The case reports describes a 43-year female patient, who attended a regional dentist for a dull pain of mandible on the right, swelling of alveolus on the vestibular and lingual side and a beginning swelling of the right cheek. The dentist performed an intraoral incision, drainage and administered antibiotics. A purulent exudation lasted despite this therapy and the patient was therefore sent to a specialized ward. The following clinical and X-ray examination established the diagnosis of periodontal cyst. The antibiotic coverage was applied before extirpation of the cyst, the cavity was filled with augmenting material Poresorb, covered with the HyproSorb membrane and the wound was occluded with feather stitches. The histological examination revealed a keratocyst. In spite of the fact that the patient failed to present any complaints and the wound healed up, two months after the operation the tooth 45 lost its vitality and an endodontic treatment became necessary.

        Key words: periodontal cyst - cyst extirpation