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Review Article
Smile analysis in orthodontics
Sapna Singla, Gurvanit Lehl
Department of Dentistry, Government Medical College and Hospital, Chandigarh, India
ABSTRACT
In the recent years, esthetics has become the primary consideration for the patients seeking
orthodontic treatment. Although ideal occlusion should be the primary functional goal of
orthodontics, the esthetic outcome is also critical for patient satisfaction and therefore essential
to the overall treatment objectives. Hence, orthodontic treatment must incorporate various
esthetic elements of smile to achieve desirable results. The article describes the principles of
smile analysis, that should be considered during orthodontic diagnosis and treatment planning.
Key words: Esthetic components of smile, smile analysis, smile designing
Introduction
Address for Correspondence:
Dr. Sapna Singla,
Department of Dentistry, Government
Medical College and Hospital,
Chandigarh, India.
E-mail: [email protected]
Date of Submission: 24-10-2013
Date of Acceptance: 20-02-2014
Access this article online
Website:
www.indjos.com
DOI:
10.4103/0976-6944.136836
Quick Response Code:
Smile is one of the most important expression
contributing to facial attractiveness. An
attractive or pleasing smile enhances the
acceptance of individual in the society by
improving interpersonal relationships.[1] With
patients becoming increasingly conscious of
a beautiful smile, smile esthetics has become
the primary objective of orthodontic
treatment.[2] Modern orthodontics deals not
only with the traditional dental and skeletal
aspects, but also face as first priority. The
most important esthetic goal in orthodontics
is to achieve a balanced smile, which can be
best described as an appropriate positioning
of teeth and gingival scaffold within the
dynamic display zone.[3] Smile analysis is
part of a facial analysis and allows dentists
to recognize positive and negative elements
in each patient’s smile. Depending on the
type of malocclusion, facial pattern of the
patient and mechanics adopted, orthodontic
treatment can prove either beneficial or
harmful to smile esthetics. Thus, it is
reasonable to regard smile analysis as an
important tool for diagnosis and orthodontic
treatment planning. The purpose of this
article is to discuss various elements of
a pleasing smile and discuss their impact
on orthodontic diagnosis and treatment
planning.
Smile analysis should involve evaluation
of certain elements in specific sequence:[4]
Indian Journal of Oral Sciences y Vol. 5 y Issue 2 y May-Aug 2014
•
•
•
•
Dento-facial analysis
Dentolabial analysis
Dento-gingival analysis
Dental analysis.
Dento-facial analysis
Midline
The starting point of the esthetic treatment
plan is the facial midline. A correctly
placed midline contributes to the desirable
effect of balance and harmony of the
dental composition. One of the goals of
the orthodontic treatment is to achieve
maxillary and mandibular midlines that are
coincident-both with each other and with
the facial midline. Coincident midline serves
both a functional and an esthetic purpose.
The most practical guide to locate the facial
midline is to use two anatomical landmarks
as references. The first is a point between
the brows known as the nasion. The second
is the base of the philtrum, also referred
to as the cupid’s bow in the center of the
upper lip.[5,6] A line drawn between these
landmarks not only locates the position
of the facial midline but also determines
the direction of the midline.[5] Ideally the
maxillary central incisor midline should
coincide with the facial midline. However if
it is not possible, then the midline between
maxillary central incisors should be strictly
vertical and parallel to the facial midline.[5-9]
Minor discrepancies between facial and
dental midlines are acceptable and in many
instances, not noticeable as long as central
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Singla and Lehl: Smile analysis in orthodontics
incisor crown is not significantly canted. Although, it is
desirable to have concordant maxillary and mandibular
midlines for occlusion purposes but mandibular midline
is not a very reliable reference point since in 75% of cases
maxillary and mandibular midlines do not coincide.[10,11]
Mismatch between maxillary and mandibular midline does
not affect esthetics since mandibular teeth are not usually
visible while smiling.[5]
Dento-labial analysis
Maxillary incisor display at rest
The starting point of a smile is the lip line at rest, with
an average maxillary incisor display of 1.91 mm in men
and nearly twice that amount, 3.40 mm in women.[12] The
amount of incisor show at rest is the most important
esthetic parameter because decreased incisor display is a
characteristic of ageing. This steady decline in maxillary
tooth exposure at rest with aging, is accompanied by an
increase in mandibular incisor display.[12,13] Therefore in an
adult patient with 3 mm of maxillary incisor display at rest,
intrusion should be planned carefully.
Numerous reports in the past have shown that an average
30-year-old woman displays about 3.5 mm of maxillary
central incisor tooth structure when the lips are at rest.[12,14,15]
For most patients who are esthetically conscious, 3-4 mm
of incisor display at rest should be ideal.[4] Excessive tooth
display is judged better at rest than on smile, because lip
elevation on smiling is quite variable. If exposure at rest is
normal, even if a considerable amount of gingival display
occurs on smiling, this should be considered normal for
that individual.
Figure 1: The entire cervicoincisal length of maxillary anterior teeth
along with interproximal gingivae. Note the parallel relation of the
incisal edges to the inner contour of lower lip during smiling
Figure 2: High smile with complete display of the entire cervicoincisal
length and a contiguous band of gingival tissues
Maxillary incisor display on smile
The lip line is the amount of vertical tooth exposure in
smiling-in other words, the height of the upper lip relative
to the maxillary central incisors. As a general guideline, the
lip line is optimal when the upper lip reaches the gingival
margin, displaying the total cervico-incisal length of the
maxillary central incisors, along with the interproximal
gingivae while smiling [Figure 1].[16,17] A high lip line exposes
all of the clinical crowns plus a contiguous band of gingival
tissue, whereas a low lip line displays <75% of the maxillary
anterior teeth [Figures 2 and 3].[1,18] Because female lip lines
are an average 1.5 mm higher than male lip lines, 1-2 mm
of gingival display at maximum smile could be considered
normal for females.[1,19,20] In a study by Kokich et al.,[21] it
was demonstrated that dental evaluators and lay people
still considered it esthetic if 2 mm of gingiva showed in
a full smile. According to Mc Laren and Cao, showing up
to 3 mm of gingival in a full smile is still in the “esthetic
zone,” especially if there is slightly more than 8 mm of lip
movement during a smile.[4]
50
Figure 3: Low smile with <75% display of the maxillary incisors
during smiling
Ideally the gingival margins of the maxillary canines should be
coincident with the upper lip and the lateral incisors should
be positioned slightly inferior to the adjacent teeth. But such
relationship is age related, as tooth display and gingival display
are more in children than adults. The amount of vertical
exposure on smiling depends on many other factors such as
vertical maxillary height, crown height, and incisor inclination
besides upper lip length and lip elevation.[22]
Smile arc
The smile arc is defined as the relationship of the contour
of the incisal edges of the maxillary anterior teeth relative
to the curvature of lower lip during a social smile.[1,18,23-26]
On the basis of this relationship, smile lines are of three
types. Consonant smile arc has the curvature of incisal
edges of the maxillary anterior teeth parallel to the
Indian Journal of Oral Sciences y Vol. 5 y Issue 2 y May-Aug 2014
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Singla and Lehl: Smile analysis in orthodontics
upper border of the lower lip [Figure 1].[27] It has been
suggested that for consonant smile arc, the centrals should
appear slightly longer or, at least, not any shorter than
the canines along the incisal plane.[1] Straight smile arc is
that in which the incisal edges of the maxillary anterior
teeth are in a straight line to the upper border of the lower
lip [Figure 4]. Reverse or non-consonant smile arc is the
one in which the incisal edges of the maxillary anterior
teeth are curved in reverse to the upper border of the
lower lip.[23,24] Reverse smile arc occurs when the centrals
are shorter than the canines along the incisal plane which
can be due to occlusal malfunction or loss of vertical
dimension.[5] Parallel and straight smiles provide better
esthetic than reverse smile.
Figure 4: Straight smile arc. Note the flat maxillary incisal edges
relative to the curvature of lower lip
Since the smile arc depends upon occlusal plane inclination
and second order crown angulations in the upper anterior
teeth, there are some limitations to the achievement of this
ideal smile arc on every patient. A reasonable objective is to
prevent a flat or reverse smile arc and to obtain some degree
of curvature that resembles, one found in the lower lip.[28]
Smile symmetry
An asymmetry in the smile can be due to asymmetric
smile curtain or transverse cant of the maxillary occlusal
plane. Transverse cant can be due to different amounts
of tooth eruption on the right and left sides [Figure 5] or
skeletal asymmetry of mandible resulting in compensatory
cant of maxilla. In an asymmetric smile curtain, there
is a difference in the relative positioning of the corners
of the mouth in the vertical plane [Figure 6].[16,29] It can
be assessed by the parallelism of the commissural and
pupillary lines. Although the commissures move up and
laterally in smiling, studies have shown a difference in the
amount and direction of movement between the right and
left sides.[30-32] A large differential elevation of the upper
lip in an asymmetrical smile may be due to a deficiency of
muscular tonus on one side of the face.[16] Myofunctional
exercises have been recommended to help overcome this
deficiency and restore smile symmetry.[16,33] It is estimated
that 8.7% of normal adults have asymmetric smiles.[32] It
is poorly documented in static photographic images and
is documented best in digital video clips.[3]
Buccal corridor
Buccal corridor refers to dark space (negative space) visible
during smile formation between the corners of the mouth
and the buccal surfaces of the maxillary teeth and is measured
from the mesial line angle of the maxillary first premolar
to the interior portion of the commissure of lips. It is
represented by a ratio of the intercommissure width divided
by the distance from the first premolar to first premolar.[34] Its
appearance is influenced by the following factors:[10]
• The width of the smile and the maxillary arch
Indian Journal of Oral Sciences y Vol. 5 y Issue 2 y May-Aug 2014
Figure 5: Smile asymmetry due to transverse cant of occlusal plane
Figure 6: Asymmetric smile due to differential elevation of the
corners of lips
• The tone of the facial muscles
• The positioning of the labial surface of the upper
premolars
• The prominence of the canines particularly at the distal
facial line angle and
• Any discrepancy between the value of the premolars
and the six anterior teeth
• Anteroposterior position of maxilla.
Buccal corridor is directly influenced by arch form.[35]
The ideal arch is broad and conforms to a U shape and
is more likely to fill the buccal corridors than narrow and
constricted arch [Figures 7 and 8]. This negative space
should be kept to a minimum as it is unattractive, but at
the same the buccal corridor should not be completely
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Singla and Lehl: Smile analysis in orthodontics
years. Moore et al.[36] recommended that having minimal
buccal corridors is a preferred esthetic feature in both
men and women, and large buccal corridors should be
included in the problem list during orthodontic diagnosis
and treatment planning. Numerous reports suggest that
buccal corridor has an effect on the esthetic evaluation
of smiles.[37-39]
Dento-gingival analysis
Gingival health
Figure 7: Fuller smile with minimal buccal corridor (too less negative
space)
The lips frame the teeth and gingiva and further gingiva acts
as the frame for the teeth; thus, the final esthetic outcome
is greatly affected by the gingival health. It is of utmost
importance that the gingival tissues are in a complete state
of health prior to the initiation of any treatment.[40] Healthy
gingiva is usually pale pink in color or consistent with the
healthy color of individual race variations, stippled, firm
and it should exhibit a matte surface.[10]
Height, shape and contour of the gingiva
Figure 8: Excessive buccal corridor
Figure 9: Decrease in size of connectors from centrals posteriorly
and progressively larger incisal embrasure from centrals to the
posterior teeth
eliminated because a hint of negative space imparts to
the smile a suggestion of depth.[10] In addition, buccal
corridors are heavily influenced by the anteroposterior
position of the maxilla relative to the lip drape. Moving
the maxilla forward will reduce the negative space because
a wider portion of the arch will come forward to fill the
intercommissure space.[23,27] Hulsey examined the influence
of buccal corridors on the smile attractiveness and
concluded that variation in buccal corridors seemed have
no significance.[16] Hulsey considered only six anterior teeth
for measuring the buccal corridors. Since buccal corridors
as defined by Frush and Fisher[24] are the distance from
the posterior teeth to the corners of the lips, thus a smile
typically includes not only the six anterior teeth but also
the first and sometimes second premolars. Fullness of
the smile is one of the important feature that determines
smile attractiveness. The effect of buccal corridor on
smile esthetics has been studied extensively in the recent
52
Establishing the correct gingival levels for each individual
tooth is the key in the creation of pleasing and harmonious
smile. The gingival margins of the central incisors should be
at the same level or slightly incisal to that of the canines, while
the gingival margins of the lateral incisors should be towards
incisal when compared to central incisors and canines. The
gingival margin of the lateral incisor is 0.5-2.0 mm below
that of the central incisors.[10] The least desirable gingival
placement over the laterals is for it to be apical to that of the
centrals and or the canines.[35] The discrepancies in the levels
of gingival margin may be caused by attrition of the incisal
edges, ankylosis due to trauma in a growing patient, severe
crowding, or delayed migration of the gingival tissue.[22] The
gingival margins can be leveled by orthodontic intrusion or
extrusion or by periodontal surgery, depending on the lip
line, the crown heights, and the gingival levels of the adjacent
teeth.[41]
Gingival shape implies the curvature of the gingiva
at the margin of the tooth. For ideal appearance, the
gingival shape of the maxillary lateral incisors should be a
symmetrical half-oval or half circle. The gingival shape of
maxillary centrals and canines should be more elliptical. The
gingival zenith (the most apical point of the gingival tissue)
is located distal to the long axis of the maxillary centrals
and canines, while the gingival zenith of the maxillary lateral
incisor coincides with its long axis.[42,43]
The contour of the gingiva (i.e. gingival scallop) to the tip of
the papilla should be between 4 mm or 5 mm, and the tips
of the papillae should have the same radiating symmetry as
the incisal edges and the free gingival margins. In an esthetic
smile, the volume of the gingiva from the apical aspect of
the free gingival margin to the tip of the papilla is about
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Singla and Lehl: Smile analysis in orthodontics
40-50% of the length of the maxillary anterior tooth and
fully fills the gingival embrasure.[43,44] In situations where this
condition does not exist, an open gingival embrasure above
the connector results, and these “black triangles” present
an unesthetic condition. In these situations, periodontal
and orthodontic procedures are the treatments of choice
to create the correct gingival architecture.[4]
Dental analysis
Contacts and connectors
The elements of tooth contacts, connectors and embrasure
morphology can be of great significance in the appearance
of smile.
There is distinction between a connector space and a
contact point. The contact points between the anterior teeth
are generally smaller areas that can be marked by passing
articulating ribbon between the teeth. The connector is a
large, broad area that can be defined as the zone in which
two adjacent teeth appear to touch. The contact points
of maxillary teeth move progressively gingivally from
the central incisors to the premolars, so that there is a
progressively larger incisal embrasure, whereas connectors
decreases in size from the centrals posteriorly. An esthetic
relationship exists between the interproximal connectors
of anterior teeth that is referred to as the 50-40-30 rule
[Figure 9].[45] According to this rule, the ideal connector
zone between maxillary central incisors should be 50% of
the length of central incisor and between a maxillary lateral
incisor and a central incisor should be 40% of the length of
the central incisor. The optimum connector zone between
a maxillary canine and a lateral incisor when seen in lateral
view should be 30% of the length of the central incisor.[5]
Embrasures
The incisal embrasures are the triangular spaces incisal to
the contact point. Ideally these should display a natural,
progressive increase in size or depth from the central to
the canine [Figure 9].[46] This is a function of the anatomy
of these teeth and as a result, the contact point moves
apically as we proceed from central to canine. The contact
points in their apical progression should mimic the smile
line. Failure to provide adequate depth and variation to the
incisal embrasure will
• Make the teeth appear too uniform and
• Make the contact areas too long and impart to the
dentition a box like appearance.
The individuality of the incisors will be los t if their incisal
embrasures are not properly developed. Also, if the incisal
embrasures are too deep, it will tend to make the teeth
look unnaturally pointed. As a rule, a tooth distal to incisal
corner is more rounded than its mesio incisal corner.[10]
Indian Journal of Oral Sciences y Vol. 5 y Issue 2 y May-Aug 2014
Crown height and width
Since the smile reveals the maxillary anterior teeth, two
aspects of proportional relationships are important
components of their appearance: The height/width
proportions of the individual teeth, and the tooth width
in relation to each other.
Crown height combined with percentage of incisor display
is the deciding factor in the amount of tooth movement
required to improve the smile index.[12] The vertical height
of the maxillary central incisors in the adult is normally
between 9 and 12 mm, with an average of 10.6 mm in men
and 9.6 mm in women. The age of the patient is a factor
in crown height because of the rate of apical migration in
the adolescent.[16,47]
The width is a critical part of smile display in that, the
proportion of the teeth to each other is an important factor in
the smile. The proportions of the centrals must be esthetically
and mathematically correct. Most references specify the
central incisors to have about an 8:10 width/height ratio.[34,35]
In one of a recent study the optimal width-to-length ratio
for the maxillary central zone was found to be between 75%
and 85% of the length.[4] Smiles with these values were most
often considered “esthetic to highly esthetic.”
Relationships of the mesio-distal width
Correct dental proportion is related to facial morphology
and is essential in creating an esthetically pleasing smile.
Central dominance dictates that the centrals must be the
dominant teeth in the smile and they must display pleasing
proportions. They are the key to the smile. The shape
and location of the centrals influences or determines the
appearance and placement of the laterals and canines.
For best appearance, the apparent width of the lateral
incisor (as one would perceive it from a direct frontal
examination) should be 62% of the width of the central
incisor, the apparent width of the canine should be 62%
of that of the lateral incisor, and the apparent width of
the first premolar should be 62% of that of canine. This
ratio of recurring 62% proportions appears in a number
of other relationships in human anatomy is referred to as
the “Golden proportion.”[48]
Conclusion
Current trends in orthodontics place greater emphasis on
smile esthetics. Although the concept of smile analysis
is not new but is often not incorporated in orthodontic
treatment planning. It is therefore emphasized that all
the above discussed elements of smile analysis should be
considered as guidelines and reference points for beginning
esthetic evaluation, treatment planning and subsequent
treatment.
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Singla and Lehl: Smile analysis in orthodontics
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How to cite this article: Singla S, Lehl G. Smile analysis in orthodontics.
Indian J Oral Sci 2014;5:49-54.
Source of Support: Nil, Conflict of Interest: None declared
Indian Journal of Oral Sciences y Vol. 5 y Issue 2 y May-Aug 2014