GTR using Osteoinductive Polyurethane Membranes in Rabbit Maxillary Osteotomies

Purpose: The development of fibrous nonunions following orthognathic surgery is thought to result in part from differential and more rapid migration of fibroblasts compared to osteoblasts into the wound site during healing. Recent experimental work has shown that guided tissue regeneration (GTR) reduced fibrous tissue in growth by approximately 64% at 4 weeks post-op in rabbit maxillary osteotomies. The present study was designed to improve bony wound healing in rabbit maxillary osteotomies by using an osteoinductive, collagen-seeded, polyurethane membranes for GTR. Methods: Bilateral, modified Le Fort I osteotomies (n=18) were produced in the maxillae of 9 adult New Zealand White rabbits. The maxillary segments were advanced approximately 6mm and rigidly fixed using bone microplates and screws. Six defects, randomly selected, were isolated with a biodegradable polyurethane membrane seeded with rabbit type-I collagen, six defects were covered with an unseeded membrane, and the remaining six defects were left uncovered. The rabbits were followed with serial dorsoventral and lateral cephalographs taken at 0, 4, and 8 weeks postoperatively and then the maxillae were harvested for histological analysis. Results: Radiographic analysis revealed that by 8 weeks postoperatively, defects covered with collagen-seeded membranes (19.29 +/- 10.8mm2) and unseeded membranes (17.63 +/-6.8mm2) showed reduced defect areas compared to uncovered control defects (24.90 +/- 8.7mm2), a reduction of approximately 40%. However, this was not significantly different (F=1.02; p>0.05). Histologically, membrane covered defects showed more rapid and organized new bone formation which bridged the osteotomy site compared to control defects. In contrast, uncovered control defects showed an increased amount of fibrous tissue and less organized bone formation in the osteotomy sites. Conclusion: While polyurethane membranes improved bony wound healing, the addition of collagen as an osteoinductive agent did not. Improved membrane pliability and the use of other osteoinductive molecules should be investigated. NIDCR T35 DE077336