Download Joseph D. Parker, D.D.S. Saint Louis University in Partial Fulfillment

EVALUATION OF INCISAL DISPLAY CHANGES
Joseph D. Parker, D.D.S.
An Abstract Presented to the Graduate Faculty of
Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2011
ABSTRACT
Objective:
The purpose of this study is to evaluate
which patient characteristics, treatment modalities, and
cephalometric variations influence incisal display
changes.
Materials and Methods:
A randomized search of
pre and post treatment smiling frontal photographs was
conducted to select 20 patients who experienced the
greatest increase and 20 patients who experienced the
greatest decrease in incisal display upon smiling.
These
patients’ dental and skeletal characteristics were
analyzed as well as the treatment rendered.
Chi-square
analysis was performed within the 2 groups for age, sex,
Angle classification, overbite, curve of Spee, protrusion,
facial type, extractions, and various treatment
modalities.
Independent t-tests of pre and post
cephalometric values were conducted.
Results:
The
incisal display change for the increase group was from
9.72 mm to 12.75 mm, a 3.03 mm increase.
The incisal
display change for the decrease group was from 11.29 mm
to 8.1 mm, a 3.19 mm decrease.
Patients in the increase
group were likely to be female, have open bites, and had
headgear treatment.
Patients in the decrease group were
likely to have deep bites and had reverse curve arch
wires during treatment.
Cephalometrically, there were no
1
differences between the increase and decrease groups when
comparing T1 and T2.
However, in comparing intra-group
T1 values against T2 values it was found that in the
increase group the occlusal plane angle increased 3.97
degrees and the upper incisors were retracted 6.83
degrees.
The significant changes found in the decrease
group include increases in the length of the mandible of
5.16 mm and in the vertical eruption of the maxillary
molars of 2.3 mm.
Conclusions:
No pretreatment
cephalometric characteristics could be identified to
predict an increase or decrease in incisal display.
Patients in the increase group were likely to be female,
had open bites, had headgear treatment, experienced an
increase in the occlusal plane angulation, and
experienced a decrease in the upper incisor proclination.
Patients in the decrease group were likely to have deep
bites, use of reverse curve arch wires during treatment,
and experienced greater mandibular length and eruption of
the maxillary molars.
2
EVALUATION OF INCISAL DISPLAY CHANGES
Joseph D. Parker, D.D.S.
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
2011
COMMITTEE IN CHARGE OF CANDIDACY:
Professor Rolf G. Behrents,
Chairperson and Advisor
Professor Eustaquio Araujo
Assistant Professor Ki Beom Kim
i
DEDICATION
To my wife, Jan, whose support has been unwavering and
has allowed me to purse my dreams.
Over the last 7 years
she has sacrificed so much for our family, for which I am
forever grateful.
To my parents, who instilled hard work and dedication
to excellence in every aspect of my life.
I am thankful
for their examples and support throughout my education.
ii
ACKNOWLEDGEMENTS
I would like to thank Drs. Beherents, Araujo, and Kim
for there support, guidance, and encouragement for the last
two and a half years.
iii
TABLE OF CONTENTS
List of Tables............................................. v
CHAPTER 1:
INTRODUCTION....................................1
CHAPTER 2:
REVIEW OF THE LITERATURE........................3
Smile Attractiveness........................... 3
Anterior Dental Esthetics...................... 5
Ideal Gingival Display......................... 6
Causes of Differing Gingival Levels............ 8
Sexual Dimorphism........................... 8
Lip Contribution............................ 9
Growth & Skeletal Contribution............. 11
Clinical Crown Length...................... 13
Gingival Hyperplasia....................... 14
Altered Passive Eruption................... 15
Treatments Altering Incisal Display........... 16
Orthodontic Treatment...................... 17
Intrusion............................... 17
Extrusion............................... 19
Other Orthodontic Treatment............. 21
Surgical................................... 21
Periodontal................................ 22
Soft Tissue................................ 24
Summary and Statement of Thesis............... 25
References.................................... 27
CHAPTER 3:
JOURNAL ARTICLE
Abstract......................................
Introduction..................................
Materials and Methods.........................
Sample.....................................
Data Collection............................
Data Analysis..............................
Results.......................................
Discussion....................................
Conclusion....................................
Literature Cited..............................
32
34
36
36
38
40
41
51
60
61
Vita Auctoris............................................. 63
iv
LIST OF TABLES
Table 3.1:
Cephalometric Measurements.....................39
Table 3.2:
Description of Treatment Rendered..............40
Table 3.3:
Statistical Analysis of Incisal Display
Changes........................................42
Table 3.4:
Statistical Analysis of Patient
Characteristics................................43
Table 3.5:
Pre Treatment Cephalometric Measures for
Increase and Decrease Groups...................45
Table 3.6:
Post Treatment Cephalometric Measures for
Increase and Decrease Groups...................46
Table 3.7:
Pre and Post Treatment Cephalometric
Measures for Increase Group....................47
Table 3.8:
Pre and Post Treatment Cephalometric
Measures for Decrease Group....................48
Table 3.9:
Statistical Analysis of Treatment Rendered.....50
v
CHAPTER 1:
INTRODUCTION
Facial attractiveness, and more specifically smile
esthetics, has received a considerable amount of interest
in dental and orthodontic literature.
This focus on
defining esthetically pleasing smiles has been in
response to society becoming more esthetically conscious.
Orthodontists not only have the responsibility to produce
functional and stable occlusions but also beautiful
smiles.
The vertical position of the upper incisors in
relation to the lips and gingival tissue is a key
determinant in the attractiveness of a smile.
As society
becomes more focused on the esthetics, it is important
for orthodontists to know which patients will have the
greatest changes in the amount of incisal display when
smiling.
There is great variation in smiles among the general
population.
Two extremes can be identified as those who
show a very little amount of tooth structure and those
who show a significant amount of gingival tissue.
Studies have confirmed that the ideal smile has the upper
lip at or slightly above the gingival margins of the
maxillary incisors and the lower lip at the level of the
incisal edges of the maxillary incisors.
Less attractive
smiles were associated with an excessive amount of
1
gingival tissue or having the upper lip cover a large
portion of the upper incisors.
Orthodontists are challenged in treating to an ideal
smile despite the incredible variety of malocclusions
that are presented to them.
While it may be impossible
for orthodontists to produce an ideal smile outcome in
every treated case, it is important to strive for this
esthetic and to be educated about the importance of the
vertical position of the maxillary incisors and how they
change during treatment.
For example, if a new patient
has characteristics that may increase or decrease the
amount of incisal and gingival tissue display, the
orthodontist and patient need to be aware of these
possible changes before treatment starts.
The purpose of this study is to identify which
treatment features or various dental or skeletal
characteristics are associated with changes in the
vertical incisal display when patients smile.
2
CHAPTER 2:
REVIEW OF THE LITERATURE
Smile Attractiveness
There is no single facial feature that determines
overall facial attractiveness. However, smiling and a
youthful appearance are noted as adding to the overall
facial attractiveness.1 Hickman noted that viewers do not
preferentially go to any single facial feature and “the
mouth, even in smile images, attracts only a small part
of visual attention when viewers look at well-balanced
faces.”2
Despite the smile playing a limited role in overall
facial attractiveness it has received great attention in
dental and orthodontic journals.3
The objectives of
dentists and orthodontists “are to improve oral health,
to establish proper occlusal function, and to create
ideal esthetics.”4
Furthermore, the demand for
orthodontic treatment is mainly driven by esthetics and
patients’ desire to improve their appearance.5
This
patient-driven focus on esthetics has incited research
that attempted to define the ideal appearance of a smile.
There are many important esthetic factors to
consider when evaluating the smile and the anterior tooth
display.
A well-balanced smile has been noted by Sabri
3
to consist of eight components:
lip line (upper lip
length, lip elevation, vertical maxillary height, crown
height, and vertical dental height), smile arc, upper lip
curvature, lateral negative space, smile symmetry,
frontal occlusal plane, dental components, and gingival
components.6
Zachrisson identified a number of anterior
tooth display components that are esthetic factors: crown
length, incisal edge contours, axial inclinations,
midlines, crown torque, smile line (smile arc), rightleft symmetry, and buccal corridors.7
It is important to note that despite all the
aforementioned factors that contribute to a beautiful
smile and esthetics that “even a well-treated orthodontic
case in which the plaster casts meet every criterion of
the American Board of Orthodontics for successful
treatment may not produce an esthetic smile.”8
However,
it has been found that orthodontic treatment does
significantly improve the appearance of the smile,
maxillary incisor torque, protrusion, and profile.9
Historically orthodontics has focused on esthetics
in terms of profile enhancements; however, lay people
view orthodontists as practitioners who creates beautiful
smiles.
Contemporary orthodontists evaluate patients not
only in terms of profile, but also frontal and vertical
4
views are considered.10
Hickman has written that “putting
dentures in the right place in the face is what it is all
about.
It really doesn’t take much to be an accomplished
tooth straightener.
The difficult task is planning and
manipulating the various forces, externally and
internally, in order to have the denture arrive in that
particular space in the face that is the best suited for
that patient.”11
Anterior Dental Esthetics
A major part of smile attractiveness is the display
of the anterior teeth.
Tjan’s findings show that “an
average smile exhibits approximately the full length of
the maxillary anterior teeth, has the incisal curve of
the teeth parallel to the inner curvature of the lower
lip, has the incisal curve of the maxillary anterior
teeth touching slightly or missing slightly the lower lip,
and displays the six upper anterior teeth and
premolars.”12
Self-perception of smile attractiveness has
been found to focus in on the size of teeth, visibility
of teeth and upper lip position, color of teeth, and
gingival display.13
This same study found that
participants who showed their front teeth in addition to
a minor amount of gingiva were regarded as the most
5
esthetic.
A decrease in esthetics was found in
participants with “low smile lines with marginal tooth
display as well as high smile lines with excessive
gingival display.”
Self-esteem was found to be
correlated with the visibility of the gingival tissue.
In determining what makes a beautiful smile, Wolfart
studied the subjective and objective perceptions of the
upper incisors and found that the “complexity of dental
appearance often can not be determined or analyzed using
single parameters.”14
Rather than single parameters or
“rules of thumbs,” an understanding of relationships and
treatment focused on the individual patient leads to the
best possible esthetic result.
Ideal Gingival Display
Husley found that the most attractive smiles had
“the upper lip at the height of the gingival margin of
the upper central incisor” and the smile line had “near
perfect harmony between the arcs of curvature of the
incisal edges of the upper incisors and the upper border
of the lower lip.”15
Many other studies have sought to
define the acceptable amount of gingival display.
Peck
and Peck defined a Gingival Smile Line as a “continuous
band of gingiva superior to the maxillary anterior teeth
6
and often posterior teeth.16
Van der Geld found that
participants with 2 to 4 mm of gingival display to be
most attractive.13
Kokich found that the distance from
the gingiva to the upper lip was not noticeable by
general dentists and lay population until it was 4 mm.
Orthodontist on the other hand found that 2 mm of visible
gingiva was excessive and unattractive.
He noted that
there is a significant difference between lay people and
general dentists in the esthetic perception of a “gummy
smile” versus the orthodontist.
“Practitioners’ goals
may not be in harmony with the patients’ goals.”17
Geron
found that the most esthetic range of exposed gingiva on
the upper incisors was between zero and 2 mm.
The most
attractive smile was 0.5 mm of lip coverage.
One
interesting finding in his study was that females were
more tolerant of upper gingival exposure than were
males.18
A study by Hunt examining the influence of
maxillary gingival display on the attractiveness of a
smile by lay people showed that 0 mm of gingival display
was rated as the most attractive in both male and female
images.
The range of acceptable attractiveness ranged
from -2 to +2 mm.
Gingival display of 3 mm or more was
progressively rated less attractive.19 Ioi found that
among Japanese orthodontists 0 mm was the most attractive
7
and among Japanese dental students -2 mm was the most
attractive.20
Singer also found gingival display was
rated as esthetically undesirable.21
The amount of lower teeth showing has been found
correlate to unattractive smiles.
Schabel stated
“extremely unattractive smiles were characterized by a
greater distance between the incisal margin of the
maxillary incisors and the lower lip.”22
This article
demonstrates that low smile lines and/or excessive lip
drape is also considered esthetic unpleasing.
Causes of Differing Gingival Levels
Sexual Dimorphism
Peck and Peck showed a sexual dimorphism in the
amount of gingival display.
Females appear to have a
predilection for high smiles lines of greater than 1 mm.
Males, on the other hand, have a predilection for low
smile lines of less than -2 mm.
It was further found
that females are twice as likely as compared to males to
have “gummy smiles.”
The reverse was found as well, that
males are twice as likely to have low smile lines
compared to females.16
In their study of 46 females and
42 males, it was shown that the average gingival display
was +0.7 mm for females and -0.8 mm for males, a 1.5 mm
8
difference.
In the same article a follow up study on
gingival smile line patients was conducted.
An
interesting note in their article stated “It was
difficult to accumulate the gingival smile sample,
particularly of male subjects, apparently caused by the
rarity of high smiles line among men.”
Vig and Brundo found that the average maxillary
incisor display at rest is 1.91 mm in males and 3.40 mm
in females, a 1.49 mm difference.
It is also noted in
their study that Caucasians show the highest amount of
incisors at rest with an average of 2.43 mm while African
American show the least at an average of 1.57 mm.23
Lip Contributions
Peck and Peck found no difference in lip length among
gingival patients and controls.
However, Sabri found
that combining various studies demonstrated that the
average lip length for males is about 23 mm and 20 mm in
females.
Sabri noted that a short upper lip can
contribute to excessive gingival diplay; however, is not
always associated with excessive gingival display.6
Singer found that in 70 gingival display females that lip
length was significantly longer in the gingival smile
group compared to the non-gingival smile sample.21
9
Peck and Peck found the interlabial gap in gingival
patients at rest was nearly twice the amount (6.2 mm
versus 3.0 mm) when compared to controls.16
A follow up
article with high gingival subjects showed how the upper
lip contributes to a gingival smile.
They found that the
elevation of the upper lip during smiling was
significantly higher than that seen in the controls, and
in addition, the resting position of the upper lip in
gingival patients was markedly higher.
It is noted that
only 56% of sample who had an interlabial gap had a
gingival smile.
The study by Peck supports the
association but not the prediction of interlabial gap and
gingival display.24
Suh also confirmed that patients with
gingival display also had larger interlabial gaps at rest.
He also found that the upper lip length was shorter and
upper lip elevation was larger.25
In a study that evaluated changes in gingival
display, Cox found that the lips, as measured on a
lateral cephalographs, moved backwards in those patients
with increased gingival display following orthodontic
treatment.
It is suggested the factors that contribute
to that this horizontal change of the lip affect the
vertical position of the lip when smiling.26
10
Sarver and Ackerman indicate that incisor
proclination can have a significant effect on the lip
position and the resultant incisor display.
Stating
“…flared maxillary incisors tend to reduce incisor
display, and upright maxillary incisors tend to increase
it.”27
Growth & Skeletal Contribution
Vertical maxillary excess or deficiency has been
considered to be one the major skeletal contributors to
the vertical display of the upper incisors.
Singer found
that patients with gingival display not only have
excessive maxillary height, but also have an upwardtilted palate and a high mandibular plane.21
Peck found
that in his sample patients with a gingival appearance
had anterior vertical maxillary excess of 2 to 3 mm in
addition to hypermobility of the upper lip and increased
overjet and overbite.24
According to Suh, patients with an increased amount
of upper incisor display also had increased anterior
maxillary height, a larger gonial angle, and a steeper
occlusal plane to sella-nasion plane angle.25
In his study of extreme variations in vertical
facial growth Isaacson found that many skeletal and
11
dental relationships vary within high and low mandibular
plane angles.
The study compared 3 groups of patients
with varying mandibular plane angles - <26 degrees, 32
degrees, and >38 degrees.
The top five predictors for
mandibular plane angles were: 1. occlusal plane to
mandibular plane angle, 2. ramus height, 3. occlusal
plane to sella-nasion angle, 4. occlusal plane to palatal
plane angle, and 5. the amount of deep bite or open bite.
Based on his study he theorized:
If the alveolar ridges and facial sutures greatly
increase vertically in excess of vertical increases at
the mandibular condyle, the mandible will rotate
backwards… Conversely, when the vertical growth amounts
at the mandibular condyle greatly exceeds amounts at the
alveolar ridges and facial sutures, forward rotation of
the mandible must occur.28
In evaluating the incisor position of the two
extremes it was found that the backward-rotating high
angle cases had a tendency for an open bite and the
forward-rotating low angle cases had a tendency for a
deep bite.
The tendency for the open bite in a high
angle patient occurs despite the fact that the maxillary
incisors are already longer.
As Isaacson stated, “These
people do not necessarily have short upper lips, but they
do have longer maxillary alveolar processes.”
The
reverse can be said of the low angle cases for despite
the fact that the maxillary alveolar process is shorter
12
they have a tendency for deep bites.28
It can be
suggested that high angle cases would have a tendency for
increased incisal display levels and low angle cases
would have a tendency for decreased incisal display
levels.
Turley described some patients with limited incisal
display as those with short faces.
He noted that reduced
lower facial height has received much less attention than
excessive lower facial height.
Patients with short faces
generally have proportionally greater posterior facial
height growth than that noted for anterior facial height.
In addition, short faces show upward and forward growth
of the condyle with decreased eruption of the posterior
teeth.
Such a counter-clockwise rotation can lead to
underdevelopment of the anterior facial height.
In his
study of short faced patients he found that reduced
maxillary molar height to the palatal plane was the
strongest measure of vertical maxillary deficiency.
Reduced incisor height to the palatal plane was
associated with deficient incisor display.29
Clinical Crown Length
The significance of the clinical crown length and its
relationship to the patient’s incisal display has had
13
differing reports.
Peck in one article suggested that
short incisor clinical crown height is a factor in
patients with an excessive amount of gingival tissue.30
However, in a follow-up study he showed that clinical
crown heights were not statistically significant between
the gingival patients and the controls.24
The clinical
crown height does not appear to be a factor in incisal
display except when considering abraded anterior teeth.31
Konikoff found that the clinical crown length of pre
and post orthodontic treatment does not change and that
continued, passive eruption continues with age.32
When
comparing various crown lengths and its role on esthetics
of a smile Wolfart found that the crown length plays a
limited role.14
Gingival Hyperplasia
Gingival hyperplasia can cover an excessive portion
of the tooth and produce the appearance of a short crown
length.
It has been noted by Panossian that gingival
hyperplasia is one of four main reasons for excessive
gingival display.
Gingival hyperplasia can be diagnosed
as normal crown length with a deep soft tissue pocket and
can be associated with bone coverage coronal to the
cementoenamel junction of a tooth.3
14
Altered Passive Eruption
Clinically short crowns due to incomplete eruption
can cause more gingival display than what is considered
esthetic. Active eruption is the movement of the tooth
until it makes contact with the teeth in the opposing
arch.
Passive eruption is the “apical migration of the
dentogingival unit adjacent to the cementoenamel
junction.”33
This is further classified into 4 stages.
In stage 1, the epithelial attachment is on the enamel
surface.
In stage 2, the epithelial attachment is at the
cementoenamel junction.
In stage 3, the epithelial
attachment is only on cementum.
In stage 4, inflammation
causes apical migration of the epithelial attachment.33
When passive eruption does not progress past stage 1
and onto stage 2 or 3 it is considered altered passive
eruption.
In this situation the location of osseous
crest is located incisally in relation to the
cementoenamel junction and the gingival margin remains on
the enamel surface.
Ideal bone level should be just
below the cementoenamel junction with the gingival
attachement at this junction.33
The ideal sulcus depth,
which corresponds to the biological width, should be
between 2 – 3 mm.3
15
Konikoff found that after orthodontic treatment,
greater than 65% of subjects had non-ideal width-length
ratio.
The average central incisor length was 9.35 mm
versus the average norm of 10.5.32
This could be
attributed to either gingival hyperplasia and/or altered
passive eruption.
In such cases esthetic crown lengthing
can be performed.
Treatments Altering Incisal Display
Treatment aimed at altering an unaesthetic incisal
display needs to be directed at the underlying cause.
As
discussed earlier the cause of excessive or deficient
incisal display for the population as a whole is multifactoral; however, on an individual level a thorough
clinical and radiographic exam may reveal the major
contributor for that individual patient.
The treatment
options can be broken down into four groups; orthodontic,
surgical, periodontal, or facial soft tissue.
Some
patients may need treatment involving all four, while
others may be strictly limited to one.
Claman stresses
the need for interdisplinary approaches between
orthodontists, periodontists, prosthodontics, and oral
surgeons to improve the total anterior esthetics.34
16
Proper diagnosis and treatment is critical in order to
obtain the most esthetic smile possible.
Orthodontic Treatment
Intrusion
Over-eruption of maxillary anterior teeth associated
with a deep bite can create a “gummy smile.”
Patients
with this type of malocclusion should have active
maxillary intrusion as a treatment goal.7
These cases
demonstrate a step between the occlusal plane and an
inferior incisal plane.
Simple intrusion mechanics of
the maxillary anterior teeth will correct this type of
“gummy smile.”35
number of means.
This can be accomplished through a
In some cases, intrusion base arches,
utility arches, or reverse curve arch wires can result in
successful orthodontic treatment.
Depending on the
mechanical force desired, an intrusive force in the
anterior may or may not need anchorage in the posterior
to prevent eruption of posterior teeth.36
If a deep bite
exists and the maxillary incisors are in the ideal
position in relationship to the smile, actively intruding
the mandibular incisors is the preferred treatment.7
When comparing forces and moments of various
intrusion mechanics, Sifakakis found that reverse curve
17
nickel-titanium arch wires produced the highest intrusion
force on the anterior incisors whereas the Burstone TMA
intrusion arch exerted the lowest force.
Other intrusion
arch mechanics fall in between the nickel-titanium
reverse curve and the Burstone TMA arch.
Reverse curve
arch wires are difficult to predict bucco-lingual moments
and varying extrusive forces since it is a continuous
arch wire.
The unpredictability of the force systems
found in reverse curve archwires is a contraindication to
their use.36
Sarver describes reverse curve arch wires as
placing an intrusive force anterior to the center of
resistance.
This results in labial crown torque and may
decrease the appearance of the crown height.8
In comparing intrusion using J-hook headgear and
implant anchorage, Deguchi found that both are effective
in reducing overjet, overbite, maxillary incisor to upper
lip, and maxillary incisor to the palatal plane.
However,
it was confirmed that the implant group had greater
intrusion amounts and a more vertical vector.
Less root
resorption was found in the implant group as well.37
The use of osseous dental implants has been shown to
be successful in treating excessive gingival display
while limiting the extrusive effects of intrusion
arches.38
Care must be taken with any anterior intrusion
18
mechanics.
Uribe demonstrated that over intrusion of
maxillary incisors can produce unfavorable esthetics if
the intrusion causes a reverse smile arc and different
levels for the posterior occlusal plane and incisal
plane.38
Zachrisson notes that patients with “over
intrusion” of the maxillary anterior in relation to their
lower lip will have a “denture mouth.”7
Sarver indicated
that emphasis on canine guidance can produce a relative
intrusion of the incisor and extrusion of the canine,
creating a flat smile arch.8
Extrusion
An anterior open bite can be corrected with vertical
elastics and extrusion of the incisors.
This is an
acceptable treatment if the patient shows little gingiva.
If the patient already shows gingiva on smiling, a
preferred treatment would be to inhibit further vertical
molar eruption or posterior intrusion thus producing a
forward mandibular rotation.28
When extruding teeth it
has been found by Pikdoken that the gingival margin
follows the amount of extrusion of the incisors by a
factor of 80%.
The mucogingival junction also follows
the incisors in the amount of 52%.39
19
Vertical molar eruption will aid in treatment of
patients with deep bites.
In particular, cervical
headgear with high outer bows can produces distal root
movement and vertical extrusion.
Isaacson found that the
maxillary posterior alveolar process was significantly
more important than the posterior mandibular alveolar
process in vertical development.28
Also, high-pull
headgear can limit the extent of vertical posterior
maxillary growth resulting in relative anterior
extrusion.8
Turley states that traditional orthodontics has
attempted to extrude posterior teeth to open the bite and
lengthen the face.
It also had been recommended that
extractions should be avoided in low-angled patients if
increasing the lower facial height is the goal.29
If the upper incisors are flared in combination with
anterior open bite, extracting the upper first premolars
and retracting the incisors will increase the amount of
incisal display.27
In this situation Sarver and Ackerman
recommend that the incisors should be retracted on round
wire so that the crowns will rotate around the bracket
slot and produce a more inferior position thus increasing
incisor display.27
20
Other Orthodontic Treatments
Wertz found in a cephalometric study following rapid
palatal expansion that the maxilla moves downward during
sutural opening.40
As the maxilla moves inferiorly 1 mm,
the mandible rotates in a clockwise manner increasing the
lower facial height.
In evaluating the effects of extracting four first
premolars and smile esthetics Johnson found that no
predictable relationship exists between the extraction of
teeth and smile esthetics.41
This study also analyzed
variations in smile height and found no difference
between the extraction and non-extraction groups.
Sarver recommends avoiding a set formula for bracket
placement.
Consideration of the relationship between the
lower lip and incisal edges should determine the
individualized design for placing appliances.8
Surgical
In treating “gummy smiles” Kokich states that if the
incisal plane and occlusal planes are coincident,
surgical maxillary intrusion is usually required due to
the overdevelopment of the maxilla.35
Generally only the
more severe “gummy smiles” require surgically
repositioning the maxilla.
Maxillary impaction with
21
rigid fixation has been found to be generally stable.42
Arpornmaeklong also found that maxillary impaction is
stable with only minor, insignificant anterior and
inferior relapse following impaction.43
Historically, treating patients with vertical
deficiencies by performing a maxillary downgraft has had
less than ideal stability.44
In a study by Perez
evaluating the stability of Lefort I maxillary downgrafts
with rigid fixation it was found that 80% of the 28
patients has less than 2 mm of relapse.
The mean
superior relapse was 28% of the original downgraft length.
Downward and backward occlusal plane rotations and pre
orthodontic treatment had no influence on stability.44
This type of surgery may be quite beneficial to patients
who show very little incisal display.
Periodontal
A simple gingivectomy is a procedure to treat
“gummy smiles” with patients who have excessive gingival
margins due to hyperplastic tissue.7
Indications for
this treatment are appropriate osseous level, more than 3
mm of tissue from bone to gingival crest, and the
anticipation that adequate attached gingiva will remain
after gingivectomy.33
22
In patients with altered passive eruption with
osseous levels at or incisal to the level of the CEJ, a
gingival flap and ostectomy is indicated for crown
lengthening.
The crestal bone should be reduced to a
level that is 2.5 to 3.0 mm from to the CEJ and the
gingival flap should be apically repositioned.33
As noted previously, Knokinoff reported that 65% of
adolescent, post orthodontic patients have non-ideal
width-to-length.
The study also found that 60% of these
patients had asymmetric gingival levels.
Although it was
found that passive eruption continues with age, if a
patient needs esthetic crown lengthening before
orthodontics the need for post orthodontic crown
lengthening remains.32
Intruding the maxilla through orthognathic surgery
can eliminate excessive gingival display; however, this
surgery also can result in shortening the facial height.
An alternative discussed by Kokich is to perform
periodontal crown-lengthing involving the maxillary
incisors.
By removing bone the gingival margin can be
moved apically.
The consequence of this treatment is a
crown-to-root ratio reduction, possible “black
triangles“ between the incisors, and possible restorative
23
needs.4
This treatment is indicated in patients with
altered passive eruption and short or abraded crowns.
Soft Tissue
Hwang studied the effects of using botulinum tox-A
(BXT-A) for supplemental treatment of “gummy smile.”
Three evelator muscles were investigated: levator labii
superioris, levator labii superioris alaeque nasi, and
zygomaticus minor.
The study used predetermined surface
landmarks for injection points and showed that the
muscles are symmetric and converge onto a safe and
reproducible injection point for BTX-A.
Hwang suggests
this treatment should directed toward patients with
hyperactive lip elevator muscles.45
A study by Polo of 30 subjects with “gummy smiles”
secondary to hyper-functional upper lip elevator muscles
showed significant improvement in decreasing the visible
gum tissue by using BTX-A.
The pre-injection gingival
display levels had a mean of 5.2 mm.
At 2 weeks post-
injection the gingival display had declined to a mean of
0.1 mm.
The gingival display gradually increased over
the 24 weeks of the study.
It was predicted that the
gingival display would return to it pre-injection levels
by 30 to 32 weeks.
It is worth noting that this
24
treatment was rated as highly favorable among the
patients receiving the BTX-A treatment.
Although the
effect of BTX-A is temporary and necessitates repeated
treatments, it has been shown to be an effective
treatment for hyperactive lip elevator muscles.46
Ezquerra has reported successful treatment of “gummy
smiles” by altering tissue attachment of the lip and
muscles of the lip.
Several techniques have been
described that involve vestibular mucosa resection,
reduction of upper maxillary vestibular reduction,
myectomy and resection of levator labii superioris, and
lip lengthening through rhinoplasty.47
A recent study
conducted by Ishida showed 14 female patients with an
average gingival display of 5.22 mm having a mean
gingival reduction of 3.31 mm through myotomy of the
levator labii superioris muscle and lip repositioning.
The study demonstrated stable results 6 months following
surgery.48
Summary and Statement of Thesis
The literature is clear that an ideal smile has the
upper lip at or slightly above the gingival margins of
the maxillary incisors and the lower lip at the level of
the incisal edges of the maxillary incisors.
25
Orthodontists are challenged in treating to this ideal
despite the incredible variety of malocclusions that are
presented to them.
While it may be impossible for
orthodontists to produce an ideal smile outcome in every
treated case, it is important to strive for this esthetic
and to be educated about the importance of the vertical
position of the maxillary incisors and how they change
during treatment.
The purpose of this study is to identify which
treatment aspects or various dental or skeletal
characteristics are associated with changes in the
vertical incisal display when patients smile.
The
identification of such characteristics might allow
orthodontists to predict tendencies for incisal display
changes, for better or for worse, in a given patient.
26
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13. Van der Geld P, Oosterveld P, Van Heck G, KuijpersJagtman A. Smile attractiveness. Self-perception and
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18. Geron S, Atalia W. Influence of sex on the perception
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19. Hunt O, Johnston C, Hepper P, Burden D, Stevenson M.
The influence of maxillary gingival exposure on dental
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20. Ioi H, Nakata S, Counts A. Influence of gingival
display on smile aesthetics in Japanese. Eur J Orthod.
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21. Singer R. A study of the morphologic, treatment, and
esthetic aspects of gingival display. Am J Orthod.
1974;65(4):435-436.
22. Schabel B, Franchi L, Baccetti T, McNamara J.
Subjective vs objective evaluations of smile esthetics.
Am J Orthod Dentofacial Orthop. 2009;135(4 Suppl):S72-79.
23. Vig R, Brundo G. The kinetics of anterior tooth
display. J Prosthet Dent. 1978;39(5):502-504.
24. Peck S, Peck L, Kataja M. The gingival smile line.
Angle Orthod. 1992;62(2):91-100.
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25. Suh Y, Nahm D, Choi J, Baek S. Differential diagnosis
for inappropriate upper incisal display during posed
smile: contribution of soft tissue and underlying hard
tissue. J Craniofac Surg. 2009;20(6):2006-2012.
26. Cox J. Treatment determinants of the gingival smile.
[Unpublished master's thesis]. St. Louis: Saint Louis
University; 2010.
27. Sarver D, Ackerman M. Dynamic smile visualization and
quantification: Part 2. Smile analysis and treatment
strategies. Am J Orthod Dentofacial Orthop.
2003;124(2):116-127.
28. Isaacson J, Isaacson R, Speidel T, Worms F. Extreme
variation in vertical facial growth and associated
variation in skeletal and dental relations. Angle Orthod.
1971;41(3):219-229.
29. Turley P. Orthodontic management of the short face
patient. Semin Orthod. 1996;2(2):138-153.
30. Peck S, Peck L, Kataja M. Some vertical lineaments of
lip position. Am J Orthod Dentofacial Orthop.
1992;101(6):519-524.
31. Kokich V. Esthetics and anterior tooth position: An
orthodontic perspective. Part I: Crown Length. J Esthet
Dent. 1993;5(1):19-23.
32. Konikoff B, Johnson D, Schenkein H, Kwatra N, Waldrop
T. Clinical crown length of the maxillary anterior teeth
preorthodontics and postorthodontics. J Periodontol.
2007;78(4):645-653.
33. Foley T, Sandhu H, Athanasopoulos C. Esthetic
periodontal considerations in orthodontic treatment--the
management of excessive gingival display. J Can Dent
Assoc. 2003;69(6):368-372.
34. Claman L, Alfaro M, Mercado A. An interdisciplinary
approach for improved esthetic results in the anterior
maxilla. J Prosthet Dent. 2003;89(1):1-5.
29
35. Kokich V. Esthetics and anterior tooth position: An
orthodontic perspective part II: Vertical position. J
Esthet Dent. 1993;5(4):174-179.
36. Sifakakis I, Pandis N, Makou M, Eliades T, Bourauel C.
A comparative assessment of the forces and moments
generated with various maxillary incisor intrusion
biomechanics. Eur J Orthod. 2010;32(2):159-164.
37. Deguchi T, Murakami T, Kuroda S, et al. Comparison of
the intrusion effects on the maxillary incisors between
implant anchorage and J-hook headgear. Am J Orthod
Dentofacial Orthop. 2008;133(5):654-660.
38. Uribe F, Havens B, Nanda R. Reduction of gingival
display with maxillary intrusion using endosseous dental
implants. J Clin Orthod. 2008;42(3):157-163.
39. Pikdoken L, Erkan M, Usumez S. Gingival response to
mandibular incisor extrusion. Am J Orthod Dentofacial
Orthop. 2009;135(4):432.e1-6.
40. Wertz R, Dreskin M. Midpalatal suture opening: a
normative study. Am J Orthod. 1977;71(4):367-381.
41. Johnson D, Smith R. Smile esthetics after orthodontic
treatment with and without extraction of four first
premolars. Am J Orthod Dentofacial Orthop.
1995;108(2):162-167.
42. Espeland L, Dowling P, Mobarak K, Stenvik A. Threeyear stability of open-bite correction by 1-piece
maxillary osteotomy. Am J Orthod Dentofacial Orthop.
2008;134(1):60-66.
43. Arpornmaeklong P, Shand J, Heggie A. Skeletal
stability following maxillary impaction and mandibular
advancement. Int J Oral Maxillofac Surg. 2004;33(7):656663.
44. Perez M, Sameshima G, Sinclair P. The long-term
stability of LeFort I maxillary downgrafts with rigid
fixation to correct vertical maxillary deficiency. Am J
Orthod Dentofacial Orthop. 1997;112(1):104-108.
30
45. Hwang W, Hur M, Hu K, et al. Surface anatomy of the
lip elevator muscles for the treatment of gummy smile
using botulinum toxin. Angle Orthod. 2009;79(1):70-77.
46. Polo M. Botulinum toxin type A (Botox) for the
neuromuscular correction of excessive gingival display on
smiling (gummy smile). Am J Orthod Dentofacial Orthop.
2008;133(2):195-203.
47. Ezquerra F, Berrazueta M, Ruiz-Capillas A, Arregui J.
New approach to the gummy smile. Plast Reconstr Surg.
1999;104(4):1143-1150; discussion 1151-1152.
48. Ishida L, Ishida L, Ishida J, et al. Myotomy of the
levator labii superioris muscle and lip repositioning: a
combined approach for the correction of gummy smile.
Plast Reconstr Surg. 2010;126(3):1014-1019.
31
CHAPTER 3:
JOURNAL ARTICLE
Abstract
Objective:
The purpose of this study is to evaluate
which patient characteristics, treatment modalities, and
cephalometric variations influence incisal display
changes.
Materials and Methods:
A randomized search of
pre and post treatment smiling frontal photographs was
conducted to select 20 patients who experienced the
greatest increase and 20 patients who experienced the
greatest decrease in incisal display upon smiling.
These
patients’ dental and skeletal characteristics were
analyzed as well as the treatment rendered.
Chi-square
analysis was performed within the 2 groups for age, sex,
Angle classification, overbite, curve of Spee, protrusion,
facial type, extractions, and various treatment
modalities.
Independent t-tests of pre and post
cephalometric values were conducted.
Results:
The
incisal display change for the increase group was from
9.72 mm to 12.75 mm, a 3.03 mm increase.
The incisal
display change for the decrease group was from 11.29 mm
to 8.1 mm, a 3.19 mm decrease.
Patients in the increase
group were likely to be female, have open bites, and had
headgear treatment.
Patients in the decrease group were
likely to have deep bites and had reverse curve arch
32
wires during treatment.
Cephalometrically, there were no
differences between the increase and decrease groups when
comparing T1 and T2.
However, in comparing intra-group
T1 values against T2 values it was found that in the
increase group the occlusal plane angle increased 3.97
degrees and the upper incisors were retracted 6.83
degrees.
The significant changes found in the decrease
group include increases in the length of the mandible of
5.16 mm and in the vertical eruption of the maxillary
molars of 2.3 mm.
Conclusions:
No pretreatment
cephalometric characteristics could be identified to
predict an increase or decrease in incisal display.
Patients in the increase group were likely to be female,
had open bites, had headgear treatment, experienced an
increase in the occlusal plane angulation, and
experienced a decrease in the upper incisor proclination.
Patients in the decrease group were likely to have deep
bites, use of reverse curve arch wires during treatment,
and experienced greater mandibular length and eruption of
the maxillary molars.
33
Introduction
Facial attractiveness, and more specifically smile
esthetics, has received a considerable amount of interest
in dental and orthodontic literature.1
This focus on
defining esthetically pleasing smiles has been the result
of society becoming more esthetically conscious.
Orthodontic treatment is mainly driven by the patients’
desire to improve their smile and overall esthetics.2
Given the esthetic demand, orthodontists not only have
the responsibility to produce functional and stable
occlusions but also beautiful smiles.
The vertical
position of the upper incisors in relation to the lips
and gingival tissue is a key determinant in the
attractiveness of a smile.
There is great variation in smiles among the general
population.
Two extremes can be identified as those who
show a very little amount of tooth structure and those
who show a significant amount of gingival tissue.
Van
der Geld found that in self-perception of patients’
smiles a full display of the maxillary anterior teeth
with a minor amount of gingival tissue was regarded to be
the most esthetic.3
Other studies have confirmed that
the ideal smile has the upper lip at or slightly above
34
the gingival margins of the maxillary incisors and the
lower lip at the level of the incisal edges of the
maxillary incisors.4-7
Less attractive smiles were
associated with an excessive amount of gingival tissue or
having the upper lip cover a large portion of the upper
incisors.8
Orthodontists are challenged to produce an ideal
smile despite the incredible amount of variation in
malocclusions that are presented to them.
While it may
be impossible for orthodontists to produce an ideal smile
outcome in every treated case, it is important to strive
for this esthetic outcome and to be educated about the
importance of the vertical position of the maxillary
incisors and how they change during treatment.
The purpose of this study is to identify which
treatment features or various dental or skeletal
characteristics are associated with changes in the
vertical incisal display when patients smile.
35
Materials and Methods
Sample
To obtain the sample, a random search of the
archives of Saint Louis University Center for Advanced
Dental Education was conducted.
Inclusion criteria for
the sample included being an orthodontic patient with a
pretreatment age of 10 to 14 years old; the availability
of pre and post orthodontic photographs, models, lateral
cephalometric radiographs; and, treatment records
describing the type of care rendered.
Only patients who
had a remarkable increase or decrease in the incisal
display position based on the pre and post frontal smile
photographs were included.
A total of 127 patients were
initially selected, 69 who had an increase in incisal and
gingival display and 58 who had a decrease in incisal and
gingival display.
In order to focus on the extreme
variations the top 20 patients who experienced the
greatest change (increase or decrease) in incisal display
were selected for this study.
To determine the amount of incisal display the
saggital width of the pre and post treatment upper left
central incisor was measured by a digital caliper.
It is
important to note that the incisor width measurement was
not the mesiodistal width of the tooth as any rotation of
36
that tooth would give skewed measurements when used
against a flat photograph.
Instead a flat saggital view
and measurement of the upper left incisor width was used
for both pre and post treatment photographs.
This
ensures that the measurement used for calibration
involving the models is as close as possible to the
actual photographs in the Dolphin software (Dolphin
Imaging & Management Solutions, version 10.5, Chatsworth,
CA).
These mesiodistal measurements were then calibrated
into Dolphin on the patient’s pre and post orthodontic
smiling frontal photographs.
Once the saggital calibration was completed in
Dolphin, a measurement of the vertical height was
obtained from the incisal edge of the maxillary left
incisor to the inferior border of the upper lip.
These
measurements were completed on both pre (T1) and post
(T2) frontal smiling photographs.
The measurement of T2
was subtracted from T1 to obtain the extent of the change.
The measurements were recorded in hundredths of a
millimeter.
Subjects were grouped according to which
patients experienced the greatest change (increase or
decrease) in their incisal display.
Further scrutiny on the extent of their smile was
conducted to ensure pre and post smiling photographs had
37
similar head and lip position.
Some patients who had
ranked very high in having the greatest change were
excluded from the final sample due to differences in the
extent of their smiles.
Although this may have excluded
some patients who truly did experience a significant
change, it was the purpose of this study to account for
change in their smiles that does not come from varying
lip position.
The pre and post incisal display
measurements were entered in to an Excel spreadsheet to
determine the change.
Data Collection
A number of additional sets of data were collected
from the final sample, including; age, sex, Angle
classification (I, II, or III), overbite position (open,
closed – less the 50% overbite, or deep – greater than
50% overbite), curve of Spee (flat – 0 mm, moderate – 1
to 3 mm, or deep – 4 mm or greater), protrusiveness, and
facial type (dolichofacial, mesofacial, or brachyfacial).
Cephalometric measurements from T1 and T2 were
digitized in Dolphin.
(see table 3.1)
38
Table 3.1 Cephalometric Measurements
Measurement
Sella-Nasion to A-point Angle
Sella-Nasion to B-point Angle
A-Point-Nasion to B-Point Angle
Wits Appraisal (mm)
Convexity Angle (Nasion-A-Pt. to A-Pt.-Pogonion)
Posterior Nasal Spine to A-Pt. (mm)
Mandibular Length - Articular to Gnathion (mm)
Pogonion to Nasion-B-Point (mm)
Maxillary Mandibular Differential (mm)
Frankfort Mandibular Angle
Sella-Nasion to Mandibular Plane Angle
Y - axis Angle (Sella-Gnathion to Sella-Nasion)
Cranio-Max. Base/Sella-Nasion-Palatal Plane Angle
Occlusal Plane to Sella-Nasion Angle
Anterior Face Height (mm:)
Upper Face Height (mm)
Upper Face Height:Total Facial Height (%)
Lower Face Height (mm)
Lower Face Height:Total Facial Height (%)
Posterior - Anterior Face Height (%)
Sella - Gonion (mm)
Upper Incisor to Sella-Nasion Angle
Upper incisor to Nasion-A-Point Angle
Upper incisor to Nasion-A-Point (mm)
Incisor Mandibular Plane Angle
Frankfort Mandibular Incisal Angle
Lower Incisor Protrusion
Lower Incisor to Nasion-B-Point Angle
Lower Incisor to Nasion-B-Point (mm)
Upper Molar to Ptyergomaxillary Fissure (mm)
Interincisal Angle
Upper Lip to E-Plane (mm)
Lower Lip to E-Plane (mm)
Z Angle
Abbreviation
SNA
SNB
ANB
WITS
NA-APo
PNS - A
Ar-Gn
Pog - NB
Co-Gn - Co-ANS
FMA
SN - GoGN
SGN - SN
CMB/SNPP
OP - SN
NaMe
N-ANS
N-ANS/N-Me
ANS - Me
ANS-Me/N-Me
S-Go/N-Me
S-Go
U1-SN
U1-NA
U1-NA
IMPA
FMIA
L1-Apo
L1-NB
L1-NB
U6 - PT
U1-L1
UL - E
LL - E
Z
Additional data was collected from the treatment
records including; length of treatment, treatment
philosophy, extractions, headgear, rapid maxillary
expansion, facemask, instrusion arch/mechanics, reverse
39
curve wires, bite plate, functional treatment, elastic
type and duration, and Class II elastics on upper round
arch wires.
(See table 3.2)
Table 3.2 Description of Treatment Rendered
Treatment
Length of Treatment
Treatment Philosphy
- Tweed
- Tip Edge
- Standard Edgewise
- Straight wire
Extractions
- 4 Premolars
- Upper Premolars Only
Treatment Mechanics
- Headgear
- Rapid Palatal Expander
- Face Mask
- Intrusion Arch/Mechanics
- Reverse Curve Arch Wires
- Bite Plate
- Functional
- Elastics - Triangles over 6 months
- Elastics - Class II's over 6 months
Data Analysis
Independent t-tests were used to determine the
statistically significance of the incisal changes and the
cephalometric changes.
Chi-square analysis was used to
compare the patient characteristics and treatment
modality differences.
All statistical computations were
calculated by means of standard computer software (SPSS
40
for Windows, release 18.0.0, Inc., Chicago, IL).
Statistical significance was set at P <0.05.
Results
SPSS was used to determine the average heights of
incisal display, the average change for each group, and
the statistical significance.
The increase group at T1
had an average incisal display of 9.72 mm and at T2 had
an average display of 12.75 mm.
The increase group had
an average increase of 3.03 mm.
The decrease group at T1
had an average incisal display of 11.29 mm and at T2 had
an average incisal display of 8.10.
The decrease group
had an average decrease of 3.19 mm.
Analysis of the
incisal display found significant changes in both the
increase and decrease group (see table 3.3).
This also
validates that this sample is appropriate for studying
changes in incisal display.
41
Table 3.3 Statistical analysis of
incisal display changes
Group
Increase
Decrease
Significance
Initial
Incisal
Display
Standard
(mm)
Deviation
9.72
1.31
11.29
1.84
*0.004
Final
Incisal
Change in
Display
Incisal
Standard
(mm)
Deviation Display (mm)
12.75
1.27
3.03
8.1
2.07
-3.19
**0.000
**0.000
*p<0.01
**p<0.001
Analysis of the patient characteristics showed that
statistically significant variations among the two groups.
Patients in the increase group were significantly female
and had open bites.
Patients in the decrease group were
near equally male or female and significantly had deep
bites.
Statistically insignificant characteristics are
age, dental class, curve of Spee, and profile
protrusiveness and facial type. (see table 3.4)
42
Table 3.4 Statistical analysis
of patient characteristics
Group
Mean Age
Increase
Decrease
13.0
12.6
Significance
0.235
Sex
Female - 17
Male - 3
Female - 11
Male - 9
Angle Class
Class I - 11
Class II - 7
Class III - 2
Class I - 11
Class II - 9
Class III - 0
Overbite
Open - 10
Closed - 9
Deep -1
Open - 0
Closed - 5
Deep - 15
Curve of Spee
Flat - 3
Moderate - 11
Deep - 6
Flat - 5
Moderate - 11
Deep - 4
0.638
Protrusive
Yes - 10
No - 10
Yes - 11
No - 9
0.752
Facial Type
Dolicho - 5
Meso - 13
Brachy - 2
Dolicho - 2
Meso - 11
Brachy - 7
0.121
* 0.038
0.325
**0.000
* p<0.05
** p<0.001
Cephalometric analysis showed no significant
difference between T1 of the increase group and T1 of the
decrease group (see table 3.5).
Furthermore, no
significant difference was found between T2 of the
increase group and T2 of the decrease group (see table
3.6).
When comparing T1 to T2 within each group there
were significant changes.
This is expected as all these
patients started treatment between the ages of 10-14
43
years old and growth alone would change their
cephalometric measurements.
However, the most meaningful
and significant measurements are those that changed in
one group, but did not change in the other group.
In the increase group the maxillary mandibular
length differential, occlusal plane to sella-nasion plane
angle, anterior face height, sella to gonion distance,
and upper incisor to sella-nasion angle were all
significantly different from T1 to T2.
In the decrease
group mandibular length, maxillary mandibular length
differential, anterior facial height, sella to gonion
distance, and maxillary molar to ptyergomaxillary fissure
distance were all significantly different from T1 to T2.
With eliminating what changed in both groups it is
possible to identify that in the increase group the
occlusal plane significantly increased by 3.97 degrees
and that the upper incisor to sella-nasion angle
decreased by 6.83 degrees. (See table 3.7)
Again, with eliminating what changed in both groups
it is possible to identify that in the decrease group the
mandibular length significantly increased by 5.16 mm and
that the vertical eruption of the maxillary molar
significantly increased by 2.3 mm.
44
(See table 3.8)
Table 3.5 Pre treatment cephalometric
measures for increase and
decrease groups
Variable
SNA
SNB
ANB
WITS
NA-APo
PNS - A
Ar-Gn
Pog - NB
Co-Gn - Co-ANS
FMA
SN - GoGN
SGN - SN
CMB/SNPP
OP - SN
NaMe
N-ANS
N-ANS/N-Me
ANS - Me
ANS-Me/N-Me
S-Go/N-Me
S-Go
U1-SN
U1-NA (degree)
U1-NA (mm)
IMPA
FMIA
L1-Apo
L1-NB (degree)
L1-NB (mm)
U6 - PT (mm)
U1-L1
UL - E
LL - E
Z
T1 Increase T1 Decrease Difference
80.73
81.48
0.75
77.39
77.77
0.38
3.34
3.70
0.37
1.10
0.72
-0.38
5.60
6.64
1.04
45.16
45.65
0.49
111.31
109.33
-1.98
0.95
0.93
-0.02
30.11
28.17
-1.94
26.32
25.76
-0.56
34.68
32.87
-1.81
69.54
68.30
-1.24
5.77
7.15
1.38
15.52
16.53
1.01
111.89
109.48
-2.42
48.52
48.75
0.23
42.60
44.01
1.42
65.49
62.17
-3.32
57.41
55.99
-1.42
71.10
69.29
-1.82
62.28
62.61
0.33
105.94
104.01
-1.94
25.20
22.51
-2.69
6.33
5.15
-1.19
92.78
93.35
0.57
60.90
60.91
0.01
3.78
2.56
-1.22
27.53
26.87
-0.65
6.10
5.20
-0.90
18.72
16.66
-2.06
123.93
126.94
3.01
-0.67
-0.65
0.03
1.90
1.45
-0.45
69.46
71.05
1.60
No significance found
45
Sig
0.597
0.770
0.696
0.762
0.663
0.701
0.339
0.976
0.259
0.775
0.385
0.407
0.276
0.448
0.253
0.824
0.082
0.061
0.082
0.332
0.839
0.452
0.269
0.212
0.833
0.997
0.238
0.814
0.413
0.108
0.465
0.984
0.759
0.688
Table 3.6 Post treatment cephalometric
measures for increase and
decrease groups
Variable
SNA
SNB
ANB
WITS
NA-APo
PNS - A
Ar-Gn
Pog - NB
Co-Gn - Co-ANS
FMA
SN - GoGN
SGN - SN
CMB/SNPP
OP - SN
NaMe
N-ANS
N-ANS/N-Me
ANS - Me
ANS-Me/N-Me
S-Go/N-Me
S-Go
U1-SN
U1-NA (degree)
U1-NA (mm)
IMPA
FMIA
L1-Apo
L1-NB (degree)
L1-NB (mm)
U6 - PT (mm)
U1-L1
UL - E
LL - E
Z
T2 Increase T2 Decrease Difference
79.30
80.77
1.47
76.30
77.96
1.66
3.21
2.81
-0.40
-1.22
-0.27
0.95
4.54
3.92
-0.62
45.69
46.20
0.51
114.37
114.49
0.12
1.48
1.78
0.31
33.79
33.16
-0.63
26.49
26.33
-0.16
35.30
33.03
-2.27
71.20
69.03
-2.18
7.03
7.50
0.47
19.48
16.57
-2.92
117.51
115.91
-1.60
50.39
50.76
0.37
42.64
43.62
0.98
68.48
66.41
-2.07
57.36
56.39
-0.98
74.63
73.82
-0.81
63.00
64.13
1.13
99.11
102.93
3.82
19.81
22.17
2.36
4.80
4.15
-0.65
94.01
94.90
0.89
59.51
58.83
-0.68
4.02
3.19
-0.83
28.57
28.71
0.13
6.37
5.64
-0.74
19.93
18.96
-0.97
128.61
126.32
-2.29
-2.01
-2.52
-0.51
0.70
-0.47
-1.17
72.12
74.18
2.05
No significance found
46
Sig
0.263
0.205
0.627
0.295
0.784
0.619
0.961
0.659
0.709
0.936
0.257
0.132
0.689
0.059
0.495
0.716
0.269
0.302
0.269
0.656
0.463
0.115
0.322
0.473
0.710
0.749
0.329
0.941
0.406
0.381
0.429
0.632
0.390
0.573
Table 3.7 Pre and post cephalometric
measures for increase group
Variable
SNA
SNB
ANB
WITS
NA-APo
PNS - A
Ar-Gn
Pog - NB
Co-Gn - Co-ANS
FMA
SN - GoGN
SGN - SN
CMB/SNPP
OP - SN
NaMe
N-ANS
N-ANS/N-Me
ANS - Me
ANS-Me/N-Me
S-Go/N-Me
S-Go
U1-SN
U1-NA (degree)
U1-NA (mm)
IMPA
FMIA
L1-Apo
L1-NB (degree)
L1-NB (mm)
U6 - PT (mm)
U1-L1
UL - E
LL - E
Z
T1 Increase T2 Increase
80.73
79.30
77.39
76.30
3.34
3.21
1.10
-1.22
5.60
4.54
45.16
45.69
111.31
114.37
0.95
1.48
30.11
33.79
26.32
26.49
34.68
35.30
69.54
71.20
5.77
7.03
15.52
19.48
111.89
117.51
48.52
50.39
42.60
42.64
65.49
68.48
57.41
57.36
71.10
74.63
62.28
63.00
105.94
99.11
25.20
19.81
6.33
4.80
92.78
94.01
60.90
59.51
3.78
4.02
27.53
28.57
6.10
6.37
18.72
19.93
123.93
128.61
-0.67
-2.01
1.90
0.70
69.46
72.12
*P<0.05
47
Change
-1.43
-1.09
-0.13
-2.32
-1.07
0.53
3.07
0.53
3.68
0.17
0.62
1.66
1.26
3.97
5.61
1.87
0.05
3.00
-0.05
3.53
0.72
-6.83
-5.39
-1.54
1.24
-1.39
0.24
1.05
0.27
1.21
4.69
-1.34
-1.20
2.67
Sig
0.304
0.393
0.879
0.058
0.623
0.654
0.128
0.473
*0.034
0.930
0.735
0.210
0.309
*0.005
*0.004
0.070
0.957
0.056
0.957
*0.031
0.594
*0.009
0.054
0.157
0.604
0.537
0.806
0.614
0.763
0.357
0.177
0.275
0.387
0.456
Table 3.8 Pre and post cephalometric
measures for decrease group
Variable
SNA
SNB
ANB
WITS
NA-APo
PNS - A
Ar-Gn
Pog - NB
Co-Gn - Co-ANS
FMA
SN - GoGN
SGN - SN
CMB/SNPP
OP - SN
NaMe
N-ANS
N-ANS/N-Me
ANS - Me
ANS-Me/N-Me
S-Go/N-Me
S-Go
U1-SN
U1-NA (degree)
U1-NA (mm)
IMPA
FMIA
L1-Apo
L1-NB (degree)
L1-NB (mm)
U6 - PT (mm)
U1-L1
UL - E
LL - E
Z
T1 Decrease
81.48
77.77
3.70
0.72
6.64
45.65
109.33
0.93
28.17
25.76
32.87
68.30
7.15
16.53
109.48
48.75
44.01
62.17
55.99
69.29
62.61
104.01
22.51
5.15
93.35
60.91
2.56
26.87
5.20
16.66
126.94
-0.65
1.45
71.05
T2 Decrease
80.77
77.96
2.81
-0.27
3.92
46.20
114.49
1.78
33.16
26.33
33.03
69.03
7.50
16.57
115.91
50.76
43.62
66.41
56.39
73.82
64.13
102.93
22.17
4.15
94.90
58.83
3.19
28.71
5.64
18.96
126.32
-2.52
-0.47
74.18
*P<0.05
48
Change
-0.71
0.19
-0.89
-0.99
-2.72
0.55
5.16
0.85
4.99
0.57
0.16
0.73
0.35
0.04
6.44
2.01
-0.39
4.25
0.39
4.54
1.52
-1.08
-0.34
-1.00
1.55
-2.08
0.63
1.84
0.44
2.30
-0.62
-1.88
-1.92
3.13
Sig
0.598
0.890
0.325
0.305
0.272
0.627
*0.045
0.180
*0.006
0.776
0.942
0.648
0.771
0.979
*0.015
0.059
0.638
0.054
0.638
*0.033
0.396
0.661
0.865
0.183
0.571
0.459
0.487
0.483
0.688
*0.034
0.866
0.089
0.184
0.441
Analysis of the treatment rendered shows that two
treatment mechanics are statistically significant between
the two groups.
First, headgear was significantly more
common in the increase group.
Second, reverse curve arch
wires were significantly used more often in the decrease
group than the increase group.
Statistically
insignificant treatment characteristics include: length
of treatment, treatment philosophy, extractions, rapid
palatal expanders, facemask, intrusion arch
wires/mechanics, biteplates, functional appliances,
triangular elastics for over 6 months, Class II elastics
for over 6 months, and Class II elastics on round wire.
(see table 3.9)
Patient compliance issues were not
recorded.
49
Table 3.9 statistical analysis of
treatment rendered
Treatment
Number
Length of Treatment
Range of Length of Treatment
Treatment Philosphy
- Tweed
- Tip Edge
- Standard Edgewise
- Straight wire
Extractions
- 4 Premolars
- Upper Premolars Only
Treatment Mechanics
Headgear
Rapid Palatal Expander
Face Mask
Intrusion Arch/Mechanics
Reverse Curve Arch Wires
Bite Plate
Functional
Elastics - Triangles over 6 months
Elastics - Class II's over 6 months
Elastics - Class II's on round wire
* p<0.05
50
Increase
Group
20
22.0
17 - 31
Decrease
Group
20
23.6
16-31
2
1
5
12
0
4
2
14
Sig
0.712
0.155
0.115
4
0
7
3
6
2
1
3
6
2
3
6
11
6
1
1
0
2
13
2
1
4
13
9
*0.037
0.548
0.311
0.633
*0.027
1.000
0.292
0.256
0.519
0.327
Discussion
This study follows a previous study conducted at
Saint Louis University in 2009 that examined the lateral
cephalometric radiographs of patients who experienced the
greatest change in gingival display following orthodontic
treatment.9
This current study also investigated
subjects who experienced the greatest change (increase or
decrease) in incisal display following orthodontic
treatment.
In addition to the previous study that
examined lateral cephalometric measurements, the purpose
of this study was to determine if any aspects of
treatment or various dental or skeletal characteristics
are associated with changes in the incisal display when
smiling.
The independent t-tests comparing the increase and
decrease groups validate the statistical difference
between the two groups and the appropriateness of the
sample for this study.
The increase group experienced a
mean increase of 3.03 mm while the decrease group
experienced a mean decrease of 3.19 mm.
It is
significant to note the difference in incisal display at
T1 between the two groups.
The increase group had a mean
incisal display of 9.72 mm while the decrease group had a
51
mean incisal display of 11.29, a difference of 1.57 mm.
Given that the mean pre orthodontic crown height of the
maxillary central incisor is 9.4 mm, it can be said at T1
that the increase group has a near ideal incisal display
and the decrease group shows a moderate amount of
gingival tissue when smiling.10
The T2 measurements show
a significant reversal in the incisal display with the
increase group having a “gummy smile” at 12.75 mm of
incisal display and the decrease group having a
significant decrease of incisal display at 8.1 mm.
Chi-square analysis of patient pre-treatment
characteristics revealed 3 significant findings.
First,
patients who experienced the greatest increase in incisal
display were significantly female.
Second, the increase
group also had a significant prevalence of open bites at
the start of treatment.
Third, patients who experienced
that greatest decrease in incisal display significantly
had deep bites at the start of treatment.
The female predilection for “gummy smiles” is in
agreement with the literature.11-13
The fact that 85% of
the patients in the increase group were female indicates
a very strong female association.
The study showed a
near equal amount of females and males in the decrease
group.
52
The strongest statistical variable between the 2
groups is the overbite.
Half of the patients in the
increase group had an open bite while none of the
patients in the decrease group had an open bite.
Alternatively, 15 of the patients in the decrease group
had deep bites while only 1 of the patients in the
increase group had a deep bite.
The effect of open and
deep bites in determining whether the patient would be
associated with changes in their incisal display appears
logical.
A goal of orthodontic treatment in a patient
with an open bite would be to close the bite to a normal
amount of overbite.
A goal of orthodontic treatment in a
deep bite patient would be to open the bite to a normal
amount of overbite.
Pure extrusion and intrusion of the
anterior teeth may be the simplest mechanical treatments
to achieve those desired goals. Such mechanics would have
the greatest effect on incisor position and explain, in
part, the change in incisal display.
Cephalometrically, independent t-tests showed that
the no pretreatment characteristic could be significantly
identified.
Although weak, there was a tendency shown in
the increase group to have an association of larger lower
facial height as compared to the decrease group.
This
increased length from the anterior nasal spine to menton
53
correlates well with the prevalence of open bites in the
increase group mentioned previously.
Isaacson found that
patients with open bites have longer maxillary alveolar
processes.14
Other studies have found vertical maxillary
excess to be associated with “gummy smiles.”11,15,16
No significant post treatment cephalometric
measurement could be identified; however, there was one
noted weak association between the two groups.
The
occlusal plane to the sella–nasion angle tends to be
higher in the increase group.
Suh found that patients
with an increased amount of upper incisor display also
had a steeper occlusal plane to sella-nasion plane
angle.15
Isaacson found a high correlation between the
occlusal plane angulation and patients with a high
mandibular plane who have a tendency for an open bite.14
This clockwise rotation of the occlusal plane indicates
either a relative intrusion of the posterior maxillary
dentition and/or a relative extrusion of the anterior
maxillary dentition.
The clockwise rotation would likely
produce additional vertical display of the maxillary
incisors.
When comparing the intra-group cephalometric numbers
there were a number of significant measurements within
both groups.
The patients were ages 10 to 14 years old
54
at the start of treatment and growth without treatment
would produce significant changes when comparing T1 to T2.
Eliminating the similarities in both groups brings to
light what significant changes occurred between the two
groups.
The significant similarities eliminated in both
groups which can be attributed to growth are: maxillary
mandibular length differential, anterior face height, and
sella to gonion distance.
The significant changes that were unique to the
increase group include the increased occlusal plane to
sella–nasion angle and the decreased upper incisor to
sella-nasion angle.
The occlusal plane rotated clockwise
by 3.97 degrees to an angle of 19.48 degree, representing
a relative intrusion of the maxillary molars and relative
extrusion of maxillary incisors.
This confirms the
finding by Suh and Isaacson, previously mentioned, that
an increased occlusal plane angle is associated with
increased incisal display.
The upper incisor
proclination was reduced 6.83 degrees to 99.11 degrees.
The upper incisors at T2 represent a retroclined position
of the upper incisors.
Although insignificant, the
interincisal angle increased 5 degrees due to this
retroclined position of the upper incisors.
This is
confirmed by the lower incisors not changing position, as
55
recorded by IMPA.
Sarver found that incisor proclination
can effect the visual perception of incisal display
stating “… flared maxillary incisors tend to reduce
incisor display, and upright maxillary incisors tend to
increase it.”17
Examining the weak tendencies within the increase
group suggests other cephalometric changes that could
contribute to the change in incisal display.
First, the
upper incisor to nasion-A-point decreased by 5.39 degrees.
This corresponds well to the fact that the upper incisor
to sella-nasion angle decreased significantly.
Second,
the Wits appraisal showed a weak association within the
increase group, beginning at 1.1 mm and ending at -1.22
mm, a change of 2.32 mm.
With all else being equal, an
increase in the occlusal plane angle would produce a
negative change in the Wits appraisal.
This supports the
significance of the occlusal plane angle and the role it
plays in the increase of incisal display.
Significant changes that were unique to the decrease
group include the mandibular length and maxillary molar
to ptyergomaxillary fissure distance.
The mandibular
length increased 5.16 mm from T1 to T2 in the decrease
group.
This compares to 3.07 mm from T1 to T2 in the
increase group.
The maxillary molars erupted 2.3 mm in
56
the decrease group compared to the increase group at 1.2
mm.
The additional eruption of the maxillary molars
suggests that in such patients a clockwise rotation of
the occlusal plane does not occur and consequently limits
additional eruption or extrusion of the upper incisors.
The mechanics of the treating the decrease group
involve opening a deep bite.
It can be suggested that
the effects of leveling the arches through opening a deep
bite produces an extrusive force on the maxillary molars.
Intra arch mechanics like intrusion arches or reverse
curve arch wires not only intrude the maxillary anterior
dentition but also extrude the maxillary molars.18
Chi-square analysis of the treatment showed that
patients with increased incisal display had a
significantly higher prevalence of headgear at 30%, and
patients with decreased incisal display had a
significantly higher prevalence of reverse curve arch
wires during some point in their treatment at 65%.
The
significance of headgear to the increase group is not
easily ascertained.
The use of headgear is multifold
including, but not limited to Class II molar correction,
intrusion, and increased anchorage.
Although the reason
behind treating with a headgear and the associated
headgear mechanics were not recorded, it is important to
57
note that patient compliance is a major factor in
headgear treatment.
It is with caution that headgears
are associated with increased incisal display due to a
lack of cause-and-effect in directly changing the incisor
position.
The frequency of use and significance of reverse
curve arch wires in the decrease group can best be
associated with the predominance of deep bites.
The
mechanics of reverse curve arch wires produces an
intrusive force labial to the center of resistance on the
anterior teeth and consequently produces an extrusive
force in the posterior teeth.18
The use of reverse curve
arch wires correlates extremely well with the fact that
patients in the decrease group started treatment with
deep bites and had significant eruption of the maxillary
molars.
The findings of this study suggest that special care
should be taken in treating females with open bites.
These patients will have the greatest probability of an
increase in incisal display.
It can also be suggested
that treatments which produce increased incisal display
are associated with increasing the occlusal plane angle
and uprighting the maxillary incisors.
58
From this study it can be suggested that patients
with deep bites will experience a decrease in their
incisal display levels.
The treatments and related
growth which produce decreased levels of incisal display
are associated with increasing the eruption of the
maxillary molars, greater mandibular length, and the use
of reverse curve arch wires.
59
Conclusion
The findings of this investigation showed the
following:
1.
Patients with the greatest probability for an
increase in incisal display will be female and have
open bites.
Patients with the greatest chance for a
decrease in incisal display will likely have deep
bites.
2.
Headgear treatment appears to be associated with
increases in incisal display, but a direct causeand-effect could not be determined. Reverse curve
arch wires appear to be associated with decreases in
incisal display.
3.
Cephalometricly, patients who experience an increase
in incisal display have a clockwise rotation of the
occlusal plane angle and end treatment with less
protrusive incisors.
Patients who experience a
decrease in incisal display have greater mandibular
growth and increased vertical eruption of the
maxillary molars.
60
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62
VITA AUCTORIS
Joseph D. Parker was born in Logan, Utah on December
31, 1974 to Brent D. and Sharon Z. Parker.
He is the
third of six children
He grew up in Wellsville, Utah and graduated from
Mountain Crest High School in May 1993.
He attended Utah
State University in Logan, Utah where he obtained a
Bachelor of Arts degree in 1998.
He obtained his Doctor
of Dental Surgery from the University of Michigan in May
2008.
In June 2008, he began his orthodontic residency
program at Saint Louis University, Center for Advanced
Dental Education, where he expects to receive a Master of
Science in Dentistry in January 2011.
Joseph met his wife, Jan, while attending Utah State
University.
They were married on May 8, 1999.
four children.
They have
Upon graduation, they plan to move to
Ellensburg, Washington where Joseph will enter private
practice.
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