as well as the Cartesian system used for
horizontal and vertical measurements.
33
Maxillary superimposition was done first using
the anterior surface of the zygomatic process28 and overbite pre-and post-treatment was measured perpendicular to
the functional occlusal plane. Subsequently, a line was
drawn averaging each series’ Sella-Nasion, from which 7
degrees were subtracted to draw a horizontal line which
served as the x-axis of a Cartesian system. The following
structures were projected on the y-axis and their vertical distance from the x-axis were measured and recorded:
1. Anterior Nasal Spine (ANS)
2. Upper First Molar (U6)
3. Upper Central Incisor (U1)
4. Gonion (Go)
5. Menton (Me)
There was a single projection on the x-axis:
6. Upper First Molar (U6)
34
Angular variables measured are listed below:
7. Sella-Nasion to Gonion-Menton (SNGoMe)
8. Sella-Nasion to Functional Occlusal Plane
9. Structural Rotation, measured using the fiducial
lines.
Figure 2.1. Measurements based on maxillary superimposition.
35
The two tracings were then superimposed on the
mandible using the inner cortex of the inferior border of
the symphysis, the mandibular canal and the third molar
germ if present.29 A line was drawn averaging each series’
Gonion-Menton, which served as the x-axis. This was done
to measure dental changes within the mandible. As above,
the projections of the following structures on the coordinate system were measured:
10. Lower First Molar (L6)
11. Lower Central Incisor (L1)
Figure 2.2. Measurements based on mandibular superimposition.
36
Electronic digital calipers were used for linear
measurements and angular measurements were done with a
cephalometric protractor. Age was converted to decimal
years by way of an online calculator.30 Treatment time was
measured in days calculated by a different online calculator.31 Differences between pre-and post-treatment measurements were calculated using Microsoft Excel to subtract the T1 from the T2 value. A positive value for
change designates a downward displacement for vertical
variables and a forward displacement for horizontal variables.
Error Study
To assess reliability of measurements, subjects
were assigned numbers from 1 to 191, which numbers were
then used to generate a random set of 20 patients based
on www.randomizer.org.32 The cephalograms of those patients were then retraced and remeasured to test for intra-observer reliability, which showed a high level of
consistency, as determined by Cronbach’s alpha. The lowest value was .945, for lower incisor vertical displacement.
Statistical Analysis
Descriptive statistics were calculated for each
group pre-and post-treatment. Analysis of variance was
37
performed to test for significant differences in SN-GoMe
between the 3 groups pre-treatment and to compare the
mean treatment times. Because treatment time was significantly different between the non-extraction and the extraction groups, analysis of covariance was selected as
the most appropriate statistical test. The T2-T1 differences were calculated, and ANCOVA was performed to compare the 3 groups with treatment time as the covariate.
Because certain assumptions of ANCOVA were violated, such
as linearity of measurements and normality of distribution, the results were confirmed with ANOVA and KruskalWallis. Tukey’s alpha and Mann-Whitney U test was performed to identify where the differences lay between the
3 groups. All analyses were done using SPSS (version
22.0, SPSS Inc., Chicago, IL).
38
Results
Descriptive statistics for treatment time are included in the following table.
Table 2.2. Means and standard deviations for treatment
time in days.
Non-extraction
(n=67)
Mean
SD
745.1
329.6
4s
(n=61)
Mean
SD
939
302.2
5s
(n=63)
Mean
SD
1015.4
299.3
Analysis of variance revealed statistically significant differences in treatment time between the 3
groups (F(2,188)=13.096, p<.001). Post-hoc analysis was performed to identify where the differences lay among the 3
groups. The results are shown in table 2.2. The nonextraction group displayed significantly reduced treatment time compared to the extraction groups. The differences in mean treatment time between the first and second
premolar groups were not statistically significant.
39
Table 2.3. Post-hoc analysis for treatment time between
groups.
Contrast
p
Non-extraction
4s
.002
Non-extraction
5s
<.001
4s
5s
.360
Descriptive statistics for pre- and post- treatment cephalometric values are summarized in tables 2.3
and 2.4. Descriptive statistics for change are summarized
in table 2.5. The only variables showing significantly
different extent of change among the 3 groups are upper
molar horizontal displacement, lower molar horizontal
displacement and lower incisor vertical displacement. Table 2.6 shows adjusted means for change after controlling
for treatment time by way of ANCOVA.
40
Table 2.4. Descriptive statistics pre-treatment.
Non-extraction
(n=67)
Mean
SD
OB(mm)
3.4
1.9
4s
(n=61)
Mean
SD
3.0
2.1
5s
(n=63)
Mean
SD
3.2
1.7
ANS
Y-axis (vertical distance in mm)
44.9
3.4
44.9
3.9
44.8
3.1
U6
65.1
4.6
65.2
4.7
65.2
4.5
U1
74.7
5.1
75.1
5.2
75.1
4.4
Gonion
74.2
5.8
73.9
5.9
75.5
7.3
Menton
109.9
6.7
111.8
7.6
111.4
8.6
L6
26.5
3.1
26.8
3.2
26.6
3.0
L1
38.9
3.9
40.7
3.5
40.1
3.9
U6
X-axis (horizontal distance in mm)
37.5
5.5
38.4
5.2
39.4
4.1
L6
39.8
5.1
41.5
4.9
Angular measurements
40.4
4.4
SN-FOP
19.2
4.3
19.0
4.2
18.4
4.3
SNGoMe
36.2
5.5
38.4
4.7
36.9
5.3
FOP = Functional Occlusal Plane
41
Table 2.5. Descriptive statistics post-treatment.
Non-extraction
(n=67)
Mean
SD
OB(mm)
1.9
0.7
4s
(n=61)
Mean
SD
1.6
0.7
5s
(n=63)
Mean
SD
1.87
0.8
ANS
Y-axis (vertical distance in mm)
46.3
3.6
46.3
3.9
46.5
3.4
U6
67.8
4.5
68.1
4.8
68.5
4.5
U1
76.7
5.1
77.2
5.3
76.9
6.3
Gonion
78.2
5.9
78.1
6.8
79.5
7.3
Menton
115.1
7.2
116.8
8.0
116.5
9.3
L6
28.9
2.9
29.8
3.1
29.5
2.9
L1
40.7
4.0
41.9
3.6
40.7
3.6
U6
X-axis (horizontal distance in mm)
39.1
5.4
41.2
5.3
42.8
4.2
L6
40.7
4.9
43.7
4.7
Angular measurements
43.5
4.3
SN-FOP
18.8
4.1
19.1
3.7
18.6
4.0
SNGoMe
36.7
5.5
38.4
4.8
37.1
5.4
FOP = Functional Occlusal Plane
42
Table 2.6. Descriptive statistics for increments of
change.
Non-extraction
(n=67)
Mean
SD
OB(mm)
ANS
4s
(n=61)
Mean
SD
5s
(n=63)
Mean
SD
-1.46
1.78
-1.40 2.03 -1.32
Y-axis (vertical changes in mm)
1.44
1.05
1.40
1.04
1.71
p
1.63
ns
1.18
ns
U6
2.69
1.65
2.87
1.69
3.30
2.21
ns
U1
1.99
1.73
2.15
1.91
1.94
4.07
ns
Gonion
3.91
2.47
4.11
2.56
3.98
2.76
ns
Menton
5.18
2.91
5.04
3.11
5.14
3.24
ns
L6
2.41
1.24
2.98
1.62
2.92
1.53
ns
L1
2.10
*
U6
1.74
1.18
1.24
1.34
0.62
X-axis (horizontal changes in mm)
1.56
1.38
2.77
1.36
3.40
1.85
**
L6
0.92
SN-FOP
3.03
1.41
**
-0.36
0.65
2.17
1.30
Angular changes
3.10
0.07
3.61
0.22
3.12
ns
SN-GoMe
0.54
2.98
0.01
1.66
0.19
1.86
ns
StRot
-0.22
2.06
-0.53
2.03
0.06
2.70
ns
ns, p>.05; *p<.05; **p<.001
FOP = Functional Occlusal Plane; StRot = Structural Rotation, measured using fiducial lines.
43
Table 2.7. Descriptive statistics for increments of
change adjusted for treatment time according to ANCOVA.
OB(mm)
Non-extraction
(n=67)
Mean
SE
4s
(n=61)
Mean
SE
-1.51
-1.38
0.23
p
-1.28
0.23
ns
ANS
Y-axis (vertical changes in mm)
1.64
0.13
1.34
0.13
1.55
0.13
ns
U6
3.03
0.22
2.77
0.22
3.04
0.22
ns
U1
2.16
0.35
2.11
0.35
1.81
0.35
ns
Gonion
4.27
0.31
4.01
0.32
3.70
0.32
ns
Menton
5.78
0.36
4.88
0.36
4.67
0.36
ns
L6
2.63
0.17
2.91
0.17
2.74
0.18
ns
L1
0.19
*
U6
1.94
0.19
1.19
0.19
0.46
X-axis (horizontal changes in mm)
1.69
0.19
2.74
0.19
3.30
0.19
**
L6
0.95
0.14
0.14
3.02
0.15
**
SN-FOP
-0.44
Angular changes
0.41
0.09
0.42
0.28
0.42
ns
SN-GoMe
0.57
0.29
0.00
0.29
0.16
0.29
ns
StRot
-0.13
0.29
-0.55
0.29
0.00
0.29
ns
2.17
0.23
5s
(n=63)
Mean
SE
ns, p>.05; *p<.05; **p<.001
FOP = Functional Occlusal Plane; StRot = Structural Rotation, measured using fiducial lines.
44
ANCOVA
The increased treatment time for the extraction
groups must be considered when analyzing the effects of
treatment and growth. In order to eliminate the differences that may be caused by this discrepancy, ANCOVA was
performed to control for treatment time.
There was a significant effect of different extraction patterns on the horizontal displacement of the
upper first molars after controlling for the effect of
treatment time, F(2,187)=16.208, p<.001. Post-hoc analysis
revealed that there was significantly more horizontal
displacement in the four first premolar extraction group
(2.77 ± 1.36mm, p=.001) and the second premolar extraction group (3.4 ± 1.85mm, p<.001) compared to the nonextraction group (1.56 ± 1.38mm). There were no statistically significant differences between the first and second premolar extraction groups.
There was also a significant effect of different
extraction patterns on the horizontal displacement of the
lower first molars after controlling for the effect of
treatment time, F(2,187)=45.837, p<.001. Post-hoc analysis
revealed significantly greater horizontal displacement in
the four first premolar group (2.17 ± 1.3mm, p<.001) and
the four second premolar group (3.03 ± 1.41mm, p<.001)
compared to the non-extraction group (0.92 ± 0.65mm).
45
A significant effect was also observed for lower
incisor vertical displacement, F(2,187)=13.308, p<.001.
Post-hoc tests showed statistically significantly greater
extrusion in the non-extraction group (1.74 ± 1.18mm,
p<.001) compared to the four second premolar extraction
group (0.62 ± 2.1mm). No other variables showed statistically significant differences when controlling for treatment time.
Certain assumptions of ANCOVA, however, were violated. The dependent variables were not normally distributed for all groups. Homogeneity of variances was also
not equal for all variables according to the Levene statistic, and treatment time was not linearly related to
the dependent variables for each group according to the
scatterplots.
To confirm the results of the ANCOVA, ANOVA was
performed as well as Kruskall-Wallis one-way analysis of
variance. Both tests and their post-hoc analyses (Tukey’s
post-hoc analysis and Mann-Whitney U test) confirmed the
differences detected by ANCOVA. The findings are summarized in the appendix.
46
Discussion
Limitations
In order to be able to better interpret the results of the present study, it is important to
acknowledge certain limitations. As with any retrospective study, it is difficult to guard against selection
bias, given that individuals are not randomly assigned to
each group. Depending on their initial vertical measurements, they may be more likely to be treated with different approaches, creating a biased measure of association.
However, there were no statistically significant differences between group means for initial SNGoMe as shown by
one-way ANOVA (F(2,188)=2.844, p=.061). There were also no
statistically significant differences between group means
for initial overbite (F(2,188)=.513, p=.60).
Exposure identification bias is not a concern,
since misclassification was avoided easily by referring
to patient charts and extraction orders. This study is
also relatively immune from recall bias, as there is no
reason to assume a patient treated with extractions has a
higher or lower probability of completing orthodontic
treatment versus one that was treated non-extraction.
A long-term recall of patients treated with different extraction protocols may be less accurate in de-
47
termining the validity of the wedge hypothesis, due to
recall but also temporal bias. The present study measured
subjects immediately post-treatment and therefore is advantageous in that regard.
Interviewer bias is not easy to guard against,
since a single investigator classified the subjects,
traced their radiographs and measured the tracings. In an
effort to minimize the risk, however, there were no identifiers on the tracings regarding each patient’s extraction pattern.
It should be noted that the subjects in the present study were treated by numerous clinicians over a
span of 3 decades. A variety of appliances and treatment
modalities were used; however, it was not the purpose of
this investigation to evaluate the effects of each protocol. In fact, controlling for different mechanics and use
of directional forces can be very challenging. For example, it would require a reliable method for assessing
compliance with use of headgear or intermaxillary elastics.
Another factor not taken into account was the
amount of crowding in each case. If anchorage is maintained and the extraction space is used to relieve anterior crowding or reduce protrusion, one would expect less
mesial movement of molars. However, the results of the
48
present study for horizontal displacement of upper and
lower molars are similar to those reported by other authors.20,21
It was determined that the most efficient design
for the present investigation would be to group subjects
only by extraction pattern, disregarding factors such as
Angle classification, amount of crowding, and
treatment
mechanics. Instead, treatment time was selected as the
most important differentiating factor. Extraction groups
showed significantly longer treatment times compared to
the non-extraction group, which could produce greater
changes due to growth thus making the results difficult
to interpret.
The Wedge Hypothesis
As expected, molars in the 3 groups showed different increments of mesial displacement. If the wedge
hypothesis is true, this should result in different
amounts of change in vertical dental and skeletal measurements. However, the only vertical measurement significantly different between the 3 groups was the amount of
lower incisor extrusion. Mandibular rotation was assessed
by measuring the SN-GoMe angle before and after treatment
and also by using fiducial lines. This was done to examine basal bone rotation as well as possible compensatory
surface changes that might serve to mask it by keeping
49
SN-GoMe relatively unchanged. Both showed similar increments of change.
Results Compared to Literature
The results of the present study are in agreement
with those reported by some authors14-25 but contradict
others that reported significant vertical changes.5-11 Table 2.8 summarizes findings from similar studies.
Molar displacement in the first premolar extraction group is similar to the findings of Paquette and
coworkers,13 Kim and coworkers,20 and Komolpis.25 On the
contrary, Aras8 reported higher values, as one might expect due to the fact that one of the inclusion criteria
for his study was use of most of the extraction space for
forward movement of molars. Cusimano and coworkers,15 too,
showed more molar displacement, but no error study was
conducted and their sample was relatively small. Klapper
and coworkers23 also found a significantly higher value,
which could be due to their methodology. They used the
distal contact point of the upper first molar (possibly
more sensitive to the tipping that could occur during
space closure) to a vertical drawn from the pterygomaxillary fissure. It is also worth pointing out that no error
study was reported.
50
For molar displacement in the second premolar extraction group, the findings of the present study are
similar to those of Aras,8 and Kim and coworkers.20 Komolpis25 reported a slightly higher value for the lower
molars, which could be due to the fact that sliding mechanics with elastic chains were used for space closure.
An interesting observation worth analyzing is the
finding that upper molars displaced forward slightly more
than the lower molars. One might expect identical values
for both, given that most of the subjects studied were
Class I. The reason behind this discrepancy may be
growth; as the mandible outgrows the maxilla in the present sample consisting mainly of growing patients, the
upper molars move forward more within the maxillary alveolar bone than the lowers in order to maintain intercuspation. Another important point to consider is the methodology used, which examined molar displacement relative
to basal bone. If changes were measured along the functional occlusal plane the values would probably have been
different; however, it is not within the scope of the
present investigation to analyze the effects of growth in
an antero-posterior direction.
In terms of vertical changes, anterior face
height increased by almost identical increments in all
three groups. For the non-extraction group, Staggers,16
51
Luppanapornlarp and Johnston,14 Kumari and Fida21 and Kocadereli17 reported similar values. The slightly larger increase detected by Paquette and coworkers13 could be due
to sample selection, which only included Class II, division 1 patients. If Class II elastics were used, molar
extrusion could explain this discrepancy.
In the four first premolar group, Aras,8
Staggers,16 Paquette and coworkers,13 and Kocadereli17 show
results similar to those of the present study. Kumari and
Fida21 reported
significantly less increase in anterior
face height, which could be explained due to the fact
that their extraction group had a greater pre-treatment
value. In the four second premolar group, Aras8 and Komolpis25 showed similar increases in anterior face height
that agree with the findings of this investigation.
Mandibular plane angle showed similar magnitude
of change in all reviewed studies and the results of the
present investigation are in agreement with the literature.
52
Table 2.8. Results compared to similar studies.
Non-extraction
4s
5s
Menton
(mm)
5.18
U6H
(mm)
1.56
L6H
(mm)
0.92
MPA
(°)
-0.22
Menton
(mm)
5.04
U6H
(mm)
2.77
L6H
(mm)
2.17
MPA
(°)
0.01
Menton
(mm)
5.14
U6H
(mm)
3.40
L6H
(mm)
3.03
MPA
(°)
0.19
Aras8
. .
. .
. .
. .
5.40
3.66
4.14
-0.20
4.00
3.89
3.72
-1.06
Komolpis25
. .
. .
. .
. .
7.02
3.11
2.10
0.24
4.80
3.92
3.66
0.05
Kim et al.20
. .
. .
. .
. .
. .
2.72
2.14
0.56
. .
3.84
3.62
0.52
Cusimano et al.15
. .
. .
. .
. .
. .
5.00
4.10
0.40
. .
. .
. .
. .
Paquette et al.13
7.00
1.00
0.10
-2.00
5.40
2.50
3.30
0.30
. .
. .
. .
. .
Luppanaporlarp &
Johnston14
5.00
0.80
. .
0.70
. .
. .
. .
. .
. .
. .
. .
. .
Kocadereli17
5.98
. .
. .
0.27
4.67
. .
. .
0.10
. .
. .
. .
. .
Kumari & Fida21
5.50
. .
. .
0.60
1.50
. .
. .
-0.20
. .
. .
. .
. .
Klapper et al.23
. .
1.27
. .
. .
. .
4.43
. .
. .
. .
. .
. .
. .
Staggers16
5.08
. .
. .
0.14
5.38
. .
. .
0.11
. .
. .
. .
. .
. .
. .
. .
. .
7.20
. .
. .
. .
. .
. .
. .
. .
Author(s)
Present study
Bayirli et al.
10
U6H = Upper 6 horizontal displacement, L6H = Lower 6 horizontal displacement,
MPA = Mandibular plane angle
53
Overview and Future Research
The present study examined a sample larger than
any of its predecessors mentioned in the literature review. Even so, it failed to produce evidence that would
indicate a forward rotation of the mandible and better
vertical control for the extraction groups. However, this
does not mean orthodontists are powerless when it comes
to managing problems in the vertical dimension. Instead,
it should perhaps serve as an indication that forward
mandibular rotation as a result of moving posterior teeth
forward into the extraction spaces may not be a realistic
expectation. Using directional extra-oral forces33 or temporary anchorage devices to intrude or minimize extrusion
of posterior teeth34 may be a less aggressive and more effective approach.
Schudy35 argued that, in deep-bite patients, levelling should be done by extruding molars due to the inherent instability in extrusive or intrusive movement of
upper and lower incisors35 but presented no evidence to
support this statement. This argument has been disproven
by other authors.36,
37
Managing incisors in the vertical
direction by using extra-oral forces, temporary anchorage
devices, or intermaxillary elastics are reasonable approaches and should not be discounted, although more research is needed to determine which modality provides
54
greatest long-term stability. Surgical solutions, such as
maxillary impactions or sub-apical osteotomies may also
be indicated for certain patients.
In summary, the dentofacial complex apparently
does not behave like a hinge. Addressing vertical dimension problems should take all factors into account, including facial soft tissue and skeletal proportions,
growth potential, eruption patterns, habits, lip length,
gingival display, Angle classification and crowding.
There is a significant body of evidence against the wedge
hypothesis and it is in the best interest of our profession and our patients to acknowledge it rather than
anachronistic and unproven concepts.
55
Conclusions
The present investigation failed to detect differences in amounts of vertical change between extraction
and non-extraction orthodontic treatment.
As expected, first molars showed greater mesial
displacement in the four second premolar extraction
group, followed by the four first premolar extraction
group and the non-extraction group. However, the alleged
counterclockwise rotation of the mandible and subsequent
bite closure was not evident.
Treatment decisions should be based on all available diagnostic parameters and the alleged improved vertical control does not suffice as justification for extractions in absence of other discrepancies, such as
crowding or dental and soft tissue protrusion.
56
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60
Appendix
ANOVA
One-way ANOVA confirmed that there was a significant difference in horizontal displacement of upper first
molars between groups, F(2,188)=23.576, p<.001. A Tukey’s
post-hoc test revealed that there was significantly more
horizontal displacement of upper first molars in the four
first premolar extraction group (2.77 ± 1.36mm, p<.001)
and the second premolar extraction group (3.4 ± 1.85mm,
p<.001) compared to the non-extraction group (1.56 ±
1.38mm).
It was also confirmed that there was a significant difference in horizontal displacement of lower molars between the 3 groups, F(2,188)=54.514, p<.001. However,
Tukey’s post-hoc analysis showed significantly more horizontal displacement of lower first molars between all
groups. The lower molars in the four second premolar extraction group showed the greatest forward movement (3.03
± 1.41mm, p<.001), the four first premolar group showed
less change (2.17 ± 1.3mm, p<.001) and the non-extraction
group showed minimal displacement (.92 ± .65mm). The difference between the four first premolar and four second
premolar extraction groups was statistically significant
at p<.001.
61
A statistically significant difference was also
confirmed in the amount of lower incisor extrusion,
F(2,188)=8.125, p<.001. Tukey’s post-hoc analysis showed
more lower incisor extrusion in the non-extraction group
(1.74 ± 1.18mm, p<.001) compared to the four second premolar extraction group (.62 ± 2.1mm).
No other variables showed statistically significant differences in amount of change between the 3
groups.
Non-parametric Tests
Figure A.1. Upper first molar horizontal displacement.
A Kruskal-Wallis H test showed that there was a
statistically significant difference in upper molar hori-
62
zontal displacement between the 3 groups, χ2=42.211,
p<.001, with a mean displacement of 1.56mm for the nonextraction group, 2.77mm for the four first premolar extraction group and 3.4mm for the four second premolar extraction group.
A Mann-Whitney U test was used to determine where
the among-groups differences lay. Distributions were not
similar, as assessed by visual inspection. Upper first
molar horizontal displacement in the four first premolar
extraction group (mean rank=82.10) was significantly
greater than in the non-extraction group (mean
rank=48.48), U=970, z=-5.122, p<.001. The four second
premolar extraction group (mean rank=85.17) showed significantly greater upper first molar horizontal displacement compared to the non-extraction group, U=871.5, z=5.772, p<.001. The four first premolar group (mean
rank=56.45) and the four second premolar group (mean
rank=68.36) were not significantly different, U=1552.5,
z=-1.844, p=.065.
It was also confirmed that there was a statistically significant difference in lower molar horizontal
displacement among the 3 groups, χ2=75.871, p<.001, with a
mean displacement of .92mm for the non-extraction group,
2.17mm for the four first premolar extraction group and
3.03mm for the four second premolar extraction group.
63
Figure A.2. Lower first molar horizontal displacement.
Again, a Mann-Whitney U test was used to determine where the differences lay between the groups. Distributions were not similar, as assessed by visual inspection. Lower first molar horizontal displacement in
the four first premolar group (mean rank=83.73) was significantly greater than in the non-extraction group (mean
rank=46.99), U=870.5, z=-5.596, p<.001. The four second
premolar extraction group (mean rank=94.02) showed significantly greater lower molar horizontal displacement
than the non-extraction group (mean rank=38.68), U=313.5,
z=-8.372, p<.001. The four second premolar group (mean
rank=72.99) showed significantly greater horizontal dis64
placement than the four first premolar extraction group
(mean rank=51.66), U=1260.5, z=-3.304, p=.001.
The lower incisor vertical displacement was also
significantly different between the 3 groups, χ2=8.265,
p=.016, with a mean displacement of 1.74mm for the nonextraction group, 1.24mm for the four first premolar
group and .62mm for the four second premolar extraction
group. No other variables showed statistically significant differences.
Figure A.3. Lower incisor vertical displacement.
Once more, a Mann-Whitney U test was run to identify the differences between the 3 groups. Distributions
were not similar, as assessed by visual inspection. Lower
65
incisor vertical displacement in the non-extraction group
(mean rank=70.49) and the four first premolar extraction
group (mean rank=57.93) were not significantly different,
U=1642.5, z=-1.913, p=.056. The non-extraction group
(mean rank=74.39) showed statistically significantly
greater lower incisor vertical displacement than the four
second premolar group (mean rank=56.05), U=1515, z=2.774, p=.006. The four first premolar group (mean
rank=65.53) and the four second premolar group (mean
rank=59.56) were not significantly different, U=1736.5,
z=-.925, p=.355.
A possible explanation for the outliers in the
four first premolar and four second premolar extraction
groups may be that patients with deep curves of Spee are
more susceptible to extraction treatment, keeping in mind
that levelling requires space. When levelling, lower incisors may be intruded or tipped forward, which would result in a negative value for lower incisor vertical displacement.
66
Vita Auctoris
Vasileios Charalampakis was born on July 28, 1986
in Athens, Greece. He received his D.D.S. degree from the
National and Kapodistrian University of Athens in 2011.
In June 2012 he moved to the United States of America and
began his orthodontic residency program at the Center for
Advanced Dental Education at Saint Louis University, in
Saint Louis, Missouri. He is presently a candidate for
the degree of Master of Science in Dentistry.
67