Experimental Study On Absorbable Poly-L-lactide Miniplate And Screw For The Internal Fixation Of Fracture

Objective: The purpose of this study is to research the effect of usingadsorbable polylactide plates and screws to fix the fracture ofmandible in dogs. Methods: 15 adult poochs were chosen, which were weighed 10-15kg,female and male at random, and that were divided into 5 groups: onemonth group, two months group, three months group, six monthsgroup and twelve months group. There were three dogs in each group.After being anesthetized with 846 composition (0.08-0.1ml/kg.BW.i.m), fracture models were created artificially on both side ofthe mandible between molar teeth and premolar teeth in each dog andtwo methods were adopted to heal the fracture,one side was fixed withpoly-L-lactide (PLLA) plates and screws and the other side was fixedwith titanium plates and screws. To compare the effect of the twomethods of internal fixation of mandibular fracture, dogs of eachgroup were sacrificed in the 1st, 2nd, 3rd, 6th and 12th months afterthe operation. Mandible of dogs from each group were took out.Morphological observation, roentgenographic investigation, Histologyobservation, SEM examinationand haematological examination werecarried out.Results:Morphological observation: Some bony callus were seen aroundthe fracture gad one month after the operation and there were alsomany new bone tissue in the 3th months group. Six months later afeterthe operation, fracture of both side were healed normally.Roentgenographic investigation: Bony callus could be seen after1 month;fracture line got blur 2 and 3 months later;the fracture inboth groups gad were united normally after 6 months.Histologic observation:Bone trabecula and new bone could beseen after 1 month;new bone and normal bone coalesced after 2months;a lot of new bone could be seen after 3 months;Bonetrabecula rebuild and the countersink became blur after 6 months.SEM examination: The collagen fibers get thickening andcollagenoblast lessen in the 1st month group;the new bone could beseen in the 2nd month group;a lot of new bone trabecula and electrondense PLLA screws degradation grains could be seen in the 3rd monthgroup;Bone trabecula rebuild, the countersink became blur andelectron dense PLLA screws degradation grains could be seen in the6th month group.Haematological examination: blood cell paramorphia were notdetected, haemoglobin content, lencocyte count, the rate ofleukomonocyte, heterophil granulocyte and acidophilic cell is normalin the 1st, 2nd, 3rd, 6th and 12th months after the operation.Conclusions:Compared with titanium plates and screws system, moresatisfactory effect we can get by using adsorbable polylactideminiplates and screws for internal fixation of the fracture of mandiblein dogs. Absorbable polylactide miniplates and screws system is amuch safer method for internal fixation and it has much betterhistocompatibility.The method represents the direction of thedevelopment of the materials of internal fixation.