Influência da estratégia de silanização e do condicionamento do esmalte na resistência de união e estabilidade cromática de facetas de dissilicato de lítio

Abstract

Adhesive cementation of lithium disilicate veneers depends on two interfaces, ceramic–cement and cement–enamel. Universal resin systems aim to simplify it by incorporating silane into the adhesive and dispensing with phosphoric acid etching of enamel, but it is unclear whether this simplification preserves bond strength and color stability. This thesis evaluated the influence of enamel etching and silanization strategy on these two outcomes in veneers cemented with a universal resin system. Two randomized in vitro experiments were conducted with blinded outcome assessment. In the mechanical experiment, 40 bovine enamel–lithium disilicate assemblies were allocated to four groups (n = 10) in a 2 × 2 factorial design: non-etched enamel (E−) or enamel etched with 37% phosphoric acid (E+), and ceramic treated only with the silane-containing universal adhesive (SI; Scotchbond Universal Plus) or with prior application of a separate ceramic primer (SS; RelyX Ceramic Primer). After cementation with RelyX Universal and 10,000 thermal cycles, shear bond strength and failure modes were evaluated. In the color experiment, 20 assemblies, all with etched enamel, were allocated to SI or SS (n = 10) and stored in water for 90 days, and color changes (ΔL*, Δa*, Δb*, ΔEab, and ΔE00) were calculated. Both enamel etching (p < 0.001; η²p = 0.841) and the separate primer (p < 0.001; η²p = 0.631) increased bond strength, with no significant interaction between the factors (p = 0.162). Mean values ranged from 5.95 ± 1.08 MPa (E−/SI) to 25.82 ± 4.58 MPa (E+/SS). Failure modes differed among groups (p = 0.001): without etching, failures at the enamel–cement interface predominated; with phosphoric acid, failures occurred mainly at the cement– ceramic interface. In the color evaluation, nominal exploratory differences were observed in ΔL* (p = 0.042) and Δa* (p = 0.008), with no difference in Δb*, ΔEab (p = 0.363), or ΔE00 (p = 0.277); an exploratory equivalence analysis (TOST) was compatible with global equivalence between the strategies. In conclusion, for the materials tested, the universal adhesive used alone did not reproduce the mechanical performance of the separate ceramic primer, and omitting enamel etching markedly reduced bond strength, whereas the global color change was similar between the strategies. In the laboratory setting, maintaining phosphoric acid etching of enamel and the separate ceramic primer maximizes bond strength.