Spectrophotometric Evaluation of Color Reproduction by Dental Laboratories at UWC

Objective: Spectrophotometric evaluation of color reproduction of metal-ceramic and all-ceramic crowns fabricated by dental laboratories for the UWC Oral Health Centers. Materials and Methods: Thirty two metal ceramic and all ceramic crowns fabricated for maxillary anterior teeth between March and May 2006 were used in the study. Measurements of both the shade tabs and crowns were performed by a pre-calibrated examiner using a spectrophotometer (Konica Minolta, CM-2600d). The measurements were made at the incisal half of the shade tabs and crowns and the CIE L*a*b* color coordinates were directly recorded on the spectrophotometer's detector area using a standard light source. The data was analyzed with a pair-wise comparison of the color coordinates (Wilcoxon signed-rank test) at p<0.05. Color differences (DE, DL, Da and Db) between prescribed shade tabs and the fabricated crowns were calculated. Results: Color reproduction was significantly different (p<0.05) for the fabricated crowns at the measured sites. Most of the crowns were found to be brighter (higher L* values), more reddish (higher a* values) and more yellowish (higher b* values) compared to the prescribed shade tabs. Mean color differences (DE) from shade tabs ranged from 1.6 to 15.9 units. Conclusion: Within the limitations of this study, metal-ceramic and all-ceramic crowns differed in all coordinates (L*, a* and b*) of the CIE L*a*b* color system from the prescribed shade tabs. In most cases the crowns fabricated by the dental laboratories, when compared to the shade tabs, were above the clinical threshold for an acceptable shade match under intraoral conditions (DE 3.7).