Download TRANSVERSE ARCH DIMENSIONAL CHANGES IN ClASS I BICUSPID EXTRACTION PROTOCOLS

TRANSVERSE ARCH DIMENSIONAL CHANGES IN ClASS I
NONEXTRACTION, EARLY AND LATE FIRST
BICUSPID EXTRACTION PROTOCOLS
Michael Larson, 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
2010
Abstract
The primary reason for treatment sought by patients is
crowding.
Among the possible ways to alleviate crowding,
extraction is one of the treatments of choice.
With the
use of extractions and fixed orthodontic appliances the
crowding is resolved and the remaining spaces are closed
and as a result alignment of the dentition is complete.
The purpose of this study was to evaluate maxillary
and mandibular arch development in the transverse dimension
utilizing extractions at varying times (early vs. late
protocols).
In this study we defined “early” as a period
of time before the permanent maxillary cuspids have erupted
and “late” as the period of time following eruption of the
permanent maxillary cuspids.
The sample consisted of 90 dental casts from a
population of orthodontically treated Class I malocclusion
mixed dentition subjects.
All dental models were collected
from a single private practice and all records were final
models taken at time of fixed appliance removal.
Specific
points on the dentition were measured to gather information
including: intercanine width, intermolar width, and arch
depth.
1
Analysis of the data showed no significant difference
between the early extraction and late extraction groups.
All values in the early group were slightly less in
dimension than the late extraction group.
Statistical
analysis showed significance when the maxillary and
mandibular intermolar dimensions and maxillary intercanine
dimensions of the nonextraction group were compared to the
extraction groups.
The nonextraction intermolar dimensions
were larger than both extraction groups. The late
extraction group had a larger intercanine transverse
measure.
The consideration of tooth removal has been thought to
negatively affect the breadth of the arch and accordingly
smile esthetics.
Extractions before total canine eruption
have no narrowing effects in comparison to extractions in
the permanent dentition.
2
TRANSVERSE ARCH DIMENSIONAL CHANGES IN CLASS I
NONEXTRACTION, EARLY EXTRACTION AND LATE
FIRST BICUSPID EXTRACTION PROTOCOLS
Michael Larson, 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
2010
COMMITTEE IN CHARGE OF CANDIDACY:
Professor Eustaquio Araujo,
Chairperson and Advisor
Professor Rolf G. Behrents
Assistant Professor Ki Beom Kim
i
Dedication
To my girlfriend Jessica who has given more than her
fair share of compassion and support these past several
years.
The example she has set has enabled me to endure
academics and our long distance relationship.
I love her
much and appreciate her tireless love and support.
ii
Acknowledgements
I would like to extend special thanks Dr. Araujo for
his guidance and expertise through this project.
Araujo’s knowledge has been invaluable.
Dr.
As well, Dr.
Kittleson has entrusted his time and office resources for
this study. Without his generosity I would have not been
able to collect my data at a convenient time.
I am also grateful for Dr. Behrents availability and
insight on this project.
I have much appreciation for his
generosity of time.
Dr. Kim’s time investment has been much help. I thank
him for his dedication and inspiration through this busy
time.
iii
Table of Contents
List of Tables.........................................v
List of Figures.......................................vi
CHAPTER 1: Introduction................................1
CHAPTER 2: Literature Review
History.....................................4
Extractions................................10
Dental arch development....................16
General transverse arch changes............17
Intercanine width..........................19
Intermolar width...........................21
Sexual dimorphism..........................22
Arch length................................24
Effects of treatment on arch form..........26
Reference List.............................28
CHAPTER 3: Journal Article
Abstract...................................32
Introduction...............................34
Materials and Methods......................37
Statistical Analysis.......................39
Results....................................41
Discussion.................................45
Conclusions................................53
References.................................54
Vita Auctoris.........................................57
iv
List of Tables
Table 2.1
Indications and contraindications for serial
extraction procedure.........................13
Table 3.1
Wilcoxon signed-rank test....................39
Table 3.2
Descriptive statistics for nonextraction group
.............................................42
Table 3.3
Descriptive statistics for early extraction
group........................................42
Table 3.4
Descriptive statistics for late extraction
group........................................42
Table 3.5
Independent samples t-test for nonextraction
versus early extraction and late extraction
groups.......................................43
Table 3.6
Independent samples t-test for early versus
late extractions.............................44
v
List of Figures
Figure 2.1
Four first bicuspid extraction trend:
40 Year study................................8
Figure 2.2
Stages of root development..................16
Figure 2.3
Human development: Cephalocaudal growth from
2 months to 25 years of age.................17
Figure 2.4
Average transverse arch changes from birth
to 25 years.................................19
Figure 2.5
Intercanine distance........................21
Figure 2.6
Intercanine width changes between sexes;
mixed dentition, early permanent and late
permanent dentitions........................23
Figure 2.7
Intermolar width changes in males and
females.....................................23
Figure 2.8
Male and female arch length changes.........26
Figure 3.1
Transverse arch dimensions..................40
Figure 3.2
Arch depth dimensions.......................40
Figure 3.3
Maxillary mean transverse measurements for
nonextraction, early extraction and late
extraction groups...........................48
Figure 3.4
Mandibular mean transverse for
nonextraction, early extraction and late
extraction groups...........................48
Figure 3.5
Mean arch transverse dimensions for serial
extraction study compared to early
extraction study...........................51
vi
Figure 3.6
Mean arch values for nonextraction data from
Bishara study compared to early and late
extraction transverse data.................52
vii
Chapter 1: Introduction
The patient’s best interest are at heart when
orthodontic therapy is sought.
Technology has assisted
practitioners in reaching this goal.
Modern cements have
been employed allowing for a significant decrease in the
use of orthodontic bands, prescription bracketry, and
specialized x-ray equipment allow orthodontists to
thoroughly consider all options for the patient.
When a
patient presents with a differential between arch size and
excess tooth mass, extraction is a treatment of choice.
There are three primary reasons for extraction therapy;
1)dental crowding,2)incisor protrusion and 3)camouflaging
of skeletal imbalances.
Dental crowding ranks highest
amongst indications for extraction.1
When it is determined that dental crowding is evident
at an early age, for example in the mixed dentition, when
should orthodontic intervention occur?
For a clinician to
orchestrate procedures at varying ages it is important that
an understanding of growth and the differing effect
treatments could have on arch development.
Arch development is facilitated by the eruption of
succedaneum teeth and accompanying bone.
1
The teeth as well
as the supporting bone add width and height to a patient’s
smile.2
The literature regarding arch development primarily
consider anteroposterior arch changes.
Moorrees
investigated the changes in arch length from the primary
dentition to the permanent dentition, with special
consideration of leeway space.3
This facilitated the
rationale for a resurgence of early treatment mid-century.
It came in the form of a procedure referred to as serial
extraction.
Serial extraction allowed for decreased
crowding, decreased treatment duration, to name a few
advantages.
This procedure was not without
shortcomings,including lingual tipping of incisors,
increased overbite, and mesial migration of the buccal
segments.4-7
This era was followed by retention studies
concluding that no greater stability of the arches was
achieved with serial extraction.8
Of the studies that exist which evaluate the effects
of early extractions of first bicuspids on the developing
dentition few address changes in the transverse
dimension.9,10
This study will explore the effects of four bicuspid
extraction in the transverse dimension of the upper and
lower dental arches performed at different time points.
2
In
this study “early” is defined as a period of time before
the permanent maxillary cuspids have erupted and “late” as
the period of time following eruption of the permanent
maxillary cuspids.
treatment casts.
The data will be collected from post-
The sample will consist of three groups;
the first group will consist of a non-extraction protocol,
the second group will involve an early extraction protocol
and the third group will involve extractions at a later
time.
The purpose in this study will be to determine whether
four bicuspid extraction performed at different times(early
versus late) would have an impact on arch dimensions in the
transverse dimension.
3
Chapter 2: Literature Review
This literature review will proceed through the factors
correlated to extractions in orthodontics and the effect
they have on the dentition.
For a complete understanding
of the development of the human dentition this review will
initiate thoughts and concerns of dental arch development
and a discussion of arch length and its maturation and
changes through an individual’s life.
Though past
literature has given much consideration to arch depth and
how this factor contributes to Angle’s Class I occlusion a
discourse on arch width will be the focus of this review.
History
In the early nineteenth century extractions were
commonplace.
The primary rational was removal of teeth
that were severely malaligned.
The method and reasoning of
this liberal time fell out of favor in the late nineteenth
century as E.H. Angle’s philosophy came into prominence.
Angle’s ideals surrounded the concept of focusing on the
relationships of the teeth and jaws and balance.
With
these set in place harmony and proportions would follow.
Angle’s philosophy necessitated a full complement of teeth
in their normal positions thus balance, harmony and proper
proportions would be achieved.11
4
Additionally, this
philosophy of expansion was consistent with Wolff’s law
that bone would form in response to stress placed on it,
hence bone would follow where teeth were placed.
Angle’s prominence was wide-spread.
Angle was the
first to start an orthodontic school and thus able to
influence many educators.
His influence lasted for many
years and even now some of his philosophy continues to be
practiced.
In the late 1800s one opponent to Angle’s nonextraction dogma was Calvin S. Case.
Case placed emphasis
on facial esthetics and their relationship to orthodontics
and extractions.
In “The extraction debate of 1911” Case
confronted the nonextractionists with a strong statement,
“While I should dislike to destroy or even weaken the
theological belief of anyone who finds comfort in his
religion, I feel that a question of such importance demands
the whole truth from the advanced standpoint of evolution.”
It opened an important discussion on extractions in
orthodontics.
Case presented 15 bimaxillary protrusion
cases to clarify that in rare instances a need for
extractions should be considered.12
He had a persuasive
argument suggesting that the public would demand better
profiles and that would cause orthodontics to reflect upon
changes.
The level of extractions suggested by him was a
5
small percentage in the practice of orthodontics, 6%.13
Unfortunately, Case’s ideas were generally ignored by
mainstream orthodontia.
Events unfolded and the non-extraction dogma began to
weaken.
Roughly 30 years passed with stability issues
arising from the expansion camp.
arose was relapse.
The primary issue that
Lundstrom introduced the term apical
base and its association with orthodontic limits.14
The
author believed that if teeth are placed over a deficient
apical base relapse will occur at the end of the retention
period.
Following Lundstrom’s thesis Tweed and Begg
philosophies became prominent.
Tweed was disappointed with
profile changes and relapse and followed up on 100 cases
with four 1st bicuspid extractions.
Tweed developed his
analysis with a main focus on the position of the
mandibular incisors.
Many followed Tweed’s principles and
are still convinced they are able to provide a better
diagnosis and treatment.
Seminars were and still are
conducted on his philosophy.
On a similar note Begg
independently abandoned the non-extraction policy.
Located
in Australia, Begg devised his own treatment mechanics with
the multiloop light-wire technique.
Begg made the
assumption that the tooth size variation was the cause for
malocclusion and without natural interproximal wear
6
crowding would result.15
The author suggested that tooth
size irregularity was as much at fault to malocclusion as
jaw size.
By mid-twentieth century the extraction debate was
once again reopened.
A publication by Riedel in the late
1950s highlighted facial esthetics as the prime objective
of orthodontic therapy.
This study investigated profiles
of beauty contestants in Seattle, Washington.
It is stated
that soft tissue is closely related to the skeletal and
dental tissues beneath.
The top contestants recorded
measurements within one degree or one millimeter of Down’s
means.
In many ways the publics’ concept of facial
esthetics are in close agreement with orthodontists’
standards of normal occlusion, however, a more protrusive
profile was sought by those who judged the participants.16
For an understanding of the changes in extraction
frequency over the past century the data from the
University of North Carolina serves as a benchmark for
reference.
In this clinical review Proffit outlines a
forty year time period.
The extraction trends observed are
most pertinent to the removal of four first bicuspids.
Other extraction choices, for example one lower incisor or
three first bicuspids and one second bicuspid over the
duration of the study were consistently approximated at 15%
7
of the total extraction frequency and were not
statistically significant.
During the early 1950s
extractions were utilized in approximately 30% of the total
patient population.
The peak of extractions took place in
the 1960s with 76% of patients receiving extraction
therapy.
By the early 1990s extraction protocols were on
the decline, constituting approximately 28% of the
orthodontic therapies.17
This trend can be observed in the
first bicuspid extraction frequency in Figure 2.1.
Four first Bicuspid extractions
Percent Patients
60
50
40
30
20
10
0
1953
1958
1963
1968
1973
1978
1983
1988
1993
Year
Figure 2.1 Four decades of extraction trends at UNC.
Adapted from Proffit.17
The trend of extraction protocols has shown a rise and
fall over the past century.
Early in the twentieth century
the push by Calvin Case for extractions surrounded the
8
topic of esthetics and the need to provide a therapy for
the protrusive profiles that expansion treatments were
falling short of.13
By the 1930s stability was in question,
arches collapsed and relapse was a concern.
Both Begg and
Tweed who were taught under the expansion philosophy chose
to abandon the non-extraction treatment and devise their
own mechanics and/or modify what was in use.
They led the
discussion on this philosophy, each having his own idea for
the nature of collapsed arches.17
Unfortunately, their
methods were unsubstantiated and relapse still occurred.
Little and co-workers contributed with relapse studies.
Little’s 10 year longitudinal study highlighted the fact
that a significant percentage of patients(73%) experienced
unsatisfactory anterior alignment postretention.8
Additionally, esthetics became a factor and the public felt
that profiles were being flattened and the greater dental
community was criticizing orthodontist’s extraction
guidelines.18
Despite literature supporting a lack of
connection between extractions and temporomandibular
dysfunction the threat of lawsuits also helped decrease
extractions.19
Along with these concerns technology also had a part,
contributing to changes in extraction decision making.
Managing borderline extraction cases became easier with
9
decreased interproximal band material and the introduction
of bonded brackets with modern cements.20
Andrew’s straight
wire appliance also eased the technical difficulties
encountered with standard edgewise appliances.21
Orthopedics became a factor with the re-introduction of
extraoral anchorage by Silas Kloehn, palatal expansion and
the popularity of functional appliances.22
Earlier
treatment was then proposed with literature supporting the
use of leeway space to help resolve crowding.
Gianelly
reported that 72% of cases with an average of 4.4 mm of
crowding can be resolved by preserving the leeway space.
Furthermore, patients that lost a primary canine early can
expect even more crowding and a 40% chance of resolving
this level of crowding with leeway space preservation.23
Management of borderline cases helped as well with more
approaches to expansion of the arches.24
Furthering the
incentives for nonextraction protocols are literature
stating a 3-6 month less treatment time than extraction
treatments.25
With all these factors practitioners nowadays
highly consider nonextraction treatment.
Extractions
One of the most common reasons patients seek orthodontic
therapy is to correct dental crowding.
In general,
practitioners have three primary methods to choose from
10
when correcting crowding: extraction, expansion, and molar
distalization.
This discussion will touch lightly on
expansion and distalization, yet focus on extractions and
how this form of therapy can be best used to meet the
patient’s chief complaint of a crowded dentition.
Goals for extraction therapy cover three primary
areas; 1)dental crowding, 2)incisor protrusion, and
3)camouflaging of skeletal imbalances.
Baumrind and co-workers elaborated on why clinicians
would choose to extract.
Four main areas were noted,
dental crowding, incisor protrusion, improved profiles, and
camouflaging of skeletal imbalances.
Upon review of the
findings, crowding was found in 72% of the individual
clinician decisions to extract, followed by incisor
protrusion with 35%, and profile improvement at 27%.
In
71% of the entire sample at least one of these three
criteria were consistently considered first when the
decision to extract was made.1,26
In agreement with these
extraction criteria Paquette and co-workers found that in
the decision to extract three of the four mentioned by
Baumrind are also chosen; crowding, protrusion and
profile.27
Strang believed that with the extraction of dental
units and the distalization of the canines came slight
11
buccal expansion.28
Strang suggested this movement was in
better agreement with the muscular balance.
The above criteria addresses patients in the permanent
dentition, however, if the patient arrives at a period of
time that correction of the malocclusion could occur at a
younger age should consideration be given to initiate
orthodontic therapy?
For example, if an exam is completed
at a young age with special notes made to space analysis
yielding an arch length discrepancy, should the extractions
begin at this time?
Serial extraction was widely used in orthodontics,
especially in the 1950s and 1960s.
It is a well known
procedure that severe dental crowding in the mixed
dentition can be addressed through a sequential removal of
deciduous and permanent teeth.
The approximate age range
for serial extraction is 7-10 years.
It is often indicated
for Class I skeletal and dental relationships and for
severe crowding ranging from 7-10mm.
This procedure
necessitates a sequential and timely removal of specific
primary and permanent teeth in order to guide the eruption
of the permanent teeth and thus minimize the severity of
12
Table 2.1 Indications and contraindications for serial
extraction procedure.
Indications
Contraindications
Arch length discrepancy
Class II Diagnosis
Impacted lateral incisors
Class III Diagnosis
Unilateral deciduous canine
loss
Crowding in one arch only
Inability to follow case
to completion
Abnormal resorption
Gingival recession at
mandibular incisors
the malocclusion.29
Congenitally missing teeth
Table 2.1 outlines indications and
contraindication for serial extraction procedures.
Though other extraction sequences can be chosen the
most common extraction sequence for serial extraction is
the removal of primary followed by permanent dental units,
deciduous Cs and Ds and first bicuspids.30
The use of periapical radiographs in guiding the
timing of extractions is recommended.31
It was believed
that extraction of primary dental units prior to their
exfoliation could influence the erupting succedaneous
dentition.
Dewell believed that early extractions of
primary teeth delayed the development and growth of an
already compromised dental arch.
13
Furthermore, he suggested
that early enucleation of dental follicles would impede the
growth of the alveolar process.32
Fanning’s studies advanced knowledge of the effects of
timing of primary extractions in relation to accompanying
succedaneous tooth eruption.
Fanning conducted a
longitudinal study on tooth eruption and was a split mouth
design where half the arch underwent unilateral early
extraction of primary molars.
The control side underwent
normal development and eruption of permanent teeth.
The
findings suggested a spurt in the eruption of the first
premolars regardless of its stage of development or the age
at which the primary molar was removed.
And the extraction
of primary units had no effect on root development of the
permanent premolar.
Additionally, the eruption of first
premolars was observed early only when the primary tooth
was extracted with a more mature permanent tooth root.
Otherwise, if permanent root development is not mature
enough a delay will be experienced in its eruption
velocity.
Fanning suggested that the delay is related to
scar tissue development.33
Moorrees et al. combined a previous study of tooth
maturity to clarify the timing of early extractions in the
mixed dentition.
The use of periapical radiographs allowed
the grouping of 3 key intervals, ¼ to ½, ½ to ¾ and ¾ to
14
fully a developed root(figure 2.2).
This publication
established the importance of timing and in general ¾ of
root development was achieved before eruption of
succedaneous teeth.
The emphasis was to gauge extractions
on root development and not chronological age.
The
requirement was made that periapical radiographs should be
taken every three to six months to follow the root’s
development.
Moorrees et al. advised that extraction of
primary dental units may occur with a minimum of ½ root
development for a delay in the eruption of the succedaneous
tooth not to occur.
The only exception to this protocol is
if the developing tooth is in close proximity to the
alveolar crest, thus just ¼ root development would be
required in this scenario.34
15
Figure 2.2 Stages of root development. Correlation of root
development to dental maturity.34
Dental arch development
Much is known about the growth and development of the
head and face.
In general, growth and development
progresses in a cephalocaudal direction.
Figure 2.3 body proportions are depicted.
For example, in
The head
consumes approximately fifty percent of a two month old
fetus as compared to 30% by birth.17
During growth the
skull changes in shape and size are determined by sutural,
cartilaginous, periosteal and endosteal bone deposition and
resorption.35
Overlayed on these basic trends is the
dimensions of the face that terminate their growth at set
times during development.
The first dimension to finalize
16
is the face’s width at approximately 12 years of age or
just before puberty, then the anteriorposterior dimension
at approximately 14 years followed by height, and this
dimension will continue to grow thoughout an individual’s
life.
Figure 2.3 Human development. Cephalocaudal growth from 2
months to 25 years of Age.17
General transverse arch changes
A review in the area of arch width normally surrounds
three variables, intercanine, intermolar and general
transverse arch changes.
latter.
The review will begin with the
The growth of the dental arches generally precedes
the eruption of the groups of teeth and further there is
similarity in the maxillary and mandibular arch width
changes.36
Burson chose to use as the reference of
beginning of the growth spurt the eruption of the lower
17
incisors because he noted that a relationship existed
between the spurt and the eruption of the permanent
incisors.33,37,38
The majority of cases in Burson’s sample
began their growth spurt one to two years before the lower
central incisors erupted, or approximately five to six
years of age in the deciduous dentition.
Sillman
highlights this character by the use of five time points,
4, 8, 12, 16, and 20 years of age(figure 2.4).36
Generally
from birth to 4 years much of the transverse jaw growth is
achieved.
From four years of age on the growth increments
are less pronounced.
The difference between the mandible
and the maxilla is seen between the time intervals of 8 and
12 years with the maxilla having a larger rate of change
than the mandible.
And the decrease in transverse
dimension observed from ages 16 to 20 years may not be
clinically perceptible.
Completion of growth in width
according to Burson is six years past the eruption of the
central incisors(11 years of age).
Similarly, Morrees’s
average intercanine graphs indicate a plateau at
approximately the same time, six years post eruption of the
central incisors or 11 years of age.
Conversely, authors
Barrow and White and Sillman argue that intercanine width
18
Figure 2.4 Average transverse arch changes from birth
to 25 years.36
decreases during the maturation of the permanent
dentition.39
Intercanine width
A University of Iowa longitudinal study by Knott
reports on growth findings over a twenty year span.
The
width between the permanent canine teeth averaged
approximately 2.0mm greater than between the deciduous
canine teeth.
Mean increases for males and females are
19
between 5.5 and 6.0mm for deciduous maxillary incisor width
to permanent incisor width, roughly 3.5 mm for mandibular
incisor width and 2.8 mm for both maxillary and mandibular
deciduous canine width.40
When addressing intercanine dimension Barrow states:
The essential findings under this heading were: (1)
there was little intercanine arch width change from 3
to 5 years of age; (2) the intercanine width increased
very rapidly from 5 to 8 or 9 years of age. (The
amount of change was approximately 4mm in the
maxillary arch and 3mm. in the mandibular arch.) (3)
in most cases the maxillary and mandibular intercanine
arch widths steadily decreased in amount varying
between 0.5mm. and 1.5mm. after 14 years of age.39
Moorees et al. agree with this general trend.
With the
emergence of the permanent maxillary and mandibular
incisors comes an increase in arch width(figure 2.5).34
In
an average boy or girl the arch has enough space to
accommodate the difference in size of the permanent
incisors, approximately 7.4mm. wider than the primaries.41
Moorrees agrees with a decrease in intercanine distance
from 10 to 12 years, however it does not indicate a steady
decrease, conversely he suggests that intercanine width
will remain stable into adulthood.
Sinclair, as well
agrees on the finding that intercanine width will remain
stable once permanent canines have erupted.34
Moorrees
illustrates that intercanine width in the mandibles and
20
maxillas of males and females does not change significantly
past age 10 and 12, respectively.
Figure 2.5 Transverse canine dimension from deciduous to
permanent dentition.34
Intermolar width
Barrow studied 528 sets of serial casts from 51
children and drew conclusions on arch width.39
In the
primary dentition, between the ages of 5 and 10 years width
measured at the second primary molars in maxillary and
21
mandibular arches increased approximately 1.5mm.
This
increase in width is likely due to remodeling of alveolus
and transverse jaw growth.
For the transverse dimension of the permanent first molars
Barrow indicates:
from 7 to 11 years of age the average increase in
intermolar width was 1.8mm in the maxillary arch and
1.2mm in the mandibular arch. From 11 to 15 years of
age there was an average decrease in intermolar width
of 0.4mm in the maxillary arch and 0.9mm in the
mandibular arch. This decrease in intermolar width
following the 11 year reading was due, in our opinion,
to mesial drift of the first permanent molars after
the loss of the primary molars.2
Moorrees disagree with a decrease in intermolar widths
between ages nine and 14.
Their paper describes a
significant increase in intermolar width during this time.
In ages beyond 14 years the dimension stays the same.3
Sinclair agrees with intermolar widths remaining stable.41
Sexual dimorphism
When considering sexual dimorphism and
intercanine widths, Sinclair reports that both sexes
displayed significant decreases of mandibular intercanine
width from mixed to early adulthood(figures 2.6,2.7).
22
Intercanine width (mm)
26
25.5
Male
25
Female
24.5
24
T1
T2
T3
Time
Figure 2.6 Intercanine width changes between sexes.
Intercanine changes at mixed, early permanent,
late permanent dentitions, T1, T2, and T3 respectively.
Adapted from Sinclair.41
Intermolar width (mm)
45
44
Female
43
Male
42
T1
T2
T3
Time
Figure 2.7 Intermolar width changes in males and females.
Intermolar changes at mixed, early permanent,
late permanent dentitions, T1, T2, and T3,respectively.
Adapted from Sinclair.41
23
Males had a gradual decrease and females had a major
decrease between early permanent and early adult
dentitions.
For the entire sample both populations showed
significant changes in intermolar width between timepoints
T1 and T3.
Between T2 and T3 females had a significant
decrease in intermolar width.
And an increase was observed
in the male population.41
Arch length
The literature has many references to crowding and the
importance of arch length.
This dimension is the focus of
many discussions when comparing deciduous to permanent
dentitions.
For example, utilization of leeway space for
late mixed dentition treatments is the rationale for
employing early treatment.
In the analysis of 49
individuals the total arch depth decreased from deciduous
to permanent dentitions according to Speck.42
Similarly,
Moorrees et al. recorded a decrease in arch length during
the transition to permanent dentition.
Referring to figure
2.8 the arch length is greatest at age three, at three
years of age the primary dentition is complete.
The next
significant change that occurs is upon the exfoliation of
the primary second molars at approximately 10 years of age.
24
With the loss of primary dental units the space that is
lost is mesial to the first molars.
The arch length will
roughly stabilize by age 14 in most individuals with the
eruption of the permanent second molars.
From the Moorrees
data arch length remains stable up to 18 years of age.
Sillman agrees with this trend of loss of arch length and
stability in arch length up to the eruption of the third
molars.
The maxilla arch length decreases 1.5mm per side
and 2.0 mm per side in the mandible.36
Additionally, these
values have been reported with values of 1.2mm loss per
side in the maxilla and 2.2mm loss in the mandible.3
With
progressing age arch length will continue to decrease by a
small amount.2,43
DeKock found a one percent difference between the
sexes(males with greater loss) regarding arch length loss
thus, concluded no sexual dimorphism existed as it related
to arch length.44
25
Figure 2.8 Male and female arch length changes.34
Effects of treatment on arch form
With the literature to date practitioners are hard
pressed to find definitive answers regarding treatment for
borderline extraction cases.
Even with the addition of
headgear, TADs, technologically advanced cements and
prescription brackets on many occasions it comes down to,
do we extract or expand?
Extraction therapy allows space
for teeth in the arch as well could cause widening of the
arches that are controversial in their own right.28,45-47
Some have stated that stable expanded arch dimensions can
26
be maintained while others require a lifetime of retention
to maintain any and all orthodontic therapies.8,48-50
Paquette and coworkers state that between their
longitudinal study of borderline extraction and nonextraction the two groups displayed virtually the same
pattern of relapse during post-treatment.
Here this
stability problem was correlated to variable growth amongst
individuals than on treatment protocol.27
difficult concept to predict.
Growth is a
How can orthodontists debate
that expansion or extraction is a better philosophy when
many changes that occur are regulated by the individual’s
genetics already.
Diversity is the rule when it comes to
growth and development amongst subjects.
Further
complicating an analysis of changes is where to place
landmarks.
Which are most reliable since we are
essentially placing a lot of emphasis on what is
accessible; intermolar, intercanine and contact points, for
instance.
These locations are inherently labile and can
change easily with torque or tip placed in brackets.
So
yes we need to assess the fruits of our labor by measuring
these locations and realize that they can be seen as a
clinically significant outcome by simply placing brackets
and wire on the arches.
27
Reference List
1. Baumrind S, Korn EL, Boyd RL Maxwell R. The decision to
extract Part 1-Interclinician agreement. Am J Ortho
Dentofac Orthop 1996;109:297-309
2. Barrow,G. Developmental Changes of the maxillary and
mandibular dental arches. Am J Orthod 1952;22:41-46.
3. Moorrees CF, Gron AM, Lebret LM, Yen PK, Frohlich FJ.
Growth studies of the dentition: A Review. Am J Orthod
1969;55:600-616.
4. Ringenberg, Q.M. Influence of Serial extraction on
growth and development of the maxilla and mandible. Am J
Orthod 1967:53:19-26.
5. Dewell,B. Serial extraction: Its limitation and
contraindications in orthodontic treatment. Am J Orthod
1967;53:904.
6. Graber T.M. Serial extraction: A continuous diagnostic
and decisional process. Am J Orthod 1971;60: 541-575.
7. Wagner, M. Serial extraction or premolar extraction in
the permanent dentition? Comparison of duration and outcome
of orthodontic treatment. J Orof Orthop 2000;61:207-216.
8. Little RM,
Serial extraction of first premolarsPostretention evaluation of stability and relapse. Angle
Orthod 1994;60:213-226.
9. Wilson, JR, Little RM, Joondeph DR, Doppel DM.
Comparison of soft tissue profile changes in serial
extraction and late premolar extraction. Angle Orthod
1999;69:165-174.
.
10. Johnson DK, Smith RJ. Smile esthetics after orthodontic
treatment with and without extraction of four first
premolars. Am J Orthod Dentofac Orthop 1995;108:162-7.
11. Bernstein L. Edward H Angle versus Calvin S. Case:
Extraction versus nonextraction. Historical revisionism
Part II. Am J Orthod Dentofac Orthop 1992;102:546-551.
12. Case C. The extraction debate of 1911 by Case, Dewey
and Cryer. Am J Orthod 1964;50:900-912.
28
13. Wahl, N. Orthodontics in 3 millennia. Chapter 6: More
early 20th-century appliances and the extraction
controversy. Am J Orthod Dentofac Orthop 2005;128:795-800.
14. Lundstrom A. Malocclusions of the teeth regarded as a
problem in connection with the apical base. Int J Orthod
Oral Surg 1925;11:591-612.
15. Begg PR. Stone age man’s dentition. Am J Orthod 1954;
40:373-383.
16. Riedel RA. An analysis of dentofacial relationships. Am
J Orthod 1957;43:103-119.
17. Proffit WR. Forty-year review of extraction frequencies
at a university orthodontic clinic. Angle Orthod
1994;64:407-414.
18. Erdinc AE, Nanda RS, Dandajena TC. Profile changes of
patients treated with and without premolar extractions. Am
J Orthod Dentofac Orthop 2007;132:324-331.
19. Luther F. Orthodontics and the temporomandibular joint:
Where are we now? Part 1.Orthodontic treatment and
temporomandibular disorders. Angle Orthod 1998;68:295-304.
20. Evans LS, McGrory KR, English JD, Ontiveros JD, Powers
JM, Frey GN, Duke J. A comparison of shear bond strengths
among different self-etching primers. Tex D J 2009;126:3129.
21. Andrews LF. The straight wire appliance. J Clin Orthod
1976;114:174-195.
22. Darendeliler N, Taner-Sarisoy L. The influence of
orthodontic extraction treatment on dental structures: a
two-factor evaluation. Eur J Orthod 2001;23:295-303.
23. Gianelly AA. Treatment of crowding in the mixed
dentition. Am J Orthod Dentofac Orthop 2002;121:569-571.
24. Brust EW. Arch dimensional changes concurrent with
expansion in the mixed dentition[thesis]. Ann Arbor:
University of Michigan, 1992.
25. Skidmore KJ, Brook KJ, Thomson WM, Winifred JH. Factors
influencing treatment time in orthodontic patients. Am J
Orthod Dentofac Orthop 2006;229:230-8.
29
26. Baumrind S, Korn EL, Boyd RL Maxwell R. The decision to
extract: Part II. Analysis of clinicians’ stated reasons
for extraction. Am J Ortho Dentofac Orthop. 1996;109:393402.
27. Paquette DE, Beattie JR, Johnston LE. A long-term
comparison of nonextraction and premolar extraction
edgewise therapy in “borderline” Class II patients. Am J
Ortho Dentofac Orthop 1992;104:1-14.
28. Strang RHW. The fallacy of denture expansion as a
treatment procedure. Angle Orthod 1949;19:12-17.
29. Araujo EA. The effect of serial extraction on Class I
malocclusions: A one year report on the behavior of the
incisors and canines. Masters thesis, University of
Pittsburgh 1981.
30. Dewell BF. A critical analysis of serial extraction in
orthodontic treatment. Am J Orthod 1959;45:424-455.
31. Hotz RP. Guidance of eruption versus serial extraction.
Am J Orthod 1970;58:1-20
32. Dewell BF. Serial extraction in orthodontics:
Indications, objectives and treatment procedures. Am J
Orthod 1954;40:906-926
33. Fanning EA. Effect of extraction of deciduous molars on
the formation and eruption of their successors. Am J Orthod
1962;32:44-53.
34. Moorrees CF, Fanning EA, Gron AM. Consideration of
dental development in serial extraction. Angle Orthod
1963;33:44-59.
35. Enlow DH, Bang S. Growth and remodeling of the human
maxilla. Am J Orthod 1965;51:446-464.
36. Sillman JH. Dimensional changes of the dental arches:
Longitudinal study from birth to 25 years. Am J Orthod
1964;50:824-842.
37. Meredith HV, Hopp WM. A longitudinal study of dental
arch width at the deciduous second molars on children 4 to
8 years of age. J D Res 1956;35:879-889.
30
38. Goldstein MS, Stanton FL. Changes in dimension and form
of the dental arches with age. Int J Orthod Oral Surg
1935;21:357-380.
39. Barrow GV, White JR. Developmental changes of the
maxillary and mandibular dental arches. Angle Orthod
1952;22:41-46.
40. Knott V. Longitudinal study of dental arch widths at
four stages of dentition. Angle Orthod 1972;42:387-394.
41. Sinclair P. Maturation of untreated normal occlusions.
Am J Ortho Dentofac Orthop 1983;83:114-123.
42. Speck NT. A longitudinal study of developmental changes
in human lower dental arches. Angle Orthod 1950:20:215-228.
43. Brown VP, Dagaard-Jensen I. Changes in the dentition
from the early teens to the early twenties. Acta Odontol
Scand 1951;9:177-192.
44. DeKock WH. Dental arch depth and width studied
longitudinally from 12 years of age to adulthood. Am J
Orthod 1972;62:56-66.
45. Steiner CC. Orientation of the teeth in the dental
arches. Angle Orthod 1934;4:35-56.
46. MacCauley D. The canine and its function in retention.
Int J Orthod 1944;30:196-205.
47. Uhde MD,Sadowsky C, Begole EA. Long-term stability of
dental relationships after orthodontic treatment. Angle
Orthod 1983;53:240-252.
48. Walter DC. Changes in the form and dimensions of dental
arches resulting from orthodontic treatment. Am J Orthod
1953;23:3-18.
49. Sadowsky C, Schneider BJ, BeGole EA, Tahir E. Long-term
stability after orthodontic treatment: Nonextraction with
prolonged retention. Am J Ortho Dentofac Orthop
1994;106:243-9.
50. Glenn G. Nonextraction orthodontic therapy:
Postreatment dental and skeletal stability. Am J Orthod
1987;92:321-8.
31
Chapter 3: Journal Article
Abstract
The primary reason for treatment sought by patients is
crowding.
Among the possible ways to alleviate crowding,
extraction is one of the treatments of choice.
With the
use of extractions and fixed orthodontic appliances the
crowding is resolved and the remaining spaces are closed
and as a result alignment of the dentition is complete.
The purpose of this study was to evaluate maxillary
and mandibular arch development in the transverse dimension
utilizing extractions at varying times (early vs. late
protocols).
In this study we defined “early” as a period
of time before the permanent maxillary cuspids have erupted
and “late” as the period of time following eruption of the
permanent maxillary cuspids.
The sample consisted of 90 dental casts from a
population of orthodontically treated Class I malocclusion
mixed dentition subjects.
All dental models were collected
from a single private practice and all records were final
models taken at time of fixed appliance removal.
Specific
points on the dentition were measured to gather information
including: intercanine width, intermolar width, and arch
depth.
32
Analysis of the data showed no significant difference
between the early extraction and late extraction groups.
All values in the early group were slightly less in
dimension than the late extraction group.
Statistical
analysis showed significance when the maxillary and
mandibular intermolar dimensions and maxillary intercanine
dimensions of the nonextraction group were compared to the
extraction groups.
The nonextraction intermolar dimensions
were larger than both extraction groups. And the late
extraction group had a larger intercanine transverse
measure.
The consideration of tooth removal has been thought to
negatively affect the breadth of the arch and accordingly
smile esthetics.
Extractions before total canine eruption
have no narrowing effects in comparison to extractions in
the permanent dentition.
33
Introduction
The patient’s best interests are at heart when
orthodontic therapy is sought.
Technology has assisted
practitioners in reaching this goal; modern cements have
been employed allowing for a significant decrease in the
use of orthodontic bands, prescription bracketry, and
specialized x-ray equipment allow orthodontists to
thoroughly consider all options for the patient.
When a
patient presents with a differential between arch size and
excess tooth mass, extraction is a treatment of choice.
There are three primary reasons for extraction therapy;
1)dental crowding,2)incisor protrusion and 3)camouflaging
of skeletal imbalances.
Dental crowding ranks highest
amongst indications for extraction.1,2
When it is determined that dental crowding is evident
at an early age, for example in the mixed dentition, when
should orthodontic intervention occur?
For a clinician to
orchestrate procedures at varying ages it is important that
an understanding of growth and the differing effect
treatments could have on arch development.
Arch development is facilitated by the eruption of
succedaneum teeth and accompanying bone.3
34
The teeth as well
as the supporting bone add width and height to a patient’s
smile.
The literature regarding arch development primarily
consider anteroposterior arch changes.
Moorrees
investigated the changes in arch length from the primary
dentition to the permanent dentition, with special
consideration of leeway space.4
This facilitated the
rationale for a resurgence of early treatment mid-century.
It came in the form of a procedure referred to as serial
extraction.
Serial extraction allowed for decreased
crowding, decreased treatment duration, to name a few
advantages.
This technique was not without
shortcomings,including lingual tipping of incisors,
increased overbite, and mesial migration of the buccal
segments.5-8
This era was followed by retention studies
concluding that no greater stability of the arches was
achieved with serial extraction.9
Of the studies that exist which evaluate the effects
of early extractions of first bicuspids on the developing
dentition few address changes in the transverse
dimension.10,11
This study will explore the effects of four bicuspid
extraction in the transverse dimension of the upper and
lower dental arches performed at different time points.
35
In
this study “early” is defined as a period of time before
the permanent maxillary cuspids have erupted and “late” as
the period of time following eruption of the permanent
maxillary cuspids.
treatment casts.
The data will be collected from post-
The sample will consist of three groups;
the first group will consist of a non-extraction protocol,
the second group will involve a early extraction protocol
and the third group will involve extractions at a later
time.
Our purpose in this study will be to determine whether
four bicuspid extraction performed at different times(early
versus late) would have any impact on arch form in the
transverse dimension.
36
Materials and Methods
The inclusion criteria for the two extraction groups
included bilateral extractions of first bicuspids indicated
in both jaws.
The sample consisted of 90 dental casts from
a population of orthodontically treated CI malocclusion
subjects.
All dental models were collected from a single
private practice.
All records were final models taken at
time of fixed appliance removal.
The total sample was
divided into three groups of 30 each, following these
criteria.
Group 1, nonextraction, Group 2, early four
bicuspid extraction performed before the eruption of the
maxillary canines, Group 3, late four bicuspid extraction,
extraction following maxillary canine eruption with
moderate to severe crowding followed by fixed appliance
therapy.
The inclusion criteria for the nonextraction
group was mild crowding, full complement of teeth and fixed
appliance therapy.
Subjects for all three groups were
excluded in cases of congenitally missing primary or
permanent teeth excluding permanent third molars, single or
multiple tooth crossbite, Class II or Class III Angle
classification, anterior openbite, and impacted or
ankylosed teeth.
37
The orthodontic casts were randomly assigned a
sequential number by the treating orthodontist and were
then evaluated for inclusion by the principal investigator.
Data collection involved photocopying dental casts on
an office copy machine.
All copies were made on the same
photocopier by the investigator.
A 100mm ruler was
utilized during copying to account for magnification error
that occurred through recording.
To further decrease the
likelihood of magnification error the casts were placed
with the occlusal plane face down and as parallel to the
surface of the copier as possible.
The sample was digitized using Dentofacial Planner
software.
A total of seven landmarks were recorded.
The
digitized landmarks are, the cusp tip of each permanent
canine, midpoint of contact point between the permanent
central incisors, contact point of permanent second
bicuspid and first molar, and the centroids of the molars.
These seven landmarks were used to determine six variables
between the maxillary and mandibular arches: intercanine
width was calculated by the straightline connecting right
and left canine cusp tips within each arch, intermolar
width was measured by a similar straightline value taken
from between the molars, and arch depth was calculated by
taking the line that connects the contact points of the
38
first molar and second premolar and intersect this line
with the contact of the central incisors(Figures 3.1 and
3.2).
Reliability was established by randomly choosing 10%
of the sample to re-digitize one month after the data was
entered in Dentofacial Planner software.
The reliability
was tested using the Wicoxon rank-signed Test.
No
significance was found for both the maxillary and
mandibular measurements(Table 3.1).
All data was reliable.
Table 3.1 Wilcoxon signed-rank test
Group
Maxillary Intercanine
Mandibular Intercanine
Maxillary Intermolar
Mandibular Intermolar
Maxillary Arch Depth
Mandibular Arch Depth
Significance
0.187
0.717
0.203
0.167
0.831
0.722
* Significant at p < 0.05.
Statistical Analysis
Descriptive statistics were computed for the six
values mentioned earlier.
To test between the three groups
an Independent samples t-test was performed.
All
differences in mean measurements were held to the 5%
confidence level.
39
Figure 3.1 Transverse arch dimensions. Distance between
centroids of molars for intermolar width and canine cusp
tips for intercanine widths.12
Figure 3.2 Arch depth dimensions. Arch depth calculated
from line connecting contact points of second premolar and
molar to contact of central incisors.12
40
Results
Each group comprised 30 patients for a total of 90
individuals with measurements taken from the maxillary and
mandibular dental models.
The entire sample had 63 female
and 27 male patients and was divided into three groups of
30 each, following these criteria.
Group 1, nonextraction,
Group 2, early four bicuspid extraction performed before
the eruption of the maxillary canines, Group 3, late four
bicuspid extraction, extraction following maxillary canine
eruption.
In Table 3.2 the nonextraction descriptive values are
represented.
This group has 23 females and 7 males. Table
3.3 represents the early extraction sample with 15 female
and 15 male patients.
Table 3.4 shows the late extraction
sample with 25 female and 5 male patients.
For comparison of nonextraction to early extraction
and late extraction independent samples t-tests were
performed.
Three linear measurements in the early and late
extraction groups, maxillary intercanine, maxillary
intermolar and mandibular intermolar distances were
significantly different (p < .05)(Table 3.5)from the
nonextraction group.
The mean maxillary intercanine
distance for late extraction was 35.09 mm, maxillary
intermolar distance for late extraction was 44.07mm,
41
Table 3.2 Nonextraction group descriptive
statistics,minimum, maximum, average and standard
deviation.
NonExtraction Group
Min.
Max.
X
S.D.
Maxillary Intercanine
Mandibular Intercanine
32.2
24.0
38.0
28.3
34.18
25.96
1.53
0.94
Maxillary Intermolar
Mandibular Intermolar
42.8
36.7
54.2
46.6
47.28
41.09
2.54
2.36
Maxillary Arch Depth
Mandibular Arch Depth
24.9
21.0
31.1
26.6
26.96
23.21
1.17
1.26
Table 3.3 Early extraction group descriptive
statistics, minimum, maximum, average and standard
deviation.
Early Extraction Group
Min.
Max.
X
S.D.
Maxillary Intercanine
Mandibular Intercanine
31.3
24.0
39.2
29.0
34.59
26.13
1.81
1.31
Maxillary Intermolar
39.7
47.6
43.66
2.18
Mandibular Intermolar
Maxillary Arch Depth
Mandibular Arch Depth
33.9
17.9
15.7
41.7
24.1
25.6
37.68
20.82
18.03
1.77
1.58
1.88
Table 3.4 Late extraction group descriptive
statistics, minimum, maximum, average and standard
deviation.
Late Extraction Group
Min.
Max.
X
Maxillary Intercanine
Mandibular Intercanine
Maxillary Intermolar
Mandibular Intermolar
Maxillary Arch Depth
Mandibular Arch Depth
31.4
24.1
39.4
33.2
19.1
15.3
38.5
29.4
46.8
41.2
24.9
20.9
35.09
26.53
44.07
37.78
20.93
17.92
42
S.D.
1.56
1.32
2.02
1.57
1.27
1.16
Table 3.5 Independent Samples t-test
Non Extraction treatment versus Early and Late Extraction
treatment results of independent t-test(2 tailed) and
associated p values.
Arch
Dimension
Maxillary
Intercanine
Mandibular
Intercanine
Maxillary
Intermolar
Mandibular
Intermolar
Non Extraction vs. Early
Extraction
p values
Non Extraction
vs. Late
Extraction
p values
0.353
0.028*
0.567
0.058
0.000*
0.000*
0.000*
0.000*
* Significant at p <.05
and the mandibular intermolar was 37.78mm.
In comparison
to nonextraction dimensions; 34.18mm, 47.28mm, 41.09mm,
respectively.
The mean early extraction values that show
significance are the maxillary intermolar and mandibular
intermolar dimensions, 43.66mm, 37.68mm in the early
extraction group.
The nonextraction respective mean
intermolar values are 47.28mm and 41.09mm. There were no
statistical differences in intermolar, intercanine and arch
length between the early and late extraction groups(Table
3.6).
Furthermore arch depth was not evaluated when
comparing nonextraction to extraction therapies because the
extraction of the first bicuspid obligates significance.
43
Table 3.6 Independent samples t-test
Arch Dimension
Maxillary Intercanine
MandibularIntercanine
Maxillary Intermolar
Mandibular Intermolar
Maxillary Arch Depth
Mandibular Arch Depth
Early Extraction vs. Late Extraction
0.261
0.242
0.458
0.824
0.761
0.774
* Significant at p <.05.
44
Discussion
Few studies have evaluated the transverse dimension of
the dental arches with and without orthodontic treatment.
The literature presents much discussion on the effects of
anteroposterior changes, i.e. leeway space, 1st and 2nd
bicuspid extraction effects and retention studies4,9,12 on
the dental arches, but little in the transverse dimension.
In addition, the literature that discusses this dimension
mostly investigated qualitative factors.
Few studies
evaluated quantitative changes in mixed and permanent
dentitions with regard to bicuspid extraction in the
transverse dimension.
Lay people perceive their attractiveness based on
their smile.
This facial view obligates the orthodontist
to place greater attention to frontal photographs and
enhancing these dentofacial characteristics for optimal
facial esthetics.
Additionally practitioners understand
that genetic makeup, environmental influences and cultural
background all play an important role in a patient’s
appearance.13
Premolar extraction treatments have been
characterized by various authors to narrow the dental
arches and a decrease the fullness of the dentition within
the mouth during smiling.14,15
45
Also, the practitioner is
influenced by advertising supporting a full dentition, ie
nonextraction, and the suggestion that this treatment will
have a lesser degree of buccal corridors.16
In light of
these anecdotal criticisms the refereed literature
evaluates extraction vs. nonextraction on the frontal
facial form and contradicts what advertising and previous
literature has stated supporting the nonextraction
argument.17-20
Johnson and Smith report that there is no predictable
relationship between the extraction of premolars and the
width of the dentition or esthetics of the smile and
suggested that the largest variable to smile esthetics was
the practitioners themselves.11
Furthermore, Gianelly
reports that extraction patients do not have narrower
arches in the anterior or posterior with 4 first-premolar
extractions.21
Does the timing of first bicuspid extractions have an
impact on the transverse dimension of dental arches?
The
purpose of this study was to evaluate arch width and the
impact extractions have on this dimension.
Figures 3.3 and 3.4 present maxillary and mandibular
arch measurements.
For comparison of early extraction to
late extraction treatments, the early extraction group is
slightly narrower in every dimension except mandibular arch
46
depth.
However, no values reached statistical significance
between early extraction and late extraction groups in the
transverse or sagittal directions.
Considering virtually identical transverse and
sagittal arch values for the early and late extraction
groups one must value the fact that growth was occurring at
the time extractions occurred in both groups.
The subjects
in the early extraction group underwent bicuspid
extractions before the maxillary canines erupted, yet
orthodontic appliances were not placed until the permanent
dentition had fully erupted.
The literature supports a
significant arch width development occurs from six to 10
years of age.3,22,23
By allowing the dentition to erupt
passively following the premolar extractions no hinderance
to development in the transverse dimension occurred.
47
50
47.28
45
40
Millimeter(mm)
35
30
*
*
43.66
44.07
EE
LE
*
34.18
34.59
35.09
NE
EE
LE
26.96
25
20.82 20.93
20
15
10
5
0
NE
EE
LE
Mx Arch Depth
NE
Mx I-Canine
Mx I-Mol
Figure 3.3 Maxillary mean transverse measurements for
three groups; NE=nonextraction, EE=early extraction and
LE=late extraction.
45
41.1
40
* 37.8
*
37.7
Millimeter(mm)
35
30
25
25.9 26.2 26.5
23.2
20
18
17.9
EE
LE
15
10
5
0
NE
NE
Mn Arch Depth
EE
LE
Mn I-Canine
NE
EE
LE
Mn 1-Mol
Figure 3.4 Mandibular mean arch values for comparison of
nonextraction, early extraction and late extraction
groups. NE=nonextraction, EE=early extraction and LE=late
extraction.
48
The nonextraction group differed significantly from
both early and late extraction groups.
The maxillary
and
mandibular intermolar widths were both larger. And the late
extraction group displayed significance with the
maxillary
intercanine distance being approximately 1mm larger than
the non-extraction group. The remaining transverse
variables, mandibular intercanine in the early and late
groups and the early maxillary intercanine values were very
similar in measure to the nonextraction values.
The
nonextraction measures for maxillary intermolar distance of
47.28mm and mandibular intermolar distance of 41.1mm were
approximately 3mm, 4mm greater than the extraction groups,
respectively.
This finding suggests that molars were
mesially positioned to a narrower and more anterior
location within the arches.
In contrast, Gianelly reports
that maxillary and mandibular intercanine and intermolar
measures are the same with the exception of the mandibular
intercanine distance.
The author reported a 0.94mm wider
mandibular intercanine measure in the extraction group.21
Contrary to Gianelly, West found statistical
significance with maxillary intercanine and mandibular
intermolar dimensions.24
Both values were found to be
narrower in the serial extraction group.
West’s study
investigated the effect serial extraction had on the
49
development in the transverse dimension.
The trends
observed between the current study and West’s study are
similar.
The serial extraction group reported a lesser
value in transverse dimension than the group that had
extractions performed in the permanent dentition.
Similarly, this study’s early extraction group had slightly
lesser values than the late extraction group(figure 3.5).
West attributed the smaller transverse dimension to the
immediate placement of orthodontic appliances.
West’s
conclusions are reasonable considering our data were
collected from a sample where the dentition was allowed to
erupt fully before orthodontic appliances were placed.
The
transverse arch values of this study display partial
similarity to nonextraction transverse dimensions.
to Figure 3.6 for comparison of transverse data.
Refer
The
nonextraction values are represented by a study performed
by Bishara, maxillary and mandibular nonextraction
intercanine measurements are within 1mm of the early and
late extraction values.25
Where the data differ is in the
posterior, maxillary nonextraction intermolar mean values
are approximately 8mm greater than extraction values.
And
the mandibular nonextraction data are approximately 7mm
greater than the extraction intermolar values.
50
The
47.57
46.46
43.66
44.07
39.2
40.76
37.7
37.8
33.78 34.59 35.24 35.09
Mx I-Canine
Mn I-Canine
Mx I -Mol
SE
EE
4B i
LE
SE
EE
4B i
LE
SE
EE
4B i
LE
26.13 26.2 27.01 26.5
SE
EE
4B i
LE
M illim eter (m m )
50
45
40
35
30
25
20
15
10
5
0
Mn I -Mol
Figure 3.5 Mean arch transverse dimensions for serial
extraction study and early extraction study. Serial
extraction study,24 SE=serial extraction,4Bi=extraction in
permanent dentition. Current study, EE=early extraction,
LE=late extraction.
intercanine measurements of both arches in the
extraction groups support findings by Strang and King that
as the the teeth are distalized there is a similar increase
in width,26,27 see table 3.5 with a significantly wider
maxillary intercanine dimension for the late extraction
group in comparison to nonextraction.
The same logic
applies to the molar transverse values where they were
mesially positioned into a more anterior part of the arch
thus filling the bicuspid extraction space and having a
smaller transverse measurement.
51
60
51.75
M illim e te r (m m )
50
43.66 44.07
44.45
37.7 37.8
40 34.1
34.59 35.09
25.5 26.2 26.5
30
20
10
Mx I-Canine
Mn I-Canine
Mx I -Mol
LE
EE
N Eb
LE
EE
N Eb
LE
EE
N Eb
LE
EE
N Eb
0
Mn I -Mol
Figure 3.6 Mean arch values for nonextraction group from
Bishara et al. study compared to early and late extraction
transverse data.25 NEb=Bishara nonextraction, EE=early
extraction, LE=late extraction
52
Conclusions
The conclusions of this study indicate that:
1. Early versus late extraction protocols yield no
significance with regard to transverse dimension.
2. Nonextraction maxillary and mandibular intermolar
widths are significantly wider than both early and
late extraction groups.
3. Late extraction maxillary intercanine width is
significantly wider than nonextraction intercanine
dimensions.
53
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Vita Auctoris
Michael Larson was born in Corning, California on
August 28, 1976.
He received his primary education in the
California Public School District.
Michael left high
school early with a certificate of Proficiency and attended
junior college at Shasta College in Redding California.
At Shasta College he focused his education on the predental sciences.
After five semesters he transferred to
University of California, Davis.
At Davis he majored in
Physiology and completed his undergraduate education in
2001.
Following his undergraduate career Mr. Larson was
accepted into dental school at University of California,
San Francisco in 2003.
Mr. Larson focused on research
receiving two publications. The author was conferred the
title of D.D.S. in 2007.
In June of 2007, Michael commenced specialty training
in orthodontics at Saint Louis University-Center for
Advanced Dental Education.
Here he is a candidate for the
degree, Master of Science in Dentistry, Orthodontics.
57