Alveolar bone resorption in response to orthodontic tooth movement
In apical and interradicular regions of the periodontium in rats, the generation of osteoclasts in response to mechanical pressure created by orhtodontic tooth movement has been studied quantitatively with light microscopy. Young male Sprague-Dawley rats were sacrificed at 12, 18, 24, 30, 36, 44, 48, 54 and 72 hours post-orthodontic stimulation. The proliferative activity of PDL cells in the interradicular region was assessed by determining the mitotic index of PDL cells following the administration of vinblastin sulfate. The rats for this study were sacrificed at 12, 18, 24, 30 and 36 hours post-orthodontic stimulation.
Following orthodontic tooth movement, maximal pathologic tissue changes such as hyalinization of PDL and vascular disruption in the apical region were observed by 30 hours post-stimulation. The repair of periodontal tissues in this region was apparent by 54 hours. A significant increase in the number of osteoclasts was observed at all experimental periods. The total number of osteoclasts was maximal by 44 hours post-stimulation. In the interradicular region, significant pathologic tissue disruption was not observed. A significant increase in the number of osteoclasts was observed at all experimental periods. These cells were generated at a rate of 0.32 osteoclast per hour. A significant increase of alveolar bone loss was observed by 44 hours post-stimulation. The mitotic activity of the PDL cells was maximal by 24 hours post-stimulation. The data obtained from this study indicate that mechanical pressure generated by orthodontic tooth movement can stimulate osteoclastic alveolar bone resorption. This resorption activity is required to accommodate the displacement of the mesial root of the first maxillary molar within its bone socket. The histogenesis of osteoclasts in interradicular region occurred in the absence of inflammation. The quantitative data obtained from this study can serve as the basis for future studies of osteoclast generation in the periodontium.