| Summary: | 碩士 === 國立陽明大學 === 臨床牙醫學研究所 === 96 === The smile arc defined as the relationship of the curvature of the incisal edges of the maxillary incisors and canines to the curvature of the lower lip in the posed smile. The ideal smile arc has the maxillary incisal edge curvature parallel to the curvature of the lower lip upon smile. Review of the literature, it is generally considered that although orthodontic treatment straightened teeth, it flatten the incisor edges and makes unpleasant smile arc. Whatever, it seems conflict that most of the time orthodontic treatment gets better result and nice appearance.
The study aimed to the change of upper incisor edge and canine curvature result from the orthodontic movement of maxillary anterior teeth. Besides, the observation distance and angle of elevation were also changed to see the influence on the curvature presented. Analysis of maxillary anterior teeth curvature with the computer vision technique is totally different from 2-dimensionally photographic methodology in mostly smile arc studies in the past. Besides, it makes more precisely simulation of tooth movement and alters the variables of interest.
We scan an upper dental cast model and a 3-dimensional computer model was obtained, which can be manipulated in FreeForm software. The maxillary anterior teeth curvature is more curve if the observer is at a farer conversational distance, the bigger angle of elevation, occlusal plane posterior upward canting, narrower archform, incisor edge vertical height position is lower than canines, or incisor inclination is more upright. Besides, the opposite is also the truth.
This study had found that upper anterior teeth curvature indeed be changed by orthodontic tooth movement or by the observer conversational distance and angle of elevation.
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