The Experimental Study Of Reconstruction Of Mandibular Angle Defect Using Individulized Titanium Prosthesis

PartⅠ:The experimental study and clinical application of reconstruction of mandibular angle defect with individulized precast titanium prosthesis using rapid prototyping technologyObjective To explore the method of reconstruction of mandibular angle defect with individulized precast titanium prosthesis using computer aided design(CAD)and rapid prototyping(RP)technology,and provide experimental foundation and preliminary clinical experience for clinical wide application of this method.Methods In the part of animal experiment,We divided 16 minipigs into two groups equally,and established mandibular angle defect models of minipigs(8 minipigs of group A received mandibular angle osseotomy on the left sides,and the other 8 minipigs of group B received mandibular angle osseotomy on the bilateral sides).Basing on the data resource from CT,we manufactured the three dimensional cranial models and designed the individulized precast pure titanium prostheses using three dimensional reconstruction and rapid prototyping technology.We repaired the mandibular angle defects on the left sides of 16 minipigs using the individulized titanium prostheses.The left sides were all experimental sides and the right sides(the normal sides of group A and the simple mandibular angle osseotomy sides of group B)were all control sides.We carried out a control study with experimental sides and control sides by in general,light microscope and electron microscope.In the part of clinical research,we adopted this method to produce individulized precast titanium prostheses and repair mandibular angle defects in three cases. Results In the part of animal experiment,the precast titanium prostheses tallied with the shape of mandibular angle defects perfectly.The formation of titanium-osseointegration could be seen gradually after long-term histological and electron microscope observation. Only one minipig in group A appeared infection 6 months postoperatively,and there were no complications in other minipigs.In group A,it was symmetry in early postoperative stage,but with the minipigs growing,the experimental sides(the left sides)appeared a little smaller than the normal sides(the right sides).In group B,the simple mandibular angle osseotomy sides(the right sides)had partial recovery,but were still smaller than the experimental sides(the left sides)markedly.In the part of clinical research,the defects of the patients had been repaired and the symmetry was fine.There were no complications and the results were satisfactory.Conclusions Individualized precast titanium prosthesis using rapid prototyping technology can reshape favorable and normal contour of mandibular angle,form ideal titanium-osseointegration and has an extensive prospect of clinical application. PartⅡ:The Experimental Study of titanium ions release and surface elements change after titanium implants implantationObjective To study regularity of titanium ion release,effect,surface topography and elements composition change after titanium implants implantation,and provide an experimental data for clinical application of titanium implants.Methods In the part of animal experiment:16 minipigs in experimental group received reconstruction of mandibular angle defects on their left sides using individulized precast pure titanium prostheses;4 minipigs in control group had not any titanium implantations. (l)We completed the quantitative detection of titanium ion level in blood serum,urine, hair before implantation and at the 1st,3rd,6th,12th,18th month after implantation,and completed the quantitative detection of titanium ion level in distant organs(including liver,spleen,lung,kidney,submandibular lymph nodes,spinal cord)of control group and experimental group at the 3rd,6th,12th,18th month after implantation using Inductively coupled plasma mass spectrometry(ICP-MS).(2)We detected the elements composition change of titanium prostheses and the regularity of titanium ion content change in bone using Energy-dispersive X-ray analysis(EDAX)before implantation and at the 3rd,6th,12th,18th month after implantation,and observed the surface topography using Scanning electron microcopy(SEM).(3)We studied the histological change of adjacent tissues and distant organs using light microscope after implantation.In the part of clinical research:(l)We detected the titanium ion in blood serum and urine of one patient who had implanted a titanium alloy prosthesis before implantation and at the 1st,2nd week and the 1st,3rd,5th month after implantation,and analyzed the changing regularity.(2)We detected the elements change with different depth and contact surfaces of the unused plates and the plates implanted 6 months using Auger electron spectroscopy(AES).Results In the part of animal experiment:(1)The titanium ion concentrations of postoperation in blood serum,urine,hair,in liver,spleen,lung,kidney,submandibular lymph nodes,spinal cord were all higher than those of preoperation and control group. The peak value of titanium ion in urine appeared at the 1st month postoperatively,the peak value of titanium ion in hair appeared at the 6th month postoperatively,and others appeared at the 3rd month postoperatively.The titanium ion presented descended tendency of different degree in all the tissues and organs 6 months postoperatively except kidney.(2)We found that the Ti content of the prostheses surface decreased with the implanted period going on using EDAX,and found the surface became rough using SEM. The limit of detection of Ti was 250-300μm from the titanium-osseointegration interface in bone.(3)We found dark stain in capsule at the 3rd month after implantation,and found black particles by light microscope,but all of them disappeared 6 months after implantation.There were no adverse effects,denaturation,necrosis and pathological hyperplasia related to the implants during the postoperative observation of 18 months.In the part of clinical research:(l)The peak value of titanium ion in blood serum appeared at the 3rd month postoperatively and decreased later;and the peak value of titanium ion in urine appeared at the 2nd week postoperatively and decreased later. (2)Using AES we found that the Ti content of the plates implanted 6 months was lower than the unused plates on the surface and at the 10nm depth(P＜0.01).The Ca content of the side contacted bones was higher than the unused plates and the side contacted soft tissues on the surface and at the 10nm depth(P＜0.01).The content of Ti increased with the depth(P＜0.01),while Ca decreased.(P＜0.01).Conclusions There is phenomenon of titanium ions release,deposition and elements exchange in vivo which is just trace and not enough to cause structure,function change and metallosis of tissues and organs.Titanium has good biocompatibility and chemical stability,but the safety of much longer term after implantation still needs observation and study. PartⅢ:The Experimental Study of masseter volume change after reconstruction of mandibular angle defect using individulized precast pure titanium prosthesisObjective To study the masseter volume changing regularity after reconstruction of mandibular angle defect using individulized precast pure titanium prosthesis.Methods We divided 16 minipigs into two groups equally,then established mandibular angle defect models on the left sides of group A and bilateral sides of group B.Then 8 minipigs of group A received reconstruction of mandibular angle defects on the left sides using individulized precast pure titanium prostheses,the other 8 minipigs in group B received reconstruction of mandibular angle defects on the left sides using individulized precast pure titanium prostheses and dissection of masseter on the right sides.According to the CT scanning data of the 3rd,6th,12th,18th month postoperation,we completed image processing to segment masseter from CT scans,and three-dimensional(3D) reconstruction and volume measurement using picture segmenting and partial reconstruction techniques.Furthermore,we carried out a control study on masseter volume change between the reconstructive sides(the left sides)and the normal sides(the right sides)of group A,as well as between the reconstructive sides(the left sides)and the simple mandibular angle osseotomy sides(the right sides)of gourp B.Results The masseter volume of the reconstructive sides(the left sides)using individulized precast titanium prosthesis were all smaller than the normal sides(the right sides)in group A,and the volume difference tended to diminish;bilateral masseter volume had statistical difference at the 3rd,6th and 12th month(the 3rd and 6th month P＜0.01,the 12th month P＜0.05),and had no statistical difference at the 18th month postoperatively(P＞0.05).The masseter volume of the reconstructive sides(the left sides) using individulized precast titanium prosthesis were all larger than the simple mandibular angle osseotomy sides(the right sides)in group B,and the volume difference tended to largen;bilateral masseter volume had statistical difference at the 3rd,6th and 12th month (P＜0.01),and had no statistical difference at the 18th month postoperatively(P＞0.05)Conclusions Certain extent of atrophy happens to masseter after madibular angle osseotomy.Madibular angle reconstruction using individulized precast pure titanium prosthesis is beneficial to masseter volume recovery;but the volume is still smaller than normal.