12-Month color stability of enamel, dentine, and enamel-dentine samples after bleaching

The study aimed to quantify the color regression of enamel (E), dentine (D), and combined enamel-dentine (ED) of differently bleached ED specimens over a period of 12 months in vitro. Two ED samples were obtained from the labial surfaces of bovine teeth and prepared to a standardized thickness with the enamel and dentine layer each 1 mm. The ED samples were distributed on four groups (each n = 80), in which the different bleaching products were applied on enamel (1, Whitestrips; 2, Illuminé 15%; 3, Opalescence Xtra Boost) or dentine surfaces (4, mixture of sodium perborate/distilled water). Eighty ED samples were not bleached (control). Color (L*a*b*) of ED was assessed at baseline, subsequently after bleaching and at 3, 6, and 12 months of storage after bleaching (each 20 samples/group). E and D samples were prepared by removing the dentine or enamel layer of ED samples to allow for separate color analysis. Bleaching resulted in a significant color change (DeltaE) of ED specimens. Within the observation period, DeltaL but not Deltab declined to baseline. L* values of E and D samples also declined and were not significantly different from control samples after 12 months, while b* values did not decrease to baseline. Generally, no differences between the bleaching agents could be observed. Color change of enamel, dentine, and combined ED of in vitro bleached tooth samples is not stable over time with regard to lightness. However, yellowness did not return to baseline within 1 year

In vitro evaluation of the whitening effect of mouth rinses containing hydrogen peroxide

The aim of this study was to evaluate the bleaching effect of two mouth rinses containing hydrogen peroxide. Thirty premolars were randomly divided into two groups (n = 15): Listerine Whitening (LW) and Colgate Plax Whitening (PW). The teeth were fixed on a wax plate and with acrylic resin, at a distance of 5 mm between each other, exposing the buccal surfaces. All teeth were stored in artificial saliva for 45 days, being removed twice a day to be immersed for 1 min in each mouthwash, followed by 10-second washing in tap water. The pH of each product was measured. Digital images of each tooth were captured under standardized conditions. These images were cut in areas previously demarcated and analyzed in Adobe Photoshop 7.0 using the CIEL*a*b* color space system. Data were statistically analyzed by a paired t test and an independent samples t test (p < 0.05). The pH values were 5.6 and 3.4 for LW and PW, respectively. Both treatment groups showed a decrease in the b* parameter (p < 0.01), but a decrease of a* was observed only for PW (p < 0.01). While the LW group showed an improvement in lightness (L*) (p = 0.03), the PW group had a decrease in the L* parameter (p = 0.02). Within the limitations of this study, it is possible to conclude that both products caused some degree of whitening; however, extreme care should be taken when using Colgate Plax Whitening, since its decline in luminosity might be due to its lower pH

Chemical Composition and Microhardness of Human Enamel Treated with Fluoridated Whintening Agents. A Study in Situ

BACKGROUND: Dental whitening has been increasingly sought out to improve dental aesthetics, but may cause chemical and morphological changes in dental enamel surfaces. OBJECTIVE: Assess in situ the effects of high-concentration hydrogen peroxide with and without fluoride on human dental enamel using the ion chromatography test (IC) and the Knoop hardness test (KHN). MATERIAL AND METHODS: Nineteen enamel specimens were prepared using third human molars. These specimens were fixed on molars of volunteers and were divided into groups: OP38-Opalescence Boost PF38%, PO37-Pola Office 37.5% and CO-Control group. For chemical analysis (n= 3), the dentin layer was removed, keeping only the enamel, which was subjected to acidic digestion by microwave radiation. It was necessary to perform sample dilutions for the elements fluorine (F), calcium (Ca) and phosphorus (P) for quantification using the IC test. The KHN (n= 5) was performed before and after the treatments. Five indentations were made, separated by 100 µm, for each specimen using a load of 25 gf for 5 seconds in the microdurometer. The data were analyzed using ANOVA with a 5% significance level. RESULTS: The OP38 group had the largest concentrations of F, Ca and P ions. The PO37 group showed the lowest concentrations of F and Ca ions. The average KHN was not significantly different between the OP38 and PO37 groups. CONCLUSION: Enamel whitened with hydrogen peroxide containing fluoride had greater concentrations of F, Ca and P ions. The presence of fluoride in the whitening agent did not influence the enamel microhardness