Abstract: Objective　This article was aimed to analyze the influence of different time of force upon orthodontic traction after extracting the supernumerary tooth and provide the traction theory of impacted maxillary central incisor. Methods　After constructing 3-dimensional finite element model of impacted maxillary central incisor, we applied equal forces during different healing periods and analyzed the initial force and displacement of impacted central incisor, periodontal membrane and alveolar bone. Results　As the healing of alveolar bone, both the maximum force of tooth and periodontal membrane and the maximum displacement of alveolar bone decreased, whereas maximum force of alveolar increased. Conclusions　After the elimination of supernumerary tooth, force on the impacted teeth can be applied. But inclination trend of early tooth movement was appearent, so we suggested that the initial force should be smaller which beneficially for the whole movement of the impacted teeth.

Key words: three-dimentional finite, impacted teeth, newly born alveolar bone, stress analysis