Effect of recombinant human bone morphogenetic protein-2 in dehiscence defects with non-submerged immediate implants: An experimental study in Cynomolgus monkeys

Background: Alveolar ridge aberrations commonly compromise optimal dental implant installation. To offset any variance between an aberrant alveolar ridge and prosthetic designs, bone augmentation procedures become necessary. The objective of this study was to evaluate bone formation and osseointegration at alveolar dehiscence defects following augmentation of the defect site with recombinant human bone morphogenetic protein-2 (rhBMP-2) in an absorbable collagen sponge carrier (ACS) at dental implant installation including transmucosal positioning of the dental implant. Methods: Four adult male Cynomolgus monkeys received dental implants in contralateral extraction socket sites with surgically created 6 × 4 mm buccal dehiscence defects following elevation of mucoperiosteal flaps. Contralateral sites received rhBMP-2/ACS (rhBMP-2 at 1.5 mg/ml; 0.1 mg/defect) or served as sham-surgery controls. The flaps were adapted and sutured around the healing abutments leaving the implants in a transmucosal position. The animals were sacrificed at 16 weeks postsurgery and block sections of the implant sites were harvested and prepared for histometric analysis. Results: One dental implant from each treatment group failed to osseointegrate. Another 3 dental implants (sham-surgery controls) failed to osseointegrate with newly-formed bone in the defect area. Thus, 7 of 8 defect sites (4/4 animals) receiving rhBMP-2/ACS compared to 4 of 8 sites (2/4 animals) receiving sham-surgery exhibited evidence of osseointegration with newly formed bone in the defect area. Mean ± SD defect height amounted to 5.3 ± 0.2 and 5.4 ± 0.1 mm for the rhBMP-2/ACS and sham-surgery sites, respectively. Vertical bone gain in rhBMP-2/ACS treated defects (3.9 ± 0.3 mm) did not differ significantly from that in the sham-surgery control (3.7 ± 0.4 mm; P >0.05; paired t-test, N = 4). There were also no significant differences noted for coronal bone-implant contact (3.0 ± 0.6 versus 3.6 ± 0.5 mm), and bone-implant contact within the defect site (28.5% ± 15.1% versus 27.4% ± 31.7% and within resident bone (46.9% ± 26.8% versus 47.8% ± 39.4%) for the rhBMP-2/ACS and control sites, respectively. Conclusions: The observations in this study point to a substantial native osteogenic potential of the alveolar process that has previously not been explored and show that surgical reentry observations of new bone formation may not necessarily indicate that osseointegration has occurred. Bone formation in control defects was substantially greater than predicted, limiting the value of adding an osteoinductive biologic construct.