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A STUDY ON THE POSITIONS OF THE MAXILLARY INCISORS IN
ANTERIOR OPEN BITE CASES
Daniel J.
Floyd, D.M.D.
A Thesis Presented to the Graduate Faculty of
Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2015
COMMITTEE IN CHARGE OF CANDIDACY:
Professor Eustaquio A. Araujo,
Chairperson and Advisor
Professor Rolf G. Behrents
Assistant Clinical Professor Hiroshi Ueno
i
Dedication
This work is dedicated to my family.
Thank you for
your unending love and support as I pursue my dreams.
ii
Acknowledgements
This project was completed with the help of the
following important individuals:
Dr. Eustaquio Araujo.
Thank you for all of your ideas
and encouragement with this project and for sharing your
seemingly unending wealth of knowledge in the classroom and
in clinic.
You have been the biggest influence on me as a
clinician and your lessons will never be forgotten.
Dr. Rolf Behrents.
Thank you for all of your help
with this project and for this opportunity to pursue my
dreams in orthodontics.
Dr. Hiroshi Ueno.
Thank you for all of your extra
time spent on attention to details and ensuring that
residents get the most out of our experience at Saint Louis
University.
Your caring nature is ever abounding with each
interaction I have with you.
iii
Table of Contents
List of Tables........................................... vi
List of Figures......................................... vii
Chapter 1: Introduction................................... 1
Chapter 2: Review of the Literature....................... 4
The Anterior Open Bite .................................. 4
Skeletal Open Bite Characteristics and Contributing
Factors ................................................. 6
Dental Open Bite Characteristics and Contributing Factors 9
Combination Skeletal and Dental Open Bite .............. 12
Open Bite Treatments ................................... 13
Potential Problems with Open Bite Treatments ........... 18
Vertical and Angular Change Effects of Maxillary
Incisors ............................................. 20
Horizontal Change Effects of Maxillary Incisors ...... 22
Statement of Thesis .................................... 23
List of References ..................................... 24
Chapter 3: Journal Article............................... 30
Abstract ............................................... 30
Introduction ........................................... 32
Materials and Methods .................................. 35
Sample ............................................... 35
Methodology .......................................... 36
Measurements ......................................... 42
Statistical Analysis ................................. 43
Reliability .......................................... 44
Results ................................................ 45
Pre-treatment Measurements ........................... 45
Treatment Changes .................................... 47
Discussion ............................................. 50
Conclusions ............................................ 60
Appendix................................................. 61
iv
List of References ..................................... 64
Vita Auctoris............................................ 66
v
List of Tables
Table 3.1: Descriptive pre-treatment data................
Table 3.2: Treatment changes non-extraction group........
Table 3.3: Treatment changes extraction group............
Table 3.4: Treatment change between non-extraction and
extraction groups .....................................
Table A.1: Landmarks and definitions.....................
Table A.2: Planes and definitions........................
vi
46
47
48
49
61
62
List of Figures
Figure
Figure
Figure
Figure
Figure
3.1:
3.2:
3.3:
A.1:
A.2:
Landmark location............................
Reference planes.............................
Functional occlusal plane....................
Drawbridge effect illustration...............
Drawbridge effect............................
vii
37
39
41
63
63
Chapter 1: Introduction
Beginning with Norman Kingsley, the “father of
orthodontics,”1 in the 19th century, anterior open bites
have proven to be one of the most difficult malocclusions
to treat and retain.2,3 There are many reasons for this and
many factors that need to be kept in mind when attempting
to tackle the difficult task of correcting an open bite.
Much of the difficulty lies in the fact that the etiology
is often multi-factorial and the relationships of the
teeth, soft tissues, and skeletal structures are all
important when diagnosing, treating, and maintaining
correction of an open bite malocclusion.4
Open bites can be of either dental or skeletal origin,
or often a combination of both, with the latter being the
most frequent.
Since most open bites exhibit both dental
and skeletal characteristics, it can often be difficult to
make an etiologic distinction and develop an appropriate
treatment plan.
Disproportionate soft tissues such as a
large tongue or a short upper lip can exacerbate an
existing dental or skeletal problem.
Due to the wide range
of influences, one single, universally appropriate way to
treat an open bite does not exist.
Open bites can either
be treated by orthodontics alone, often with a compromised,
1
camouflaged outcome or they can be treated with a
combination of orthodontics and surgery.5
While a combination of surgical and orthodontic
treatment may yield the best esthetic and functional
treatment result, this may not be feasible or desired by
many patients and the orthodontic camouflage route may be
the only option to provide them with an acceptable result.
Due to the difficulty of treating this malocclusion, a wide
variety of non-surgical treatment modalities have been
developed and utilized to treat open bites.
One of the
most commonly employed methods is the use of dental
extractions.
Even though extracting teeth is a common method of
open bite treatment, a widely held view by many
orthodontists is that the closure of the extraction space
always causes much more extrusion of the anterior teeth
than non-extraction treatment.
If this occurs in the
patient where pre-treatment esthetics don’t dictate the
need for anterior teeth extrusion, this side effect can
have deleterious effects on the post-treatment esthetics
involving the teeth and the surrounding soft tissues.
The purpose of this study is to evaluate the vertical
and horizontal position of maxillary incisors comparing
2
non-extraction and extraction of maxillary first premolar
orthodontic treatments in anterior open bite patients.
3
Chapter 2: Review of the Literature
The Anterior Open Bite
Anterior dental open bite can be defined as a
malocclusion having no vertical overlap or contact of the
anterior teeth when the posterior teeth are in occlusion.8
The correction of this type of deviation has been regarded
as a challenge to the specialty as stated by Cangialosi:
“the cases which have proved most difficult to treat and
which have the least favorable prognosis are frequently
those in which there is a vertical discrepancy that is
manifested anteriorly either as a deep overbite or as an
open bite.”9
The author went on to say that “the phenomenon
of anterior open bite is multifactorial, and there is an
almost infinite variety to the dentoskeletal configuration
and the magnitude of dysplasia associated with it.”9
This
multi-factorial nature of open bites, therefore, makes them
one of the most difficult malocclusions to treat and
retain.4,10
A few of the possible causes of open bites are
genetics, patient habits, influences of the facial soft
tissues, and trauma.
Studies show the prevalence of
anterior open bites is between 1.5 to 11% depending upon
4
ethnic groups.5,11
The relatively high number of individuals
who possess this malocclusion and the broad spectrum of
contributing factors, make for a common problem with a wide
range of issues that one needs to be aware of and
continually monitoring throughout the course of treatment.
The presence of an anterior open bite presents many
problems for both patients and orthodontists.
For patients
such problems involve speech, swallowing and mastication.
For the orthodontist tasked with the difficult challenge of
correcting this malocclusion, a short list of problems
includes: difficulty with diagnosis due to multi-factorial
causation, issues with obtaining proper esthetics, and
predictably being able to ensure long term retention of the
malocclusion correction.2,4,10,12
Open bites have been classified as skeletal, dental or
a combination of both.5,9,13-19
By definition, a skeletal
abnormality does not contribute to the dental open bite.
However, a skeletal open bite, has some contributions made
by vertical facial form which cause the anterior teeth to
be positioned in relation to each other in such a way where
there is no vertical overlap between them.14
More often
than not though, there is a combination of skeletal and
dental contributions to the resultant open bite.17
5
Skeletal Open Bite Characteristics and Contributing Factors
The distinct characteristics of open bites of skeletal
origin are commonly determined by evaluating
cephalograms.4,18,20
Individuals with a skeletal open bite
show large gonial and cranial base angles and the
mandibular ramus is short with an accentuated antegonial
notch on its lower border.
Posterior facial height is
significantly smaller than anterior facial height, up to
half the size.
The excessive height of the upper anterior
face from cranial base to molars and the short posterior
facial height give rise to the downward and backward
rotation of the mandible.
Lower anterior facial height
exceeds the upper anterior facial height and the opposite
is true in the posterior face.
The mandibular plane angle
is larger than normal and is often classified as
“hyperdivergent,” such that the angle between the cranial
base and the mandibular plane (SN-MP) is larger than
normal.
In the growing patient, there is often a vertical
growth pattern with the cranial base and mandibular plane
angle becoming more obtuse.4,18,21
It is important to note,
that a long face skeletal pattern alone does not in and of
itself determine the depth of a dental bite.22
6
The
contributing dental effects of the open bite will soon be
discussed.
In part, due to the vertically directed growth, open
bite individuals have a mandibular symphysis that is small
anteroposteriorly and large vertically.
Subsequently, when
looking at the profile view of the individual, a small chin
is often evident,21 and commonly, the mandible as a whole is
retrognathic.2
Examining the other three dimensional views
of the individual, the cranium is dolichocephalic and the
frontal face is leptoprosopic.
Theories of skeletal shape and form suggest that the
musculature plays a primary role in the architecture of the
skeletal components of the cranium.23
Therefore, it is of
no surprise that individuals with open bites have
similarities in the size and span of musculature and its
underlying skeleton.
Often in open bite individuals, the
temporal fossa and the temporalis muscle are small which
suggests the individual has weak musculature.11
In open
bite individuals, this weak and posteriorly positioned
musculature, especially the masseters, allows
hyperdivergence and tendency towards vertically directed
growth to develop.2,21
In contrast, deep bite patients, who
often have large, strong musculature, demonstrate
7
large
temporal fossa and large, wide spanning temporalis
muscles.21
Individuals with skeletal open bites have similarities
involving the soft tissues as well.
Despite the orifice of
the mouth frequently being wide and broad, vertically short
lips have difficulty closing at rest and mouth breathing is
subsequently very common.
As previously mentioned, the
skeleton of the chin is commonly long, narrow, and
retrognathic.
Correspondingly, lip incompetence from the
short lips causes strain of the mentalis muscle when the
lips are forcibly closed together and this further lends
the individual to the appearance of a lack of
chin.15,17,21,24
Examination of the dentition shows frequent impaction
of the 3rd molars and teeth tend to be proportionally larger
than normal with crowding and bi-maxillary protrusion
commonly being present.
The incisors form an acute
interincisal angle and even though the incisors are often
more extruded in individuals with open bites, the extrusion
is not enough to allow for contact between the maxillary
and mandibular incisors.21
Ultimately, the cause of the skeletal open bite can be
determined by viewing the position of the molars.
Over
eruption of the molars occurs as the palatal plane tips
8
down in the posterior and up anteriorly.11
This posterior
tipping of the palatal plane therefore causes the bite to
open in the anterior.
The tipping of the maxillary
occlusal plane then generates a backward and downward
rotation of the mandible.
This subsequent divergence of
the occlusal planes causes a large palatomandibular plane
angle and an increase in anterior facial height.21
Therefore, skeletal open bite is a consequence of the
tipping of the palatal plane through over eruption of
maxillary posterior teeth and the maxillary sutures moving
inferiorly.2,25
Although the dentition plays a role in the
clinical presentation of the open bite, it is secondary to
the abnormal skeletal morphology that is to blame for the
relationship of the anterior dentition.
Dental Open Bite Characteristics and Contributing Factors
The true dental open bite with no contribution from an
abnormal skeleton has a much smaller list of
characteristics and contributing factors.
Dental open bite
is associated with the following characteristics: normal
craniofacial pattern, proclined incisors, undererupted
anterior teeth, normal or only slightly excessive molar
height, and little to no gingival display.11,20
9
Open bites of dental origin can be due to trauma, oral
habits, influences of the oral and facial soft tissues, and
eruption and relationship of the dentition.5,14,18
cause of dental open bite is digit sucking.
A common
Incidence of
digit sucking is 30% at one year of age, 12% at 9 years,
and 2% by 12 years of age.
Females are more likely than
males to be persistent digit suckers.
The influence of the
digit sucking on the dentition and the surrounding tissues
is determined by the age until which this habit persists
and the frequency and intensity of the habit.
If cessation
of the habit occurs before or during growth, the remaining
growth of the individual will likely transition back to its
underlying, normal pattern.4,14,18
Worms et al.,26 found 80%
spontaneous correction of simple open bites, those with no
overlap from canine to canine, in individuals ranging from
ages 7 to 12.
If this cessation does not occur before
growth is complete, the clinical presentation will be a
persistent anterior open bite and a high, narrow palate and
maxillary arch.
Along with the lack of vertical overlap of
the anterior teeth, the habit can cause an asymmetrical
canting of the occlusal plane and a counter clockwise
rotation of the palatal skeleton.14
Abnormal tongue function is thought to be another
habit where oral soft tissues have direct effects on the
10
creation and maintenance of an open bite.
A common
abnormal tongue function that can cause or perpetuate an
anterior open bite is the tongue thrust or forward resting
position habit.4,5,14
Proffit8 has suggested that the open
bite is not created through the transient thrusting of the
tongue, but rather the open bite is caused by the tongue’s
forward resting position between and against the anterior
teeth.
Cangialosi raised the same question of whether the
abnormal tongue function caused the open bite or whether
the reverse is true.9
The absolute answer to the question,
however, is unknown.
Open bite associated with abnormal tongue function is
an example of a dental open bite of either primary or
secondary origin.
Primary open bite is due to excessive
contraction of circumoral musculature during swallowing.
With primary open bite, the anterior occlusion begins
closed, but the action of the musculature on the dentition
causes the bite to open.
In comparison, the secondary
cause of an open bite, perpetuates an open bite that
already exists as the tongue frequently rests in between
the maxillary and mandibular incisors and positions itself
between the incisors in order to create an oral seal during
swallowing.14
For both individuals with digit sucking
11
habits and abnormal tongue function, six hours or more per
day is required to cause a resultant malocclusion.8,14
Anterior open bite might also be the result of
excessive axial inclination of the anterior teeth.19,27 The
idea of the “drawbridge effect” has been used to describe
an anterior open bite created by excessive proclination of
the maxillary and mandibular incisors. The more these
incisors are proclined, the larger the amount of open bite
that results. As they are retroclined, as in the closing of
the two halves of a drawbridge, the smaller the open bite
becomes until it eventually closes and positive overbite
occurs.5,11,28
Combination Skeletal and Dental Open Bite
The third and most prevalent source of an open bite is
the combination skeletal and dental open bite.
It is a
secondary dental open bite with skeletal contributions.
Due to the short ramus and the high, narrow positioning of
the palatal vault, the airway space is more constricted.
As a result, these individuals tend to position their
tongues forward in order to breathe.
Making matters worse,
if an individual also has enlarged tonsils, the tongue will
rest and act in an even more anterior position, thus
12
causing the secondary bimaxillary protrusive presentation
and acting to reinforce the dental open bite, ensuring it
remains and becomes even more severe.21
Open Bite Treatments
Treatment of an anterior open bite depends on the
cause of the malocclusion, age and the expectations of the
patient.
Since open bites either have a dental or skeletal
etiology, there must be treatment methods that are unique
to addressing the malocclusion of each origin.
An
interesting recommendation to keep in mind is the idea that
90% of patients with true skeletal anterior open bite are
best treated with a combination of orthognathic surgical
and orthodontic procedures.2,25
This occurs generally
because skeletal open bites only become more severe as a
patient grows, often regardless of any attempts at growth
modulation.
Whereas, open bites of purely dental origin,
if addressed early enough in a growing patient, may
spontaneously close.
When they don’t fully close, they are
mild enough that generally only orthodontic treatment is
necessary.4,14
There are four common treatment modalities for the
correction of open bites: observation and myofunctional
13
therapy intervention of early problems, interceptive
treatment, orthodontics alone, or a combination of
orthodontics and surgery.5,11,14,18
The observation and
intervention of early problems modality involves discussing
and working through habit modification and cessation with
patients.
A more active approach to treatment in the use
of appliances is interceptive treatment which involves
growth regulation and modulation.4,14
Both methods along
with the orthodontic and surgery methods will be discussed
in greater detail.
Abnormal tongue function and non-nutritive sucking are
examples of open bite contributing factors seen in young
patients where early intervention could allow for growth
modification and correction of at least part of the open
bite malocclusion.
Abnormal tongue function, also referred
to as a tongue thrust, are treated with myofunctional
training therapy often in combination with appliances such
as tongue cribs and rakes.
Non-nutritive sucking can also
be treated with orthodontic appliances, but extraoral
procedures such as chemical aversion and hand wraps are
also often used.
It is important to be mindful that
patients may have a psychological dependence on the sucking
habit, so addressing the habit as early as possible is most
effective.4,5,8
14
Interceptive treatment takes aim at an early
intervention in the growth of the jaws.
Intervening before
the pubertal growth spurt can be important in preventing
future, more complicated procedures in order to correct the
malocclusion.
At this stage, treatment focuses on avoiding
over eruption of posterior teeth, controlling and
attempting to redirect growth in all three dimensions with
intraoral or extraoral forces.
A short list of these
passive or active appliances are as follows: vertical
holding appliance, vertical chin cup, posterior bite
blocks, high pull headgear, Frankel IV regulator, spring
loaded bite block, and the active vertical corrector.
Pressures from the soft tissues, extraoral anchorage,
dental eruption blockage, active forces through springs and
magnets are all mechanisms that have been utilized with
these appliances.4,5,8
Once growth is complete, if the open bite is mild,
camouflage treatment with orthodontics alone can be
considered.
Both functional and esthetic considerations
must be made prior to commencing treatment.
Of course,
closing an open bite so that a patient can speak, swallow
and masticate properly are very important, obtaining
acceptable esthetics through orthodontic treatment should
be a priority as well.
15
When a patient exhibits a lack of esthetic incisor and
gingival display, extrusion of anterior teeth is necessary.
This is often done with vertical elastics in the anterior
region.14,16
However, when a patient exhibits normal or
excessive gingival display, treatment that would prevent or
minimize an increase in the incisor and gingival display
must be rendered.29
This is best done through extraction or
intrusion of posterior teeth.30
Both will be discussed
later in greater detail.
There are a variety of ways to treat an anterior open
bite with orthodontics.
Perhaps the most common involves
the extraction of posterior teeth.5
Extractions are
justified in treating anterior open bites due to two
possible mechanisms. The first is the theory that mesial
movement of the teeth posterior to the extractions will
decrease the “wedge effect” and reduce the mandibular plane
angle as the mandible rotates forward.31
However, whether
this occurs or not is still quite controversial.32,33
The
second mechanism is when premolars are extracted, the
previously mentioned “drawbridge effect” occurs.5,11,28
The
closure of this space involves the retraction of and the
resultant relative extrusion of the maxillary incisors
which can cause the closure of the bite.3,14
16
Sarver and Weissman3 have suggested that if this does
in fact occur, there are certain selection criteria for
open bite patients that must be kept in mind prior to
initiating treatment.
First, the patient should have
proclined maxillary incisors and minimal to no gingival
display.
Second, the skeletal pattern of the face should
not be leptoprosopic, as extraction of mandibular teeth to
resolve mandibular incisor proclination could result in
mandibular molar extrusion during space closure and this
could further increase the mandibular plane angle and cause
greater bite opening.
Third, the maxillary incisor to lip
relationship is important as the retraction and uprighting
of the incisor will result in an inferior positioning of
the maxillary incisor which could compromise esthetics
involving soft tissues.3
More recently, the intrusion of posterior teeth has
also been a treatment of choice anchored by bone plates and
mini screw implants with elastics or NiTi springs.5
Through
a similar mechanism, clear aligner therapy has been
advocated for this purpose, though validity is still in
question.34
When the patient displays inadequate maxillary
incisor and gingiva, the use of vertical elastics with
multiloop edgewise archwire (MEAW) technique via the
“rocking chair” effect has been utilized attempting to
17
close open bites by extruding the anterior teeth and
through very slight intrusion of the posterior teeth.
The
MEAW technique can also be utilized when minimal extrusion
of the maxillary incisors is desired in the case of a
patient with normal or excessive incisor and gingival
display.
This variation, employs a combination of the MEAW
and mini screw implants for greater posterior
intrusion.16,17
Anterior vertical elastics can be used with straight
wires as well, but attention must be paid to minimizing
posterior extrusion through mini screw implants or
headgear.4,14
If the extrusion of posterior teeth is not
prevented, the bite will open further and the anterior
teeth will need to be extruded more to close the bite.
This could cause inadequate incisor or gingival display.35
Potential Problems with Open Bite Treatments
Esthetics is a priority of an orthodontic treatment
and must be considered when selecting mechanics and
analyzing the consequence of resulting force vectors. Side
effects of all treatments need to be studied when deciding
which treatment modality to utilize.
18
Negative side effects
can occur in three dimensional facial esthetics.
One of
which involves the amount of incisor and gingival
display.2,3,5,7,16,36,37
It has been expected that incisors will be more
retroclined when treated with extractions compared to nonextraction treatment.38
When the open bite is due to the
excessive proclination of the incisors, the aforementioned
“drawbridge effect” is the desired mechanism.5,11,28
However,
when this effect occurs in patients with upright or
retroclined incisors, such as in Class II, division 2
patients, the result is excessively retroclined incisors.
Previous studies have shown, on average, 2-3 mm retraction
of the incisors with first premolar extraction
treatment.39-41
If pre-treatment esthetics does not warrant
it, this posterior movement of the incisor causes
retraction of the lips and negative effects on the smile.
This could cause the lips to sink back and cause inadequate
vermillion display of the upper lip and a more “dished in”
profile.3,38,40,42-44
In contrast to extraction treatment, it has been shown
that non-extraction treatment results in more proclined
incisors.38
Therefore, sufficient attention should be paid
to proper diagnosis when deciding between an extraction and
a non-extraction treatment plan.
19
Maintenance of adequate
incisor angulation throughout treatment avoiding excessive
retraction of the incisors can help in obtaining proper
soft tissue esthetics.
Before setting out to attempt to correct an open bite
malocclusion, one must first ensure their diagnosis is
comprehensive and correct.9
Then, the selected treatment
method must be screened for potential undesirable side
effects.
Caution should be exercised to not allow palatal
cusps of posterior maxillary teeth to hang down, thus
opening the bite further.14,18
One must also think about
retention prior to initiating treatment to ensure all
treatment objectives are achieved to minimize posttreatment relapse.
Considering open bites are one of the
least stable malocclusions, beginning with the end in mind
would be a prudent approach.10,45
Vertical and Angular Change Effects of Maxillary Incisors
According to Downs46, the normal interincisal angle
should be 135°, while Steiner47 states it should be 131°.
Previous studies have shown an increase of 4.5° in the
interincisal angle and posterior movement of the incisal
edge of the maxillary incisors in extraction treatment.48
This could mean the angulation of the maxillary incisor has
20
decreased which subsequently could cause the incisor to
relatively extrude.
However, the interincisal angle uses
the angulation of the maxillary and mandibular central
incisors.
According to this study, it is unknown how much of
this angular reduction is due to the maxillary or
mandibular central incisors individually.
Perhaps lending
evidence to the contribution of the maxillary central
incisor to the interincisal angle reduction is Bishara’s
study49 in which maxillary incisors in the four first
premolars extraction group compared to the non-extraction
group retroclined 2.3° more in males and 4.6° more in
females.
Related and pertinent, Ramos et al.,42 studied
changes to the maxillary central incisors in maxillary
first premolar extraction patients and showed the incisor
extruded 0.06 mm to 0.65 mm in relation to the lower
curvature of the upper lip.
Therefore, according to these
studies, after extraction and during the retraction of the
anterior teeth, the maxillary central incisors decrease in
angulation and extrude.
It is important to note that no studies have compared
the amount of extrusion in patients treated with
extractions versus non-extraction.
21
Also, it is unknown how
much of the incisor extrusion was via pure extrusion or
relative extrusion.
Horizontal Change Effects of Maxillary Incisors
Evaluating the anteroposterior movement of the
maxillary central incisor, three studies showed very
similar results.
Bishara found the maxillary central
incisor retracted 4.6 mm and 1.5 mm in the extraction and
non-extraction groups, respectively.49
Although a non-
extraction group was not studied, Ramos et al.,42 found
comparable retraction ranging between 3.7 and 5.6 mm for
patients treated with extractions.
Similar, though not as
much retraction in the extraction group was found in the
Luppanapornlarp study evaluating four first premolar
extraction treatment in “borderline” patients.
The results
showed maxillary central incisor retraction of 2.8 mm in
the extraction group and 1.4 mm in the non-extraction
group.
Luppanapornlarp suggested this retraction then
caused 2-3 mm of retraction of the upper lip, thus causing
a decrease in the convexity of the patient profile.40
Ramos
et al.,42 found that changes in the incisor position and
angulation affected the position of the upper lip as well.
Another important finding was that changes to the cervical
22
portion of the maxillary central incisor had almost twice
as much correlation to changes in the upper lip angle than
the changes in the incisal edge.
Therefore, retraction of
the cervical portion of the incisor affects the lips more
than retraction of the incisal edge.
Many studies40,42,46,47,49 have shown these changes in the
incisor position and angulation have direct effects on the
esthetics of the smile.
Therefore, when orthodontically
treating patients, one must be knowledgeable of the
composition of the smile.
Taking this a step further, one
should be familiar with the esthetic normative values of
these components and how certain treatments ultimately
influence their post-treatment esthetics.50-76
Statement of Thesis
This study aims to evaluate the vertical and
horizontal position changes of maxillary incisors when
comparing non-extraction and extraction of maxillary first
premolar orthodontic treatments in anterior open bite
patients.
23
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29
Chapter 3: Journal Article
Abstract
Purpose:
The purpose of this study is to evaluate the
vertical and horizontal position of maxillary incisors when
comparing non-extraction and extraction of maxillary first
premolar orthodontic treatments in anterior open bite
patients.
Materials and Methods:
The sample of 60
subjects was selected from the records at Saint Louis
University Center for Advanced Dental Education.
The cases
were selected on the basis of the following inclusion
criteria: 1) Class I or Class II, division 1, 2) anterior
open bite from canine to canine, 3) canines shouldn’t be in
occlusion but an end to end relationship was acceptable, 4)
all permanent incisors had to be present and fully erupted,
5) high quality pre- and post-treatment cephalograms.
Group 1 had no extractions of permanent teeth during
treatment and group 2 had extractions of at least maxillary
first premolars.
Temporary anchorage devices could have
been used for anterior and posterior movement of teeth, but
not for intrusion mechanics.
used.
No extraoral appliances were
Patients with a syndrome, a congenital deformity
like cleft lip and palate or missing one or more incisors
were excluded from the study.
Results:
Both groups
experienced statistically significant changes in the
30
position of the maxillary central incisors in the
horizontal and vertical directions.
However, the mean
change of the position of Prosthion in the horizontal and
vertical directions was not statistically significant
between the two groups.
In the non-extraction group, the
maxillary central incisor extruded 2.97 mm and retracted
0.56mm.
In the extraction group, the maxillary central
incisor extruded 3.52 mm and retracted 2.19 mm.
Conclusions:
The results of this study show that maxillary
central incisors are extruded similar amounts in extraction
and non-extraction treatment of anterior open bite.
However, the changes in the horizontal position of the
extraction group were significant and greater than the nonextraction group.
31
Introduction
Beginning with Norman Kingsley, the “father of
orthodontics,”1 in the 19th century, anterior open bites
have proven to be one of the most difficult malocclusions
to treat and retain.2,3 There are many reasons for this and
many factors that need to be kept in mind when attempting
to tackle the difficult task of correcting an open bite.
Much of the difficulty lies in the fact that the etiology
is often multi-factorial and the relationships of the
teeth, soft tissues, and skeletal structures are all
important when diagnosing, treating, and maintaining
correction of an open bite malocclusion.4
Open bites can be of either dental or skeletal origin,
or often a combination of both, with the latter being the
most frequent.
Since most open bites exhibit both dental
and skeletal characteristics, it can often be difficult to
make an etiologic distinction and develop an appropriate
treatment plan.
Disproportionate soft tissues such as a
large tongue or a short upper lip can exacerbate an
existing dental or skeletal problem.
Due to the wide range
of influences, one single, universally appropriate way to
treat an open bite does not exist.
Open bites can either
be treated by orthodontics alone, often with a compromised,
32
camouflaged outcome or they can be treated with a
combination of orthodontics and surgery.5
While a combination of surgical and orthodontic
treatment may yield the best esthetic and functional
treatment result, this may not be feasible or desired by
many patients and the orthodontic camouflage route may be
the only option to provide them with an acceptable result.
Due to the difficulty of treating this malocclusion, a wide
variety of non-surgical treatment modalities have been
developed and utilized to treat open bites.
One of the
most commonly employed methods is the use of dental
extractions.
Even though extracting teeth is a common method of
open bite treatment, a widely held view by many
orthodontists is that the closure of the extraction space
always causes much more extrusion of the anterior teeth
than non-extraction treatment.
If this occurs in the
patient where pre-treatment esthetics don’t dictate the
need for anterior teeth extrusion, this side effect can
have deleterious effects on the post-treatment esthetics
involving the teeth and the surrounding soft tissues.
The purpose of this study is to evaluate the vertical
and horizontal position of maxillary incisors comparing
33
non-extraction and extraction of maxillary first premolar
orthodontic treatments in anterior open bite patients.
34
Materials and Methods
Sample
The sample of 60 subjects was selected from the
records at Saint Louis University Center for Advanced
Dental Education.
The cases were selected on the basis of
the following inclusion criteria: 1) Class I or Class II,
division 1, 2) anterior open bite from canine to canine, 3)
canines shouldn’t be in occlusion but an end to end
relationship was acceptable, 4) all permanent incisors had
to be present and fully erupted, 5) high quality pre- and
post-treatment cephalograms.
Group 1 had no extractions of
permanent teeth during treatment and group 2 had
extractions of at least maxillary first premolars.
Temporary anchorage devices could have been used for
anterior and posterior movement of teeth, but not for
intrusion mechanics.
No extra-oral appliances were used.
Patients with a syndrome, a congenital deformity like cleft
lip and palate or missing one or more incisors were
excluded from the study.
35
Methodology
All cephalograms were taken on the same cephalometer
within Dolphin Imaging Software (Dolphin Imaging Software,
Inc., Dolphin Imaging, Version 11.5, Chatsworth,
California).
Following collection of each of the patient
records, all pre- and post-treatment cephalograms were
digitized using Dolphin Imaging software.
Nine hard and
soft tissue landmarks were located: S (Sella), N (Nasion),
ANS (Anterior Nasal Spine), PNS (Posterior Nasal Spine),
U1a (maxillary central incisor apex), U1i (maxillary
central incisor incisal edge), PR (Prosthion), L1i
(mandibular central incisor incisal edge), SS (Stomion
Superiorus).
A diagram of landmark location can be seen in
Figure 3.1 and their definitions are located in Appendix
Table A.1.
The digitized cephalograms were then printed at
a 1:1 ratio to ensure no change in magnification.
36
Figure 3.1: Landmark location
37
An X-Y coordinate grid was constructed on the
cephalograms.
The most superior X-axis was represented by
a horizontal constructed line, which was created by
subtracting 7° from the Sella to Nasion line (SN-7°).
The
Y-axis was represented by a vertical line perpendicular to
SN-7° from Sella.
The B plane X-axis was represented by a
horizontal line perpendicular to the Y-axis through Stomion
Superiorus (SS).
The C plane X-axis was represented by a
horizontal line perpendicular to the Y-axis through the
incisal edge of the maxillary central incisor (U1i).
reference planes are depicted in Figure 3.2 and their
definitions are located in Appendix Table A.2.
38
These
Figure 3.2: Reference planes
39
The amount of open bite was obtained using the
functional occlusal plane (FOP) as the reference.
The FOP
was represented by the line bisecting the maxillary and
mandibular first molars and premolars, not taking into
account the position of the incisors.8
The measurement of a
line drawn perpendicular from the FOP to the incisal edge
the maxillary and mandibular incisors was recorded.
The
sum of these distances was the amount of pre-treatment open
bite (OB).
The sum of this distance minus the post-
treatment positive overbite was the amount of open bite
closure that occurred.
The FOP plane is shown below in
Figure 3.3.
40
Figure 3.3: Functional occlusal plane8
41
Measurements
The following manual measurements were taken using a
digital caliper and compared using multiple two sample ttests and paired t-tests:
Millimetric linear measurements
- A plane to B plane
- B plane to C plane
- U1a to SN minus 7°: The maxillary central incisor
root apex to S-N line minus 7°.
- U1i to SN minus 7°: The incisal edge of the
maxillary central incisor to S-N line minus 7°.
- PR to SN minus 7°: The most anterior point on the
maxillary alveolar process in the midline to S-N
line minus 7°.
- PR to Y-axis: The most anterior point on the
maxillary alveolar process in the midline to Y-axis.
- U1a to Y-axis: The maxillary central incisor apex to
Y-axis.
- U1i to Y-axis: The incisal edge of the maxillary
central incisor to Y-axis.
- U1i to FOP: The maxillary central incisor incisal
edge to the functional occlusal plane.
- L1i to FOP: The mandibular central incisor incisal
edge to the functional occlusal plane.
42
Angular measurements
- SN-MP: Angle between Sella to Nasion line and plane
connecting Gonion and Menton.
Gonion determined by
bisecting the angle formed by tangents to the
posterior border of the ramus and inferior border of
the mandible.
- SN-PP: Angle between Sella to Nasion line and line
from anterior nasal spine to posterior nasal spine.
- U1-SN: Angle between Sella to Nasion line and line
through long axis of the maxillary central incisor.
Pre-treatment to post-treatment horizontal and
vertical changes were computed by subtracting the pretreatment landmark position from the post-treatment
landmark position.
Statistical Analysis
Descriptive data was obtained for all measurements and
statistical analysis was done utilizing the Statistical
Package for the Social Science (IBM SPSS, Version 20,
Armonk, NY).
Independent sample t-tests were used for each
variable to detect differences at the start of treatment
between the non-extractions and extractions groups.
Paired
t-tests were used for each variable to detect differences
between pre-treatment and post-treatment measurements
43
within the non-extraction or extraction groups.
Independent sample t-tests were used for each variable to
detect differences in mean changes between the nonextractions and extractions groups.
A significance level
of p <.05 was set to detect differences for all statistical
analyses.
Reliability
To determine the consistency of measurements,
Chronbach’s alpha was used.
Intra-class correlations
greater than or equal to 0.80 were considered to be
reliable.
All measurements for 12 randomly selected
subjects were re-measured to test of intra-examiner
reliability.
measurements.
Chronbach’s alpha was above 0.80 for all
This indicates original and repeated
measurements were at an acceptable level of reliability for
accuracy of measurements.
44
Results
Pre-treatment Measurements
Descriptive data was obtained for pre-treatment
measurements.
Independent sample t-tests were calculated
for each of the 14 variables to detect differences at the
beginning of treatment between the non-extractions and
extractions groups.
The results showed statistically
significant differences between the non-extraction and
extraction groups in the distance from the maxillary
central incisor incisal edge and Stomion Superiorus.
There
was also statistically significant difference in the SN to
MP angle.
A statistically significant difference was found
in the distance from the maxillary central incisor incisal
edge to the occlusal plane.
Details are shown below in
Table 3.1.
45
Table 3.1: Descriptive pre-treatment data
Pre-Treatment Measurements non-extractions and extractions
Group
NonExtractions
extractions
Variable
Mean
SD
Mean
SD
Sig.
A – B (mm)
69.45
5.53
69.21
5.30
0.866
0.006*
B – C (mm)
1.49
1.46
2.68
1.74
U1a to SN-7 (mm)
49.03
4.63
50.50
4.71
0.227
U1i to SN-7 (mm)
70.08
5.76
71.86
5.42
0.223
PR to SN-7 (mm)
59.06
5.33
60.12
4.94
0.428
PR to Y-axis (mm)
68.67
6.82
67.02
8.37
0.407
U1a to Y-axis (mm)
61.31
6.41
59.01
7.17
0.195
U1i to Y-axis (mm)
70.65
7.72
69.08
9.60
0.488
0.015*
U1i to FOP (mm)
3.09
1.78
1.90
1.88
L1i to FOP (mm)
-0.78
1.57
-0.43
1.58
0.403
OB (mm)
2.31
1.63
1.58
1.43
0.070
0.037*
SN - MP°
35.19
6.12
38.25
4.90
U1 - SN°
107.45 9.21 109.82
9.98
0.343
SN - PP°
17.46
4.57
17.74
5.24
0.824
*P<.05
All measurements in millimeters or degrees as indicated
46
Treatment Changes
Descriptive data was obtained for the pre- and posttreatment changes for each of the 14 variables.
Paired t-
tests were calculated for each variable.
In the non-extractions group, A-B, B-C, U1a to SN
minus 7°, U1i to SN minus 7°, Prosthion to SN minus 7°, U1i
to Y-axis, SN-MP°, U1-SN°, U1-FOP, and amount of open bite
showed statistically significant changes.
The maxillary
central incisors were extruded and retracted.
The
mandibular plane increased slightly and the angulation of
the maxillary central incisor decreased.
Details are shown
below in Table 3.2.
Table 3.2: Treatment changes non-extraction group
Pre- to Post-Treatment Change
Variable
Mean
SD
Sig.
change
0.001*
A – B (mm)
1.95
3.00
0.014*
B – C (mm)
0.83
1.74
U1a to SN-7 (mm)
2.68
2.31 <0.001*
U1i to SN-7 (mm)
3.20
3.06 <0.001*
PR to SN-7 (mm)
2.97
3.02 <0.001*
PR to Y-axis (mm)
-0.56
2.74
0.274
U1a to Y-axis (mm)
-0.18
3.01
0.741
0.002*
U1i to Y-axis (mm)
-1.63
2.63
U1i to FOP (mm)
2.69
2.12 <0.001*
L1i to FOP (mm)
0.51
1.55
0.084
OB (mm)
-3.19
1.61 <0.001*
0.006*
SN - MP°
1.22
2.24
0.002*
U1 - SN°
-4.48
7.09
SN - PP°
0.76
3.96
0.302
*P<.05
All measurements in millimeters or degrees as indicated
47
In the extractions group, A-B, U1a to SN minus 7°, U1i
to SN minus 7°, Prosthion to SN minus 7°, Prosthion to Yaxis, U1i to Y-axis, U1-SN°, SN-PP°, U1-FOP, and amount of
open bite showed statistically significant changes.
The
maxillary central incisor vertically were extruded and
retracted.
The palatal plane increased slightly and the
angulation of the maxillary central incisor decreased.
Details are shown below in Table 3.3.
Table 3.3: Treatment changes extraction group
Pre- to Post-Treatment Change
Variable
Mean
SD
Sig.
change
0.001*
A – B (mm)
2.53
3.72
B – C (mm)
0.50
1.77
0.135
U1a to SN-7 (mm)
2.95
3.63 <0.001*
U1i to SN-7 (mm)
3.13
3.31 <0.001*
PR to SN-7 (mm)
3.52
3.47 <0.001*
0.003*
PR to Y-axis (mm)
-2.19
3.77
U1a to Y-axis (mm)
-0.10
2.49
0.827
U1i to Y-axis (mm)
-4.47
5.57 <0.001*
U1i to FOP (mm)
2.36
2.24 <0.001*
L1i to FOP (mm)
0.41
1.69
0.190
OB (mm)
-2.96
1.41 <0.001*
SN - MP°
0.43
3.00
0.439
U1 - SN°
-11.53 11.16 <0.001*
0.010*
SN - PP°
2.42
4.81
*P<.05
All measurements in millimeters or degrees as indicated
48
Independent sample t-tests were calculated for each of
the 12 variables to detect differences in mean changes
between the non-extractions and extractions groups.
The
results showed a significant reduction in the distance
between the maxillary incisor incisal edge to the Y-axis
and a reduction in the angle between the SN line and the
long axis of the maxillary central incisor.
Details are
shown below in Table 3.4.
Table 3.4: Treatment change between non-extraction and
extraction groups
Pre- to Post-Treatment Change
Group
NonExtractions
extractions
Variable
Mean
SD
Mean
SD
Sig.
change
change
A – B (mm)
1.95
3.00
2.53
3.72
0.511
B – C (mm)
0.83
1.74
0.50
1.77
0.464
U1a to SN-7 (mm)
2.68
2.31
2.95
3.63
0.736
U1i to SN-7 (mm)
3.20
3.06
3.13
3.31
0.932
PR to SN-7 (mm)
2.97
3.02
3.52
3.47
0.510
PR to Y-axis (mm)
-0.56
2.74
-2.19
3.77
0.060
U1a to Y-axis (mm)
-0.18
3.01
-0.10
2.49
0.907
0.014*
U1i to Y-axis (mm)
-1.63
2.63
-4.47
5.57
OB (mm)
-3.19
1.61
-2.96
1.41
0.546
SN - MP°
1.22
2.24
0.43
3.00
0.255
0.005*
U1 - SN°
-4.48
7.09
-11.53 11.16
SN - PP°
0.76
3.96
2.42
4.81
0.149
*P<.05
All measurements in millimeters or degrees as indicated
49
Discussion
The purpose of this study was to attempt to bring
to light additional evidence for or against the commonly
held axioms that extraction orthodontic treatment
negatively effects post-treatment esthetics.
This study
sought to add another layer to the evidence base involving
orthodontic treatment and facial esthetics by attempting to
correlate the effects premolar extraction treatment has on
post-treatment gingival display by looking at the
horizontal and vertical changes of the maxillary
incisors.3,6
Empirical, though not completely unequivocal,
conclusions could perhaps be inferred from this study
regarding the amount of post-treatment gingival display in
patients with anterior open bites.
These conclusions could
be used to guide orthodontic practitioner’s decisions in
treating these patients rather than assumptions based
primarily in theory and observations not substantiated by
evidence.
The literature reveals little information regarding
the effect on intraoral esthetics, specifically in amount
of gingival display, between orthodontic treatment
completed with extractions of permanent teeth and nonextraction treatment.6,7,9-12
Throughout the orthodontic
community, there has been a widespread, accepted belief
50
that extracting maxillary first premolars causes a greater
increase in post-treatment gingival display than does
orthodontic treatment without extractions.
However, no
studies have been performed to confirm or disprove this
assertion.
The present study aimed to provide evidence to whether
or not extraction and non-extraction orthodontic treatment
causes similar or different changes on the vertical and
horizontal position of the maxillary incisors and attempt
to correlate it with gingival display.
This study looked
at 60 orthodontic patients with anterior open bite from
canine to canine, with either extraction of maxillary first
premolars or non-extraction orthodontic treatment.
All
patients were either Class I or Class II, division I pretreatment.
In comparing pre-treatment measurements, a significant
difference was found between the extraction and nonextraction groups in the distance between the inferior
curvature of the upper lip, Stomion Superiorus, and the
maxillary incisor incisal edge.
This distance was 1.49 mm
in patients treated without extractions and 2.68 mm in
patients treated with extractions.
This shows that, in the
extraction group, the maxillary central incisors began more
inferior to the upper lip than the non-extraction group.
51
Patients treated without extractions show less pretreatment hyperdivergence than patients treated with
extractions as their mandibular plane angles were 35.19°
and 38.25°, respectively.
Both of these findings were
found to be statistically significant.
There was also a
significant difference in the distance of the maxillary
incisor incisal edge to the functional occlusal plane
between the extraction and non-extraction groups of 1.90 mm
and 3.09 mm, respectively.
On average, the amount of pre-
treatment anterior open bite was 2.31 mm in the nonextraction group and 1.58 mm in the extraction group.
This
difference, however, was not significant between the two
groups.
Therefore, in regards to pre-treatment amount of
open bite, the groups are similar and accurate conclusions
can be drawn from comparison of the groups.
Evaluation of the pre- and post-treatment changes
between the non-extraction and extraction groups shows
there was no significant difference in the amount of open
bite closure.
The non-extraction group had 3.19 mm and the
extraction group had 2.96 mm of open bite closure.
Therefore, the amount of open bite closure is nearly
identical between both groups at around 3 mm.
The data
also shows that the open bite was closed primarily due to
the extrusion of the maxillary central incisors with
52
relatively little contribution coming from the minimal
extrusion of the mandibular central incisors.
An important, non-statistically significant finding
was that the maxillary central incisors extruded vertically
during treatment, regardless of treatment group.
The non-
extraction group showed 2.97 mm and the extraction group
showed 3.52 mm of extrusion when viewing the vertical
changes of Prosthion.
With no vertical change differences
evident, significant differences between the two groups
begin to become noticeable when looking at anteroposterior
and incisor angulation changes.
By way of the anteroposterior change of Prosthion, the
maxillary incisors were retracted 2.19 mm in the extraction
group and 0.56 mm in the non-extraction group.
This was
not a statistically significant difference, but a P-value
of 0.060 shows there is a near significant change.
Although the retraction of Prosthion did not prove to be
significant, there was a statistically significant change
in the anteroposterior position of the maxillary central
incisor incisal edge in both groups.
The incisal edge was
retracted 4.47 mm in the extraction group and 1.63 mm in
the non-extraction group.
These findings coincide with
those in previous studies.13-17
Comparing this data to the
change in the maxillary central incisor apex, 0.18 mm in
53
the non-extraction group and 0.10 mm in the extraction
group, open bite closure occurs primarily through tipping
around the center of rotation rather than bodily movement
through the center of resistance.
Due to the greater
amount of retraction during space closure, the extraction
group demonstrates much more tipping than the nonextraction group.
Upon evaluation of the change in the angulation of the
maxillary central incisor, the data revealed a
statistically significant change in both groups.
In the
non-extraction group, this angle decreased 4.48° and in the
extraction group, the angle decreased 11.53°.
Angulation
of the maxillary incisors is important for the esthetics of
the teeth themselves as well as influencing the esthetics
of the surrounding soft tissues.
The effects of the
incisor position on the vertical position of the upper lip
and the gingival soft tissues will be discussed in detail.
Observers who believe extraction treatment compared to
non-extraction treatment causes an increase in gingival
display due to a greater amount of extrusion, as referenced
earlier, may be surprised by the findings of this study.
Comparing the amount of vertical extrusion between nonextraction and extraction patients reveals no statistical
difference.
The data shows that in the treatment of open
54
bites, maxillary incisors extrude nearly equal amounts in
non-extraction and extraction treatments.
Therefore, if
one believes the extrusion of maxillary incisors is the
most important factor in causing an increase in gingival
display, then both groups could cause this increase in
nearly equal amounts.
However, while the impact of
vertical extrusion of the incisors on gingival display
could be important, there are other influences to keep in
mind as well.
The previously mentioned “drawbridge effect”5,18,19 is at
work in evaluating the increase in downward and backward
tipping and angulation decrease of the maxillary central
incisor crowns.
This decrease in angulation of the
incisors within the extraction group corresponds with the
relative extrusion idea mentioned in orthodontic literature
and textbooks.2,3,20,21
When the angulation of the maxillary
incisors decreases, relative extrusion causes an increase
in the display of the gingiva.
The incisor crown tips back
and even though it is not vertically extruded, it appears
to relatively extrude as more of the crown becomes
visible.3,21
In the present study a significant extrusion
difference between the extraction and non-extraction groups
was not evident.
Therefore, if proper orthodontic
55
mechanics are employed, the “drawbridge” relative extrusion
effect may not occur.
This concept demonstrates the dynamic relationship of
the teeth to the soft tissues.
However, the gingiva is not
the only soft tissue directly affected by changes in the
position of the maxillary incisors.
As the maxillary
incisors are extruded and retracted, the lips can also be
directly affected.
Many studies have proven that changes in the position
of the incisors affect the spatial position of the lips.
During non-extraction or extraction orthodontic treatment,
as the maxillary incisor moves, its interaction with the
upper lip will change in the vertical and horizontal
directions.
This study looked at the vertical changes of
the lip in this relationship.
An important finding was that the vertical change of
the incisor to Stomion Superiorus is different for the nonextraction and the extraction group.
There was a
statistically significant increase in the distance between
the incisal edge and Stomion Superiorus in the nonextraction group of 0.83 mm.
If one still believes that
only extraction treatment causes a significant amount of
extrusion, this change, along with the previously mentioned
amount of measured extrusion, confirms the extrusion of the
56
incisors during treatment without extractions.
Interestingly, even though this distance in the extraction
group also increased 0.50 mm, the change was found to not
be statistically significant.
The explanation of this
finding could involve the retraction of the incisor.
When
the incisor is retracted in the anteroposterior direction,
the upper lip will also be retracted.
inferiorly, the lip will follow.
As the incisor moves
This inferior movement of
the upper lip potentially offsets some of the vertical
extrusion of the maxillary incisor.
Ramos et al.,17 had
similar findings involving the vertical changes of the
upper lip in extraction cases, showing 0.06 to 0.65 mm
greater vertical display of the incisor compared to Stomion
Superiorus.
The present study showed the upper lip moved
inferiorly 1.95 mm in the non-extraction group and 2.53 mm
in the extraction group.
The vertical movement of the
upper lip in this study coincides with that found in
previous studies.6,7,9-12,17
This finding is important when
one correlates these findings with Sabri’s22 conclusion that
the average elevation of the upper lip is 7-8 mm, with a
range of 2-12 mm.
If one assumes the activity of the
musculature remains the same, this inferior movement of
Stomion superiorus could help to mask 2/3rds of the effect
57
the vertical extrusion of the maxillary central incisor has
on the amount of post-treatment gingival display.
Although
it does not signify that it causes less gingival display
than the non-extraction group, in the extraction group the
lip covers more of the incisors and a conclusion could be
drawn that this dynamic relationship could at least not
cause increased gingival display.
Mackley23 demonstrated similar findings as well.
An
evaluation of pre- and post-treatment photographs compared
with a cephalometric analysis of patients showed that this
was achieved in the patients with the smallest increase or
even decrease in the Stomion Superiorus to maxillary
incisor edge distance.
He also found that the least amount
of gingival display post-treatment was seen in the patients
with the greatest U1-SN angulation.
Therefore, Mackley’s
findings verify the conclusions of this current study.
As
the SS to U1i distance increases, vertical extrusion
increases and as the U1-SN angle decreases, relative
extrusion occurs and the net result contributes to an
increase in gingival display as more of the crown is
visible and the gingiva moves inferiorly.
According to the data of this study, changes by hard
and soft tissues visible on the cephalograms can shed some
light onto how the maxillary gingiva likely responds during
58
treatment.
The findings of this study do not support the
rationale behind the common assumption that extracting
permanent teeth unequivocally causes an increase in
maxillary incisor extrusion and gingival display compared
to non-extraction treatment due to vertical extrusion of
the maxillary incisors alone.
However, extraction
treatment without proper angulation maintaining orthodontic
mechanics control, could cause an increase in gingival
display due to the relative extrusion during retraction.3,21
Due to the limitations of this study, however,
absolute conclusions regarding gingival display cannot be
drawn.
Two dimensional cephalometric radiographs do not
affirm absolute conclusions related to amount of gingival
display change.
Further study is necessary to attempt to
glean more absolute conclusions.
59
Conclusions
Given the results of this study, the following conclusions
can be made:
1. Maxillary incisors in both the extraction and nonextraction groups moved vertically similar amounts.
2. Amount of open bite closure was similar in both
groups.
3. Greater tipping and retraction in the horizontal
direction and greater decrease in maxillary incisor
angulation occurred in the extraction group.
4. The maxillary incisor incisal edge extruded more in
relation to Stomion Superiorus in the non-extraction
group.
60
Appendix
Table A.1: Landmarks and definitions
Landmark
Sella
Abbreviation
S
Nasion
N
Prosthion
PR
Maxillary incisor
apex edge
U1a
Maxillary incisor
incisal edge
Stomion Superiorus
U1i
Mandibular incisor
incisal edge
L1i
SS
61
Definition
The center of the
pituitary fossa.
The most anterior point of
the frontonasal suture.
The most anterior point on
the maxillary alveolar
process in the midline.
The most apical point of
the maxillary central
incisor.
The incisal edge of the
maxillary central incisor.
The most inferior point on
the curve of the upper
lip.
The most incisal point of
the mandibular central
incisor.
Table A.2: Planes and definitions
Plane
Y-axis
Abbreviation
Y
A plane
A
B plane
B
C plane
C
Mandibular plane MP
Palatal plane
PP
Functional
occlusal plane
FOP
62
Definition
Vertical plane originating
at Sella perpendicular to
Sella to Nasion plan minus 7
degrees.
Sella to Nasion plane minus
7 degrees.
Perpendicular from Y-axis to
Stomion Superiorus.
Perpendicular from Y-axis to
maxillary central incisor
incisal edge.
Line connecting Gonion and
Menton. Gonion determined by
bisecting the angle formed
by tangents to the posterior
border of the ramus and
inferior border of the
mandible.
Line from Anterior Nasal
Spine to Posterior Nasal
Spine.
Line bisecting the maxillary
and mandibular first molars
and premolars, not taking
into account the position of
the incisors.
Figure A.1: Drawbridge effect5,18,19 illustration
Figure A.2: Drawbridge effect.5,18,19 Incisors rotate around
the center of rotation away from the occlusal plane as they
are proclined and toward the occlusal plane as they are
retroclined. This retroclination causes the incsisors to
relatively extrude.3,21
63
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65
Vita Auctoris
Daniel James Floyd was born on September 8, 1983 in
Corvallis, Oregon to Donald and Carol Floyd.
He grew up in Albany, Oregon and graduated from
Santiam Christian High School in 2002.
After high school,
he attended Arizona State University in Tempe, Arizona and
concentrated his studies in business and biology for four
years.
In 2006, he began dental school at Oregon Health
Sciences University in Portland, Oregon and graduated with
a Doctor of Dental Medicine degree in 2010.
as a general dentist for three years.
He then worked
In 2013, he began
his orthodontics residency at Saint Louis University.
He
expects to receive his Masters of Science in Dentistry
degree in December 2015.
Daniel plans to practice in Oregon after receiving his
degree.
Go Hawks.
66