Experimental bilayer zirconia systems after aging: mechanical, optical, and microstructural characterization

Author(s)

Edisa de Oliveira Sousa

• Document type: Master's Dissertation
• Press: Bauru.
• Institution: Universidade de São Paulo (USP). Faculdade de Odontologia de Bauru (FOB/SDB)
• Defense date: 2024-12-09

Examining board members

Estevam Augusto Bonfante; Larissa Marcia Martins Alves; Tiago Moreira Bastos Campos

• Advisor: Estevam Augusto Bonfante

Abstract

This study evaluated the microstructural, optical, and mechanical properties of two experimental zirconia bilayer systems. Commercial zirconia powders (Tosoh) were used to produce the bilayer systems: 3Y-TZP+5Y-PSZ (3Y+5Y/BI) and 4Y-PSZ+5Y-PSZ (4Y+5Y/BI), along with control groups 3Y-TZP (3Y/C), 4Y-PSZ (4Y/C), and 5Y-PSZ (5Y/C). After uniaxial pressing, the samples were sintered (1550 °C for 2 hours). Half of the specimens were subjected to hydrothermal aging (134°C - 20h, 2.2 bar), resulting in immediate and aged subgroups. Microstructural characterizations were performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. The optical properties were assessed by the translucency parameter (TP) and contrast ratio (CR). The mechanical properties were evaluated through the biaxial flexural strength (BFS) test according to ISO 6872. Experimental groups showed relative density ranging from 98% to 99% after sintering. The 3Y-TZP and 4Y-PSZ zirconias exhibited degradation regions identified in SEM micrographs after aging, in both the bilayer systems and controls. XRD and Raman spectroscopy also detected the presence of the monoclinic phase in both zirconias. For TP and CR, significant differences (p<0.001) were observed between the bilayer and control groups. The bilayer systems presented intermediate characteristic strength values compared to the controls, with significant differences among the groups. A significant increase in characteristic strength was observed after aging for all groups, except for the 5Y/C group. At 800 MPa, the immediate bilayer groups showed a reduction in probability of survival. The experimental bilayer systems demonstrated lower mechanical properties than the monolithic controls 3Y/C and 4Y/C. The bilayer groups did not perform adequately for extensive posterior fixed dental prostheses. However, the zirconia systems did not show negative effects due to hydrothermal aging. (AU)

• FAPESP's process: 22/07733-2 - Physical and mechanical characterization of a bilayered zirconia system: influence of hydrothermal aging
• Grantee: Edisa de Oliveira Sousa
• Support Opportunities: Scholarships in Brazil - Master