Fluoride and dental health
Anthony Blinkhorn and Kareen Mekertichian
Fluoride has made an incredible impact on the oral health of millions of adults and children. Physiologically, fluoride is a unique member of the halogen family, in that it is termed a ‘seeker of mineralized tissue’. It is this affinity with mineralized tissues which explains how fluoride can strengthen the teeth and prevent or heal dental caries.
Mechanism of action
Concepts of how fluoride prevents caries have changed markedly since the first water fluoridation schemes were introduced in the USA in the late 1940s and early 1950s. When ingested systemically, fluoride is incorporated into developing tooth enamel. The fluoride ion displaces some hydroxyl groups in hydroxyapatite to form fluorapatite. The smaller anion causes crystal stress but results in a significantly less soluble material. Initially, researchers focused on the systemic effect of fluoride as the key factor in the reduction of dental caries. However, the evidence for the systemic effect has been superseded by the realization that the reaction of the fluoride at the microenvironment of the plaque enamel interface encouraging remineralization is of major significance in terms of reducing the levels of dental caries (Centres for Disease Control and Prevention, 2001).
The important points to remember are:
• Fluoride has some effect on the glycolytic pathway of oral microorganisms reducing acid production and interfering with the enzymatic regulation of carbohydrate metabolism. This reduces the accumulation of intracellular and extracellular polysaccharides and leads to lower volumes of plaque.
There are three ways to offer fluoride on a community-wide basis: utilizing water, salt and milk.
The natural level of fluoride in drinking water is very variable. However, in reticulated community water supplies that are fluoridated, the concentration of fluoride is adjusted to approximately 0.8–1 ppm.
The majority of International Health Agencies agree with the World Health Organization in support of the continuation of community water fluoridation, as it is an effective, efficient, socially equitable and safe population approach to caries prevention.
The reduction in dental caries in fluoridated communities ranges from 20% to 40%, which is considerably less than was the case when it was first introduced in the USA because of the general increase in availability of fluoride from other sources (Downer and Blinkhorn, 2007). However, when fluoridation programmes have been discontinued, there is rapid increase in dental caries within a short time frame (Burt et al., 2000).
There are a number of points of which many members of the public are unaware when considering the value of water fluoridation:
The market for bottled water has grown rapidly in the last decade, and for many individuals water consumption from this source may have fully replaced reticulated water. The fluoride content of bottled water is usually very low, and consumers of bottled water in fluoridated communities will miss out on the benefits of fluoride.
Some water filters may remove fluoride, although this is mostly limited to those with reverse osmosis, bone or charcoal filters, distillation or ion exchange. Normal membrane filters will not remove a small ion such as fluoride. Ceramic and carbon filters retain fluoride in the filtered water. Filters that do not remove fluoride should be clearly labelled.
Salt enriched with iodide has been used in many countries as an effective means of preventing goitre. It was a logical step to include fluoride in domestic table salt. It has the advantage of offering choice and does not encourage salt consumption as it is marketed as an alternative to the standard product. The amount of fluoride added is 250 mg F−/kg salt (250 ppm).
Switzerland was the first nation to pioneer salt fluoridation and it is now available in Spain, Hungary, France and parts of Brazil. It is certainly a practical alternative to water fluoridation, but the research base is much more limited on its absolute effectiveness, especially now that fluoride toothpaste is readily available.
Bovine milk is used as a food for babies and young children, plus in many countries free milk is offered to children at school. These positive points were noted by researchers as a potential way to supplement children’s fluoride intake.
Despite its practical simplicity, milk fluoridation has not been implemented on a wide scale, mainly because of logistical difficulties and the fact that fluoride toothpaste is readily available. It may well have a place in developing countries, where the milk will improve nutrition as well as offering the benefits of fluoride.
Topical fluorides for home use
Lifetime protection against dental caries results from the continuous presence of fluoride in low concentrations, that will enhance the remineralization of white spot lesions, control initial invasive carious lesions and limit lesions occurring around existing restorations for both adults and children (Adair, 2006). An optimal concentration of fluoride each day at both the plaque/enamel interface and in saliva, will help minimize the risk of caries. Factors that should be considered when advising on a fluoride regimen include:
Of all the different ways of offering topical fluoride, the most common and simplest way in which to maintain elevated fluoride concentrations at the plaque/enamel interface, is the use of a toothpaste containing fluoride. Fluoride is added to toothpastes in one of the following forms:
The use of fluoride toothpastes has led to a 25% reduction in the prevalence of caries in many countries (Davies et al., 2002). It is recommended that children should brush twice a day with a toothpaste containing an appropriate concentration of fluoride, preferably last thing at night before bed and on one other occasion, ideally after breakfast. It is essential to ensure all parents are aware that vigorous rinsing after brushing will reduce the preventive effect of the toothpaste because the active agent ‘Fluoride’ will be washed away.
Advice on the type of toothpaste which young children should use, in terms of fluoride concentration is problematic (Franzman et al., 2006), as international guidelines differ. Members of the dental team must familiarize themselves with the guidelines appropriate for their own country and practice location. In Australia and the USA, fluoridation of public water supplies is quite common, whereas in Europe there are only a few community water fluoridation schemes (Walsh et al., 2010). However, there are a number of factors that health professionals must consider when offering advice to parents on fluoride toothpaste usage, namely:
• Young children (up to the age of 7 years) should be supervised when brushing as this monitors toothpaste usage, has been associated with greater reductions in dental caries and reduces the chances of fluorosis in the upper anterior teeth.
• Children over 10 years of age and considered to be at high risk of developing caries or have active carious lesions may be prescribed a toothpaste containing >1400 ppm fluoride. The availability of these high fluoride toothpastes varies from country to country. They may only be available on prescription in some locations.
• Brushing with a fluoride toothpaste is at the heart of any preventive programme. There is no ‘right way’ to brush. The important goal is to make sure the toothpaste is used twice a day and not washed away by rigorous rinsing.
Fluoride mouth rinses
In some countries, school-based daily fluoride mouthrinse (0.05% sodium fluoride) programmes have been used to offer protection from dental caries. While rinses do offer a benefit, their use as a public health measure has declined for a number of reasons:
Nevertheless, in some countries where people live in remote locations and toothpaste is expensive, local school-based fluoride rinsing programmes can be an effective public health measure. Members of the dental team may also offer fluoride rinses to individual patients with active caries, provided they are over 6 years of age.
Two types of rinses are available.
The most popular rinse is the daily one as it is simpler to rinse on a regular basis than trying to remember to use a product just once a week. Also maintaining a low level of fluoride in the mouth on a daily basis fits in with our understanding of the mode of action of fluoride on the remineralization of enamel.
It is important to use the rinse at a different time to brushing with a fluoride toothpaste as using them together does not offer an additive effect. A good time to rinse is when a child returns home from school, as there will be plaque present which incorporates the fluoride and releases it slowly over time.
There are a number of patient groups who will benefit from the prescription of a daily fluoride rinse:
Fluoride rinses are not recommended for children before the eruption of the permanent incisors because many younger patients will swallow the rinse and this may cause fluorosis.
Tooth mousse or casein phosphopeptide-amorphous calcium phosphate crèmes
CPP-ACP and CPP-ACPF are available as crèmes for topical application at home (Tooth Mousse®; Tooth Mousse Plus®, GC Corp, Japan) to be applied to surfaces at risk of caries, erosion or with white spot lesions. CPP-ACPF releases fluoride, calcium and phosphate ions for local remineralization of enamel (Reynolds, 2008).
The crème is applied to teeth after brushing by smearing across tooth surfaces with a clean finger or cotton-tipped applicator. The crème should not be rinsed out.
At one time, fluoride tablets were widely recommended as a useful caries preventive measure. However, they have been superseded, as fluoride toothpastes now dominate the market and offer a better level of protection from dental caries. In addition, research has shown that compliance with tablet taking regimes is very poor and the consumption of up to 1 mg of fluoride in 1 tablet is linked to fluorosis. Thus fluoride tablets are no longer routinely recommended (Den Besten, 1999; Tubert-Jeannin et al., 2011).
Stannous fluoride gel
A stannous fluoride (SnF2) treatment gel in a methylcellulose and glycerine carrier (marketed as Gel Kam® by Colgate Oral Care) can be used at home for the remineralization of white spot and hypomineralization lesions of enamel (e.g. molar or incisor hypomineralization). Anecdotal clinical reports support the efficacy />