The shape of a normal smile: implications for facial paralysis reconstruction.

Sophisticated smile reconstruction for facial paralysis requires an understanding of the facial movements during a normal smile. This study analyzes the direction and extent of movement of the upper and lower lips, nasal labial folds, and nasal base during smiling. Twenty normal subjects were analyzed using cine studies. A stop frame vector analysis was done on reference points on the lips and lower face. The greatest movement occurred at the commissure and upper lip. Intersubject variation in direction and extent of movement is great. Intrasubject variation in movement in comparing left and right sides was also quite large. Techniques of facial paralysis reconstruction that apply forces to the mouth, which mimic the vectors of movement on the patients' normal side, are most likely to provide a symmetrical smile reconstruction.