Stereolithography Formation And Properties Of Zirconia-Based Gradient Functional Ceramics For Dental Implants

Factors such as natural aging,external damage,and developmental deformities can lead to tooth loss,and more than 2.4 million people nationwide perform dental implants every year.As the third set of human teeth,implants are mainly composed of different materials and segmented structures.Patients need multiple operations,which lasts more than one year and experiences multiple pains.Immediate implantation does not require recovery of the socket,and the implant socket can be directly prepared,effectively reducing the number of operations and the pain of patients.However,it is difficult to fabricate implants suitable for immediate implantation and integrated with gradient functions,which hinders the progress of immediate implantation technology seriously.In this study,taking gradient functional integrated dental implants as an object,the synergistic mechanism between zirconia(ZrO2)and graphene oxide(GO)was studied,and a fabrication method of ceramic paste suitable for stereolithography apparatus(SLA)was proposed.Through SLA-3D printing and post-processing,the effect of printing and sintering parameters on the formation and performance of ceramic parts was revealed.ZrO2ZrO2/GO gradient composition and triply periodic minimal surface(TPMS)gradient structure model were designed to create ZrO2-based ceramics with excellent mechanical and biological properties.This study has a wide range of application prospects and important theoretical and practical significance,and the main contents are as follows:According to the performance requirements of the integrated dental implant,ZrO2/GO composite ceramics with different GO contents were developed by water bath,ball milling,and hot press sintering.The physical and chemical properties of the composites were analyzed.ZrO-C bonds were formed between ZrO2 and GO particles,which verified the effectiveness of the material preparation.The influence of GO content on the mechanical and tribological behaviors of composites was studied.The fracture toughness and flexural strength rose and then declined with the GO content increasing.The toughening mechanisms involved crack deflection,crack bridging,and GO pull-out.Correspondingly,the friction coefficient and wear rate also declined and then rose with the increase of GO content.The anti-friction and anti-wear mechanisms included GO self-repairing wear surface,enrichent to form GO lubricationg film,GO efficient heat dissipation,and GO toughening.The GO content was preferably 0.15 wt.%of the total ZrO2,and the biological performances were analyzed.GO could improve the wettability of composites with no cytotoxicity,and promoted cell proliferation,adhesion,and osteogenic differentiation.Based on the evaluation index of ceramic paste,using ZrO2 and ZrO2/GO composite ceramic powder with 0.15 wt.%GO content as raw materials,the effects of polymer and powder on the stability and rheology of paste were analyzed.Using KH560 as the surface modifier,preferably the ratio of prepolymer Di-TMPTA and diluent NPG2PODA to be 60 vol.%and 40 vol.%,a uniformly dispersed paste with high solid content was prepared.A prediction model for the cure depth and width of the ceramic paste was established.Through linear fitting,the penetration depth and critical exposure of ZrO2 ceramic paste were calculated as 17.06 μm and 4.68 mJ/cm2,respectively;the penetration depth and critical exposure of ZrO2/GO ceramic paste were 11.80 μm and 22.80 mJ/cm2,respectively.The effect of laser power and scanning speed on the formability of the ceramic body was clarified,then the parameters were optimized.The optimal printing parameters of ZrO2 ceramic body were 154 mW and 6000 mm/s,and the optimal printing parameters of ZrO2/GO were 208 mW and 2000 mm/s.The debinding and sintering process was designed based on the thermal decomposition temperature region of polymers in the green body.The influence of sintering temperature,holding time,and sintering rate on the formability of ceramic parts was clarified.The average linear shrinkage rates of ZrO2 and ZrO2/GO ceramic parts were 29.00%and 23.67%,respectively,and the average Ra values of the XOY surfaces of the ceramic parts were 0.75 μm and 2.25 μm,respectively,meeting the 0.5-2.0 μm requirements for dental implants.With the increase of sintering parameters,the mechanical properties of ceramic parts first rose and then declined.The optimal sintering process of ZrO2 ceramics was obtained,sintering at 1500℃with 4℃/min for 60 min.The average relative density,HV,and fracture toughness were 96.18%,13.30 GPa,and 6.35 MPa·m1/2,respectively.Meanwhile,the optimal sintering process of ZrO2/GO ceramics was obtained,sintering at 1300℃ for 60 min.The average relative density,HV,and fracture toughness were 97.24%,15.16 GPa and 7.34 MPa·m1/2,respectively.Based on the gradient functional properties of the integrated dental implants,ZrO2-based gradient composition and TPMS gradient structure model were constructed,respectively.According to the optimal 3D printing parameters and sintering parameters,ZrO2-ZrO2/GO gradient composition ceramics were prepared,and the influence of GO composition on the formability of the gradient interface was analyzed.The results showed the gradient interface had a good bonding interface,the profile reference difference was 49.48 μm,and the average surface roughness was 5.37 μm.The hardness and elastic modulus at the gradient interface were 13.78～14.86 GPa and 254.91～301.46 GPa,respectively,presenting an obvious size effect.Taking Schwarz-P(P type),Gyroid(G type),Diamond(D type),and I-Wrapped(IWP type)as examples,a continuous Log-sigmoid function as the weight coefficient was proposed.The same structure with variable porosities,variable structures with the same porosity,and variable structures and porosities gradient structure models were constructed ranging from the porosity of 40～60%and pore size of 400～600 μm.The failure modes of the TPMS gradient structures were analyzed,and the porosity,pore size,and structure type were optimized.The formability of ZrO2 ceramic parts with G and IWP type gradient structures were prepared and studied,and the average Ra values were 3.3 μm and 3.5 μm,respectively.The average hardness 11.04 GPa and 11.26 GPa,and the elastic modulus were 226.53 GPa and 231.72 GPa,respectively.As a result,the condtructed ZrO2-ZrO2/GO gradient composition and TPMS gradient structure of ZrO2 ceramics could match the non-uniform structure and anisotropic performance of the integrated dental implants,effectively reducing the "stress shield" effect.