Influence of oestrogen deficiency and excessive mechanical stress on condylar head of mandible.

OBJECTIVE We assessedthe etiology of idiopathic condylar resorptionby examining the effects of oestrogen and compressive mechanical stress under a low systemic oestrogen condition in temporomandibular joints (TMJ) caused by an ovariectomy. MATERIALS AND METHODS Female rabbits were divided into non-ovariectomy (non-OVX) and ovariectomy (OVX) groups. A cortical osteotomy was performed witha custom device that wasincreased in length by 0.25 mm every 12 hoursfor 1 week after the operation,during which the TMJsin the rabbits received compressive mechanical stress. Samples from both groups were examined with micro-computed tomography and histological staining. RESULTS Area and depth of bone resorption were both greaterin the OVX group.Furthermore, a significantly earlier and greater prevalence of sub-condylar bone resorptionwasnoted in that group, while cells positive fortartrate-resistant acid phosphatase were increased in the OVXgroup. CONCLUSIONS The present findings suggest that oestrogeninduced a much greater amount of bone resorption on the anterior surfaceof the condylar headat an earlier stage in the TMJs of the present model rabbits. Thereafter, restoration of TMJ function appeared to occur in a normal manner.