Influence of powder/liquid mixing ratio on porosity and translucency of dental porcelains

STATEMENT OF PROBLEM: Dental technicians use a variety of techniques when condensing dental porcelains. It is unclear whether these techniques affect the total porosity and translucency of dental porcelains. PURPOSE: The objective of this study was to determine whether varying the powder/liquid ratio during condensation affects porosity and translucency of porcelains.Material and methods Duceram LFC dentin, Duceram LFC incisal, IPS Eris dentin, and IPS Eris incisal porcelains were studied. For each specimen, 1.0 g of porcelain powder was mixed with 1 of 3 different volumes of deionized water to form a slurry with a thin, medium, or thick consistency. The slurries were condensed in a plastic syringe mold, fired, and polished to a 3-microm finish to form 12 groups of 4 specimens each (14-mm diameter, 1.10-mm thickness). The apparent density (g/mL) of each specimen was measured using Archimedes method, and the porosity (%) calculated. Each specimen was coupled to standard ceramic tiles using an immersion liquid, and the color shade was measured in CIE Yxy coordinates using a tristimulus colorimeter. Translucency was assessed by calculating the contrast ratio of shade value (Y) in front of black versus white backgrounds. Two-way analysis of variance and Tukey's multiple comparison tests (alpha = .05) were used to test for significant effects of factors. RESULTS: Porcelain type and powder/liquid ratio had a significant interactive effect on the apparent density (P < .001) and on total porosity (P = .003); however, there was no consistent trend. The powder/liquid ratio did not significantly affect translucency (P = .28), but porcelain type had a significant effect on translucency (P < .001). CONCLUSION: In this in vitro study, total porosity of specimens prepared using 4 porcelains was found to be sensitive to powder/liquid ratio; whereas translucency was found to be insensitive to powder/liquid ratio.