Which hard and soft tissue factors relate with the amount of buccal corridor space during smiling?

OBJECTIVE To investigate which hard and soft tissue factors relate with the amount of buccal corridor area (BCA) during posed smiling. MATERIALS AND METHODS The samples consisted of 92 adult patients (19 men and 73 women; 56 four first bicuspids extraction and 36 nonextraction treatment cases; mean age = 23.5 years), who were treated only with a fixed appliance and finished with Angle Class I canine and molar relationships. To eliminate the crowding effect on the buccal corridor area, lateral cephalograms, dental casts, and standardized frontal posed smile photographs were obtained at debonding stage and 28 variables were measured. Pearson correlation analysis, multiple linear regression analysis, and independent t-test were used to find variables that were related with buccal corridor area ratio (BCAR). RESULTS Among the lateral cephalometric and dental cast variables, FMA, lower anterior facial height, upper incisor (U1) exposure, U1 to facial plane, lower incisor (L1) to mandibular plane, L1 to N-B, Sn (subnasale) to soft tissue menton (Me'), Sn to stomodium superius (stms), stms to Me', and interpremolar width were significantly negatively correlated with BCAR. Occlusal plane inclination and buccal corridor linear ratio did not show any significant correlation with BCAR. Multiple linear regression analysis generated a three-variable model: Sn to Me', U1 exposure, and sum of tooth material (STM) (R(2) = 0.324). There was no significant difference in BCAR between extraction and nonextraction groups. CONCLUSIONS To control the amount of BCA for achieving a better esthetic smile, it is necessary to observe the vertical pattern of the face, amount of upper incisor exposure, and sum of the tooth material.