| Objectives:Due to their similar elastic modulus to bone, excellent biocompatibility and mechanical properties and corrosion resistance in biological environment,titanium alloys have been widely studied and widely used in clinic. Mandibular fracture are the most commom injuries in maxillofacial trauma, rigid internal fixation is the most common modus to treat mandibular fracture. The aim of this study was to evaluate biocompatibility of Ti-6Al-7Nb alloy by cytotoxicity test, hemolysis test and tissue implant test. To evaluate biomechanical stability of a bulge core type rigid internal fixation device that was made by Ti-6Al-7Nb alloy was used for treatment of mandibular linear fracture in the dog.Methods:1.Cytotoxicity test: According to National Standard of Medical Appliance (GB/T16886), the cytotoxicity test was conducted in vitro among five groups: Ti-6Al-7Nb alloy group,Ti-6Al-4V alloy group,pure titanium groups,pure plumbi group and blank group. L-929 cells at logarithmic growth phase were used to prepare the cellular suspension of 1×107/L after trypin digestion and then were incubated on plate, which was followed by adhesive growth of cells,removal of primary medium, and wash with buffer phosphate. Then leaching liquor by four kinds of materials and DMEM were added respectively. Inverted phase containing MTT was wash with buffer phosphate, added with dimethyl sulfoxide and leaching liquor was extracted.Enzyme-linked immunoassay was adopted for optical density value at the wave length of 490 nm. Then relative growth rate of cells was calculated according to the formula.2. Acute hemolysis test:Fresh anticoagulated and attenuated blood was sampled from 20 mL New Zealand rabbits. Ti-6Al-7Nb alloy and Ti-6Al-4V alloy of each 5g were soaked into tube containing 10 mL saline, while distilled water and saline of each 10 mL into positive control group and negative control group, respectively, supernatant liquid was removed after centrifugation. Spect rophoto- meter was used to assay optical density value and then hemolysis rate was calculated by formula.3. Short-term tissue implant test: Implantation materisl was prepared in subcutaneous bladder and muscle in 20 New Zealand rabbits, the length from bladder bottom to incision was more than 10 mm and the interval between the two bladders was more than 10 mm, in order to prevent the contact. Each rabbit was implanted with four kinds of materials, one for each kind. There rabbits were executed after anesthesia at weeks 1, 4, 8, 12 post-operation to conduct hemat- oxylin-eosin staining in the surrounding tissues of materials and observe the number and type of inflammatory cells, together with thickness of fibrous coating membrane, which were all indices of tissue reaction degree.4. biomechanical test: Ten dogs were chosen randomly, mandibular linear` fracture was made in two sides of mandible. Mandibular fractures were fixed by trial group(bulge core type rigid internal fixation device) and control group (common rigid internal fixation device). All animal was sacrificed after two weeks. The biomechanical stability in two groups was evaluated by testing MBS,MBS and MPS,marked decrease in the load-deflection curve.Results:1. In cytotoxicity test, L-929 cells soaked in titanium materials for seven days were confluenced in normal morphology and regular arrangement. A large amount of cells died in pure plumbi group.The level of cytotoxicity of Ti-6Al-7Nb was grade 0.2. The hemolysis degree of Ti-6Al-7Nb alloy was 0.9% which was lower than 5%.3. In the short-term tissue implant test, the fibrous membrane coated with titanium materials was transparent and thin, whereas that with pure plumbi was translucent and ivory white. And 12 weeks post-operation, the inflammatory cells surrounding titanium materials were lower in density, coating membrane became thinner. The number of inflammatory cells and coating thickness in pure plumbi group was higher than those titanium material groups, and the tissue reaction was more serious.The inflammatory cell / tissue reaction degree was gradeâ… in Ti-6Al-7Nb alloy.4. In the trial group, the vertical MBS,MAS were 275±33N,1136±117N,the lateral MBS,MAS were 103±11N,1035±115N . In the control group, the vertical MBS,MAS were 185±23N,895±53N,the lateral MBS,MAS were 80±7N,657±43N.The MPS of trial group and control group were 351±14N and 262±10 N.All the biomechanicl results of the trial group were superior to control group. Conclusion:Ti-6Al-7Nb alloy having excellent biocompatibility is an ideal biomedical titanium alloy. The bluge core type rigid internal fixation device posses good biomechanic property and can produce firm fixation for mandibular linear fracture, it wsa superior to common rigid internal fixation device. |
