Color Evaluation of Porcelain Laminate Veneer Restorations Bonded with a Single-shade Resin Composite

抄録

 Purpose: To evaluate the effect of single-shade resin composites on the color of porcelain laminate veneer (PLV) restorations comprising lithium disilicate (LDS) cemented to an underlying tooth of two different shades. The evaluation was carried out using the CIEDE2000 color-difference formula and a translucency parameter.

 Methods: Ceramic blocks (A2, HT, IPS e.max CAD, Ivoclar) of 1 mm thickness were fired and assumed to be PLV. Their adhered surfaces were polished with grit-silicon carbide paper (#1200), and their measurement surfaces were mirror-polished. Four resin composites were used as luting materials to fill the 50-μm space between the PLV and the 2-mm-thick standardized underlying tooth, which was then photo-polymerized to serve as the specimen. The following luting materials were used in the present study: single-shade GRACEFIL Universal LoFlo (GC), Clearfil Majesty ES Flow (Kuraray Noritake Dental), Omnichroma Flow (Tokuyama Dental), and A2 shade GRACEFIL LoFlo (GC). A2 and A4 resin composites (Filtek Supreme Ultra, 3M ESPE) polished with water-resistant polishing paper (#600) were assumed as the underlying tooth (underlying structure). Forty specimens were produced and immersed in distilled water at 37°C for 30 days. There were two conditions for the color of the underlying structure and four conditions for the luting material (n＝5). A Vitae Easy Shade V (VITA) digital spectrophotometer was used to determine the color of each specimen. The PLVs were investigated before and after cementation, and after immersion in water (Day 1, 3, 7, and 30) on the underlying structure. The data were analyzed using the 1976 CIEL^＊a^＊b^＊ color system and CIEDE2000 (ΔE₀₀). ΔE₀₀ was calculated for the underlying structure spacing and compared to a threshold considered acceptable in clinical practice (ΔE₀₀＞1.8). The translucency parameter (TP), determined by the color difference between the black and white backgrounds, was also evaluated. The statistical significance of each of the ΔE₀₀ and TP values at Day 30 was determined by the Shapiro-Wilk and Levene tests and one-way analysis of variance (ANOVA).

 Results: The one-way ANOVA results showed no significant differences in the ΔE₀₀ (p＝0.32) or TP (p＝0.23) values between the luting materials at Day 30. However, the ΔE value between the underlying structure of A2 and A4 exceeded the threshold value (ΔE₀₀＞1.8).

 Conclusion: The present study suggests that the color of the underlying tooth has more influence on the final color of the PLV restoration than the single-shade resin composite.