Three-dimensional Finite Element Analysis Of Porcelain Veneer With Different Thickness Under The Action Of Cyclic Temperature And Bite Force

ObjectiveBased on the three-dimensional finite element analysis,we evaluated the effect on the stress distribution of different thickness of porcelain veneers under the action of cyclic temperature and bite force in the mandibular central incisor.The stress and stress distribution were observed under the condition of different load according to the clinical treatment plan to build the different thickness of models,in order to provide the reference for the porcelain veneer tooth preparation,production in biomechanics perspective.Materials and MethodsThe mandibular central incisor three-dimensional entity model was obtained via Mimics 18.0 software,Geomagic Studio 2012 software,Creo Parameric 4.0 software from CBCT scanning the extracted mandibular central incisor.On this basis,the thin and thick type of porcelain veneers in the mandibular central incisor entity model were established.The each group model was imported into the finite element analysis software Ansys Workbench,divided mesh automatically,set the assumptions,boundary conditions and parameters.We chose the Von Mises stress and maximum principal stress as analysis indicators for the finite element analysis.The experimental conditions were divided into three types:1.Cyclic temperature loadThe clinical crown outside surface of the each group models was set the cyclic temperature loading area with the initial temperature of 37 ℃.For the simulation of heat load,the temperature of the outer surface of the tooth crown increased to 60 ℃within 1 s,and then return to 37℃ within 4s.For the cold load,the temperature reduced to 0 ℃ within 1 s,and then return to 37℃ within 4s.2.Cyclic bite force loadThe forward loading direction was consistent with the tooth length axis.,and the loading position was selected at the incisal edge.Oblique loading at the direction of 45° with the long axis of the tooth from the lip side to the lingual side was applied on the edge of the lip side of the incisal.The loading method was selected the surface loading with magnitude of 150N.The loading time was 0.2s,the time increment was determined by the software automatically,and the time step function was sine function:f(t)=150*sine[(1-t/0.2)*π).3.Cyclic temperature superposed cyclic bite force loadWe calculated the stress under cyclic temperature superposed cyclic bite force based on the finite element,the calculation was large and time consuming.We decided to only calculate the thick porcelain veneer model.According to the time of the two processes,this experimental condition was to add 25 bite force cycles in the 5s temperature cycle.Results1.The experimental condition l:the stress analysis under cyclic temperature load(1)The stress value of the Von Mises of the porcelain veneer under low cyclic temperature was greater than that under the high cyclic temperature.Moreover,the variation was basically consistent.In the process of the temperature rising or falling of the first Is,the stress value increased continuously.In the process of temperature recovering,the stress value decreased firstly and then rose and finally gradually decreased.(2)For the whole model,greater temperature changes were generated on the lingual side,and the stress on the lingual side was greater than the lip side.(3)Under the low cyclic temperature,the center of the lip of the porcelain veneer was the tensile stress concentration zone,and the maximum tensile stress peak was greater than that under the high cyclic temperature.The peak value stress was less than the flexure strength of the material.(4)Under the low cyclic temperature,the clinical tooth crown of the porcelain veneer model was mainly subjected to tensile stress,and the lingual side was the stress concentration zone.Under the high ccyclic temperature,The tensile stress of the clinical tooth of the porcelain veneer model was less,and the center of the tongue was the compressive stress concentration area.(5)Under low and high cyclic temperature,the peak value of Von Mises stress was little difference between the thin porcelain veneer and the thick porcelain veneer,the peak value of maximum principal stress(tensile stress)was a bigger difference.The peak value of stress of the thin porcelain veneer was greater than the thick porcelain veneer.2.The experimental condition 2:the stress analysis of cyclic bite force load(1)In the positive and oblique cyclic load of the two sets of models,the peak value of the Von Mises stress and maximum principal stress on the porcelain veneer wassinusoidal continuous change over time.(2)The incisal edge and the cervical margin of the porcelain veneer were the stress concentration areas,which were prone to fracture.(3)The cyclic bite force load had a great influence on the stress of the porcelain veneer of different thickness,among which the stress value of the thin porcelain veneer was larger,and it was easier to break in the process of using.(4)It was easier to cause the stress concentration and then fracture of the porcelain veneer with the simulation of protrusive occlusions.(5)Under the oblique cyclic bite force load,the cervical margin of thin and thick porcelain veneer was the tensile stress concentration zone,and the peak value of maximum tensile stress was 28.242MPa and 28.699MPa.Under the positive cyclic bite force load,the incisal edge loading area of the thin and thick ceramic veneer was the tensile stress concentration zone,and the maximum tensile stress was small.(6)whether it was thin or thick porcelain veneer,the peak value of stress of the two loading conditions was less than that Stress extremum of porcelain material.3.The experimental condition 3:the stress analysis of cyclic temperature and cyclic bite force(1)In the process of cyclic high temperature,the peak value of Von Mises stress of the porcelain veneer was 31.653MPa and increased by 60%when superposed forward cyclic bite force.The peak value of Von Mises stress peak stress of the porcelain veneer was 52.052MPa and increased by 151%when superposed oblique cyclic bite force.Similarly,in the process of cyclic low temperature,the peak value of Von Mises stress of the porcelain veneer was 37.507MPa and increased by 29%when superposed forward cyclic bite force.The peak value of Von Mises stress of the porcelain veneer was 43.152MPa and increased by 88%when superposed oblique cyclic bite force.(2)Under different temperature conditions,the variation law and distribution of stress concentration areas of porcelain veneer were basically consistent.When cyclic temperature superposed forward cyclic bite force,the stress concentration of the middle of the lip side area was enlarged and gradually shifted to the cervical margin,the stress concentration of the edge of the lingual side was increased and the stress concentration area of the lingual side was increased.When cyclic temperature superposed oblique cyclic bite force,the porcelain veneer was concentrated at the edge of the lip and lingual of the cervical margin.(3)In the case of cyclic low temperature superposed forward cyclic bite force,the lip side of the center of the thick porcelain veneer was the tensile stress concentration zone,and the peak of the maximum tensile stress was 29.546MPa.When the high cyclic temperature superposed forward cyclic bite force,the adjacent contact area was the tensile stress concentration zone,and the tensile stress was small,which was 9.2235MPa.When the cyclic low temperature superposed the oblique cyclic bite force,the center of the lip of the thick porcelain veneer and the cervical margin were the tensile stress concentration area,and the peak of maximum tensile stress was 47.677MPa.When the high temperature cycle superposed the oblique cyclic bite force,the stress distribution on the lip side of the thick porcelain veneer was uniform,and the tip of the tongue side was the stress concentration zone,and the peak of maximum tensile stress was 25.214MPa.(4)In the range of the temperature change along with the increase of cycles,the stress of porcelain veneers with temperature rise or fall.Finally,at the temperature reached maximum or minimum,the stress value of porcelain veneers tend to be constant.Conclusion1.The changing temperature in the mouth can cause the thermal stress of the restoration,and the thermal stress generated in the low temperature cycle was higher than that in the high temperature cycle.The tensile stress produced by the porcelain veneer in the low temperature cycle was larger,the capacity of the porcelain material suffering the tension stress was poor,indicating that the porcelain veneer was more likely to break down in the low temperature environment.The cyclic temperature had an influence on the stress distribution of porcelain veneer with different thickness,and the peak stress of the thin porcelain veneer was greater than that of the thick porcelain veneer.The stress caused by simple temperature change could not lead to the fracture of the restoration,and the thin porcelain veneer was the most likely to be destroyed under the action of low temperature cycle.2.The cyclic bite force load had a greater influence on the stress of different thickness of porcelain veneer,and the stress value of the thin porcelain veneer was larger.It was more likely to cause the stress concentration of the cervical margin and then cause the fracture of the porcelain veneer in the protrusive occlusions.Therefore,in the clinical application,we should pay attention to the design and production of porcelain veneer thickness and cervical margin,especially the adjustment of the protrusive occlusions.3.Under the action of single cyclic temperature and cyclic bite force load,there is almost no possibility to damage the porcelain veneer,but the cyclic bite force load has a certain strengthening effect on the thermal load.At the same time,both the cyclic temperature and cyclic bite force load will increase the risk of failure of porcelain veneer.