The Science of Teeth Whitening
So how exactly does teeth whitening work? There are two ways in which teeth whitening occurs. By acting on the tooth stains on the outer layer of the tooth and below the enamel surface and/or preventing new stains from occurring. This is achieved by stain removal, stain bleeching and stain protection.
The Removal of Surface Stains
The act of stain removal whitens teeth by using chemical and physical actions, such as abrasion, chemical stain disruption and stain removal. These different actions either destroy or disrupt the stain at the top of the enamel, exposing cleaner, whiten enamel. Several teeth whitening products base their benefits on these types of actions.
- Teeth whitening pastes contain special silica molecules that polish the enamel.
- Teeth whitening pastes and rinses can also contain sodium hexametaphosphate (SHMP) that helps prevent the formation of future stains and disrupts the stain pellicle, facilitating its removal.
- Toothbrushes remove stains on the outer layer of the tooth by the mechanical action of the bristles on the tooth surface.
The Removal of Stains Beneath the Enamel
To remove stubborn stains that accumulate below the enamel surface, bleaching is an appropriate option. Bleaching is a chemical process in which colour is eliminated by oxidation of stain molecules. The bleaching power of the different teeth whitening products varies according to their particular concentration of hydrogen peroxide, a bleaching agent commonly used in whitening procedures at the dental office and in home teeth whitening kits such as Crest 3D Whitening Strips.
How White is White? Colour Measurement
Colour is a subjective response of the observer to the physical interaction of the object of view with light. This subjectivity is seen when describing tooth colour. Researchers have noted that aesthetic aspects of tooth colour are difficult to quantify, making tooth colour perception highly prone to individual variation. Disagreement in shade matching the same tooth has been widely observed, both between professionals and when the same professional is grading the colour of the same tooth at different occasions.
As it is particularly important to scientifically track the success of new technologies that whiten teeth, a large body of research has been conducted to objectively measure the color of the tooth.
While a variety of scales and measurement techniques have been used to assess tooth colour, some may be subjective and non-linear, making progress tracking difficult. A common method of measuring tooth colour utilises shade guides, such as the Vita Shade Guide in which the tooth and the guide are observed simultaneously. The results of using this guide depend on several factors, including the observer’s experience, external light and the observer’s physiological condition.
A more successful mechanism of measuring colour was developed by the Commission International de l’Eclairage (CIE), which defined a colour space CIE Lab using the accepted theory of colour perception based on three separate colour receptors: blue, red, and green. With this system, colour differences can be objectively expressed in units that can be related to both visual perception and clinical significance.
This methodology has been successfully applied to determine the efficacy of teeth whitening systems by transforming digital high-resolution images of anterior dentition of the teeth taken with standard polarised lighting conditions into numerical values. The whitening benefit is defined as a decrease in b (decrease in yellowness), decrease in a (decrease in redness) and increase in L (increase in lightness).