Finite Element Analysis Of Different Soft And Hard Segment Proportions And Thickness Of Polyurethane Elastic Layer

Objective:This experiment aimed to use the finite element analysis method to calculate the stress distribution of polyurethane elastic layer with different soft and hard segment proportions,and analyze the optimum ratio of soft and hard segments and thickness of PU elastic layer to prolong the clinical life of the composite resin.Methods:Two kinds of PU prepolymer,Pre-PU-A and Pre-PU-B,were synthesized using solution polymerization method with isophorone diisocyanate（IPDI）,polytetramethylene ether glycol 2000（PTMEG 2000）,1,6-hexanediol and2-hydroxyethyl methacrylate（HEMA）.A series of mixtures containing Pre-PU-A/Pre-PU-B at volume ratios of 2.5:1,2.75:1,3.0:1,3.25:1,and 3.5:1,were prepared for the PU elastic layer and characterized by the Fourier transform infrared（FTIR）spectrum.The Young’s modulus and Poisson’s ratio of 5 groups of PU elastic layers were measured by universal testing machine and stress-strain tester.CBCT was used to obtain the image of dentition.Meanwhile,the Geomagic software was used to build the three-dimensional model of teeth,and the control group was set up at the same time.Based on the control group,three different thicknesses of PU elastic layers were placed between the adhesive and the resin to build the experimental group model.The model was imported into ANSYS Workbench software to analyze the stress and distribution of tooth tissue,adhesive,resin,and bonding interface.Results:1.The FTIR confirmed that the PU elastic layer was successfully synthesized.The mechanical properties test results are as follows:For the PU_2.5:1,the values of Young’s modulus and Poisson’s ratio were assumed to be 0.413GPa and 0.40,respectively.Values of 0.470 GPa and 0.42 for PU_2.75:1,0.512 GPa and 0.46 for PU_3.0:1,0.440 GPa and 0.47 for PU_3.25:1,0.382 GPa and 0.45 for PU_3.5:1.2.The stress maximum of the adhesive in the PU-30μm and PU-40μm groups was slightly higher than that in the control group.The stress distribution appeared at the edge of the adhesive layer,which was not significantly different from the control group.The stress maximum of the adhesive in the PU-50μm group was significantly lower than that in the control group,and the stress distribution was significantly different from that in the control group,which only appeared at the edge of the lingual hole.3.The stress maximum of the resin in the PU-30μm,PU-40μm,and PU-50μm groups was basically the same as that in the control group.The stress distribution was concentrated on the occlusal surface and the resin interface corresponding to the enamel.Compared with the control group,which was more uniform than that in the control group.4.The stress maximum and distribution of dentin in the PU-30μm,PU-40μm,and PU-50μm groups were not significantly different from those in the control group.5.The stress maximum of enamel in the PU-30μm group was slightly higher than that in the control group,while the stress distribution was basically the same as that in the control group.The stress maximum of enamel in the PU-40μm and PU-50μm groups was slightly lower than that in the control group and significantly lower than that in the PU-30μm group.Their stress distribution was on the occlusal surface near the edge of the hole,which was more uniform than that in the control group.6.The stress maximum of the adhesive（PU contact surface）in the PU-30μm and PU-40μm groups was slightly higher than that in the control group,and the stress distribution appeared near the hole edge of the adhesive layer,which was not significantly different from the control group.The stress maximum of the adhesive in the PU-50μm group was significantly lower than that in the control group,and the stress distribution was significantly different from that in the control group,which only appeared in the middle of the lingual hole edge.7.The equivalent stress of the adhesive（dentin-enamel junction contact surface）in the PU-30μm and PU-40μm groups was mainly distributed in the buccal and lingual walls.Their stress maximum was slightly higher than that in the control group,and their stress distribution was basically the same as that in the control group.The stress maximum in the PU-50μm group was slightly lower than that in the control group,and the stress distribution only appeared in the buccal wall.Conclusions:1.The PU elastic layer can effectively absorb the adhesive interface stress with Pre-PU-A/B=3:1 and 50μm thickness,which is the best ratio and thickness of the PU elastic layer.2.The PU elastic layer needs to maintain a certain thickness to buffer the adhesive interface stress.If the PU elastic layer is too thin,it will lead to a more significant stress concentration,which cannot protect the tooth tissue and prolong the clinical life of the composite resin.