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

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.

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 (ΔE_ab, ΔE₀₀ and ΔWI_D) 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).

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.

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.

Evaluating gels after 72 h may supports safe reuse, maintaining efficacy while reducing material waste.