Changes in optical properties of enamel porcelain after repeated external staining.

Statement of problem. After staining a porcelain restoration, increasing the lightness (value) and decreasing the chroma of a restoration is not practically easy to accomplish. Purpose. The purpose of this study was to determine the color change of enamel porcelain after repeated external staining procedures over the enamel porcelain surface. Changes in translucency and differences in surface roughness were also measured. Material and methods. Enamel porcelain (VITA OMEGA 900 Metal Ceramics) disks (1 X 12 mm) of 1 shade (EN2) were prepared, and 1 of 4 types of external stains (VITA Akzent stains) was applied over the specimens and fired. Firing was repeated 3 times after application of the same stains. Color of the specimens before and after stainings was measured with a reflection spectrophotometer. Two-factor repeated- measures analysis of variance with the fixed factors of the stain type and number of staining cycles for the changes in CIE L*, CIE a*, CIE b*, color (Delta E*(ab)), and chroma (Delta C*(ab)) after repeated staining was performed (alpha=.05). Chroma change was calculated as Delta C*(a)=(Delta a*(2) + Delta b*(2))(1/2). Changes in translucency (translucency parameter and masking effect) and difference in surface roughness (Ra) after the third staining cycle were also determined. Results. Color change after the first staining cycle was perceptible (AE*(ab) >2) for 2 of 4 types of stains and was perceptible for all 4 types of stains investigated after the third staining cycle (Delta E*77(ab)=2.36-11.04). Lightness generally increased, and chroma also increased after staining but varied by the type of stains and number of staining cycles. Translucency generally decreased after repeated staining. Surface roughness varied by the type of stain (P<.001). Conclusion. Color difference and lightness increased significantly after repeated staining cycles, but chroma change was small after repeated staining cycles. Therefore, repeated staining may be a method to increase the lightness of enamel porcelain.