Abstract
Three cases of cystic lesion of the mandible with difficulties in establishing definite diagnosis and understanding its pathogenesis are presented. All cases were radiologically identified as a unicystic radiolucent lesion involving the apex of the molar or premolar root and thus resembled that of a radicular cyst, however, the involved teeth were vital determined with pulp electrodiagnosis. These lesions were clinically associated with a cyst-like cavity, containing pus-like fluid, which was lined by a relatively thick granulation tissue without epithelium in two cases and with epithelium in one case. These findings are consistent with neither those of radicular cyst nor typical simple bone cyst even if infected. One of the patients had another unicystic radiolucent lesion involving the apex of the premolar root, which was non-vital as determined with pulp electrodiagnosis but had no apparent reason to devitalize the pulp. All patients had undergone relatively long-term high dose steroid therapy for rheumatoid arthritis or Behchet's disease, possible involvement of steroid-induced osteonecrosis in the development of these lesions is discussed.
