Influence of underlying resin composite shade and material thickness on color matching of single-shade resin composites.

<h4>Purpose</h4>To assess the influence of the resin-based substrate shade and the single-shade resin composite thickness on color matching ability.<h4>Methods</h4>Discs (Ø6 x 2 mm) made from a conventional resin composite (Z350 XT) simulated high- (B1B), medium- (A3B), and low-luminosity (C3B) substrates. Each disc (n=10) received sequential increments of the following single-shade resin composites: Palfique Omnichroma (PO) or Vittra APS Unique (VU), at thicknesses of 0.5, 1 and 2 mm. Color parameters [CIEL*a*b*, Vita Scale (SGU), ΔEab, and ΔE₀₀] were determined for conventional resin composite and post-application measurement of single-shade resin composite thicknesses. Statistical analyses included the Mann-Whitney, Kruskal-Wallis, Dunn, Friedman, or Nemenyi tests (α= 0.05).<h4>Results</h4>The ΔEab and ΔE₀₀ values were significantly lower for PO than for VU (P< 0.05). At 1 mm, a decrease in L* values were observed for both resin composites and substrates (P< 0.05). The lowest ΔSGU values were recorded on the high-luminosity substrate (B1B), regardless of the applied thickness (P< 0.05).<h4>Clinical significance</h4>Single-shade resin composites did not completely match the resin substrate. Palfique Omnichroma outperformed Vittra APS Unique in all aspects, particularly in showing less overall color change, and especially when applied over high-luminosity resin substrates.