Shear Bond Strength of a Universal Adhesive to Enamel at Immediate, 7-Day and 14-Day Intervals After 40% Hydrogen Peroxide Bleaching: An In Vitro Study

High-concentration in-office bleaching reduces resin–enamel bond strength, but the required waiting interval remains unresolved, and much evidence predates universal adhesives. This study evaluated the apparent shear bond strength (SBS) of Palfique Universal Bond (Tokuyama Dental, Tokyo, Japan; lot no. 162E01), in etch-and-rinse mode after 37% phosphoric acid etching, at three intervals after 40% hydrogen peroxide bleaching. Eighty human premolar slabs, stored in artificial saliva at 37 °C, were allocated to a 14-day unbleached reference or to bleached specimens bonded immediately, at 7 or at 14 days, with one of two composites (n = 10 per group). Experimental condition significantly affected SBS (p < 0.001); no statistically significant effect of composite material or material × condition interaction was detected. Pooled across composites, SBS fell below the reference (4.62 MPa) after immediate bonding (4.18 MPa), at 7 days (3.81 MPa), and at 14 days (4.04 MPa; all adjusted p ≤ 0.034). With approximately 80% power to detect 0.55 MPa against observed differences of 0.14–0.37 MPa, the interval comparisons are inconclusive rather than evidence of equivalence; lacking time-matched controls at earlier intervals and conventional absolute values, the findings are within-study comparative evidence. Against the time-matched 14-day unbleached reference, however, apparent SBS remained significantly lower at 14 days, and restoration to the unbleached reference level should not be assumed for the protocol tested.