The interest in tooth whitening has exploded, and it seems just about everyone wants a more attractive smile to feel their confident best, as seen by the popularity of cosmetic dentistry procedures (e.g., veneers; in-office bleaching) and at-home products like whitening strips. Tooth shade dulling and discoloration can be the consequence of natural aging wherein the enamel thins and becomes more translucent after years of wear, or from other intrinsic factors.136 It can also commonly stem from extrinsic staining like that generated by smoking, dark beverages, and inadequate oral hygiene.137
Fresh from a prophylaxis or bleaching treatment, patients will want to retain their whiter smiles. However, biofilm and dietary-driven (e.g., coffee and tea tannins) extrinsic stains tend to reaccumulate rapidly. Many seek out dentifrices formulated for stain removal and/or whitening as an affordable means of enhancing or maintaining their preferred shade. What exactly are ‘whitening’ toothpastes? These products typically contain ingredients that work in one (or a combination of both) of the following ways: mechanical stain control and chemical stain control.
Mechanical Stain Control Toothpaste abrasive systems are the foundation of a dentifrice’s ability to physically remove extrinsic stains during brushing. As discussed in the What Exactly is Dentifrice? section, commonly used abrasives like hydrated silica, calcium carbonate, and sodium bicarbonate have been shown to be safe and effective in removing surface stains with adequate, regular toothbrushing.138 See below: Toothpaste Abrasivity and Safety for more information. Other ingredients can serve indirectly to augment the mechanical stain removal leading to whiter teeth. Tartar control agents like zinc citrate reduce calculus buildup which has a propensity to incorporate stain into its rough, porous structure.
Toothpaste Abrasivity and Safety
Toothpaste abrasives are clearly integral to effective cleaning, and patients are motivated to brush when they experience cleaner, smoother teeth and fewer surface stains from the mechanical polishing and stain lifting action of abrasives. But when selecting a toothpaste, how important is its RDA (relative dentin abrasivity) number? Does lower mean ‘better’ and safer to enamel?
A laboratory-confirmed limit of less than 1 mm of confirmed dentin loss for every 100,000 brushing strokes was the abrasive safety standard set decades ago, and became the basis for today’s industry-wide abrasivity testing methods.139 It had been determined that over 90% of stain removal could be accomplished without higher levels of abrasivity in a toothpaste. In the 1970s an ADA-led group partnering with industry researched and developed the now standard RDA evaluation method. In 1980 in the anti-caries monograph, the FDA set a tooth wear limit for anti-caries dentifrices of 2.5 times the abrasiveness of the laboratory reference abrasives (e.g., ≤250), based on extensive real-life data and exaggerated usage by patients of varying ages, brushing styles, etc. Put another way, this limit provides assurance that usage of a toothpaste with ≤250 RDA won’t result in greater than 1mm of dentin wear and is safe for a lifetime of usage.139
Importantly these laboratory methods are not, and weren’t intended to be, representative of real-life wear conditions. Toothpastes range in RDA values. Generally speaking, a higher abrasivity level dentifrice will remove more stain and enhance whitening and have a higher PCR (pellicle cleaning ratio) measure. All toothpastes with the ADA seal of approval have an RDA below 250 and are therefore recognized as containing sufficiently gentle abrasive systems for cleaning without undue harm to hard tissues. The ADA does not acknowledge different classes of toothpastes as being more or less safe for use based on their relative RDA values. As long as they meet the standard of ≤250 they are considered equally safe for long-term daily use.
Chemical Stain Control and Whitening There are two potential mechanisms by which chemical agents in dentifrices lighten teeth. One means is oxidative via disruption of carbon bonds within the color-reflecting materials of stain to effectively lighten the stain for a whiter appearance.140 Hydrogen peroxide is an example of an agent that works this way. Historically it has been challenging to formulate in a dentifrice and provide meaningful whitening efficacy at the customary 1% concentration and clinical trial effectiveness results have been mixed.19 Recently, however, toothpastes have been introduced with higher peroxide concentrations. Colgate Optic White became the first toothpaste to earn the ADA Seal of Acceptance in the home bleaching category.141 Crest HD has a two-step system to ensure stability of the 3% hydrogen peroxide for maximum effectiveness.142
A second chemical mechanism can be found with agents like polyphosphates for both lifting and removing existing stain and also preventing new stain uptake and adherence to the tooth surface by displacing stain molecules from binding sites on the tooth surface and the pellicle. An example of this ingredient is sodium hexametaphosphate (also a tartar control agent) and is found in some marketed whitening dentifrices.143
Two ingredients with a shorter history and more limited usage in toothpastes marketed to whiten teeth than those reviewed previously may be mentioned. Blue covarine is a blue pigment that is applied to the enamel in a dentifrice during toothbrushing, reporting changing the tooth color – as evaluated by the L*a*b* color system – from yellow to more blue, for an immediate effect in making teeth appear whiter.144 Activated charcoal, a porous form of carbon, can augment a toothpaste’s abrasive system in fighting surface stains but does not provide a bleaching action. A literature review published in the Journal of the American Dental Association concluded that more clinical research establishing charcoal’s whitening effectiveness is needed.145