Tissue remodeling and factors governing tooth movement

Tooth movement is largely considered a reaction to the application of force. However, this mechanism is unable to explain the phenomenon of rapid vertical eruption and horizontal drift (movement) of the teeth when of unopposed (unloaded). To better understand the rote of force in the bone remodeling that occurs during the movement of erupted teeth we have developed mouse models of hyper-occlusion, orthodontic tooth movement and unopposed tooth drift. In these models we examined chronology of osteopontin and RANKL expression and osteoclast response. In the orthodontic tooth movement study we have documented the coordinated expression of bone remodeling factors in response to force. The data from our hyper-occlusion study provided evidence that the maintenance of a physiological occlusal state is achieved primarily by the effect of occlusal forces on the inhibition of bone apposition rather than by equilibrium between continuous apical mineralized tissue apposition, off-set by occlusal force-stimulated bone resorption. Finally, we proposed a new mechanism for physiologic tooth drift. We have demonstrated that OPN is required for site-directed changes in the RANKL expression and associated osteoclast distribution during tooth drift. Specifically, data from our mode) of unopposed tooth drift indicates that increased OPN expression during unloading-induced drifting of teeth may directly enhance RANKL expression and osteoclast formation. Although OPN is necessary in the molecular and cellular bone remodeling events that take place during the drift of teeth, our data indicate that OPN is not required for the continuous eruption of un-opposed teeth.