Sintering mode of a translucent Y-TZP: Effects on its biaxial flexure fatigue strength, surface morphology and translucency.

Abstract

This investigation evaluated the effect of two sintering modes of a translucent zirconia (Y-TZP) on its surface roughness, topography, phase-transformation (t → m), translucency and biaxial flexure fatigue strength. To do so, 50 Y-TZP discs (Ø=15 mm; thickness=1.2 mm; IPS e.max ZirCAD LT) were prepared and divided into two groups: Standard mode (SM) and Fast mode (FM). Staircase fatigue testing was performed (piston-on-three balls set-up, ISO 6872:2015), as well as surface roughness, profilometry, scanning electron microscopy (SEM-FEG), energy dispersive X-ray spectroscopy (EDX), phase transformation (t → m) using X-ray diffraction analysis (XRD), translucency parameter analysis (TP and TP00 ) and fractography. The results showed no statistical significant differences for roughness parameters (p > 0.05, SM: Ra=0.13 ± 0.02, Rz=1.21 ± 0.26 and RSm=24.91 ± 2.19; FM: Ra=0.14 ± 0.03, Rz=1.32 ± 0.25 and RSm=24.68 ± 2.16) or flexural fatigue strength (SM: 512 (464-560) MPa; FM: 542 (472-611) MPa) between the groups. In addition, similarity in surface morphological features (SEM and profilometry), composition and phases (EDX and XRD) was observed between the firing protocols. Fractography showed that the failure origin occurred on the tensile side. Sintering mode did not affect the TP (F=0.001, p=0.97) and TP00 (F=0.12, p=0.72). Therefore, the fast-sintering mode is suggested as a viable alternative to the standard mode since it does not influence the evaluated surface morphology, microstructure, fatigue strength and translucency of a translucent monolithic zirconia. The fast sintering mode is a viable alternative for zirconia without compromising its topography, microstructure, mechanical performance or translucency.