Effect of grinding and aging on subcritical crack growth of a Y-TZP ceramic.

Marina Amaral,Luiz Felipe Valandro,Tais Silvestri,Luis Felipe Guilardi,Gabriel Kalil Rocha Pereira,Isabela Sandim Souza Leite Weitzel

doi:10.1590/1807-3107bor-2018.vol32.0032

Marina Amaral, Luiz Felipe Valandro + Show 4 more

Open Access

https://doi.org/10.1590/1807-3107bor-2018.vol32.0032

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Abstract

This study aimed to investigate slow crack growth (SCG) behavior of a zirconia ceramic after grinding and simulated aging with low-temperature degradation (LTD). Complementary analysis of hardness, surface topography, crystalline phase transformation, and roughness were also measured. Disc-shaped specimens (15 mm Ø × 1.2 mm thick, n = 42) of a full-contour Y-TZP ceramic (Zirlux FC, Amherst) were manufactured according to ISO:6872-2008, and then divided into: Ctrl - as-sintered condition; Ctrl LTD - as-sintered after aging in autoclave (134°C, 2 bar, 20 h); G - ground with coarse diamond bur (grit size 181 μm); G LTD - ground and aged. The SCG parameters were measured by a dynamic biaxial flexural test, which determines the tensile stress versus stress rate under four different rates: 100, 10, 1 and 0.1 MPa/s. LTD led to m-phase content increase, as well as grinding (m-phase content: Ctrl - 0%; G - 12.3%; G LTD - 59.9%; Ctrl LTD - 81%). Surface topography and roughness analyses showed that grinding created an irregular surface (increased roughness) and aging did not promote any relevant surface change. There was no statistical difference on surface hardness among different conditions. The control group presented the lowest strength values in all tested rates. Regarding SCG, ground conditions were less susceptible to SCG, delaying its occurrence. Aging (LTD) caused an increase in SCG susceptibility for the as-sintered condition (i.e. G < G LTD < Ctrl < Ctrl LTD).

Highlights

The long term clinical behavior of zirconia especially with postsintering alterations is still a concern
A compression layer is created by transformation of the zirconia crystals from the tetragonal to the monoclinic phase when mechanical or chemical stimuli are applied to the ceramic.[6,7]
Phase analysis Control group (Ctrl) had no monoclinic phase, followed by ground group (G), while the groups subjected to the degradation in autoclave (Ctrl low-temperature degradation (LTD) and G LTD) presented the highest content of monoclinic phase (Table 2)

Summary

Introduction

The long term clinical behavior of zirconia especially with postsintering alterations is still a concern. The literature reports ceramic degradation and decrease in strength after air-abrasion, grinding or aging,[1,2,3] studies have reported an enhance in fatigue limits and strength after those procedures.[4,5] The different findings might be caused by the different conditions and parameters used for grinding and aging. A compression layer is created by transformation of the zirconia crystals from the tetragonal to the monoclinic phase when mechanical or chemical stimuli are applied to the ceramic.[6,7] The transformed layer is responsible for the increased strength and fatigue bearing ability of the material.[5,6,7]

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