Objectives: The purpose of this study was to determine the possibility of predicting the coefficient of thermal expansion (CTE) of mixtures of two veneering ceramics by using the rule of mixture and to determine a compatible ceramic for a fluorcanasite core ceramic.

Methods: Rods were made from a fluorcanasite, a feldspar (Vita Alpha^TM), and a high leucite (IPS Classic^TM) ceramic, and varying percentages of feldspar: high leucite composition. The CTE was measured from 300⁰C to 400⁰C using the Electronic Dilatometer 402 EP. The data was plotted to formulate a regression equation of the CTE and % feldspar ceramic (replaced with high leucite). The predicted CTE values were calculated from the rule of mixtures equation. The appropriate feldspar: high leucite composition was applied to fluorcanasite discs, which were sectioned and viewed by light microscopy.

Results: The mean CTE was 7.59 ppm/ ⁰C for fluorcanasite, 6.14 for Vita Alpha^TM, 7.67 for 75% feldspar, 9.72 for 50% feldspar, 11.35 for 25% feldspar and 13.54 for IPS Classic^TM. The best line fit to the CTE data versus % ratio of the feldspar was a straight line with a linear regression coefficient of R2=0.99. The experimental CTE values, when compared with the predicted CTE values, produced a straight line fit given by the equation Y=1.0151X with an R value of 0.99. An 81 vol% feldspar and 19% vol high leucite composition showed no evidence of a thermal mismatch with the core ceramic.

Conclusion: The CTE of mixtures of feldspar and high leucite ceramics can be presented as a linear equation. The experimental data was in good agreement with the results obtained from the rule of mixtures. 81 vol% Vita Alpha^TM and 19 vol% vol IPS Classic^TM was found to be compatible with the fluorcanasite.

Vita Alpha^TM, Vita Zahnfabrik, Germany; IPS Classic^TM, Ivoclar Vivadent, Liechtenstein

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