Download Contents of toothpaste – safety implications

Contents of toothpaste – safety implications
Eric C. Reynolds, Associate Professor and Reader, School of Dental Science, University of
Melbourne, Melbourne
Summary
A typical toothpaste contains an abrasive, humectant, binder, detergent, flavour, preservative and
therapeutic agent. Apart from an unsubstantiated hypothesis linking the ingestion of silica
abrasives with the development of Crohn’s disease, toothpaste abrasives are considered safe for
human use. The humectants, binders, flavours, preservatives and colourings are used routinely in
the food and pharmaceutical industries and should pose minimal health risks when used in
toothpaste. The flavours, colourings or preservatives may give rise to allergic reactions, but these
are relatively rare. The detergent or essential oil flavours may produce localised mucosal
irritation, but this is also rare. As ingestion of excessive amounts of fluoride toothpastes by
young children has been implicated in dental fluorosis, parents should supervise tooth cleaning in
order to minimise toothpaste ingestion. For the majority of people, toothpastes, when used
properly, are safe and help to maintain dental health.
Aust Prescr 1994;17:49-51
References at bottom – correspond to (1)’s
Introduction
The primary purpose of brushing the teeth with a dentifrice (dens – tooth, fricare – to rub) is to
clean the accessible tooth surfaces of dental plaque, stains and food debris. Tooth cleaning with
dentifrices dates back over 2000 years, while cleaning with toothpicks and brushes is an even
older practice. Abrasive dentifrice materials came to be used when it was found that brushes,
while facilitating the cleaning of soft deposits from teeth, were inadequate for the removal of
harder deposits and stains. Dentifrices have been prepared in several forms such as powders,
pastes and gels. The most popular forms are the pastes and gels with over 5 billion tubes used
worldwide each year.
Several studies (1) have shown that toothpaste has a key role in helping to remove dental plaque
– the major cause of dental caries and periodontal diseases. Apart from aiding cleaning of teeth
directly, toothpaste has a role, arguably its most valuable role, in encouraging people to clean
their teeth. Most people in the developed world use toothpaste largely for cosmetic reasons.
Modern developments in toothpaste formulation have led to the addition of agents to provide
therapeutic, as well as cosmetic, benefits. Frequently used, modern toothpastes can help prevent
dental caries and limit the regrowth of dental plaque.
The exact composition of a particular toothpaste varies with each manufacturer, but a typical
formulation is abrasive 10-40%, humectant 20-70%, water 5-30%, binder 1-2%, detergent 1-3%,
flavour 1-2%, preservative 0.05-0.5% and therapeutic agent 0.1-0.5%.
Abrasives
For efficient tooth cleaning, the dentifrice requires a degree of abrasiveness. The common
abrasives used include dicalcium phosphate dihydrate, insoluble sodium metaphosphate, calcium
pyrophosphate, calcium carbonate, alumina trihydrate, magnesium trisilicate and, more recently,
silica gels. These abrasives have a hardness ranging between that of dentine and a value below
that of enamel in order to be safe but effective stain removers. Nevertheless, cervical tooth
abrasion can occur, creating wedge-shaped notches usually near the gingival margin. In severe
cases, pulpal pathosis and periapical lesions may result. However, factors other than toothpaste
abrasivity play the major role in cervical abrasion e.g. injudicious tooth brushing with a hardbristle toothbrush and excessive pressure.(1) The hypothesis associating Crohn’s disease with the
ingestion of silica from toothpaste has been reviewed.(2) Enteric lesions similar to Crohn’s were
reported in 1950 after mixing talc or fine sand in the feed of dogs or by injecting their intestinal
lymphatics with silica dust.(3) In 1969, silica and silicates were evaluated for acceptable daily
intake by the joint FAO/WHO Expert Committee on Food Additives. After consideration of a
large number of short- and long-term animal studies and observations in man, the committee
concluded that the available data on orally administered silica and silicates substantiated their
biological inertness. Therefore, no restriction was placed on daily intake. Silica and silicates
occur ubiquitously in the environment and are contained in certain foods such as potatoes, milk
and in the drinking water. While the hypothesis linking Crohn’s disease with toothpaste ingestion
should not be ignored, at present there is little substantiating scientific evidence.
Humectants and binders
Humectants are used in dentifrices to prevent loss of water and subsequent hardening of the paste
when it is exposed to air. The most commonly used humectants are glycerol and sorbitol.
Binders are hydrophilic colloids which disperse or swell in the presence of water and are used to
stabilise toothpaste formulations by preventing the separation of the solid and liquid phases.
Examples of binding agents used in toothpaste include the natural gums (arabic, karaya and
tragacanth), the seaweed colloids (alginates, Irish moss extract and gum carrageenan) and
synthetic celluloses (carboxymethyl cellulose, hydroxyethyl cellulose), with the latter now being
used increasingly for economic reasons. These substances are used routinely in the food and
pharmaceutical industries and should pose a minimal health risk when used in toothpaste.
However, sorbitol may cause diarrhoea in large doses as it acts as an osmotic laxative. The
FAO/WHO Expert Committee on Food Additives recommends that the intake of sorbitol be
limited to 150 mg/kg/day. Therefore, the use of 60-70% sorbitol gel toothpastes by small
children should be supervised by parents.
Detergents, flavours, preservatives and colourings
Detergents lower the surface tension and therefore help loosen plaque deposits and emulsify or
suspend the debris removed from the tooth surface during cleaning. Detergents also contribute to
the foaming property of dentifrices, an effect which appeals to consumers. The commonly used
detergent in toothpaste is sodium lauryl sulphate. Flavours constitute only a minor part of a
dentifrice, but are important components for consumer acceptance. The flavour of a toothpaste is
usually a blend of several components. The principal flavours used are peppermint, spearmint
and wintergreen modified with other essential oils of anise, clove, caraway, pimento, eucalyptus,
citrus, menthol, nutmeg, thyme or cinnamon. The humectants and some of the binders in
toothpastes can act as nutrients for various micro-organisms. Microbial contamination of
dentifrices is restricted by a low water activity and by the inclusion of preservatives such as
benzoates. Colouring agents are also added to dentifrices. These include titanium dioxide for
white pastes and various food dyes for coloured pastes and gels.
Contact sensitivity or mucosal irritation by dentifrices is relatively rare. Occasionally, the
flavours, colourings or preservatives can cause allergic reactions in some individuals.(4) These
may include desquamation and oedema of the lips and tongue, perioral dermatitis, angular
cheilitis, gingivitis and intra-oral ulceration. Some toothpastes can cause mild irritation of the
oral mucosa which disappears after use and is usually attributable to the detergent or essential oil
flavours. This again is quite rare as the majority of people prefer the more flavoured dentifrices
as the tingling sensation makes the mouth feel fresh and clean, albeit for only a few minutes.
Therapeutic agents
The use of fluoride dentifrices is beneficial in the prevention of dental caries.(5) Most dentifrices
today contain 0.1%(1000 ppm) fluoride, usually in the form of sodium monofluorophosphate
(MFP); 100 g of toothpaste containing 0.76 g MFP (equivalent to 0.1 g fluoride). The
concentration of fluoride in toothpaste is limited in Australia to a maximum of 1000 ppm by a
recommendation of the Standard for Uniform Scheduling of Drugs and Poisons No. 6 (NHMRC,
1992). The suggested toxic dose of fluoride ion is 5 mg fluoride per kg body weight.(6) For a 10
kg child, this corresponds to approximately half the contents of a 90 g tube of toothpaste.
Therefore, young children should not be allowed unsupervised access to fluoride dentifrices. A
review of fluoride benefits and risks by the U.S. Public Health Service(7) concluded from more
than 50 human studies that no evidence existed showing an association between fluoride and
cancer. However, there is evidence of an increase in the prevalence of mild dental fluorosis.(8)
The consumption of excessive amounts of fluoride during enamel formation may result in
dental fluorosis.
This is a continuum of changes in the enamel varying from fine white lines in mild cases to very
chalky, opaque enamel which breaks apart soon after tooth eruption. Since fluoride appears to
affect the activity of the ameloblast, especially during the late secretion or early maturation of
enamel, excessive fluoride intake is of concern during the first 7 years of life. Toothpastes have
been identified as a significant source of fluoride for the young child. The NHMRC has reported
in its review of the effectiveness of fluoridation, that fluoride from toothpaste accounts for up to
53% of the total fluoride intake of children aged two years.
(9) For the purpose of enhancing the safe use of fluoride dentifrices by children, several
measures should be taken to minimise the risk of developing dental fluorosis. Parents should be
advised to supervise tooth cleaning closely using only small (pea-size) quantities of toothpaste.
Manufacturers should be encouraged to market a low fluoride dentifrice (e.g.400-500 ppm
fluoride) for infant use. This level of fluoride in toothpaste, given that all other sources are
constant and low, should result in a total fluoride intake which does not exceed the recommended
upper limit of 0.07 mg/kg of body weight for a child between 2 and 7 years of age.10 A low
fluoride, sorbitol-based toothpaste designed specifically for children is available (Colgate Junior
Toothpaste) and contains 0.304% MFP (400 ppm fluoride). Data from several independent
studies indicate that, although a dose-response relationship does exist for fluoride levels in
toothpaste and caries, use of a 400 ppm fluoride-containing paste by children under 7 years of
age instead of the standard 1000 ppm fluoride paste should not increase their caries risk. There is
currently no glycerol-based, 400-500 ppm fluoride toothpaste available in Australia.
In addition to claims of the anticaries activity of fluoride, new therapeutic dentifrices are being
promoted to the public and the dental profession for the control of dental plaque and gingivitis.
Triclosan (2,4,4′-trichloro-2′-hydroxy diphenyl ether), an antimicrobial agent used extensively in
deodorants, soaps and other dermatological preparations, is the active agent in these new
dentifrices. In various clinical studies, brushing with a 0.3% triclosan-containing dentifrice when
compared with a control paste resulted in significant reductions in dental plaque formation and
gingival inflammation.11 From animal toxicity, mutagenicity, teratogenicity and carcinogenicity
studies, as well as pharmacokinetic studies in man, it has been proposed by the major toothpaste
companies that 0.3% triclosan-containing toothpastes are safe for human use. However, the
U.S.A. Food and Drug Administration has stated that new drug approval will be required for a
toothpaste containing triclosan because the ingredient has not been used in any intra-oral drug or
cosmetic preparation previously.
Conclusion
Dentifrices have evolved and improved over the last 2000 years. The most significant
improvement was the introduction of fluoride in the 1960s resulting in the development of
toothpastes with anticaries efficacy. For the majority of people, modern toothpastes, when used
properly, are safe and help to prevent dental caries, dental plaque formation and gingival
inflammation. However, the use of fluoride-containing pastes by young children should be
closely supervised by parents to restrict fluoride ingestion.
REFERENCES
1. Forward GC. Role of toothpastes in the cleaning of teeth. Int Dent J 1991;41:164-70.
2. Sullivan SN. Hypothesis revisited: toothpaste and the cause of Crohn’s disease [see
comments]. Lancet 1990;336:1096-7. Comment in: Lancet 1990;336:1580-2.
3. Chess S, Chess D, Olander G, Benner W, Cole WH. Production of chronic enteritis and other
systemic lesions by ingestion of finely divided foreign materials. Surgery 1950;27:221-34.
4. Machackova J, Smid P. Allergic contact cheilitis from toothpastes. Contact Dermatitis
1991;24:311-2.
5. Rolla G, Ogaard B, Cruz R de A. Clinical effect and mechanism of cariostatic action of
fluoride-containing toothpastes: a review. Int Dent J 1991;41:171-4.
6. Whitford GM. Fluoride in dental products: safety considerations. J Dent Res 1987;66:1056-60.
7. U.S. Department of Health and Human Services. Review of fluoride benefits and risks: report
of the Ad Hoc Subcommittee on Fluoride of the Committee to Coordinate Environmental Health
and
Related Programs. Washington: Public Health Service, 1991;8:79,81.
8. Mason JO. Too much of a good thing? Questions about fluorosis explored. J Am Dent Assoc
1991;122:93-6.
9. National Health and Medical Research Council. The effectiveness of water fluoridation.
Canberra: Australian Government Publishing Service, 1991.
10. Burt BA. The changing patterns of systemic fluoride intake. J Dent Res 1992;71:1228-37.
11. Palomo F, Wantland L, Sanchez A, DeVizio W, Carter W, Baines E. The effect of a
dentifrice containing triclosan and a copolymer on plaque formation and gingivitis: a 14-week
clinical study. Am
J Dent 1989; 2:231-7.