Altered physical-chemical properties of home bleaching gels after an accelerated stability study and their effects on tooth enamel.

ABSTRACT

OBJECTIVES: To investigate the physical-chemical properties of home bleaching gels based on Carbamide Peroxide (CP) and Hydrogen Peroxide (HP) after accelerated stability (AS) and its effects on enamel. MATERIALS AND METHODS: A total of 360 bovine teeth blocks were divided (n = 12) Control, CP10%-Whiteness Perfect, CP10%-Pola Night, HP7.5%-Pola Day, and HP7.5%-White Class Calcium. Microhardness (KHN), roughness (Ra), color (ΔE and ΔE00), hardness, compressibility, elasticity, cohesiveness, adhesiveness, weight, pH, and calcium (Ca) quantification in enamel were analyzed without storage of the bleaching gels and after AS at 1 and 3 months. Data of Ca, KHN, and Ra were analyzed through mixed models for repeated measurements and the Tukey-Kramer test. Values of weight, hardness, compressibility, and elasticity were analyzed with two-way ANOVA and Tukey's test. ΔE/ΔE00 data, cohesiveness, and adhesiveness were analyzed with Kruskal-Wallis and Dunn tests (α = 0.05). RESULTS: Groups subject to AS had lower ΔE and ΔE00 compared to those without storage. Lower KHN and higher Ra values were found after bleaching treatment in all groups compared to controls. Higher amounts of Ca were found on the first day of evaluation in the gels subject to AS for 3 months, regardless of the bleaching agent used. CONCLUSIONS: Incorrectly stored bleaching gel accentuates adverse effects on enamel. Temperature and humidity interfere directly with the chemical stability of bleaching agents, reducing their properties. CLINICAL RELEVANCE HP is an unstable oxidizing agent when stored at high temperatures. Therefore, pH becomes more acidic and potentiates the demineralizing effect on enamel.