OBJECTIVES: This study aimed to synthesize and evaluate the in vitro effects of varying concentrations (0.25%, 0.5%, and 1%) of calcium-substituted sodium trimetaphosphate (CaNaTMP) incorporated into 17.5% and 35% hydrogen peroxide (HP) whitening formulations on enamel color change, microhardness, morphology, surface roughness, mineral content, and transamelodentinal diffusion of HP. MATERIALS AND METHODS: Enamel/dentin discs (N = 288) were allocated into eight groups according to the bleaching gel: (1) 35% HP
(2) 35% HP + 0.25% CaNaTMP
(3) 35% HP + 0.5% CaNaTMP
(4) 35% HP + 1% CaNaTMP
(5) 17.5% HP
(6) 17.5% HP + 0.25% CaNaTMP
(7) 17.5% HP + 0.5% CaNaTMP
and (8) 17.5% HP + 1% CaNaTMP. Gels were applied for 40 min across three weekly sessions. Evaluated parameters included total color change according to CIELab (ΔE), CIEDE2000 equation (ΔE RESULTS: All bleaching gels caused significant color changes after treatment (p <
0.001), with similar ΔE, ΔE CONCLUSIONS: This study demonstrated that the addition of CaNaTMP to bleaching gels with 17.5% and 35% HP reduces mineral loss, changes in roughness, and surface morphology of enamel, as well as decreasing trans-amelodentinal diffusion of H₂O₂, without compromising the bleaching efficacy. The incorporation of 1% CaNaTMP was particularly more effective in protecting the dental enamel. CLINICAL RELEVANCE: The incorporation of CaNaTMP to 17.5% and 35% HP bleaching gels enhances safety and biocompatibility by reducing enamel damage. The lower HP concentration (17.5%) combined with 1% CaNaTMP provides a safer whitening option, maintaining effectiveness while minimizing adverse enamel changes, aimed at improving patient comfort during treatment.