Stress Analysis Of Different Designs On Implant Fixed Edentulous Mandible By Finite Element Method

The number of implants plays a key role in the implant supported mandibularfull-arch fixed prostheses.In the context of maintaining the stable and functionalprosthesis,the optimal number of implants seems essential to be studied. Due to the specialanatomical structure and bone resorption of mandible, most scholars believe that at least6paralleled implants should be inserted into the interforaminal region to support theedentulous mandible; however,the―All-on-Four‖protocol which used four dental implantsin the interforaminal region with the posterior implants being tiled30°distally found a highsuccess rate.Recent studies have reported good clinical outcomes when a combination ofaxial and tilted implants was used to support a mandibular full-arch fixed prosthesis, butmost of them were short-term retrospective clinical study, lacking of long-termobservations. The conclusion of titled terminal implant varies from research toresearch.There is still no unified view on wheather different angles of titled terminalimplant have positive effects on the biomechanical performance of mandibular full-archfixed prostheses.Therefore, study the effect of implant number and inclination on stressdistribution about components of implant prostheses reflects a certain clinical significance.Objective：To study the effect of implant number and inclination on stress distributionabout implant,implant-bone interface and framework of implant supported mandibularfull-arch fixed prostheses with3-D finite element analysis．Methods：A special denture is made for an edentulous mandible cast to collect3-dimensional finite element data. Six3-dimensional finite element models wereconstructed.Three6paralleled implants modles, inserted into; Three4paralleled implants modles, inserted into.Model1：6paralleled implants; Model2:4paralleled implants;Model3:6implants, the two terminal implants were tilted30degree distally. Model4:4implants, the two terminal implants were tilted30degree distally.Model5:6implants, the two terminal implants were tilted45degree distally. Model6:4implants, the two terminal implants were tilted45degree distally. A240N load was appliedto the central fossa of the right second molar.Results:1.For all the modles, the peak values of stress were near the cervical area ofthe distal implant and implant-bone interface.The highest stess values of framework wereconcentrated in the distal area of the connection between the terminal implant andframwork.2. The effect of implant numbers on stress distribution （1）modle1and modle2:,the maximum stress values of and implant, the implant-bone interface in modle1were lower, decreased by26.35%,3.65%and7.26%respectively compared withmodle2and the framework was similar.（2）modle3and modle4:The maximum stressvalues of and implant, the implant-bone interface decreased by42.87%,3.27%and14.79%respectively than modle4,but the framework increases3.05%.（3）modle5andmodle6:The maximum stress values of and implant decreased by46.53%,4.89%than modle6, the implant-bone interface and framework decreased11.00%and3.46%.3.The impact of implant inclination on stress distribution （1）modle3and modle5cmparedwith modle1:The maximum stress values of implant in modle3and modle5reduced by49.86%and62.00%respectively than modle1,the implant also reducedby10.10%and27.74%.The implant-bone interface reduced by34.06%and34.52%, andthe framework also reduced by4.32%and5.18%.（2）modle4and modle6compare withmodle2:The maximum stress values of implant in modle4and modle6reduced by35.37%and47.66%respectively than modle2, implant reduced by and10.45%and26.80%respectively than modle2.The implant-bone interface reduced by28.23%and31.77%, and the framework in modle4also reduced by6.26%, the framework in modle6only slightly smaller than modle2.Conclusion：Within the limitation of this study1.Remaining the same inclination ofthe terminal implant, the maximum stresses of implants and the implant-bone interface canbe reduced by increasing the number of implant, but the framework was not significantlyaffected.2.When fixed the edentulous mandible with the same implant numbers,theterminal implant inclined30°,the stress of the implants and implant-bone interface can bereduced;icreasing the inclination to45°,stresses will be further decreased.3. Whetherincreasing the number of implants or the inlination of the terminal implant, the level ofreduced stresses of anterior implant and implant-bone interface were more effective thanthe terminal implant.4.The biomechanical advantages performed more pronounced in theprostheses of4implants with the terminal implant being titled than6paralleled implants.