Experimental 70% Al2O3 - 30% ZrO2 composites: structural, topographical and mechanical characterization before and after aging

Author(s)

Ernesto Byron Benalcazar Jalkh

• Document type: Doctoral Thesis
• Press: Bauru.
• Institution: Universidade de São Paulo (USP). Faculdade de Odontologia de Bauru (FOB/SDB)
• Defense date: 2021-11-03

Examining board members

Estevam Augusto Bonfante; Edmara Tatiely Pedroso Bergamo; Paulo Noronha Lisboa Filho; Sergio Mazurek Tebcherani

• Advisor: Estevam Augusto Bonfante; Paulo Francisco Cesar

Abstract

Objectives: To evaluate the effect of aging on the crystalline structure, surface topography and mechanical properties of an experimental zirconia-toughened-alumina (ZTA) composite comprised by 70% Al2O3 and 30% of a 2nd-generation 3mol% yttria tetragonal zirconia polycrystal (3Y-TZP), compared to its individual counterpart materials. Materials and Methods: Disc-shaped ceramic specimens were divided in four groups (n=10/material): 1) 3YSB-E (1st-generation 3Y-TZP), 2) Zpex (2nd-generation 3Y-TZP), 3) Alumina, and 4) ZTA-Zpex 70/30. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the crystalline content and microstructure. Reflectance tests were performed to determine the contrast-ratio (CR) and translucency-parameter (TP). Mechanical properties were assessed by biaxial-flexural-strength (BFS) test to determine Weibull parameters. ZTA and its isolated materials were tested under nanoindentation to record elastic modulus (E) and hardness (H); and Interferometry to assess 3D surface roughness parameters (Sa, Sq). All analyses were conducted before and after autoclave aging (20h, 134oC, 2.2bar). Optical parameters were evaluated through repeated-measures analysis of variance and Tukey tests (p<0.05), BFS data were analyzed using Weibull statistics (95% CI); and nanoindentation and topographic results were analyzed using linear mixed-model and least square difference pos-hoc tests (a=5%). Results: High density values were found for all materials and SEM images exhibited a dense microstructure. While XRD patterns revealed the preservation of crystalline content in the ZTA composite, an increase in the monoclinic phase was observed for pure zirconias after aging. Higher CR and lower TP values were observed for ZTA, followed by Alumina, 3YSB-E, and Zpex. The highest characteristic stress was recorded for 3YSB-E, followed by intermediate values between ZTA and Zpex, and the lowest for Alumina. Conversely, Al2O3 yielded the highest H and E values, followed by ZTA-70/30 and Zpex. Aging affected the optical and mechanical properties of both zirconias, while remained stable for ZTA and alumina. Aging did not affect the surface roughness parameters of ZTA and Alumina, although a significant increase in Sa was recorded for Zpex following aging. Conclusion: The synthesis of the experimental 70-30% ZTA composite was successful and its relevance for dental applications relies on its higher masking ability, aging resistance, and strength similar to zirconia. (AU)

• FAPESP's process: 18/03072-6 - Experimental 70% Al2O3-30% ZrO2 composites: structural characterization and survival probability before and after aging
• Grantee: Ernesto Byron Benalcazar Jalkh
• Support Opportunities: Scholarships in Brazil - Doctorate