Bone-remodeling in TMJ induced by unilateral occlusal loss in Rat

Objective: Occlusal loss is considered to induce bone resorption and morphologic change of articular components of TMJ. This study aimed to reveal dynamic changes of bone metabolism at TMJ using bone scintigraphy, X-ray imaging. Gene expression of OPG and RANKL was also examined.

Materials and Methods: Right maxilla molars of five-weeks-old rats were extracted under anesthesia. Samples of TMJ images and specimens were categorized into 3 groups, i.e. TMJs at the extracted side, at contralateral intact side of the extracted rats, and TMJs of controls without extraction. Scintigraphic images were obtained after intravenous injection of Technetium-99m-methylene diphosphonate (Tc-99m-MDP) (74MBq/rat). Soft X-ray images were taken to measure the density of Hydroxyapatite as bone density. The mandibular condyles were resected for histological analyses to count the number of osteoclasts and gene expression of OPG and RANKL were measured. These factors were compared among 3 groups statistically.

Results: Accumulation counts of Tc-99m-MDP of TMJs at the extracted side were significantly higher than the contralateral intact side since the 3rd day after extraction (Mann-Whitney U test p<0.05). In soft X-ray image, bone density of extracted side was significantly higher than the contralateral intact side on the 14th day after extraction (Kruskal-Wallis test p<0.05). The number of osteoclasts at the condyle of extracted side was decreased on the 7th day after extraction (Kruskal-Wallis test p<0.05). In the gene expression, concentrations of OPG of the extracted side were significantly increased and RANKL/OPG ratio was significantly decreased compared to the controls on the 7th day after extraction (Kruskal-Wallis test p<0.05).

Conclusion: These results revealed clearly that unilateral occlusal loss induced bone remodeling at TMJ of the extracted side. Bone metabolism turned up immediately after teeth extraction and subsequent remodeling lasted. These changes might be an adaptation to mechanical stress transmitted to the TMJ.