BOVINE HYDROXYAPATITE FOR MAXILLARY SINUS GRAFTING - COMPARATIVE HISTOMORPHOMETRIC FINDINGS IN SHEEP

This experimental study in animals examines the value of bovine hydrox yapatite as grafting material in one-stage sinus lift procedure. The S chneiderian membrane was elevated from extraorally in 54 sinuses of 27 adult female mountain sheep. Two titanium plasma-flame-spray coated c ylindrical implants were placed in each sinus in the same session. In 2 groups of 18 sinuses each, the subantral hollow space was filled wit h bovine hydroxyapatite and autogenous cancellous bone from the iliac crest, respectively. Eighteen sinuses that were left empty served as a control group. Polyfluorochrome sequential labelling (tetracycline, c alcein green, alizarin complexon) was carried out 4 weeks postoperativ ely, 2 weeks before the animals were sacrificed, and halfway through t he observation period to assess new bone formation. The selected obser vation periods were 12 weeks, 16 weeks, and 26 weeks. Six sinuses per observation period and test group were available for histologic evalua tion. All implants showed favourable osseointegration into local bone. New bone formation was observed ina triangular area bound by the impl ant surface, the local buccal antral wall, and submucous connective ti ssue in all implants. Bovine hydroxyapatite adjacent to local bone was mainly surrounded by bone tissue. There was a great variation in the extent of bony sheathing of the hydroxyapatite particles, irrespective of the animals' survival time. Macrophages were found around HA parti cles that were not surrounded by bone as well as on free implant surfa ces. The mean length of the bone-implant bond was 3.86 mm in the group of empty sinuses, 4.87 mm in the group augmented with hydroxyapatite, and 5.66 mm in the group augmented with autogenous cancellous bone. D uring the observation period, the relative length of bone in direct co ntact with the implant surface increased from 20.0% to 25.1% in the co ntrol group, from 30.4% to 35.5% in the group treated with autogenous cancellous bone, and from 27.4% to 34.7% in the HA group. Autogenous c ancellous bone showed a significantly greater bone-implant contact tha n did the control group (P=0.0004) and the HA group (P=0.0499). When t he apical implant portions were examined separately, both HA (P=0.006) and autogenous cancellous bone (P=0.005) showed a significantly bette r bone-implant bond than did the control group.