Reconstruction Of Canine's Temporomandibular Joint And Mandible With Bone Allograft

Reconstruction of the temporomandibular joint and massive mandibular defect is a challenging problem in oral and maxillofacial surgery. Reconstruction has generally been accomplished in the past with tissue harvested from the patient. Autogenous bone has been shown experimentally and clinically to be superior to allogeneic bone. However, because of the inadequate supply and donor-site morbidity, harvesting of autogenous bone is limited. In the past 20 years, bone allografts were widely used as substitution by orthopedists to reconstruct the defects of extremities and had achieved great success. But the mandible's anatomical structure and fix manner are greatly different with limbs, the properties of bone healing and remodeling are still not very clear. The purpose of this study was to investigate the feasibility of reconstruct the TMJ and mandibular defect with frozen and freeze-dried bone allograft.Part 1:Effects of Freezing and Freeze-drying on the BiomechanicalProperties of Canine's MandibleObjective: To investigate the effects of freezing and freeze-drying on the biomechanical properties of canine's mandible. Methods: Twelve fresh mandible of beagle dogs were randomly divided into two groups:group I were randomly divided into control group and freezing group; group II were control group and freeze-drying group. Each group had six half mandible. All the test pieces of mandible underwent bending and compression tests. Results: There were no significant differences among the fresh bone, freezing bone and freeze-drying bone in the compression test. The maximal bending rigidity offreezing group and freeze-drying group were greatly higher than the fresh group but the maximal bending load decreased 24 percents and 30 percents respectively. Conclusions: The freezing and freeze-drying canine mandibles had the similar anti-compressing properties compared with fresh mandibles. They were strong enough to reconstruct the mandible. Part 2: Establishment of an Experimental Model for the Reconstruction ofCanine's Temporomandibular Joint and Mandible with MandibleAllograft—the Clinical and Pathological Study.I An Experimental Model for the Reconstruction of Canine's Temporomandibular Joint and Mandible with Mandible AllograftObjective: To establish an experimental model for the reconstruction of canine's TMJ with frozen and freeze-dried mandible allograft and determine the feasibility of reconstruction the segmental mandible defect including condyle with mandibular bone allograft. Methods: Eighteen dogs were randomly divided into three groups and received bone transplantation respectively, group I :autogenous mandible, group II : frozen mandible allograft, group III: freeze-dried mandible allograft. The reconstructive scope was the back part of ramus, including the condyle. After 24 weeks, the animals were killed and evaluated clinically, radiographically . Results: All the animals were thriving and no wound infection postoperatively. Sixteen weeks after the operation, there were no significant decrease of maximum mouth opening. The height of transplant bone decreased 6.80%, 14.65% and 24.09% respectively in twenty-four weeks postoperatively. Conclusions: The frozen and freeze-dried mandible allografts of canine achieved clinical healing successfully and had normal function of temporomandible joint.II Reconstruction of Canine's Temporomandibular Joint and Mandible with Allograft Mandible— the Study of Radionuclide SPECT Imaging and Bone Mineral Density.Objective: To access the mandibular defect repair for the reconstruction ofcanine's TMJ with frozen and freeze-dried mandible allograft. Methods: Eighteen dogs were randomly divided into three groups and received bone transplantation respectively: group I, autogenous mandible, group II, frozen mandible allograft, group III, freeze-dried mandible allograft. The SPECT imagings were taken in 4 weeks, 12weeks, 24weeks postoperatively. Twenty-four weeks after the operation, the animals were killed, the BMD of transplants were evaluated. Results: The regenerative bone deposition was found four weeks postoperatively, twelve weeks after surgery the radioactive ratio of bone grafts/control sides reached the highest level. In contrast with the original level, twenty-four weeks after the surgery, there were no significant changes of allograft bone's BMD. Conclusions: All the bone allografts were survived and BMD of allografts had no significant changes 24 weeks postoperatively.HI Reconstruction of Canine's Temporomandibular Joint and Mandible with Allograft Mandible—the Pathological Study.Objective: To study the histological properties of temporomandibular joint and the host graft union twenty-four weeks after the reconstruction of mandible defects with bone allografts. Methods: A group of 18 mongrel dogs underwent unilateral resection of back part ramus. They were immediately reconstructed by autogenous bone grafts, frozen bone allografts and freeze-dried bone allografts respectively. The recipient animals were killed under general anesthesia at 24 weeks postreconstruction. The mandibles, disks and fossas were resected, fixed in 10% neutral buffered formalin and 3% glutaraldehyde. The formalin fixed specimens were embedded in methylmethacrylate and four micrometer sagittal sections were cut. The scanning electromicroscope observation were performed with the glutaraldehyde fixed specimens. Results: Histologically, all the grafted condyles had revascularized and new live bone were found in them. In contrast with normal control, there were thickened fibrous layers on the cartilage of grafted condyles, especially in the bone allografts. The most evident change of ultrastructre was the vanish of granular material layer of the grafed joint surface.The collagen fibers were thickened and arranged disorderly of the bone allografts. The incorporation of autografts were very good, the host-graft interfaces were not clear. The host-graft interfaces of bone allografts were still clear, they had united by means of lamellar bone and osteoid. filling the gaps perpendicular to the long axis of the bone. No difference in the histological appearance of host-graft interface was noted among the frozen/freeze-dried groups. All the grafts were revascularized—that is, vessels and living tissue were visible in the intertrabecular spaces throughout the grafts. Conclusions The frozen and freeze-dried bone allografts can achieve bone union with hosts. Provided that there were some degenerations in the condyles and disks, mandible allografs were good replacements for reconstruction of massive mandibular defect. Part 3: Immunological Study after Allograft Mandible Transplantation inCaninesObjective: To study the immune reaction after the transplantation of mandible allografts in caninies. Methods: A group of 18 mongrel dogs underwent unilateral resection of back part mandibular ramus. They were immediately reconstructed by autogenous bone grafts, frozen bone allografts and freeze-dried bone allografts respectively. Peripheral blood samples were obtained for radioimmunoassay of IL-2, IL-4 and IL-6 in operation day, 2, 4, 8, 16 and 24 weeks post operation. Results: IL-2 increased significantly 2 weeks after transplantation of autogenous group. IL-2 and IL-6 increased significantly 2 weeks post operation and IL-4 decreased significantly 2, 4, 8 weeks post operation of frozen allograft group. IL-2 and IL-6 increased significantly 2 weeks after transplantation, of freeze-dried group. Conclusions: Comparing with autografts, The frozen and freeze-dried bone allografts did not lead to consistent abnormality of IL-2, IL-4 and IL-6 of host peripheral blood. Transplantation of frozen/ freeze-dried bone allograft will not lead to serious immunological rejection..