Effect of changes in divine proportion on esthetic perception of smile in frontal view.

OBJECTIVES: In orthognathic surgery, the surgeon is capable of creating new dimensions to the patient's face. Because a beautiful smile could be related to the divine proportion, the purpose of the current study was to evaluate the changes in the perception of smile after approximating some components of smile to the divine proportion orthodontically or surgically.

MATERIAL AND METHODS: Ten 20- to 25-year-old women with pleasant smiles and no obvious malocclusions participated in this study. Five standard photographs were taken from each participant in a posed smile, and the most natural one was selected and scanned into black and white pictures. Ten anthropometric landmarks were detected on each image and 10 ratios including Labial inferioris (Li)/right chelion (RCh)-right antegonion (RAgo), subnasale (Sn)-Li/left chelion (LCh)-left antegonion (LAgo), RCh-RAgo/labial superioris (Ls)-Li, LCh-LAgo/Ls-Li, Ch-Ch/Ls-Li,stomion (St)-Sn/St-Li, the maxillary central incisor width/maxillary centralincisor height, Ls-right cuspid (RCus)/RCh-RCus, Ls-left cuspid (LCus)/LCh-LCus, and LCus-RCus/Ch-Ch were measured on each picture. The numerators or denominators of the mentioned ratios were then changed in a way that mentioned the divine proportion (1/1.618) was approximated. All the 110 pictures were evaluated by 40 judges in 2 sessions using a visual analog scale. Intraclass correlation coefficient was also calculated (single measure, 0.644; F = 26.27; P < 0.001). The level of significance for this study was P = 0.05. The tests used to analyze the data were general linear model, the Friedman, and Wilcoxon tests.

RESULTS: This study showed that LCus-RCus/Ch-Ch, Ls-Lcus/LCh-Lcus, and Ls-RCus/RCh-RCus (with mean scores of 64.2, 57.2, and 56.1, respectively) had the most positive effects on the esthetic perception of smile. However, RCh-RAgo/Ls-Li with a mean score of 29.1 and LCh-LAgo/Ls-Li with a mean score of 24.5 had the mostnegative effects. There were significant differences among the variables with each other except for A0 to J0 and A6 to J6 (F = 450.6; P = 0.001).

CONCLUSIONS: Approximating the ratio RCus-LCus/Ch-Ch to the divine proportion may definitely help in achieving a more pleasant smile. On the next level, altering the ratios Ls-LCus/LCh-LCus and Ls-RCus/RCh-RCus could also play a role in making a beautiful smile.