Effect of Porcelain Shade and Application Time on Shade Reproduction.

PURPOSE: To determine the variability in shade reproduction of metal ceramic restorations fabricated by different laboratory technicians at different fabrication times.

MATERIALS AND METHODS: One hundred thirty five metal copings for metal ceramic restorations were fabricated with a standardized method and distributed among three dental laboratory technicians (n = 45). Each technician was requested to match three different shade specifications including 2L1.5, 3M2, 4R2.5 shade tabs of 3D Master shade guide following the manufacturer's instructions. The technicians were instructed to build up each shade 15 times using the same porcelain at three time periods namely first thing in the morning (T1 ), middle of the work day (T2 ), and at the end of the work day (T3 ) (n = 5). Color difference (∆E) was determined with a spectrophotometer. Each restoration was measured and recorded nine times. Data were tabulated and statistically analyzed using a univariate general linear model with Scheffe post hoc test, and one-way ANOVA at 5% level of significance RESULTS: The color difference (∆E) was significantly different among technicians, time of application, and shade matched. Technician 1 demonstrated good color reproduction for all shades in T1 . That was the same as technician 2 for shades 3M2 and 4R2.5, but the lighter shade (2L1.5) was better in T2 and T3 . Technician 3 had better results at T3 . The lowest mean value of ∆E was calculated with technician 3 while the highest mean value was with technician 2. T2 was associated with higher ∆E values in contrast to the other two times for technicians 1 and 2, while T3 was associated with lower ∆E values for technicians 2 and 3.

CONCLUSION: Within the limitations of this study, it can be concluded that the shade reproduction is affected by the time of porcelain application. The ability to reproduce the target shade differed among laboratory technicians. No specific time can be considered for all technicians to reproduce the shades with more accuracy.