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A comparison of the long-term stability of three different treatment philosophies
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Content
A COMPARISON OF THE LONG-TERM STABILITY OF THREE
DIFFERENT TREATMENT PHILOSOPHIES
by
Adam J. Brand
A Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(CRANIOFACIAL BIOLOGY)
May 2002
Copyright 2002 Adam J. Brand
UNIVERSITY OF SOUTHERN CALIFORNIA
THE GRADUATE SCHOOL
UNIVERSITY PARK
LOS ANGELES. CALIFORNIA 90007
This thesis, written by
under the direction of h.i>, Thesis Committee,
and approved by all its members, has been pre
sented to and accepted by the Dean of The
Graduate School, in partial fulfillment of the
requirements for the degree of
r.-
ON/a
DiOM
Date....
TI- El
3cr^^ 0 r
A>-.
—-y
Chairman
f
DEDICATION
This thesis is dedicated to my fiance Carina for her
unwavering encouragement and support.
11
ACKNOWLEDGEMENTS
I would like to thank my mentor, Peter Sinclair
for his guidance and assistance throughout this
project. I am also grateful for the warm southern
hospitality that Dr. Jim Boley and Dr. Wick Alexander
exhibited during our Texas excursion. I would also
like to thank Robert Keim for his statistical guidance
and expertise.
iii
TABLE OF CONTENTS
Dedication ii
Acknowledgements iii
List of Tables V
List of Figures VI
Chapter 1: Introduction 1
Chapter 2: Review of the Literature 6
Chapter 3: Materials and Methods 14
Chapter 4: Research Questions 20
Chapter 5: Results 21
Chapter 6: Discussion 86
Chapter 7: Conclusions 96
References 98
iv
LIST OF TABLES
Table I ABO Individual Components Summary 69
Table II Correlations 82-83
Table III Reliability Statistics 85
V
LIST OF FIGURES
Figure 1 Incisor Irregularity Comparison 23
Figure 2 Mandibular Intercanine Width Comparison 26
Figure 3 Arch Length Comparison 29
Figure 4 PAR Comparison 33
Figure 5 PAR Percent Change 34
Figure 6 PAR at T2 35
Figure 7 PAR at T3 36
Figure 8 ABO Overall Comparison 40
Figure 9 ABO Point Deductions at T2 41
Figure 10 ABO Point Deductions at T3 42
Figure 11a ABO- Alignment 45
Figure 11b ABO- Alignment 46
Figure 12a ABO- Marginal Ridges 49
Figure 12b ABO- Marginal Ridges 50
Figure 13a ABO- Buccal-Lingual Inclination 53
Figure 13b ABO- Buccal-Lingual Inclination 54
Figure 14a ABO- Occlusal Contacts 57
Figure 14b ABO- Occlusal Contacts 58
Figure 15a ABO- Occlusal Relationships 61
Figure 15b ABO- Occlusal Relationships 62
vi
Figure 16a ABO- Overjet 65
Figure 16b ABO- Overjet 66
Figure 17 ABO- Components Summary 68
Figure 18a Tweed Class I vs. Class II 71
Figure 18b Alexander Class I vs. Class II 72
Figure 18c Washington Class I vs. Class II 73
Figure 19a T3 PAR Scores Based on Treatment
Quality 76
Figure 19b T3 ABO Scores Based on Treatment
Quality 77
Figure 19c Post-Retention Incisor Irregularity
Based on Treatment Quality 78
Vll
Chapter 1: INTRODUCTION
Orthodontics is unique within dentistry because it
focuses on a range of normal biologic variation that is
essentially deficient of pathology or disease.
Therefore, orthodontic treatment is not entirely
mandatory and inevitably subjective about the criteria
used to evaluate prevalence, severity, and treatment
success. This subjectivity has led to a lack of
conformity between practitioners as to what constitutes
the finest treatment and has also led to a plethora of
treatment techniques and approaches. Because each of
these techniques straightens teeth to an acceptable
standard, the goal of practitioners must be to determine
what is the optimum treatment approach to allow for the
healthiest and most stable long-term result in the
greatest number of patients.
The question of the long-term stability of
orthodontic treatment outcomes has engaged and frustrated
the profession for years. The improvements achieved from
lengthy and conscientious treatment may be lost to
various degrees after the appliances are removed. Many
1
previous studies have focused on this very topic but few
have been able to entirely objectify their results and
1,5,6,7,43 have often used different measures on small samples.
A fully comprehensive study of the numerous
different treatment techniques in orthodontic treatment
is needed to determine the optimum approach to maximize
the stability of orthodontic treatment. Many previous
samples have been individually analyzed, but a synthesis
and evaluation of the data is needed to formulate
orthodontic generalizations about relapse. Not only
will a collaboration of data increase the sample size.
but also will allow for a comparison of the differing
treatment styles and philosophies. In addition, this
approach could identify associations between numerous
occlusal and treatment variables and their effect, or
lack there of, on post-treatment stability. Once the
variables that specifically effect post-treatment relapse
independent of treatment technique are identified, the
treatment techniques can be modified to produce superior
outcomes not just at debonding but for years thereafter.
Long-term retention studies, evaluating cases 10 and
20 years post-retention, from the University of
2
Washington have shown the elusiveness of long-term
1,2,3,4 orthodontic stability. The data of the most cited
study from these patients showed adequate stability in
only one third of the sample with questionable stability
13 in the other two thirds. According to these findings.
orthodontic relapse is the norm, not the exception.
These assertions have often been questioned by many
in the orthodontic community based on experience with
their own patients whom they claim experience far less
relapse. In particular, the Tweed practicing
orthodontists have long questioned the Washington results
5,6,7 based on research design and sample selection. Many
have reported far greater long-term stability rates; for
example, Gorman reports over 50% stability^, Sadowsky
85%^, and Sandusky 90% stability.’ The cases in the
Washington sample were a mixture of cases treated by
faculty, residents, and private practitioners; each group
and each individual with a different definition of
treatment completion. The skeptics imply that a single
practitioner with more experience can superiorly treat
the cases and thus improve long-term stability.^
3
The following questions have yet to be answered in a
scientific manner. Do specific treatment philosophies
have an effect on stability? What measures can be used
to quantify stability? Is there a correlation between
quality of treatment and stability? Do cases that the
ABO would classify as passing have improved stability?
Do failing ABO cases have decreased stability? Does the
maintenance of specific principles like intercanine width
improve stability?
Today there exist several objective methods for the
evaluation and grading of orthodontic treatment results.
These grading scales can be used to quantify the initial
difficulty of a case and can be used to evaluate the
final treatment outcome. The two most commonly used
scales are the American Board of Orthodontics and Peer
8,9 Assessment Review grading scales. Each of these scales
emphasize different concepts, the PAR is best at grading
relationships while the ABO is a more specific occlusal
grading scale. These scales were used concurrently in
this study in order to balance the strengths and
10 weaknesses of each grading index.
4
This study applied the ABO and PAR grading scales to
the dental casts of three groups of bicuspid extraction
cases at three time intervals; the original University of
Washington sample, a Tweed sample, and an Alexander
Discipline sample. It attempted to develop correlations
between treatment philosophies and the quality of the
long-term stability. In addition, the outcomes of
individual components of the malocclusion were dissected
to attempt to identify areas of consistency and areas
that might be dependent on the treatment approach used to
treat them.
5
Chapter 2: LITERATURE REVIEW
In 1907, Edward Angle maintained that orthodontic
correction will remain stable if the teeth are aligned
into a normal occlusion and provided with adequate
11 retention and vigorous masticatory function. However,
orthodontists have observed that their treatment results
are susceptible to at least as much damage as untreated
occlusions, and that there certainly are limitations in
the long-term stability of corrected relationships.
Numerous factors have been reported to effect post
treatment relapse, although no definite conclusions have
been formulated regarding the relative importance of each
12
to the final stability.
Arch form:
One of the most controversial subjects in
orthodontics has been the stability of an orthodontic
increase in arch width. During normal untreated arch
development, a moderate increase in arch width is seen
until permanent cuspid eruption, in turn followed by a
decrease in intercanine width during adolescence and into
6
14,15,16
adulthood. The intermolar width, however, remains
14,15,16 constant from 13 to 20 years of age. It has also been
found that with normal aging, there is a decrease in
overall arch length and increase in incisor irregularity
14,15,16
over time.
Although constantly violated, one of the most
accepted dogmas of post-treatment instability is the
alteration of the original arch form. Studies have
concluded that intercanine and intermolar width increases
17,18 during treatment will lead to post-treatment relapse.
Exceptions may occur when narrow maxillary arches are
expanded along with the mandibular arch to obtain a more
19,20
normal arch form. Some studies have shown that an
increase of up to 3mm may be obtained and be stable.
while others have shown that only the maxillary arch is
stable to increases and that the mandibular arch is
19,20,21 extremely susceptible to expansion relapse. The
patient's pretreatment arch form appears to be the best
guide for post-treatment relapse^^, but certainly is no
guarantee of post-treatment stability.
7
Gingival Tissues:
As a malpositioned tooth is rotated orthodontically.
a resulting stretch of the collagen fibers ensues. These
stretched fibers have been implicated in the rotational
post-treatment relapse of teeth by pulling back to their
24,25,26,27 original position. Numerous experimental approaches
have been attempted to eliminate these fibers including
immediate torsion with forceps, removal of cortical bone.
and removal of attached gingiva. Circumferential
supracrestal fiberotomies have been proposed to allow
release of soft tissue tension and subsequent
reattachment of the fibers in a passive orientation after
26,27 orthodontic alignment. Studies have shown when a
circumferential supracrestal fiberotomy is done, a
decrease in incisor irregularity compared to control
28 subjects occurs. This theory has recently been
questioned through histologic studies of dogs with
results that conclude that the rotational relapse may
derive from the elastic properties of the whole gingival
tissue rather than solely the stretching of the collagen
29
fibers.
8
Incisor dimensions and shape:
Peck and Peck's original article on untreated
normal occlusion showed an increase in stability of
individuals with a specific faciolingual/mesiodistal
30
ratio of the lower incisors. It has since been shown
that there is only a weak association of long term
irregularity and either incisor width or
31,32,33.34 faciolingual/mesiodistal ratio.
Neuromuscular Balance:
The initial presenting position of the lower
incisors has been publicized as the best guide to the
36,37,54 most stable long-term incisor position. In these
studies, over half of the long-term lower incisor
positions ended up in a location between the pre
treatment and post-treatment positions. Therefore, in
order to maximize stability, the pretreatment lower
incisor must not change. The suggestion is that all
incisors lie in a narrow zone of stability in equilibrium
between the opposing muscle pressure of the lips, cheeks
38,39 and tongue.
9
Occlusion:
A functional and firm occlusion is repeatedly
associated with long-term stability, and is habitually
36,39,40
stressed in a well-treated case. Optimum interincisal
contact angle may thwart overbite relapse and maximum
posterior intercuspation may prevent relapse transversely
and antero-posteriorly. A decreased amount of
mesiodistal movement is associated with an absence of
12
occlusal stress and a CO-CR slide was found to have a
statistically significant influence on mandibular incisor
55 irregularity postretention.
Influence of the original malocclusion is another
factor associated with relapse. The amount of overbite
corrected either by decreasing or increasing it, had an
effect on retention, as bites tended to relapse toward
3,13,43,44 their original position. In addition, as stated
previously, rotated teeth tend to relapse toward their
original position and it has been shown that teeth that
needed more correction tended to show the most rotational
41 relapse. Although many studies show malocclusions to
relapse toward the pre-treatment rotations and
10
displacement. Little observed that 50% of relapse is in
13 the opposite direction to the original malocclusion.
Grading Indices:
It is apparent that virtually all orthodontic
treatment achieves some measure of success, but how do we
measure that success? It is necessary to utilize an
objective, practical, and reliable outcome measure in
order to accurately measure and compare treatment
outcomes. Over the years. a variety of occlusal indices
have been developed for a variety of different uses:
diagnostic, epidemiological, the determining of treatment
23 need, treatment complexity, and treatment success rates.
Presently, there exist several objective methods for
the grading and evaluation of the quality of completed
orthodontic cases. The two used in this study were the
Peer Assessment Rating and the American Board of
Orthodontics grading index. Both the PAR and the ABO
dental cast measuring scales use specific criteria to
assign numerical scores to a case.
18 The PAR scale, developed by Richmond in 1989^ is
used in two ways to calculate scores; one, reduction in
11
the weighted PAR score and two, the percentage reduction
in the PAR score over time. In the last 10 years, the
46 9,48 PAR has been used both in the US’” and UK to evaluate
treatment outcomes. It has also been used to assess
extraction versus non-extraction treatment and to
49,50,51 evaluate the need for two-phase treatment.
The ABO cast grading scale was developed by the
American Board of Orthodontics in the 1990's to assess
8
candidates seeking board certification more objectively.
Although the PAR had good reliability and validity, it
did not measure precisely enough to distinguish between
the minor inadequacies of tooth position that are found
in board cases. Through a series of field tests, the ABO
has refined the scale over the last seven years and it is
now in use and accessible for candidates to use
themselves.
In a recent study at the University of Southern
California, the ABO and PAR scales were critically
examined in the areas of reliability, validity, and
10 applicability. The research stated that the ABO grading
scale is capable of measuring the fine detail of finished
cases; however, it does not accurately record overbite
12
and midline. The PAR index was found to accurately
measure finished cases; however, it does not measure
specifics of occlusion like torque and marginal ridge
discrepancies. Additionally, both indices demonstrated
acceptable inter-grader reliability. Because these two
indices have differing strengths and weaknesses, used
concurrently these scales can become an extremely
powerful tool for measuring treatment outcomes on an
accurate and reproducible scale.
13
Chapter 3: MATERIALS AND METHODS
The data set for this study included 154 cases,
divided amongst three groups, consisting of a Tweed
sample, an Alexander discipline sample, and the original
University of Washington retention sample. Each of the
samples was limited to Class I or Class II malocclusions
treated with routine extraction of four first or second
bicuspids. Class III malocclusions or orthognathic
surgery cases were excluded in this study. Each case had
complete dental cast records before treatment, after
treatment. and at least six years after treatment with an
average post-treatment time of 15.6 years.
The Tweed sample came from the office of Dr. James
Boley. Each of the cases was treated with the strict use
of the Tweed philosophy and its principles. This sample
consisted of 62 cases treated exclusively by Dr. Boley
that he has collected over the years. The average time
post-retention was 14.7 years.
The Alexander sample came from the office of Dr.
Richard "Wick" Alexander. Each of the 40 cases in this
sample was treated by Dr. Alexander. The average time
post-retention time was 16.5 years.
14
The Washington sample consisted of 52 of the
original 65 cases selected for the University of
12 Washington stability study. Of the original cases, 13
with insufficient records were rejected to generate a
final sample of 52. The overall post-retention time was
16.0 years.
All the cases received retention measures as
dictated by the philosophy and practitioner of the
individual case. The Tweed and Alexander philosophies
typically call for fixed lower canine-to-canine retainers
for at least 1-3 years post-treatment, although no
definite time frame was used. There were various amounts
of interproximal reduction at the time of bonded retainer
removal for the Alexander cases. The Washington sample
received differing retentive measures based on the
treating doctor, which included both fixed and removable
retainers.
Each of the samples was measured at pre-treatment
(Tl), post-treatment (T2), and post-retention (T3) for
the following variables in random order by one of the two
examiners:
15
Incisor Irregularity- As suggested by
13 Little, the summed displacement of the
anatomic contact points of the lower anterior
teeth.
Mandibular Intercanine Width- The distance
between the cusp tips or estimated cusp tips
in cases of wear facets.
53 Arch Length- As suggested by Nance, the sum
of the right and left distances from mesial
anatomic contact points of the first
permanent molars to the contact point of the
central incisors or to the midpoint between
if spaced.
Peer Assessment Rating Index- (Appendix #1)
American Board of Orthodontics Grading Scale-
(Appendix #2)
The data collection from the Washington sample was
collected from the Master's Thesis of Dr. Anthony
Fernandes'*"^ and the original University of Washington
12 study.
Examiner bias was controlled in the original
Washington study by the random grading of casts by
16
various examiners. Measurement error was evaluated by
the random selection and re-measuring of 21 casts on
three different occasions. The mean error in the incisor
irregularity index measurement was 0.30mm; the mean error
in the mandibular intercanine width and arch length
measurements ranged from 0.11-0.19mm. To ensure the
reliability of the PAR and ABO scores, 9 cases were re
examined and all the scores were found to have a
correlation of greater than 0.93.
In the current study, to objectively grade the
initial difficulty of the case and the quality of the
final post-treatment outcome, two dental cast occlusal
indices were applied to the sample. The Peer Assessment
Rating (PAR) examines several dental features of a pre
treatment cast to derive an overall preliminary severity
score. This score, ranging from 0 to as much as 70
provides an overall rating of the initial case
irregularity. A score of more than 40 represents a
highly complex or irregular malocclusion. The post
treatment casts were then scored using the same index. A
score of 5 or less represents a well-treated case. The
17
percentile difference between the initial and final score
indicates the degree of improvement of the case.
The five criteria to grade the dental casts using
the PAR:
I. Upper and lower anterior segments
II. Left and right buccal occlusion
III. Overjet
IV. Overbite
V. Midline
These criteria were then scored using the PAR guidelines
(Appendix #1) at pre-treatment (Tl), post-treatment (T2),
and post-retention (T3).
The second dental cast occlusal index used in this
study was the American Board of Orthodontists (ABO) scale
(Appendix #2). The ABO scale was modified in order to
only reflect dental cast measurements, not radiographs or
treatment objectives or results. The modified ABO
grading scale uses six criteria to grade the treatment
results:
I. Alignment
II. Marginal ridges
III. Buccolingual inclination
18
IV. Occlusal contacts
V, Occlusal relationships
VI. Overjet
The seventh dental cast measurement, interproximal
contacts was not included because it was added to the ABO
scoring after the data collection for the Washington
47 sample"' was completed. The ABO scale, because it is
designed for orthodontically treated cases, and not for
pre-treatment malocclusions, was calculated only at times
T2 and T3.
To account for validity of measurements, both
graders were calibrated and certified in the PAR grading
system for accuracy and reliability by Dr. Stephen
Richmond, the originator of the PAR. There is no such
certification system for the ABO scale. In order to
account for reliability of measurements, 10 subjects were
randomly selected and graded a second time, independent
of the first score, by the second grader. The correlation
of the PAR and ABO repeat scores between graders was
greater than 0.95, indicating a high reliability of
measurements.
19
Chapter 4: RESEARCH QUESTIONS
1. Are the three samples matched in pre-treatment
case severity?
2. Is there a difference in the quality of the final
treatment outcome of the three groups?
3. Is there a difference in the quality of the long
term post-retention outcomes of the three groups?
4. Does occlusal settling post-retention lead to a
greater or lesser quality of treatment outcome
over the long term?
5. Are there any individual ABO components that are
predictors of long-term stability?
20
Chapter 5: RESULTS
Descriptive Statistics
Incisor Irregularity (Figure 1)
Tweed
At Tl, the Tweed pre-treatment sample mean was
5.3mm with standard deviation of 3.0mm and a range of 0
to 14.6mm. At T2, post-treatment, the mean was 0.5mm
(std dev. +/- 0.5, range 0-2.4). At T3, the post
retention the mean was 2.2mm (std dev. +/- 2.2, range 0-
5.7) . The mean incisor irregularity improved by 4.8mm,
or 90.1% from Tl to T2 and relapsed 1.7mm during post
retention. This lead to a final T3 incisor irregularity
of 2.2mm reflecting an improvement of 42% of the initial
irregularity.
Alexander
At Tl, the Alexander sample mean incisor
irregularity was 8.4mm (std dev. +/- 4.1, range 1.3-
15.2). At T2, the mean was 0.9mm (std dev. +/- 0.6,
range 0-2.2) and at T3 the mean was 3.2mm (std dev. +/-
3.2, range 0.4-9.6). The mean incisor irregularity
21
improved 7.Smm, or 89% during treatment and relapsed
2.3mm during post-retention. This left a final T3
incisor irregularity of 3.2mm, or 38% of the original
irregularity.
Washington
At Tl, the Washington sample mean incisor
irregularity was 7.4mm (std dev. +/- 4.2, range 0.7-
18.1). At T2, the mean was 1.8mm (std dev. +/- 0.8,
range 0.5-5.8) and at T3 the mean was 4.5mm (std dev. +/-
2.2, range 1.2-8.7). The mean incisor irregularity
improved 5.6mm, or 76% during treatment and relapsed
2.7mm during post-retention. This left a final incisor
irregularity of 4.5mm or 61% of the original
irregularity.
Overall, the Tweed cases began treatment with
significantly less incisor irregularity (p < 0.01) than
either of the other samples. All three philosophies
significantly improved (p < .01) the incisor irregularity
with treatment, although the Washington sample had
significantly more incisor irregularity both after
22
treatment (p < .01) and at post-retention (p < .05)
compared to the other two philosophies.
23
★ ★★
Figure 1 =<.05 =<.01 (P values)
Incisor Irregularity Comparison
9
8
A
7
6
•k
5
mm
4
3 ★
2
1
0
T1 T2 T3
■ Tweed 5.3 0.5 2.2
□ Alexander 8.4 0.9 3.2
□ Washington 7.4 1.8 4.5
K>
Mandibular Canine to Canine Width (Figure 2)
Tweed
At Tl, the Tweed sample had a mean 3-3 width of
24.9mm (std dev. +/- 2.2, range 19.1-30.7). At T2, the
mean increased to 26.1mm (std dev. +/- 1.5, range 23.1-
30.3), and by T3 the mean decreased to 24.6mm (std dev.
+/- 1.8, range 21.4-29.9). Therefore, the intercanine
width in the Tweed sample increased 1.2mm during
treatment and decreased 1.5mm during post-retention. The
5% increase in intercanine width during treatment was
completely lost during post-retention plus an additional
1% for a total change of -0.3mm from Tl to T3.
Alexander
At Tl, the Alexander sample mean intercanine
width was 25.2mm (std dev. +/- 1.8, range 20.2-29.1). At
T2, the mean was 25.8mm (std dev. +/- 1.3, range 21.2-
29.0) and at T3 the mean width was 24.9mm (std dev. +/-
1.4, range 21.7-29.2) . In this sample, the mean width
was increased 0.6mm during treatment (2%), and relapsed
up to and past the original width 0.9mm (3%), like the
Tweed group, for a total loss of -0.3mm from Tl to T3.
25
Washing-ton
At Tl, the Washington sample had an initial
intercanine width of 26.2inm (std dev. +/- 2.4, range
19.4-30.7). At T2, the mean width was 27.8mm (std dev.
+/- 1.4, range 25.2-30.8) and at T3 the mean was 25.7mm
(std dev. +/- 1.9, range 21.8-29.8). The mean width from
Tl to T2 increased by 1.6mm or 6%. The mean width from
T2 to T3 decreased by 1.9inm or 7% and from Tl to T3 it
decreased by 0.5mm, or 2%.
While demonstrating no statistically significant
differences, the clinical trends revealed that the
Washington sample increased the intercanine width the
most during treatment and had the most loss of width
after treatment. The Alexander sample was expanded the
least during treatment and demonstrated the least relapse
post-treatment.
26
Figure 2
Mandibular Intercanine Width Comparison
28.0
27.0
26.0
mm 25.0
24.0-
23.0
22.0
T1 T2 T3
■ Tweed 24.0 26.1 24.6
□ Alexander 25.2 25.8 24.9
□ Washington 26.2 27.8 25.7
K)
<1
Arch Length (Figure 3)
Tweed
At T1 the mean arch length was 58.4mm (std dev.
+/- 4.7, range 45.0-68.1). After bicuspid extraction
treatment, at T2 the mean arch length decreased to 49.5mm
(std dev. +/- 3.9, range 43.0-66.1) and at T3 to 47.2mm
(std dev. +/- 3.9, range 38.7-63.6). The mean arch
length decreased 8.9mm (15%) during treatment, 2.3mm
(4.6%) during retention, for an overall arch length
decrease of 11.2mm or 19.2% from T1 to T3.
Alexander
At T1 the mean arch length was 57.0mm (std dev.
+/- 6.6, range 25.8-66.1). At T2 the mean was 49.0mm
(std dev. +/- 1.8, range 45.9-56.5) and at T3 the mean
was 46.7mm (std dev. +/- 2.3, range 42.5-55.3). The mean
arch length decreased 8mm (14%) during treatment, 2.3mm
(4.7%) during post-retention, for an overall change of
11.3mm or a 19.8% decrease in arch length from T1 to T3.
28
Washington
At T1 the mean arch length was 60.Gram (std dev.
+/- 5.2, range 46.1-73.9), at T2 the mean was 52.0mm (std
dev. +/- 2.4, range 46.2 58.0), and at T3 the mean was
49.6mm (std dev. +/- 2.8, range 48.9-54.4). The mean
arch length decreased by 8.6mm, or 14% during the
extraction treatment. The mean arch length during post
retention decreased 2.4mm, or 5%. The overall mean arch
length from T1-T3 decreased by 11.0mm, or 18%.
On the whole, each of the philosophies had similar
arch length changes at all time intervals and each
demonstrated similar amounts of overall arch length
change from T1 to T3. All three lost 14-15% of arch
length during treatment, 4-5% of arch length during
retention, for an overall similar loss of 18-19.8% loss
of arch length from T1 to T3.
29
Figure 3
Arch Length Comparison
70
60
50
40 .i.
mm
30
20
T2 T3
■ Tweed 58.4 49.5 47.2
□ Alexander 57.0 49.0 46.7
□ Washington 60.6 52.0 49.7
U)
O
PAR (Figures 4-7)
Tweed
The initial pre-treatment PAR score was 31.6
(std dev. +/- 10.0, range 10-53). The post-treatment PAR
score was reduced to 4.1 (std dev. +/- 2.4, range 0-14).
The post-retention PAR score increased to 7.6 (std dev.
+/- 4.3, range 1-21). Therefore, the mean percentage PAR
reduction during treatment was 87% and the mean case
score was in the well-treated range of less than five.
Over the post-retention time period, the PAR score
increased for an overall T1-T3 improvement of 76%. When
the cases are divided into well-finished (PAR < 5) and
poorly-finished (PAR > 10), 63% of the Tweed cases were
considered well-treated at T2 and 3% were finished
poorly. At T3, only 21% of the cases could still be
considered well-treated, a drop from 63%, and 26% would
be considered poorly-treated versus the minimal number at
T2.
Alexander
The initial Alexander group PAR score was 32.7
(std dev. +/- 10.6, range 13-61). The post-treatment PAR
31
score was 3.4 (std dev, +/- 1.8, range 0-8). The post
retention PAR score was 7.5 (std dev. +/- 4.3, range 0-
20) . The mean percentage PAR reduction from T1 to T2 was
90%. From T2 to T3 the PAR increased to leave an overall
reduction in PAR from T1 to T3 of 73%. When the cases
are divided into well-finished (PAR < 5) and poorlyfinished (PAR > 10), 78% of the Alexander cases were
well-treated at T2 and none were finished poorly. At T3,
only 27% of the cases could still be considered welltreated and 29% would be considered poorly-treated.
Washington
The initial pre-treatment PAR score was 32.1
(std dev. +/- 11,1, range 3-57), The PAR at T2 was 4.1
(std dev. +/- 3.7, range 1-16), and the PAR at T3 was 8.8
(std dev, +/- 5.5, range 2-29). The mean percentage PAR
reduction from T1 to T2 was 87%. From T2 to T3 the PAR
increased to leave an overall reduction of PAR from T1 to
T3 of 73%. When the cases are divided into well finished
(PAR < 5) and poorly finished (PAR > 10), 75% of the
Washington cases were well-treated at T2 and 15% were
finished poorly. At T3, only 22% of the cases could
32
still be considered well-treated and 38% would be
considered poorly treated.
Overall, the initial severity of the cases from the
three philosophies was similar. Each of the philosophies
treated their cases to an acceptable average with the
Alexander cases treated slightly better according to mean
PAR score, although this difference was not statistically
significant. All three philosophies had some
relapse/increase in PAR after treatment and during
retention. The Washington sample underwent a
significantly (p < .05) greater amount of percentage
relapse in PAR during retention than the Tweed sample.
but not versus the Alexander sample.
In addition, when the PAR was divided into wellfinished (PAR < 5) , average-finished (PAR 5-10), and
poorly-finished (PAR > 10), the Alexander sample at T2
had the highest percentage of well-finished (78%), while
the Tweed had the lowest at 63%. The Tweed sample had
the highest percentage of average-finished cases 34%
versus 22% of Alexander and 10% of Washington. The
Washington sample had the highest amount of poorly33
treated cases at 15% versus only 3% of the Tweed and none
of the Alexander cases.
34
Figure 4
PAR Comparison
35
30
25
20
PAR
T1 T2 T3
■ Tweed 31.6 4.1 7.6
□ Alexander 32.7 3.4 7.5
□ Washington 32.1 4.1 8.8
U)
Figure 5
PAR % Change
100-r
:1 ri
% Change
-50
-100
' *
' \ '
-150
T1-T2 T2-T3 T1-T3
■ Tweed 87 -85 76
□ Alexander 90 -121 73
□ Washington 87 -115 73
U)
o^
Figure 6
Percent of Cases Treated Well\Average\Poorly
at T2 By PAR Score
80
70
60
50
% of Cases 40
f
30
20
f-.
10
0
12 5-10
(Average)
T2 <5 (Well) 12 >10 (Poorly)
■ Tweed 63 34 3
□ Alexander 78 22 0
□ Washington 75 10 15
U)
Figure 7
Percent of Cases Treated Well\Average\Poorly at
T3 By PAR Score
60
50
40
% of Cases 30
20
10
0 T3 5--10 (Average) T3>10 (Poorly)
■ Tweed 21 53 26
□ Alexander 27 44 29
□ Washington 22 40 38
U)
00
ABO (Figures 8-10)
The ABO score is determined by combining the
subtotals from the five contributing sections which when
added give a maximum raw ABO score of 256 points.
(Appendix #2) There is a possible 64 points in the
alignment component. The marginal ridge component totals
32 points. The posterior inclination component totals 40
points. The occlusal contacts component totals 64
points. The occlusal relationships component totals 24
points. The overjet component totals 32 points. When
these components are added, a perfect case totals 256
points.
Tweed
At T2, the mean ABO score was 227 (std dev. +/-
12, range 199-247) out of the total 256 points or 89%
success. From T2 to T3 the mean ABO score improved eight
points to 235 (std dev. +/- 11.6, range 181-253), or 92%
of the total possible points.
39
Alexander
At T2, the mean ABO score was 225 (std dev. +/-
11.3, range 187-244) out of the possible 256 points. or
88%. From T2 to T3, the mean ABO score increased six
points to 231 (std dev. +/- 9.3, range 213-249), or 90%.
Washington
At T2 the mean ABO score was 220 (std dev. +/-
9.1, range 198-241), or 86%. From T2 to T3 the mean ABO
score improved four points to 224 (std dev. +/- 9.4,
range 203-242), or 88%.
Overall at T2, the Tweed sample demonstrated the
best ABO score, closely followed by the Alexander sample.
The Washington sample scored the lowest at post-treatment
and was significantly lower than the Tweed sample (p <
.01) . There was a general increase in ABO score over the
post-retention period for all three groups of 5 to 8
points. The Tweed group improved the most and the
Washington group the least. At post-retention, the
Washington sample had significantly lower\worse ABO
scores than both Tweed and Alexander samples (p < .01).
40
When the ABO scoring is broken down into cases that
would probably pass (having less than 20 points
deducted), borderline (deductions of 20-30 points), and
failing (deductions greater than 30 points) cases, there
are distinctions between the three groups. (Figure 9) At
post-treatment (T2), the Tweed sample had the highest
percent of cases that most likely would pass (27%) and
the lowest amount of probable failures (42%) . The
Washington sample had the lowest percentage of passing
scores at 4% and the most probable failures at 65%. When
examined at post-retention, (Figure 10) the distinctions
become more distinct with 56% of the Tweed cases passing
and only 13% failing. The Washington sample again was
the worst with only 13% of the cases passing and 52%
failing, with the Alexander group in the middle with 32%
of cases passing and 24% failing.
41
Figure 8 ★ =<.05 =<.01
ABO Overall Comparison
256
240
★★
★
ABO score 224
."fill
•.j.'-.rS-"'.,... ...
t!
■ll
206 ' .r '■ mm■f§: .:i:
!i 'i. ^'!f. >J»T
t;■4
m
liii 192
T2 T3
■ Tweed 227 235
□ Alexander 225 231
□ Washington 219 224
K)
Figure 9
ABO Point Deductions at T2
(Passing\Boderiine\Faiiing)
80
60
/—71 % of cases 40
20
0 Borderline (-20-
Pass (-<20) Fail (->30)
30)
■ Tweed 27 31 42
□ Alexander 12 39 49
□ Washington 4 31 65
4:^
U)
Figure 10
ABO Point Deductions at T3
(Passing\Borderiine\Failing)
80
60
% of Cases 40
20
0 Borderline (-20-
Pass (-<20) Fail (->30)
30)
■ Tweed 56 31 13
□ Alexander 32 44 24
□ Washington 13 35 52
-1^
4^
ABO Individual Components
Contrary to the PAR scores, the mean ABO scores
increased from post-treatment to post-retention.
Therefore, the ABO scores were dissected and analyzed
into their individual components. This further analysis
was done to attempt to identify which components
contributed to relapse and which components contributed
to improvement.
ABO Individual Components-Alignment (Figure 11a,b)
Tweed
The alignment component of the ABO scale totals
a possible 64 points. It is a measure of anterior and
posterior rotations. At T2, the mean alignment score was
59.9 (std dev. +/- 3.1, range 51-64) and at T3 the score
was 57.3 (std dev. +/- 2.6, range 43-63). The Tweed
alignment score decreased\worsened by 2.6 points. or
4.3%.
Alexander
At T2, the mean alignment score was 59.8 (std
dev. +/- 2.6, range 53-64) and at T3 it was 57.0 (std
45
dev. +/- 3.3, range 50-63). The Alexander alignment
score decreased 2.8 points during post-retention, or 4.7%
Washington
The T2, mean alignment score was 57.2 (std dev.
+/- 2.3, range 52-62) and at T3 the score was 54.7 (std
dev. +/- 3.0, range 48-61). The mean alignment score
decreased\worsened by 2.5 points, or 4.4%.
Overall^ the ABO alignment score of the Washington
sample was significantly worse at post-treatment
(p < .01) and at post-retention (p < .01) versus the
other two groups. There were similar decreases in
alignment over time of approximately 4% for all three
groups.
46
Figure 11a ★★ =<.01
ABO Individual Components- Alignment
60.0 71 irk
59.0
58.0
57.0
Alignment Score
out of 64
56.0
55.0
54.0
53.0
52.0
T2 Alignment Score T3 Alignment Score
■ Tweed 59.9 57.3
□ Alexander 59.8 57.0
□ Washington 59.0 54.7
Figure 11b
ABO Individual Components- Alignment
61
60
59
58
57 ♦ Tweed
—11— Alexander
“ - -A- - - Washington
ABO Score for Alignment out
of 64
56
55
A
54 ★★
53
52 4
T2 Alignment Score T3 Alignment Score
Time
00
ABO Individual Components- Marginal Ridges (Figure 12a,b)
Tweed
The marginal ridge component of the ABO scale
is out of a total of 32 points. It measures the
consistency of marginal ridge heights in the posterior
occlusion. The Tweed mean marginal ridge score at T2 was
24.9 (std dev. +/- 4.0, range 16-32) and at T3 is was
28.3 (std dev. +/- 3.0, range 18-32). Therefore, there
was a 13.6% improvement in marginal ridge score over
time.
Alexander
The mean Alexander marginal ridge score was
24.6 (std dev. +/- 3.5, range 17-30) at T2 and 27.4 (std
dev. +/- 3.6, range 17-32) at T3. This is an improvement
of 2.8 points or 11.4% from post-treatment to post
retention.
Washington
The T2 mean marginal ridge score was 29.3 (std
dev. +/- 2.0, range 25-32) and at T3 was 30.9 (std dev.
+/- 4.5, range 25-32). There was an improvement of 1.6
49
points, or 5% from T2 to T3 for the Washington sample.
The Washington sample had a statistically
significant (p < .01) better\higher ABO marginal ridge
score than either the Tweed or the Alexander groups. All
three groups improved their scores over time from T2 to
T3, although the Washington improved the least of the
three. The Tweed cases improved the most from T2 to T3
with a 13.6% improvement.
50
Figure 12a <.01
ABO Individual ComponentsMarginal Ridges
★★
★★
30
28
Marginal Ridge
Score out of 32
26
24 T2 Marginal Ridge
Score
T3 Margial Ridge
Score
■ Tweed 24.9 28.2
□ Alexander 24.6 27.4
■ Washington 29.3 28.9
Figure 12b
ABO Individual Components- Marginal Ridges
30
it ★★
29
★★
CM
CO 28
o
o
2> 27
o
■♦—Tweed
♦-Alexander
-A—Washington
3. 26 2
0^
(0
B 25
I
S 24
23
22
T2 Marginal Ridge Score T3 Margial Ridge Score
Time
Lh
K)
ABO Individual Components- Buccal-Lingual Inclination
(Figure 13a,b)
Tweed
The maximum buccal-lingual inclination score in
the ABO scale is 40 points. It is a measure of posterior
torque. The mean T2 buccal-lingual inclination score
from the Tweed sample was 36.8 (std dev. +/- 3.5, range
19-40) and the mean T3 score was 37.2 (std dev. +/- 2.7,
range 30-40). There was a mild improvement in the
buccal-lingual inclination score of 0.4 points or 1%.
Alexander
The mean buccal-lingual inclination score at T2
was 35.7 (std dev. +/- 2.5, range 28-40) and at T3 was
36.9 (std dev. +/- 2.4, range 31-40). There was an
increase in inclination score of 1.2 points or 3.3% over
time.
Washington
The T2 mean buccal-lingual inclination score
for the Washington cases was 30.3 (std dev. +/- 3.1,
53
range 24-36) and for T3 it improved slightly to 30.6 (std
dev. +/- 3.3, range 20-40). This demonstrated a 0.3
point or 1% increase from T2 to T3.
Overall, in comparing the three groups, the
Washington sample had significantly lower (p < .01)
buccal-lingual inclination score than the Tweed or
Alexander samples. All three groups scores increased
slightly over time, with the Alexander cases improving
the most at 3.3%.
54
Figure 13a ** = <.01
ABO Individual ComponentsBuccal-Lingual Inclination
40 ★★
30
B-L Inclination
Score out of 40 20
10
0
T2 B-L Inciination T3 B-L Inciination
■ Tweed 36.8 37.2
□ Alexander 35.7 36.9
□ Washington 30.3 30.6
Figure 13b
ABO Individual Components- Buccal-Lingual
Inclination
40
35 i
2
o
30 ▲
★★ ★★
o
o 25
to
■♦—Tweed
Alexander
♦—Washington
o
- 20
ffi
£
15 £
o
o
(0
10
5
0 4
T2 B-L Inclination T3 B-L Inclination
o^
ABO Individual Components- Occlusal Contacts (Figure
14a,b)
Tweed
The occlusal contacts component of the ABO is
graded out of a possible 64 points. It is a measure of
the vertical contacts of the posterior occlusion. The T2
mean occlusal contacts score for the Tweed cases was 54.6
(std dev. +/- 5.4, range 35-63) and at T3 was 60.7 (std
dev. +/- 2.8, range 47-64). There was an improvement of
6.1 points, 11.1% from T2 to T3.
Alexander
The T2 mean occlusal contacts score was 54.4
(std dev. +/- 4.3, range 45-64) and at T3 was 60.3 (std
dev. +/- 4.3, range 45-64). There was a percentage
improvement of 10.8%, or 5.9 points.
Washington
The T2 mean occlusal contact score was 57.5
(std dev. +/- 4.9, range 36-64) and at T3 was 61.8 (std
dev. +/- 2.6, range 53-64). This demonstrates an
improvement of 4.3 points, or 7.5%.
57
Overall, the Washington cases were statistically
better (p < .01) at T2 for the marginal ridges component
of the ABO than the other two groups. By T3 though, all
three groups had improved but the Tweed and Alexander
cases improved more than the Washington cases.
Consequently, the Washington sample was no longer
significantly better than the other groups at T3.
58
Figure 14a ★ = <.05
ABO Individual ComponentsOcclusal Contacts
64
60 ★
Occlusal
Contacts Score
out of 64
56
52
T2 Occlusal Contacts T3 Occlusal Contacts
■ Tweed 54.6 60.7
□ Alexander 54.4 60.3
□ Washington 57.5 61.8
VO
Figure 14b
ABO Individual Components- Occlusal Contacts
64
62
s
o 60
o
♦ Tweed
'HiH-Alexander
—At—Washington
o
I 58
o
★
o
8
? 56
a
£
8
^ 54
O
CQ
<
52
50
T2 Occlusal Contacts T3 Occlusal Contacts
On
O
ABO Individual Components- Occlusal Relationships (Figure
15a,b)
Tweed
The occlusal relationships component of the ABO
scale totals 24 points. It is a measure of the buccal
occlusion from the canine to the most distal molar. The
Tweed T2 mean occlusal relationship score was 21.2 (std
dev. +/- 3.2, range 10-28) and at T3 was 21.7 (std dev.
+/- 3.3, range 9-24). There was a 0.5 point increase in
occlusal relationships from T2 to T3, or 2.4%.
Alexander
The mean T2 occlusal relationship score was
20.4 (std dev. +/- 3.6, range 9-24) and at T3 was 19.8
(std dev. +/- 4.0, range 10-24). There was a 0.6 point
reduction\worsening of the occlusal relationship score.
or 2.9%.
Washington
The mean T2 occlusal relationship score was
18.2 (std dev. +/- 3.6, range 9-24) and at T3 was 17.7
61
(std dev. +/- 4.1, range 8-24). This demonstrates a 0.5
reduction in score from T2 to T3, or 2%.
After treatment, the Washington cases had a
significantly worse (p < .01) occlusal relationship score
in comparison with the other two groups. Over time, the
Washington and Alexander groups' scores got worse, while
the Tweed sample improved slightly from T2 to T3. At T3,
the Washington cases were still significantly worse
(p < .01) than either the Tweed or Alexander cases.
62
★ ★★
Figure 15a <.05 <•01
ABO Individual ComponentsOcclusal Relationships
24
22
Occlusal
Relationships 20
Score out of 24
★★
18
16 T3 Occiusal
Relationships
T2 Occlusal
Relationships
■ Tweed 21.2 21.7
□ Alexander 20.4 19.8
□ Washington 18.2 17.7
On
U)
Figure 15b
ABO Individual Components- Occlusal
25 Relationships
♦
N 20 i
o
o A
' ★★
★ I 15
■♦-Tweed
♦-Alexander
Washington
&
o
6^ 10
£
o
5
0
T2 Occlusal Relationships T3 Occlusal Relationships
ABO Individual Components- Overjet (Figure 16a,b)
Tweed
The overjet component of the ABO contains a
possible 32 points. It is a measure of the posterior and
anterior overjet. The T2 mean overjet score for the
Tweed cases was 29.7 (std dev. +/- 2.3, range 23-32) and
at T3 was 29.9 (std dev. +/- 2.5, range 22-32). There
was a small increase in score from T2 to T3 of 0.2
points, 0.7%.
Alexander
The mean overjet score at T2 for the Alexander
cases was 30.2 (std dev. +/- 1.9, range 24-32) and at T3
was 30.0 (std dev. +/- 2.5, range 23-32). There was a
small decrease in overjet score over time of 0.2 points.
0.7%.
Washing-ton
At T2, the mean overjet component score was
27.4 (std dev. +/- 3.7, range 15-32) and at T3 was 28.8
(std dev. +/- 3.5, range 18-32). Therefore, the overjet
component increased 1.4 points, or 4% over time.
65
In comparison, the Washington sample had a
significantly lower (p < .01) overjet score at post
treatment, but improved the most of the three groups over
time. This lead to a slightly lower, but statistically
insignificant, lower overjet score at T3 for the
Washington cases compared to the other two groups.
66
★★
Figure 16a <•01
ABO Individual ComponentsOverjet
32
^ /I
30
Overjet Score
out of 32
28
26 T2 OverJet T3 Overjet
■ Tweed 29.7 29.9
□ Alexander 30.2 30
□ Washington 27.4 28.8
o^
O
£ 28
£
o
W 27.5
★ ★ 27
26.5
26 T
T2 Overjet T3 Overjet
o^
00
ABO Components Sviinmary (Figure 17,Table 1)
When the ABO grading scale is broken down into its
individual components it is apparent why the overall ABO
score increased from post-treatment to post-retention.
Five of the six components either improved or remained
about the same from T2 to T3. Four of the six components
demonstrated improvement in all three samples while one
got worse and one had mixed trends. The greatest
improvement was in the marginal ridge and occlusal
contact parameters with moderated improvement noted in
the buccal-lingual inclination and overjet components.
The alignment score was the only category to
significantly decrease over time.
69
Figure 17
ABO Individual Com ponents-Sum m ary
■ Tweed nAlexander ■Washington
8
o
u
(/>
O
m
<
CO
<1
O
Table 1
ABO Individual Components- Summary
Relative Increase (+) or Decrease (-) from T2 to T3
Tweed Alexander Washington
Alignment
Marginal
Ridges
+++ ++ +
B-L
+ + +
Inclination
Occlusal
Contacts
+++ +++ ++
Occlusal
Relationships
+
Overjet + + ++
-\+ = Minor improvement\worsening
— \++ = Moderate improvement\worsening
\+++ = Severe improvement\worsening
71
Dental Class I vs. Class II (Figure 18a,b,c)
Overall, the initial severity of the dental class II
malocclusions was greater (p < ,05) according to the PAR,
than the class I malocclusions. All three philosophies
treated the class I and II malocclusions to remarkably
similar final PAR and ABO scores. After retention.
though, there were some differences in the relapse
patterns of the class I and II's. The class II's
relapsed to a significantly (p < .05) higher PAR than the
class I malocclusions. Using the ABO scale, the
Washington and Tweed class II cases relapsed more than
the Class I's, but not to a significant level. The
Alexander class I and II cases remained extremely similar
over the post-retention time period.
72
Figure 18a
Tweed Class I vs. Class II
1000
100
PARVABO Score
10
'liic
1
T1 T2 T3
Par ABO
□ Tweed Class I 30.1 4.1 5.7 224.7 238.4
■ Tweed Class II 32.1 4.1 8.2 227.8 234
U)
Figure 18b
Alexander Class I vs. Class II
1000
100
PAR\ABO Score
10 ^
1
T1 T2
T2 T3 T3
Par ABO
□ Alexander Class I 29.3 3.3 6.2 225.1 231.5
■ Alexander Class II 35.7 3.5 8.6 225.2 231.3
-t*.
Figure 18c
Washington Class I vs. Class II
1000 Y
PAR\ABO Score
□ Washington Class I
■ Washington ^ lass 11 223.3
Good vs. Mediocre vs. Poorly Treated Cases (Figures
19a,b,c)
All three groups were combined and examined for the
effect of treatment on retention stability. The PAR at
post-treatment was divided into groups of well-treated
(PAR < 5), moderately treated (PAR 5-10), and poorly
treated (PAR >10) cases. These cases were then examined
for PAR at T3, ABO at T3, and incisor irregularity. The
mean PAR score at post-treatment was 3.9 when all three
groups were combined. At post-retention the PAR relapsed
as expected reflecting a trend for the better treated
cases to have a lower PAR score at T3. The PAR scores
became 7.3 for the well treated cases, 9.1 for the
mediocre cases, and 11.5 for the poorly treated cases.
The T3 ABO score for the well treated group was
determined to be 231.5, compared to 229.7 for the
mediocre group and 222.9 for the poorly treated group;
reflecting a trend for the poorly treated group to have
lower scores than the other two samples. The incisor
irregularity at T3 for the well treated group was 3.4,
2.3 for the mediocre group, and 4.5 for the poorly
treated group. It is interesting to note that the
76
mediocre cases as defined by the PAR had the least
incisor irregularity of the three groups, even less than
the well treated cases. Therefore, it can be deduced
that the quality of treatment defined by the PAR does not
effect the amount of lower incisor crowding over time.
The ABO score was also used to examine the effect of
treatment outcome to long-term stability. The ABO was
divided into two groups, a passingXborderline group and a
failing group. The passing and borderline scores were
combined in order to have an acceptable sample of each
type. The passing group's T3 PAR was 7.5, while the
failing group became 8.3. The ABO score at T3 for the
passing group was 235.2 at T3 and the failing was 226.8.
The incisor irregularity was 2.9 for the passing group
and 3.5 for the failing group. In summary, the cases
with passing T2 ABO scores had nearly passing ABO scores
at T3, while the PAR and Incisor Irregularity scores did
not exhibit this pattern.
11
Figure 19a
T3 PAR Scores Based on T2 Treatment Quality
12 Y
10
8
PAR Score at T3 6
4
2
0
PassingIBorderli
ne ABO Score
Failing ABO
Score
PARatT2<5 PAR at T2 5-10
PARatTS 7.5 8.3 7.3 9.1
00
Figure 19b
T3 ABO Scores Based on T2 Treatment Quality
236 Y
234
232
230 -
228 —^
ABO Score at T3 226
224
222
220
218
2t6
PassingIBorderli
ne ABO Score
Failing ABO
Score
226.8
PAR at T2 < 5 PAR at T2 5-10 PAR at T2 >10
ABO at T3 235.2 231.5 229.7 222.9
''O
Figure 19c
Post-Retention Incisor Irregularity Based on Treatment
Quality
4.5 Y
4
3.5
3
2.5
Inc Irreg at T3 (mm)
2
1.5
1 -
0.5
0
Passing|Borderl
ine ABO Score
Failing ABO
Score
PAR at T2 < 5 PAR at T2 5-10 PAR at T2 >10
Inc Irreg at T3 2.9 3.5 3.4 2.3 4.5
00
o
Correlation Statistics (Table 2)
Correlation statistics were applied to the collected
samples in order to ascertain relationships between the
scores. When the ABO at post-treatment is considered for
correlations. it was found that the ABO was only mildly
correlated to the final post-retention ABO score (r =
.448, p < .001). This suggests that the final treatment
outcome as measured by the ABO score is only a weak
predictor of the final long-term result. A similar but
even weaker association was noticed between the PAR at T2
and the PAR at T3 (r = .308, p < .001). The data
suggests that the overall scores for the PAR and the ABO
are not sensitive enough measures and that individual
components will need to be evaluated to identify the
specific parameters that contribute to stability.
Subsequently, the individual ABO components were
broken down and correlated to themselves over time. When
the components of the ABO scale are broken down, the
highest correlation was noted in the buccal-lingual
inclination (torque) component of the ABO (r = .731, p <
.001) . Slightly weaker but still significant outcomes
81
were seen for the areas of alignment (r = .601, p < .001)
and occlusal relationships (r = .585, p < .001). Very
weak associations were also noted between the quality of
marginal ridges (r = .446, p < .001) and overjet (r =
.403, p < .001) outcomes and their long-term stability.
Occlusal contacts, although still somewhat correlated.
was the least correlated probably because those cases
that were not contacting at post-treatment would have
improved the most due to settling over time and therefore
would improve more than those that were already
contacting.
It was interesting to note that the amount of
irregularity at T3 was not correlated to the final post
treatment PAR score, and was minimally correlated to the
PAR score at T3 (r = .214, P .007) . The post-retention
incisor irregularity was weakly correlated to the post
treatment (r = -.175, P = .029) and post-retention (r = -
.252, P .002) ABO scores. Some correlation at T3 might
be anticipated, because lower incisor crowding is
indirectly measured by both the PAR and ABO grading
scales. It can be concluded that the quality of the
final treatment outcome as measured by the PAR has no
82
correlation with the amount of incisor irregularity and
the ABO score at post-treatment is only very weakly
associated.
The amount of intercanine width relapse was then
correlated to the PAR and ABO. The change in intercanine
width from T2 to T3 had no correlation with either the
PAR or ABO. Therefore, the amount of intercanine width
relapse over the post-retention time period is not
related to how well the case was treated nor how well it
maintained its occlusion.
It is also interesting to note the only mild
relationship of the PAR and the ABO grading scales to
each other. There is only a weak correlation of the PAR
and ABO scores at post-treatment (r = -.278, p < .001)
and at post-retention (r = -.218, p < .01). This
demonstrates the differences between the two grading
scales and how they measure different factors in order to
obtain a score.
83
Table 2
Correlations
Statistical
Significance
r P
Inc Irreg at T3
vs, PAR at T2
.054 .502 No correlation
Inc Irreg at T3
vs. ABO at T2
Mild (-)
correlation
-.175 .029
Inc Irreg at T3
vs. PAR at T3
.214 .007 Mild correlation
Inc Irreg at T3
vs. ABO at T3
Mild (-)
correlation
-.252 .002
PAR at T2 vs.
PAR at T1
.099 .218 No correlation
PAR at T2 vs.
PAR at T3
.308 <.001 Mild correlation
PAR at T2 vs.
ABO at T2
Mild (-)
correlation
-.278 <.001
PAR at T2 vs.
ABO at T3
Mild (-)
correlation
-.201 .012
PAR at T3 vs.
ABO at T2
Mild (-)
correlation
-.218 .006
PAR at T3 vs.
ABO at T3
Moderate (-)
correlation
-.481 <.001
ABO at T2 vs.
PAR at T3
Mild (-)
correlation
-.218 .006
ABO at T2 vs.
ABO at T3
Moderate
correlation
.448 <.001
84
Table 2 (cont.)
Statistical
Significance
r P
A 3-3 at T3 vs.
PAR at T2
.075 .352 No correlation
A 3-3 at T3 vs.
PAR at T3
-.082 .308 No correlation
A 3-3 at T3 vs.
ABO at T2
-.005 .952 No correlation
A 3-3 at T3 vs.
ABO at T3
-.057 .483 No correlation
ABO Align at T2
vs. ABO Align at .601 <.001 High correlation
T3
ABO MR at T2 vs.
ABO MR at T3
.446 <.001 Moderate correlation
ABO B-L at T2 vs.
ABO B-L at T3
.731 <.001 High correlation
ABO Occl Rel at
T2 vs. ABO Occl
Rel at T3
.585 <.001 High correlation
ABO Overjet at T2
vs. ABO Overjet
at T3
.403 <.001 Moderate correlation
ABO Occl Cont at
T2 vs. ABO Occl
Cont at T3
.204 .011 Mild correlation
85
Reliability Statistics (Table 3)
In order to ensure reliability of measurements
between graders for the PAR and ABO scores, 10 cases were
re-scored by the opposite examiner. A paired t-test was
applied to the duplicate measurements at assess the
degree of reliability. The a value was set to 0.01 and
no significant differences were found. In addition.
correlation values were generated for the paired samples.
The correlation (r) values for the original and repeated
groups suggest a strong correlation and reliability of
measurements between graders.
86
Table 3
Reliability Statistics
Statistical
Significance
Paired Samples N r
PAR at Tl:
Original-repeat 10 .996 Highly correlated
PAR at T2:
Original-repeat 10 .975 Highly correlated
PAR at T3:
Original-repeat 10 .993 Highly correlated
ABO at T2:
Original-repeat 10 .961 Highly correlated
ABO at T3:
Original-repeat 10 .997 Highly correlated
87
Chapter 6: DISCUSSION
Were the three samples matched in pre-treatment case
severity?
According to the PAR grading scale a case greater
than 40 is considered difficult. All three of the groups
begin treatment with very similar PAR scores, between
31.6 and 32.7, and no statistically significant
difference was found between the groups. Although, when
comparing incisor irregularity, the Tweed cases began
treatment with significantly less irregularity than the
other groups. Therefore, it can be assumed that all the
cases began at relatively the same difficulty, although
the Tweed cases had the least lower incisor crowding
before treatment.
Was there a difference in the quality of the final
treatment outcome of the three groups?
According to the PAR all three groups significantly
decreased their cases PAR scores very similarly. All
three groups improved their cases between 87 and 89.6%.
This left analogous T2 PAR scores of around four. A PAR
score less than five signifies a well-treated case.
88
therefore all three group's cases can in general be
considered well-treated according to the PAR analysis.
Of the three groups, the Alexander cases were treated to
the lowest PAR score of 3.4, although this was not
statistically different from the other two groups.
According to the ABO scale, the Tweed and Alexander
cases were treated to a higher quality (p < .01) than the
Washington cases. None of the group means as a whole
would be able to pass the ABO board. When looking at
percentages, the Tweed cases had the highest number of
passing ABO scores (27%) versus only 4% of the Washington
cases. Therefore, according the ABO grading scale, the
Washington cases were not treated to the same quality as
the Tweed or Alexander cases (p < .01).
When examining incisor irregularity, all three
groups significantly reduced the irregularity. The Tweed
and Alexander cases had the lowest irregularity post
treatment at 0.5 and 0.9mm, while the Washington cases
had 1.8mm. Once again, the Washington cases can be
considered more poorly treated (p < .02) than the other
two groups.
89
On the whole, when comparing the three groups using
the more specific occlusal measurements of ABO and
incisor irregularity, the Washington cases were not
treated as well as the Tweed or Alexander cases. This
validates the Tweed group and others assumptions that
because many of the Washington cases were treated by
graduate residents that they were not treated to the same
quality as those of an experienced private practitioner.
Was there a difference in the quality of the long-term
post-retention outcomes of the three groups?
According to the PAR, as expected, all three groups
underwent some relapse of treatment. The Tweed group
experienced the lowest percentage relapse. The
Washington cases at T3 had the highest mean PAR score of
8.8, which would no longer be considered well-treated.
According to the ABO scale, all three groups
experienced a surprising increase\improvement in ABO
score over time. Although, the Washington group
underwent the least amount of ABO score improvement of
the groups.
90
According to incisor irregularity, the Washington
cases again relapsed the most of the three groups.
whole, the Washington cases were the least stable and
As a
experienced the most relapse of the three groups.
How did the ABO pass\fail rate change over time for each
of the groups?
It is interesting to note the change in percent of
cases that would pass versus fail the ABO for the three
groups over time. From T2 to T3 the Tweed pass rate
improved from 27% to 56%. The Alexander pass rate
improved from 12% to 32% and the Washington pass rate
improved from 4% to 13%. The failure rates for the three
groups decreased over time. The failing Tweed cases
decreased from T2 to T3 from 42% to 13%, the Alexander
failure rate decreased from 49% to 24%, and the
Washington cases failure rate decreased from 65% to 52%.
Did occlusal settling post-retention lead to a greater
lesser quality of treatment outcome over the long term?
or
The patterns of the ABO and PAR scores over the time
intervals did not display the same relationship as one
91
might expect as both are designed to measure treatment
guality. The PAR scale expectedly worsened during post
retention, while the ABO improved. The PAR is a measure
of relationships rather than precise occlusal details.
The ABO was designed for the specific measurement of
cases that are of a high quality and does not focus on
gross relationship measurements. The ABO scores improved
2-3% over the post-retention period. The categories that
contributed the most to its improvement were occlusal
contacts and marginal ridges. These two improvements can
be attributed to the occurrence of settling over time.
As one ages, the teeth will continue to erupt and wear
until they each find an equilibrium point. This settling
will only increase the amount of occlusal contact.
thereby improving the occlusal contact score. The
marginal ridge scores will also improve due to settling.
wear, and the application of dental restorations over
time. Each of these conditions will improve the marginal
ridge score and therefore improve the ABO score.
92
Were there any individual ABO components that are
predictors of long-term stability?
When the ABO is broken down into its individual
components there are major trends that all the groups
follow, but there are also subtle differences that should
be noted. As expected, the alignment score, which is a
measure of rotations, for all groups decreased similarly
over time. The marginal ridge score improved the most in
the Tweed cases (14%), moderately in the Alexander cases
(11%), and somewhat in the Washington cases (5%). These
differences may be explained by the appliance and
philosophy used. The Tweed philosophy of treatment
includes tip back bends in the second bicuspid and molars
to the point where there is no posterior occlusion at the
54,56 point of debonding. During the retention phase, the
teeth erupt and then over time come in contact with each
other. This would lead to an increase in marginal ridge
continuity over time. Tip backs, although not as
extreme, are also included within the Alexander
prescription. The Alexander Discipline uses a 6° tip
back on the lower first molars. Therefore, the same
phenomenon occurred to a lesser degree in the Alexander
93
cases. These tip back bends and prescription
modifications also can account for the occlusal contact
score improvement differences between the Tweed and
Alexander groups (11%), versus the milder improvement of
the Washington cases (7%). The Tweed cases also showed a
mild improvement in the occlusal relationship score,
which is a measurement of the final cusp tip to embrasure
occlusion, versus the Washington and Alexander groups.
This may be explained by the more active over-correction
of the Tweed cases at post-treatment. It is standard
Tweed procedure to overcorrect malocclusions anterior54,56 posteriorly as well as vertically. These over
corrections will then detract from the T2 score but will
hopefully improve over time more than those cases that
were not overcorrected.
What was significant about the correlations?
It was found that the PAR and ABO grading scales are
modestly correlated to each other in the measuring of
cases. When studied at the same time interval, both are
mildly correlated to each other in examining case
finishes (r = .278 (T2) and r = .481 {T3)).
94
Demonstrating the difference in emphasis of each of the
two grading scales.
It can be clearly stated that how well a case was
treated according to either the PAR and ABO was a poor
predictor of the amount of lower incisor crowding that
occurred post-retention. The PAR had no correlation
whatsoever (r = .054) and the ABO was only mildly
correlated (r = .214). This was apparent even when the
subjects were divided into good, mediocre, and poorly
treated cases. The mediocre cases as defined by the PAR
actually were left with less incisor irregularity than
even the well-treated cases.
The change in intercuspid width that occurs in
untreated as well as treated patients over time also did
not correlate with how well a case was treated nor how
stable it was post-treatment.
Three of the ABO components are very good predictors
of their own relapse patterns, and one is a relatively
poor predictor. The least interrelated of the components
was the occlusal contacts score. This may be explained
by the differing treatment styles. Because the Tweed
cases are purposefully left open vertically in the
95
posterior, obviously there was more improvement over time
and consequently there was more variation of this
component among the offices. The three components that
were found to be consistently associated over the long
term were buccal-lingual inclination (torque), occlusal
relationships, and marginal ridges. These factors,
especially posterior torque, are extremely predictable
over the long term and therefore in order to obtain the
highest stability, these components must be carefully
controlled at treatment termination.
What were some of the limitations of this study?
Although this study used a reasonably large number
it is difficult to make generalizations
about philosophies with only 40 to 60 cases for each
office.
of subjects.
One element of the complexity in the study of
long-term stability is the difficulty in obtaining long
term retention records. Until more practitioners or
institutions are able to accumulate more long-term
records this will continue to be a major obstacle.
Another limitation is the fact that generalities are
being concluded about philosophies based on a single
96
practitioner of that philosophy. Much of the quality of
the finished case could be attributed to the practitioner
rather than the appliance or philosophy.
A further constraint is that because there is
virtually no way to compare consecutively treated
long-term, the samples themselves are partially biased.
There is no blind acquirement of cases therefore there
cases
could be some sample acquisition bias there. Meaning a
case that is not stable or extremely stable could be
overlooked based on the desires of the sample collector.
When comparing philosophies, one must also include
the retention procedure and patient compliance with that
protocol. The long-term records are very dependent on
patient compliance with the retention plan,
possible that much of the stability inst
It is
ability could
be attributed to patient motivation and cooperation by
or
the treating doctor and staff. In addition, the role of
fixed versus removable retainers is also a variable that
cannot be ignored when comparing these treatment
philosophies.
An additional limitation of this study is the
absolute calibration of graders. There is no
97
standardized calibration course or certification for the
American Board of Orthodontists grading scale. Although
the graders for the Tweed and Alexander groups were shown
to correlate extremely well with each other, there was no
calibration between them and the measurements done for
the Washington sample because it was done two years
The PAR scorers were all calibrated and should
be fairly consistent.
earlier.
but there is no universal
calibration for the ABO.
98
Chapter 7: CONCLUSIONS
• According to the ABO grading scale, the Tweed and
Alexander philosophies treated their cases better
and relapsed less than the Washington cases.
• According to incisor irregularity measurements, the
Tweed and Alexander philosophies treated their cases
to a better result and relapsed less than the
Washington cases.
• When the ABO is divided into passing and failing
scores, the Tweed and Alexander cases had higher
percentages of passing and lower percentages of
failures than the Washington cases.
• There is no correlation between the loss of
intercanine width over time and the final PAR or ABO
scores.
• There is no correlation between how well a case is
treated using the PAR and lower incisor crowding
over time, as measured by incisor irregularity.
99
• There is only a very weak correlation between how
well a case was treated using the ABO scale and
lower incisor crowding over time, as measured by
incisor irregularity.
• The improvement of the ABO scores over time can be
attributed to improvements in the marginal ridges
and occlusal contacts components of the ABO and are
presumably due to settling and wear.
• Alignment, posterior torque, and occlusal
relationships are highly correlated over the long
term and therefore for maximum stability these
factors must be scrutinized before treatment
conclusion.
100
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Brand, Adam J.
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Core Title
A comparison of the long-term stability of three different treatment philosophies
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Master of Science
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Craniofacial Biology
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2002-05
Publication Date
03/29/2002
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