Experimental Research Of Porous Calcium Phosphate Cement In Repairing Mandible Defect

Objective The purpose of this study was to investigate the role of the porous calcium phosphate cement in repairing rabbits mandible defects,and to find a good repairing material for bone defect reconstruction.Methods Six healthy adult New Zealand rabbits were randomly assigned to three groups,with two rabbits in each group,the mandible bone defect animal model was established with the self-control contrast method.In one side of the mandible area,two bone defects,both of the size 0.6cm by 0.6cm,were created with a distance of 0.3cm between each other.The integrity of the lingual periosteum was retained as well as the lower edge of the mandible.Experimental and control groups were implanted with porous calcium phosphate cement and hydroxyapatite ceramics respectively.The three groups of rabbits were then sacrificed at the end of four,eight and twelve weeks after operation,and the new bone formation of the experimental group and the control group in different periods of time was observed by means of general observation,X-ray, histology and environmental scanning electro microscopy.Results1.General observation showed that 4 weeks after the implantation of porous CPC,there was more callus growth one the surface of the jaw defect area,and the boundary between the jaw bone and material was blurring.In addition,small absorption depressions and a few material particles were found on the bone surface.Concerning the jaw defect area implanted with HA crystal,there was a small amount of callus growth on the surface,and the boundary area was distinct.There were also small absorption depressions but more granular materials could be seen on the bone surface. Eight weeks after the implantation of porous CPC,with more callus growth,the jaw bone became more compact on its surface,but its intensity was still lower than that of normal bone tissues.In addition,the boundary between the jaw bone and material became invisible.Meanwhile,the jaw bone with HA crystal implantation also experienced more callus growth on its surface.However,there were a small number of material granules in the centre of the defect area,and the boundary between the repairing material and the jaw bone was still clear.Twelve weeks after operation,the jaw bone implanted with porous CPC had healed on the surface with the intensity of normal bones.The implanted material and the mandible were integrated completely, and no obvious fibrous capsule was found in all groups of animals.On the other hand, the jaw bone implanted with HA Crystal also had more callus on its surface,but there were still a small number of material granules in the center of the defect,and the boundary between materials and the jaw bone was blurring but still distinguishable.2.X-ray examination showed that 4 weeks after operation,for the experimental group,the bone density of the repaired area was lower than that of the surrounding bone tissue,and the boundary line was comparatively obvious.Meanwhile,the bone density of the control group was significantly lower than that of the surrounding bone tissue, and the junction was very clear.Eight weeks after operation,the repaired area of experimental group was integrated into the surrounding bone tissue and the junction line disappeared.However,the repaired bone of the control group looked similar to the surrounding bone in density,but the junction was still visible.Twelve weeks after the operation,the bone density of the repaired area was similar to that of the surrounding bone for both the experimental group and the control group,and the junction line disappeared completely.3.Observation under the morphological light microscopy showed that after four weeks,small islands of bone had formed in the repairing material of the experimental group.The bone staining was pale,and in the adjacent area of the repair material there were typical "cement absorption and bone formation units." It indicated that the osteoclasts were absorbing the bone cement followed by transition zone with spindle cells attaching to bone cement wall,and then the osteoblasts generated osteoid,which finally led to the formation of new bone mineralization.Meanwhile,the control group experienced little degradation of the material and only a few new bones were formed. After eight weeks,the experimental group had undergone most of the material degradation with a large number of osteoblast-like cells in the surrounding area of the repairing material,and the blood vessels were increasing in number.There was more new bone formation alone the boundary line between the bone and the repairing material.Concerning the control group,part of the material was degraded,and new blood vessels as well as new bone formation were found.After twelve weeks,almost all the repairing material of the experimental group had been degraded,and a considerable amount of new bone had been formed.In contrast,the repairing material of control group had not yet been fully degraded,and the amount of new bone was less than that of the experimental group.4.Environmental scanning electron microscope showed that after four weeks,the bone tissue had a clear interface with the repairing material in the experimental group, and the material began the process of decomposition and integration.Then the original structure was destroyed,and the new bone began forming.Comparatively,for the control group,the interface between bone tissue and materials was also quite clear,but there was less degradation of the repairing material and the new bone formation was not so obvious.After eight weeks,more new bone could be seen in the repairing material of the experimental group.The integration of new bone and materials was much significant and more materials degraded.The control group also showed newly formed bone and its close attachment with the materials,but more undecomposed materials could be seen.After twelve weeks,little repairing material could be found in the experimental group and the defect area had been replaced by a large number of new bone tissues.The interface between bone tissues and the material was very close, similar to normal bone tissues.For the control group,comparatively more material remained undecomposed,and the new bone formation was relatively slower.The interface between bone and materials was also less close. Conclusions The porous CPC,with better quality for degradation and osteogenesis,is a good material to repair bone defects.