Continuous Force on Rat Molars Increases Osteopontin in Alveolar Bone

Objectives: Osteopontin (OPN) is a major noncollagenous bone matrix protein that is believed to play a key role in wound healing and cellular responses to mechanical stress. Orthodontic tooth movement is possible by alveolar bone remodeling, which consists in a sequence of events that results in bone resorption and deposition. We have previously showed the concomitant presence of these two antagonist tissue reactions at the pressure areas of rat alveolar bone in upper first molars submitted to continuous orthodontic force. The aim of the present study was to investigate the presence and distribution of OPN in alveolar bone at the pressure areas when molars were submitted to continuous orthodontic force.

Methods: Ten 2½ months old male Wistar rats were used. Eight rats had their upper first molars moved for 3d (n=4) and 7d (n=4) with a 15cN continuous force, while the remaining two rats had their molars non-moved and were processed as controls. The rat maxillae were dissected out and quickly immersed in 0.1% glutaraldehyde + 4% formaldehyde and fixed under microwave irradiation. Then, specimens were decalcified and processed for high-resolution colloidal gold immunocytochemistry with an anti-OPN antibody.

Results: At both studied times the immunolabeling was present recovering the resorbed alveolar bone surfaces thus forming a lamina limitans. Other regions showed wide strips with intense immunoreactivity for OPN. These regions were detected even when active osteoblasts were absent suggesting the deposition of circulating OPN on these surfaces. Later, when new bone matrix was laid out over these strips, wide cement (reversal) lines strongly labeled for OPN were observed.

Conclusions: This study showed that OPN is overexpressed at alveolar bone surfaces adjacent to rat molars submitted to continuous orthodontic force. Financial support by FAPESP (grant 03/06554-6) and CNPq (Brazil).