Bone Abstracts

Objectives: Sex hormones and mechanical overload have been regarded as main causative factors in the pathogenesis of temporomandibular joint (TMJ) osteoarthritis. However, there was no report regarding the relevance of mechanical overload on the mandibular condyle with serum estrogen level. This study aimed to investigate changes of the mandibular condyle of TMJ in ovariectomized rat under increased loading, and to evaluate the inhibitory effect of systemic administration of 17β-estradiol (E2) on the degenerative change of mandibular condyle.

Methods: Female Sprague-Dawley rats were mechanically loaded 8 weeks after ovariectomy (OVX) by connecting the mandibular angle and zygomatic arch using orthodontic elastic with a force of 50 g. Exogenous E2 (500 μg/kg) was subjected to daily intramuscular injection for 28 days on induced TMJ arthritis after mechanical load and OVX. Changes in the condyles were analyzed using micro-CT, histochemical/immunohistochemical staining 12 weeks after OVX.

Results: OVX induced the reduction of size, and osteoporotic change in the condyles. OVX led to more obvious changes of the microarchitecture parameters at the posterior area of the condyle with reduced bone mineral density and bone volume/tissue volume (BV/TV). Incidence of arthritis of the mandibular condyles was 25.0 and 61.9% without and with loading in OVX rats, respectively. The mandibular condyle of loaded-OVX rats showed a tendency toward reduced AP length. E2 administration recovered osteoporotic change in the mandibular condyles but did not arthritic changes in the short term. Immunohistochemically, loaded group increased the expression of tumor necrosis factor-α or estrogen receptor-α in the presence of E2.

Conclusions: Current findings showed that the synergistic effects of estrogen deficiency and mechanical overloading on the mandibular condyles are probably main contributing factors for the occurrence of TMJ arthritis. Systemic estrogen therapy might reverse the osteoporotic changes of the mandibular condyle, suggesting an intriguing alternative to improve the degenerative change.