Extended glaze firings for porcelain-veneered zirconia: Effects on the mechanical and optical behavior |
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Authors: | Camila da Silva Rodrigues Iana Lamadrid Aurélio Sara Fraga Marina da Rosa Kaizer Yu Zhang Liliana Gressler May |
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Affiliation: | 1. Graduate Program in Dental Sciences, Federal University of Santa Maria, 1000 Roraima Av., T Street, Building 26F, 97105-900 Santa Maria, RS, Brazil;2. Department of Conservative Dentistry, Federal University of Rio Grande do Sul, 2492 Ramiro Barcelos Street, 90035-003, Porto Alegre, RS, Brazil;3. Graduate Program in Dentistry, Positivo University, 5300 Prof. Pedro Viriato Parigot de Souza Street, 81280-330, Curitiba, PR, Brazil;4. Department of Preventive and Restorative Sciences, University of Pennsylvania, 240 S. 40th Street, Levy 109, Philadelphia, PA 19104, USA;5. Department of Restorative Dentistry, Federal University of Santa Maria, 1000 Roraima Av., T Street, Building 26F, 97105-900 Santa Maria, RS, Brazil |
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Abstract: | ObjectiveThis study evaluated the effect of dwell time (conventional or extended) and cooling protocol (fast or slow) of self-glaze firings on the mechanical (flexural strength and crack propagation) and optical (color and translucency) properties of a porcelain-veneered zirconia system.MethodsBilayer disc-shaped samples were prepared (Vita VM9 + In-Ceram YZ) and divided according to the final thermal treatment: glaze firing followed by slow cooling (furnace opening at 200 °C) (G-S) or fast cooling (furnace opening at 600 °C) (G-F, manufacturer-recommended protocol), extended glaze firing (15 min of dwell time) followed by slow cooling (EG-S) or fast cooling (EG-F), or no thermal treatment (CTRL). Porcelain roughness (Ra and Rz) was measured before and after glaze firings. Color (ΔE00) and translucency (TP00) alteration were also evaluated. Flexural strength was measured with the piston-on-three-ball test and crack propagation analysis was performed after Vickers indentations. Complementary analyzes of crystalline phase and scanning electron microscopy were carried out.ResultsSignificant effect of dwell time was observed, with extended glaze leading to higher flexural strength and shorter crack lengths. Cracks of EG groups were observed to end in clusters of crystals. Color and translucency changed below perceptibility thresholds. All treatments led to a smoother surface and EG groups reached the lowest Rz values. An extra SiO2 peak was revealed in control and EG groups. No effect of cooling protocol was found.SignificanceExtended glaze firing was able to improve the resistance to crack initiation and propagation of porcelain-veneered zirconia without clinically perceptible changes in optical properties. |
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Keywords: | Dental ceramics Porcelain fused to zirconia Cooling protocols Heat treatments Flexural strength |
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