The contour of the incisal edges of the maxillary anterior teeth relative to the curvature of the lower lip during a social smile is called:

# The contour of the incisal edges of the maxillary anterior teeth relative to the curvature of the lower lip during a social smile is called:

Line of occlusion

b. Curve of Spee

c. Curve of Monson

d. Smile arc

The correct answer is D. Smile arc.

The smile arc is defined as the contour of the incisal edges of the maxillary anterior teeth relative to the curvature of the lower lip during a social smile. For best appearance, the contour of the incisal edges of these teeth should parallel the curvature of the lower lip. If the lip and dental contours match, they are said to be consonant.

A flattened (non-consonant) smile arc can pose either or both of two problems: It is less attractive, and it tends to make you look older (because older individuals often have wear of the incisors that tends to flatten the arc of the teeth). The characteristics of the smile arc must be monitored during orthodontic treatment because it is surprisingly easy to flatten it in the pursuit of other treatment objectives. The data indicate that the most important factor in smile esthetics, the only one that can change the rating of a smile from acceptable to unesthetic, is the smile arc.

Ref: Contemporary Orthodontics, William R. Proffit, 6th Edition.