ORTHODONTIC BONE REMODELING IN RELATION TO APPLIANCE DECAY

This study examined alveolar bone turnover and orthodontic tooth movem ent after appliance decay. One group of rats (N=54) received orthodont ic force (40 g initial activation) while the other (N=36) was sham-tre ated. Groups of six rats were sacrificed at various times following ac tivation. Tooth movement and appliance decay were monitored cephalomet rically, and bone turnover was monitored locally by histomorphometry a nd phosphatase chemistries and systemically by serum phosphatase and o steocalcin changes. A significant association was found between spring forces assessed by direct measurement and by cephalometric images (R( 2)=0.784; p=0.02). The cephalometric method indicated appliances were at least 93% deactivated by day 16. Tooth movement continued beyond th e point of appliance decay (p<0.001). This was accompanied by a dramat ic decline in osteoblast surface (p<0.0001) and an increase in osteocl ast surface to control levels (p<0.001). A significant peak in bone fo rmation rate was also noted around appliance decay (p=0.005). Serum ac id phosphatase and osteocalcin also increased after appliance decay (p <0.05), but alkaline phosphatase did not. Bone acid phosphatase was ch aracterized by a peak after appliance decay (p=0.0004), but alkaline p hosphatase remained depressed (p<0.0001). These data demonstrate that significant amounts of alveolar bone turnover continue for an indeterm inant period following appliance decay.