Whitening toothpastes are ineffective in recovering color from previous dental bleaching - In vitro study

The objective of this study was to evaluate the influence of whitening toothpastes on color recovery after dental bleaching and on enamel microhardness. Sixty bovine enamel blocks (6×6×2 mm) were obtained and bleached with 40% hydrogen peroxide (N = 30) ([40% HP] Opalescence Boost 40% PF) or 10% carbamide peroxide (N = 30) ([CP 10%] Opalescence 10% PF). The specimens were subjected to coffee staining for 14 days. The specimens were subdivided into six groups according to whitening treatment and whitening toothpaste (n = 10) and submitted to 14,600 mechanical brushing cycles: 3% HP whitening toothpaste (Colgate Luminous White Glow), whitening toothpaste containing activated charcoal (Colgate Luminous White Activated Charcoal), and conventional toothpaste (Colgate Triple Action). Color changes (ΔE00) and the difference in the Whitening Index for Dentistry (ΔWID) were evaluated after whitening, coffee staining, and mechanical toothbrushing using a spectrophotometer CM-3700A (Konica-Minolta), as well as microhardness (HMV-2; Shimadzu). Data were analyzed by 2-way ANOVA (ΔE00, ΔWID), 2-way ANOVA with repeated measures (microhardness), and Tukey's test (α = 0.05). No significant differences were observed in ΔE00, regardless of the toothpaste used. The ΔE00 and ΔWID mean values were statistically higher for the groups whitened with 40% HP. No difference was observed among the toothpastes when whitened with 40% HP. When whitened with 10% CP, the traditional toothpaste obtained a higher ΔWID mean value. For microhardness, traditional toothpaste showed the highest KHN mean value. Whitening toothpastes did not influence the color recovery or reduce the microhardness of dental enamel.