Evaluation of an anorganic bovine-derived mineral with P-15 hydrogel bone graft: preliminary study in a rabbit cranial bone model

Objectives: The present investigation aimed to assess the bone-regenerative potential of two formulations of anorganic bovine-derived mineral bound to a P-15 (ABM/P-15) bone graft the particulate and the hydrogel forms in a delayed healing rabbit cranial defect model. Material and methods: Ten adult male New Zealand White rabbits were used to create two 8 mm transcortical cranial defects per rabbit and each one received randomly the test material (ABM/P-15 carboxymethyl cellulose (CMC)-hydrogel graft), the standard control material (ABM/P-15 particulate graft) or remained empty as a negative control. The defects were allowed to heal for 2 and 4 weeks. Qualitative and quantitative histological outcomes were assessed on undecalcified sections. Results: In the defects grafted with the test material, at both time points, there was a marked random migration of the bone substitute particles. As a consequence, the space maintenance provision was lost and new bone formation was reduced compared with the control particulate graft material. The histomorphometric analysis showed that the control material attained better results, with an average of 13.8 +/- 1.9% and 18.2 +/- 4.4% of new bone at 2 and 4 weeks, compared with 8.5 +/- 2.4% and 13 +/- 2.9% for the test material. These differences were significant at 2 weeks (P=0.05), but not at 4 weeks (P>0.05). Additionally, there was a significant difference in the total area of mineralized tissue (new bone plus particles), favoring the standard control over the test material: 43.2 +/- 14.4% vs. 14.2 +/- 5.3% at 2 weeks and 56.9 +/- 4.2% vs. 24.2 +/- 9.6% at 4 weeks, respectively. Conclusions: The test ABM/P-15 CMC-hydrogel graft material behaved in this animal model by migration of the graft particles, what determined an unpredictable osseoconduction and, consequently, a decreased quality and quantity of bone regeneration as compared with the osseopromotive behavior exhibited by the standard particulate form of the ABM/P-15 control graft. It is therefore suggested to restrain the application of the hydrogel graft form in non-contained anatomical bone defects.