Characterization of Osteocyte Apoptosis in a Mouse Model of Orthodontic Tooth Movement

Background: Osteocyte apoptosis is regularly observed in the alveolar bone during orthodontic tooth movement (OTM). In this study, we wanted to further investigate its occurrence and localization. Method: Sixteen 10-12 week old male CD1 mice were loaded with NiTi springs between the right first maxillary molar and incisor delivering 10-12g of force. Left hemimaxillae served as unloaded controls. Four mice were sacrificed at each of the following time points: 6 hours, 12 hours, 3 days and 7 days after loading. Apoptosis was detected by TUNEL assay and caspase-3 and RipK-1 were detected by immunostaining on histological sections. Results: The ratio of TUNEL-positive osteocytes was increased on the compression side at 12 hours and, to a lesser extent, 3 days. There was a trend for increased caspase-3 expression at 12 hours, but RipK-1 expression levels did not follow this same trend. Conclusions: Caspase-3 expression correlates with increased osteocyte apoptosis during OTM. These results provide a better understanding of the molecular mechanism of osteocyte death during OTM.