Recombinant Human Bone Morphogenetic Protein-2 (rhBMP-2) on a Collagen Ceramic Sponge (CCS) for Mandibular Continuity Defects in Non-human Primates

Purpose: In the surgical bony defect site frequently seen in oral and maxillofacial surgery, it is necessary to have a graft material that will maintain the space of the soft tissue periosteal envelope.  If the material is not able to maintain this space during the crucial 3 to 8 week post-operative period, the periosteal envelope will collapse and a minimal amount of bone will be regenerated. The aim of our study was to examine osseous repair of a full continuity defect of the mandible, facilitated by rhBMP-2 released from a collagen ceramic sponge (CCS). In this study, rhBMP-2/CCS treatment was explored at two concentrations: 0.75 mg/cc and 1.3 mg/cc, stabilized with a titanium reconstruction plate.

Materials and Methods: Six male non-human primates (Rhesus Macaques) were used in this bilateral study, allowing for 12 investigational sites.  Animals underwent general anesthesia and were then prepared for surgical mandibular resection by extraction of the posterior mandibular teeth from canine through 2nd molar, leaving the 3rd molar teeth and the incisors intact to maintain occlusal interarch distance and to afford a natural tooth occlusion for post-operative diet. The maxillary canines were also removed to prevent damage to the soft tissue of the mandible. The alveolar sites were allowed to heal after tooth extraction for a minimum of 3 months.

Following healing of the soft tissue, animals received a staged, bilateral hemimandibulectomy using a submandibular approach. There was a 5-week delay between each mandibulectomy received by the same primate. The mandibular ostectomy produced a complete discontinuity defect including the mandibular inferior border with the resected area measuring in excess of 2.5 cm in antero–posterior length. The defect was filled with rhBMP-2/CCS at 0.75 or 1.3 mg/cc, stabilized with a titanium reconstruction plate, and the tissues were closed in layers. Tetracycline labels were given 3 weeks after resection/reconstruction to measure new bone growth and 16 weeks later in order to label bone turnover. The animals were maintained on a soft diet and observed for 6 months post-final reconstruction. 

Animals were then euthanized with intravenous pentobarbital, underwent cannulation of bilateral carotid arteries and were perfused with 10% formalin. The mandible was subsequently harvested. Following sacrifice and tissue harvesting, microCT scans were performed on each of the specimens in order to provide objective measurements in evaluating the quality of the newly regenerated bone.  Following imaging, specimens were fixed for 48 hours in a 10% neutral-buffered solution, sequentially dehydrated in 70%, 95%, and 100% ethanol, and then infiltrated and embedded in methylmethacrylate.  Embedded specimens were sectioned to 25-um thickness and examined under ultraviolet light to evaluate new bone formation as marked by tetracycline labeling.