Smile Arc
The curvature of the upper teeth edges in relation to the lower lip.
The smile arc describes the relationship between the curvature of the upper teeth's incisal edges and the curvature of the lower lip during smiling. A consonant (parallel) smile arc — where the upper teeth follow the curve of the lower lip — is considered the most aesthetically pleasing and is found in attractive natural smiles. A flat smile arc (straight incisal edges not following the lip curve) appears less attractive and can result from aggressive orthodontic leveling or improper restoration design. A reverse smile arc (edges curve opposite to the lip) is least attractive. In treatment planning, preserving or creating a consonant smile arc is a primary goal. Techniques include differential intrusion/extrusion during orthodontics, veneer design with varying incisal edge positions, and crown contour adjustments.