A Critical Review of Modern Concepts for Teeth Whitening
Teeth whitening is a growing interest for many people. With so many options, many patients/consumers aren’t sure what the best options to achieve their whitening goals. This puts pressure on dental professionals to stay informed and up to date on the latest and most effective whitening options. In a review published in August 2019 in the Dentistry Journal, the authors discuss the many options that are currently available along with a few emerging products.1
Staining of the tooth surface is quite a complex event. Chromophores, both organic and inorganic origin, are colored compounds in the tooth that absorb and reflect light. A few examples of organic chromophores include tea, coffee, red wine, and fruits. Inorganic chromophores are metal ions such as iron, copper, and manganese. In some cases, the stain can be a combination of both inorganic and organic chromophores are present, one such instance would be in the presence of hemoglobin. Hemoglobin contains porphyrin ligand (organic) and iron ions (inorganic) chromophores. These stains are generally considered extrinsic and most can be removed mechanically or chemically.
Intrinsic stains can be a bit more challenging to address. Intrinsic stains occur during development, prior to tooth eruption. Some of the causes include developmental malformations, fluorosis, tetracycline incorporation, and several metabolic diseases and systemic factors. However, in certain circumstances, the intrinsic stain can occur after the eruption. The primary culprit of intrinsic stain after the eruption is pulpal hemorrhage after trauma. These stains are rarely removed completely chemically or mechanically from the outside of the tooth.
In-office bleaching “power bleaching” uses high concentrations of peroxide and water, typically 35 wt%. Special precautions are necessary to prevent damage to the soft tissues. Some patients reported dental pulp irritation after in-office bleaching. In addition to applying the peroxide solution, the treatment is often accompanied by irradiation. Irradiation with a heat lamp is meant to enhance the oxidative action of the peroxide, however, from a chemical viewpoint, this can only enhance the reaction rate but does nothing to change the oxidative effect. Several studies have concluded that there is little to no benefit in using irradiation during in-office bleaching treatments.
Overnight/take-home bleaching is achieved by applying 10-20% carbamide peroxide gel in a customized tray. Due to the lower concentration of peroxide, multiple applications are necessary for visible results. Other at-home bleaching options include paint-on gels and strips. The chemical process that occurs during bleaching is complex. To avoid a lengthy chemical description, the mechanism of action essentially is that the peroxide leads to oxidation of organic chromophores to non-colored organic chromophores so that the light is no longer absorbed making the teeth appear whiter. The overall kinetics of the chemical reaction is still unknown. It is assumed that some if not all organic chromophores are removed after oxidation by subsequent “washing steps”.
Whitening toothpaste is a hot commodity. These kinds of toothpaste often contain abrasives and certain whitening agents. Whitening toothpaste can contain harder abrasives at higher amounts than conventional toothpaste. The abrasives are meant to remove external stains, however, in the process, they can damage the enamel. Commonly used abrasives include silica calcium carbonate and alumina. Abrasiveness can depend on size, hardness, water content, particle shape, and particle size. A newer promising abrasive is particulate hydroxyapatite, it is biomimetic (meaning it mimics the biochemistry of the tooth) and has a whitening effect not only due to the abrasiveness but also because the particles attach to the enamel. The RDA (radioactive dentin abrasion) is the scale often used to determine the abrasive performance of toothpaste. In general, an RDA below 250 is acceptable. Though other factors should be considered like toothbrush filaments.
Bleaching compounds in toothpaste are peroxide-based. Due to the potential harm, they are regulated. The allowable amount of hydrogen peroxide in cosmetic toothpaste is limited to 1 wt%; in the EU it is limited to 0.1 wt%. It is questionable if this low concentration along with the short contact of the teeth during brushing will lead to enough oxidative power to lighten teeth. There is conflicting evidence, in one study the author concluded whitening toothpaste work primarily by the abrasives and not from bleaching compounds. In another study, the author concluded that toothpaste containing 1% peroxide showed a significant whitening effect, however only in vitro studies were mentioned in this case. In addition to bleaching compounds other whitening agents include surfactants, antiredeposition agents, colorants, enzymes, and polyaspartate.
Currently, a wildly popular ingredient in whitening toothpastes is activated charcoal. It is important to know that activated charcoal in toothpaste has not been studied in detail. Ultimately the efficacy of whitening toothpaste is debated in the literature. In a previous review cited, the author concluded “Although whitening toothpaste can prevent extrinsic tooth stains, the whitening effect obtained seems not to be clinically significant”.
There are some potential risks associated with teeth whitening agents. There have been reports of weakening of the tooth from aggressive bleaching. High concentrations of peroxide can potentially cause structural damage of enamel surface prisms and decrease integration of the calcium phosphate crystals. Though it is notes that a chemical reaction between calcium phosphate and peroxide is unlikely. Sensitivity is the most reported side effect of chemical bleaching; this usually subsides over time. Using products that contain particulate hydroxyapatite or potassium nitrate can help reduce sensitivity. Ultimately, it is undetermined if bleaching leads to long term damage of the teeth.
The authors conclude by saying “the modes of action of many whitening agents in vivo are still unknown. Thus, mechanistic studies are required to understand the mechanisms of action from a chemical and biological viewpoint, which is an important requirement for the development of more efficient teeth whitening formulations.”
How do you determine what whitening products to recommend to patients? Does your office do in-office bleaching? What chemical bleaching process do you prefer for your patients, overnight, strips, in-office, etc.? What whitening products have you used that have given the best results?
- Epple M, Meyer F, Enax J. A Critical Review of Modern Concepts for Teeth Whitening. Dent J (Basel). 2019;7(3):79. Published 2019 Aug 1. doi:10.3390/dj7030079
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