Delayed versus immediate reconstruction of mandibular segmental defects using recombinant human bone morphogenetic protein 2/absorbable collagen sponge

Purpose: To compare the efficiency of recombinant human bone morphogenetic protein 2 (rhBMP2)/absorbable collagen sponge (ACS) in the delayed versus immediate reconstruction of mandibular segmental defects in a canine model. Methods: We randomized 11 dogs into 2 groups: immediate reconstruction (group 1, n = 6) and delayed reconstruction (group 2, n = 5). A 35-mm osteoperiosteal segmental defect was created on the left side of the mandible. Reconstruction with rhBMP2/ACS was carried out in the same setting in group 1 or at 4 weeks postoperatively in group 2. The contralateral side acted as an internal control. Animals were monitored both clinically and radiographically throughout the experiment. Twelve weeks after the application of rhBMP2/ACS, the quantity of bone formation was evaluated using regenerate mapping and histomorphometric analysis. Qualitative evaluation was performed based on bone mineral density and Vickers microhardness (μHV) testing. Results: Postoperative seromas were observed in 83.3% of group 1 dogs only. Group 1 showed significantly larger physical dimensions than group 2 in most regenerate zones. Successful regeneration was achieved in 83.3% of group 1 dogs (discontinuity defect was seen in 1 of 6 dogs in group 1). Meanwhile, none of the 5 dogs in group 2 could be considered to have undergone successful regeneration (3 dogs had discontinuity defects, bony union occurred only in the basal third in the fourth dog, and the last dog showed union with only a shell of bone). The percent bone area and percent defect filling were significantly higher in group 1 than in group 2 (percent bone area, 52.4% ± 5.6% in group 1 and 36.6% ± 11.2% in group 2 [P =.02]; percent defect filling, 56.3% ± 5.5% in group 1 and 38.5% ± 10.8% in group 2 [P =.01]). Group 1 showed higher bone mineral density (0.7 ± 0.3 mg/cm³ in group 1 and 0.4 ± 0.1 mg/cm³ in group 2, P =.1). Finally, μHV was significantly higher in group 1 (20.3 ± 2.6 μHV) than in group 2 (13.2 ± 2.4 μHV) (P =.01). Conclusions: Delaying the application of rhBMP2/ACS for 4 weeks attenuated the quantity and quality of regenerated bone in mandibular segmental defects.