Background and objectives: Idiopathic condylar resorption (ICR) mainly occurs in mandibular retrognathic patients who show high mandibular plane angle. The etiology of ICR is multifactorial, and hypoestogenemia is suggested as one of the multiple factors. The aims of this study were to analyze the etiologic factor of ICR with blood analysis and Dexa bone densitometry, and to identify the correlation between the etiologic factors and the progression of disease.

Methods: IRB approval was obtained for this study (CRI11003G). 19 patients was participated in this study, who were divided into 2 groups depending on panoramic radiography; group I, ICR patients ( n = 12); group II, high risk patients who did not show ICR in spite of mandibular retrognathism with high mandibular plane angle ( n = 7). Blood analysis according to menstrual cycle, Dexa bone densitometry, bone SPECT of temporomandibular joint were performed. Each result was integrated, and the correlation between the etiologic factors and the progression of disease on bone SPECT was evaluated.

Results: 8 patients of group I and 6 patients of group II showed hypoestrogenemia. 7 patients revealed osteopenia by Dexa bone densitometry (group I: 6 patients; group II: 1 patient). Among patients with osteopenia, 5 patients of group I showed hypoestrogenemia concurrently, on the other hand, high risk patient had normal serum level of estrogen. Bone SPECT finding was not consistent with the results of blood analysis and bone densitometry, in addition, there was no significant difference of bone SPECT findings between two groups.

Conclusion: Both ICR and high risk patients have a tendency to low serum level of estrogen, however, the incidence of osteopenia was higher in ICR group than high risk group. Bone SPECT finding did not coincide with other clinical findings. Further study with many subjects is needed to elucidate the etiologic factors of ICR.