Low-dose rhBMP2/7 heterodimer to reconstruct peri-implant bone defects: a micro-CT evaluation

Objectives: To delineate the dynamic micro-architectures of bone induced by low-dose bone morphogenetic protein (BMP)-2/7 heterodimer in peri-implant bone defects compared to BMP2 and BMP7 homodimer. Material and Methods: Peri-implant bone defects (8 mm in diameter, 4 mm in depth) were created surrounding SLA-treated titanium implants (3.1 mm in diameter, 10 mm in length) in minipig's calvaria. We administrated collagen sponges with adsorbed low-dose (30 ng/mm(3)) BMP2/7 to treat the defects using BMP2, BMP7 or no BMP as controls. 2, 3 and 6 weeks after implantation, we adopted micro-computer tomography to evaluate the micro-architectures of new bone using the following parameters: relative bone volume (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), connectivity density, and structure mode index (SMI). Bone implant contact (BIC) was also revealed histologically. Results: Consistent with 2 and 3 weeks, after 6 weeks post-operation, BMP2/7 resulted in significantly higher BV/TV (63.033 +/- 2.055%) and significantly lower SMI (-4.405 +/- 0.500) than BMP2 (BV/TV: 43.133 +/- 2.001%; SMI: -0.086 +/- 0.041) and BMP7 (BV/TV: 41.467 +/- 1.850%; SMI: -0.044 +/- 0.016) respectively. Significant differences were also found in Tb.N, Tb.Th and Tb.Sp at all time points. At 2 weeks, BMP2/7 resulted in significantly higher BIC than the controls. Conclusions: Low-dose BMP2/7 heterodimer facilitated more rapid bone regeneration in better quality in peri-implant bone defects than BMP2 and BMP7 homodimers.