Failure to induce supracrestal bone growth between and around partially inserted titanium implants using bone morphogenetic protein (BMP): an experimental study in dogs

The effect of bone morphogenetic protein on supracrestal bone growth around partially inserted implants in a dog model is described. The lower premolar teeth (P1, P2, P3 and P4) were extracted on both sides of the mandible in six dogs. At a surgical exposure 12 weeks later, two 10-mm turned titanium implants were partially inserted, approximately 15 mm apart, in the areas of the P1 and P3 in each side of the mandible, allowing five threads to protrude from the bone crest. A titanium mesh was fastened to the coronal aspect of the two fixtures and the space beneath the mesh was filled with bone morphogenetic protein (S300 BMP) in combination with an insoluble bone matrix carrier, or with the carrier alone. The mesh was covered with an ePTFE membrane. Thus, a space for potential bone formation was created between the two implants. The surgical flaps were coronally positioned and secured with vertical mattress sutures. After 16 weeks of healing, biopsy specimens were retrieved and examined histologically. Bone was not formed around the protruding implants or in the created space between the implants in any case. The carrier was incompletely resorbed. We conclude that supracrestal bone growth beyond the crestal limit with or without BMP in such a large space as in this experimental design may not be possible.