| Since most of the standardized metal implants have high elastic modulus,there will be a large mismatch between them and the human jaw bone,resulting in the "stress shielding" effect,resulting in postoperative implant failure and other adverse reactions.In the field of medical implants,graded porous metal materials are widely used to solve the stress shielding effect because of their low elastic modulus,good plasticity and strength.Based on the above background and foundation,the structure design idea of TPMS gradient porous dental implants was proposed in this paper.Selective Laser Melting(SLM)was used to produce porous samples with different porosity gradients.The influences of the structure of Triply Periodic Minimal Surfaces(TPMS),radial gradient surfaces and porosity on the mechanical properties of gradient porous surfaces are studied by simulation and experimental system.The main research contents are as follows:(1)Model construction and structural optimization of TPMS porous dental implant.The relationship between porosity and threshold C was established based on TPMS,and porous dental implants with Primitive,Gyroid,Diamond and I-WP surfaces were designed.The results of ANSYS simulation show that Primitive structure has lower equivalent stress and more balanced stress distribution,which is suitable to be used as the basic element of implant gradient structure.(2)Preparation of gradient porous structure.The mathematical model of SLM preparation process was established by response surface.The influence of SLM process parameters on the density,surface roughness and porosity of TPMS-P gradient porous sample was studied by using Ti6Al4 V alloy as material.The experimental results show that the optimal process parameters are laser power 240 W,scanning speed 1400mm/s and scanning spacing 0.08 mm.(3)Experimental analysis of mechanical properties of gradient porous structure.By means of quasi-static compression experiments,the elastic modulus and yield strength of gradient porous structures with different gradient change rates and different average porosity are tested,and multivariate nonlinear prediction models of average porosity,elastic modulus and compressive strength are established.The experimental results show that the gradient porous structures with smaller edge porosity and larger center porosity have higher elastic modulus and yield strength.Compared with the homogeneous porous structure with the same porosity,the gradient structure has better performance strength,the elastic modulus is in line with the range of human bone,the yield strength is higher than that of cortical bone,and the flexor elastic ratio is excellent,which meets the application requirements of medical porous structure.(4)Finite element analysis of mechanical properties of gradient porous implant.The equivalent stress-strain values and relative fretting values of porous dental implants and bone tissue with different average porosity gradients were simulated through the simulation of average bite force in oral environment.The finite element results showed that the fretting value of the gradient porous implant met the initial stability requirements,and the equivalent stress-strain value of bone tissue was suitable for bone growth,meeting the long-term stability requirements.The stress value of the gradient porous implants with porosity less than 40% met the design strength requirements of the root,and the equivalent stress difference between the gradient porous implants and the surrounding bone tissue was the lowest when the average porosity was 30%,which was more conducive to the formation of stable bone integration. |
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