The effect of a coupling medium on color and translucency of CAD-CAM ceramics

To evaluate color and translucency of ceramics and the influence of a coupling medium (G - glycerin) on these optical properties, testing the hypothesis that glycerin influences the translucency values regardless the evaluation method.

Five specimens from A2-shaded ceramics (IPS e.max CAD HT and LT, IPS Empress CAD HT and LT, Paradigm C, and Vita Mark II) were fabricated from ceramic blocks and polished to 1.0 ± 0.01mm in thickness. A spectrophotometer (Vita Easys hade) was used to measure the CIELAB coordinates and the reflectance value (Y) of specimens placed on white and black backgrounds. The translucency parameter (TP) and the contrast ratio (CR) were calculated. Another spectrophotometer (Lambda 20) was used to measure the direct light transmittance (T%) of the specimens. The color and the CIELAB coordinates were evaluated using the Vita Easy shade on neutral grey background and values were used to calculate difference in color (ΔE). All evaluations were repeated using G and values were recorded. Data were statistically analyzed using Anova, Tukey and Student's t-test (α=0.05) and Pearson's correlation.

Although the mean translucency values were significantly different for each method (TP and CR), they were strongly correlated (r²=0.97), even when G was used (r²=0.96).

The coupling medium significantly influenced the mean values of ΔE and translucency.

Color and translucency values cannot be compared if measured using different coupling media (e.g. air and liquid glycerin).