FIXED PROSTHODONTICS l OPERATIVE DENTISTRY SECTION EDITORS [608414]

FIXED PROSTHODONTICS l OPERATIVE DENTISTRY SECTION EDITORS
GORDON J. CHRISTENSEN SAMUEL E. GUYER
WILLIAM LEFKOWITZ WILLIAM F. P. MALONE ROBERT C. SPROULL
Some esthetic factors in a smile
Anthony H. L. Tjan, Dr. Dent., D.D.S.,* Gary D. Miller, D.D.S.,“* and
Josephine G. P. The, Dr. Dent.+**
University of Southern California, School of Dentistry, Los Angeles, Calif.
E sthetics have become increasingly important in the
practice of modern restorative dentistry and are synon-
ymous with a natural, harmonious appearance.’ An
attractive or pleasing smile clearly enhances the accep-
tance of an individual in our society by improving the
initial impression in interpersonal relationships. A
defective smile might be considered properly as a
physical handicap. The smile is one of the most
important facial expressions and is essential in express-
ing friendliness, agreement, and appreciation.
Often the demand for esthetics motivates the patient
to seek dental treatment.2-4 However, beauty is not
absolute and is extremely subjective. It is dictated often
by cultural or ethnic factors and individual prefer-
ences.
It would be useful to describe some average desirable
characteristic features of smiles to help achieve opti-
mum results in esthetic oral rehabilitation. This study
formulates a standard of normalcy in an esthetic smile
relative to (1) smile type (high, average, low); (2)
parallelism of the maxillary incisal curve with the
lower lip; (3) position of the incisal curve relative to
touching the lower lip; and (4) the number of teeth
displayed in a smile. The standard may serve as a
guideiine for restoration or enhancement of esthetics
for the anterior component of the dentition.
MATERIAL AND METHODS
A comparative analysis of the characteristic dental
and facial features of esthetic smiles was conducted
with 454 full-face photographs of dental and dental
hygiene students with open smiles (smiles displaying
teeth). The subjects were 207 men and 247 women
from 20 to 30 years of age. Each subject was compared,
analyzed, and evaluated by careful visual judgment
rather than by mathematical measurements. However,
*Clinical Professor and Director, Fixed Prosthodontics; Associate
Chairman, International Student: [anonimizat].
**Assistant Professor, Fixed Prosthodontics; Cochairman. Interna-
tional Student: [anonimizat].
“‘Private practice, Covina, Calif.
24 to minimize possible evahtator preferences that can
occur in this type of survey, we analyzed the data
independently. Differences between smile type and
parallelism of the maxillary in&& curve relative to
touching the lower lip were determin& statistically
with z scores
Definition of terms
Open smiles were divided into three categories
(Fig. 1).
High smile (SJ. Reveals the total cervicoincisal
length of the maxillary anterior teeth and a contiguous
band of gin&a (Fig. 1, center and Fig. 2, A).
Average smile (SJ. Reveals 75% to 100% of the
maxillary anterior teeth and the interproximal gingiva
only (Fig. 1, bottom and Fig. 2, B).
LOW smile (SJ. Displays less than 75% of the
anterior teeth (Fig. 1, top and Fig. 2, (=>.
RESULTS
Smile type. The survey revealed that 48 (10.57%)
persons were classified as having a high smile (S,), 313
(68.94%) as having an average smile (S,), and 93
(20.48%) as having a low smile (SJ (Table I and
Fig. 3).
The differences in smile type between men and
women were significant statisticalIy: (p <.05)
(z[S,] = 2.33; z[S,] =I 2.75; z[S-,] = 4.50; critical region
z = 1.96).
Parallelism of the maxillary incrsal curve u&h the
lower I+ Three hundred eighty-five (84.8%) subjects
showed parallelism of the upper in&al curve with the
inner curvaturce of the lower lip, 63 (13.88%) showed a
straight rather than a curved line, and six (1.32%)
showed a reverse smile line (Fig. 4 and Table II). The
differences between men and women were insignificant
statistically.
Position of the in&d curve relative to touching the
Lower lip. Three groups were identified: (I) the in&al
curve of the maxillary anterior teeth touched the lower
lip (Cl) (Fig. 5, A), (2) the incisal curve of the
maxillary anterior teeth did not touch the lower lip
(C2) (Fig. 5, .B), and (3) the in&al portions of the
JANUARY 1984 VOLUME 53 NUMBER 1

ESTHETIC FACTORS IN A SMILE
maxillary anterior teeth were slightly covered by the
lower lip (C3) (Fig. 5, C).
The data revealed that 192 (46.61%) subjects
showed the maxillary anterior teeth touching the lower
lip, 134 (34.627) o were not touching the lower lip, and
61 (15.76%) had the incisal portions of the anterior
teeth covered by the lower lip. The differences between
men and women in groups Cl and C2 were significant
statistically: & < .OS) (z[Cl] = 3.65; z[C2] = 3.0;
z[C3] = 0.75; critical region z = 1.96) (Table III).
Differences between men and women in group C3
were not significant statistically.
The number of teeth displayed in a smile.
The
number of teeth displayed in a smile were as follows:
six anteriors only, 7.01%; six anteriors and first
premolars, 48.6%; six anteriors and first and second
premolars, 40.65%; six anteriors, first and serond
premolars, and first molars, 3.74%.
The results of this experiment show that a typical or
average smile has the following characteristics:
1. The overall cervicoincisal length of the maxillary
anterior teeth are displayed.
2. Gingiva does not show (except the interproximal
gingiva) .
3. The incisal curvature of the maxillary anterior
teeth parallels the inner curvature of the lower lip.
4. The incisal curvature may be either totally touch-
ing or slightly touching the lower lip.
5. The six maxillary anterior teeth and the first or
second premolars are displayed.
6. The midline coincides with a harmonious balance
of the smile.
7. Stereotyped “feminine” and “masculine” tooth
anatomy characteristics could not be related to the
sample.
DISCUSSION
Consideration of the criteria of a smile obtained from
this study may be very useful in improving the esthetic
value of restorations; for example, establishing the
length of the maxillary teeth and the interincisal dis-
tances between the anterior teeth.
A correct interincisal distance among the centrals,
laterals, and canines is necessary to create an attractive
incisal curvature that parallels the inner curvature of
the lower lip, and it also creates the esthetically
required “dynamic negative space.“5
In an open smile the upper and the lower teeth
usually maintain a slight interocclusal clearance. This
space might be equal to the interocclusal space of
vertical dimension of rest.
Artists use the “eye unit” (the unit of facial measure-
ment) theory to describe the topographic interrelation- Fig. 1. Three general types of smiles. Top,
low; center,
high; and bottom,
average.
ship of facial features. The distance between the base of
the nose and the lower border of the lower lip is equal
to one eye unit (length of the individual’s eye). This
distance remains unchanged whether at rest or during
a smile, because the upper lip is stretched laterally and
becomes shorter (Fig. 6).6 Further research is necessary
to confirm this hypothesis.
The established criteria of an average smile should
not be interpreted as rules but should be considered
biologic guidelines. It is impossible to formulate an
overall rigid rule for the visual characteristics of an
attractive smile.
The midline is the most important focal spot in an
esthetic smile.5 An off-center midline is readily recog-
nized by the patient. A properly placed midline in
conjunction with a long solid interproximal contact
relationship between the two central incisors produces
a desirable effect of “cohesiveness” or “oneness” of the
dental composition.
Several guidelines were introduced on how to locate
the midline, and all were related to certain features of
the face. Unfortunately, no single facial feature is
THE JOURNAL OF PROSTHETIC DENTISTRY
25

TJAN, MILLER, AND THE
Fig. 2. photographs illustrating smile types. A, High smile (S,). B, Average smile (S,). C,
Low smile (S,).
%
100
so
ea Total
00
cl-
70
00
50
40
30
20
10
0
Sl 912
Fig. 3. Comparison between smile types of men and
women. S, * High smile; S2 = average smile; S3 = low
smile.
absolutely symmetrical or centered. Patients tend to
relate their midline to the upper lip rather than to other
facial features that are further from the mouth. &I
imaginary line dividing the midline lobe of philtrum
into equal OF symmetrical halves may be used to
establish the midline (Fig. 7, A and B).
Midline diastema seems to divide the dental compo-
sition into two separate entities that disturb the cohe- Fig. 4. Types Iof maxillary anterior incisai curvature
in relationship to lower lip; that is, parallel, reverse, or
straight.
26 JANUARY 1984 VOLUME Jl NUMBER 3

ESTHETIC FACTORS IN A SMILE
Tab de I. Fig. 5. Maxillary anterior incisal edges: A, touching (Cl). B, Not touching (C2). C,
Slightly covered by lower lip (C3).
Comparison between smile types of men and women
High smile (S,) Average smile CSJ
Total No. No. % No. % Low smile (S,)
No. %
Total 454 48 10.57
Men 207 14 6.76
Women 247 34 13.79
p < .05; critical region: z = 1.96. S, = 2.33; Sz = 2.75; S, = 4.50. 313 68.94 93 20.48
131 63.28 62 29.95
182 73.71 31 12.50
Table II. Types of incisal curvature
Total No. Parallel Straight Reverse
No. % No. % No. %
Total 454 385 84.80 63 13.88 6 1.32
Men 207 173 83.57 30 14.49 4 1.93
Women 247 212 85.77 33 13.56 2 0.6
p < .05; critical region: z = 1.96 (N.S.).
Table III. The position of maxillary anterior incisal curvature relative to lower lip
Total No. Touching Not touching Slightly covered
(Cl) (C2) (C3)
No. % No. % No. %
Total 387 192 49.61 134 34.62 61 15.76
Men 173 68 39.31 75 43.35 30 17.34
Women 214 124 57.89 59 27.63 31 14.47
p < .05; critical region: .z = 1.96. Cl = 3.65; C2 = 3.0; C3 – 0.75 (N.S.).
THE JOURNAL OF PROSTHETIC DENTISTRY 27

TJAN, MILLER, AND THE
Fig. 6.
Eye unit used by artists to measure proportion-
al distances between various facial body parts. Dimen-
sion between base of nose and border of lower lip
remains unchanged between rest and smiling.
Fig. 7. A and B,
Midline is determined by dividing
middle lobe of upper lip.
siveness or oneness of the dentition (Fig. 8). A distur-
bance in the cohesiveness of the dentition may also be
observed in patients who lack interproximal contacts
(Fig. 9).
SUMMARY AND CONCLUSIONS
A survey of the characteristics of an open smile was
conducted with 454 full-face photographs of randomly
selected dental and dental hygiene students.
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 in&al curve of
the maxillary anterior teeth touching slightly or miss-
ing slightly the lower lip, and displays the six upper
anterior teeth and premolars. Consideration of the
characteristics may be useful in improving the esthetics
of restorations.
We acknowledge with appreciation the illustrations that were
prepared for this article by Mr. George Robbins. Fig.
8. Midline diastema divides dental composition
into two separate entities.
Fig.
9. Lack of interproximal contacts disturbs cohe-
siveness of dentition.
REFERENCES
1. Pilkington. 1:. L.: Esthetics and optical illusion in dentistry. J
Am Dent Assoc 23:641, 1936.
2. Goldstein, R. E.: Study of need for esthetics in dentistry. .J
PROSTHE~ DENT 21:589, 1969.
3. Miller, I. F., and Belsky, M. W.: Cosmetics in restorative
dentistry. Dent Clin North Am l&l 1, 1967
4. Culpepper, W. D., Mitchell, P. S., and Blass, M. S.: Esthetic
factors in anterior tooth restoration. J PR~ST~K~ DENT 30~576,
1973.
5. Lombardi, R. E.: The principles of visual perception and their
clinical application to denture esthetics. J PROSTHET Dwr
293358, 1973.
6. Hamm, J.: Clrawing the Head and Figure. New York. 1976,
Grosset & Dunlap, pp 8-12.
Reprint requests
to’
DR. ANTHONY H. 1,. TJAN
UNIVERSITY OF SOUTHERN CALIFORNIA
SCHOLL OF DENTISTRY
Los ANGELES, CA 90007
28 JANUARY 1984 VOLUME $1 NUMBER 1