Augmentation of calvarial tissue using nonpermeable silicone domes and bovine bone mineral - An experimental study in the rat

The aim of the present study was to evaluate the effect of bovine bone mine ral placement as an adjunct to a guided bone regeneration (GBR)-barrier in experimental bone augmentation. Some 18 Sprague-Dawley rats underwent flap surgery in which non-permeable silicone domes were placed on the calvaria. A test group of 9 animals received domes filled with cancellous deproteiniz ed bovine bone mineral (Bio-Oss(R)). The domes of 9 control animals were le ft empty. The experiment was terminated after 8 weeks of healing. Inspectio n after histologic preparation found no signs of any foreign body reaction to the implanted bovine bone mineral, which seemed to be well integrated wi th the augmented tissue. The control specimens healed uniformly with new bo ne inside the domes at the base of the calvaria. The tissue inside the dome s of the test specimens had a completely different architecture with new bo ne both at the base of the calvaria and at a distance from the base, surrou nded by and in close contact with non-mineralized tissue and remaining bovi ne bone mineral. Some ingrowth of soft connective tissue, most likely from the sagittal skull suture could be seen in most test and control specimens. Histomorphometric analysis revealed that the total amount of augmented tis sue was significantly greater in the test group ((x) over bar=1.93+/-0.21 m m(2)) than in the control group ((x) over bar=0.99+/-0.22 mm(2)), P<0.001). The control domes contained 0.73+/-0.28 mm(2) augmented bone, while the co rresponding value for the test specimens was 0.35+/-0.13 mm(2), significant ly less than the controls (P<0.01). The test domes contained 0.83+/-0.15 mm (2) newly-formed non-mineralized calvarial tissue, significantly more than the controls ((x) over bar=0.26+/-0.16 mm(2)), P<0.001), Remaining particle s of bovine bone mineral constituted 0.76+/-0.14 mm(2), or 39%, of the tota l amount of augmented tissue in the test group. A considerable shrinkage to about 69% of the height of the initial fill of bovine bone mineral at surg ery appeared in the test domes after 8 weeks of healing. The reason for thi s was probably more due to a denser packing of the bovine bone mineral duri ng healing than to resorptive activity. It was concluded that implantation of bovine bone mineral combined with GBR technique significantly enhances a ugmentation of calvarial tissue. Early mineralization, however, seems to be retarded compared to non-filled control specimens. Further studies should be made to determine the long-term maturation of augmented tissue including resorption pattern of the bovine bone mineral.