Download Shuka Moshiri, B.A., D.M.D. CEPHALOMETRIC EVALUATION OF ADULT ANTERIOR OPEN BITE

CEPHALOMETRIC EVALUATION OF ADULT ANTERIOR OPEN BITE
NONEXTRACTION TREATMENT
WITH INVISALIGN
Shuka Moshiri, B.A., 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:
Associate Professor Ki Beom Kim,
Chairperson and Advisor
Professor Eustaquio A. Araujo
Assistant Clinical Professor Julie F. McCray
i
DEDICATION
I dedicate this work to my parents, Fariba and Farhad
Moshiri, whose unending love and support has enabled me to
become the person I am today.
I have never witnessed two
people pour so much of their heart and energy into their
children.
They are the ultimate example of self-sacrifice and
unconditional love, and I’m beyond grateful to have them as
parents.
To my brother, Mazyar Moshiri, who has not only
gracefully carried forth our family’s legacies, but has
surpassed our expectations. He is an inspiration to me and I
couldn’t be more proud to call him my brother; his leadership
has impacted my life greatly.
To my friends who, along with family, are the backbone of
my life.
To the faculty at Saint Louis University, who are the
heartbeat of our program.
The knowledge you impart onto your
students is a gift that lays the groundwork for their future;
this is absolutely invaluable.
ii
ACKNOWLEDGEMENTS
The following individuals deserve special
acknowledgement for their contribution to this project:
Dr. Ki Beom Kim.
Thank you for accepting the role as
my advisor and chairperson of my thesis committee.
Your
constant patience, guidance and support were integral to
the completion of this work.
The dedication you give
towards your students resonates in our program.
Dr. Eustaquio Araujo.
Thank you for your
encouragement and mentorship through this process.
You are
an instrumental figure in many lives and to be called your
student is an honor.
Dr. Julie F. McCray. Thank you for taking time out of
your busy private practice schedule to teach us clinically
at SLU.
Your time and genuine interest in my thesis
project was always greatly appreciated.
Dr. Willy Dayan.
Thank you for working tirelessly
with me to help procure the majority of my thesis sample.
You opened up your practice and home to me and treated me
like family.
Your hospitality and guidance will forever be
remembered.
Dr. Mazyar Moshiri and Dr. Jonathan Nicozisis.
Thank
you for providing the additional records used for my
sample.
In spite of your demanding practice schedules, you
iii
were both extremely prompt in your correspondences with me
and went out of your way to help.
the support you’ve shown.
iv
I’m very grateful for
TABLE OF CONTENTS
LIST OF TABLES......................................... viii
LIST OF FIGURES.......................................... ix
CHAPTER 1: INTRODUCTION................................... 1
CHAPTER II: REVIEW OF THE LITERATURE...................... 5
Anterior Open Bite ...................................... 5
Definition ............................................ 5
Etiology .............................................. 5
Thumb and finger sucking............................. 7
Tongue thrust........................................ 8
Airway.............................................. 11
Skeletal growth aberrations......................... 16
Temporomandibular joint pathology................... 17
Morphology of Skeletal Open Bite ..................... 17
Face height......................................... 18
Palatal plane....................................... 19
Occlusal plane...................................... 20
Cranial base........................................ 21
Mandibular plane.................................... 21
Morphology of Dental Open Bite ....................... 23
v
Diagnosis ............................................ 23
Treatment ............................................ 24
Multiloop edgewise archwire......................... 26
Extractions......................................... 27
Skeletal anchorage systems.......................... 29
Fixed appliance therapy............................. 30
Surgery............................................. 32
Invisalign ............................................. 33
Statement of Thesis .................................... 37
LITERATURE CITED ....................................... 39
CHAPTER 3: JOURNAL ARTICLE............................... 46
Abstract ............................................... 46
Introduction ........................................... 47
Purpose ................................................ 50
Materials and Methods .................................. 50
Sample ............................................... 50
Data Collection ...................................... 52
Statistical Methods .................................. 57
Results ................................................ 57
Discussion ............................................. 60
vi
Angular Measurement Changes .......................... 62
Linear Measurement Changes ........................... 64
Conclusion ............................................. 70
Appendix ............................................... 71
Literature Cited ....................................... 73
Vita Auctoris .......................................... 77
vii
LIST OF TABLES
Table 3.1 - Measurement definitions . . . . . . . . . . . . . 54
Table 3.2 - Descriptive statistics of T1 and T2 . . . . . . . 58
Table 3.3 - Descriptive statistics of treatment changes . . . 59
Table 3.4 – Reliability statistics . . . . . . . . . . . . .
59
Table A.1 - Sample treatment duration . . . . . . . . . . . . 71
Table A.2 - Sample angle classification and crowding . . . . .72
viii
LIST OF FIGURES
Figure 2.1 – Example of maxillary MEAW wire . . . . . . . . .
27
Figure 2.2 - Example of maxillary Invisalign aligner . . . .
34
Figure 3.1 – Anatomical landmarks . . . . . . . . . . . . . .
53
Figure 3.2 - Cephalometric angular measurements . . . . . . .
55
Figure 3.3 – Cephalometric linear measurements . . . . . . .
56
Figure 3.4 – Sample superimposition of patient #12 . . . . . . 65
ix
CHAPTER 1: INTRODUCTION
Open bites pose as one of the more challenging
dentofacial deformities in the orthodontic world, as they
tend to defy treatment.1-3
Indeed, many researchers contend
that vertical discrepancies are more difficult to manage
than those in the anteroposterior dimension.4,
5
The
complexity of this particular bite stems from both the
mechanics needed to treat it and the efforts to combat its
high relapse tendency.
Due to lack of anterior contact,
anterior open bites can lead to excessive wear of the
posterior dentition, as the patient lacks anterior
disclusion.
Impairments with mastication and speech, in
addition to dissatisfaction with the esthetics of an open
bite, can negatively impact patients on a psychological and
emotional level.6
The etiology of anterior open bites is complex and
multifaceted.
It may develop from either oral habits,
excessive growth of lymphatic tissues, tongue position, or
a genetic predisposition.
While growing patients with oral
habits may be treated with interceptive orthodontic
appliances, treatment of adult patients presents a more
complex picture.
As Nahoum7 stated: “The diagnosis of a growing child is
different from that of an adult.
1
The adult presents us
with a fait accompli.
There is no hope for improvement
without treatment.” Thus, non-growing patients with
anterior open bites are often prescribed a treatment plan
involving a combination of surgery and orthodontics.8
Greenlee et al.’s9 meta-analysis on the long-term
stability of treatment of anterior open bites found that
both surgical and non-surgical correction had success rates
greater than 75% (with an 82% mean stability value for
patients treated surgically and 75% for patients treated
with orthodontics only).
This indicates that nonsurgical
orthodontics has nearly equal long-term stability outcomes,
while overall being a less invasive and more economical
option for the patient.
Non-surgical adult treatment of
anterior open bites involves either extrusion of the
anterior segment or, less commonly, intrusion of over
extruded posterior segments.
The rising popularity of
adult orthodontics, and lack of guaranteed stability with
both fixed appliance therapy and surgery, has generated
impetus to discover more effective treatment modalities for
anterior open bites.
One alternative practitioners have
turned towards is that of clear aligner therapy.
Upon arrival to the market, Invisalign (registered
trademark of Align Technology, Inc., Santa Clara, CA) was
promoted as an esthetic alternative to fixed labial
2
appliances.10 Initially, it was indicated for low complexity
cases, without skeletal discrepancies, mainly involving
mild crowding.
Since its inception, the appliance has
undergone several iterations to improve its ability to
achieve proper alignment and occlusion.
The Invisalign
system has rapidly evolved into what is now its sixth
generation; newly incorporated features ostensibly have
enabled it to treat more complex malocclusions.
Although the literature examining orthodontic
treatment with Invisalign is limited, a few investigators
have demonstrated its successful management of mild
anterior open bites.11-13
The appliance is purported to have
a bite block effect and to maintain vertical control, two
traits that make it an ideal treatment modality for open
bite cases.
Unfortunately, the few published studies are
case reports that do not adequately evaluate the
appliance’s capacity to maintain vertical control, a
parameter that is often worsened by the extrusive effects
of fixed appliance therapy.
The purpose of this study is to evaluate the vertical
effects of non-extraction, adult anterior open bite
treatment with the Invisalign system.
A cephalometric
appraisal will be conducted, as no current studies have
assessed the vertical dimension in this manner. It would be
3
beneficial to understand Invisalign’s influence on this
dimension in order to understand the appliance’s capacity
for vertical control.
4
CHAPTER II: REVIEW OF THE LITERATURE
Anterior Open Bite
Definition
Several conflicting definitions for dental anterior
open bites exist1, but the explanation that prevails in the
literature defines anterior open bites as a lack of
vertical overlap of the incisors.14-17
Its prevalence and
severity varies among different races; for the U.S.
population alone, studies have reported open bites in 16.3%
of black children and 4% of white children.18
The incidence
of open bites is reported to decrease from the mixed
dentition period into adulthood.19
This decline is a
byproduct of normal eruptive patterns, involution of the
adenoids, development of a normal adult swallow, and
cessation of oral habits.6
Although the prevalence appears
low, approximately 17% of orthodontic patients possess
anterior open bites20, indicating that thorough knowledge of
its diagnosis and treatment is paramount.
Etiology
A myriad of etiological influences may contribute to
the development of an anterior open bite.
Practitioners
often focus so closely on the dental and skeletal complex
5
that they overlook other external factors, such as muscular
and soft tissue components, that may be variables to
consider in the malocclusion. The treatment indicated, and
thus rendered, should depend upon the etiology behind each
specific case.
Vertical relationships are established and
dictated by the dynamic interplay between neuromuscular
activity, skeletal growth, dentoalveolar bone growth,
eruption patterns and oral habits.19
Some hereditary and
environmental factors contributing to open bites include:
vertical facial growth pattern, nasal airway obstruction,
abnormal tongue size or posture, and nonnutritive sucking
habits.6
Open bites during the primary and mixed dentition
years are mostly self-limiting.
In a cross-sectional study
examining 1,408 Navajo children ranging between ages 7-21
years of age, Worms19 discovered 80% had spontaneous
correction of their anterior open bites as they progressed
from mixed dentition into permanent dentition.
In
particular, a marked decrease in prevalence was noted
between the transition from the age group of 7-9 to 10-12
years of age.
Much of the correction observed was
attributed to growth that occurs between transitional
dental periods and the acquisition of normal swallowing
patterns.
Overall, it was found that open bites are in a
6
constant state of flux during the growth period and that
the prevalence varies with age and sex. If the open bite
extends into the permanent dentition phase, however,
orthodontic and/or surgical correction may be needed to
close the bite.
Thumb and finger sucking
Non-nutritive sucking continues to be one of the major
causes of anterior open bite amongst children.8
Distinguishing characteristics of a habitual dentoalveolar
open bite enables the practitioner to differentiate it from
one that is skeletal in nature. Anterior teeth are usually
over-erupted in skeletal open bites; whereas they tend to
be under-erupted with inadequate development of the
anterior alveolar processes, due to pressure of the foreign
object, in a habitual open bite.4
Often, the spatial
disposition of the teeth lends evidence to the offending
oral habit.
Common features of a thumb-sucker, for
example, include proclined maxillary incisors, retroclined
mandibular incisors1, and an asymmetric anterior open bite
mirroring the shape of the thumb.
An open bite due to over
usage of a pacifier would, instead, manifest as undereruption of maxillary and mandibular incisors, with the
open bite assuming a circular form.6
7
In a persistent thumb sucker, the tongue adopts an
inferior position which, along with hyper function of the
perioral musculature, causes maxillary constriction.
According to Graber21, thumb sucking in the first four years
of life is normal and may be a significant component of the
child’s psychological and emotional development.
It is
believed that that the habit is self-limiting and will
decline with normal growth and development.
Beyond
approximately 3.5 years of age, a continuation of the habit
may be indicative of delayed psychological maturation.21
Ultimately, the duration and intensity of the habit will
determine the severity of the open bite.1
More importantly,
if the habit does not cease at an appropriate time, the
sequela may remain permanent.
The open bite and increase
in overjet that follows a thumb-sucking habit may gradually
lead to secondary dysfunctions such as perioral muscle
aberrations, compensatory tongue thrust during deglutition
and mentalis strain.21
The concern, then, lies in the
potential for the sucking habit to pave the way for more
harmful forces to enhance the open bite.
Tongue thrust
In the longstanding debate over etiology of anterior
open bites, the exact influence of the tongue remains
8
unresolved.
A tongue thrust occurs when the tongue
protrudes against or between the incisors during
deglutition, resulting in excessive circumoral activity.16
The question still persists: Does the tongue thrust cause
the open bite or does the open bite cause the tongue
thrust? While some researchers consider the tongue thrust
as the primary etiological factor behind open bites, others
argue that tongue thrust is a result of the open bite
itself.
Straub22 submits that abnormal swallowing and
tongue thrusts cause open bites, but no data is presented
to substantiate his assertion.
Subtelny & Sakuda17 suggest,
instead, that the tongue adapts secondarily to the anterior
opening created by the thumb or finger.
This, they reason,
is why spontaneous self-correction of habit-related open
bites occurs once the habit is eradicated.
When the habit
ceases, anterior teeth erupt and the tongue readapts to the
new occlusion.
Nevertheless, they do acknowledge that an
excessively large or hyperactive tongue with a protruded
position may cause an open bite.
Tongue thrusting may be a result of multiple
influences.
Use of tongue thrusts during deglutition, also
referred to as infantile swallowing, may be the primary
mode of swallowing up to ten years of age.16
As previously
noted, the maturation of this swallowing reflex might serve
9
to explain the spontaneous correction of open bites Worms19
discovered to occur between the mixed and permanent
dentition phases.
In addition to compensatory tongue
thrust secondary to anterior open bites, Subtelny and
Sakuda17 suggested that severely enlarged tonsils and
adenoids may lead to mechanical obstruction of the
oropharynx and subsequent posturing of the tongue in a
forward position.
It is worth noting that the prevalence of tonguethrusting is greater than the open bite malocclusion
itself.16
Those who ascribe to the camp that tongue
pressure from thrusting is insufficient to cause the open
bite believe that the resting posture of the tongue is more
likely the culprit behind the malocclusion.
The teeth
appear to be unaffected by pressures exerted from the lip
and tongue during abnormal swallowing; resting posture
holds greater weight, as it can affect the eruption of
teeth.
As per the equilibrium theory, tooth movement is a
consequence of light, continuous forces, where the duration
of force outweighs force magnitude.23
Proffit23 argues that
the dentition is able to resist the short-acting forces of
tongue thrusting, which he believes to be more of an
effect- than cause- of open bites. In further support of
this idea, individuals may demonstrate consistent, abnormal
10
swallowing activity with tongue thrusts but have a normal
occlusion.24
Airway
The influence of naso-respiratory obstruction on
facial growth and form has long been a contentious matter.
The most common cause of mouth breathing is due to enlarged
adenoids6,
25
, although chronic allergies, nasal infections,
blocked turbinates and a deviated septum are other known
causes.16
When an oral mode of respiration dominates,
postural changes take place that aid in opening the oralpharyngeal airway, namely the lips separate and the
mandible drops down and back. It is thought that a more
vertical pattern of facial growth will ensue; with the
mandible open, this would promote eruption of the posterior
teeth and increase the lower anterior facial height, which
may heighten the potential for an anterior open bite to
develop.6,
26
There are several features supposedly typical of
persons with enlarged adenoids who are mouth-breathers, and
the term “adenoidal facies” has been coined to describe
this condition.
Common characteristics of adenoidal facies
include downward and backward posturing of the mandible,
incompetent lips, increased lower face height, and small
11
underdeveloped nostrils.3
Intraorally one might encounter a
constricted maxillary arch, a high palatal vault and
possibly a posterior crossbite.
Many researchers have
tried to resolve the form and function debate behind this
craniofacial morphology and respiratory behavior.
some25,
27
While
argue that adenoidal facies is the manifestation
of an obstructed airway, others28,
29
oppose with the idea
that the condition is genetically predetermined and thus
inherited.
Many researchers stand firmly behind the notion that
enlarged adenoids affect the mode of breathing and, in
turn, facial growth and characteristics of the dentition.
Linder-Aronson30 studied a group of children scheduled to
undergo adenoidectomies and found that mouth breathing was
prevalent in children with large adenoids and a small
nasopharynx.
The children presented with constricted
maxillary arches, crossbites or a crossbite tendency and
retroclination of the upper and lower incisors.
Furthermore, nasal obstruction due to adenoids was seen
most in leptoprosopic children who had a small nasopharynx.
While acknowledging the complexity of the issue, he admits
that other causal relationships are likely involved, and
suggests that perhaps the size of the nasopharynx is what
causes the mouth-breathing and possibly dictates the size
12
of the adenoids. In their study examining facial growth
patterns in children who are mouth-breathers versus nose
breathers, Bresolin et al.27 discovered that their mouth
breathers had longer faces, larger gonial angles, deeper
and narrower palatal vaults, and more retrognathic
mandibles as compared to nose breathers, which gives
further credence to the claim that upper respiratory
obstruction and mouth breathing leads to deviant facial
growth.
A well-known study designed to test the relationship
between mouth breathing and malocclusion was conducted by
Harvold31 in 1981.
Nose plugs were used to obstruct the
nasal passages in a group of rhesus monkeys in order to
induce mouth breathing and examine the resulting changes.
The animals responded differently, but eventually all
acquired facial and dental characteristics different from
that of the control group, including increased facial
height, mandibular plane angle and gonial angle.31
Caution
must be taken in extrapolating these findings to understand
mouth breathing in humans, as total nasal obstruction is a
rare occurrence in humans.
Rather, a combination of oral
and nasal airflow more accurately describes the human
respiratory mode.
13
Other investigators assert that mouth-breathing is not
capable of affecting facial growth considerably enough to
result in adenoid facies.
Ballard28 asserts his
longitudinal studies confirm that orofacial morphology is
generally constant throughout growth and the deviations
observed with adenoid facies are, in fact, predetermined
morphological traits.
Others have noted that adenoidal
facies does not necessarily exist in all children with
obstructive adenoids29 and not all patients with enlarged
adenoids achieve nasal respiration after an adenoidectomy.3
Fields et al.32 attempted to compare breathing behaviors
between normal and long-faced adolescents.
Even though
differences in airway variables, such as minimal crosssectional nasal area and tidal volume, were not
statistically different between the two groups, long-faced
subjects had a reduced percentage of nasal breathing.
In
other words, although measures of respiratory function were
comparable between both groups, they still demonstrated
significantly different modes of breathing.
This implies
that airway patency is not always related to breathing
mode.
Perhaps some individuals with normal airways remain
mouth breathers out of a habit stemming from a previously
established behavior.
14
A definitive cause and effect relationship cannot be
established between breathing mode and vertical dentofacial
morphology, as many unanswered questions still remain.
Most studies that examine the interaction between
respiratory obstruction and facial morphology are
subjective in nature and fail to adequately define nasal
obstruction.
Furthermore, the diagnostic tests that
otorhinolaryngologists use to assess airway obstruction are
neither valid nor reliable.3
There are, likewise, several flaws inherent in airway
studies, mainly that they base their quantification of
airway size and patency off of cephalometric radiographs.
While such studies may reveal a positive correlation
between these airway measurements and airflow, one must
assess the validity in exploring a three-dimensional
structure via a two-dimensional depiction.2,
3
Another
concern is that investigators use nasal resistance to
explain respiratory behavior, but nasal resistance
measurements have limitations that do not enable it to be
correlated with respiratory mode.2
At present, we do not
know what amount of nasal obstruction must be present to
influence facial growth or during which time period this
impediment exerts its greatest effect.3
15
Until these
concerns are addressed, we can at best acknowledge these
associations with caution.
Skeletal growth aberrations
In open bites that continue into, or even develop in,
the late stages of growth, one must consider aberrant
skeletal growth as a causative factor.
As Nanda33 mentions
in his study examining vertical growth, “The expression of
disharmonious proportions in the facial skeleton can be
attributed to the failure of normal, coordinated growth of
the various regions of the craniofacial complex in terms of
timing, magnitude, and direction.”
A favorable growth
pattern could perhaps close the bite and improve the
prognosis of the treatment.
Conversely, if a particular
structure exhibits deviant growth while other sites grow
normally, an open bite could result.
Bjork34 states genetic
and environmental factors that induce growth in the molar
region, without adequate compensatory growth at the condyle
or ramus can lead to an anterior open bite.
Schudy35 adds
that overbite is dictated by the relationship between
vertical and horizontal growth.
He believes that downward
movement of the maxillary molar during growth is the most
important determinant of facial height and accounts for
seventy per cent of vertical facial growth.
16
Therefore
growth in strategic sites, such as the posterior face
height, may ultimately govern the success of treatment.7
Temporomandibular joint pathology
Condylar resorption may result from an array of
etiologies including condylar fractures, autoimmune
diseases, rheumatoid arthritis, orthognathic surgery, and
TMJ internal derangement.
It should be considered in the
differential diagnosis of patients who present with an
acquired and progressive open bite.
Open bites due to
condylar resorption may lead to clockwise rotation of the
mandible, with a resultant Class II malocclusion and
mandibular retrognathia.36
Morphology of Skeletal Open Bite
Categorizing an open bite as entirely skeletal or
dentoalveolar is problematic, as many open bites feature
elements of both kinds of dysplasia.
Nevertheless, the
skeletal morphology between a skeletal versus a habitual
dentoalveolar open bite is quite different. Various
skeletal components have been studied in an attempt to
characterize skeletal open bites.
Unfortunately, no single
site can be pinpointed as a marker for all skeletal open
bite cases.
Rather, the sites of dysplasia are numerous
17
and differ for each individual patient, but all must be
taken into account. According to Taibah et al,37 most
researchers agree upon certain elements of an open bite,
namely increased mandibular plane angle, increased gonial
angle, increased lower anterior face height and decreased
interincisal angle. Most disagreement has centered around
the following features: palatal plane angle, cranial base
angle, ramus height, upper face height, posterior facial
height and dental heights.7,
13, 17, 33, 37-40
Findings for
several of these dimensions will be elaborated upon
briefly.
Face height
Most investigators7,
17, 37, 41, 42
agree that skeletal open
bite patients have a larger lower anterior facial height
(LAFH), which is often attributed to an upward cant of the
anterior aspect of the palatal plane.
It is thought by
some that the upward cant produces a short upper anterior
face height (UAFH), thereby lengthening the LAFH7.
This
finding is at variance with other studies, however, which
reported normal upper facial dimensions.40,
42
Similar controversy exists over the posterior
dimension.
In their longitudinal study comparing open
versus deep bite subjects, Sassouni and Nanda43 discovered
18
their open bite subjects had shorter rami, but
Richardson’s44 retrospective study found no difference.
Subtelny & Sakuda17 carried out a cephalometric comparison
between twenty-five subjects with persistent open bites and
thirty subjects with normal occlusions and reported no
significant differences in the posterior vertical
dimensions of the open bite patients.
Other authors4,
38, 41
contend there is a definite decrease in the posterior
vertical dimension.
Nahoum7 believed that the ratio of upper anterior
facial height to lower anterior facial height (UAFH/LAFH)
was a vital measurement that should be used in diagnosing
open bite cases.
He submits that patients with a dental
open bite and a UAFH/LAFH ratio below .650 will have a poor
orthodontic prognosis and should be considered surgical
candidates.
Palatal plane
It has also been suggested that the posterior segment
of the palatal plane is tipped downward; this would
displace the molars downward, leading to clockwise rotation
of the mandible and an increased lower anterior facial
height.41
With anterior nasal spine (ANS) being the point
that divides UAFH from LAFH, Nahoum39 maintained that the
19
palatal plane contributes significantly to the anterior
facial height ratio. He postulated that the tipping of the
palatal plane results in a smaller upper face height and
concomitant increase in LAFH in open bite subjects.
This
claim is substantiated through his data that depicted SN-PP
angle measures that were smaller, and PP-MP angle measures
that were greater, on average, for open bite subjects than
for normal subjects.
This remains controversial, however,
as other authors have noted the SN-PP angle does not differ
in open bite groups.17
Occlusal plane
The occlusal plane is generally regarded as being
steep in open bite patients.41
Conventionally, the
constructed (bisected) occlusal plane bisects the overlap
of the mesial cusps of the first permanent molars and the
incisor overbite or open bite. Nahoum7 felt it was
inaccurate to use this plane in open or deep bite cases
and, instead, defined two separate, maxillary and
mandibular occlusal planes.
He observed the maxillary
occlusal plane tends to cant upward alongside the palatal
plane, versus the mandibular occlusal plane which tips
downward.
Nahoum38 and Taibah37 only reported significant
increases in the mandibular occlusal plane angle, as
20
compared to control groups, while Nanda45 found no
difference in the occlusal plane angle in open bite
subjects.
Cranial base
It has been asserted that the cranial base angle is
reflective of the glenoid fossa and temporomandibular joint
positions.
Therefore, an acute angle would suggest a
forward position of the mandible, whereas an obtuse angle
would reveal a retrusive position.45
Some investigators
further advanced the idea that the cranial base angle is
obtuse in open bite patients.41 Other authors contend that
the cranial base angle is not significantly different in
open bite patients and that the angle should not be
utilized as a marker for identifying vertical dysplasias of
the face.7,
45
Mandibular plane
There is more consensus regarding hallmark features of
the mandible, including an increased mandibular plane angle
in open bite subjects.1,
37, 41
It is thought that an
increased mandibular plane angle is indicative of a
backwards rotational growth pattern, which increases the
anterior facial height.
Some investigators have attempted
21
to use the mandibular plane as a prognostic criteria in
diagnosis of facial types and as a predictor of the
direction of facial growth.46
However, Bjork34 asserts that
an increased mandibular plane angle is apparent in both
backward and forward mandibular growth patterns and is,
therefore, not a valid predictor of facial growth.
Although some angular and linear features prevail in
skeletal open bites, no causal relationship can be
established between these skeletal variations.
Previous
studies exhibit conflicting findings, likely owing to
differences in methodology and sampling.
While some
studies are cross-sectional, others are longitudinal in
design.
Furthermore, the data sources are mixed, as
certain studies compared open bites subjects to deep bite
subjects, versus others compared open bite groups to normal
control groups.
This could introduce bias into the study,
potentially skewing the results.
Suffice it to say,
several features do, in fact, have strong associations with
skeletal open bites which, when identified, will enable the
clinician to make a more apt diagnosis.
22
Morphology of Dental Open Bite
Dentoalveolar open bites will exhibit characteristics
indicative of the etiology.
Since the bite opening is
often due to a habit involving a foreign object, the open
bite is usually restricted to the incisor region.
Cephalometric analysis may show a decrease in alveolar
height in the maxillary incisor region, as well as angular
and linear evidence of protruded maxillary incisors.1
The
mandibular incisors may be retroclined and crowded if a
thumbsucking habit exists but the patient may not display
skeletal characteristics related to vertical dysplasia,1
i.e., greater eruption of the dentoalveolar segments near
the maxillary molars and incisors.17
Diagnosis
For diagnostic measures, open bites have generally
been grouped into two categories: 1) Dentoalveolar
2) Skeletal.1,
7
As previously discussed, dentoalveolar
bites tend to be acquired via habits and do not display any
overt craniofacial dysplasia.
Skeletal open bites, on the
other hand, are persistent bites that are likely linked to
skeletal growth aberrations.
The treatment plan must focus
on the origin of the malocclusion for a favorable prognosis
to occur.
Given the complex nature of open bites, it is
23
often difficult to pinpoint the exact cause.
Practitioners
may be unable to correct the problem even if the cause is
known, as would be the case with a patient who refuses to
wear elastics or refuses surgery.
Prognosis of treatment is contingent upon correct
analysis of the open bite as one that derives from either a
skeletal dysplasia or from a dentoalveolar origin.
Proper
attention must be given towards the methods used for
diagnosis.
Cephalometry, for instance, lacks the ability
to account for functional patterns such as oral habits,
nasal obstruction, abnormal swallowing and speech patterns,
and atypical posturing of the tongue.4
As a result, the use
of cephalometry alone for diagnostic purposes can
potentially lead to misdiagnosis.
This may be one of many
reasons open bite cases are prone to relapse.47
As with
most differential diagnosis, all probable genetic and
environmental factors should be taken into account.
Treatment
Proper treatment of anterior open bites rests strongly
on correct diagnosis and understanding of its
multifactorial nature, and is the reason behind the
multiple treatment modalities that exist to correct it.
The practitioner must take care to employ the correct
24
mechanics and avoid worsening the open bite via further
clockwise rotation of the mandible, which could lead to an
increased anterior face height.
Even more, the treatment
plan should pertain to the etiology of the malocclusion for
the prognosis to be stable. Orthodontists must be cognizant
of what sorts of anatomic liabilities their mechanotherapy
may have.
For instance, if supra-eruption of maxillary
incisors is prevalent in a skeletal open bite case,
treatment with vertical elastics to extrude the incisors
would prove fruitless.
Treatment can be broken down into four main
modalities: 1) Orthodontic mechanotherapy 2) Myofunctional
therapy 3) Surgery 4) Combination of orthodontics &
surgery.
Some examples of treatments include high pull
headgear, chin cups, multi-loop edgewise archwires, bite
blocks, functional appliances, habit control, extractions
and surgery. It is essential for the orthodontist to
diagnose the etiology of the open bite carefully so that he
or she may select the treatment most suitable for the
patient.
A few treatment modalities for adult open bites
will be discussed briefly.
25
Multiloop edgewise archwire
The multiloop edgewise archwire (MEAW) technique
employs the use multilooped archwires and anterior vertical
elastics to close anterior open bites.
The objective of
this technique is to achieve positive overbite, to correct
the cant of the occlusal planes, and to address the mesial
inclination of the posterior teeth.15
This is purportedly
achieved via uprighting and retrusion of the posterior
dentition, and retraction and extrusion of the anterior
teeth, which enables the occlusal planes to converge.15
MEAW has been shown to have more dentoalveolar than
skeletal effects. In a cephalometric evaluation of the
treatment effects of MEAW, Endo et al.48 demonstrated that
open bite correction with MEAW is predominantly due to
extrusion and uprighting of the maxillary and mandibular
incisors.
Additionally, it was found that extrusion of the
posterior segments caused unfavorable downward and backward
rotation of the mandible.48
While MEAW has proved itself capable of treating
anterior open bites, no significant skeletal changes are
seen in nongrowing patients.49
A non-biased assessment of
treatment efficacy is difficult, as most MEAW cases are
performed in conjunction with extractions.
Regarding
stability, Kim et al.49 found a relapse rate of 6% in
26
growing patients and 10% in non-growing patients treated
with his MEAW technique.
These relapse rates appear low
but, of the 55 patients he treated, the two-year follow up
examined only 27 patients.
The technique, albeit useful,
is labor intensive, makes hygiene difficult, and requires
full patient compliance with elastic wear.
Figure 2.1 Example of maxillary MEAW wire15
Extractions
Removal of first molars, second molars, and premolars
have all been suggested as extraction options for treatment
of anterior open bites.
Many investigators believe that
extractions contribute to a bite-closing effect. It is
hypothesized that protraction of premolars or molars,
without extrusion, into the extraction spaces will decrease
the palatomandibular wedge, enabling counterclockwise
rotation of the mandible.50 This would prove particularly
beneficial for patients with high mandibular plane angles
and increased facial heights. In reality, the potential
27
extrusive effects of orthodontic tooth movement may offset
the benefits of the “wedge effect.”51 Extraction treatment
in anterior open bite cases does not always lead to a
mandibular rotational change or an improvement of the
vertical dysplasia.
Chua et al.52 reported that non-
extraction treatment resulted in a downward and backward
rotation of the mandible, accompanied by an increased LAFH.
No significant changes in LAFH, however, were observed in
subjects treated with extractions.
Interestingly, when
Zafarmand and Zafarmand51 examined the effects of bicuspid
extraction on LAFH, they found LAFH increased significantly
in their extraction groups.
This was attributed to the
“inherent extrusive effect of most orthodontic treatment
modalities, i.e., molar protraction, which can be adversely
compensative to facial height reduction.”51
While the
aforementioned studies observed these effects in normodivergent patients, Cusimano et al.53 found that mandibular
plane angle increased slightly, but not significantly, in
their high angle patients post-extraction. They posit that
occlusal movement of the molars nullified the bite-closing
effect of posterior protraction.
Therefore, it appears
extractions either maintain the vertical dimension or
slightly open it in high angle patients.
Although some
investigators believe extraction treatment of
28
hyperdivergent facial types reduces the vertical, these
studies indicate that extraction treatment alone may not be
sufficient in controlling the vertical.
Skeletal anchorage systems
Many investigators contend that maxillary incisor
extrusion in adult patients may compromise the periodontal
structures, lead to root resorption and ultimately
jeopardize smile esthetics.54
Other authors have shown
extruded teeth to be less stable than intruded teeth55 and
have, instead, turned their efforts towards posterior
intrusion.
Molar intrusion is often needed if a skeletal open
bite is to be corrected non-surgically.56
The use of
skeletal anchorage systems, such as mini-implants and
miniplates, has been promoted for closure of anterior open
bites via molar intrusion.
The studies conducted have
shown promise, with true maxillary and mandibular molar
intrusion leading to counterclockwise rotation of the
mandible and, consequently, closure of the bite.54,
56
Concomitant reduction of the mandibular plane angle and
anterior face height usually follow.
Other advocated treatment alternatives such as highpull headgear, vertical chin cup, vertical holding
29
appliance, or an active vertical corrector cannot achieve
effective molar intrusion in adult patients due to lack of
rigid anchorage.56 Presumably, open bite closure through
posterior intrusion and little to no anterior extrusion
leads to more stable outcomes.55
Baek et al.57 investigated
the long term stability of anterior open bite correction
after intrusion of maxillary posterior teeth; they observed
22.88% relapse of the maxillary molars and 17% relapse of
the incisal overbite after a three year follow up period.
Unfortunately, the majority of literature involving
skeletal anchorage and open bites are case reports lacking
long-term follow up studies examining stability.20
Fixed appliance therapy
Most of the literature evaluating the dento-skeletal
effects of open bite therapy is centered on early treatment
of growing patients.
With the exception of case reports,
there is a lack of sound data examining the effects of
fixed appliance therapy in adult anterior open bite
patients.
When Remmers et al.58 evaluated treatment results
and stability in a large group of anterior open bite
adolescent patients, they discovered mean overbite
increased from -3.2 mm pre-treatment to .4 mm posttreatment, with 71% of the sample obtaining a positive
30
overbite.
Mean values for MP-PP and SN-MP decreased
insignificantly, while the mean value for SN-PP increased
insignificantly post-treatment.
There were no appreciable
differences in these angular measurements over five years
post-treatment.
The relapse rate was 27% five years post-
treatment and, overall, 44% of the sample had an open bite
at five years follow-up.
The authors admit, “The poor
treatment response between Ts and T0 in the present study
raises the question whether conventional edgewise treatment
can adequately control the vertical dimension.”58
One variation of the MEAW technique uses upper
accentuated-curve and lower reverse-curve NiTi arch wires
with intermaxillary elastics; this theoretically offsets
the anterior intrusive forces of the wire and allows the
posterior intrusive forces to take effect while extruding
the anterior teeth.
Once incisal overlap is achieved,
stainless steel wires are placed and patients are directed
to wear box elastics.
Kucukkeles et al.59 observed the
dentofacial effects of this method on adult anterior open
bite patients and found that LAFH increased significantly
by 2.5 mm (p < .001) post-treatment, which the authors
believed to be a consequence of molar extrusion.
Interestingly, the mandibular plane angle was maintained
throughout treatment. SN to the functional occlusal plane
31
(FOP) decreased by 2.09˚ (p <.01) and the FOP-MP increased
by 2.38˚ (p <.001). The counterclockwise rotation of the
FOP can be accounted for by the extrusion of the lower
premolars and uprighting of the lower molars. Upper and
lower incisors and first molars were all extruded while
being uprighted.
As compared to the MEAW technique, this
method proves to be more efficient, hygienic and
comfortable for the patient.
However, bite-closure is
primarily achieved through extrusion of the incisors which
is not always ideal, particularly in those individuals
already presenting with excess gingival display at the
outset of treatment.
Surgery
If patients present with a true skeletal open bite, a
combined surgical-orthodontic approach is often encouraged
to attain an esthetic and stable treatment result. A common
surgical technique utilized for skeletal open bites is
posterior maxillary impaction.
Superior repositioning of
the maxilla allows for autorotation of the mandible,
closure of the bite, and a decreased LAFH.60
If the open
bite it not severe, however, it is hard to justify the
risks and trauma involved with surgery to achieve a
correction with no guaranteed stability.
32
Invisalign
Invisalign, clear removable aligners, was first
introduced to the U.S. market in 199961; sixteen years
later, the technology is still met with much skepticism.
Initially, this was not unwarranted, as the earliest
version of the system attempted to accomplish tooth
movement solely via the aligner, without the use of
auxiliaries or attachments.
At that point in time, fixed
appliances were undoubtedly better suited for treatment of
moderate to severe malocclusions.10
Even after the second
generation’s incorporation of attachments and buttons for
the use of inter-maxillary elastics, crown and root
movement limitations were still apparent.
The appliance
has continued to evolve rapidly, however, and is
continuously modified in attempt to produce forces
comparable to what fixed appliances exert.10 Development of
improved attachments and tray material is postulated to
have enabled better control of tooth movements that were
originally unpredictable, i.e., rotational control, root
torqueing, extrusion and closure of extraction spaces.10,
61
At present, the usage of the appliance has broadened to
include treatment of complex malocclusions, including
surgical cases and those involving extractions.13,
33
61
There
is a paucity of literature pertaining to orthodontic
treatment with the Invisalign system, even more only a
handful related to treatment of open bites.
Figure 2.2 Example of maxillary Invisalign aligner62
Invisalign has been suggested as a viable treatment
option for mild anterior open bites.
It has been
hypothesized that the thickness of the aligners across the
occlusal surfaces, in concert with masticatory forces,
creates an intrusive force in the posterior segments, thus
resulting in bite closure.61
Schupp et al.13 presented two
case reports of anterior open bite patients treated
successfully with Invisalign via a combination of incisor
extrusion and molar intrusion.
34
Both cases were reported as
stable one year post-treatment, with no noted relapse of
the open bite.
Apart from bite closure, treatment effects
cannot be further assessed in these cases since no
cephalometric analysis was presented.
Guarneri et al.11
similarly illustrate an 18-month Invisalign treatment that
achieved bite closure of a 4 mm open bite in a 35-year-old
female via incisor extrusion.
The superimposition of their
pre- and post-treatment cephalometric tracings reveals the
mandibular plane angle remained the same during treatment.
This is in agreement with Boyd’s61 findings, as well.
Harnick12 concurs that clear aligner therapy, as compared to
fixed appliances, provides the biomechanical advantage of
vertical control. Nonetheless, caution must be exercised in
drawing conclusions from these case reports.
As previously noted, it is hypothesized that the biteblock effect of Invisalign makes the system an ideal
candidate for open bite treatment, as the thickness of the
aligners supposedly contributes a posterior intrusive
effect.
As Iscan and sarisoy63 found, posterior bite blocks
improve open bites by increasing the vertical dimension of
the patient, thereby exerting pressure on the mandible’s
neuromuscular system.61
The resultant vertical forces act
to intrude the buccal segments and lead to a
counterclockwise rotation of the mandible.
35
Other studies
corroborate that a decrease in mandibular plane angle
results from forwards and upward rotation of the mandible
after treatment with posterior bite-blocks.64,
65
Invisalign has become increasingly sought after with
adult orthodontics and demand for esthetic alternatives on
the rise.
The subtlety of the appliance appeals to
patients, particularly adults who have undergone previous
orthodontic treatment with fixed appliances and have no
desire for retreatment in braces.61,
66
The appliance is
still relatively new to the orthodontic world, however, and
there are many unanswered questions concerning its clinical
efficacy.
Ultimately, the success of the Invisalign system rests
in the hands of both the orthodontist and the patient.
While patient compliance is essential, clinical expertise
and a mastery of the ClinCheck system by the orthodontist
plays a crucial role in the overall treatment outcome.
As
with fixed appliance therapy, each Invisalign treatment
plan has a unique set of mechanics and methodologies behind
resolving malocclusions.
36
Statement of Thesis
The search for effective treatment modalities for
anterior open bites continues.
Controversy remains over
the treatment indications for Invisalign and the complexity
of cases that can be treated effectively with this system.67
To date, the majority of published studies pertaining to
treatment of open bites with Invisalign are case reports.
The lack of sound scientific evidence continues to feed the
suspicion of many clinicians towards the appliance.
As
orthodontists, we are responsible for understanding and
embracing the latest technological advancements in our
field, albeit cautiously in order to protect our patients.
Many patients, who would otherwise not have sought
treatment, have considered orthodontic care because of the
esthetic, removable nature of Invisalign.
Until further
investigation is conducted, its clinical potential will
remain uncertain.
A paucity of scientific data exists regarding
treatment of adult anterior open bite patients with
Invisalign.
The purpose of this study is to conduct a
cephalometric evaluation of the vertical effects of
nonextraction, anterior open bite treatment in adult
patients with the Invisalign system.
37
As such, this study
will enable practitioners to consider an alternative
treatment modality they can adopt into their orthodontic
armamentarium.
38
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45
CHAPTER 3: JOURNAL ARTICLE
Abstract
Objective:
The purpose of this study is to evaluate, via
cephalometric appraisal, the vertical effects of nonextraction treatment of adult anterior open bites with the
Invisalign system.
Materials and Methods: Lateral
cephalograms of thirty adult anterior open bite patients
treated with Invisalign (22 females, 8 males; mean age at
start of treatment: 28 years 10 months; range: 16y11m –
54y3m) were collected from three private practitioners.
Pre- and post-treatment cephalograms were traced to compare
the following vertical measurements: SN to maxillary
occlusal plane (SN-MxOP), SN to mandibular occlusal plane
(SN-MnOP), mandibular plane to mandibular occlusal plane
(MP-MnOP), SN to mandibular plane (SN-MP), SN to palatal
plane (SN-PP), SN to gonion-gnathion plane (SN-GoGn), upper
1 tip to palatal plane (U1-PP), lower 1 tip to mandibular
plane (L1-MP), mesiobuccal cusp of upper 6 to palatal plane
(U6-PP), mesiobuccal cusp of lower 6 to mandibular plane
(L6-MP), lower anterior facial height (LAFH), and overbite
(OB).
Paired t-tests and descriptive statistics were
utilized to analyze the data and note any significant
changes resulting from treatment. Results: Statistically
46
significant differences were found in overall treatment
change for SN-MxOP, SN-MnOP, MP-MnOP, SN-MP, Sn-GoGn, L1MP, L6-MP, LAFH, and OB.
Conclusions: The Invisalign
system is a viable therapeutic modality for non-extraction
treatment of adult anterior open bites.
Bite closure was
achieved by a combination of lower molar intrusion and
lower incisor extrusion.
Introduction
Open bites pose as one of the more challenging
dentofacial deformities in the orthodontic world, as they
tend to defy treatment.1-3
Indeed, many researchers contend
that vertical discrepancies are more difficult to manage
than those in the anteroposterior dimension.4,
5
The
complexity of this particular bite stems from both the
mechanics needed to treat it and the efforts to combat its
high relapse tendency.
Due to lack of anterior contact,
anterior open bites can lead to excessive wear of the
posterior dentition, as the patient lacks anterior
disclusion.
Impairments with mastication and speech, in
addition to dissatisfaction with the esthetics of an open
bite, can negatively impact patients on a psychological and
emotional level.6
47
The etiology of anterior open bites is one that is
complex and multifaceted.
It may develop from either oral
habits, excessive growth of lymphatic tissues, tongue
position, or a genetic predisposition.
While growing
patients may be treated with interceptive orthodontic
appliances, treatment of adult patients presents a more
complex picture once growth has ceased and habit-related
sequela assume permanence.
As Nahoum7 frankly stated: “The diagnosis of a growing
child is different from that of an adult.
presents us with a fait accompli.
The adult
There is no hope for
improvement without treatment.” Thus, nongrowing patients
with anterior open bites are often prescribed a treatment
plan involving a combination of surgery and orthodontics.8
Greenlee et al.’s9 meta-analysis on the long-term
stability of treatment of anterior open bites found that
both surgical and non-surgical correction had success rates
greater than 75% (with an 82% mean stability value for
patients treated surgically and 75% for patients treated
with orthodontics only).
This indicates that nonsurgical
orthodontics has nearly equal long-term stability outcomes,
while overall being a less invasive and more economical
option for the patient.
Non-surgical adult treatment of
anterior open bites involves either extrusion of the
48
anterior segment10 or, less commonly, intrusion of overextruded posterior segments.10-12
The rising popularity of
adult orthodontics, and lack of guaranteed stability with
both fixed appliance therapy and surgery, has generated
impetus to discover more effective treatment modalities for
anterior open bites.
One alternative practitioners have
turned towards is that of clear aligner therapy.
Upon arrival to the market, Invisalign was promoted as
an esthetic alternative to fixed appliances.13
Initially,
it was indicated for low complexity cases, without skeletal
discrepancies, mainly involving mild crowding.
Since its
inception, the appliance has undergone several iterations
to improve its ability to achieve proper alignment and
occlusion.
The Invisalign system has rapidly evolved into
what is now its sixth generation; newly incorporated
features ostensibly have enabled it to treat more complex
malocclusions.
Although the literature examining orthodontic
treatment with Invisalign is limited, a few investigators
have demonstrated its successful management of mild
anterior open bites.14-16
The appliance is purported to have
a bite block effect and to maintain vertical control, two
traits that make it a possible treatment alternative for
open bite cases.
Unfortunately, the few published studies
49
are case reports that do not adequately evaluate the
appliance’s capacity to maintain vertical control, a
parameter that is often worsened by the extrusive effects
of fixed appliance therapy.
Purpose
The purpose of this study is to evaluate the
vertical effects of non-extraction, adult anterior open
bite treatment with the Invisalign system.
A cephalometric
appraisal will be conducted, as no current studies have
assessed the vertical dimension in this manner. It would be
beneficial to understand Invisalign’s influence on this
dimension in order to understand the appliance’s capacity
for vertical control.
Materials and Methods
Sample
Pre-treatment (T1) and post-treatment (T2) lateral
cephalograms of thirty adult anterior open bite patients
treated with Invisalign were collected from three private
practice orthodontists.
Anterior open bite was defined as
a lack of vertical overlap between the upper and lower
incisors.
The sample was comprised of 22 females and 8
males, with a mean age of 28.81 years (range: 16y11m –
50
54y3m) at the outset of treatment.
No discrimination as to
Angle classification of malocclusion was made. The sample
consisted of 24 Angle Class I patients and 6 Angle Class II
patients.
Twenty-four sets of records were obtained from
practice A, four sets of records were obtained from
practice B, and two sets of records were obtained from
practice C.
The patient selection criteria were as
follows:

Patients were all non-growing at the outset of
treatment, determined via the cervical vertebral
maturation technique

No vertical overlap between the upper and lower
incisors, with edge-to-edge canines deemed
acceptable

No extractions of permanent teeth were performed
during treatment

No orthognathic surgery was performed as a part
of treatment

The patients were treated exclusively with
Invisalign and anteroposterior elastics during
treatment

Pre- and post-treatment lateral cephalograms were
available for each patient
51
Care was taken to ensure that all private
practitioners had at least elite provider status,
indicating that they treat, at minimum, up to one hundred
Invisalign cases per year.
The overall goal of each treatment was to achieve
overbite reduction in order to attain vertical overlap, or
positive overbite, of the maxillary and mandibular
incisors.
Data Collection
Pre-treatment and post-treatment digital and analog
lateral cephalograms were collected, scanned, and traced
for each patient digitally in the Dolphin Imaging software
program (Dolphin Imaging version 11.8 Premium).
Thirty-
three hard tissue landmarks were identified and traced, in
addition to two reference landmarks on each radiograph
(Figure 3.1).
The mandibular and maxillary occlusal planes
were manually traced and all occlusal plane measurements
were measured manually.
Six linear and six angular
measurements were completed (Figure 3.2, Figure 3.3).
52
Figure 3.1. Anatomical landmarks: Sella(1); Nasion(2); Posterior
nasal spine(3); Anterior nasal spine(4); U6 mesiobuccal cusp(5);
L6 mesiobuccal cusp(6); U1 incisor tip(7); L1 incisor tip(8);
Gnathion(9); Menton(10); Inferior gonion(11).
53
Table 3.1.
Measurement definitions
Measurement Definition
SN-MxOP
Angle formed by SN and the maxillary occlusal plane (plane
drawn through the mesiobuccal cusp tip of the maxillary
molar to the upper central incisor tip)
SN-MnOP
Angle formed by SN and the mandibular occlusal plane (plane
drawn through the mesiobuccal cusp tip of the mandibular
molar to the lower central incisor tip)
MP-MnOP
Angle formed by mandibular plane (inferior gonion to menton)
and the mandibular occlusal plane
SN-PP
Angle formed by SN to palatal plane (ANS to PNS)
SN-MP
Angle formed by SN to mandibular plane (inferior gonion to
menton)
SN-GoGn
Angle formed by SN and the plane drawn through the points
inferior gonion and gnathion
U1-PP
The millimetric distance between U1 tip and the palatal
plane (ANS to PNS)
L1-GoGn
The millimetric distance between L1 tip and the plane drawn
through inferior gonion-gnathion
U6-PP
The millimetric distance between the mesiobuccal cusp tip of
the maxillary molar and the palatal plane (ANS to PNS)
L6-GoGn
The millimetric distance between the mesiobuccal cusp tip of
the mandibular molar and the plane drawn through inferior
gonion-gnathion
LAFH
The millimetric distance between ANS and menton
OB
The vertical millimetric distance from U1 tip to L1 tip
54
Figure 3.2. Cephalometric angular measurements: SN-GoGn(1); SNMP(2); SN-MxOP(3); SN-MnOP(4); SN-PP(5); MP-MnOP(6).
55
Figure 3.3. Cephalometric linear measurements: U6-PP(1); U1PP(2); OB(3); LAFH(4); L1-GoGn(5); L6-GoGn(6).
56
Statistical Methods
The data in this study was analyzed via IBM SPSS
Statistics 23.0 statistical analysis software (SPSS Inc.,
Chicago, Illinois).
Descriptive statistics and paired t-
tests were used to compare the changes between pre- and
post- treatment measurements.
All digital and manual
tracings were performed by the same investigator.
To
evaluate intra-examiner reliability, 10% of the
cephalograms were chosen at random and re-traced;
Cronbach’s alpha test was used to determine measurement
reliability.
Intra-class correlation values of at least
0.80 were considered acceptable in terms of reliability.
Results
Descriptive statistics (Table 3.2) and paired t-tests
(Table 3.3) used to analyze the data revealed that nine of
the twelve variables measured were statistically
significant in overall treatment change. Statistically
significant (p<.01) changes were found in SN-MxOP, SN-MnOP,
MP-MnOP, SN-MP, SN-GoGn, LAFH, overbite, and L1-MP.
Statistically significant (p<.05) changes were also
observed in L6-MP.
SN-PP, U1-PP, and U6-PP did not undergo
any statistically significant changes.
57
Chronbach’s alpha tests for intra-examiner reliability
was above 0.80 for all variables except for overbite
(Cronbach’s alpha= 0.63).
With regard to accuracy of
measurements, overall, the original and repeated
measurements were at an adequate level of reliability.
Table 3.2. Descriptive statistics of T1 and T2.
Measurement
SN-MxOP (˚)
Pre-treatment (T1)
Mean
S.D.
18.0
5.0
Post-treatment (T2)
Mean
S.D.
20.6
5.4
SN-MnOP (˚)
20.7
5.5
16.2
5.6
MP-MnOP (˚)
20.2
5.1
24.7
4.6
SN-PP (˚)
7.8
4.2
7.5
4.7
SN-MP (˚)
40.8
7.2
39.9
6.9
Sn-GoGn (˚)
37.6
7.1
36.7
6.9
LAFH (mm)
74.3
5.3
72.8
5.2
OB (mm)
-1.8
1.2
1.5
.9
U1-PP (mm)
30.7
2.8
31.2
2.6
L1-MP (mm)
38.3
2.8
39.1
3.1
U6-PP (mm)
25.4
2.2
25.0
2.3
L6-MP (mm)
31.3
2.5
30.7
2.4
58
Table 3.3. Descriptive statistics of treatment changes.
T1-T2 Difference
Measurement
Mean
S.D.
Significance
SN-MxOP (˚)
2.6**
2.4
<0.001
SN-MnOP (˚)
-4.6**
4.2
<0.001
MP-MnOP (˚)
4.5**
3.7
<0.001
SN-PP (˚)
-0.3
2.4
0.505
SN-MP (˚)
-0.9**
1.5
0.002
Sn-GoGn (˚)
-0.9**
1.6
0.006
LAFH (mm)
-1.5**
2.8
0.006
OB (mm)
3.4**
1.4
<0.001
U1-PP (mm)
0.5
2.0
0.137
L1-MP (mm)
0.8**
1.2
<0.001
U6-PP (mm)
-0.4
1.4
0.118
L6-MP (mm)
-0.6*
1.4
0.022
* denotes changes are significant at p<.05
** denotes changes are significant at p<.01
Table 3.4. Reliability Statistics
Variable
Cronbach’s Alpha
SN-MxOP
.958
SN-MnOP
.864
MP-MnOP
.965
SN-PP
.950
SN-MP
.983
SN-GoGn
.987
LAFH
.993
OB
.629
U1-PP
.837
L1-MP
.923
U6-PP
.946
L6-MP
.825
59
Discussion
This study endeavored to evaluate the vertical effects
of non-extraction, anterior open bite treatment in adult
patients with the Invisalign system.
A plethora of
evidence lends credence to the idea that skeletal open bite
patients tend towards high mandibular plane angles1,
and large lower anterior facial heights (LAFH).7,
17, 18
12, 17-19
Schudy20 claimed the main goal of open bite treatment should
be to prevent an increased anterior face height and
emphasized that molars should not be extruded during
treatment.
However, the success of anterior open bite
treatment is often gauged by positive maxillary and
mandibular incisal overlap, which is usually obtained at
the expense of adverse sequela. Fixed appliance therapy has
a tendency to worsen the vertical dimension in open bite
patients, who more often present as hyperdivergent, longfaced individuals.6,
17, 21, 22
Non-surgical options for correction of anterior open
bites in adults are limited.
It is commonly thought that
extractions enable a bite-closing effect by allowing
protraction into the extraction space, thereby decreasing
the palatomandibular wedge.
The literature regarding
extraction treatment does not support this idea, however,
as several authors have shown that extractions can, in
60
fact, lead to an increased lower anterior facial height23
and a larger mandibular plane angle.24
In actuality,
protraction during space closure may cause occlusal
movement of the posterior segments, which essentially
cancels out the so-called “wedge effect.”
Post-treatment increases in lower anterior facial
height have been observed in non-extraction treatment as
well.25
Anterior segments must be extruded via elastics, or
posterior segments intruded, to achieve bite closure with
fixed appliances.
The multiloop edgewise archwire (MEAW)
technique employs anterior elastics to achieve positive
overbite, to correct the cant of the occlusal planes, and
to address the mesial inclination of posterior teeth.26
Although the technique has proven capable of attaining bite
closure, it is mainly via anterior extrusion.27
Previous
cephalometric evaluation of the technique revealed
insignificant changes in lower anterior face height and in
the mandibular plane angle during treatment.27
Another
variation of Kim’s26 technique instead uses reverse and
accentuated curve NiTi archwires with elastics to achieve
anterior extrusion.
An appraisal of this method in adult
anterior open bite patients found that lower anterior
facial height increased significantly post-treatment, while
the mandibular plane angle was maintained.28 Neither of
61
these modalities appear to contribute vertical improvements
in non-growing patients.
Bite closure via extrusion of anterior teeth may not
be indicated for all adult patients presenting with
anterior open bites.
Even more, extrusion of the maxillary
incisors is deemed unstable.29
Some investigators believe
that maxillary incisor extrusion in adult patients may
compromise the periodontal structures, lead to root
resorption and ultimately jeopardize smile esthetics.10
Without the use of skeletal anchorage devices, true molar
intrusion is very difficult to achieve in adult patients
using fixed appliances.30
The use of skeletal anchorage
systems for molar intrusion has proven effective with bite
closure and resultant decreases in facial height,
mandibular plane angle, and occlusal plane angle.10,
30
Unfortunately, the literature in this area is predominately
compromised of case reports that lack long-term follow up
studies investigating stability.
Angular Measurement Changes
In this study, the decision to split the occlusal
plane angles was made, as Nahoum7 felt it was inaccurate to
use one plane in open or deep bite cases and, instead,
defined two separate, maxillary and mandibular occlusal
62
planes.
SN-MxOP showed a statistically significant mean
increase of 2.6˚.
Conversely, Sn-MnOP decreased
significantly by a mean of 4.6˚, indicating that again the
bite closed either by incisor extrusion and/or molar
intrusion.
MP-MnOP increased significantly by a mean of
4.5˚; this finding indicates a decreased steepening of the
mandibular occlusal plane due to bite closure. A
statistically significant mean decrease of 0.9˚ in the SNMP angle and mean decrease of 0.9˚ in the SN-GoGn angle was
observed, which we can attribute to counterclockwise
rotation of the mandibular plane.
For the sake of
reliability, two mandibular planes were utilized: 1) one
plane connecting inferior gonion to gnathion 2) one plane
connecting inferior gonion to menton.
We would expect to
see a higher mean value with SN-MP than we would with SNGoGn, which is the case. However, the mean decreases posttreatment in both planes are equivalent.
This rotation was
not substantial enough to decrease the MP-MnOP angle, as
the treatment effects on the mandibular occlusal plane
superseded the skeletal autorotation.
SN-PP did not
display any significant change, as we might expect in a
non-growing patient.
63
Linear Measurement Changes
Following significant mandibular plane closure, there
was also a statistically significant decrease in the lower
anterior facial height by 1.5mm.
Overbite increased
substantially with a statistically significant mean
increase of 3.4mm; this can be attributed to a combination
of molar intrusion and incisor extrusion, as 1 mm of molar
intrusion can lead to 3mm of anterior bite closure.29 U1-PP
increased by a mean of 0.5mm and U6-PP decreased by a mean
of 0.4mm.
Although this indicates general extrusion of the
maxillary incisors and intrusion of the maxillary molars,
these changes were not statistically significant.
However,
L1-MP increased significantly by 0.8mm and L6-MP decreased
significantly by 0.6mm.
This indicates statistically
significant mandibular molar intrusion and mandibular
incisor extrusion in this sample.
These results reveal
that, overall, most of the dental treatment effects were
greater in the mandibular arch (Figure 3.4).
One possible
reason for significant mandibular changes is that IPR was
prescribed more in the mandibular arch; this would lead to
more mandibular incisor extrusion during retraction and
space closure.
64
Figure 3.4. Sample superimposition of patient #12
Green: before; Black: after
65
In this study, Invisalign successfully achieved
anterior open bite closure via positive incisal overlap
without negatively impacting the vertical dimension.
Average treatment time for this sample was 21 months (Table
A.1).
The changes observed in the vertical parameters
displaying statistical significance are indicative of bite
closure and decreases in the vertical dimension.
As previously noted, fixed appliance therapy has the
potential to exert unwanted extrusive forces that may
enhance the open bite and consequently worsen the vertical
dimension.
Additionally, anterior-posterior (AP) elastics
used with fixed appliances tend to have extrusive effects
that increase the vertical dimension.
The majority of our
sample presented with an Angle Class I malocclusion, with
only six Class II patients.
Klein reported control of the
vertical, and even a decrease in the vertical dimension
(SN-MP), in his study examining Class II correction with
Invisalign and elastics.31
This finding was attributed to
the constant presence of aligner material. The improvements
in the vertical dimension seen in this study are akin to
those observed subsequent to molar intrusion in skeletal
anchorage cases, i.e. reduction in occlusal plane angle,
mandibular plane angle, and lower anterior facial height.10,
30
66
It has been previously postulated that Invisalign
exerts a bite-block effect during treatment.32
Most
literature on bite-block therapy describes its
effectiveness in treatment of children and growing
patients.
This functional appliance aims to control
maxillary vertical skeletal and dental growth primarily by
opening the patient past their normal vertical dimension.29
Typically, the amount of acrylic in the first molar area of
these bite blocks may range in thickness from 5-10mm; this
induces an artificial increase in the vertical dimension,
thereby triggering a muscular response that creates a
vertical intrusive force in the buccal segments, leading to
counterclockwise rotation of the mandible.33
It is unlikely that Invisalign has the ability to
exert the same intrusive forces in adults as we observe in
children with bite block therapy.
The thickness of each
Invisalign aligner is 0.030 inches34 (equivalent to 0.76mm)
which, when combined intraorally, may not be of adequate
thickness to exceed the freeway space considerably enough
to create a neuromuscular response.
Additionally,
functional contact of opposing teeth occurs approximately
18 minutes per day29, which is not of long enough duration
to exert a significant intrusive force.35
Intrusive forces
from the aligner must be requested by the provider in the
67
ClinCheck and programmed into the trays through the
Invisalign technicians.
The combined effect of the
sequential progression of trays, with judicious selection
and placement of attachments, ultimately dictates the
amount of intrusion and tooth movement observed clinically.
Given the appliance’s relatively recent inception and
continual evolution, literature regarding efficacy of tooth
movement is lacking.
Schupp et al.16 reported 1mm of molar
intrusion in their case report but there is not enough
substantial evidence to understand how much posterior
intrusion Invisalign is capable of achieving.
The
advantage of Invisalign in treating open bite malocclusion
stems mainly from its full occlusal coverage effect.
While
intruding dentition, adverse or unwanted reciprocal
extrusive movements are less likely to occur because of the
presence of the aligner.15
Retention in anterior open bites is critical,
especially when considering the vertical dimension of
facial growth is the last to be completed. Extrusion of the
posterior teeth, most commonly the maxillary molars, is
cited as the most common cause for anterior open bite
relapse in growing patients.29
Retention should therefore
incorporate a means to control eruption of the posterior
teeth, even in young adults.
68
As adult open bite malocclusions are uncommon and
their treatment with Invisalign is a relatively new
approach, one limitation of this study was obtaining a
large sample size.
Additionally, the retrospective nature
of this study did not enable control of all treatment
variables.
Each case was treated with a different
ClinCheck set-up that was contingent upon the patient’s
specific diagnosis as well as the orthodontic provider’s
devised treatment plan. Depending on the treatment
warranted, providers may have either primarily requested
molar intrusion, or anterior extrusion, or a combination of
both.
Future studies should incorporate a matched control
group treated solely with fixed appliance therapy for
further comparison of these modalities’ effects on the
vertical dimension.
Research focusing on the amount of
molar intrusion that can be achieved with the appliance
would be of great value. Lastly, prospective investigation
lending insight into relapse of open bite cases treated
with Invisalign is vastly important in order to appreciate
the appliance’s capacity to preserve control of the
vertical.
69
Conclusion
1) The Invisalign system is a therapeutic modality that
can be effectively employed in non-extraction
treatment of adult anterior open bites.
2) Bite closure was achieved by a combination of lower
molar intrusion and lower incisor extrusion.
70
Appendix
Table A.1. Sample treatment duration
Pt #
T1 Ceph
T2 Ceph
1
5/29/08
12/8/10
Tx time
(mo)
18
2
6/21/10
11/10/11
17
3
2/2/11
12/11/12
22
4
10/20/11
4/8/13
18
5
6/28/07
11/18/08
17
6
12/13/06
3/12/09
27
7
2/22/10
6/27/11
16
8
1/12/12
10/7/13
21
9
4/27/11
2/20/13
22
10
5/26/11
2/4/13
21
11
8/23/12
7/28/14
23
12
9/24/12
2/24/14
17
13
7/19/12
11/20/13
16
14
11/14/12
2/10/15
27
15
11/18/12
7/7/14
19
16
2/25/13
12/8/14
22
17
10/10/12
8/5/15
34
18
11/20/12
11/18/14
24
19
11/5/12
7/7/15
32
20
7/9/2009
6/1/11
23
21
10/24/12
6/10/14
20
22
8/9/12
2/3/15
30
23
4/9/13
11/26/14
19
24
2/2/14
1/7/15
11
25
3/04/12
8/20/13
17
26
7/18/11
4/23/13
21
27
7/7/11
2/5/14
31
28
7/8/11
2/6/14
31
29
4/3/12
3/4/14
23
30
10/22/13
9/30/15
23
71
Table A.2. Sample angle classification and crowding
1
Angle
Classification
Class I
Maxillary
Crowding
Moderate
Mandibular
Crowding
Moderate
2
Class I
None
None
3
Class I
None
None
4
Class I
Mild
Moderate
5
Class I
Mild
Mild
6
Class I
None
Mild
7
Class I
Mild
Mild
8
Class II
None
Mild
9
Class I
Moderate
Mild
10
Class I
Moderate
Moderate
11
Class I
Moderate
Moderate
12
Class II
Mild
Mild
13
Class II
None
None
14
Class I
None
Mild
15
Class I
None
Mild
16
Class I
None
None
17
Class I
None
None
18
Class II
None
Moderate
19
Class II
None
Mild
20
Class I
None
Mild
21
Class I
Mild
Mild
22
Class I
None
Mild
23
Class I
Moderate
Moderate
24
Class I
None
None
25
Class I
Mild
Mild
26
Class I
Mild
Moderate
27
Class II
None
Mild
28
Class I
Mild
Moderate
29
Class I
None
Mild
30
Class I
Mild
None
Pt #
72
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Vita Auctoris
Shuka Moshiri was born on January 11, 1985 in St.
Louis, Missouri to Dr.’s Farhad and Fariba Moshiri.
preceded by her brother, Dr. Mazyar Moshiri.
She is
After
graduating from John Burroughs high school in 2003, she
attended Washington University in St. Louis where she
obtained her Bachelor of Arts degree with a major in
Psychology.
She then moved to Kentucky, where she received
her Doctor of Medicine in Dentistry degree at the
University Of Louisville School Of Dentistry in 2011.
Following her graduation, she completed an advanced year of
training at a general practice residency program at Mercy
Hospital in St. Louis.
In 2013, she began her residency at
Saint Louis University’s Orthodontic program with the goal
of receiving her Master of Science degree in 2015.
After
she completes her training, she looks forward to working
alongside her father and brother in their St. Louis family
orthodontic practice.
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