Spectrophotometric observations about the chromatic correspondence of some shade guides

Objectives: the purpose of the study was twofold: 1. to evaluate the correspondence between the colorimetric parameters evaluated by a spectrophotometer and the indexes of colour scales available on the market; 2. to compare the galvanic technique and the lost wax fusion technique in their ability to accurately reproduce the colorimetric parameters detected on a natural tooth by spectrophotometry. Methods: for the achievement of objective 1., the parameters difference in lightness (DeltaL), difference in hue (DeltaA and DeltaB), and difference in chroma (DeltaS) were evaluated for the colour scales Vita, Truebyte, Ivoclar, CeramCo. For the achievement of objective 2., all the colorimetric parameters of the upper left incisor in a young patient were defined by spectrophotometry. Then, two porcelain crown were prepared for this tooth, one following the galvanic technique, the other one with the lost wax fusion procedure. Each prosthetic crown was then analyzed with the spectrophotometer. Results: Objective 1: in none of the evaluated colour scales the colorimetric parameters were found to precisely correspond with those defined by the spectrophotometer. Objective 2. The porcelain crown made with the galvanic technique exhibited a closer correspondence with the colour-mapping of the natural tooth defined by the spectrophotometer. Conclusions: the colour scales available on the market provide only general indications to the clinician for the definition of the colour of natural tooth. For this purpose ideally a spectrophotometer should be used. Prosthetic crowns made with the galvanic technique reproduce the colour-map of a natural tooth more closely than crowns made with the lost wax fusion procedure.