Osteoconductivity of an Injectable Allograft in Critical-size Rat Calvarial Defects

Objectives: Demineralized Bone Matrix (DBM) are currently used in reconstructive surgery. Developing injectable DBM is crucial as such substitutes will enable an easy and rapid surgical placement in bone defects while achieving optimal defect filling capacity. For these reasons, a new formulation of an injectable Partially DBM (PDBM) issued from viro-inactivated spongious human bone was prepared by BioBank^®. The objective of the proposed study is to assess its osteoconductivity in critical-sized defects.
Methods: PDBM was mixed with deionised water according to BioBank instructions. Eight mm-diameter bicortical critical size defects were performed on calvarium of 12-week old, male, Wistar rats and were either left empty (n=6) or filled with the PDBM paste using a syringe (n=6). In vivo micro-computerized tomography (micro-CT) analysis was performed at day 0, 15, 30, 45 and 60. At day 60, explants were collected and processed for non-decalcified histology. Histological and histomorphometrical analyses were carried out to assess PDBM biocompatibility and bone forming ability.
Results: Micro-CT analysis showed significant increase of radiopacity only in 8-mm defects filled with PDBM from day 0 up to day 60 (p=0.00005); the radiopacity volume was significantly greater in defects filled with the allograft than in those left empty (21.82 ± 6.96 mm3 vs 6.27 ± 5.09 mm3; p=0.0006). At this time point, no defects exhibited foreign body reaction or inflammation. Moreover, bone formation was observed throughout the defects filled with PDBM. Newly formed bone was found either surrounding or bridging PDBM particles. In contrast, it was predominantly located at the edge of the defects left empty. Most importantly, new bone formation in defects filled with PDBM was 16-fold superior to that of defects left empty (p<0.001).
Conclusions: The PDBM allograft tested presents osteoconductive properties and could be practical as injectable bone substitute in maxillofacial and periodontal surgery.