Immunohistochemical localization of alphavbeta3 integrin receptor during experimental tooth movement.

During orthodontic treatment, multinucleated clast cells carry out the resorption of mineralized tissues. Adhesion of clast cells to the mineralized tissues is mediated by transmembrane cell-surface glycoproteins called integrins, specifically by the alphavbeta3 integrin, which plays an important role in the process of bone resorption. The role of the alphavbeta3 integrin in bone resorption leading to osteoporosis has been demonstrated, but its role in alveolar bone and root resorption during orthodontic tooth movement is unknown. This study examined the expression of the alphavbeta3 integrin during experimental tooth movement. Tooth movement was achieved in 16 male Sprague-Dawley rats (each weighing 120-200 g) with elastic bands between their maxillary first and second molars. The molar-bearing segments were dissected and processed for histologic and immunohistochemical examination. The expression of alphavbeta3 integrin was examined with 2 primary antibodies: a polyclonal anti-alphav integrin subunit antibody and a polyclonal anti-beta3 integrin subunit antibody. Negative controls were similarly processed but without incubation with primary antibodies. The alphavbeta3 integrin was expressed both by osteoclasts associated with alveolar bone resorption and by odontoclasts associated with root resorption during experimental tooth movement. Furthermore, the beta3 integrin subunit was expressed by the epithelial rests of Malassez in the periodontal ligament. Negative controls did not show immunolabeling. The alphavbeta3 integrin adhesion receptor is expressed during experimental tooth movement and might be involved in the process of mineralized tissue resorption and the functions of the epithelial rests of Malassez.

Proliferation of epithelial rests of Malassez during experimental tooth movement.

The epithelial rests of Malassez (ERM), remnants of Hertwig's epithelial root sheath, are found near the root surface in the periodontal ligament. The functional significance of the ERM is still unknown. The purpose of this study was to examine the behavior of the ERM during experimental tooth movement. Tooth movement was achieved in 12 male Sprague-Dawley rats (each, 120-200 g) by placing elastic bands between the maxillary right first and second molars. The left molars served as controls. The rats were killed after 6, 12, 18, 24, 60, and 72 hours. The mitotic activity of the ERM was assessed by injecting the animals with 5-bromo-2'-deoxyuridine (BrdU) 2 to 3 hours before killing by intracardial perfusion with 4% paraformaldehyde. The molar-bearing segments were dissected and processed for histological examination. The incorporated BrdU was detected by immunohistochemistry. The number of cells in each ERM cluster was counted in all groups. In the 18-, 24-, 60-, and 72-hour experimental groups, the cell numbers were significantly higher than in the controls. The surface areas of the ERM clusters were also measured in all groups, but only in the 18-, 24-, 60-, and 72-hour specimens were the areas significantly higher in the experimental than in the control groups. The ERM cells in the experimental specimens were labeled with anti-BrdU, while those in the controls were not. It was concluded that experimental tooth movement stimulates ERM cells to proliferate and increase in size. These increased activities of the ERM are consistent with a putative role for these cells in collagen turnover in the periodontal ligament that is accelerated during tooth movement.