Stain Control/Whitening Agents
Stain control and whitening are key benefits of modern dentifrices. These are accomplished via ingredients that target specific types of tooth stain. Stains can be classified as extrinsic (surface stains) or intrinsic (below the enamel surface), and their management is based primarily on that classification (Table 3). Dentifrices primarily work against extrinsic stains. Bleaching products that contain hydrogen peroxide (i.e., whitening strips) or carbamide peroxide (i.e., dental office bleaching trays) and allow longer contact time with the dentition address intrinsic stains as well as extrinsic stains.48,71
Table 3. Tooth stain: Sources and treatments of extrinsic and intrinsic stains.48
|Sources of Stain||Agents to Remove/Prevent Stain|
|Extrinsic tooth stain||Daily diet (coffee, cola, tea, red wine)|
Poor oral hygiene
|Intrinsic tooth stain||Natural aging of dentition|
Tetracycline use in children
Prolonged tobacco use
|Peroxide (hydrogen, carbamide)|
Extrinsic stain. Despite being extremely hard, the tooth’s surface can be stained. Extrinsic (surface) stains can generally be relatively easily removed on a daily basis by proper tooth brushing with a dentifrice. If extrinsic stains are not frequently removed, they can firmly attach to the tooth surface, and may require a professional cleaning (prophylaxis) for their removal. Surface stains can be removed daily through either physical or chemical action, as described below.48,71
Physical action. Most dentifrices contain mild abrasives that help clean precipitated stain particles from the tooth surface, controlling surface stains with home care. While dentifrice abrasives are desirable to keep stains off teeth, they are designed to not wear down the tooth enamel over time with repeated brushing.72
The abrasivity of dentifrice is measured in terms of Relative Dentin Abrasivity, or RDA. This rating was introduced in the early 1970s and is used by professional dental societies and boards of health to rate the abrasivity of commercial dentifrices.72,73
RDA values are obtained in the laboratory by comparing the amount of tooth structure worn away by a standardized tooth brushing protocol using any given dentifrice with that of a standard dentifrice. The standard protocol integrates factors such as pressure, time, temperature, and humidity. Because dentifrices with lower RDA values are less abrasive, they also tend to remove less surface stain. The International Standards Organization (ISO) specification states that a dentifrice should not exceed an RDA of 250, which is considered safe for hard tissues for a lifetime of use. Although there is a wide range of RDA values for various dentifrices, there are no relative degrees of safety between 0 and 250. In other words, a dentifrice with an RDA of 200 is as safe as one with an RDA of 50 for daily usage. Having an effective abrasive system in a dentifrice is important for cleaning the teeth and removing extrinsic stain.74
Fluoride ions are very reactive and can interact with common dentifrice abrasives, rendering the fluoride inactive for caries control. Also, many dentifrice abrasives have a very porous, negatively charged surface that can bind many dentifrice ingredients (e.g., stannous), lowering their bioavailability. For this reason, formulating dentifrices with the right abrasive is critical to achieving the desired benefits of other ingredients (Table 4).
Chemical action. Polyphosphates, which are dentifrice ingredients used to control calculus, also target extrinsic stain. One of the most effective ingredients with this dual action is SHMP, which is used in several marketed dentifrices. SHMP controls stain with a chemical action. Stain molecules, or chromogens, are usually negatively charged molecules; they have an affinity for positively charged ions like calcium (Ca2+) that reside in the tooth enamel and cross-link pellicle proteins. SHMP is also negatively charged, with a strong affinity for calcium. SHMP can displace stain molecules from calcium binding sites. It binds to the tooth surface and integrates into the pellicle to prevent additional stain molecules from binding (Figure 19).48,49,75
Table 4. Abrasives: Commonly used dentifrice abrasives are presented along with compatible fluorides below.
Abrasive Compatible Fluoride Alumina SMFP Calcium carbonate SMFP Calcium pyrophosphate SMFP, NaF, SnF2 Dicalcium phosphate dihydrate SMFP Silica SMFP, SnF2, NaF
Figure 19. Stain Removal and Prevention.
Negatively charged SHMP molecules displace negatively charged stain molecules from positively charged binding sites (i.e., Ca2+) in the pellicle and on tooth enamel. This both removes existing stain and helps prevent future stains from adhering.
Intrinsic stain. Intrinsic stains are stains and discolorations that are located below the enamel surface. Due to their diverse etiology, intrinsic stain treatment varies with the cause. Bleaching is usually used to remove or minimize intrinsic discolorations. The most popular bleaching agent is hydrogen peroxide (H2O2), in concentrations that range from 3% – 35%. Typically the higher concentration products are used for in-office bleaching, whereas products with 15% or lower concentrations are often used in home-applied whitening protocols (e.g., whitening strips).71,76,77 Whitening efficacy is dependent upon both hydrogen peroxide concentration and contact time with the dentition. Dentifrices typically do not remove intrinsic tooth stain because longer contact times are needed than what is achieved while brushing the teeth. Although some dentifrices or gels on the market for toothbrushing do contain hydrogen peroxide, concentration and contact time do not seem to be high enough to deliver intrinsic whitening. Rather, these products whiten teeth by the bleaching of surface stains.
Video 9. Formation of Extrinsic Stain.
Video 10. Removal of Extrinsic Stain.
Video 11. Inhibition of Extrinsic Stain.