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case report I test revealed necrosis in teeth 31 and 41 to 43. The soft tissue surrounding the radiolucent lesion was intactandshowednosignsofinflammation.There were neither fistulas nor swelling. In the physical examination, neither sensitivity of the gingiva nor pain was noted. Cyst enucleation was performed under local anaesthetic with 4% articaine. Teeth 31 and 41 to 43 were treated endodontically. Upon elevation of a trapezoid mucoperiosteal flap from teeth 33 to 43, the destruction of the vestibular cortical bone was evident (Fig. 4). The cyst was enucleated and sent for histopathological examination (Figs. 5 & 6). The roots of teeth 31, 41 and 42 were resected.6 Tooth 43, although non-vital, was not directly in- volved in the cystic lesion and thus was not sub- jected to root-end resection. The root canals were prepared and filled with MTA (Fig. 7). After thor- oughdebridement,thelargebonedefectwithpar- tial destruction of the vestibular and lingual corti- calbonewallswasfilledwithasyntheticbonesub- stitute (easy-graft CRYSTAL, Degradable Solu- tions; Fig. 8). The material consists of biphasic calcium phosphate, which is composed of 60% hydroxyapatite and 40% ß-tricalcium phosphate. Bone substitute granules adhere to each other, forming a mouldable but porous mass. The mate- rial hardens into a stable scaffold upon contact with blood. After application, the material was covered with a porcine collagen membrane using a double-layer technique. Teeth 41 and 42 re- mainedmobileafterfillingthedefect,butmobility did not increase during apicectomy and cyst enu- cleation.Thewoundwasclosedusing6.0nylonsu- tures. The patient received analgesics and 1,200 mg clindamycin twice a day for six days. The post-op- erative healing was uneventful. The sutures were removedaftersevendays.Sixmonthsafterthecys- tectomy, the patient returned for a clinical and ra- diological follow-up visit (Figs. 9–11). Clinical ex- aminationshowednosensitivityofthegingiva,nor did the patient report pain. The shape and volume ofthealveolarridgewerenormal,andtheteethdid not show mobility. Slight scarring was observed at the sites of the vertical incisions. Radiological examination (panoramic tomo- gram and CT scan) after six months confirmed that the alveolar bone had been reconstructed within the anatomical contours and the hard tissue at the formerdefectsiteshowedradiopacitysimilartothe surrounding bone (Figs. 9–11). A small region of re- duced opacity was detected around the apex of tooth 42, which may be an effect of remodelling. This region will remain under observation. _Discussion Thediagnosisandtreatmentofbonecystsofthe jaws, including radicular cysts, is very common in oral and maxillofacial surgery. After the removal of a cyst, the bone defect will usually be filled with blood.Thebloodclotcontractsduringearlyhealing, which results in loss of contact between the clot and the walls of the surrounding bone. The forma- tion and in-growth of blood vessels and, conse- quently, oxygen and nutrient supply—a prerequi- site for bone regeneration—may be disturbed. Fur- thermore, the blood clot may be destroyed by the fibrinolytic activity of bacteria from the oral cavity, Fig. 4_Local status after flap opening. Fig. 5_Cyst after removal. Fig. 6_Histopathological examination of a fragment of the cyst wall showed the characteristics of congestion, including chronic lymphocytic and plasmocytic inflammatory infiltration by foamy macrophage clusters (40x, hematoxilin & eosin staining). Fig. 7_The bone defect and roots of 31, 41, and 42 after the cyst removal and resection. Fig. 8_ easy-graft® CRYSTAL in situ. Fig. 9_Panoramic radiogram after six months. I 35implants1_2013 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9