Effect of Hydrothermal Aging Method on Physical and Mechanical Properties of 3Y-TZP Zirconia

• Grant number: 24/16352-8
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: November 01, 2024
• End date: October 31, 2025
• Field of knowledge: Health Sciences - Dentistry - Dental Materials
• Principal Investigator: Estevam Augusto Bonfante
• Grantee: Paulo Eduardo Alves Silveira
• Host Institution: Faculdade de Odontologia de Bauru (FOB). Universidade de São Paulo (USP). Bauru , SP, Brazil
• Associated research grant: 21/06730-7 - Towards sustainable zirconia recycled from milling waste and boosted by glass infiltration for restorative use, and of the development of strong, graded, and aging resistant multilayered zirconia blocks, AP.JP2

Abstract

Zirconia systems stabilized with 3 mol% yttrium oxide (3Y-TZP) are recognized for their excellent mechanical properties and biocompatibility. However, 3Y-TZP is vulnerable to low-temperature degradation (LTD), a phenomenon that leads to the gradual transformation of the tetragonal phase into a monoclinic phase, potentially compromising the material's properties. In-vitro evaluation of the effects of LVD in dentistry has been controversial due to the difficulty of extrapolating laboratory results to clinical scenarios. Therefore, evaluating the effects of different ageing methods is of enormous interest in the characterization of zirconia-based materials, which is the subject of the Young Researcher Grant 2 # to which this proposal is linked. The aim of this scientific initiation project is to investigate the effect of the hydrothermal ageing method (submerged or in steam) on the composition and optical and mechanical properties of 3Y-TZP zirconia for monolithic use. 150 disc-shaped specimens of a second-generation 3Y-TZP (Zpex, Tosoh Corporation) will be synthesized and divided into three experimental groups: 1) immediate (3Y-i), 2) aged in a steam hydrothermal reactor (3Y-v) and 3) aged in a water-submerged hydrothermal reactor (3Y-s). The specimens will be synthesized by uniaxial pressing, sintered according to the manufacturer's recommendations, and polished to obtain discs with a diameter of 12 mm and a thickness of 1.2 mm (ISO 6872). Groups 3Y-v and 3Y-s will be aged in a hydrothermal reactor at 134°C and 2.2 bar for 10 hours by steam or submerged in water, respectively. All the experimental groups will be evaluated superficially and in cross-section by X-ray diffraction (XRD), to determine the content of crystalline phases, and by scanning electron microscopy (SEM) for microstructural evaluation. The effect of DBT on optical and mechanical properties will be evaluated by reflectance and biaxial flexural strength (BFR) tests with fractographic evaluation, respectively. The optical properties data will be subjected to normality tests and analysis of variance with Tukey's test for comparison between groups and the BFR data will be analyzed using Weibull statistics to determine the Weibull modulus and characteristic strength of the experimental groups.