99mTc-medronate uptake in the temporomandibular joints of young rats treated with a mandibular hyperpropulsor.

To correct maxillomandibular sagittal discrepancies in growing children, most functional appliances position the mandible more anteriorly than its habitual relation with the maxilla. The aim of this study was to evaluate the effects of such a procedure on the mineralization of the temporomandibular joints in young growing rats. Temporomandibular joint uptake of a radioactive bone marker, technetium 99 m methylene diphosphonate ( 99m Tc-MDP), was measured over time as a hyperpropulsor appliance was being worn intermittently 12 hours/day. As the uptake of 99m Tc-MDP decreased in control animals, it increased significantly in the joints of treated rats before returning to the baseline level after 5 weeks of treatment. These results suggest that intermittent anterior positioning of the mandible induces a high rate of bone and cartilage remodeling in the joints of growing rats and that bone-seeking radiopharmaceutical uptake, with 99m Tc-MDP, may be a useful technique to monitor joint adaptation to an experimental functional change.