| It is well known that dental implants need to have good mechanical properties and biocompatibility at the same time.The traditional solid compact structure,which has a high elastic modulus,poor biocompatibility,is prone to stress shielding problems under long-term load.In this study,titanium alloy(TC4)powder was used as raw material to design and prepare a new type of three-dimensional porous dental implant using SLM molding technology.The obtained elastic modulus of implant was greatly reduced,and the implant shows good biocompatibility in the simulated body fluid while meeting the biomechanical requirements after heat treatment and surface modification.The main work and research results are listed as follows:(1)In this study,the finite element method was used to optimize the pore size,hole shape and hole position arrangement of the three-dimensional porous implant.The obtained three-dimensional perforated porous implant structure is characterized by a 400～600 μm square hole at the middle and lower end and a small round hole of 300 μm at the upper end.The left and right adjacent holes are evenly distributed in the middle of the anti-support thread along the included angle of 30°,and the upper and lower adjacent holes are staggered.While the maximum stress of the porous implant is 423.16 MPa,and the maximum deformation is 0.03 mm when the occlusion is simulated by static mechanics.Implant fatigue performance is much higher than the national standard,and no fatigue failure occurred after 10 million cycles of 25-250 N cyclic loading.(2)This study optimized the process parameters of SLM technology to form porous dental implants.By controlling the laser power and scanning speed,and taking the density and the surface hardness of the sample as the assessment indicators,the following conclusions are obtained.The optimal energy density of titanium powder input per unit volume is between 119.05～166.67 J/mm3,and the optimal forming parameters are laser power 200 W,scanning speed 600 mm/s,spreading thickness 0.04 mm,scanning distance 0.06 mm.The density of the sample reaches 97.41%,and the surface hardness is 440.5 HV.(3)Then the molded implant was heat-treatment to increase the yield strength of the porous implant.The primary α phase in the structure is obviously coarsened,and the volume of the precipitated short rod-shaped secondary β phase and α phase increases after being kept at 950℃ for 2 h and cooled in the furnace.The results show that the yield strength and impact toughness increase by 3%～5%and 10%～17%,respectively(σb=1049.8 MPa、σ0.2=963.4 MPa、δ≥10%、ψ≥12%).The yield strength of the porous section is 537 MPa and the elastic modulus is about 35 GPa.(4)The average roughness of the implant surface is reduced from Ra=15.12μm to 4.47 μm after sandblasting and acid etching,meeting the standard requirements of "Titanium and Titanium Alloy Dental Implants".The surface of the implant formation nano-scale micropores after acid etching,which is more conducive to inducing sediment enrichment.(5)The dental implant with porous structure was immersed in saturated SBF simulation fluid for 14 d,and the surface of the implant with a uniformly distributed sediment layer was obtained.Most of the pore walls are deposited and extend inward along the aperture,and part of the aperture has been completely filled.EDS and XRD tests show that the main component of the sedimentary layer is hydroxyapatite.The three-dimensional perforated porous dental implant prepared in this paper has good mechanical properties and biocompatibility at the same time.By adjusting the porosity,it is suitable for patients with different bone types to realize the customization of personalized dental implants. |
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