The effects of whitening toothpastes and agents on extrinsic stain: studies in vitro

Abstract

Background - There are various toothpaste products, available on the market, labelled “whitening". Most of these appear to contain ingredients to inhibit or remove extrinsic stains rather than change natural tooth colour. This type of stain control can be achieved by physical or chemical means. Aims - the aims of these studies was to assess the abrasion, stain removal and stain inhibition of a number of agents. Materials and Method - 8 separate studies were conducted which involved 44 agents and water, which was used as the negative control and oxidising mouthrinses as positive controls. Out of the 44 agents 7 of these were experimental formulations and 2 were oxidising mouthrinses. The formulations and controls varied in each study. For stain removal (Studies 1-5 and 7) acrylic blocks were cycled through saliva/chlorhexidine/ tea to an optical density of at least 2.0. The stained specimens were then put into groups of 6 and exposed to standard slurries/solutions for 5x1 minute time periods with optical density measurement taken at each time point. The stain inhibition experiment (study 6) used the saliva/product/chlorhexidine/tea model with an optical density reading after each cycle, and cycles were repeated until a mean optical density of 2.0 was obtained with one treatment. Finally for the abrasion experiment (study 8), acrylic samples were inserted into a toothbrush machine, with standard toothpaste slurries and measurements were taken after 1,000, 5,000, 10,000, 15,000 and 20,000 strokes. Results - 3 toothpaste products and 2 experimental toothpastes removed 100% stain by 5 minutes with the oxidising mouthrinses and one other experimental formulation achieving >90%. The majority of other products removed less stain than the positive controls and some were little different from the negative control, water. For the stain inhibition experiment (study 6), one product produced 100% inhibition and another >80% inhibition. The remaining products produced <50% to <20% inhibition. Lastly the abrasion experiment (study 8) the toothpaste which, approached the nearest linearity was Colgate Whitening where increments to each 5,000 strokes was approximately 5 microns. With the exception of this particular toothpaste, the range of abrasion depth for the other products was quite narrow and ranged from approximately 5-9 microns, with the majority lying within 6-8 microns. Water produced negligible effects on acrylic being just outside the acceptance profile of ±0.3 microns after 20,000 strokes. Conclusion - only a very small number of actual products approached complete stain removal within the test period selected, which suggests the majority are unlikely to achieve their claimed benefits through chemical stain removal. Stain inhibition of note was only seen with 2 products suggesting the majority of pastes would not achieve significant chemical stain inhibition. In the abrasion experiments (study 8) most but not all smokers toothpastes showed substrate loss greater than the conventional fluoride toothpaste but most products appeared to lay within international standards limits. The results of these studies may be extrapolated with caution into clinical effects until in vivo or in situ data becomes available.