HISTOMORPHOMETRIC AND BIOCHEMICAL-STUDY OF OSTEOCLASTS AT ORTHODONTICCOMPRESSION SITES IN THE RAT DURING INDOMETHACIN INHIBITION

Prostaglandins affect the numbers of osteoclasts at compression sites in orthodontic tooth movement. They may also have a role in tooth move ment and influence the extent of root resorption. The purpose was to e xamine the effect of indomethacin on the activity of resident osteocla sts, recruitment of new osteoclasts and root resorption al orthodontic compression sites. Two separate populations of osteoclasts were studi ed: those resident at the sites after initial appliance activation and those recruited by a subsequent activation. Orthodontic appliances we re activated to provide mesially directed forces of 40 g on the maxill ary molars of rats. The appliances were activated with the same force after 4 days. The rats were killed at 1, 3, 6 and 10 days after initia l activation. Half of the rats were injected with indomethacin. Tooth movement was measured cephalometrically; osteoclast numbers, sizes, nu mbers of nuclei per osteoclast and root resorption were assessed histo morphometrically tartrate-resistant acid phosphatase (TRAP) in alveola r bone was measured biochemically. Indomethacin inhibited both initial tooth displacement and that following the delay. It also reduced the increase in osteoclast numbers. total osteoclast surface and alveolar bone TRAP at day 10. It had no effect on the surface area of each indi vidual osteoclast or number of nuclei in each osteoclast. Root resorpt ion increased in both groups but it was enhanced at day 10 in the indo methacin group. These data suggest that orthodontic tooth movement aft er appliance activation requires the recruitment of osteoclasts to sit es of compression and that this is indomethacin-sensitive. Furthermore , indomethacin enhances root resorption at compression sites 10 days a fter appliance reactivation. (C) 1997 Elsevier Science Ltd.