Download extraction decision-making in class i malocclusions

EXTRACTION DECISION-MAKNG IN CLASS I MALOCCLUSIONS:
A
SURVEY IDENTIFYING VALUES FOR DEFINITE EXTRACTION
AND NON-EXTRACTION THERAPY
Samuel I. Gentry, D.D.S.
An Abstract Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2009
Abstract
Purpose:
It was the purpose of this study to test the
opinion of orthodontists as to the values they hold that
direct the need for extractions based on individual
measurements.
Methods:
A survey of 18 questions
pertaining to 9 diagnostic measurements was sent to 10,315
AAO members.
Respondents were also asked to indicate
his/her gender, years of experience in orthodontics, and
general orthodontic technique.
surveys were completed.
Results:
A total of 992
Ranges of responses representing
the middle 80% of respondents abutted without overlap for
crowding, L1-APog, midline deviation, and FMA.
Similar
ranges overlapped for curve of Spee and Bolton discrepancy
while there appeared ranges of values separating the ranges
for B-line, IMPA, and nasolabial angle.
Practitioners with
fewer than 5 years of experience responded differently from
those with more years of experience for 8 of 9 nonextraction measurements.
Conclusions:
There was an
apparent shift toward more protrusive teeth and lips as
acceptable treatment goals.
Experience plays a significant
role in the decision to treat a case non-extraction making
the decision to extract more clear-cut.
1 EXTRACTION DECISION-MAKNG IN CLASS I MALOCCLUSIONS:
A
SURVEY IDENTIFYING VALUES FOR DEFINITE EXTRACTION
AND NON-EXTRACTION THERAPY
Samuel I. Gentry, D.D.S.
A Thesis Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2009
COMMITTEE IN CHARGE OF CANDIDACY:
Professor Eustaquio A. Araujo
Chairperson and Advisor
Professor Rolf G. Behrents
Adjunct Professor Peter H. Buschang
Professor Gus Sotiropoulous
i
DEDICATION
This thesis is dedicated to my wife Stephanie, who did
not move home without me; to my parents for assuring me
that an education is the one investment in which you
control the returns; and to Dr. Stephen L. Wallace, whose
handshake was as meaningful as any legal document.
ii
ACKNOWLEDGEMENTS
I would like to thank the following individuals for their
contributions to this thesis:
Dr. Araujo, an old soul, for getting this project up
and running, and for his constant encouragement,
Dr. Behrents for helping me understand the importance
of attention to detail,
Dr. Buschang for his dedication to the profession
which poured over into my research experience,
Dan Kilfoy for his expertise and willingness to help.
iii
TABLE OF CONTENTS
List of Tables.............................................v
List of Figures...........................................vi
CHAPTER 1:
INTRODUCTION...................................1
CHAPTER 2:
REVIEW OF THE LITERATURE
Orthodontic Extractions ........................3
History ...................................3
Extraction Trends .........................7
Extraction Effects ........................7
The Borderline Patient .........................9
Clinical Classification ..................10
Cephalometric Classification .............14
Nonextraction Treatment Options ..........18
Extraction Treatment Options .............21
Decision-Making Aids .....................22
Summary and Statement of Thesis ...............23
References ....................................24
JOURNAL ARTICLE
Abstract ......................................31
Introduction ..................................33
Materials and Methods .........................35
Results .......................................39
Sex differences ..........................44
Experience ...............................44
Bracket Prescription .....................47
Discussion ....................................49
Conclusions ...................................53
References ....................................54
CHAPTER 3:
Appendix A (copy of survey)...............................57
Appendix B (distribution charts for all measurements).....65
Vita Auctoris.............................................70
iv
LIST OF TABLES
Table 3.1:
Survey measurements with respective answer
choices ......................................35
Table 3.2:
Descriptive statistics of completed surveys...39
Table 3.3:
Differences in extraction and non-extraction
treatment decisions between female and male
respondents ...................................45
Table 3.4:
Summary of one-way ANOVAs of experience
differences in extraction and non-extraction
variables .....................................46
Table 3.5:
Results of Bonferroni post hoc tests comparing
the different levels of experience for
extraction and non-extraction variables .......47
Table 3.6:
Summary of independent t-tests of bracket
prescription differences in extraction and nonextraction variables ..........................48
v
LIST OF FIGURES
Figure 2.1:
Extraction rates of the 20th century..........8
Figure 3.1:
Example question utilizing visual aid........36
Figure 3.2:
Survey modes with 10th and 90th percentiles
for individual measurements..................40
Figure 3.3:
Distribution of responses to millimetric
values of crowding ..........................40
Figure 3.4:
Distribution of IMPA responses...............44
Figure A.1:
Distribution of responses for crowding.......65
Figure A.2:
Distribution of responses for curve of Spee
.............................................65
Figure A.3:
Distribution of responses for Bolton
discrepancy .................................66
Figure A.4:
Distribution of responses for FMA............66
Figure A.5:
Distribution of responses for IMPA...........67
Figure A.6:
Distribution of responses for L1-APog........67
Figure A.7:
Distribution of responses for B-line.........68
Figure A.8:
Distribution of responses for nasolabial angle.
.............................................68
Figure A.9:
Distribution of responses for midline
deviation ...................................69
vi
CHAPTER 1:
INTRODUCTION
What drives the decision to extract?
In the early
1900s, few orthodontists extracted teeth due to Angle’s
popularity.1
The advent of cephalometrics coupled with
clinical evidence of improved treatments via extraction in
the 1940s turned the tide to promote extractions in order
to improve dental, skeletal, and facial relationships.2
Subsequently, extraction rates rose to almost 75% in the
1960s.3
Current extraction rates are estimated to be
between 25 to 30%.4-6
This reflects improved non-extraction
techniques and empirical evidence of uncertainty with
respect to the stability of extractions.7-14
There exist many objective rating systems to assess
malocclusion severity, but the decision to extract is up to
the clinician.
This study explored clinicians’ opinions
regarding extraction treatment because, indeed, every
clinician has his or her own opinions of what severity of
malocclusion requires extraction treatment.
The
investigation attempted to organize these opinions on
measurements that are common directives regarding
extraction and non-extraction treatment.
It was the purpose of this study to test the opinion
of orthodontists as to the values they hold that direct the
1 need for extractions based on individual measurements.
Certainly no orthodontist makes extraction decisions based
on a single measurement.
Yet, 992 orthodontists completed
a survey identifying values which related individual
measurements to a need for definite extraction or nonextraction treatment.
2 CHAPTER 2:
REVIEW OF LITERATURE
Orthodontic Extractions
History
For over one hundred years, the extraction of teeth to
facilitate orthodontic treatment has fostered heavy debate
within the profession.
Extractions create space to align
teeth when crowding is present and to reduce protrusion of
the teeth and overlying soft tissues.
The alternative to
extraction of teeth is expansion of the arches.
Therefore,
in any borderline case of crowding and/or protrusion, there
is a choice to be made:
Does one extract or expand?
In 1907 Edward Angle proposed that normal occlusion
could be achieved through the expansion of arches.1
The
widespread acceptance of Dr. Angle’s teachings led to a
quarter century of expansion orthodontics showing few
examples of tooth extraction.
Furthermore, Angle believed
that when the teeth were placed in ideal occlusion, the
resulting facial features were, regardless of patient
opinion, “the best facial appearance for him or her,” and
failure of the dentition to remain stable meant a failure
on the part of the treating orthodontist to place the teeth
in proper occlusion.2
Many early orthodontists believed
malocclusions developed after birth and represented the
manifestation of “degenerating or growth-perverting
3 influences”3 on the individual; that orthodontic treatment
would, therefore, alter the local environment returning the
individual to a path of perfection.
Angle’s occlusal concepts did not go unopposed.
In
well-publicized debates, Dr. Calvin Case argued against the
idea that man is made perfect and that environment is
responsible for malocclusions.
In fact, with only
rudimentary knowledge of genetics, Case noted that under
the “laws of heredity, union of dissimilar types creates
inharmonious sizes and relations of teeth and jaws.”3
Case
presented cases in which the buccal teeth were in normal
occlusion, yet decided protrusion was evident.
Those
individuals presenting bimaxillary protrusion, and cases
which would trade skeletal imbalance for dental protrusion
through non-extraction therapy were precisely Case’s
reasons for extraction.
He noted that non-extraction
therapy would result in “almost certain probability of
ultimately stamping a most unhappy facial deformity for
life upon the patients.”3
Investigations into relapse after non-extraction
orthodontic treatment led two men, independently of one
another, to the idea that, in some cases, extraction of
teeth led to greater stability.
Charles Tweed and Raymond
Begg modified Angles’ appliance in search of improved
4 therapies.
Tweed, dissatisfied with the orthodontic
creation of protrusive faces and unstable results,
retreated one hundred cases by extracting four first
bicuspids; after treatment he noted an improvement in
stability and attributed this effect to the placement of
the mandibular incisors upright over basal bone.4
Simultaneously, Begg began extracting teeth and likewise
noted improved treatment results.
Their presentations of
finished cases paved the way for a shift in attitude toward
extraction.
Results of genetic and cephalometric studies further
disputed Angle’s belief in the origins of malocclusion and
bone adaptation following orthodontic treatment.
Stockard
and Johnson publicized genetic heritability in crossbred
dogs, representing conclusive evidence of inherited
malocclusion.5
Brodie et al. published early cephalometric
work in which they concluded that “actual bone changes
accompanying orthodontic management seem to be restricted
to the alveolar process.”6
Stockard and Johnson’s findings
flew in the face of previous theory that malocclusions were
the result of environmental influence.
Likewise, Brodie et
al.’s evidence repudiated the belief that bony response
occurred anywhere other than the alveolar processes.
5 Historically, there has been little debate regarding
the rationale behind extracting teeth.
Case advocated
extraction to correct dental and soft-tissue protrusion and
to prevent the transition of a single protrusive arch
coupled with a skeletal imbalance from becoming a double
protrusion.3
Eighty years later, Baumrind et al. found
crowding, incisor protrusion, and profile improvement to
be, in order of importance, the reasons orthodontists
extract teeth.7
Lending further support, Paquette et al.
found that maxillary and mandibular crowding and
protrusion, mandibular irregularity, and profile convexity
to be the most significant variables influencing
extraction.8
Vaden and Kisel offered a slightly different
perspective with respect to the limits of the dentition,
such that the decision to extract is guided by the
anterior, posterior, vertical, and transverse dimensions.
The author noted that extractions may be necessary to
preserve the integrity of these dimensions or facial
harmony may be sacrificed.9
6 Extraction Trends
The first quarter of the twentieth century saw
overwhelming support for Angle’s non-extraction approach to
treatment.
Accordingly, extraction rates hovered near ten
percent (Figure 2.1).2
Once the orthodontic community
accepted evidence in support of extraction therapy in
search of stability, rates of extraction soared to a peak
of seventy percent in the 1960s.10 Extraction rates declined
during the 70s11 and 80s in response to research which
concluded both extraction and non-extraction therapies as
being associated with instability.12
In response to
improved non-extraction techniques, a public desire for
fuller profiles and prominent lips, as well as claims that
extraction therapy causes TMD, current extraction rates
seem to have settled at approximately thirty percent,
nearing the levels of the early 1900s.10,13-15
Extraction Effects
Cephalometric studies have clarified the quantitative
and qualitative effects of extraction.
Quantitative
changes include a retrusion of the lips two to four
millimeters and an increase in the nasolabial angle by five
to ten degrees.16-19
However, Drobocky and Smith noted that
7 Figure 2.1: Extraction rates of the 20th century1 cephalometric differences may not necessarily coincide with
subjective interpretation of what is considered desirable
or undesirable.
Thus, “evaluation of profile esthetics by
the quantitative methods…must be interpreted with
caution.”16
Further studies have utilized lay people, dentists,
and orthodontists to evaluate the effects of extraction and
non-extraction treatments.
Boley et al. found that neither
dentists nor orthodontists could determine which treatment
a patient had received any better than a flip of a coin.20
The authors concluded that “fear of a significant
detrimental effect on the face is unjustified” with respect
to four bicuspid extraction.
On the other hand, Xu et al.
found a preference for the extraction profile in borderline
8 patients.21
Other studies investigated this conclusion in
the long-term.
Stephens et al., in a follow-up to the
Boley study, concluded that “treatment modality does not
affect long-term soft tissue profile changes,” and that
there was no preference regarding treatment between lay
people and orthodontists, males and females, and the
extraction and non-extraction patients.22
Paquette et al.
also showed that patients, whether treated extraction or
non-extraction, showed no tendency in esthetic preference
in the long-term even though choice of treatment created a
two millimeter difference in denture and lip protrusion.8
Additionally, the authors found differences at the end
of treatment to be similar ten to fifteen years posttreatment.
Whether the patients studied were similar prior
to treatment or immediately post-treatment, the results
laid to rest a decades-old accusation that extraction
creates dished-in profiles.
The Borderline Patient
The borderline patient is that individual caught
between definitive extraction and non-extraction;
“Empirical evidence of uncertainty exists with these
patients.”23
For a patient population which has been
estimated by Alexander in the neighborhood of 30%,24 a
disproportionate research effort has taken place compared
9 to Class II treatment, a patient population estimated near
15%.2
Much of the debate regarding class II treatment has
focused on proper timing and technique.
Johnston has drawn
the conclusion that early, late, single-phase, or two-phase
treatments do little to produce significantly different
results.
Similarly, the borderline patient “can be treated
either way.”8
But when “some skilled clinicians…would be
likely to make opposite decisions”21 and disagree “as to
whether extraction or nonextraction (sic) therapy was the
optimum treatment”,25 the idea that there exists only one,
single-best treatment should drive further investigation to
establish diagnostic methods to aid the borderline
individual.
Clinical Classification
The most common form of malocclusion treated by
orthodontists is tooth-size arch length deficiency (TSALD).2
The National Health and Nutrition Estimates Survey
(NHANES III) showed only one third of adults and 45.5% of
children ages 8 to 11 have well-aligned mandibular
incisors.
Additionally, nearly fifteen percent of
adolescents and adults have incisor irregularity greater
than ten millimeters.
10 Little developed the Irregularity Index to give
greater objective and quantitative meaning to ambiguous
clinical terminology, e.g., crowding, overlap,
irregularity.26
The author noted “epidemiologic
studies…would benefit from a quantitative measure” and, in
fact, the Irregularity Index found its way into the NHANES
III survey discussed above.
Mandibular anterior
irregularity is measured by adding the linear distances
between the five adjacent anterior contact points.
perfectly aligned incisors, the score is zero.
increases with increasing malalignment.
With
The score
Little noted a
score greater than 6.5 millimeters indicates severe
irregularity and, thus, greater likelihood for
extraction.12,26,27
One will find a substantial gray area in the
scientific literature defining the borderline of extraction
relating to dental discrepancy (crowding).
Carey and
McNamara set arbitrary borderlines of 2.5 to 5.0
millimeters and 3 to 6 millimeters, respectively.28,29
Gust,
in a search to specifically define the borderline,
concluded “the amount of maxillary arch length discrepancy
may be the most important factor in differentiating the
borderline patient” between extraction and non-extraction
treatments.23
The author found the range to be 6 to 8
11 millimeters of discrepancy.
Luppanapornlarp and Johnston
further developed the borders by describing the amount of
discrepancy in definitive extraction and non-extraction
cases.18
This study found roughly one millimeter of
crowding in either arch to constitute definitive nonextraction, while definitive extraction therapy in the
maxillary and mandibular arches was 5.8 and 7.3
millimeters, respectively.
Literature defining the
borderline of extraction with respect to crowding involves
a mixture of Class I and Class II malocclusions.
In this
regard, Baumrind et al noted “Angle classification appear
to tell one little about clinician consensus on
extraction.”25
As a rule of thumb, many clinicians have believed
leveling the Curve of Spee carries a liability ratio of
1:1; leveling the curve increases incisor protrusion.
Tweed advocated tip-backs and Class III elastics during
resolution of a deep bite to prevent incisor flaring.30
Recent studies conclude the real effect to be closer to
1:3; for every three millimeters of curve leveled, arch
circumference increases one millimeter.31-34
Roth considered
3 to 6 millimeters of curve of Spee mild (1.5 to 3.0 per
side),35 and Baldridge added that greater than six
millimeters is severe.31
In a borderline extraction case,
12 the deeper the Curve of Spee, the greater the need for
extraction.
An interarch tooth-size discrepancy may provide
incentive to extract in order to establish a proper
occlusion.
This diagnostic variable has been popularized
as the Bolton discrepancy.36
Regardless of its recognition,
the task of measuring teeth from first molar to first molar
in both arches prevents many clinicians from treatment
planning according to interarch discrepancies.
Ballard
introduced tooth size asymmetry, both intra- and interarch,
as a necessary factor in diagnosis and treatment planning
and found more than half of his cases had a discrepancy of
two millimeters or more, a magnitude preventing ideal
occlusion.37,38
Additionally, the author noted “conditions
prejudicial to perfect balance of the denture were found in
nine patients out of ten.”38
The prevalence of
discrepancies of this magnitude should encourage an
evaluation of tooth size discrepancy a place in every
clinician’s evaluation.
Neff, in an effort to simplify
diagnostic evaluation, noted an ideal maxillary to
mandibular cuspid-to-cuspid ratio of 1.22.39
The anterior
Bolton ratio of .772 is an approximation of the inverse of
Neff’s findings.
As clinicians have utilized interproximal
reduction to resolve interarch tooth size discrepancies,
13 Bolton noted a four millimeter limit to anterior
reduction.40
Thus, extraction may be necessary to resolve a
discrepancy greater than this.
A proper assessment of facial, skeletal, and dental
symmetry is essential in orthodontic diagnosis.
A
deviation of the dental midline(s) may indicate a skeletal
asymmetry and require surgery for correction.
Dental
midline deviations in the presence of acceptable facial and
skeletal balance can be treated orthodontically; with
increasing dental midline deviation, extraction becomes
more likely.
The literature provides little data on
quantity of deviation relating to the borderline of
extraction.
Cephalometric Classification
The analysis of lateral cephalograms has provided
orthodontics with standards not only for the hard tissues,
but also for the soft tissue profile.
As Paquette et al.
noted, “comparison between extraction and nonextraction
treatments can have meaning only for the borderline
patient.”8
The authors found an average two millimeters
difference in lip protrusion after treatment.
Therefore,
it is essential to incorporate the effects of treatment
when considering extraction versus non-extraction therapy
for each borderline case.
14 There exists a wealth of normative data relative to
profile lip position in well-balanced faces.
These data
allow the clinician to plan treatment in order to achieve
the best possible esthetics after treatment.
A borderline
case with pre-treatment lip protrusion may be better served
with extraction.
Similarly, a more retrusive profile may
be improved without removing teeth.
Ricketts first identified the esthetic plane, relating
lip position to a line from the nasal tip to soft tissue
Pogonion.41
In the aging face, lips become relatively more
retruded, creating a natural difference in proper lip
positions between different age groups.
In the adolescent,
the lower lip is about two millimeters behind the esthetic
plane, or E line, with a standard deviation of three
millimeters.
The adult lower lip is ideal about four
millimeters behind the E line with a similar standard
deviation.
Burstone found it advantageous to consider lip
position relative to a line connecting subnasale and soft
tissue pogonion because it is based on a “plane of minimal
variation in the face.”42
The author noted the nose is an
area of great variation, “approximately twice” the standard
deviation as lower lip protrusion (2.8 versus 1.6).
The
investigator found the lower lip to be ideally positioned
15 about +2.2mm +/-1.6mm in adolescents.
Since lip protrusion
can disrupt an otherwise pleasing face, extraction may be
necessary the further a patient is from ideal.
Another morphological characteristic important in
diagnosis is the nasolabial angle.
There is a great deal
of variation in the literature as to what constitutes the
ideal value.
In Burstone’s 1967 evaluation of lip
relation, the author found a preferable nasolabial angle of
73.8 degrees +/- 8.
More recent studies find more suitable
values in the range of 90 to 115 degrees.43-46 Extraction of
four bicuspids was noted to increase the nasolabial angle
5.2 degrees by Drobocky and Smith.16
Therefore, extraction
of teeth in a borderline patient with a nasolabial angle
greater than the normative values should be avoided.
Facial balance is an issue involving dimensions
assessed through lateral and frontal imaging.
The
dimension common to both views is the vertical.
Schudy
argues the vertical dimension is the most important to the
clinician.47
The study utilized the angle formed at the
intersection of the sella-nasion and mandibular planes
(SN-MP)to aid in his assessments, and found the value of
thirty-three degrees to be average for balanced vertical
facial types, with a range of 31 to 34 degrees.
Another
measure of vertical skeletal relationships is the Frankfort
16 mandibular plane angle (FMA).
The FMA provides an
additional vertical appraisal to the SN-MP measurement.
A
normal value for the FMA is in the range of 20 to 30
degrees.48
Values above these normal ranges are associated
with skeletal open bite, whereas values below are typically
associated with skeletal deep bite.
Sassouni and Nanda’s
“four bony planes of the face” provide an additional
assessment of vertical relationships.49
A center 0, defined
as the area of convergence of these planes, when located
far posterior to the lateral view of the cranium as a
result of hypodivergence of the planes is indicative of a
skeletal deep bite.
Hyperdivergence of the facial planes
creates a center 0 much more anterior and is common in the
skeletal open bite type.49,50
Regardless of the clinician’s
form of vertical assessment, there is agreement among these
measurements regarding extraction and non-extraction
therapy.
Treatment geared toward achieving facial balance
is more likely to extract in skeletal open bite and not
extract in cases with skeletal deep bite.
Orthodontists may disagree which incisor is of greater
diagnostic value, the maxillary versus the mandibular.
Consequently, clinical cephalometrics may assess the
angular and positional values for both.48,51-53
Charles Tweed
used the orientation of the mandibular incisor to aid in
17 treatment planning to create facial balance and harmony.48
He noted a need for “upright” and “vertical” lower
incisors.
Margolis proposed the incisor mandibular plane
angle (IMPA) to quantitatively define these two qualities.54
He proposed IMPA to be 90+/-3 degrees in normal, balanced
faces.
According to Tweed, this value can range between 85
and 95 degrees, and vary according to ethnicity.48
Values
above this range are indicative of extraction to improve
functional and esthetic imbalance.53
McNamara found the
proper position of the mandibular incisor to be 1 to 3
millimeters anterior to the line from point A to Pogonion
(A-Pog) in a well-balanced face, regardless of age.52
Steiner set the ideal positions of the maxillary and
mandibular incisors to be four millimeters anterior to the
lines connecting Nasion and point A, and Nasion and point
B, respectively.51
The maxillary and mandibular incisors
should form angles of 22 and 25 degrees to their respective
diagnostic lines.
Extraction becomes more likely as
incisor positions and angles exceed these values.
Non-Extraction Treatment Options
Treatment to resolve TSALD either involves reduction
in tooth mass or expansion of the arches.
A reduction in
tooth mass may mean extraction of one or more dental units;
it may also mean interproximal reduction of enamel.
18 Expansion encompasses those techniques which increase arch
length and/or width to stretch the boundaries within which
the teeth must fit.
Regardless of treatment, the quality
of the result is ultimately judged by stability.
Proponents of non-extraction therapy have looked to
timing of treatment as an ally.
Moreira and Araujo sampled
678 patients in a Brazilian orthodontic clinic and found
that as growth potential decreased, extraction rates
increased.55
Additionally, preservation of arch length can
satisfy TSALD in approximately 75% of all patients.56
Gianelly added that this number increases to 84% with the
use of a lip bumper to distalize molars one millimeter.
Therefore, treatment in the mixed dentition may provide
more opportunities to effectively treat the borderline
patient non-extraction.
Since the 1960s, extraction rates have steadily
decreased, due, in part, to increased investigation into
expansion/distalization treatments.
If “biologic systems
are best able to adapt developmentally during periods of
maximum change,”57 then mixed dentition therapy may
ultimately improve stability.
Buschang et al. tested this
hypothesis in a series of clinical tests.
The authors
concluded the lip bumper “can gain or maintain 6-7
millimeters of space without substantially flaring
19 incisors” through a combination of molar expansion and
uprighting, incisor tipping, and maintenance of leeway
space.57
These findings have been supported by Ferris et
al. who concluded results from active, early expansion are
stable long-term.58
Other studies elaborate on expansion/distalization
techniques which reduce the need for extractions.59,60
McNamara reviewed a series of his expansion/early treatment
efforts.29
The author noted that intervention in the mixed
dentition utilizing leeway space and rapid maxillary
expansion may provide “sufficient arch space to resolve
borderline crowding,” which he defined as 3 to 6
millimeters.
One might argue against interproximal reduction (IPR)
being non-extraction therapy.
Because one winds up with
less tooth mass, some might say that the only difference
between extraction and IPR is an injection.
Regardless,
whether in the form of an air-rotor disk or lightning
strips, IPR provides a viable treatment option for the
borderline patient to prevent removal of teeth.
Over 45
years ago, Bolton noted a four millimeter limit to anterior
stripping.40
Tuverson explained that each incisor surface
allows 0.3 millimeters and 0.4 millimeters at the cuspids,
totaling 4.0 millimeters.61
Sheridan stretched previous
20 limits of IPR by removing enamel from molar to molar, thus
allowing for a cumulative space gain of up to
8.0 millimeters.62
This quantity makes air-rotor stripping
an alternative to tooth extraction bridging the gap
separating definite extraction and non-extraction with
respect to TSALD.
Extraction Treatment Options
The decision to extract in the borderline case
oftentimes hinges on the clinician’s desire for facial
change.
Non-extraction therapy in the presence of mild
denture and lip protrusion may cause a bimaxillary
protrusion and facial imbalance.
On the other side of the
coin, four first bicuspid extraction in a case with mild
lip retrusion could create an undesirable facial result.
As a result, some clinicians advocate alternative
extractions such as second bicuspids or a mandibular
incisor to lessen the effect on the soft tissue profile
while maintaining stability.61,63-65
Though mandibular incisor extraction may have little
effect on the profile and resolves anterior TSALD, there
are pitfalls to this treatment which necessitate proper
diagnosis and case selection.
Bite deepening and increased
overjet commonly occur after treatment with only three
mandibular incisors.
Therefore, clinicians note proper
21 diagnostic criteria to be anterior interarch tooth size
discrepancy (Bolton discrepancy of mandibular excess), a
diagnostic wax setup, and mandibular anterior crowding.64,65
As opposed to four bicuspid extraction, incisor extraction
has other advantages such as reduced treatment time,
simpler mechanics, and favorable stability.65
Decision-making Aids
In 1948, Downs discussed acceptable ranges of ten
diagnostic variables after studying twenty patients with
normal occlusions and exhibiting facial balance and
harmony.53
This work formed one of the earliest
cephalometric analyses in orthodontics.
Notably, he
concluded “single readings are not so important; what
counts is the manner in which they all fit together.”
Three years later, Vorhies and Adams took Downs’
analysis one step further to ease the “difficulty of
developing a suitable mental picture.”66
The authors
organized the data describing acceptable ranges for each
characteristic into a wigglegram, an adaptation of
Hellman’s early anthropometric work.67
The illustration
provided an efficient method to analyze cephalometric
measures.
In 2002, Rody and Araujo adapted the idea of a
wigglegram to facilitate decision-making in Class I
22 borderline extraction cases.68
Similar to Downs’
Wigglegram, the authors illustrated acceptable deviations
of diagnostic normative data.
Vorhies and Adams related
variations of the Downs norms to Class II and Class III
characteristics.
Rody and Araujo illustrated relationships
of dental, skeletal, and facial cephalometric measurements
to extraction and non-extraction treatment.
In the
authors’ Extraction Decision-Making Wigglegram (EDMW), the
center line represents the average value for each
measurement.
For each patient, values to the left of
center support extraction, and values to the right support
non-extraction.
The range of acceptable values for each
measurement, both above and below the norm, represent the
borderline for each variable.
Plotting all diagnostic
values on the EDMW allows the clinician to weigh all
“votes” for and against extraction.
Summary and Statement of Thesis
This study aims to investigate current practitioner
opinions on values which indicate extraction or nonextraction treatments, and determine what influences
gender, length of time as an orthodontic practitioner, and
bracket prescription may have on the decision to extract in
Class I malocclusions.
23 References
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30 CHAPTER 3:
JOURNAL ARTICLE
Abstract
Purpose:
It was the purpose of this study to test the
opinion of orthodontists as to the values they hold that
direct the need for extractions based on individual
measurements.
Methods:
A survey of 18 questions
pertaining to 9 diagnostic measurements was sent to 10,315
American Association of Orthodontists (AAO) members.
Respondents were also asked to indicate his/her gender,
years of experience in orthodontics, and general
orthodontic technique.
were completed.
Results:
A total of 992 surveys
Ranges of responses representing the
middle 80% of respondents abutted without overlap for
crowding, L1-APog, midline deviation, and Frankfort
Mandibular Plane Angle (FMA).
Similar ranges overlapped
for curve of Spee and Bolton discrepancy while there
appeared ranges of values separating the ranges for B-line,
Incisor Mandibular Plane Angle (IMPA), and nasolabial
angle.
Practitioners with fewer than 5 years of experience
responded differently from those with more years of
experience for 8 of 9 non-extraction measurements.
Conclusions:
There was an apparent shift toward more
protrusive teeth and lips as acceptable treatment goals.
Experience plays a significant role in the decision to
31 treat a case non-extraction making the decision to extract
more clear-cut.
32 Introduction
What drives the decision to extract?
In the early
1900s, few orthodontists extracted teeth due to Angle’s
popularity.1
The advent of cephalometrics coupled with
clinical evidence of improved treatments via extraction in
the 1940s turned the tide to promote extractions in order
to improve dental, skeletal, and facial relationships.2
Subsequently, extraction rates rose to almost 75% in the
1960s.3
Current extraction rates are estimated to be
between 25 to 30%.4-6
This reflects improved non-extraction
techniques and empirical evidence of uncertainty with
respect to the stability of extractions.7-14
There exist many objective rating systems to assess
malocclusion severity, but the decision to extract is up to
the clinician.
This study explored clinicians’ opinions
regarding extraction treatment because, indeed, every
clinician has his or her own opinions of what severity of
malocclusion requires extraction treatment.
The
investigation attempted to organize these opinions on
measurements that are common directives regarding
extraction and non-extraction treatment.
It was the purpose of this study to test the opinion
of orthodontists as to the values they hold that direct the
need for extractions based on individual measurements.
33 Certainly no orthodontist makes extraction decisions based
on a single measurement.
Yet, 992 orthodontists completed
a survey identifying values which related individual
measurements to a need for definite extraction or nonextraction treatment.
34 Methods and Materials
The opinions of orthodontists regarding the
characteristics that influence definite extraction and nonextraction treatment were measured using a survey developed
using an online design application.15
A digital format was
chosen as an efficient method to control participant
anonymity, cost, and ease of use.
Each survey recipient was asked to respond to 18
questions pertaining to the nine diagnostic measurements
found in
Table 3.1.
Positive and negative values indicate positions
anterior or posterior to the reference line, respectively.
For each measurement, the respondent was asked the
following question: “When on the borderline of extraction,
please indicate the quantity of (measurement) which
corresponds to definite extraction” or “non-extraction.”
Table 3.1:
Survey measurements with respective answer choices
Crowding
Curve of Spee
Bolton discrepancy
L1-APog
B-line
Midline deviation
FMA
IMPA
Nasolabial angle
Answer ranges
0mm to 14mm
0mm to 10mm
0mm to 10mm
-6mm to +8mm
-6mm to +14mm
0mm to 10mm
10° to 50°
70° to 120°
70° to 140°
35 Answer increments
1mm
1mm
1mm
1mm
2mm
1mm
5°
5°
10°
Figure 3.1:
Example question utilizing visual aid
Visual aids were included to better define FMA, IMPA,
and L1-APog (Figure 3.1).
Additionally, each participant
was asked his/her sex, typical orthodontic technique, and
years of experience as an orthodontist.
Responses to the
open-ended question of orthodontic technique were
translated into a category that related the type brackets
utilized by the practitioner.
Only responses which
specifically identified bracket prescription were
categorized as “pre-adjusted” or “standard edgewise.”
All
others were categorized as “unknown,” and were not
subjected to statistical comparison.
Thirty residents and faculty from the Saint Louis
University Center for Advanced Dental Education
participated in a pilot survey.
Participants stated the
survey question was unclear and/or ambiguous and needed
36 clarification.
Subsequently, the initial version of the
survey was modified to produce a final version of greater
simplicity and reduced ambiguity.
The final version of the survey (Appendix A) was
approved by the Board of Directors of the American
Association of Orthodontists (AAO) to be sent to all active
and lifetime, domestic and international orthodontists and
orthodontic residents with a valid email address.
The AAO
membership database produced a list of 10,315
orthodontists.
In order to maintain anonymity and privacy
of respondents, the survey was forwarded by the AAO to all
email addresses on the list.
Results of the survey were
recorded and maintained devoid of participant identifiers
(e.g., email address) on the SurveyMonkey® server
(Surveymonkey.com, Portland, OR).
At the end of the two week survey window, data from
992 completed surveys had been collected.
All completed
survey data collected were analyzed using SPSS 14.0 (SPSS
Inc., Chicago, IL).
Modes were chosen instead of means to
present survey results because answer choices were
categorical, not continuous.
numbers as answer options.
Subjects only had whole
So unless the mean value was a
whole number, that value could not be selected by any
participant. Percentiles were used rather than standard
37 deviations because percentiles lend a better sense of the
number of clinicians indicating a range of values.
Independent t-tests were used to evaluate differences in
the means according to gender and technique. One-way
analysis of variance (ANOVA) was used to determine
differences related to three experience groupings, 11+
years, 6-10 years, and 0-5 years. When differences were
identified, a Bonferroni post hoc test was used to identify
differences between group pairs.
38 Results
Distribution charts for each measurement can be found
in Appendix B.
Table 3.2 summarizes the descriptive
statistics for the overall survey.
Figure 3.2 illustrates
modes with respective 10th and 90th percentiles.
All values
for crowding, curve of Spee, Bolton discrepancy, L1-APog,
B-line, and midline deviation are in millimeters and FMA,
IMPA, and nasolabial angle are in degrees.
Four millimeters was the mode (most common) nonextraction crowding value (Figure 3.3).
roughly 1/3 of all respondents.
This represented
Eighty percent of
respondents indicated values between 2mm and 6mm.
Table 3.2:
Descriptive statistics of completed surveys
Non-Extraction
Extraction
Percentile
10
90
Mode
Range
Range
Crowding
4.0
14
2.0
6.0
8.0
14
6.0
12.0
Curve of Spee
2.0
10
0.0
4.0
4.0
10
3.0
8.0
Bolton
2.0
10
0.0
4.0
6.0
10
2.0
8.0
L1-APog
0.0
14
-4.0
3.0
5.0
14
3.0
7.0
Lip Protrusion
Midline
Deviation
FMA
0.0
20
-4.0
6.0
10.0
12
8.0
14.0
2.0
10
0.0
3.0
4.0
10
3.0
7.0
20.0
40
10.0
30.0
40.0
40
30.0
50.0
IMPA
85.0
50
75.0
95.0
110.0
40
100.0
120.0
Nasolabial
Angle
110.0
70
90.0
130.0
70.0
70
70.0
80.0
39 Percentile
10
90
Mode
*Non-extraction = red; Extraction = blue
Figure 3.2: Survey modes with 10th and 90th percentiles for individual
measurements
350
300
250
200
150
100
50
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Non-extraction = red; Extraction = blue
Figure 3.3: Distribution of responses to millimetric values of
crowding
40 Respondents indicated a broader range of values
describing the need for extraction due to crowding.
Eighty
percent of respondents chose extraction from 6mm to 12mm.
Eight millimeters of crowding was the mode, representing
about 1/4 of respondents.
About ½ of respondents chose 2mm of curve of Spee to
indicate non-extraction treatment.
Eighty percent of
respondents indicated non-extraction treatment between 0mm
and 4mm of curve of Spee.
To indicate a need for extraction, roughly 1/4 of
respondents chose 4mm of curve of Spee.
Eighty percent of
respondents chose a range of 3mm to 8mm of curve of Spee to
indicate extraction treatment.
The mode for non-extraction Bolton discrepancy was
2mm.
This represented roughly 1/3 of respondents.
Eighty
percent of orthodontists would not extract if the Bolton
discrepancy is between 0mm and 4mm.
The mode for extraction Bolton discrepancy was 6mm,
indicated by more than 1/4 of respondents.
Eighty percent
of respondents indicated 2mm to 8mm of Bolton discrepancy
to represent a need for extraction.
Nearly 1/4 of respondents indicated a L1-APog value of
0mm to indicate non-extraction treatment.
41 Values between
-4mm and +3mm indicated non-extraction treatment by 80% of
respondents.
The mode for L1-APog indicating extraction treatment
was +5mm.
The mode represented more than 1/4 of
respondents.
Eighty percent of respondents chose values
between +3mm and +7mm.
The mode for non-extraction B-line was 0mm.
1/4 of respondents indicated this value.
Nearly
Eighty percent of
respondents selected non-extraction B-line vales between 4.0mm and +6.0mm.
Respondents provided a narrower range of values to
indicate extraction treatment based on the B-line.
Eighty
percent of respondents selected values from +8mm to +14mm.
The mode was +10mm, selected by more than 1/3 of
respondents.
Eighty percent of respondents indicated non-extraction
treatment based upon midline deviations up to 3mm.
Roughly
45% of respondents indicated the mode as 2mm of midline
deviation.
The mode for extraction midline deviation was 4mm.
This represented roughly 1/3 of respondents.
Eighty
percent of respondents selected values between 3mm and 7mm.
Eighty percent of respondents indicated non-extraction
treatment based upon FMA values between 10° and 30°.
42 The
mode was 20°.
This value represented more than 1/3 of
respondents. The mode for extraction FMA values was 40°.
value represented more than 1/3 of respondents.
This
Values
between 30° and 50° were selected by 80% of respondents.
Eighty percent of respondents indicated non-extraction
treatment based upon IMPA values between 75° and 95°
(Figure 3.4).
The mode was 85°.
This value was selected
by more than 1/4 of respondents.
Eighty percent of respondents indicated extraction
treatment based upon IMPA values between 100° and 120°.
Respondents most commonly selected 110°, and this
represented roughly 1/3 of respondents.
The mode for non-extraction nasolabial angle values
was 110°.
This represented almost 30% of respondents.
Eighty percent of respondents selected values between 90°
and 130°.
Eighty percent of respondents indicated extraction
treatment based upon nasolabial angle values between 70°
and 80°.
Seventy degrees was commonly selected to indicate
extraction treatment.
Roughly 70% of respondents selected
this value.
43 350
300
250
200
150
100
50
0
70 75 80 85 90 95 100 105 110 115 120
Non-extraction = red; Extraction = blue
Figure 3.4: Distribution of responses for IMPA
Sex Differences
Female respondents tend to require greater
discrepancies from normal values than male respondents in
deciding when to extract.
The mean measurements of male
and female respondents show statistically significant
extraction differences for crowding, FMA, and nasolabial
angle and non-extraction differences for lip protrusion and
nasolabial angle (Table 3.3) (p<0.05).
Experience
Results comparing the means of the three experience
groups revealed statistically significant differences in
eight of nine non-extraction measurements.
44 All non-
Table 3.3:
Differences in extraction and non-extraction treatment
decisions between female and male respondents.
Females
Males
Extraction
Mean
SD
Mean
SD
Sig.
Crowding
8.4
2.2
8.0
2.4
0.046*
Curve of Spee
5.1
2.0
5.1
2.3
0.770
Bolton
5.5
2.2
5.3
2.4
0.305
L1-APog
4.9
1.9
5.0
1.9
0.274
Lip Protrusion
10.6
2.3
10.3
2.3
0.087
Midline Deviation
4.9
1.4
4.8
1.6
0.865
FMA
39.9
6.4
38.9
6.4
0.049*
IMPA
108.6
7.3
108.9
6.7
0.589
Nasolabial Angle
73.2
6.5
75.8
11.5
0.005*
Non-extraction
Crowding
4.1
1.9
4.1
2.0
0.883
Curve of Spee
2.5
1.8
2.4
1.7
0.567
Bolton
2.5
1.5
2.5
1.7
0.553
L1-APog
-0.7
2.5
-0.4
2.6
0.088
Lip Protrusion
0.1
3.8
0.9
3.9
0.013*
Midline Deviation
2.0
1.1
2.1
1.4
0.194
FMA
20.8
6.9
21.2
7.2
0.480
IMPA
85.7
7.5
86.6
8.4
0.192
Nasolabial Angle
114.6
15.2
110.6
16.2
0.003*
* denotes significance of p<0.05
extraction differences were due to the means of the group
of least experience.
Statistically significant differences were found for
all non-extraction variables except midline deviation and
extraction crowding, L1-APog, and nasolabial angle (Table
3.4).
The post hoc tests determined which groups are
different for each measurement (Table 3.5).
The only
difference between means of the 11+ and 6-10 year
experience groups was for extraction based on L1-APog.
Statistically significant extraction differences between
45 Table 3.4:
Summary of one-way ANOVAs of experience differences
in extraction and non-extraction variables
Experience
Extraction
Crowding
Curve of Spee
Bolton
L1-APog
B - line
Midline Deviation
FMA
IMPA
Nasolabial Angle
11+ years
7.9
5.2
5.3
5.2
10.3
4.9
38.9
108.8
75.9
Non-extraction
Crowding
4.1
Curve of Spee
2.5
Bolton
2.5
L1-APog
-0.3
B - line
0.9
Midline Deviation
2.2
FMA
21.7
IMPA
86.9
Nasolabial Angle
111.0
* denotes significance p<0.05.
6-10 years
8.3
5.0
5.3
4.8
10.2
4.6
39.2
108.3
74.6
4.5
2.6
2.7
0.0
1.7
2.1
21.4
87.3
109.0
0-5 years
8.6
4.9
5.3
4.6
10.3
4.8
39.8
109.7
73.8
3.9
2.2
2.2
-1.1
-0.3
1.9
19.2
84.2
113.7
Sig.
0.001*
0.151
0.991
<0.000*
0.740
0.059
0.211
0.116
0.045*
0.016*
0.022*
0.049*
<0.000*
<0.000*
0.143
<0.000*
<0.000*
0.023*
11+ and 0-5 years experience groups were found for crowding
and L1-APog.
For the same groups, non-extraction
differences were found for curve of Spee, FMA, IMPA, L1APog, and lip protrusion.
There were no extraction
differences found between the 0-5 and 6-10 years of
experience groups.
For the same two groups, there were
statistically significant non- extraction differences for
crowding, FMA, IMPA, L1-APog, lip protrusion, and
nasolabial angle. 46 Table 3.5:
Results of Bonferroni post hoc tests comparing
the different levels of experience for
extraction and non-extraction variables
Experience
11+ vs. 6-10
Extraction
Crowding
0.283
Curve of Spee
1.000
Bolton
1.000
L1-APog
0.043*
B - line
1.000
Midline Deviation
0.053
FMA
1.000
IMPA
1.000
Nasolabial Angle
0.638
Non-extraction
Crowding
0.098
Curve of Spee
1.000
Bolton
1.000
L1-APog
0.457
B - line
0.067
Midline Deviation
1.000
FMA
1.000
IMPA
1.000
Nasolabial Angle
0.554
* denotes significance p<0.05 11+ vs. 0-5
0.001*
0.173
1.000
<0.000*
1.000
1.000
0.237
0.253
0.054
0.433
0.027*
0.109
0.001*
0.001*
0.163
<0.000*
<0.000*
0.108
6-10 vs. 0-5
0.705
1.000
1.000
1.000
1.000
0.400
1.000
0.164
1.000
0.012*
0.082
0.077
<0.000*
<0.000*
1.000
0.012*
0.002*
0.024*
Bracket Prescription
The comparison of means for respondents utilizing preadjusted versus standard edgewise brackets can be found in
Table 3.6.
Statistically significant extraction
differences were found in crowding, curve of Spee, and
nasolabial angle.
Non-extraction statistically significant
differences were found in crowding and Bolton discrepancy.
47 Table 3.6:
Summary of independent t-tests of bracket
prescription differences in extraction and nonextraction variables
Bracket Prescription
Extraction
Pre-adjusted
Crowding
8.2
Curve of Spee
5.2
Bolton
5.4
L1-APog
5.1
B - line
10.3
Midline Deviation
4.8
FMA
39.2
IMPA
108.8
Nasolabial Angle
74.7
Non-extraction
Crowding
4.2
Curve of Spee
2.5
Bolton
2.5
L1-APog
-0.4
B - line
1.0
Midline Deviation
2.1
FMA
21.3
IMPA
86.6
Nasolabial Angle
111.2
* denotes significance p<0.05.
48 Standard
Edgewise
7.8
4.8
5.1
4.9
10.3
4.7
38.7
108.8
76.8
0.039*
0.033*
0.077
0.167
0.811
0.125
0.337
0.968
0.007*
3.9
2.4
2.3
-0.4
0.5
2.1
20.8
86.4
111.5
0.012*
0.418
0.046*
0.983
0.084
0.955
0.357
0.670
0.787
Sig.
Discussion
Each orthodontist has an opinion on when it is proper
or improper to extract teeth.
As evidenced by the number
of emails questioning the nature of the survey, forcing an
orthodontist to quantify values which indicate extraction
treatment based on a single measurement can “hit a nerve.”
The specialty of orthodontics does not require its members
to answer for their decisions, and so it was expected that
some survey recipients would become upset when asked to do
so.
It was never the purpose of the study to propose
extraction guidelines or to even impose an idea of what is
proper.
Furthermore, the results of this study are not
intended to encourage the establishment of extraction
guidelines.
This study “took the temperature” of current
extraction decision-making for Class I malocclusions using
nine common diagnostic measurements.
While it may be
interesting to note average values, some may find it more
relevant to know how their own decision-making compares to
those who participated in the study.
The borderline patient is currently described as one
whom provokes indecision, “can be treated either way,” or
causes disagreement as to whether extraction or nonextraction therapy is the best treatment.16,17
49 Results show
that for crowding, L1-APog, midline deviation, and FMA, the
decision to extract becomes more clear-cut at 6mm, 3mm,
3mm, and 30°, respectively.
Respondents also indicate that
3mm to 4mm of curve of Spee and 2mm to 4mm Bolton
discrepancy can be treated either way, as evidenced by the
overlap of ranges for these values.
On the other hand,
gray areas, illustrated in Figure 3.2 as ranges between the
middle 80% of the two decision groups, are found for B-line
values between 6mm and 8mm, IMPA values from 95° to 100°,
and nasolabial angles between 80° and 90°.
The findings of this study, in which 8mm of crowding
held significance for the extraction decision, add
practical support to the orthodontic literature.
Rody and
Araujo found that conservative non-extraction treatments
for the resolution of crowding have about an 8mm limit.18
Other studies noted borderline crowding limits between 6mm
and 8mm.7,19,20
Results for IMPA and B-line show a large number of
practitioners tolerating protrusion of the lower incisors
and lips.
It is somewhat surprising to find practitioners
showing ambivalence toward IMPA values between 95° and
100°.
According to the literature, IMPA values above 96°
indicate esthetic and/or functional impairment, yet many
respondents wouldn’t extract until values reach positions
50 rarely found in nature (110° or more).21-23
Furthermore,
respondents indicated an unwillingness to extract teeth to
improve lip protrusion until treatment couldn’t possibly
attain positions indicated by Burstone as being harmonious
and in balance (B-line 1mm-4mm).24
These data indicate not
only a tolerance for dental and soft tissue protrusion, but
also may reveal a preference for it, representing a shift
in treatment goals in orthodontics.
Experience appears to make the extraction decision
more clear-cut.
It was found that clinicians push the non-
extraction envelope with increasing years of experience.
This has the effect of narrowing the ranges of values
between the means for definite extraction and nonextraction.
Therefore, there is less gray area in
extraction decision-making for practitioners with more than
5 years of experience.
There exists a lack of research regarding what effects
bracket prescription and gender may have on the decision to
extract.
This study found statistically significant
differences for both.
However, correlation does not
necessarily mean causation.
The differences could very
well be spurious because the survey forced answers even
though clinicians do not base the decision to extract on a
single measurement, or because means taken to the tenth of
51 a millimeter or degree were derived from categorical,
whole-number answer choices.
Nonetheless, these
differences are real and call for further investigation.
52 Conclusions
This study found that orthodontists indeed have
different opinions as to what constitutes a definite need
for extraction or non-extraction treatment in Class I
malocclusions.
It also revealed practitioners will
tolerate a more protrusive dentition.
Experience plays a
significant role in the decision to treat a case nonextraction, and seems to shrink the gray areas describing a
borderline patient making the decision more clear-cut.
Previous orthodontic literature reveals little regarding
what effects experience and gender may have on the
extraction decision, and this study reveals a need for
consideration of these areas.
53 References
1. Proffit WR, Fields, H.W. Contemporary Orthodontics.
Saint Louis: Mosby; 2000.
2. Tweed CH. Indications for the Extraction of Teeth in
Orthodontic Procedure. Am J Orthod 1944;30:405-428.
3. Proffit WR. Forty-year review of extraction frequencies
at a university orthodontic clinic. Angle Orthod
1994;64:407-414.
4. O'Connor BM. Contemporary trends in orthodontic
practice: a national survey. Am J Orthod Dentofacial Orthop
1993;103:163-170.
5. Turpin DL. Percentage swings in extraction frequencies.
Angle Orthod 1994;64:403.
6. Weintraub JA, Vig PS, Brown C, Kowalski CJ. The
prevalence of orthodontic extractions. Am J Orthod
Dentofacial Orthop 1989;96:462-466.
7. McNamara JA, Jr. Early intervention in the transverse
dimension: is it worth the effort? Am J Orthod Dentofacial
Orthop 2002;121:572-574.
8. Gianelly AA. Crowding: timing of treatment. Angle Orthod
1994;64:415-418.
9. Buschang PH, Horton-Reuland, SJ, Legler, L, Nevant, C.
Nonextraction approach to tooth size arch length
discrepancies with the Alexander discipline. Sem Orthod
2001;7:117-131.
10. Ferris T, Alexander RG, Boley J, Buschang PH. Long-term
stability of combined rapid palatal expansion-lip bumper
therapy followed by full fixed appliances. Am J Orthod
Dentofacial Orthop 2005;128:310-325.
54 11. Cetlin NM, Ten Hoeve A. Nonextraction treatment. J Clin
Orthod 1983;17:396-413.
12. Ten Hoeve A. Palatal bar and lip bumper in
nonextraction treatment. J Clin Orthod 1985;19:272-291.
13. Tuverson DL. Anterior interocclusal relations. Part I.
Am J Orthod 1980;78:361-370.
14. Sheridan JJ. Air-rotor stripping. J Clin Orthod
1985;19:43-59.
15. Surveymonkey.com. 2008.
16. Paquette DE, Beattie JR, Johnston LE, Jr. A long-term
comparison of nonextraction and premolar extraction
edgewise therapy in "borderline" Class II patients. Am J
Orthod Dentofacial Orthop 1992;102:1-14.
17. Baumrind S, Korn EL, Boyd RL, Maxwell R. The decision
to extract: Part 1--Interclinician agreement. Am J Orthod
Dentofacial Orthop 1996;109:297-309.
18. Rody WJ, Jr., Araujo EA. Extraction decision-making
wigglegram. J Clin Orthod 2002;36:510-519.
19. 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;63:257-272.
20. Gust JE. A comparative analysis of borderline
extraction cases treated in two phases utilizing rapid
palatal expansion and lip bumper therapy Orthodontics.
Saint Louis: Saint Louis University; 2006: p. 115.
21. Tweed CH. The diagnostic facial triangle in the control
of treatment objectives. Am J Orthod 1969;55:651-657.
55 22. Margolis HI. The axial inclination of the mandibular
incisors. Am J Orthod Oral Surg 1943;29:571-594.
23. Downs WB. Variations in facial relationships: Their
significance in treatment and prognosis. Am J Orthod
1948;34:812-840.
24. Burstone CJ. Lip posture and its significance in
treatment planning. Am J Orthod 1967;53:262-284.
56 APPENDIX A:
COPY OF SURVEY
57 58 59 60 61 ‐6 ‐4 ‐2 0 +2 +4 +6 +8 +10 +12 +14 ‐6 ‐4 ‐2 0 +2 +4 +6 +8 +10 +12 +14 62 140° 130° 120° 110° 100° 90° 80° 70° 140° 130° 120° 110° 100° 90° 80° 70° 63 64 APPENDIX B:
DISTRIBUTION CHARTS FOR ALL MEASUREMENTS
Crowding
350
300
n
u
m
b
e
r
o
f
r
e
s
p
o
n
s
e
s
250
200
Extraction
150
Non‐extraction
100
50
0
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14
millimeters
Figure A.1:
Distribution of responses for crowding
Curve of Spee
350
300
n
u
m
b
e
r
r
e
s
p
o
n
s
o e
f s
250
200
Extraction
150
Non‐extraction
100
50
0
0
1
2
3
4
5
6
7
8
9
10
millimeters
Figure A.2:
Distribution of responses for curve of Spee
65 Bolton Discrepancy
350
300
n
u
m
b
e
r
r
e
s
p
o
n
s
o e
f s
250
200
Extraction
150
Non‐extraction
100
50
0
0
1
2
3
4
5
6
7
8
9
10
millimeters of discrepancy
Figure A.3:
Distribution of responses for Bolton discrepancy Frankfort Mandibular Plane Angle
400
n
u
m
b
e
r
r
e
s
p
o
n
s
o e
f s
350
300
250
200
Extraction
150
Non‐Extraction
100
50
0
10
15
20
25
30
35
40
45
50
Degrees
Figure A.4:
Distribution of responses for FMA
66 Incisor Mandibular Plane Angle
350
300
n
u
m
b
e
r
r
e
s
p
o
n
s
o e
f s
250
200
Extraction
150
Non‐extraction
100
50
0
70
75
80
85
90
95 100 105 110 115 120
Degrees
Figure A.5:
Distribution of responses for IMPA Lower Incisor to A‐Pog
300
n
u
m
b
e
r
r
e
s
p
o
n
s
o e
f s
250
200
150
Extraction
Non‐Extraction
100
50
0
‐6 ‐5 ‐4 ‐3 ‐2 ‐1 0
1
2
3
4
5
6
7
8
millimeters Figure A.6:
Distribution of responses for L1-APog
67 Lower lip to B line (Subnasale to Pog')
400
n
u
m
b
e
r
r
e
s
p
o
n
s
o e
f s
350
300
250
200
Extraction
150
Non‐extraction
100
50
0
‐6
‐4
‐2
0
2
4
6
8
10
12
14
millimeters
Figure A.7:
Distribution of responses for B-line
Nasolabial Angle
800
700
n
u
m
b
e
r
o
f
r
e
s
p
o
n
s
e
s
600
500
400
Extraction
Non‐extraction
300
200
100
0
140
130
120
110
100
90
80
degrees
Figure A.8:
Distribution of responses for nasolabial angle
68 70
Midline Deviation
500
450
n
u
m
b
e
r
r
e
s
p
o
n
s
o e
f s
400
350
300
250
Extraction
200
Non‐extraction
150
100
50
0
0
1
2
3
4
5
6
7
8
9
10
millimeters
Figure A.9:
Distribution of responses for midline deviation
69 VITA AUCTORIS
Samuel I. Gentry was born on the 17th of March 1980 in
Clarksville, TN.
He is the middle of three children.
Dr. Gentry graduated from Northeast High School in
1998.
He obtained his Bachelor’s degree in Biochemistry
and Molecular Biology with a minor in Economics from
Mississippi State University in 2002.
He obtained his
Doctor of Dental Surgery degree upon graduation from the
University of Tennessee, College of Dentistry in 2006.
He
was accepted into the orthodontic residency program at
Saint Louis University that same year where he is currently
a candidate for the degree of Master of Science in
Dentistry.
Dr. Gentry married his wife, Stephanie, during his
residency in March 2008. They plan to move to Clarksville,
TN where he will pursue private practice upon graduation in
January 2009.
70