Ridge Augmentation Following Implantation of Recombinant Human Bone Morphogenetic Protein-2 in the Dog

Background: Recombinant human bone morphogenetic protein-2 (rhBMP-2) in an absorbable collagen sponge (ACS) carrier induces bone for reconstruction of skeletal defects. The rhBMP-2/ACS implant is prepared by administering a rhBMP-2 solution to dry ACS. Once prepared, rhBMP-2/ACS forms a moldable, cohesive, and adhesive implant. However, rhBMP-2/ACS does not have sufficient structural strength to withstand soft tissue compression at specific anatomic sites. To more fully understand the mechanisms that affect bone induction by rhBMP-2/ACS in the presence of soft tissue compression, it would be useful to have a preclinical model that appropriately simulates such circumstances in patients. This pilot study evaluated one such potential model. Methods: Bilateral, Class III alveolar defects were surgically produced in 4 adult mongrel dogs following extraction of the mandibular fourth premolars and reduction of the alveolar ridge. After an 8-week healing interval, mucoperiosteal flaps were elevated and rhBMP-2/ACS or rhBMP-2/ ACS combined with hydroxyapatite (HA) was implanted into contralateral defects. The animals were euthanized at 12 weeks post-augmentation and block biopsies processed for histologic evaluation. Results: Limited augmentation followed implantation of rhBMP-2/ACS (0.7 ± 0.6 mm). In contrast, sites receiving rhBMP-2/ACS/HA exhibited clinically relevant ridge augmentation (5.5 ± 1.6 mm). Defects implanted with rhBMP-2/ACS exhibited dense trabeculation within the corpus of the reduced alveolar process. The cortices appeared intact without evidence of expansion into the defect area. Three defects receiving rhBMP-2/ ACS/HA exhibited sparse bone trabeculae amidst HA particles, fibrovascular tissue, and marrow. Commonly, the HA particles were encapsulated by fibrous tissue. Some particles were observed in contact with bone. Conclusions: The results suggests that rhBMP-2/ACS has limited effect alone in this augmentation model of Class III alveolar ridge defects. Inclusion of HA into the rhBMP-2 construct results in clinically relevant augmentation, however, the quality of bone is compromised.