Do bleaching gels supplied in attachable syringes maintain their bleaching efficacy 72 hours after mixing?

OBJECTIVE: Evaluate bleaching efficacy (BE), hydrogen peroxide (HP) penetration into the pulp chamber, and selected physicochemical properties (HP concentration, pH, and viscosity) of in-office bleaching agents supplied in attachable syringes from different commercial brands, assessed immediately, after mixing and after 72 h of storage. MATERIALS AND METHODS: 150 human premolars were allocated into fifteen groups (n = 10) according to (1) the commercial brand: DSP 35%, Nano White 35%, SSWhite 35%, Total Blanc 35%, HP Blue 35%, Potenza Bianco 38%, and Opalescence 40%; and (2) storage interval: immediate use or 72 h after mixing. One group stored in artificial saliva served as the negative control (no bleaching). HP concentration at both storage intervals was determined by titration, pH using a digital pH meter, and viscosity by rheometer. BE (ΔEab, ΔE00 and ΔWID) was measured with a digital spectrophotometer, and HP penetration (µg/mL) by UV-Vis spectrophotometry. Data were analyzed using ANOVA, Tukey's, and Dunnett's (α = 0.05). RESULTS: HP concentration and pH differed among brands and decreased after storage for most gels. All gels produced significantly greater BE than the control (p < 0.05). Storage time had minimal influence on BE. HP diffusion was material-dependent; Viscosity varied among brands, although most gels demonstrated shear-thinning behavior and storage-related changes. CONCLUSION: Gels showed material-dependent differences in properties, BE, and PH penetration, with minimal 72-hour storage effects on color. However, storage altered HP concentration, pH, and viscosity in some materials. CLINICAL RELEVANCE: Evaluating gels after 72 h may supports safe reuse, maintaining efficacy while reducing material waste.