| Objective: The success of dental implant requirs not only the good biocompatibility, but also a good biomechanical compatibility. The screwed surface of the implant can enhance the initial stability, increase surface area and improve the implant-bone interface stress distribution,by changing the thread design,we can change the mechanical transmission and affect interface stress distribution,wheather the interface distribution is reasonable or not will directly affect the formation and maintenance of interface, and thereby affect the long-term success rate. Therefore the design of the implant surface thread occupies a very important position in the biological mechanic desingn of which domestic and foreign scholars have conducted extensive research. This study analysizes the biomechanical compatibility of the cylinder implants with different thread through three-dimensional finite element analysis, discusses the effect of the bottom shape,the screw angle and the pitch to the implant-bone interface stress distribution by comparing interface stress distribution and stress peak of plants with different bottom shapes, different screw angles and different pitches and provides biomechanical basis for the clinical design and choose of implant.Method: Build up the three-dimensional finite element model of the mandible in the ANSYS 10.0 according to the result of CT scan,then design seven kinds of cylindrical threaded implants with diameter of 4.0mm,length of 10.0 mm, thead height of 0.5mm and with different thread shapes as follows: Build up the three-dimensional models of the implant,and then create implant - bone finite element models with different thread and mesh.The models were constrained at the nodes on the bilateral condylar in all directions,all materials used in the modeling were assumed to be homogeneous, continuous and linearly elastic,and the osseointegration of plant and bone is 100%.Then give the axial loading (vertically downward) of 160N, buccolingual loading (from the buccal to the lingual side) of 20N.Finally we obtaine the stress distribution and value of each node (the establishment of the models and the calculation was completed in the Laboratory of Engineering Mechanics, School of Aerospace , Tsinghua University).Observe the stress distribution and concentration under buccolingual and axial loading;Compair the implants of the same pitch, same angle but different bottom shapes,observe the maximum and minimum Von Mises stress under buccolingual and axial loading,the compressive and tensile stress under buccolingual loading;Compair the implants of the same pitch, same bottom shape but different angles,observe the maximum and minimum Von Mises stress under buccolingual and axial loading , the compressive and tensile stress under buccolingual loading;Compair the implants of the same bottom shape,same angle but different pitches, observe the maximum and minimum Von Mises stress under buccolingual and axial loading , the compressive and tensile stress under buccolingual loading.Result: 1 The characteristic of interface stress distribution: cylindrical screw implants with different thread patterns have influence on implant-bone interface stress and its distribution and the overall stress concentration areas are located in the neck and root tip of implants.2 The effect of the bottom shape to the distribution of implant-bone interface stress: model 1 and 2 with screw angle of 90°,1.5mm pitch, bottom shape of concave and flat are compared, the maximum Von Mises stress,compressive and tensile stress in the interface of both cancellous and cortical bone of model 1 is respectively 12.22%, 4.89%, 15.35%, 5.87% less than model 2 under buccolingual loading, the maximum Von Mises stress in the interface of both cancellous and cortical bone of model 1 is respectively 6.56%,12.25% less than model 2 under axial loading; model 3 and 4 with screw angle of 60°,1.5mm pitch, bottom shape of concave and flat are compared,the maximum VonMises stress, compressive and tensile stress in the interface of both cancellous and cortical bone of model 3 is respectively 11.02%,6.34%,10.32%,5.11% less than model 4 under buccolingual loading, the maximum Von Mises stress in the interface of both cancellous and cortical bone of model 3 is respectively 6.76%,11.46% less than model 4 under axial loading; model 5 and 6 with screw angle of 60°,1.0mm pitch, bottom shape of concave and flat are compared, the maximum Von Mises stress,compressive and tensile stress in the interface of both cancellous and cortical bone of model 5 is respectively 8.22%,1.67%,5.83%,3.93% less than model 6 under buccolingual loading, the maximum Von Mises stress in the interface of both cancellous and cortical bone of model 5 is respectively 1.66%,2.00% less than model 6 under axial loading, the stress distribution is more uniformly.3 The effect of screw angle to the distribution of implant-bone interface stress: model 1 and 3 with 1.5mm pitch, concave bottom,angles of 90°and 60°are compared, model 2 and 4 with 1.5mm pitch,flat bottom,angles of 90°and 60°are compared, the maximum Von Mises stress under both buccolingual and axial loading,compressive and tensile stress under buccolingual loading of both cancellous and cortical bone show no significant difference; model 5 and 7 with 1.0mm pitch, concave bottom, angles of 60°and 30°are compared, the maximum Von Mises stress,compressive and tensile stress in the interface of both cancellous and cortical bone of model 5 is respectively 7.25%,2.77%,16.97%,20.01% less than model 7 under buccolingual loading, the maximum Von Mises stress in the interface of both cancellous and cortical bone of model 5 is respectively 8.27%,1.11% less than model 7 under axial loading, the stress distribution is more uniformly.4 The effect of pitch to the distribution of implant-bone interface stress: model 3 and 5 with angle of 60°, concave bottom, pitch of 1.5mm and 1.0mm are compared, the maximum Von Mises stress under both buccolingual and axial loading,compressive and tensile stress under buccolingual loading of both cancellous and cortical bone show no significant difference; model 4 and 6 with. Angle of 60°, flat bottom, pitch of 1.5mm and 1.0mm are compared, the maximum Von Mises stress,compressive and tensile stress in the interface of both cancellous and cortical bone of model 6 is respectively 2.44%,2.90%,5.22%,2.18% less than model 4 under buccolingual loading, the maximum Von Mises stress in the interface of both cancellous and cortical bone of model 6 is respectively 4.28%,11.55% less than model 4 under axial loading, the stress distribution is more uniformly.Conclusion:1 Cylindrical screw implants with different thread patterns have influence on implant-bone interface stress and its distribution and the overall stress concentration areas are located in the neck and root tip of implants.2 Implants with concave bottom shape show less stress and more uniform stress distribution than the flat ones.3 Implants with screw angle of 90°and 60°show no significant difference in interface stress; screw angle of 60°show less stress and more uniform stress distribution than the 30°one.4 Implants with concave bottom shape, pitch of 1.0mm and 1.5mm show no significant difference in interface stress; Implant with flat bottom shape, pitch of 1.0mm shows less stress and more uniform stress distribution than the 1.5mm one.
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