Comparison of an absolute and surrogate measure of relative translucency in dental ceramics

PurposeThe objective was to compare absolute translucency with a frequently used surrogate measure of relative translucency (contrast ratio) from 14 all-ceramic materials having a wide range of translucencies.Materials and methodsStandardized disks were fabricated from fourteen ceramics, varying both thickness (0.3 mm, 0.5 mm, 1.0 mm, and 1.5 mm) and chroma (high and low). Absolute translucency (percent transmission) was measured using a spectroradiometer with an integrating sphere. Relative translucency was measured using a spectrophotometer as contrast ratio (contrast ratio; ratio of L* values recorded on black and white backgrounds). Non-linear regression was used to compare measurements of absolute versus relative values for each of the spectrophotometers.ResultsContrast ratio was not able to characterize translucency across the range of materials studied and became less sensitive with increasing opacity. A non-linear correlation was found between percent transmission and contrast ratio down to 50% transmission (r2 = 0.97) and contrast ratio was insensitive to transmission differences below 50% transmission.ConclusionContrast ratio is not a direct measure of translucency and cannot be used below 50% transmission.