JOURNAL OF THE ROYAL SOCIETY OF MEDICINE Volume 88 September 1995

The role of fluoride toothpastes in the prevention of dental caries

William H Bowen BDS PhD

J R Soc Med 1995;88:505-507 Keywords: toothpaste; sodiumfluoride; sodium monofluorophosphate

There appears to be no doubt that, used appropriately, Ambient levels of fluoride in the mouth are related to sodium fluoride (NaF) and monofluorophosphate (MFP) are both the prevalence and incidence of caries7. The fluoride effective caries-preventive agents. Extensive evidence exists ion can exert its caries-preventive action through several that the prevalence of caries has declined over the past 20 different mechanisms, which include effects on bacterial years in most industrialized countries, and this contribution metabolism, though these are probably not the primary to the improvement of oral health by fluoride dentifrices has influences. It also influences the synthesis of extracellular recently been recognized by the World Health polysaccharide, sugar transport system, enolase, and Organization1. In England and Wales, the percentage of ATPase, but, in contrast to NaF, MFP is essentially toothlessness has declined in 35-44 year olds from 22% to without effect on these systems. 3% and in 65-74 year olds from 79% to 56%24; such data The main effect of the fluoride ion is to promote are typical of industrialized countries, where an increasing remineralization of early caries, and prevent number of people retain their natural teeth until old age. demineralization: extremely small amounts have major The contribution of toothpaste to dental health is therefore effects on these processes. However, in the mouth, MFP not confined to children. In the USA, the decline in the has to be broken down to release fluoride whilst the fluoride prevalence of caries was not detected until 60-70% of the ion in sodium fluoride is freely and totally available as soon population were using a fluoride toothpaste. In the Isle of as it is placed in the mouth. In the absence of phosphatases in Lewis-a community which has little movement of its an in vitro system, MFP will release fluoride very slowly and school population and drinking water containing less than will not exert an effect comparable with that shown by NaF. 0.1 ppm fluoride-epidemiological studies by King in 19375 Marsh8 states that the anti-caries effect of fluoride is showed the mean decayed, missing and filled teeth (DMFT) through its ability to affect de- and remineralization of of 11 year olds to be 2.1. This increased substantially over the enamel: it may also have some metabolic effects on plaque, next 40 years to 5.7, but since 1971 and the introduction of and thus help stabilize pH values of plaque during periods of fluoride dentifrice, has declined to 1.7 in 19935. Though the acid challenge. The anti-bacterial effect of fluoride will prevalence of caries continues to decline in some depend on its concentration, but also on the local pH, so communities, there is some evidence that the caries level, that as this falls, there may be an increase in the particularly in 5 year olds, is now stabilizing. Thus, it is bioavailability of bound fluoride and in the amount of essential to continue to promote caries preventive fluoride present as hydrogen fluoride (HF), which will programmes at both an individual and community level. markedly increase the ability of fluoride (as HF) to pass Water fluoridation and fluoride toothpastes, which were through a bacterial membrane, get inside the cell, and exert introduced in the UK in 1970, appear to have an additive inhibitory effects. At pH7, much fluoride is needed to inhibit protective effect. O'Mullane6 compared the prevalence of the growth of bacteria, but at pH5, there is a 50-fold caries in the Republic of Ireland, where drinking water is increase in the sensitivity of some of the bacteria to fluoride. fluoridated, with Northern Ireland, where it is not. In subjects who consume excessive sugar, increased levels of Fluoridated toothpaste is, however, commonly used in cariogenic bateria such as Streptococcus mutans and lactobacilli both countries. Although caries prevalence in the Republic is are found. Even a small reduction in terminal pH and in the lower overall, there has also been a significant reduction in rate of acid production may help stabilize the plaque flora Northern Ireland, which can be attributed to the and take away some of the advantages to the cariogenic introduction of fluoridated toothpaste. (aciduric) organisms. In vitro, low concentration of fluoride ion promotes the remineralization of enamel lesions. The concentrations found in saliva (0.01-0.03 ppm) are in approximately the range where inhibition of solubility and Correspondence to: Professor William H Bowen, Department of Dental Research, University of Rochester, 601 Elmwood Avenue, Rochester, New York 14642- enhancement of remineralization begin to occur. In plaque, 8611, USA there are also concentrations of fluoride which might inhibit 505 JOURNAL OF THE ROYAL SOCIETY OF MEDICINE Volume 88 September 1995

acid production by plaque organisms and evoke other if these differences persist over the years, their economic metabolic effects. Plaque fluoride represents a prolonged impact increases proportionally. Even at 5% superiority retention of fluoride and is a primary reservoir in the mouth. only, sodium fluoride will have prevented 3-4 million The higher total concentration of fluoride in plaque, carious surfaces in every cohort of USA 17 year olds! compared to that in saliva, is explained by successive Furthermore, a sound tooth surface would not have mercury retention in the plaque as calcium fluoride. Plaque and saliva amalgam in it, so that not only is caries prevented, but even fluoride levels, after use of sodium fluoride dentifrices at the possibility of mercury toxicity is reduced. This various concentrations, are consistent with the observed protective effect can be achieved at a marginal cost of association between fluoride levels and clinical effect. nearly zero per person because the marginal difference in However, MFP is hydrolysed in vivo only slowly on the cost of choosing a sodium fluoride versus sodium tooth surface by phosphatases9. Hence, levels of fluoride in monofluorophosphate toothpaste is essentially zero. Under plaque are lower than those found in persons who use NaF. these conditions, meta-analyses have recognized that small There is, however, no simple relationship between the benefits can be hugely important10. fluoride content of enamel and experience of caries. Fluoride Both sales of toothpaste and the number of tooth brushes exerts its effect, in part, by reducing the solubility of enamel sold per head per year have increased substantially in the UK in plaque acids; the caries process is characterized by a slow as well as in the rest of Europe in recent years. Glass15 and discontinuous process of alternating phases of reported that 95% of toothpaste sold in the UK and demineralization and remineralization. Fluoride exerts its Republic of Ireland contains fluoride. If it is assumed that primary effect through promoting remineralization. fluoride has its main protective effects on proximal tooth In vitro, in situ, and studies in animals all give results surfaces, then the number of these surfaces which are consistent with NaF giving a better clinical result than available is increasing because teeth are being retained longer MFP10. When studies in animals compared the effects of than heretofore: the more caries is prevented, the more dentifrices containing NaF with those containing MFP, surfaces there are at risk to decay. results were invariably superior with the former, which is In 1991, there were 2 060 000 children between the ages consistent with observations made in clinical trials1I. Studies of 11 and 13 in Britain, and it can be assumed that 25% using intraoral models in humans have also shown that NaF would be caries-free. The costs of treatment over a 3 year dentifrices result in significantly greater fluoride deposition period, for that group, would be £5.75 million, which is a than MFP in incipient enamel lesions. Fluoride levels in significant saving just for one group of children. For the plaque were significantly higher in persons in a clinical trial whole country, in order to provide care for a community who used NaF dentifrice. More than 20 clinical trials of using MFP as opposed to NaF, would require an extra 95 toothpaste containing sodium fluoride or sodium dentist-years. Thus, while a difference of 7% may appear monofluorophosphate have now been reported, all small, it is highly clinically and economically important. showing substantial reductions in the test groups. A meeting on this subject was held at the Royal Society However, discussions continue on the most appropriate of Medicine in November 1994. We16 concluded from in concentration of fluoride to be used in toothpaste. Ericson12 vitro data, in situ data, rodent studies, pharmacokinetic reported that when fluoride toothpaste is used as studies in humans, and controlled clinical trials that a recommended, the risk of any toxicity is negligible. The properly formulated dentifrice containing NaF is more habits of those using it, e.g. rinsing method, frequency of effective than a dentifrice containing MFP at the same use, and amount used influence its effectiveness13. Children concentration, and that this difference in effect is clinically with a growing bone structure retain approximately 80% of relevant. The proceedings have been published in the RSM ingested fluoride, whereas in adults only 50% is retained. International Congress Series. Fluoride can be released when bone is remodelled. Meta-analysis of 12 clinical studies comparing NaF directly with MFP has shown NaF to be better than MFP by REFERENCES a about 6.8%, result that is both clinically and statistically 1 WHO. Fluorides and Oral Health: Report Of a WHO Expert Committee On significant. Stephen et al. 4, in a recently reported study, Oral Health Status and Fluoride Use. WHO Tech Rep Ser. 846 Geneva, found a similar difference of about 7%. 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5 Hargreaves JA, Baylor N, Huntington E. 26 years of caries studies in Monofluorophosphate As Anti-Caries Agents In Dentifrices. International the Isle of Lewis [Abstract]. Caries Res 1994;28:181 Congress and Symposium Series No. 209. London:RSM Press, 6 O'Mullane D. Contribution of fluoride toothpastes to oral health. In: 1995:33-42 Bowen WH, ed. The Relative Efficacy Of Sodium Fluoride and Sodium 12 Ericson T. Some aspects on the physiology and toxicity of fluorides. In: Monofluorophosphate As Anti-Caries Agents In Dentefrices. International Bowen WH, ed. The Relative Efficacy Of Sodium Fluoride and Sodium Congress and Symposium Series No. 209. London: RSM Press, 1995: Monofluorophosphate As Anti-Caries Agents In Dentifrices. International 3-8 Congress and Symposium Series No. 209. London:RSM Press, 7 Duckworth RM, Morgan SN. Oral fluoride retention after use of 1995:21-4 fluoride dentifrices. Caries Res 1991; 25:123-4 13 Chesters RK, Huntington E, Burchell CK, Stephen KW. Effect of oral 8 Marsh PD. Effect of fluorides on bacterial metabolism. In: Bowen WH, care habits on caries in adolescents. Caries Res 1992;26:299-304 ed. The Relative Efficacy Of Sodium Fluoride and Sodium Monofluorophosphate As Anti-Caries Agents In Dentfrices. International 14 Stephen KW, Chestnutt IG, Jacobson APM, et al. The effect of NaF and Congress and Symposium Series No. 209. London: RSM Press, SMFP toothpastes on three-year caries increments in adolescents. Int 1995:9-14 Dent J 1994;44:287-95 9 Pearce EIF, Jenkins GN. The decomposition of monofluorophosphate 15 Glass RL. The first international conference on the declining prevalence by dental plaque microorganisms. J Dent Res 1982;61:953-6 of dental caries. The evidence and the impact on dental education, 10 Stamm J. Clinical studies of neutral sodium fluoride and sodium dental research, and dental practice. J Dent Res 1982;61:1301-83 monofluorophosphate dentifrices. In: Bowen WH, ed. The Relative 16 Bowen WH, ed. The Relative Efficacy Of Sodium Fluoride and Sodium Efficacy Of Sodium Fluoride and Sodium Monofluorophosphate As Anti-Caries Monofluorophosphate As Anti-Caries Agents In Dentifrices. International Agents In Dentfrices. International Congress and Symposium Series No. Congress and Symposium Series No. 209. London RSM Press, 1995 209. London:RSM Press, 1995:43-58 11 Stookey GK. In situ and animal studies of NaF and Na2PO3F dentifrices. In: Bowen WH, ed. The Relative Efficacy Of Sodium Fluoride and Sodium (Accepted 2June 1995)

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