The Biological And Tribological Properties Of BaTiO₃ Modified Dental Zirconia Ceramics

Dental ceramics are a kind of substitute biomaterials for repairing and reconstructing biological hard tissue of the oral and maxillofacial systems.Acting as bioceramic materials,dental ceramics should have good biocompatibility,physicochemical stability,mechanical compatibility,friction and wear properties,etc.Although 3 mol%yttrium oxide stabilized tetragonal zirconia polycrystalline ceramics（3Y-TZP）have been widely used in the dental clinic,as an inert ceramic material,3Y-TZP’s ability to promote bone and bone bonding still needs improvement.In addition,3Y-TZP can cause the excessive wear of antagonist teeth,which might increase the probability of dentin exposure,pain,pulp infection,and even temporomandibular joint diseases.All could severely affect the occlusal function and quality of life of the patients.Therefore,developing dental ceramics that are more wear friendly to the natural teeth will contribute to upgrading of oral health related manufacturing industry,accelerating the localization of dental instruments and materials,reducing the cost of dental materials,and improving the oral health of Chinese people in this new era.Barium titanate(Ba Ti O_3,BT)is a typical ferroelectric material with a perovskite-type structure.BT has attracted the attention of researchers from the medical field in recent years due to its biocompatibility.It has been used in orthopedic materials for bone tissue engineering and tooth whitening.Cost-effectiveness and whiteness in color are two of the advantages of applying BT in dentistry.However,the highest fracture toughness of BT is 2.0 MPa·m^1/2,which is lower than the 2.5 MPa·m^1/2 of natural tooth enamel.Hence,BT alone cannot withstand the mechanical requirements of dental restoration.BT can act as a second phase to coexist with 3Y-TZP.Intriguingly,BT modified 3Y-TZP ceramic composites（BT/3Y-TZP）have uniformly distributed micropores,which might influence the biomedical and tribological properties of the material.However,only few reports were found for their investigations of BT/3Y-TZP.These reports focused on the industrial applications of BT/3Y-TZP.No reports of BT/3Y-TZP in biomedicine,notably dentistry,have been found.This research project used a modified traditional sintering process to prepare a series of BT/3Y-TZP ceramic composites.The microstructure,physical properties,mechanical properties,biocompatibility and tribological properties were studied in detail.The surface topology’s influence on osteogenic activity and tribological properties of BT/3Y-TZP were analyzed to reveal the basic fundamental mechanism.The results provided experimental reference and theoretical basis for the application of BT/3Y-TZP in dentistry.The main results are as follows:（1）BT can coexist within 3Y-TZP as the second phase.t-Zr O₂,m-Zr O₂ and t-Ba Ti O₃ phases exist in the ceramic composites system under the modified traditional sintering process.Moreover,the grain size of Zr O₂is relatively stable,ranging from 450 nm to 1.2μm,and does not change significantly with the increase of BT doping amount.However,the grain size of BT increases gradually from 1μm to 2.5μm with the increase of BT doping amount.But the density of 5 mol%BT/3Y-TZP is 5.868 g/cm³and the porosity is 0.426%,which is better than the other two BT modified groups.The microhardness of 5 mol%BT/3Y-TZP is 1250.58±48.96 HV,and the Young’s modulus is 247.50±14.00 GPa,which is smaller than other groups.The fracture toughness of 5 mol%BT/3Y-TZP can still reach7.05±0.24 MPa·m^1/2.The above indicators ensure that the strength of 5mol%BT/3Y-TZP ceramic composite can meet the needs of dental clinical application.（2）The surface of BT/3Y-TZP ceramic composites has homogeneous isotropic pores,and the size of the pores affect the porosity,density and water contact angle of the material.The average pore diameter of 5 mol%BT/3Y-TZP is the smallest,about 1μm,and the water contact angle of 5mol%BT/3Y-TZP is 64.57°±2.89°,indicating the strongest hydrophilicity.It was proved for the first time that the BT/3Y-TZP ceramic composites had good biocompatibility by using the extraction method and direct contact method.Cytological and molecular biology studies showed that the micropores on the surface of BT/3Y-TZP promote the expression of osteogenic genes in the early adhesion stage of osteoblasts.Among them,5 mol%BT/3Y-TZP ceramic composite had the best osteogenic effect,which can significantly promote the expression of four classic osteogenic genes RUX2,TGF-β,BMP4 and OCN in the early stage,suggesting that 5mol%BT/3Y-TZP may have better bone integration potential.This result provides experimental reference and theoretical basis for the application of BT/3Y-TZP ceramic composites as a biological material in the field of biomaterials,especially medical implants.（3）The tribological studies showed that 5 mol%BT/3Y-TZP ceramic composite has the best wear performance.In the simulated oral environments（dry and saliva）,the macro friction test of 5 mol%BT/3Y-TZP between natural tooth had the lowest coefficient of friction（COF）and the most stable COF-time curve in comparison with other groups as well as commercially available zirconia products.The results showed that the wear performance of 5 mol%BT/3Y-TZP is better than that of the commercially available zirconia products.（4）The tribological mechanism investigation showed that the 5 mol%BT/3Y-TZP ceramic composite had no phase transition after the friction test,and the microstructure was stable without apparent defects or cracks.The stability and wear resistance are related to the pinning effect of BT,which reduces the grain size of ceramics,increases the total grain surface area of the system and improves the strength of the material.In comparison with other groups,the natural tooth from the 5 mol%BT/3Y-TZP group had the least weight loss.These results indicated that 5 mol%BT/3Y-TZP showed more friendly wear properties against natural teeth than the other groups under the same controlled conditions.By analyzing the worn surfaces’microstructures,the interface migration behavior was noticed only for the 5 mol%BT/3Y-TZP ceramic composite.It formed a smooth transfer film of enamel on the 5 mol%BT/3Y-TZP ceramic surface even under saliva lubrication environment.The in-site formed tribofilm with self-lubricating function contributed to the lower wear rate of the antagonist tooth enamel.