Three-dimensional Finite Element Analysis On Stress Distribution In Maxillary With All-on-4Implants In Different Arch Forms

Background：Implant denture has been widely used in…Since all-on-4technology was advanced by doctors centered on Paulo Malo, it has beenclinically proved that the implant has high survival rate andsatisfactory clinical results in edentulous jaws restoration.All-on-4technology has many merits such as little trauma, flexible plant site andlow financial burden of the patients. The edentulous jaws restoration canbe finished when only4dental implants were inserted simultaneously.The most remarkable advantage of all-on-4is that the inclination angle inskeleton can be changed according to the difference of the local bonecontent and physiological and anatomical structure and thus avoid theprevention of restoration from being finished due to the damage of theimportant anatomical structure caused by the implants or the limitation ofbone defect. When people chew something, the conduction of the bitingforce in selection can be directly influenced by the inclination of theimplants. Researches show that even if the loading stress is less than theacceptable maximum value of the selection structure, it caninjure bone tissue and induce irreversible bone resorption, which finallyresults in the decrease of the plant achievement ratio in the long run.Therefore reasonable arrangement of the inclination angle of the implantin skeleton has been a research hot spot in recent years.As the technology develops, individualized reparation design based on the personal differences of the patients, which most obviouslycharacterized by the difference of the dental arch, has been a developmentdirection of oral cavity implant reparation technology. Traditionally, thedental arches were divided into three types in line with the arrangementof the six front teeth: Oval, Square round and Triangle round. Dental archcurvature difference caused by different dental arch shapes will surelyeffect the relative position relationship of the implants and the jawboneand consequently effect the stress distribution and change the conductionof the biting force. This experiment is aimed at getting different stressdistribution by building three types of computer based finite elementmodel of maxillary edentulous jaw and changing the angle of all-on-4ofteeth implant in the posterior teeth area.Objective：To explore the effect of different arch forms of maxillary models onstress distribution of peri-implant of All-on-4implants with3-dimensional finite element, and provide evidence for the improvementof implant achievement ratio in clinic.Method:1. Computer hardware and software.The computer configuration which this experiment use is CPU Intel（R） i5-3570Quad-Core Processer,16G RAM Kingston(R),2THard-Drive Seagate(R). Windows7professional operation systemMircosoftware(R). Solidworks2013software package(SolidWorks Corp.MA, U.S.). Abaqus6.13(DSS Corp. RI. U.S.).2.3-Dimensional Finite Element Model building.Using a maxillary model constructed using measurements obtainedfrom3M Corp. MBT Arch Form Templates. The length of themaxillary was set at110mm, which depended on the average value of distance of each retromolar pad. The height and width of maxillary modelwas set at25mm and11mm. Cortical-bone thickness was defined as2mm at all points.Abutment model diameter was set at4mm. The height of loadingprosthesis was10mm, and the width was8mm. The length of arc was90mm, same as the maxillary model.All four implants specification was13mm length and4.3mm atdiameter. In all models, the distance of the center of implant was set at21mm, to ensure the most slant implant would not go through themaxillary models. The2anterior implants was seeded perpendicular tothe maxillary plane. In all models the2posterior-most implants stayparalleled. The inclination of posterior-most implants was set at0°,15°,30°,45°.In this study, the situation of stress distribution in cortical bone wasmain purpose, so we saw the up-loading prosthesis, abutments andimplants as one entirety.4. Material property.In this study, the material property was set homogeneous, andisotropic linear elastic material. The data of material property came frompublished reference.5. Interface setting.Foundation condition hypothesis for all the implants created fullyosseointegration, the implants in maxillary bone was fixed contactconnection without relative sliding. The underside of maxillary bone wasset at fixed constraint.6. Loading and measuring of stress.Using finite element software Abaqus6.13(DSS Corp. RI. U.S.) toLoad and analysis the stress distribution on all model. To simulate the stress situation as chewing food, the study employed2kinds of loadingconditions. The underside of maxillary bone was set at fixed constraint,then loaded the stress, used static analysis to solve the stress distributionon all models.Result:1. Stress distribution around implant in posterior teeth areaIn the first loading case, the stress near the square round dental archimplants is obviously higher than that of the other two types. With theincrease of the inclination angle of the implant, the stress near the squareround dental arch grows noteworthily and reaches the summit of41.90Mpa at angle45°. While the stress of the oval set presents itsmaximum value of35.40Mpa when the inclination angle of the implant is15°and then the value decreases with the increase of the angle. For thetriangle round set, the maximum value appears at the inclination angle15°. Then with the increase of the angle, the change of the stress isn’tobvious. In the second loading case, the acting force was uniformlyloaded on the surface of the superstructure. The minimum stress alsoappears in the set in which the implants don’t incline. The stress aroundthe implant in the square set increases with the increase of the tilt angle ofthe implants. Under the same inclination angle, the Von-Mises value ofthe square round set is higher than that of the other two types of dentalarch. The maximum value of the stress of the oval set (4.05Mpa) appearswhen the inclination angle of the implants is15°then the stress decreasesgradually, basically the same trend with the first loading case. For thetriangle round set, the stress increases with the increase of the inclinationangle and remarkably grows to5.42Mpa at inclination angle45°.2. Stress distribution around implant in anterior teeth areaIn the first loading case, in the square round set when the angle of the implant changes from0°to30°, the Von-Miss value changescorrespondently from6.20to6.67and get to7.90Mpa at angle45; In thesecond loading case, with the increase of the tilt angle of the implants,Von-Mises decreases from3.25Mpa to2.95Mpa; For the oval set, thestress of the implant in the anterior teeth area increases with the increaseof the inclination angle of the implants in both of the two cases. For thetriangle round set, the stress doesn’t change obviously when theinclination angle of the implant increases in both of the two loadingcases.Conclusion:1: Arch forms have appreciable impact on stress distribution ofperi-implant;2: In Square arch form, Inclination of implant should be avoid;3: In Ovoid arch form, inclination angle should be under15°;4: In Tapered arch form, inclination should be under30°;5: In clinical practice, we should give different treatments depends on thedifferences of arch form on each patient.