Structure-Function Relationships of the Temporomandibular Joint in Response to Altered Loading

Aims: To elucidate the effects of decreased occlusal loading (DOL), with or without reloading (RL), on the structure and bite force function of the mandibular condylar fibrocartilage in skeletally mature male mice. Methods: At 13 weeks old, 30 wild type (WT) male mice were subjected to: (1) 6 weeks normal loading (NL); (2) 6 weeks DOL; or (3) 4 weeks DOL + 2 weeks RL. Histomorphometry, cell metabolic activity, gene expression of chondrogenic markers, and bite force tests were performed. Results: DOL resulted in a significant increase in apoptosis (P .0001) and significant decreases in fibrocartilage thickness (P .05) and hypertrophic chondrocyte markers indian hedgehog and collagen type X (P .05). A corresponding decrease in bite force was also observed (P .05). RL treatment resulted in a return to values comparable to NL of chondrogenic maturation markers (P > .10), apoptosis (P > .999), and bite force (P > .90), but not in mandibular condylar fibrocartilage thickness (P > .05). Conclusions: DOL in skeletally mature mice induces mandibular condylar fibrocartilage atrophy at the hypertrophic cell layer with a corresponding decrease in bite force. Keywords: bite force, chondrogenesis, decreased occlusal loading, mandibular condylar fibrocartilage, masticatory function