Bone resorption rate of moved and fixed teeth during alveolar bone remodeling by orthodontic treatment

Orthodontic treatment is based on the remodeling of the alveolar bone in re sponse to externally applied orthodontic force to a tooth. The rate of bone resorption is, therefore, one of the essential factors for understanding t ooth movement during orthodontic treatment. There is the basic concept of d ifferential force in orthodontics that the application of an optimal force enables the canine to be moved without moving the molar that is used as an anchor for retracting the canine. In this paper, the resorption rates of th e alveolar bone around the molar and the canine were estimated from the cli nical measurements of tooth movement and the stress analyses of tooth roots using a 3-D finite element model. The model consisted of an orthodontic sp ring, the canine, the second premolar, and the first and second molars. The bone resorption rate to a unit stress at the molar was found to be about 0 .5 micron/(kPa.day) and almost the same as that of the canine. This result suggests that the concept of differential force can be explained simply by differences in the geometry of the roots of moved and fixed teeth.