Dental caries (tooth decay) is the destruction of the hard tissues of the tooth, enamel and dentine in the crown of the tooth, cementum and dentine in the root. Its aetiology is bacterial in conjunction with dietary sugars and starches. When sugar is consumed, bacteria in plaque produce acids lowering the pH (increasing the level of acidity) in the mouth lasting for up to an hour. During this time, minerals are lost from the teeth before the pH returns to normal due to the protective properties of saliva (salivary buffering). The more frequently sugar is consumed, the more frequently the teeth are exposed to acid attack and consequently the risk of decay increases, especially with frequent sweet snacks between meals.
Prevention is vital and geared towards thorough daily plaque removal by brushing and interdental cleaning (we demonstrate good brushing techniques in our video material). Fluoride is of great benefit whether it is standard fluoride toothpaste, high concentration fluoride toothpaste prescribed by a doctor or dentist, or in the form of a fluoride varnish applied 3 monthly by a dentist or hygienist. Fluoride is present in most proprietary toothpastes in the form of either sodium fluoride or stannous fluoride. In either form, F- ions easily exchange with OH- groups in the material making up the main structures of the crown of the tooth, hydroxyapatite. Hydroxyapatite is an inorganic material with a complicated superstructure (closely related to the materials making up bones). Partially fluoridated versions of hydroxyapatite tend to be much harder materials than ordinary hydroxyapatites, as well as being less soluble at lower pH values (hence the reduced susceptibility to tooth decay).
With either of the toothpastes it is important to spit out after brushing, but not to rinse. In this way the saliva becomes saturated with fluoride and the fluoride ions remain around the teeth for much longer. For those who have no problems with chewing, chewing xylitol gum after meals may help to stimulate saliva and return pH levels to normal more quickly, also reducing the risk of dental decay.
There are a number of factors that can increase susceptibility to dental decay which are common after radiotherapy in the head and neck region. Lack of saliva due to severe xerostomia (dry mouth) as a consequence of radiation damage to salivary glands prevents the protective properties of saliva to operate in protecting teeth, while at the same time the bacterial plaque on hard surfaces in the mouth becomes concentrated and much more difficult to remove. In addition, any recession of the gums results in root surfaces being exposed, the outer layer of which is cementum, a much softer, more porous structure than tooth enamel and very prone to acid attack and decay. After radiotherapy where it is essential to avoid dental extractions, this can be a serious problem.
Another situation where dental decay can be an issue is severe trismus when people still have some or all of their natural teeth. If severely impaired mouth-opening is a long-term problem, this can make cleaning of the internal surfaces of the teeth very difficult if not impossible. A similar problem is often encountered, short-term in nature, after trauma or surgery where the teeth are wired to prevent movement in an injury site (not very common nowadays). Plaque removal is still important, but a daily oral hygiene regime will need to be tailored to an individual’s specific needs (see our video materials for some tips and tricks).
In many such circumstances a daily mouthwash can be helpful. Chlorhexidine mouthwashes are good at helping to control plaque build-up in the mouth where brushing is not viable and are generally useful in infection prevention after oral surgery. Chlorhexidine mouthwash should not be used immediately after brushing teeth as it negates the benefits of fluoride toothpastes (some high-concentration fluoride mouthwashes can also be of benefit in decay prevention by saturating the saliva with fluoride). Some chlorhexidine mouthwash preparations stain teeth and tongue in some people. These stains are not permanent and are easily removed; there are preparations available that do not stain teeth and tongue.
One important aspect about using a mouthwash in general is to ensure that it is alcohol free: an alcohol-containing mouthwash will further dry out a dry mouth.