Root resorption repair in mandibular first premolars after rotation. A transmission electron microscopy analysis combined with immunolabeling of osteopontin

Introduction: A previous study with scanning electron microscopy showed that orthodontic root resorption occurs at the lateral surfaces of premolar roots for 2 to 6 weeks after orthodontic rotation. The purpose of this investigation was to observe how resorbed cementum repairs during rotation movement. Methods: Twenty-one mandibular first premolars from 12 patients, orthodontically indicated for extraction, were used. They were intra-individually divided into 2 groups: 8 teeth were not moved (control group), and 13 were rotated (experimental group). In the experimental group, a rotational force (25 g both buccally and lingually) with a precise biomechanical model, individually calibrated, was applied for 2, 3, 4, or 6 weeks. After extraction, the teeth were fixed and decalcified, and 8 were conventionally processed for transmission electron microscopy, and 13 teeth were processed for high-resolution immunocytochemistry by using an antibody against osteopontin. The samples were analyzed in a transmission electron microscope. Results: This examination showed areas of repair in previously resorbed lacunae in the experimental group. Both the clastic cells and the root surface showed immunolabeling for osteopontin. In addition to areas of cementum resorption and various degrees of cell and extracellular matrix degeneration, active cementoblasts and fibroblasts in several stages of differentiation and activity appeared adjacent to newly synthesized collagen fibers, thus reestablishing the function of the periodontal ligament. Conclusions: We concluded that cementum repair occurs after resorption during rotation movement and that noncollagenous matrix protein osteopontin plays a role in both resorbing and repairing.