Comparison of Spectrophotometer to Colorimeter Digital Shade-Guide by Delta-E Values

Objectives:   To compare the Crystaleye spectrophotometer (Olympus) and Shadevision imaging colorimeter (X-Rite) digital shade-guide systems in terms of their concordance with a standard. 

Methods: Lab fabricated Feldspathic porcelain disks were used in four shades (A1, A2, A3, A3.5) based on Vita Classical Shade Guide, with approximately 5mm in diameter by 1.5mm thick, flat and convex surface.  A photography light tent was used to diffuse the light and a light meter was used to maintain even lighting.  The disks were scanned using three different backgrounds - black, gray, and white.  Five disks were made in each color and each disk was scanned five times and the L*a*b* values for each disk were averaged and DE was calculated.  The DE reference values came from the University of Michigan Biomaterials Properties Database.  Data were analyzed via a mixed-effects model and Tukey's test (using SAS 9.2) with one-sided 95% confidence intervals (SPSS 19.0).  P-values less than 0.05 were considered statistically significant.

Results:    In the mixed-effects model, shade was not a statistically significant predictor of DE (p= 0.126), but background, surface, and machine were significant (p <0.0001).  Samples with a gray background and convex disk had the lower DE values.  The one-sided confidence intervals indicated that under the gray-convex conditions, Shadevision's average performance is within 0.61 DE units of Crystaleye's, or better, with 95% confidence.

Conclusions:   Within the limitations of this study, Shadevison's concordance with the standard is comparable to Crystaleye's.  Background and surface also influence the DE, with gray-convex conditions yielding the lowest values.