Variations of L*a*b* values among Vitapan Classical Shade Guides

To measure the variations in L*a*b* values of a group of 25 guides and to assess whether shade guides are indeed interchangeable.

The L*a*b* values of individual shade tabs were measured with a LabScan(tm) XE scanning spectrocolorimeter (SSC) with a special attachment for reproducibly positioning shade tabs. Each shade guide (Vitapan Classical, Vident) contained 16 shade tabs. Absolute calibration of the SSC was performed with color tiles traceable to NIST. One shade guide was used to determine the reproducibility of the experimental method by measuring and then removing each shade tab of the standard 10 times. This assessed the variations in observed values induced by the measurement method and the geometry of the specimens. The entire sample consisted of 25 shade guides. The tabs of each of the 25 shade guides were read five times in the SSC, without moving the specimen. Measurements and calculations of E, L*, a*, and b* were performed using Universal Software V4.10 (Hunter Associates Laboratory). The mean, standard deviation, and range were determined of the E, L*, a*, and b* values for each one of the 16 shades in the shade guides. Differences in color are expressed as DeltaE in color science. The standard deviation of E (E(sd)) and the range of E (E(r)) for each of the shades were used as a DeltaE value to assess color differences.

For the reproducibility measurements, the shades had values for E(r) varying from 0.08 to 0.69, and E(sd) between 0.02 and 0.22. This established the detection limit for our method for each of the shades. For the group of 25 shade guides, E(r) varied from 0.75 to 3.05, and E(sd) from 0.22 to 0.54. The difference in value of E(r) obtained from the reproducibility test and the E(r) of the group of 25 guides is significant at p < 0.05. The same was found for E(sd). The largest reproducible E(r) observed was 3.05 for shade C1.

The differences observed between shade guides are larger than the variations induced by the experimental method. The difference in E values for the shades C1 and C2 is 2.19; hence the observed E(r) of 3.05 between shade tabs of the same shade (C1) is larger than the changes in color between shades. This large a variation in what are claimed as identical shade tabs is deemed of clinical importance, and therefore, the shade guides should not be considered interchangeable.