RESUMO
OBJECTIVE: The aim of this study was to assess the effect of opaque stain application to the intaglio surface of lithium disilicate glass ceramics on the masking ability of discolored substrates and bond strength to a resin-based luting agent (depending on etching time); the stain film-thickness was also assessed. MATERIALS AND METHODS: Ceramic specimens were produced with CAD-CAM blocks of lithium disilicate (IPS e.max CAD). Two opaque stains were tested at ceramic intaglio surface: opaque glassy stain for titanium frameworks (OP-ti) and low-fusion glassy stain for ceramic characterization (LFG-iv). Non-stained ceramic specimens served as controls. For optical and colorimetric analyses, A2-shaded ceramics of medium and low-translucencies were tested, in thicknesses of 1.0- and 1.5-mm (n = 10), with two coupling agents (non-shaded-glycerin and A2-shaded try-in paste). CIEDE2000 formula was used for calculation of translucency parameter (TP00) and color differences (ΔE00). Whiteness index for dentistry (WID) was also reported. ΔE00 were assessed over discolored substrates (tooth-shaded A2-reference, A4, C3, and C4; coppery metal, silvery metal, white zirconia, and PEEK). Microshear bond strength of stained and non-stained ceramic specimens to a resin-based luting agent was evaluated. Film-thickness of stains was assessed by scanning electron microscopy. RESULTS: The application of opaque stains to the intaglio surface of lithium disilicate ceramics resulted in significant reduction of TP00 (p < 0.001) and WID (p < 0.001) and differences in L*, C*, and ho color coordinates (especially with OP-ti) (p < 0.001). ΔE00 was significantly reduced in stained ceramic groups in comparison with the control, for all discolored substrates (p < 0.001). Acceptable color matching was obtained with stained ceramic specimens for all discolored substrates, depending on the type of stain, ceramic thickness, ceramic translucency, and coupling agent. The application of stains to the ceramic intaglio surface was not detrimental to bond strength to a resin-based luting agent, but depended on the time of hydrofluoric acid-etching (20 s for OP-ti and 60 s for LFG-iv) (p < 0.001). Film-thickness of stains presented mean values <70 µm. CONCLUSION: The application of opaque stains to the intaglio surface of lithium disilicate glass ceramics was effective to mask severely discolored substrates, presenting adequate bond strength to the luting agent and thin film-thicknesses. CLINICAL SIGNIFICANCE: For indirect restorations over severely discolored substrates, the application of opaque stain to the intaglio surface of lithium disilicate glass ceramic ensures acceptable color matching, with adequate bond strength to resin-based luting agents and clinically acceptable stain film-thickness.