Lip position analysis of young women with different skeletal patterns during posed smiling using 3-dimensional stereophotogrammetry.

INTRODUCTION

The aim of this study was to explore the internal relationship between posed smile characteristics, lip position, and skeletal patterns in young women.

METHODS

Fifty women between the ages of 20 and 30 years were enrolled and divided into 3 groups-vertical, average, and horizontal patterns- using the following parameters: FMA, GoGn-SN, and Jarabak ratio. Each subject was scanned in natural head position and with a posed smile. The interlabial gap, intercommissural width, and smile index were calculated. The frontal region was selected as the reference plane for superimpositions. The changes of the lip landmarks in the vertical, sagittal, and coronal directions were investigated.

RESULTS

The smile indexes were listed in the following sequence: vertical < average < horizontal. Significant differences were found in the interlabial gap among the 3 groups. Compared with the average and horizontal groups, the upper lip landmarks of the vertical group showed differences and changed more only in the vertical direction. However, the lower lip landmark showed no differences in any direction.

CONCLUSIONS

Different skeletal patterns have characteristic smile features. The vertical skeletal pattern affects upper lip movements because there is more space for upper-lip elevation. However, the vertical skeletal pattern has no effect on lower lip movement.