Jasmine Murphy, Specialist Registrar in Dental Public Health
This paper presents the evidence regarding the efficacy and safety of various fluoride interventions in reducing/preventing dental caries. The various fluoride therapy interventions are as follows:
Systemic fluoride produces its anticaries effect on pre-eruptive teeth, as it is incorporated into developing teeth. However, after tooth eruption, systemic fluoride continues to have beneficial effects on teeth by secretion through the saliva. Systemic modalities include water, milk and salt fluoridation.
Systemic and topical
Dietary fluoride supplements (tablets, lozenges, drops) were developed to provide systemic fluoride to children who are not exposed to fluoridated water. To maximize the topical effect of fluoride, tablets and lozenges should be chewed or sucked for 1--2 minutes before being swallowed.
Topical fluorides strengthen teeth already present in the mouth making them more decay-resistant by elevating the fluoride concentrations locally for a post-eruptive protective effect. Topical fluorides include toothpastes, mouthrinses and professionally applied fluoride therapies such as varnishes and gels.
Two non fluoride interventions that can be used to reduce and prevent dental caries are also discussed:
Pit and fissure sealants
Oral/Dental health education
The strength of the evidence regarding the efficacy and general safety of all interventions is important and has therefore been classified and presented into two main groups of evidence:
Systematic reviews and/or meta-analyses of randomized controlled trials (RCTs) are the gold standard for decision-making and appear at the top of the hierarchy of evidence about effectiveness. They can and should inform decisions about the appropriate use of any intervention to prevent dental caries.
Relevant original primary research studies that were not covered in the systematic reviews or meta-analyses that either support or refute the evidence presented by the reviews.
Fluoridated milk was first investigated in the early 1950s, almost simultaneously in Switzerland, the USA and Japan. Stimulated by the favourable results obtained from these early studies, the establishment of The Borrow Dental Milk Foundation (subsequently The Borrow Foundation) in England gave an excellent opportunity for further research, both clinical and non-clinical, and a productive collaboration with the World Health Organization (WHO) from the early 1980s onwards. At present, milk fluoridation programmes are running continuously in about ten countries of the world. Banoczy and Rugg Gunn (2007) have recommended that milk fluoridation programmes should:
Effectiveness Main Evidence A systematic review by Yeung et al (2005) assessed the benefits of fluoridated milk in preventing dental caries. The authors noted that there is a lack of studies with good quality evidence to sufficiently examine this issue. Therefore, the review found insufficient evidence to show the effectiveness of fluoridated milk in preventing tooth decay. However, the two Randomised Controlled Trials (RCT) that were included in the review suggested that fluoridated milk was beneficial to school children, especially their permanent dentition. There is a need for the data to be supplemented by further RCTs in order to provide the highest level of evidence for practice.
Further evidence There are three cross-sectional studies (Riley et al, 2005; Mariño et al, 2004, Weitz 2007) of interest. Cross-sectional studies are never included in systematic reviews as their evidence is considered weaker than that of RCTs. The results of these studies indicate that milk fluoridation played a significant role in caries prevention. While these studies provide only low levels of evidence for assessing the effectiveness of an intervention, their results suggest that milk fluoridation may be an effective alternative caries prevention programme in areas where either water fluoridation or other community delivered programmes are difficult to apply.
Safety Dental Fluorosis Evidence: Low level of evidence from multiple time-point cross-sectional study (Marino et al 2003).
Marino et al (2003) conducted a study to determine the prevalence and severity of enamel fluorosis in the permanent dentition of children aged 6-9 years exposed to fluoride through a milk fluoridation programme in Codegua, Chile. The results indicated that milk fluoridation is not associated with significant levels of fluorosis. A statistically significant increase in fluorosis was seen in a number of age groups following the introduction of milk fluoridation; however, the majority of this fluorosis was mild and would not be considered to be of aesthetic concern.
Salt fluoridation first began in Switzerland in 1955 and it is now estimated that fluoridated salt is available to nearly 200 million people worldwide, including Europe, Central and South America and the Caribbean. It is the preferred method of fluoridation on mainland Europe and is widely available in France, Germany, Switzerland, Austria, Belgium, Spain, Czech Republic and Slovakia. Salt fluoridation is legal throughout the European Community. It is also recommended by the WHO (1994) for communities where water fluoridation is not possible.
Effectiveness Main evidence There are no systematic reviews that have been undertaken in this area, although it should be noted that a Cochrane Review on this subject is currently being undertaken.
Further evidence Three single time-point cross-sectional studies were identified which assessed the effectiveness of salt fluoridation at reducing dental caries. All studies measured dental caries before and after the introduction of salt fluoridation. The studies were conducted in Mexico (Irigoyen and Sánchez-Hinojosa, 2000), Jamaica (Estupiñán-Day et al, 2001) and Costa Rica (Solórzano et al, 2005). It should be noted that these studies are considered of poor methodological quality as no statistical manipulation was undertaken to take potential confounding factors into account. Nevertheless, the results of these studies suggest that salt fluoridation reduces caries in populations of children aged from 6-15 years.
A further study by Sagheri et al (2007) compared dental caries levels in two communities (Dublin and Freiburg) with different oral health prevention strategies (water fluoridation and salt fluoridation). The study confirmed that both water and salt fluoridation reduced the gap in dental caries experience between medium and lower social classes. The results of the study indicate the importance of salt fluoridation where water fluoridation is not feasible.
As there are no systematic reviews or RCTs on this subject area, the evidence of effectiveness of fluoridated salt is not considered to be of high quality.
Safety Dental Fluorosis Evidence: Low level of evidence cross-sectional studies (Stephen et al 1999, Vallejos-Sánchez et al, 2006; Estupiñán-Day et al, 2001, Sagheri et al 2007, Salas-Pereira et al 2008 ).
All studies generally show an increased prevalence of dental fluorosis with fluoridated salt. However, there is no evidence relating to an increase in risk of ‘fluorosis of aesthetic concern’.
Fluoride supplements are used differently in different countries. In continental Europe, community based school programmes are common alongside individually prescribed drops and tablets usually by a paediatrician. In Scandinavia, fluoride tablets are prescribed to children and adults with a high caries activity or risk. In the British Isles these supplements have been recommended in areas with a high caries prevalence (Clarkson 1992).
Fluoride drops and tablets exercise their benefit mainly through topical means and therefore their contribution on a community basis cannot readily be compared with that of water or salt fluoridation (Stephen 1993). Furthermore, the use of fluoride supplements for caries prevention was also reviewed by a WHO expert committee (1994) which concluded that fluoride supplements have limited application as a public health measure.
Main evidence One systematic review (Ismail and Hasson 2008) examined evidence regarding the effectiveness of fluoride supplements in preventing dental caries and their association with dental fluorosis. The review showed that there is weak and inconsistent evidence that the use of fluoride supplements prevents dental caries in primary teeth. However, the evidence that such supplements prevent caries in permanent teeth is clear.
Further evidence Hu et al (1998) undertook a three-year cross-sectional study on young children attending two kindergartens aged 2 years and above. Fluoride drops were made available for over 180 days each year and they were distributed by teachers who maintained attendance records. The results demonstrated an effective caries-inhibiting effect of the fluoride drop programme. The differences were statistically significant.
Safety Dental Fluorosis Evidence: High level (two systematic reviews) and low level (cross sectional).
Both systematic reviews (Ismail and Hasson 2008, Ismail et al 1999) confirmed that in non-fluoridated communities the use of fluoride supplements is associated with a significant increase in the risk of developing mild to moderate dental fluorosis.
The cross-sectional study undertaken by Awad et al (1994) also supports the evidence of the systematic reviews that considerable dental fluorosis was found with fluoride supplements.
Topical fluorides aim to deliver high concentrations of fluoride directly to the surface of the tooth, and are not intended to be ingested. Topical fluorides include:
toothpastes and mouthrinses (self-applied), and
varnishes and gels (professionally applied).
Toothpastes and mouthrinses (self applied)
Fluoride toothpaste was first made widely available in the 1950s. Today, 98% of all toothpastes contain fluoride. In Europe, fluoride toothpastes can be sold over the counter as long as the fluoride concentration is less than 1500 parts per million (ppm). Toothpastes with a high fluoride concentration (more than 1500 ppm) are classed as a medicine and therefore need to be prescribed by a dentist. Higher concentration fluoride toothpastes (1450 ppm) have been recommended for use by the Department of Health (DH 2007).
Over the last decades, fluoride mouthrinsing has become one of the most widely used caries preventive public health measures. Two regimens have been adopted as standard for individual programmes of patient care or for school based programmes and can be used daily, weekly (or even fortnightly) depending on the fluoride concentration (low potency/high frequency or high potency/low frequency regimes). School-based fluoride mouthrinsing programmes have been recommended by the WHO (1994) in low- fluoride communities where caries activity is moderate to high. In optimally fluoridated communities, school-based fluoride mouthrinsing programmes are not recommended. The Department of Health (2007) currently recommend the prescription of daily fluoride mouth rinse for all individuals over 8 years olds who have active decay, in addition to brushing with a toothpaste containing at least 1350 ppm fluoride.
Four systematic reviews assessed the benefits of fluoridated toothpastes in preventing dental caries (Marinho et al 2003, Tweetman et al 2003, Steiner et al 2004, Amari et al 2003).
According to the reviews, there is very strong evidence for the use of fluoridated toothpastes in the permanent dentition. However, the reviews also found inconclusive evidence regarding the use of fluoridated toothpastes in the primary dentition. Both Steiner (2004) and Amari (2003) also found caries reduction to be greater with the use of 1000 ppm F toothpaste compared with 250 ppm F toothpaste.
Three systematic reviews examined evidence regarding the effectiveness of fluoridated mouthrinses in preventing dental caries (Marinho et al 2003, Tweetman et al 2004, Marinho et al 2004). The results suggest that fluoride mouthrinses may have an anti-caries effect in children with a limited background exposure to fluoride, while the benefit in children with existing fluoride exposure is unclear. A greater effect was seen with increased total intensity (frequency times concentration) of the mouth rinse application. However; long term compliance has been an issue in many of the included studies.
Further evidence Six further RCTs that were omitted from the systematic reviews (Stookey et al 2004, Biesbrock et al 2003a, Biesbrock et al 2003b, Davies et al 2002, You et al 2002, Biesbrock et al 2001) were found to support the evidence of the effectiveness of fluoridated toothpastes. However, the benefit of higher doses of fluoridated toothpaste was unclear.
One RCT that was not included in the systematic reviews (Skold et al 2005a) was also found which further supports the evidence regarding the effectiveness of fluoride mouthrinses. Levin et al (2009) also found that fluoride rinsing can be effectively targeted at children from deprived areas through school-based initiatives, with overall reductions in dental decay levels being observed.
Safety Dental fluorosis Evidence: No systematic reviews were found. A review of RCT data was undertaken by Tavener et al (2004).
Tavener found that fluoridated toothpastes may be associated with ‘any fluorosis’. However, when ‘fluorosis of aesthetic concern’ was examined, no statistically significant difference between the higher fluoride dose group and the control group was found, with the prevalence of fluorosis in the higher dose toothpaste group being low (< 2%).
Gels and Varnishes (professionally applied)
Fluoride gels and varnishes are highly concentrated forms of fluoride which are applied to the surfaces of teeth professionally.
High concentration fluoride gel has been used for more than thirty years in dental surgeries in order to reduce dental decay. These gels use higher concentrations and different formulations of fluoride from those found in most toothpastes. The gel is commonly placed on an impression tray which is then positioned over the patients’ teeth for a short time period as a one-off or six monthly procedure.
Fluoride varnishes are widely accepted in some parts of the world like Europe and Asia; and their use seems to be increasing in the world as a whole. Fluoride varnish quickly adheres to teeth and over time is slowly released to the tooth surface, promoting tooth remineralization. The varnish is usually applied by health professionals to at-risk tooth surfaces in caries susceptible individuals (Marinho 2002). The WHO (1994) recommended that fluoride varnish is applied at intervals of 3-6 months, predominantly in patients at high risk of caries (WHO 1994). The Department of Health (2007) also consider the application of fluoride varnish to be ‘one of the best options for the application of topical fluoride to teeth in the absence of water fluoridation’.
Three systematic reviews assessed the benefits of fluoride varnishes in preventing dental caries (Azarpazhooh 2008, Marinho et al 2003, Petersson et al 2004). All reviews provide high level of evidence that twice-yearly applications of fluoride varnish produce a mean caries reduction of 33% in the primary dentition and 46% in the permanent dentition. Additionally, Petersson (2004) found fluoride varnish to be more effective than other types of topical fluoride interventions. However, Marinho et al (2004) found no clear evidence that professionally applied fluoride varnish is more effective than other topical fluoride agents. Nevertheless, both Petersson (2004) and Marinho (2004) found evidence that the combination of fluoride varnish with fluoride toothpaste was significantly more effective than fluoride toothpaste alone. The only other combination to reach statistical significance was the combination of fluoride gel and fluoride mouthrinse vs fluoride gel alone (Marinho 2004).
Azarpazhooh (2008) recommends targeting twice yearly fluoride varnish applications to high-risk populations (eg. low socioeconomic status, new immigrants and refugees) unless the individual has no risk of caries, as indicated by past and current caries history.
Two systematic reviews (Marinho et al 2003, Van Rijkom et al 1998) were also found, giving high level of evidence of the effectiveness of fluoride gels in reducing dental decay. Rijkom (1998) also reported that fluoride gels would seem a cost-effective option as only three patients with a high DMFS incidence of 1.5 would need to be treated (Numbers Needed To Treat) in order to reduce dental decay in just one year. Targeting such efforts into areas of high prevalence, as part of a health improvement programme could therefore be justified.
Further evidence Skold et al (2005b) carried out a RCT and found fluoride varnishes to be more effective at preventing dental caries when compared to no fluoride varnish. The most effective varnish regimen was treatment 8 times per year (during school terms with one monthly intervals).
Two RCTs assessed the effectiveness of fluoride gels. The study by Rijkom et al (2003), found a significant benefit of fluoride gel over placebo while the study by Truin and van’t Hof (2005) found no difference.
Safety Dental Fluorosis Evidence: No evidence was found relating dental fluorosis to fluoride varnishes and/or gels.
Pit and fissure sealants
Evidence suggests that between 90% of caries in children occurs in pits and fissures (Weintraub 2001). A sealant is a clear or opaque plastic material that is applied to the pits and fissures of teeth. The purpose of the sealant is to provide a physical barrier to occlude pits and fissures and to protect them from bacteria and food. Because the sealant obliterates the deeper and more tortuous anatomy, it also facilitates oral hygiene efforts because the sealed tooth is easier to clean. The Department of Health (2007) have recently recommended that all patients (from 7 years old to young adult) who are at high risk of developing dental decay should have sealants applied to their permanent molars.
Main evidence There are three systematic reviews (Ahovuo 2008, Hiiri 2006, Azarpahooh 2008) regarding the effectiveness of pit and fissure sealants at reducing and preventing dental caries. All reviews recommend that sealants should be placed as part of an overall prevention strategy based on assessment of caries risk. Hiiri (2006) also showed that there is some evidence of the superiority of pit and fissure sealants over fluoride varnish applications in the prevention of decay in these surfaces. However, it remained unclear as to what extent there is difference between the effectiveness of pit and fissure sealants and fluoride varnishes. The researchers made no recommendations for clinical practice and it was suggested that the benefit of pit and fissure sealants and fluoride varnishes should be considered locally and individually.
Further evidence Jodkowska (2008) undertook a long-term clinical observation on the efficacy of pit and fissure sealants and showed that mean caries increment was lower in children with sealed teeth than in controls. Accordingly, the degree of caries reduction depended on the number of teeth sealed.
Safety Toxicity Evidence: High level of evidence from a systematic review (Azarpazhooh 2008).
Bisphenol A (BPA) is widely used in the manufacture of many consumer plastic products. BPA may be used in the production of other ingredients found in some dental pit and fissure sealants. Bis-DMA and bis-GMA are both produced using BPA as a starting ingredient, so residual trace amounts of BPA may be present in the final product. The evidence suggests that patients are not at risk for exposure to BPA from the use of dental sealants. To reduce the potential, if any, for BPA toxicity from sealants, dental providers should use a mild abrasive, such as pumice, either on a cotton applicator or in a prophy cup; have older children and adolescents gargle with tepid water for 30 seconds; or wash the sealant surface for 30 seconds with an air-water syringe while suctioning fluids and debris from the patient’s mouth.
Oral Health Education
Dental health education has been used to target individuals, small sectors of communities and also whole populations. It can be delivered in a range of settings (eg. dental practices, schools, workplaces etc) utilising various methods including mass media campaigns. Human behaviour is extremely complex and sustainable health behaviour changes cannot be achieved by the simple provision of information alone (Sprod 1996). There are many factors that need to be taken into account when/if developing any health education programme (eg. social, economic, environmental, cultural, political, psychological, behavioural etc).
To date, rigorous, well-designed research concerning the outcomes of dental health education is scarce. This should not be taken to mean that dental health education activities cannot be supported but that more rigorous research is required in this direction. Three systematic reviews were found (Kay 1996, Kay 1998, Nguyen 2008) that assessed the efficacy of oral health education/promotion programmes.
Although all reviews suggested a beneficial outcome, very few definitive conclusions about the effectiveness of oral health promotion can be drawn from the currently available evidence. Essentially, there is inadequate evidence to recommend a specific approach for oral health education.
According to the reviews, oral health promotion which brings about the use of fluoride is effective for reducing caries. It is well documented that dental decay can be controlled by regular toothbrushing with a fluoride toothpaste but a cost-effective method for reliably promoting such behaviour is yet to be established. It has also been shown that oral health promotion initiatives can almost always improve knowledge levels. However, whether these shifts in knowledge and attitudes can be causally related to changes in behaviour or clinical indices of disease has also not been established.
Chairside oral health promotion has been shown to be effective more consistently than other methods of health promotion. Mass media programmes have not been shown to be effective. It is necessary for forthcoming studies to evaluate sustainability and assess the appropriateness of health outcome evaluation strategies. On the whole, the quality of oral health promotion evaluation research needs to be improved.
It seems clear that there is ample evidence in favour of some of the caries preventive interventions for individuals with a high caries risk. For other interventions, the conclusions that we can draw in this respect, are limited. It has been shown that fluoride is a safe and effective agent that can be used to prevent and control dental caries. Furthermore, the evidence on the beneficial effects of topical fluorides is consistent and strong, based on a sizable body of evidence from systematic reviews and randomized controlled trials. The research evidence has shown that fluoride toothpastes, mouthrinses, gels and varnishes can all reduce dental caries, regardless of water fluoridation or other sources of fluoride exposure. The size of the reductions in caries increment in both the permanent and the deciduous dentition emphasizes the importance of including topical fluorides delivered through toothpastes, rinses, gels or varnishes in any caries preventive programme.
There was no clear benefit of any one type of topical agent or regimen over another. However, there is good evidence of the complementary efficacy of preventive strategies such as sealants and varnish, as well as toothbrushing and oral health education. Any caries preventive programme should therefore include an additional topical fluoride modality (over toothpaste) for children at higher risk of developing dental caries. Since increased effectiveness of topical fluorides is to be expected in children with higher initial DMFS scores, this practice may be considered in populations with a caries increment of around 2 DMFS per year or more (Marinho 2008).
It should be recognized, however, that such an approach reinforces targeting preventive care to high-risk sub-populations. That high-risk approach fails to deal with the majority of new caries, which occur in the population who are at lower risk (Batchelor and Sheiham 2006). Thus, the aforementioned caveat should be considered before application of the evidence related to the question on whether to use an additional topical fluoride (with toothpaste). References:
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