Background : Temporomandibular joint (TMJ) ankylosisis is a pathological fusion of the joint structures. The aim of this study was to characterize histopathologic features of human TMJ ankylosis.

Methods : Descriptive study. Subjects having clinical and histologic diagnosis of TMJ ankylosis where screened in the register of the Service of Anatomic Pathology, Faculty of Dentistry, Universidad de Chile between years 1980 and 2000. Data was obtained from clinical records and histologic sections were analyzed for presence of inflammation, calcified tissue, cartilage and bone resorption. Data were analyzed with Stata V11.

Results : A total of 15 cases were observed, 3 of them were eliminated because histologic material was not available. Age ranged from 3 to 25 years with a median of 6 (IQR 12) years, 9 male and 3 females. Inflammatory infiltrates, some of them with lymphoid follicles and connective tissue formation associated to bone resorption and osteoclasts were identified in the medullar spaces in all the cases. Additionally, 7 (63,6%) and only one (27%) cases had mineralized tissue and cartilage formation, respectively.

Conclusions : Chronic inflammation, connective tissue formation and bone resorption in the bone marrow are consistent findings of TMJ ankylosis. Mineralized tissue predominated over cartilage formation when present.