The purpose of this study was to investigate the relationship between lips and upper anterior teeth during oral functions. This relationship will help us understand the role of the lip support in oral functions. 96 subjects with normal occlusion and 36 edentulous patients were selected. Seven points on the lips were set for tracking and three points on the labial surfaces of the central incisors and the canines as marks. They were measured in three-dimensional coordinates referred by Camper's plane. And they were measured under thrusting of the lips, pulling the mouth corners backward and closing of the lips intentionally. The edentulous patients were tested with and without denture. Each data was transferred to the one coordinates and compared to each other.
The findings were as follows:
1. The movements of median points on the lips showed great variation.
2. The mouth corners moved similarly in their direction and moved on one plane.
