Inflammation, Bone Remodeling and Accelerated Tooth Movement

It has been shown that inhibition of expression of certain cytokines decreases the rate of tooth movement but the relation between the magnitude of inflammatory response and rate of bone remodeling and tooth movement is not clear. Objectives: The objective of this study is to investigate whether small perforations of cortical bone increase the expression of inflammatory cytokines and the rate of bone remodeling and tooth movement. Methods: Forty-eight rats were divided into four groups: 50-cN force applied to the maxillary first molar (O), force application plus soft tissue flap (OF), force application plus flap plus three small perforations of the cortical plate (OFP), and control group (C). After 28 days, the maxillae were analyzed by microcomputed tomography (uCT) and histology. RNA isolated at different time points was used to evaluate the expression of inflammatory markers by semi-quantitative RT- PCR. Results: Local perforation of cortical bone caused an increased inflammatory reaction as shown by both histology and expression of inflammatory cytokines. From the 92 cytokines studied, the expression of 37 cytokines increased significantly in all experimental groups with 21 cytokines showing the highest levels in the OFP group. uCT, light and fluorescent microscopy, and immunohistochemistry demonstrated higher number of osteoclasts and bone remodeling activity in the OFP group, accompanied by generalized osteopenia and increased rate of tooth movement. Conclusions: Small perforations of the cortical plate significantly increased the expression of inflammatory cytokines resulting in an increase in the rate of bone remodeling and tooth movement. This effect was not limited to the area of force application and can extend to adjacent bone. This work was supported by the NYU College of Dentistry and NIDCR (5K08DE017426).