The Effect of Heat Treatment and Feldspathic Glazing on Some Mechanical Properties of Zirconia

Abstract

Purpose In dental practice, zirconia substructures for crowns and fixed partial dentures are veneered with feldspathic porcelain for better aesthetical properties. The purpose of this study was to evaluate the effect of heat treatment during the veneering process on the mechanical properties of zirconia. Methods 105 zirconia (ICE Zirkon, Zirkonzahn, Italy) disc shaped specimens were divided into seven groups (n=15/ group) and sintered at 1500°C. Control specimens (group 1) were left as such. Specimens in the study groups were: 2) one heat treatment in a porcelain firing furnace; 3) a heat treatment with two firing cycles; 4) one heat treatment with a thin coating of feldspathic glazing on the tension side; 5) two heat treatments with a thin coating of feldspathic wash and glazing on the tension side; 6) one heat treatment with a thin coating of feldspathic glazing on the compression side; 7) two heat treatments with a thin coating of feldspathic wash and glazing on the compression side. Biaxial flexural strength and surface microhardness of the specimens (diameter 19 mm, thickness 1.2 mm) were measured. The effect of heat treatment and feldspathic glazing on the phase transformations of zirconia was determined by XRD-analysis. The data were calculated using ANOVA-analysis.Results Repeated heat treatment did not influence the mechanical properties of zirconia (p>0.05). No difference (p>0.05) was found in terms of the surface microhardness between the groups. Some transformation from the tetragonal to the monoclinic phase was seen on the surface of the specimens after heat treatment and feldspathic glazing coating. Conclusions Repeated heat treatment does not affect the strength of zirconia milled in the green-stage form.

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

“…Few information about the effect of glazing side were found in the literature. 27 Hjerppe, et al 27 (2010) reported that the application of glaze on tensile side decreased the BFS, whereas glaze on compression side was similar to control (no glazing), in non-aged condition. These results differ from our study, since none of the glazed groups showed BFS lower than control.…”

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

“…The effect of two glaze methods (spray and brush) was studied on translucent Y-TZP and it was suggested that glaze application methods did not damage the fatigue strength of the tested Y-TZP [42]. Previously it was found that glaze on the tensile side decreased the flexural strength, whereas glaze on the compression side was similar to unglazed specimens [43]. However, these results were based on three-point bending or biaxial flexural strength tests.…”

Fatigue behavior of Y-TZP ceramic after surface treatments

“…The application of a thin low-fusing glassy layer (rich in silicon oxides) on the cementation surface of the ceramic, followed by hydrofluoric acid etching and silane application has been investigated as an alternative surface treatment and showed promising results with significant improvements of the bond strength between resin cements and Y-TZP (Aboushelib et al, 2010;Kitayama et al, 2009;Vanderlei et al, 2014;Ntala et al, 2010). On the other hand, some studies indicated that, under tensile stresses, this glassy layer might undergo crack initiation and propagation with subsequent decrease in structural reliability of the specimens (Guazzato et al, 2004;Hjerppe et al, 2010).…”