Physical properties of root cementum: Part 7. Extent of root resorption under areas of compression and tension

Introduction: The aim of this article was to quantify the extent of root resorption in areas of compression or tension under light and heavy buccal tipping orthodontic forces. Methods: The sample consisted of 36 premolars in 16 patients. On 1 side, light (25 g) or heavy (225 g) buccal tipping orthodontic forces were activated for 28 days. The contralateral side in each patient served as the control (0 g). The teeth were extracted, disinfected, imaged under a scanning electron microscope, and analyzed with commercial stereo imaging computer software modified for this study. Buccal and lingual surfaces were divided into 3 equal regions: cervical, middle, and apical. The root surface areas of these regions were documented with straight-on images. Quantification of resorption craters by using volumetric analysis was performed from stereo images taken at ±3°. The degree of resorption was correlated to the amount of surface area under compression or tension. Results and conclusions: The buccal cervical region had 8.16-fold more root resorption in the heavy-force group compared with the light-force group (P <.01). The other regions did not seem to have significant differences in the force levels. In the experimental teeth, there was more root resorption in the high-compression regions than in the other regions (P <.01). There were similar amounts of resorption per unit area on the lingual apical and buccal cervical regions. Regions under compression had more root resorption than regions under tension. There was more resorption in regions under heavy compression than in regions under light compression (P <.01). There was also more root resorption in regions under heavy tension than in regions under light tension (P <.01).