The Effect of Local Application of 1,25-Dihydroxycholecalciferol on Osteoclast Numbers in Orthodontically Treated Rats

Abstract

Orthodontic tooth movement requires remodeling of periodontal tissues, especially alveolar bone. 1,25-(OH)2D3, the active form of vitamin D 3, is known to be a potent stimulator of osteoclastic bone resorption. The purpose of this study was to investigate the effect of local application of 1,25-(OH)2D3 on osteoclast numbers induced by experimental tooth movement. A piece of orthodontic elastic band was inserted between the first and second upper molars of male Wistar rats weighing about 200 g each. Twenty μL of 1,25-(OH)2D3 (10-12-10 -7 mol/L) was injected locally into the submucosal palatal area of the root bifurcation of the right first molar. The left side was injected with phosphate-buffered saline (PBS). The number of osteoclasts was counted in a 700 x 1050 μm2 area of the interradicular septum. The local injection of 1,25-(OH)2D3 caused a dose-dependent increase in osteoclast number. The effect of 1,25-(OH)2D3 reached a response plateau at 10-10 mol/L when greater than a threefold rise in osteoclast number was attained compared with the PBStreated controls. While the insertion of a piece of elastic band for three days induced a significant increase in osteoclasts in the alveolar bone, daily injections of 20 μL of 10-10 mol/M 1,25-(OH)2D 3 for three days markedly stimulated the numbers of osteoclasts induced by the insertion of an elastic band. 1,25-(OH)2D3 was apparently synergistic with mechanical stimuli, resulting in enhancement of the numbers of osteoclasts induced by mechanical stimuli alone. These findings suggest that the local application of 1,25-(OH)2D 3 acted directly to increase osteoclast number and to potentiate osteoclastic bone resorption induced by mechanical stimuli.