Tooth in a cyst - Is it always a dentigerous cyst?

We present the case report of an 18-year-old female patient who presented with unilateral nasal obstruction. Computed tomography scanning revealed an unerupted molar in the posterior wall of the right maxillary sinus with a cystic swelling in the sinus. The preoperative diagnosis was a dentigerous cyst. The patient underwent endoscopic removal of the cyst and tooth. The operative findings and histopathology showed that it was an odontogenic keratocyst. This paper stresses the importance of diagnosing this condition and that a tooth in a cyst is not always dentigerous.