Odontóloga

©2005 JCO, Inc. May not be distributed without permission. www.jco-online.com

OVERVIEW
The Eight Components of a Balanced Smile
ROY SABRI, DDS, MS

(Editor’s Note: In this quarterly column, JCO
provides a brief overview of a clinical topic of
interest to orthodontists. Contributions and suggestions for future subjects are welcome.)

I

n orthodontic treatment, esthetics hastraditionally been associated with profile enhancement.
Both the Angle classification of malocclusion
and the cephalometric analysis have focused
attention on the profile, without considering the
frontal view. Even though patients come to us
mainly to improve their smiles, the orthodontic
literature contains more studies on skeletal structure than on soft-tissue structure, and the smile
stillreceives relatively little attention.
The purpose of this article is to review the
eight major components of the smile (Fig. 1) and
discuss their impact on orthodontic diagnosis and
treatment planning.
1. Lip Line
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, thelip line is

Dr. Sabri is a Clinical Associate, Division
of Orthodontics and Dentofacial Orthopedics, American University of Beirut
Medical Center, and in the private practice of orthodontics in Beirut, Lebanon.
Contact him at P.O. Box 16-6006, Beirut,
Lebanon; e-mail: roysabri@dm.net.lb.

VOLUME XXXIX NUMBER 3

optimal when the upper lip reaches the gingival
margin, displaying the totalcervicoincisal length
of the maxillary central incisors, along with the
interproximal gingivae.1,2 A high lip line exposes
all of the clinical crowns plus a contiguous band
of gingival tissue, whereas a low lip line displays
less than 75% of the maxillary anterior teeth.3,4
Because female lip lines are an average 1.5mm
higher than male lip lines, 1-2mm of gingival
display at maximum smilecould be considered
normal for females.3,5,6 Dental professionals have
been conditioned to see a “gummy smile” as
undesirable, but some gingival display is certainly acceptable, and is even considered a sign of
youthful appearance.7,8
The starting point of a smile is the lip line at
rest, with an average maxillary incisor display of
1.91mm in men and nearly twice that amount,
3.40mm, inwomen.9 With aging, there is a gradual decrease in exposure of the maxillary incisors
at rest and, to a much lesser degree, in smiling.4,9,10 This steady decline in maxillary tooth
exposure at rest is accompanied by an increase in
mandibular incisor display.9,11
It is important to differentiate between the
posed smile and the spontaneous smile. A posed
smile is the voluntary expression madewhen introduced to someone, or when taking a passport
photograph or orthodontic records. A posed smile
is repeatable; studies have found little difference
among numerous consecutive photographs of
posed smiles by the same individuals.1,6,12-15 A
spontaneous smile, by contrast, is involuntary,
natural, and driven by emotions. With all the
muscles of facial expression involved, a spontaneoussmile always has more lip elevation than a
posed smile.16 Most studies refer to the posed
smile because it is reproducible and can therefore
be used as a reference position.13,15,17

© 2005 JCO, Inc.

155

OVERVIEW

The amount of vertical exposure in smiling
depends on the following six factors.
Upper Lip Length

The average lip length at rest, as measured
from subnasale to the mostinferior portion of the
upper lip at the midline, is about 23mm in males
and 20mm in females (Table 1). What is signifi-

cant, however, is the relationship of the upper lip
to the maxillary incisors and to the commissures
of the mouth.12 Lip length should be roughly
equal to the commissure height, which is the vertical distance between the commissure and a horizontal line from subnasale...