Two-step sintering suppresses grain growth and improves flexural strength of dental zirconia

Author(s)

Lim, Chek Hai ; Alves, Larissa M. M. ; Vardhaman, Sonaj ; Bonfante, Estevam A. ; Kim, Do Kyung ; Zhang, Yu

• Document type: Journal article
• Source: Dental Materials; v. 41, n. 2, p. 9-pg., 2025-01-16.

Abstract

Objectives: This study aimed to elucidate the effect of various two-step sintering (TSS) protocols on the physical, mechanical, and optical properties of partially stabilized zirconia with different yttria dopant concentrations (YPSZ). Methods: Disc-shaped specimens were obtained from most widely used commercial dental zirconia powders of various Y contents (Tosoh Corp.) by uniaxial pressing followed by cold-isostatic pressing. Densification was carried out using TSS protocols with varying temperatures for both sintering steps. Relative density (rho Rel), microstructure, and phase content were analyzed. Biaxial flexural strength (6) and translucency parameter (TP) were evaluated. Results: The TSS results were compared with optimized conventional sintering (CS) results from a previous study for the same Y-PSZ compositions. TSS 3Y-PSZ and 4Y-PSZ reached similar rho Rel to those of their CS counterparts, whereas 5Y-PSZ failed to achieve that regardless of TSS protocol. TSS yielded less cubic phase compared to CS, especially for 3Y-PSZ and for higher temperatures. TSS suppressed the grain growth throughout the temperature range investigated, promoting smaller grains than CS (p < 0.05). The TP values for TSS Y-PSZ were lower than those of CS (p < 0.0001), except for 3Y-PSZ. The 6 values for TSS Y-PSZ were significantly higher than those of CS (p < 0.0002). Significance: TSS increased strength without significantly jeopardizing the optical properties of various Y-PSZ compositions relative to their CS counterparts. This alternative sintering method appears to be a promising technique for controlling grain growth while eliminating porosities in dental Y-PSZ ceramics, thus potentially enhancing the clinical longevity of zirconia restorations. (AU)

• FAPESP's process: 21/07440-2 - Graduated glass infiltration in an ultra-translucent zirconia (5Y-PSZ): synthesis, processing and characterization of physical and mechanical properties
• Grantee: Larissa Marcia Martins Alves
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 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
• Grantee: Estevam Augusto Bonfante
• Support Opportunities: Research Grants - Young Investigators Grants - Phase 2
• FAPESP's process: 23/07289-8 - Influence of low temperature degradation on the wear resistance of recycled translucent zirconia
• Grantee: Larissa Marcia Martins Alves
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor