Effect of glazing application side and mechanical cycling on the biaxial flexural strength and Weibull characteristics of a Y-TZP ceramic

Abstract

Glaze application on monolithic zirconia (Y-TZP) can be a practical approach to improve the mechanical properties of this material. Objective: Our study evaluated the effect of glazing side and mechanical cycling on the biaxial flexure strength (BFS) of a Y-TZP. Methodology: Eighty sintered Y-TZP discs (Ø:12 mm; thickness: 1.2 mm-ISO 6872) were produced and randomly assigned into eight groups (n=10), according to the factors "glazing side" (control-no glazing; GT-glaze on tensile side; GC-glaze on compression side; GTC-glaze on both sides) and "mechanical aging" (non-aged and aged, A-mechanical cycling: 1.2×106, 84 N, 3 Hz, under water at 37°C). Specimens were subjected to BFS test (1 mm/min; 1,000 Kgf load cell) and fractured surfaces were analyzed by stereomicroscopy and SEM. Hsueh's rigorous solutions were used to estimate the stress at failure of glazed specimens. Two-way ANOVA, Tukey's test (5%), and Weibull analysis were performed. Results: The "glazing side", "mechanical aging" and the interaction of the factors were significant (p<0.05). Groups GC (1157.9±146.9 MPa), GT (1156.1±195.3 MPa), GTC (986.0±187.4 MPa) and GTC-A (1131.9±128.9 MPa) presented higher BFS than control groups (Tukey, 5%). Hsueh's rigorous solutions showed that the maximum tensile stress was presented in the bottom of zirconia layer, at the zirconia/glaze interface. Weibull characteristic strength (σ o) of the GC was higher than all groups (p<0.05), except to GT, GTC-A and GTC, which were similar among them. The fractography showed initiation of failures from zirconia the tensile side regardless of the side of glaze application and fatigue. Conclusion: Glazing zirconia applied on both tensile and compression sides improves the flexural strength of Y-TZP, regardless the mechanical aging.

Effect of Two Brands of Glaze Material on the Flexural Strength and Probability of Failure of High Translucent Monolithic Zirconia

“…Of note, we used a self-aligning four-point bend jig which ensured that any potential misalignment of a specimen was not exacerbated using a fixed bending jig thereby inducing the failure at an artificially induced high-stress area. In a previous fractographic study, pores were observed in the glaze layer, but these did not seem to initiate fracture [45]. We also observed voids in the glaze layer at the glaze/zirconia interface at the corner of several specimens which may have caused fracture initiation at those sites (Figure 7).…”

“…Without clear identification of where the glaze is applied to the specimen, it is difficult to directly compare our results with previous studies. A recent study by Lobo et al reported the effect of glaze application and mechanical ageing on the biaxial flexural strength of Y-TZP and found that glaze applied on both the tensile and compression sides improve the flexural strength of Y-TZP [45]. This study, however, only used a sample size of n = 10 on which to report their Weibull results.…”