Mechanical testing of recombinant human bone morphogenetic protein-7 regenerated bone in sheep mandibles

A new method was developed in this study for testing excised sheep mandibles as a cantilever. The method was used to determine the strength and stiffness of sheep hemi-mandibles including a 35 mm defect bridged by regenerated bone. Recombinant human bone morphogenetic protein-7 (rhBMP-7) in a bovine collagen type-I carrier was used for the bone regeneration. Initial tests on ten intact sheep mandibles confirmed that the strength, stiffness and area beneath the load-deformation curves of the right and left hemi-mandibles were not significantly different, confirming the validity of using the contra-lateral hemi-mandible as a control side. Complete bone regeneration occurred in six hemi-mandibles treated with rhBMP, but the quality and mechanical properties of the bone were very variable. The new bone in three samples contained fibrous tissue and was weaker and less stiff than the contra-lateral side (strength, 10-20 per cent; stiffness, 6-15 per cent). The other half had better-quality bone and was significantly stiffer and stronger (p < 0.05), with strength 45-63 per cent and stiffness 35-46 per cent of the contra-lateral side. Hemi-mandibles treated with collagen alone had no regenerated bone bridge suggesting that 35 mm is a critical-size bone defect.