Alveolar bone loss induced by the orthodontic tooth movement under hypofunctional conditions in rats

Purpose: To examine the effect of occlusal hypofunctional conditions on orthodontic tooth movement and its relation to the structure and quality of alveolar bone using the rat model. Materials and methods: Twelve-week-old male Sprague-Dawley rats were divided into 4 groups of 8 animals each: normal occlusion (N) group, normal occlusion with tooth movement (M) group, occlusal hypofunction (H) group, and occlusal hypofunction with tooth movement (HM) group. In H and HM groups, the anterior bite plate and metal cap were attached to the maxillary and mandibular incisors using a light-curing composite resin to induce the occlusal hypofunctional condition. In M and HM groups, an orthodontic force was applied in a palatal direction to the buccal surface of the maxillary first molar (M1) using a nickel‐titanium alloy wire. Micro-CT imaging and histomorphometric analysis using fluorescent bone labeling of the alveolar bone surrounding the M1s were performed in each group. Results: Tooth movement of M1 in HM group, was rather accelerated with enhanced tipping than in M group. Micro-CT analysis revealed significant decrease in bone volume fraction, bone mineral density and trabecular thickness of the interradicular bone in HM group among the experimental groups. The fluorescent labeling lines in the interradicular bone were decreased in number in H and M groups compared with N group. A few discontinuous irregular dotted lines-like labeling was observed in HM group. Conclusion: The occlusal hypofunctional condition accelerates orthodontic tooth movementoftherespectiveteeth,whileitresultsinseverebonelossinthesurroundingalveolar bone.