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 (σo) 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.
Highlights
Recent studies have shown that zirconium oxide ceramics present higher mechanical properties,1,2 biocompatibility and low bacterial adhesion characteristics.3,4 considering that the conventional zirconia, first generation of yttriastabilized tetragonal zirconia polycrystals (Y-TZP), has very low translucence, it requires a glass ceramic veneering application, which can favor the chipping and fracture of veneering ceramic,5 mainly due to the low thermal conductivity of zirconia.6 Chipping is one of the most predominant failures in bilayer zirconia restorations.5,7,8 the use of monolithic zirconia restorations have increased, 9-11 on which surfaces only polishing12 or glazing13,14 have been recommended
Considering that one of the main areas subjected to tensile stress is the internal surface of the crowns,21 glaze application in this area can decrease tensile stress of the zirconia
analysis of variance (ANOVA) revealed that the factors “Glazing side” (p
Summary
Recent studies have shown that zirconium oxide ceramics present higher mechanical properties, biocompatibility and low bacterial adhesion characteristics. considering that the conventional zirconia, first generation of yttriastabilized tetragonal zirconia polycrystals (Y-TZP), has very low translucence, it requires a glass ceramic veneering application, which can favor the chipping and fracture of veneering ceramic, mainly due to the low thermal conductivity of zirconia. Chipping is one of the most predominant failures in bilayer zirconia restorations. the use of monolithic (translucent) zirconia restorations have increased, 9-11 on which surfaces only polishing or glazing have been recommended. The amount of glaze is negligible compared to that of glass ceramic on a bilayer zirconia restoration. There is evidence that the application of a glass layer with low elastic modulus to zirconia promotes better stress distribution, because the maximum tensile stress is directed to the highmodulus zirconia, improving the mechanical properties of the material.. Glazing has been applied in the internal surfaces of zirconia crowns to improve bonding to resins.. Considering that one of the main areas subjected to tensile stress is the internal surface of the crowns, glaze application in this area can decrease tensile stress of the zirconia.. A low thickness of glaze layer can be applied under connectors areas of FDPs, especially in clinical situations where there is lack of space for veneering ceramic There is evidence that the application of a glass layer with low elastic modulus to zirconia promotes better stress distribution, because the maximum tensile stress is directed to the highmodulus zirconia, improving the mechanical properties of the material. Glazing has been applied in the internal surfaces of zirconia crowns to improve bonding to resins. considering that one of the main areas subjected to tensile stress is the internal surface of the crowns, glaze application in this area can decrease tensile stress of the zirconia. A low thickness of glaze layer can be applied under connectors areas of FDPs, especially in clinical situations where there is lack of space for veneering ceramic
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