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

Abstract

Objective 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. Materials and Methods 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. Results 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). Conclusions 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. Clinical Significance The fast sintering mode is a viable alternative for zirconia without compromising its topography, microstructure, mechanical performance or translucency.

Effect of speed sintering of monolithic zirconia with different yttria contents on color and crystal phase

“…Nevertheless, in this study, sintering temperatures of 1500˚C−1530˚C were used, so the grain size was not considered to have been affected by the sintering temperature. Micrographs displayed at high resolution showed that the speed sintering program resulted in a homogenous microstructure, which corroborates the results of previous studies [37].…”

Qualitative SEM analysis of fracture surfaces for dental ceramics and polymers broken by flexural strength testing and crown compression

“…For example, solid-state sintering applied to dental zirconia is reported not to induce crack healing. 1 Madruga et al 24 reported that fractures on disc specimens for 3Y-TZP zirconia can be initiated at the tensile surface. Jerman et al 28 reported that cracking starts at the tensile side for 4 PB tests, and all specimens (3Y, 4Y, 5Y-TZP) showed typical compression curls with fragmentation patterns that were similar for all materials, including crack branching and fragmentation due to secondary cracks indicating high-energy fractures.…”

“…For example, solid‐state sintering applied to dental zirconia is reported not to induce crack healing 1 . Madruga et al 24 . reported that fractures on disc specimens for 3Y‐TZP zirconia can be initiated at the tensile surface.…”

“…The fabrication of dental restorations has been simulated in research laboratories for in vitro studies with standardized specimens (bars and discs) to study the quality of the material as provided by the manufacturer; to expose the specimens to conditions similar to the oral environment (low-temperature degradation 7 ) and dental laboratory (finishing, polishing, and sandblasting); and to determine the mechanical properties (failure load, 8 flexural strengths, [9][10][11][12] fracture toughness, 13 wear, 14 and fatigue). 15 Fractography of broken and/or worn specimen parts (crowns, [16][17][18][19][20][21] bars, 22,23 discs 10,11,24 ) provides a means to determine where a fracture originates, whether from flaws originating from the original manufacturing process or from dental laboratory surface treatments, thereby improving the quality control of future restorations. These flaws vary in size, shape, distribution, and orientation and are the result of bulk fabrication processes (sintering or pressing pores, 25 contaminants such as Al 2 O 3 or CaO, excessive grain growth, 2nd phase grains, and/or inclusions) or surface treatments (performed by the technician and/or dentist), such as grinding damage, sandblasting damage, milling scratches or grooves, and poor handling.…”

“…Fractography of broken and/or worn specimen parts (crowns, 16–21 bars, 22,23 discs 10,11,24 ) provides a means to determine where a fracture originates, whether from flaws originating from the original manufacturing process or from dental laboratory surface treatments, thereby improving the quality control of future restorations. These flaws vary in size, shape, distribution, and orientation and are the result of bulk fabrication processes (sintering or pressing pores, 25 contaminants such as Al 2 O 3 or CaO, excessive grain growth, 2nd phase grains, and/or inclusions) or surface treatments (performed by the technician and/or dentist), such as grinding damage, sandblasting damage, milling scratches or grooves, and poor handling 2 …”