Mechanical properties of ceramic composites based on ZrO₂ co-stabilized by Y₂O₃-CeO₂ reinforced with Al₂O₃ platelets for dental implants.

Abstract

The objective of this work was the development and characterization of a ceramic composite based on (Ce,Y)-TZP/Al₂O₃ aiming an application on dental implants, comparing it with conventional monolithic 3Y-TZP ceramics, currently used for the same type of application. Ceramic samples, 3Y-TZP (n = 40) and (Ce,Y)-TZP/Al₂O₃ (n = 40), were sintered at 1500 °C - 2h and characterized by relative density, X-Ray diffraction (XRD) and microstructure. Then, the samples of both materials were divided into two groups: 1) samples with original (as sintered) surfaces; 2) samples with conditioned, polished, surfaces. All samples were submitted to hydrothermal degradation tests, on an autoclave (134 °C - 2 bar), for 10 h in artificial saliva. The degraded samples were characterized by XRD and the polished group were also characterized by their elastic moduli, Vickers hardness and fracture toughness (Vickers indentation method). Both groups were also submitted to a flexural strength test, 3B-P testing, for which the data were interpreted using Weibull statistics. All sintered specimens presented nearly full densification. After the hydrothermal degradation tests, 3Y-TZP samples presented 16.4% of monoclinic (m)-ZrO₂ phase while the composite samples withheld 100% of tetragonal (t)-ZrO₂ phase. Both materials presented equiaxial ZrO₂ grains with an average size of 0.48 ± 0.17 μm and 0.75 ± 0.22 μm, respectively, for the monolithic and composite ceramics. In the composites, is observed the presence of well distributed Al₂O₃ grains on the ZrO₂ matrix, in two distinct morphologies: equiaxial grains and platelets. The composites (Ce,Y)-TZP/Al₂O₃ presented average values of elastic moduli, Vickers hardness and fracture toughness of 228.3 ± 6.5 GPa, 1427 ± 46 HV e 11.3 ± 0.4 MPa m^1/2, respectively. An inversely proportional relationship is observed between the roughness and the bending strength, since the 3Y-TZP samples presented a average strength of 860.7 ± 81 MPa (as-sintered) and 965.4 ± 93 MPa (polished) while the (Ce,Y)-TZP/Al₂O₃ composites presented average strength of 810.6 ± 147 MPa (as-sintered) and 952.6 ± 88 MPa (polished). The composites (Ce,Y)-TZP/Al₂O₃ showed high resistance to degradation in saliva and adequate properties for use as dental implants. Values of flexural strength (>950 MPa) and Weibull modulus (m > 10) were similar to the conventional 3Y-TZP ceramics. Moreover, its hardness, elastic modulus and fracture toughness were higher than those obtained for 3Y-TZP. The expressive values of K_IC obtained for (Ce,Y)-TZP/Al₂O₃ composites are results of association of different toughening mechanisms acting simultaneously in the material.