Experimental evaluation of initial tooth displacement, center of resistance, and center of rotation under the influence of an orthodontic force

The purpose of this study was to determine the location of the center of re sistance and the center of rotation of the maxillary central incisors under the influence of a single simple force and to investigate related geometri c parameters of the teeth and the surrounding periodontal tissues. By measu ring the initial displacement of the central incisors with a magnetic sensi ng system, the location of the center of resistance and the centers of rota tion associated with various forces were determined in 3 human subjects. Th e results show that the location of the center of resistance of the maxilla ry central incisor depends on the palatal bone level and is at approximatel y two-thirds of the palatal alveolar bone height, measured from the root ap ex. A greater moment-to-force ratio is needed for any controlled movement o f the maxillary incisors during retraction in patients with reduced palatal alveolar bone height. This study suggests a method for estimating the loca tion of the center of resistance of a tooth.