Paste‐like inorganic bone matrix: preclinical testing of a prototype preparation in the porcine calvaria

Objective: To evaluate the osteoconductive properties and the volume stability of an injectable paste-like inorganic bone matrix (PBM) in porcine calvaria defects. Material and methods: We created six circumferential defects in the calvaria of 12 adult iberico pigs. The defects were filled with either PBM, Bio-Oss® of different particle size, carrier alone, or left empty. PBM was composed of Bio-Oss® with a particle size ranging from 250 to 500 μm and a hydrogel-carrier of carboxymethylcellulose and collagen. After 6 and 12 weeks of healing, the animals were sacrificed and undecalcified ground sections were prepared and subjected to histologic and histomorphometric analysis. To quantify the osteoconductive properties of PBM, bone volume per tissue volume (BV/TV) in the defect area was determined. To determine the volume stability, bone substitute volume per tissue volume (BSV/TV) was measured. Results: After 6 weeks, PBM particles in the center of the defect were surrounded by fibrous connective tissue, which was later replaced by bone. BV/TV in the PBM group increased from 29.7±12.7% (minimum 12.2%, maximum 43.7%) after 6 weeks to 43.9±14.9% (minimum 27.8%, maximum 63.9%) after 12 weeks (Mann–Whitney test; P=0.6). According to the Friedman test, BV/TV in groups containing Bio-Oss® of different particle sizes, the carrier and the empty defects was similar to the results obtained with PBM (6 weeks P=0.8; 12 weeks P=0.22). BSV/TV in the PBM group was stable over time, with 10.1±9% (minimum 3.3%, maximum 27.6%) and 16.5±12.9% (minimum 1%, maximum 32.7%), after 6 and 12 weeks, respectively (P=0.72). BSV/TV in the PBM group was comparable to the results obtained with the Bio-Oss® particles of different sizes (Friedman test; 6 weeks P=0.0503; 12 weeks P=0.56). Conclusions: The results of this preclinical study showed that the PBM is osteoconductive and maintains the augmented volume, similar to commercial Bio-Oss®. These data suggest that the osteoconductive properties of Bio-Oss® are maintained at the smaller particle size and in the presence of the carrier.