Effectiveness and mechanisms of action of whitening dentifrices on enamel extrinsic stains

Abstract

Whitening dentifrices use different mechanisms for stain removal and prevention. These approaches are abrasives, oxidizing agents, and chemical cleaning agents. The objectives of this in-vitro study were: 1) To compare the whitening effect of commercial whitening and non-whitening dentifrices; 2) To verify the mechanism of action of whitening dentifrices by contrasting two experimental models: chemical model (toothpaste exposure only) and chemo-mechanical (toothpaste exposure with tooth-brushing abrasion). The 256 bovine enamel specimens (10 mm x10 mm) were prepared and partially stained. They were assigned to 8 groups: 6 whitening dentifrices, 1 non-whitening reference dentifrice and deionized water (control); and they were further divided in 2 subgroups (n = 16), chemical and chemo-mechanical. Specimens were exposed to dentifrice slurries 2X/day for 1 min and brushed or not, according to each model. In between dentifrice treatments, specimens were exposed to the staining solution for 5 h. This protocol was repeated for 5 consecutive days and enamel color changes (∆E, ∆L) were measured by spectrophotometry after each day. The abrasivity of the toothpastes was determined using a standard test (ISO 11609). Significantly higher ∆E values (whitening effect) were observed for all groups (p < 0.05), except for the control, when tested in the chemo-mechanical model. In this model, the whitening ability of the toothpastes was mainly determined by their abrasive levels. For the chemical model, no significant differences were observed among groups (p > 0.05). Whitening dentifrices can be effective in preventing and removing enamel surface staining, when associated with tooth-brushing abrasion. This was modulated by the abrasive level of the tested toothpastes, with no chemical action attributed to the chemical agents.