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 r hBMP-2 solution to dry ACS. Once prepared, rhBMP-2/ACS forms a moldable, co hesive, and adhesive implant. However, rhBMP-2/ACS does not have sufficient structural strength to withstand soft tissue compression at specific anato mic sites. To more fully understand the mechanisms that affect bone inducti on by rhBMP-2/ACS in the presence of soft tissue compression, it would be u seful to have a preclinical model that appropriately simulates such circums tances 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 premolar s and reduction of the alveolar ridge. After an 8-week healing interval, mu coperiosteal flaps were elevated and rhBMP-2/ACS or rhBMP-2/ACS combined wi th hydroxyapatite (HA) was implanted into contralateral defects. The animal s were euthanized at 12 weeks post-augmentation and block biopsies processe d 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 alveol ar process. The cortices appeared intact without evidence of expansion into the defect area. Three defects receiving rhBMP-2/ACS/HA exhibited sparse b one trabeculae amidst HA particles, fibrovascular tissue, and marrow. Commo nly, the HA particles were encapsulated by fibrous tissue. Some particles w ere 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 augmentatio n, however, the quality of bone is compromised.