Protective Effects Of Fluoride Toothpastes Health And Social Care Essay

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1st Jan 1970 Health And Social Care Reference this

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The main aim of this report is to discuss the evidence for the protective effects of fluoride toothpastes and varnishes. In addition, I will discuss their application and mode of action.

To begin with, I will give a brief history of fluoride and how it fits into the reversal of tooth decay. I will discuss fluoride varnishes namely Duraphat, Fluor Protector and Duraflor and their effect on the DMF Index and their roles in school based prevention programmes. There are other varnishes such as Lawefluor and Bifluorid but these are less commonly used and therefore, I will not be discussing them.

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After discussing fluoride varnishes, I will consider fluoride toothpastes. I will give a description on the composition of a typical toothpaste and the effect of fluoride toothpastes on the DMF Index. In addition, I will discuss the effects of high fluoride concentration toothpastes. Finally, I will compare both toothpastes and varnishes.

Contents Pages

Summary

Contents

Introduction

Deposition of fluoride in enamel

What is tooth decay?

Fluoride: Mode of Action

Who is at risk of decay?

Optimum fluoride concentration required for remineralisation

DMF Index

Main Section

What are fluoride varnishes?

Effect on DMFT/S

The effect of fluoride varnishes according to different caries risk

School based prevention programmes

The use of fluoride varnish in inhibiting secondary carious lesions

What are fluoride toothpastes?

Use of fluoride toothpastes in clinical trials

High Fluoride toothpastes

The use of fluoride toothpastes in advanced enamel lesions

Comparison of Toothpastes and Varnishes

Conclusion

Acknowledgements

Word Count

References

Introduction

I have decided to carry out this report on fluoride as I realise the importance of its role in the prevention of tooth decay (dental caries). Fluoride is a negative ion of the element fluorine and is found naturally in water, foods, soil, and minerals such as fluorite (calcium fluoride) and fluorapatite. Fluoride can also be synthesised in laboratories where it can be added to oral hygiene products and to water. Fluoride utilisation has occurred in two phases: before water fluoridation in the 1950’s and after the widespread use of fluoridated dentifrices in the 1980s (Cury, Tenuta 2008) when less than 10% of toothpastes contained fluoride compared with 96% at present. Fluoride is most effective post-eruptively (Oganessian, Lencova & Broukal 2007) where the effects are generally topical and therefore, it is important for a constant fluoride concentration to be maintained in the oral environment. “Topically applied fluoride” provides high concentrations of fluoride to surfaces of the dentition. This provides a local protective effect and prevents ingestion of large amounts of fluoride. (Marinho et al. 2004)

Deposition of fluoride in enamel

During apatite crystal formation, low concentrations of fluoride are incorporated into the tooth structure. This leads to supersaturation with respect to fluoridated hydroxyapatite: {{66 ten Cate,J.M. 2008)

Ca10(PO4)6(OH)2+ F-= Ca10(PO4)6(F)2 + 2OH-

(Fluorapatite)

After calcification is complete and prior to eruption, additional fluoride is taken up by the surface enamel. After eruption, the enamel continues to take up fluoride from its oral environment leading to its profound topical effects (Kidd 2005).

What is tooth decay?

It is important to consider the causes of tooth decay and how fluoride can be used to reverse the carious process. Dental Caries is a multifactorial disease caused by the action of acidogenic and aciduric bacteria (Streptococcus Mutans and Lactobacilli ({{32 Featherstone,J.D. 2008}}) on fermentable carbohydrates such as sucrose. Salivary glycoproteins form a pellicle on the tooth to which these bacteria attach to forming a pathogenic biofilm and over time, acid demineralisation and proteolytic destruction of the organic component of the enamel and dentine takes place (Young, Kutsch & Whitehouse 2009).

Dental Caries can be classified in several ways

According to location-Caries may be restricted to pits and fissures but may also progress to expose the pulp.

Restorative status of the tooth- Primary caries occurs on previously unrestored teeth whereas secondary caries occurs at margins of restorations {{52 Kidd,Edwina A.M. 2005}}. Secondary caries is caused by local factors that are involved in the formation of cariogenic plaque. Most secondary carious lesions develop at the gingival margins of restorations primarily in areas of stagnation areas (Mjör, 1998). Large gaps between the restoration and the wall of the cavity preparation can create an environment that favours secondary caries formation (Mjör, 1998). Secondary caries is also known as recurrent caries.

Caries can be arrested whereby a lesion which was previously active has now stopped progressing.

Fluoride: Mode of Action

Fig 1: Demineralisation Process and the role of fluoride (Cury, Tenuta 2008)

Figure one shows how sugars such as sucrose, glucose and fructose are converted to acids in the plaque biofilm. When the pH decreases below 5.5 (critical pH of enamel), the saliva is no longer supersaturated with calcium and phosphate. Therefore, demineralisation occurs. However, in the presence of fluoride and if the pH is higher than 4.5, hydroxyapatite is converted to fluorapatite which has a lower solubility. As a result, net demineralization is reduced and the dental hard tissues are more acid resistant. Tenuta and colleagues calculated that fluorapatite would not dissolve until the pH dropped below approximately 4.4. However, researchers have found that the effect of fluoride is not only due to the decreased solubility but also due to the effect of fluoride on the rates of demineralisation and remineralisation (Stoodley et al. 2008).

In order to enter bacteria, fluoride must be combined with a hydrogen ion forming hydrogen fluoride (HF), which readily diffuses into the cell. Once inside the bacterial cell, the HF dissociates into fluoride and hydrogen ions. The fluoride inhibits intracellular bacterial enzymes such as enolase. As a result, less phosphoenolpyruvate and lactate are formed. The reduced lactate formation limits the ability of bacteria to cause caries. Similarly, the uptake of glucose is also reduced by fluoride {{63 Featherstone,J.D. September 2004}}.

The fluoride concentration in saliva increases after brushing with a fluoride toothpaste. After three minutes, the concentration is 100 times greater than the baseline value (normally 0.03ppm or 1.6umol/l) {{65 Murray, J.J 1991}}. Two hours later, the concentration returns to normal. It is important to avoid rinsing out the mouth as the most profound effects of fluoride are within two hours of brushing. Fluoride is spread throughout the oral cavity and is stored in compartments on the tooth surface and the remaining pellicle (Cury, Tenuta 2008). Calcium Fluoride globules are formed and are reservoirs of fluoride, releasing it as the pH falls, thereby, reducing time spent in the demineralisation phase. The main effects of fluoride can be attributed to the maintenance of constant fluoride levels in the biofilm.

Overall, fluoride has multiple ways of reducing caries. It is believed that the most important of these methods is the remineralisation concept {{40 Oganessian,E. 2007}}, which requires a constant flow of fluoride. Bacterial enzyme inhibition plays a supplementary role when the concentration of fluoride is high which is achieved by topical fluoride applications and toothpastes (Murray, Rugg-Gunn & Jenkins 1991).

Who is at risk of decay?

There are certain groups in the population who are at risk of decay and therefore, would benefit from the use of fluoridated dentifrices. These include patients with:

Xerostomia, which may have resulted from the radiotherapy to the head or neck leading to salivary gland exposure. This leads to a decrease in both the resting and stimulated salivary flow rates. Xerostomia is defined as the complete absence of saliva or hyposalivation. Hyposalivation leads to decreased levels of calcium, phosphate and hydrogen bicarbonate ions. As a result, there is a longer demineralisation phase

Sjögren’s syndrome- this is clinically defined as at least two of kerataoconjuctivitis sicca, Xerostomia(dry mouth) and rheumatoid arthritis or another connective tissue disease {{62 Newbrun,E. 1996}}

A high incidence of caries in their primary dentition

Hypersensitivity

Root caries

Removable orthodontic appliances and partial dentures

A poor diet and those who regularly snack on fermentable carbohydrates {{37 Evans,R.W. 2008}}. However, this risk has decreased due to better plaque control and increased fluoride exposure.

Multiple restorations suggesting a high prevalence of caries

Optimum fluoride concentration required for remineralisation

Bjarnason and Finnbogason (1991) found that fluoride levels in dentifrices had no effect on the progression of enamel lesions detected radiographically. However, a higher fluoride concentration (1000ppm F-) led to reduction in caries initiation compared to a dentifrice with a lower fluoride concentration (250ppm F-) {{69 Bjarnason, S. 1991}}. It is ultimately difficult to decide the optimum fluoride concentration required for remineralisation as different areas of the mouth are more at risk of caries due to unique ecological factors. However, it was thought that lesion progression in enamel was slowed down only in patients with low caries activity whereas patients with high caries activity still experienced rapid progression (Hellwig, Lussi 2001).

DMF Index

The DMF index is a measure of caries activity in a population and changes in the DMF index can be used to highlight the protective effects of the fluoride toothpastes and varnishes (Kidd 2005).

D: decayed teeth with untreated carious lesions

M: missing teeth (extracted teeth)

F: filled teeth

DMFT denotes decayed, missing and filled teeth

DMFS denotes decayed, missing and filled surfaces in permanent teeth and therefore, the number of surfaces attacked on each tooth are accounted for.

There are similar indices for deciduous tooth, which are the defs and deft scores. The e represents extracted teeth to differentiate(Johansen et al. 1987) between natural loss of teeth through exfoliation.

Burt in 1998 suggested that greater emphasis has to be placed on the assessment and early diagnosis of caries {{77 Burt, B.A. 1998}}. This has been backed up by cohort studies {{83 Johansen, E. 1987}} (Axelsson, Lindhe & Nystrom 1991), which found that the use of preventive strategies (fluoride application) resulted in a substantial reduction in lesion development and progression.

Fluoride varnishes

What is fluoride varnish?

Fluoride varnish was first developed in New York in 1968 by Heuser and Schmidt in the form of sodium fluoride and was marketed under the name Duraphat. The Duraphat varnish contains 22,600 parts per million of fluoride (ppm Fˉ) as shown in figure 2. In the 1970’s, there was a switch from sodium fluoride to difluorsilane which was marketed under the name Fluor Protector (7000ppm Fˉ) in Germany {{42 Azarpazhooh,A. 2008}}.

Fluoride Varnish

Type of fluoride

Fluoride Concentration(ppm)

Fluoride Concentration(%)

Duraphat

Sodium Fluoride

22,600

2.26

Duraflor

Sodium Fluoride

22,600

2.26

Fluor protector

Difluorsilane

7,000

0.70

Fig 2: The table above shows the fluoride varnishes that are most commonly used.

Other types of fluoride varnishes include:

Fluoride Varnish

Type of fluoride

Fluoride Concentration(ppm)

Fluoride Concentration (%)

Lawefluor

Sodium Fluoride

22,600

2.2

Bifluorid

Sodium and Calcium Fluoride

56,300

5.6

Fig 3: The table above shows other fluoride varnishes which are available but are less commonly used {{24 Davies,G.M. 2008}}.

Most fluoride varnishes contain fluoride in an alcoholic solution of natural tree resin. The main advantage of the varnish is that the resin base is very adherent to the tooth prolonging contact time between the fluoride and enamel {{26 Miller,E.K. et al 2008}}. Varnishes are easy to apply and relatively safe regardless of the high fluoride concentration as the amount of varnish applied to one child is only 0.5 ml on average (Ripa 1990; Petersson 1993). Varnishes are slow-releasing reservoirs of fluoride preventing immediate release of fluoride after application (Ogaard 1994). As a result, they are most effective at protecting against primary caries. The food and drug administration centre in America has not yet accepted fluoride varnish as an anti-caries agent but considered it as a liner/desensitising agent (Mason 2005).

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There is some debate as to the amount of fluoride taken up by the tooth surfaces. It was found that approximately half of the fluoride taken up by sound surfaces from Fluor Protector varnish was lost after 6 months suggesting that the large amount of fluoride taken up after one week does not bind permanently to enamel and that the effects of fluoride are more short term. There has also been a debate over whether fluoride varnish should be applied to wet or dry surfaces. Koch et al found that the fluoride uptake was much greater when the varnish was applied to dry tooth surfaces (Koch, Hakeberg & Petersson 1988).

Fluoride varnishes can be applied professionally up to two to four times a year. Marinho et al in 2002 investigated the effectiveness of fluoride varnish in preventing dental caries in children compared to a placebo or no treatment. Over 2700 systemically healthy children aged 16 or less received fluoride varnish containing 22,600ppm sodium fluoride. There was a large caries inhibiting effect on both permanent and deciduous dentition. However, the confidence intervals were relatively wide and the variation among the results was substantial. The success of the treatment may have been over estimated, as the results of the few trials may not have been representative. As a result, it is important to carry out more trials before a definite statement can be made of the effects of the fluoride varnish (Marinho 2002). In addition, more information is required on the scale of the fluoride effect and the adverse effects of fluoride.

Effect on the DMFT/dmft

Primary Dentition

There was a 33% decrease in the decayed, missing and filled surfaces (Marinho 2002). A two year randomised clinical trial carried out on children with a mean age of 1.8 years, found that the application of fluoride varnish once, twice and three times a year reduced the mean dmfs by 53%, 58% and 93% respectively {{67 Davies,G.M. 2009}}. This highlights the importance of frequent varnish application.

(Petersson, Twetman & Pakhomov 1998)Petersson et al. in 1998 found a 19% and 25% reduction in the increment of approximal caries in children with a moderate or high caries risk respectively. This shows that children with a high caries risk benefit the most from the application of fluoride varnishes (Zimmer 2001).

Ages 0-3

Weintraub and colleagues carried out a two year randomised controlled trial on 376 children aged between 6-44 months (Weintraub et al. 2006). The children were split into three groups:

Those who received counselling

Those who received counselling and the annual application of Duraphat

Those who received counselling and the twice yearly application at six monthly intervals

The number of lesions only increased in children who received counselling alone highlighting the protective effects of the varnish. Those children who received no varnish application were twice as likely of developing decay as those who received the annual application of fluoride. As the frequency of fluoride varnish application increased, the number of carious lesions decreased. One drawback of this trial was that simultaneous counselling and varnish application led to some ambiguity as to whether the effects were due to varnish application or counselling although fluoride application was seen to play a key role.

Ages 3-6

According to the Cochrane Review, there was an overall 38% reduction in the DMFS/dmfs (Marinho 2002). A two year randomised study of 1,275 children in Canada aged between 6 months and 5 years found that twice-yearly application of Durafluor led to an 18.3% reduction in the dmfs increment (Lawrence et al. 2006).

Mixed dentition

There was on average a 46% decrease in dmfs. The fluoride varnish was an effective preventive measure for partially erupted permanent molars. Equally, patients who are insufficiently co-operative benefit from fluoride varnish application (Marinho 2002).

Permanent dentition

A randomised clinical trial used to examine the impact of fluoride varnish on the incidence of approximal caries, detected radiographically in 13 year olds over a three year period, found that the varnish applied monthly and twice a year reduced caries by 76% and 57% respectively again highlighting the importance of frequent fluoride application{{67 Davies,G.M. 2009}}. The caries reduction in permanent teeth shown in the Cochrane review of trials was similar to that achieved in a metaanalysis carried out by Helfenstein in 1994 when Duraphat was applied 2 times a year in children aged 9-15 years (Helfenstein, Steiner 1994). There was a 38% reduction in the caries. It is likely that most of the participants benefited from the use of a fluoridated dentifrice as the majority of the studies were carried out in Scandinavian countries between 1973 and 1987. However, as both the Cochrane review and the Helfenstien study were carried out involving a different selection criteria, it is debatable as to whether the results from both these trials can be compared.

In conclusion, application of fluoride varnish two to four times a year on both permanent and deciduous teeth is associated with a reduction in the caries increment (Marinho 2002).

The effect of fluoride varnish according to different caries risks

Möberg Skold carried out a trial which involved the application of fluoride varnish to approximal caries in adolescents living in different caries risk areas. The trial involved 758 students aged between 13 to16 years old. The large sample size meant that the results of this study were representative. This is because as the sample size increases, the variability of the results decreases. This means that the results have a greater statistical power and smaller confidence intervals.

Fig 4: (Azarpazhooh, Main 2008) The figure above shows the groups which were chosen according to their caries risk and whether they had any fluoride in their tap water.

Duraphat was applied to the approximal surfaces from the distal surface of the canines to the mesial surface of the second molars. Each group had different intervals of application shown in the figure below:

Group

No. of participants

Frequency of Duraphat application

One

190

Twice yearly in six-monthly intervals

( 6 times in 3 years)

Two

186

Three times a year with a one week period each year(9 times in 3 years)

Three

201

Eight times a year during school terms with one month intervals

( 24 times in 3 years)

Four(Control)

181

No application

Fig 5: (Azarpazhooh, Main 2008) The frequency of Duraphat application

The results from this trial show that the biggest difference was between group one and the control group in high caries risk area (Göteborg). However, there was no significant difference between the groups regarding filled approximal lesions and approximal enamel lesions. There was a greater incidence of caries in the control group in comparison to the fluoride varnish groups in all risk areas highlighting the protective effects of the fluoride varnish (Möberg Skold et al. 2005).

Overall, it was found that the school based monthly application of fluoride varnish is the best method of preventing approximal caries in areas of medium and high caries risk (Möberg Skold et al. 2005).

School based prevention programmes

A cluster randomised trial was carried out by M.C Hardman and colleagues involving 2,091 school children living in a non-fluoridated area. One group of students (1,025 students) received the twice-yearly application of Colgate Duraphat varnish whilst the other group (1,066 students) served as a control. This study found that the twice-yearly application of fluoride varnish did not lead to a reduction in caries in children living in the community {{43 Hardman,M.C. 2007}}. This is contrary to what was found by Marinho and colleagues. They found that the biannual application of Duraphat in a school-based programme provided a caries inhibition of 38% in children aged 9-15 years (Marinho 2002). The study carried out by M.C Hardman and colleagues did not prove to be conclusive as the level of consent in the community was low. Approximately 110 students were lost during the study. The control group had lower caries levels than anticipated and therefore, it was difficult to tell the true effect of fluoride. In addition, the application of varnish was carried out under sub-optimal conditions (teeth could not be cleaned prior to application and the consumption of food and drink after application could not be controlled), which could have resulted in less profound effects. In conclusion, it was found that this type of fluoride varnish intervention is not effective in the prevention of caries in the public {{43 Hardman,M.C. 2007}}.

A similar study was carried in a small town located in the American Southwest on children attending a head start nursery using Duraflor as the varnish of choice. The trial began in the head start class of 2002. Duraflor was applied during well child visits every 9, 12, 15, 18, 24 and 30 months. The class of 2003 had no fluoride application and therefore, served as the control. The mean age was 4.40 years and approximately 168 males and 189 females took part. The results showed that children who received no treatment had a mean dmfs of 23.6 with a 95% confidence interval. Those children who received 1-3 treatments had a similar dmfs to those with no treatment. Only those children who had 4 to 5 treatments showed a reduction in dmfs again suggesting the importance of frequent application. However, this study was an observational study not a randomised study and therefore, the reliability of the results can be questioned. In addition, no attempt was made to determine whether the children who received four or more applications of fluoride varnish differed from the other children in terms of diet and oral hygiene history {{58 Holve,S. 2008}}..

The use of fluoride varnish in inhibiting secondary carious lesions

As mentioned earlier, secondary caries forms at the margins of restorations. Larger amounts of fluoride varnish may be trapped in the gap formed between the restoration and the cavity wall. This may serve as a slow releasing reservoir of fluoride, which could also provide a physical barrier against wall dissolution.

In a study carried out by M. Fontana in 1996, two experiments were carried out. Experiment one involved the application of Duraflor. Experiment two involved the application of Duraphat a year after the application of Duraflor. The effects of fluoride varnish on secondary caries remineralisation and lesion progression were measured. The varnish was applied to dry tooth surfaces and rinsing after fluoride application was prevented to enhance the remineralisation potential. The varnish was applied for 24 hours to prolong the contact time between the varnish and the tooth surface. The results from these two experiments showed that fluoride application slowed down lesion progression around both amalgam and composite restorations {{48 Fontana, M. 2002}}. The placebo varnish slowed down lesion progression to a lesser extent than the fluoride varnish suggesting that the effects may not only be attributed to the fluoride in the varnish.

These results matched those in a previous study carried out by Hellwig et al. in 1993. They examined the effect of Duraphat varnish on artificially created primary carious lesions and found that fluoride varnish led to remineralisation in the outer layers of enamel {{78 Hellwig, E.K. 1993}}. This slowed down lesion progression. Seppa suggested in 1988 that the benefits of fluoride varnish were attributed to their ability to enhance remineralisation of primary caries rather than their ability to increase the fluoride content of the tooth surface. This is contrary to what was previously thought that the effects of topical fluoride were due to their ability to maintain high levels of fluoride on the surface of the tooth. Seppa also found that the efficacy of the fluoride varnishes was dependent on the number of applications rather than the concentration of fluoride {{79 Seppä, L. 1988}}. This backs up the results found by Marinho et al that showed that the more frequent the application, the lower the incidence of new caries or the greater the decrease in mean dmfs/DMFS.

Fluoride toothpaste

What is fluoride toothpaste?

Fluoride toothpaste is the most widely used method of fluoride application in the population due to its ease of use. Fluoride toothpastes can be incorporated into community and school based prevention programmes. Most oral health care workers recommend brushing twice a day, once just before going to bed, as this is when saliva flow is at its lowest and once at another time of day{{68 Davies,R.M. 2003}}. They recommend spitting out the toothpaste after use rather than rinsing as this dilutes the fluoride concentration in the oral cavity as previously mentioned. The widespread use of fluoride toothpastes had made it more difficult to distinguish whether a reduction in caries is due to mechanical plaque removal or due to the incorporation of fluoride.

Before the widespread use of fluoride toothpastes, the importance of fluoride was illustrated in a three-year study. This study involved two groups of children aged 9 to 11 years who had benefited from supervised brushing either with or without fluoride toothpaste. Both groups showed a reduction in plaque and gingivitis but a significant reduction in caries was only seen in the group which used fluoridated toothpastes (Davies et al. 2003).

A typical toothpaste contains abrasives such as calcium carbonates, which help to remove surface debris, and stains on the tooth surface. Most toothpastes contain fluoride (added to toothpastes in the 1970s) to make the tooth more resistant to acid attack and is one of the most recognised agents in toothpastes. Stannous fluoride (also known as tin fluoride) was the first fluoride to be used due to its compatibility with the abrasive, calcium phosphate. Sodium fluoride could not be used at first as the calcium in the abrasive renders it ineffective and therefore, is not compatible. Sodium Monofluorophosphate was next used as it was compatible with the abrasives used with it. Sodium Fluoride could only be used when hydrated silica and sodium bicarbonate became the abrasive of choice. Studies have shown that the sodium bicarbonate-sodium fluoride combination lead to a caries reduction of one surface per child over two years (Murray, Rugg-Gunn & Jenkins 1991).

Fluorides have been shown to work better in combination with detergents such as sodium lauryl sulphates, which aid the remineralisation process and create foaming whilst brushing. Toothpastes contain humectants such as glycerol, which prevent the loss of water in the toothpaste. To provide taste, saccharin and other sweeteners are added. To stabilise the toothpaste, thickening agents such as seaweed colloids are included to ensure that the toothpaste stays on the toothbrush when it is applied.

The use of fluoride toothpastes in clinical trials

The Cochrane review of trials found that children who used fluoridated toothpaste had fewer decayed,missing and filled permanent teeth after three years. Brushing twice a day helps to increase the benefit of fluoride (Marinho et al. 2003 England).

Researchers believe that the effects of fluoridated toothpastes are underestimated in two to three year trials due to the life long used of fluoride. They also found that the use of fluoride toothpastes in areas of fluoridated water increased the protective effects. The normal concentration of fluoride in toothpastes is between 1000 and 1100 parts per million (ppm Fˉ). Toothpastes with higher fluoride concentrations (1500ppm) and lower fluoride concentrations (500ppm) are available in many countries. Toothpastes containing higher fluoride concentrations offer greater protection against caries (Stephen 1988; O’Mullane 1997).

Since the 1940s, more than a 100 clinical trials have been carried out and by the late 1970s, the protective effects of fluoride toothpastes were greatly accepted. As a result, many clinical trials could not have a control, as the removal of fluoride toothpaste for the trial was considered unethical. Therefore, the effectiveness of different concentrations of fluoride toothpastes have not been investigated extensively in placebo-controlled trails. The guidelines of caries trials have since been changed in order to combat this problem, by increasing the sample size so that the measurement error could be reduced (Marinho et al. 2003 England).

Children or adolescents aged sixteen or less were chosen to take part in the study carried out by Marinho et al. To assess the effect of the fluoride toothpaste, the caries increment was measured as a change in the value of the DMFS Index, in all permanent teeth erupted at the start and erupting over the course of the study.

Evidence from this study suggested that the use of fluoride toothpastes leads to a 24% decrease in dmfs. The confidence intervals for this reduction were 21-28%. This means that 1.6 children need to brush with fluoride toothpaste to prevent one decayed, missing or filled tooth surface in a population where the caries increment is 2.6 DMFS per year. Where the caries increment was lower (1.1 DMFS per year), 3.7 children needed to use a fluoride toothpaste in order to avoid one decayed, missing or filled tooth surface(Marinho et al. 2003 England). There was also a substantial reduction in caries increment (37%) of deciduous teeth in a trial carried out on 2008 children aged 6 to 9 years.

Another aim of the Cochrane review (Marinho et al. 2003 England) was to establish whether there was any relationship between the caries-preventive effects of fluoride toothpaste and the initial level of caries, previous exposure to fluoride and the frequency of fluoride toothpaste use on the prevented fraction. The prevented fraction (PF) is the proportion of disease occurrence in a population averted due to a protective risk factor or public health intervention (Gargiullo, Rothenberg & Wilson 1995). The prevented fraction was measured as the diffe

The main aim of this report is to discuss the evidence for the protective effects of fluoride toothpastes and varnishes. In addition, I will discuss their application and mode of action.

To begin with, I will give a brief history of fluoride and how it fits into the reversal of tooth decay. I will discuss fluoride varnishes namely Duraphat, Fluor Protector and Duraflor and their effect on the DMF Index and their roles in school based prevention programmes. There are other varnishes such as Lawefluor and Bifluorid but these are less commonly used and therefore, I will not be discussing them.

After discussing fluoride varnishes, I will consider fluoride toothpastes. I will give a description on the composition of a typical toothpaste and the effect of fluoride toothpastes on the DMF Index. In addition, I will discuss the effects of high fluoride concentration toothpastes. Finally, I will compare both toothpastes and varnishes.

Contents Pages

Summary

Contents

Introduction

Deposition of fluoride in enamel

What is tooth decay?

Fluoride: Mode of Action

Who is at risk of decay?

Optimum fluoride concentration required for remineralisation

DMF Index

Main Section

What are fluoride varnishes?

Effect on DMFT/S

The effect of fluoride varnishes according to different caries risk

School based prevention programmes

The use of fluoride varnish in inhibiting secondary carious lesions

What are fluoride toothpastes?

Use of fluoride toothpastes in clinical trials

High Fluoride toothpastes

The use of fluoride toothpastes in advanced enamel lesions

Comparison of Toothpastes and Varnishes

Conclusion

Acknowledgements

Word Count

References

Introduction

I have decided to carry out this report on fluoride as I realise the importance of its role in the prevention of tooth decay (dental caries). Fluoride is a negative ion of the element fluorine and is found naturally in water, foods, soil, and minerals such as fluorite (calcium fluoride) and fluorapatite. Fluoride can also be synthesised in laboratories where it can be added to oral hygiene products and to water. Fluoride utilisation has occurred in two phases: before water fluoridation in the 1950’s and after the widespread use of fluoridated dentifrices in the 1980s (Cury, Tenuta 2008) when less than 10% of toothpastes contained fluoride compared with 96% at present. Fluoride is most effective post-eruptively (Oganessian, Lencova & Broukal 2007) where the effects are generally topical and therefore, it is important for a constant fluoride concentration to be maintained in the oral environment. “Topically applied fluoride” provides high concentrations of fluoride to surfaces of the dentition. This provides a local protective effect and prevents ingestion of large amounts of fluoride. (Marinho et al. 2004)

Deposition of fluoride in enamel

During apatite crystal formation, low concentrations of fluoride are incorporated into the tooth structure. This leads to supersaturation with respect to fluoridated hydroxyapatite: {{66 ten Cate,J.M. 2008)

Ca10(PO4)6(OH)2+ F-= Ca10(PO4)6(F)2 + 2OH-

(Fluorapatite)

After calcification is complete and prior to eruption, additional fluoride is taken up by the surface enamel. After eruption, the enamel continues to take up fluoride from its oral environment leading to its profound topical effects (Kidd 2005).

What is tooth decay?

It is important to consider the causes of tooth decay and how fluoride can be used to reverse the carious process. Dental Caries is a multifactorial disease caused by the action of acidogenic and aciduric bacteria (Streptococcus Mutans and Lactobacilli ({{32 Featherstone,J.D. 2008}}) on fermentable carbohydrates such as sucrose. Salivary glycoproteins form a pellicle on the tooth to which these bacteria attach to forming a pathogenic biofilm and over time, acid demineralisation and proteolytic destruction of the organic component of the enamel and dentine takes place (Young, Kutsch & Whitehouse 2009).

Dental Caries can be classified in several ways

According to location-Caries may be restricted to pits and fissures but may also progress to expose the pulp.

Restorative status of the tooth- Primary caries occurs on previously unrestored teeth whereas secondary caries occurs at margins of restorations {{52 Kidd,Edwina A.M. 2005}}. Secondary caries is caused by local factors that are involved in the formation of cariogenic plaque. Most secondary carious lesions develop at the gingival margins of restorations primarily in areas of stagnation areas (Mjör, 1998). Large gaps between the restoration and the wall of the cavity preparation can create an environment that favours secondary caries formation (Mjör, 1998). Secondary caries is also known as recurrent caries.

Caries can be arrested whereby a lesion which was previously active has now stopped progressing.

Fluoride: Mode of Action

Fig 1: Demineralisation Process and the role of fluoride (Cury, Tenuta 2008)

Figure one shows how sugars such as sucrose, glucose and fructose are converted to acids in the plaque biofilm. When the pH decreases below 5.5 (critical pH of enamel), the saliva is no longer supersaturated with calcium and phosphate. Therefore, demineralisation occurs. However, in the presence of fluoride and if the pH is higher than 4.5, hydroxyapatite is converted to fluorapatite which has a lower solubility. As a result, net demineralization is reduced and the dental hard tissues are more acid resistant. Tenuta and colleagues calculated that fluorapatite would not dissolve until the pH dropped below approximately 4.4. However, researchers have found that the effect of fluoride is not only due to the decreased solubility but also due to the effect of fluoride on the rates of demineralisation and remineralisation (Stoodley et al. 2008).

In order to enter bacteria, fluoride must be combined with a hydrogen ion forming hydrogen fluoride (HF), which readily diffuses into the cell. Once inside the bacterial cell, the HF dissociates into fluoride and hydrogen ions. The fluoride inhibits intracellular bacterial enzymes such as enolase. As a result, less phosphoenolpyruvate and lactate are formed. The reduced lactate formation limits the ability of bacteria to cause caries. Similarly, the uptake of glucose is also reduced by fluoride {{63 Featherstone,J.D. September 2004}}.

The fluoride concentration in saliva increases after brushing with a fluoride toothpaste. After three minutes, the concentration is 100 times greater than the baseline value (normally 0.03ppm or 1.6umol/l) {{65 Murray, J.J 1991}}. Two hours later, the concentration returns to normal. It is important to avoid rinsing out the mouth as the most profound effects of fluoride are within two hours of brushing. Fluoride is spread throughout the oral cavity and is stored in compartments on the tooth surface and the remaining pellicle (Cury, Tenuta 2008). Calcium Fluoride globules are formed and are reservoirs of fluoride, releasing it as the pH falls, thereby, reducing time spent in the demineralisation phase. The main effects of fluoride can be attributed to the maintenance of constant fluoride levels in the biofilm.

Overall, fluoride has multiple ways of reducing caries. It is believed that the most important of these methods is the remineralisation concept {{40 Oganessian,E. 2007}}, which requires a constant flow of fluoride. Bacterial enzyme inhibition plays a supplementary role when the concentration of fluoride is high which is achieved by topical fluoride applications and toothpastes (Murray, Rugg-Gunn & Jenkins 1991).

Who is at risk of decay?

There are certain groups in the population who are at risk of decay and therefore, would benefit from the use of fluoridated dentifrices. These include patients with:

Xerostomia, which may have resulted from the radiotherapy to the head or neck leading to salivary gland exposure. This leads to a decrease in both the resting and stimulated salivary flow rates. Xerostomia is defined as the complete absence of saliva or hyposalivation. Hyposalivation leads to decreased levels of calcium, phosphate and hydrogen bicarbonate ions. As a result, there is a longer demineralisation phase

Sjögren’s syndrome- this is clinically defined as at least two of kerataoconjuctivitis sicca, Xerostomia(dry mouth) and rheumatoid arthritis or another connective tissue disease {{62 Newbrun,E. 1996}}

A high incidence of caries in their primary dentition

Hypersensitivity

Root caries

Removable orthodontic appliances and partial dentures

A poor diet and those who regularly snack on fermentable carbohydrates {{37 Evans,R.W. 2008}}. However, this risk has decreased due to better plaque control and increased fluoride exposure.

Multiple restorations suggesting a high prevalence of caries

Optimum fluoride concentration required for remineralisation

Bjarnason and Finnbogason (1991) found that fluoride levels in dentifrices had no effect on the progression of enamel lesions detected radiographically. However, a higher fluoride concentration (1000ppm F-) led to reduction in caries initiation compared to a dentifrice with a lower fluoride concentration (250ppm F-) {{69 Bjarnason, S. 1991}}. It is ultimately difficult to decide the optimum fluoride concentration required for remineralisation as different areas of the mouth are more at risk of caries due to unique ecological factors. However, it was thought that lesion progression in enamel was slowed down only in patients with low caries activity whereas patients with high caries activity still experienced rapid progression (Hellwig, Lussi 2001).

DMF Index

The DMF index is a measure of caries activity in a population and changes in the DMF index can be used to highlight the protective effects of the fluoride toothpastes and varnishes (Kidd 2005).

D: decayed teeth with untreated carious lesions

M: missing teeth (extracted teeth)

F: filled teeth

DMFT denotes decayed, missing and filled teeth

DMFS denotes decayed, missing and filled surfaces in permanent teeth and therefore, the number of surfaces attacked on each tooth are accounted for.

There are similar indices for deciduous tooth, which are the defs and deft scores. The e represents extracted teeth to differentiate(Johansen et al. 1987) between natural loss of teeth through exfoliation.

Burt in 1998 suggested that greater emphasis has to be placed on the assessment and early diagnosis of caries {{77 Burt, B.A. 1998}}. This has been backed up by cohort studies {{83 Johansen, E. 1987}} (Axelsson, Lindhe & Nystrom 1991), which found that the use of preventive strategies (fluoride application) resulted in a substantial reduction in lesion development and progression.

Fluoride varnishes

What is fluoride varnish?

Fluoride varnish was first developed in New York in 1968 by Heuser and Schmidt in the form of sodium fluoride and was marketed under the name Duraphat. The Duraphat varnish contains 22,600 parts per million of fluoride (ppm Fˉ) as shown in figure 2. In the 1970’s, there was a switch from sodium fluoride to difluorsilane which was marketed under the name Fluor Protector (7000ppm Fˉ) in Germany {{42 Azarpazhooh,A. 2008}}.

Fluoride Varnish

Type of fluoride

Fluoride Concentration(ppm)

Fluoride Concentration(%)

Duraphat

Sodium Fluoride

22,600

2.26

Duraflor

Sodium Fluoride

22,600

2.26

Fluor protector

Difluorsilane

7,000

0.70

Fig 2: The table above shows the fluoride varnishes that are most commonly used.

Other types of fluoride varnishes include:

Fluoride Varnish

Type of fluoride

Fluoride Concentration(ppm)

Fluoride Concentration (%)

Lawefluor

Sodium Fluoride

22,600

2.2

Bifluorid

Sodium and Calcium Fluoride

56,300

5.6

Fig 3: The table above shows other fluoride varnishes which are available but are less commonly used {{24 Davies,G.M. 2008}}.

Most fluoride varnishes contain fluoride in an alcoholic solution of natural tree resin. The main advantage of the varnish is that the resin base is very adherent to the tooth prolonging contact time between the fluoride and enamel {{26 Miller,E.K. et al 2008}}. Varnishes are easy to apply and relatively safe regardless of the high fluoride concentration as the amount of varnish applied to one child is only 0.5 ml on average (Ripa 1990; Petersson 1993). Varnishes are slow-releasing reservoirs of fluoride preventing immediate release of fluoride after application (Ogaard 1994). As a result, they are most effective at protecting against primary caries. The food and drug administration centre in America has not yet accepted fluoride varnish as an anti-caries agent but considered it as a liner/desensitising agent (Mason 2005).

There is some debate as to the amount of fluoride taken up by the tooth surfaces. It was found that approximately half of the fluoride taken up by sound surfaces from Fluor Protector varnish was lost after 6 months suggesting that the large amount of fluoride taken up after one week does not bind permanently to enamel and that the effects of fluoride are more short term. There has also been a debate over whether fluoride varnish should be applied to wet or dry surfaces. Koch et al found that the fluoride uptake was much greater when the varnish was applied to dry tooth surfaces (Koch, Hakeberg & Petersson 1988).

Fluoride varnishes can be applied professionally up to two to four times a year. Marinho et al in 2002 investigated the effectiveness of fluoride varnish in preventing dental caries in children compared to a placebo or no treatment. Over 2700 systemically healthy children aged 16 or less received fluoride varnish containing 22,600ppm sodium fluoride. There was a large caries inhibiting effect on both permanent and deciduous dentition. However, the confidence intervals were relatively wide and the variation among the results was substantial. The success of the treatment may have been over estimated, as the results of the few trials may not have been representative. As a result, it is important to carry out more trials before a definite statement can be made of the effects of the fluoride varnish (Marinho 2002). In addition, more information is required on the scale of the fluoride effect and the adverse effects of fluoride.

Effect on the DMFT/dmft

Primary Dentition

There was a 33% decrease in the decayed, missing and filled surfaces (Marinho 2002). A two year randomised clinical trial carried out on children with a mean age of 1.8 years, found that the application of fluoride varnish once, twice and three times a year reduced the mean dmfs by 53%, 58% and 93% respectively {{67 Davies,G.M. 2009}}. This highlights the importance of frequent varnish application.

(Petersson, Twetman & Pakhomov 1998)Petersson et al. in 1998 found a 19% and 25% reduction in the increment of approximal caries in children with a moderate or high caries risk respectively. This shows that children with a high caries risk benefit the most from the application of fluoride varnishes (Zimmer 2001).

Ages 0-3

Weintraub and colleagues carried out a two year randomised controlled trial on 376 children aged between 6-44 months (Weintraub et al. 2006). The children were split into three groups:

Those who received counselling

Those who received counselling and the annual application of Duraphat

Those who received counselling and the twice yearly application at six monthly intervals

The number of lesions only increased in children who received counselling alone highlighting the protective effects of the varnish. Those children who received no varnish application were twice as likely of developing decay as those who received the annual application of fluoride. As the frequency of fluoride varnish application increased, the number of carious lesions decreased. One drawback of this trial was that simultaneous counselling and varnish application led to some ambiguity as to whether the effects were due to varnish application or counselling although fluoride application was seen to play a key role.

Ages 3-6

According to the Cochrane Review, there was an overall 38% reduction in the DMFS/dmfs (Marinho 2002). A two year randomised study of 1,275 children in Canada aged between 6 months and 5 years found that twice-yearly application of Durafluor led to an 18.3% reduction in the dmfs increment (Lawrence et al. 2006).

Mixed dentition

There was on average a 46% decrease in dmfs. The fluoride varnish was an effective preventive measure for partially erupted permanent molars. Equally, patients who are insufficiently co-operative benefit from fluoride varnish application (Marinho 2002).

Permanent dentition

A randomised clinical trial used to examine the impact of fluoride varnish on the incidence of approximal caries, detected radiographically in 13 year olds over a three year period, found that the varnish applied monthly and twice a year reduced caries by 76% and 57% respectively again highlighting the importance of frequent fluoride application{{67 Davies,G.M. 2009}}. The caries reduction in permanent teeth shown in the Cochrane review of trials was similar to that achieved in a metaanalysis carried out by Helfenstein in 1994 when Duraphat was applied 2 times a year in children aged 9-15 years (Helfenstein, Steiner 1994). There was a 38% reduction in the caries. It is likely that most of the participants benefited from the use of a fluoridated dentifrice as the majority of the studies were carried out in Scandinavian countries between 1973 and 1987. However, as both the Cochrane review and the Helfenstien study were carried out involving a different selection criteria, it is debatable as to whether the results from both these trials can be compared.

In conclusion, application of fluoride varnish two to four times a year on both permanent and deciduous teeth is associated with a reduction in the caries increment (Marinho 2002).

The effect of fluoride varnish according to different caries risks

Möberg Skold carried out a trial which involved the application of fluoride varnish to approximal caries in adolescents living in different caries risk areas. The trial involved 758 students aged between 13 to16 years old. The large sample size meant that the results of this study were representative. This is because as the sample size increases, the variability of the results decreases. This means that the results have a greater statistical power and smaller confidence intervals.

Fig 4: (Azarpazhooh, Main 2008) The figure above shows the groups which were chosen according to their caries risk and whether they had any fluoride in their tap water.

Duraphat was applied to the approximal surfaces from the distal surface of the canines to the mesial surface of the second molars. Each group had different intervals of application shown in the figure below:

Group

No. of participants

Frequency of Duraphat application

One

190

Twice yearly in six-monthly intervals

( 6 times in 3 years)

Two

186

Three times a year with a one week period each year(9 times in 3 years)

Three

201

Eight times a year during school terms with one month intervals

( 24 times in 3 years)

Four(Control)

181

No application

Fig 5: (Azarpazhooh, Main 2008) The frequency of Duraphat application

The results from this trial show that the biggest difference was between group one and the control group in high caries risk area (Göteborg). However, there was no significant difference between the groups regarding filled approximal lesions and approximal enamel lesions. There was a greater incidence of caries in the control group in comparison to the fluoride varnish groups in all risk areas highlighting the protective effects of the fluoride varnish (Möberg Skold et al. 2005).

Overall, it was found that the school based monthly application of fluoride varnish is the best method of preventing approximal caries in areas of medium and high caries risk (Möberg Skold et al. 2005).

School based prevention programmes

A cluster randomised trial was carried out by M.C Hardman and colleagues involving 2,091 school children living in a non-fluoridated area. One group of students (1,025 students) received the twice-yearly application of Colgate Duraphat varnish whilst the other group (1,066 students) served as a control. This study found that the twice-yearly application of fluoride varnish did not lead to a reduction in caries in children living in the community {{43 Hardman,M.C. 2007}}. This is contrary to what was found by Marinho and colleagues. They found that the biannual application of Duraphat in a school-based programme provided a caries inhibition of 38% in children aged 9-15 years (Marinho 2002). The study carried out by M.C Hardman and colleagues did not prove to be conclusive as the level of consent in the community was low. Approximately 110 students were lost during the study. The control group had lower caries levels than anticipated and therefore, it was difficult to tell the true effect of fluoride. In addition, the application of varnish was carried out under sub-optimal conditions (teeth could not be cleaned prior to application and the consumption of food and drink after application could not be controlled), which could have resulted in less profound effects. In conclusion, it was found that this type of fluoride varnish intervention is not effective in the prevention of caries in the public {{43 Hardman,M.C. 2007}}.

A similar study was carried in a small town located in the American Southwest on children attending a head start nursery using Duraflor as the varnish of choice. The trial began in the head start class of 2002. Duraflor was applied during well child visits every 9, 12, 15, 18, 24 and 30 months. The class of 2003 had no fluoride application and therefore, served as the control. The mean age was 4.40 years and approximately 168 males and 189 females took part. The results showed that children who received no treatment had a mean dmfs of 23.6 with a 95% confidence interval. Those children who received 1-3 treatments had a similar dmfs to those with no treatment. Only those children who had 4 to 5 treatments showed a reduction in dmfs again suggesting the importance of frequent application. However, this study was an observational study not a randomised study and therefore, the reliability of the results can be questioned. In addition, no attempt was made to determine whether the children who received four or more applications of fluoride varnish differed from the other children in terms of diet and oral hygiene history {{58 Holve,S. 2008}}..

The use of fluoride varnish in inhibiting secondary carious lesions

As mentioned earlier, secondary caries forms at the margins of restorations. Larger amounts of fluoride varnish may be trapped in the gap formed between the restoration and the cavity wall. This may serve as a slow releasing reservoir of fluoride, which could also provide a physical barrier against wall dissolution.

In a study carried out by M. Fontana in 1996, two experiments were carried out. Experiment one involved the application of Duraflor. Experiment two involved the application of Duraphat a year after the application of Duraflor. The effects of fluoride varnish on secondary caries remineralisation and lesion progression were measured. The varnish was applied to dry tooth surfaces and rinsing after fluoride application was prevented to enhance the remineralisation potential. The varnish was applied for 24 hours to prolong the contact time between the varnish and the tooth surface. The results from these two experiments showed that fluoride application slowed down lesion progression around both amalgam and composite restorations {{48 Fontana, M. 2002}}. The placebo varnish slowed down lesion progression to a lesser extent than the fluoride varnish suggesting that the effects may not only be attributed to the fluoride in the varnish.

These results matched those in a previous study carried out by Hellwig et al. in 1993. They examined the effect of Duraphat varnish on artificially created primary carious lesions and found that fluoride varnish led to remineralisation in the outer layers of enamel {{78 Hellwig, E.K. 1993}}. This slowed down lesion progression. Seppa suggested in 1988 that the benefits of fluoride varnish were attributed to their ability to enhance remineralisation of primary caries rather than their ability to increase the fluoride content of the tooth surface. This is contrary to what was previously thought that the effects of topical fluoride were due to their ability to maintain high levels of fluoride on the surface of the tooth. Seppa also found that the efficacy of the fluoride varnishes was dependent on the number of applications rather than the concentration of fluoride {{79 Seppä, L. 1988}}. This backs up the results found by Marinho et al that showed that the more frequent the application, the lower the incidence of new caries or the greater the decrease in mean dmfs/DMFS.

Fluoride toothpaste

What is fluoride toothpaste?

Fluoride toothpaste is the most widely used method of fluoride application in the population due to its ease of use. Fluoride toothpastes can be incorporated into community and school based prevention programmes. Most oral health care workers recommend brushing twice a day, once just before going to bed, as this is when saliva flow is at its lowest and once at another time of day{{68 Davies,R.M. 2003}}. They recommend spitting out the toothpaste after use rather than rinsing as this dilutes the fluoride concentration in the oral cavity as previously mentioned. The widespread use of fluoride toothpastes had made it more difficult to distinguish whether a reduction in caries is due to mechanical plaque removal or due to the incorporation of fluoride.

Before the widespread use of fluoride toothpastes, the importance of fluoride was illustrated in a three-year study. This study involved two groups of children aged 9 to 11 years who had benefited from supervised brushing either with or without fluoride toothpaste. Both groups showed a reduction in plaque and gingivitis but a significant reduction in caries was only seen in the group which used fluoridated toothpastes (Davies et al. 2003).

A typical toothpaste contains abrasives such as calcium carbonates, which help to remove surface debris, and stains on the tooth surface. Most toothpastes contain fluoride (added to toothpastes in the 1970s) to make the tooth more resistant to acid attack and is one of the most recognised agents in toothpastes. Stannous fluoride (also known as tin fluoride) was the first fluoride to be used due to its compatibility with the abrasive, calcium phosphate. Sodium fluoride could not be used at first as the calcium in the abrasive renders it ineffective and therefore, is not compatible. Sodium Monofluorophosphate was next used as it was compatible with the abrasives used with it. Sodium Fluoride could only be used when hydrated silica and sodium bicarbonate became the abrasive of choice. Studies have shown that the sodium bicarbonate-sodium fluoride combination lead to a caries reduction of one surface per child over two years (Murray, Rugg-Gunn & Jenkins 1991).

Fluorides have been shown to work better in combination with detergents such as sodium lauryl sulphates, which aid the remineralisation process and create foaming whilst brushing. Toothpastes contain humectants such as glycerol, which prevent the loss of water in the toothpaste. To provide taste, saccharin and other sweeteners are added. To stabilise the toothpaste, thickening agents such as seaweed colloids are included to ensure that the toothpaste stays on the toothbrush when it is applied.

The use of fluoride toothpastes in clinical trials

The Cochrane review of trials found that children who used fluoridated toothpaste had fewer decayed,missing and filled permanent teeth after three years. Brushing twice a day helps to increase the benefit of fluoride (Marinho et al. 2003 England).

Researchers believe that the effects of fluoridated toothpastes are underestimated in two to three year trials due to the life long used of fluoride. They also found that the use of fluoride toothpastes in areas of fluoridated water increased the protective effects. The normal concentration of fluoride in toothpastes is between 1000 and 1100 parts per million (ppm Fˉ). Toothpastes with higher fluoride concentrations (1500ppm) and lower fluoride concentrations (500ppm) are available in many countries. Toothpastes containing higher fluoride concentrations offer greater protection against caries (Stephen 1988; O’Mullane 1997).

Since the 1940s, more than a 100 clinical trials have been carried out and by the late 1970s, the protective effects of fluoride toothpastes were greatly accepted. As a result, many clinical trials could not have a control, as the removal of fluoride toothpaste for the trial was considered unethical. Therefore, the effectiveness of different concentrations of fluoride toothpastes have not been investigated extensively in placebo-controlled trails. The guidelines of caries trials have since been changed in order to combat this problem, by increasing the sample size so that the measurement error could be reduced (Marinho et al. 2003 England).

Children or adolescents aged sixteen or less were chosen to take part in the study carried out by Marinho et al. To assess the effect of the fluoride toothpaste, the caries increment was measured as a change in the value of the DMFS Index, in all permanent teeth erupted at the start and erupting over the course of the study.

Evidence from this study suggested that the use of fluoride toothpastes leads to a 24% decrease in dmfs. The confidence intervals for this reduction were 21-28%. This means that 1.6 children need to brush with fluoride toothpaste to prevent one decayed, missing or filled tooth surface in a population where the caries increment is 2.6 DMFS per year. Where the caries increment was lower (1.1 DMFS per year), 3.7 children needed to use a fluoride toothpaste in order to avoid one decayed, missing or filled tooth surface(Marinho et al. 2003 England). There was also a substantial reduction in caries increment (37%) of deciduous teeth in a trial carried out on 2008 children aged 6 to 9 years.

Another aim of the Cochrane review (Marinho et al. 2003 England) was to establish whether there was any relationship between the caries-preventive effects of fluoride toothpaste and the initial level of caries, previous exposure to fluoride and the frequency of fluoride toothpaste use on the prevented fraction. The prevented fraction (PF) is the proportion of disease occurrence in a population averted due to a protective risk factor or public health intervention (Gargiullo, Rothenberg & Wilson 1995). The prevented fraction was measured as the diffe

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