Thermal Compatibility of Ceramic Veneers to a High Strength Core Material

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Pannapa Sinthuprasirt Sarah Pollington Richard van Noort


The purpose of this study is to determine the extent to which the coefficient of thermal expansion mismatch between a veneering and core ceramic affects the thermal shock resistance. This study is also to establish what is the ideal coefficient of thermal expansion for a veneering ceramic in relation to its core ceramic. Veneering ceramics matching the CTE of three ceramic core materials were manufactured by measuring the CTE of ceramics with a range feldspar/high leucite ratios and using a linear regression equation. Discs of the core ceramics were veneered with varying wt% ratios of leucite/feldspar with CTE values ± 3 ppm/°C. The thermal shock resistance was determined by preheating the specimens to 90°C, quenching them in cold water, then reheating to 90°C followd by cooling to room temperature and inspecting for crazing. If no failure occurred, the specimens were tested at increasing increments of 10°C until failure. Statistical analysis was undertaken using two-way ANOVA and Tukey post-hoc tests for the CTE of the varying feldspar/high leucite compositions; and one-way ANOVA with Tukey’s multiple comparison tests for the thermal shock resistance. The CTE of the mixtures of feldspathic and leucite veneering ceramics presented as a linear equation, obeying the rule of mixtures, thus enabling matched CTE ceramic systems to be created. For IPS emax CAD and VITA In Ceram YZ, when veneered with their recommended ceramic, the mean ΔT values were significantly lower (192 ± 12°C and 179 ± 18°C) than when veneered with a ceramic with a matched CTE (225 ±15°C and 218 ± 9°C) (p<0.05). However, for the fluorcanasite, the matched CTE ceramic produced a mean ΔT value of 232 ± 25°C, which was significantly higher than the two commercial systems (p<0.05). Significance: For high strength ceramic cores, the best thermal shock resistance is achieved with a veneering ceramic that has a CTE the same as the core ceramic.


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