Effect of zirconia thickness and firing cycle on porcelain veneers properties
Date
2016
DOI
Authors
Alayad, Abdullah Saeed
Version
OA Version
Citation
Abstract
Objectives: With the increased demands of esthetic restorations, all-ceramic restorations became popular and achieved patients' needs of having a functional dental restoration with good esthetic. Core-veneered all ceramic restorations have gained a lot of popularity and attention in the last few years, combining the strength of ceramic cores and esthetics of veneering porcelain. The use of zirconia-based ceramics for dental restorations has risen in popularity due to their superior fracture strength and toughness compared with other dental ceramic systems. Although porcelain fused to zirconia restorations account for a large percentage of all-ceramic restorations, there are numerous reports of chipping of the veneer porcelain. Several theories for chipping have been proposed: low thermal conduction of zirconia, heating and cooling too fast, differences in thermal expansion, and surface finish. Zirconia does have a low thermal conduction preventing transfer of heat to the veneer porcelain. Peak firing temperature of the porcelain combined with the zirconia thickness may be a cause of chipping. Zirconia thickness in the pontic area can easily be as much as 5 - 8 mm. If thermal conduction is a problem then low firing porcelains might be significantly affected by zirconia thickness. Objectives of this study were to evaluate and compare the effects of different zirconia thicknesses and different firing cycles on strength, density, surface roughness and microstructural changes of two porcelain veneers.
Materials and methods: One core material Vita In-Ceram YZ and two porcelain veneers, IPS e.max Ceram and Vita VM9 were used in this study. Vita YZ zirconia blocks (Vita Zahnfabrik, Germany) were sectioned and sintered to provide slabs of 0.5, 1.0, and 5.0 mm thickness. Vita VM9 and e.max Ceram porcelain (Ivoclar, Liechtenstein) were mixed with deionized water, condensed in a mold, and sintered: (l) According to the manufacturer's instructions; (2) Two cycles at peak temperature above the recommended value for each veneer material. A layer of carbon paint was applied to the zirconia to allow removal of the porcelain discs. Biaxial flexure strength was determined using an Instron, crosshead speed of 0.5mm/min. Density of the veneering porcelains were calculated using this formula: p = m/v where p is the density, m is the mass and v is the volume. The surface roughness were measured and then specimens analyzed by SEM. Data were statistically analyzed using ANOVA and Post Hoc tests Tukey-Kramer HSD test for multiple comparisons at a=0.05.
Result: The mean and standard deviation of biaxial strength, density and surface roughness values of porcelain veneers after firing using different zirconia thicknesses and firing cycles are shown in table below:
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Description
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Thesis (MSD)--Boston University, Henry M. Goldman School of Dental Medicine, 2016 (Department of Restorative Sciences and Biomaterials)
Includes bibliographic references: leaves 135-151.
Thesis (MSD)--Boston University, Henry M. Goldman School of Dental Medicine, 2016 (Department of Restorative Sciences and Biomaterials)
Includes bibliographic references: leaves 135-151.
License
This work is protected by copyright. Downloading is restricted to the BU community. If you are the author of this work and would like to make it publicly available, please contact open-help@bu.edu.