Seventh Meeting 5th April 2001

Presentation by Professor John Clarkson,
Presentation by Professor Hannu Hausen

Presentation by Professor John Clarkson

Professor Clarkson, Professor of Dental Public Health and Dean of the Dublin Dental School and Hospital, presented a paper entitled ‘Overview of Future Fluoride Delivery Systems’.

The talk was introduced with an overview of the history of fluoridation: from the observation of mottled enamel in Colorado Springs in 1901 to the studies of H. Trendley Dean in the 1930s of the inverse relationship between caries and mottling. Dean’s “21 city study” resulted in the observation that 1 ppm of fluoride in the water resulted in minimum mottling and maximum caries reduction.

Professor Clarkson made the point that many people forget that fluoride is a naturally occurring substance.

In looking at the mode of action of fluoride, Professor Clarkson referred to the original concept that the effect was systemic, a belief which was accepted for 20 to 30 years.

The current view is that the effect is primarily post-eruptive or topical, and that frequent low concentration exposure is most effective. The post-eruptive action consists of the following:

  • Promotion of re-mineralisation
  • Inhibition of de-mineralisation
  • Inhibition of glycolysis and
  • Inhibition of extracellular polysaccharides, which results in a reduction in the adherence of plaque.

The knowledge of this post-eruptive effect has been exploited in the development of “topical” methods of delivery of fluoride treatments.

Professor Clarkson went on to look at the optimal intake / exposure to fluoride. In the case of children the optimal intake is expressed in mg / kg body weight. The current estimate proposed by Burt is 0.05 to 0.07 mg / kg body weight, and is generally accepted internationally. (1) At this level the incidence of both fluorosis and caries is low.

In infants, the type of feeding employed influences total fluoride intake. Breast fed infants receive 0.002 mg / kg / day, which is well below the recommended optimal intake. (2) Infants fed on formula milk reconstituted with low fluoride water, receive 0.021 mg / kg / day. (3) However, infants receiving some formula milks, which have not had the fluoride levels adjusted and are reconstituted with fluoridated water, can be exposed to a significant amount of fluoride – in excess of 0.085 mg / kg / day. This is a risk factor for fluorosis in primary teeth. (1, 3-6)

Children between 6 months and 3 years on a mixed diet, receive 0.03 mg / kg / day in a non-fluoridated area, and 0.05 mg / kg / day in a fluoridated area. When fluoridated toothpaste (once a day) is added to this exposure, the amount received in the latter group can rise to 0.06 to 0.08 mg / kg / day if toothpaste is ingested.

When brushing with fluoridated toothpaste is increased to twice a day and fluoride supplements or rinses are used, the level of exposure can result in mild to moderate levels of fluorosis.

The critical risk factors for the development of fluorosis are as follows:

  • The age tooth brushing commences
  • The amount of toothpaste used and swallowed
  • Consumption of fluoridated water
  • Formula feeds reconstituted with fluoridated water and
  • The un-coordinated use of multiple sources of fluoride, i.e. supplements and rinses.

In older children the bio- availability of fluoride is possibly increased due to the reduced consumption of milk.

Professor Clarkson next spoke on the subject of dental fluorosis, which he defined as ‘a dose response effect caused by fluoride ingestion during pre-eruptive development of teeth’. This permanent hypo-mineralization of enamel is characterised by changes in the appearance of the tooth ranging from increased surface / subsurface porosity, fine white lines (which are difficult to see), a non translucent white enamel to pitting or staining of enamel.

The daily intake of fluoride influences the development of fluorosis in the following manner:

The original studies of Dean in the 1940s showed that water containing 1ppm of fluoride can result in a level of fluorosis at the questionable grade (Dean) in 30 to 35 % of children and in definite fluorosis (very mild / mild: Dean) in 10 to 15% of children. (7)

Water containing 2 ppm consumed at a level of 0.08 mg / kg / day will result in fluorosis in 50% of children and moderate fluorosis in 5%.

The prevalence of very mild / mild dental fluorosis is currently observed to be twice as prevalent as that observed in the 1940s. Historically, in fluoridated areas in the United States, very mild and mild fluorosis was seen in 10 to 15 % of children. Currently, 19% of 17 years olds and 26% of 9 year olds demonstrate very mild / mild dental fluorosis.

The prevalence of fluorosis (questionable / very mild ) in non-fluoridated areas in the United States is 10 to 20 times more prevalent than in the 1940’s; objectionable fluorosis ( ‘slight aberrations in the translucency of normal enamel, ranging from a few white flecks to occasional white spots, 1 to 2 mm in diameter’) has been reported as ranging from 0 to 2.4%.

In Ireland changes have been mainly seen in the questionable grade. Professor Clarkson illustrated this point with data from studies of children in the Eastern Health Board region.

The severity of dental fluorosis is dependent on the dose and duration and timing of exposure to fluoride. The crucial time for exposure is during the transitional and early maturation stage of the permanent teeth, which for maxillary incisors is at 15 – 24 months in males and at 21 to 30 months in females. Over the age of six years of age the risk of developing fluorosis in most permanent teeth is nil.

In the Eastern Health Board in 1984, 5% of 8-year-old children had questionable fluorosis and 2% had very mild fluorosis. (8)

In 1993 in the same age group the presence of questionable fluorosis had increased to 20%: very mild 2% and mild fluorosis 1%.

In 1997 in children in the Eastern Health Board, the prevalence of questionable fluorosis was 14%, very mild 6%, mild 3% and moderate 1%. (9)

Professor Clarkson proceeded to discuss the various indices employed to describe the extent and severity of dental fluorosis.

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Dean’s Index: The teeth are examined when wet; the questionable grade is difficult to see and calibrate examiners.

Thylstrup /Fejerskov Index: The teeth are examined when artificially dried (unnatural state). Scores 1 and 2 equate approximately to Dean’s questionable grade.

Tooth Surface Index of Fluorosis: This is more sensitive than Dean’s Index.

Developmental Defects of Enamel (DDE): This describes the full range of defects developmental defects than can affect enamel and is not as such an index of fluorosis. In this method the mouth is observed and a score is given to what is seen by the examiner and no differentiation is made between fluorosis and other defects of enamel.

The York Review included the DDE, which in Professor Clarkson’s view was unfortunate because it was not recording fluorosis ALONE.

Professor Clarkson proceeded to look at the risk factors for the development of dental fluorosis:

  • Fluoridated water
  • Fluoridated Supplements
  • Fluoride toothpaste
  • Infant formula feeds

With respect to risk associated with fluoridated water, fluorosis is greater in fluoridated areas than in non-fluoridated areas. In Ireland very mild and mild fluorosis can occur in up to 9% of children, with a small percentage with moderate fluorosis. As water consumption in general has not changed over the years, it would appear that the use of fluoridated dental products and possibly infant feeding practices are responsible for increases in fluorosis. As there is a clear association between the use of fluoride supplements and the risk of developing fluorosis, it is important that new dosing schedules should be used and supplements should not be used in fluoridated areas. A list of studies reporting an association between early fluoride supplement use and enamel fluorosis was presented at this point.

With regard to fluoride toothpastes, Professor Clarkson listed the following as risk factors:

  • The amount of toothpaste used
  • Swallowing the tootpaste
  • The age of brushing ( < 2 years)
  • Rinsing and
  • The frequency of brushing

The risk of developing fluorosis is higher if fluoridated toothpaste is used in early childhood, versus using it at a later date or not using it at all. However, the risk is not as high as that associated with the use of fluoride supplements. There is less risk of fluorosis if a pea size amount of toothpaste is used and also if paediatric toothpastes are used. These points were reinforced by reference to a number of studies linking early toothpaste use and the development of enamel fluorosis.

The risk factors associated with infant formula feeds were next considered. The consumption of some formula feeds reconstituted with fluoridated water is a possible risk factor for fluorosis in primary teeth. (4, 10, 11) The fluoride content since 1979 is less than 0.3 ppm in formula feeds manufactured in the United States. Again the points made were illustrated with reference to a number of international studies. (3-5)

The proportion of mild / moderate fluorosis attributed to excessive toothpaste use or fluoride supplements has been quoted as 78%; the cause of the remaining 22% is unknown. (12)

Professor Clarkson next considered methods employed to control dental fluorosis with respect to the various sources of fluoride.

  • Water: monitoring of fluoride levels and of intake
  • Fluoride supplements: The correct dose must be used in non-fluoridated areas in children over 6 years. Usage must be supervised and considered in children with a high risk of caries.
  • Fluoride toothpaste: Paediatric pastes should be considered for young children and tooth brushing should be supervised in young children. A small (pea size) amount of paste should be used in children less than 3 years of age.
  • Fluoride rinses: Generally not recommended in children under 6 years of age, but if used should be supervised.
  • Formula feeds: The powdered formula must be low in fluoride and their use should conform with infant feeding practices.

The objective of these measures is to balance the development of mild dental fluorosis against the development of rampant caries. At this point Professor Clarkson showed a number of slides depicting rampant dental caries as frequently seen in the 1960s, various degrees of dental fluorosis and demarcated dental opacities, which are often mistakenly labelled as dental fluorosis.

The various methods by which fluoride may be delivered were next considered.

  • Water fluoridation
  • Salt fluoridation
  • Milk fluoridation
  • Fluoridated sugar
  • Fluoride supplements
  • Fluoride toothpastes

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Water Fluoridation

In the case of water fluoridation, Professor Clarkson considered the benefits, the requirements for its application, the effectiveness and recommendations for the future.

Benefits

  • Involves modification of an existing environmental factor
  • No action required on the part of the consumer
  • Reaches all sectors of the community
  • Lower socio-economic groups have the greater benefit
  • Root caries is controlled in adults
  • A low continuous dose is available
  • There is a pre and post eruptive effect on teeth
  • It is a cost effective measure

Requirements

The World Health organisation has laid down a number of conditions, which must be in place in order for water fluoridation to be a viable proposition.

  • A level of dental caries in the community that is high or moderate
  • An attainment in the country of a moderate level of economic and technological development
  • Availability of water supplies that are good, consumed by the public and adequately funded
  • Availability of equipment in water treatment plants
  • Availability of a reliable supply of fluoride chemicals of acceptable quality
  • Availability of trained plant personnel

Effectiveness

With regard to the effectiveness of water fluoridation, Professor Clarkson showed the marked decline in dental caries that has occurred in 12 year old children living in Co. Dublin since 1961 and used the number of decayed, missing and filled teeth (DMFT) to illustrate this point.

Year

DMFT

1961

6.7

1970

4.5

1984

2.2

1993

1.2

The DMFT figures for children in other health boards (fluoridated and non-fluoridated areas) were then shown as were figures for Northern Ireland.

Fluoridated

Non-fluoridated

Year

Western HB

1.6

2.2

1992

Eastern HB

1.4

N/A

1993

Southern HB

1.3

1.8

1995

North Eastern HB

1.3

1.6

1995

Northern HB (N Irl)

None

3.3

1996 / 1997

The possibility of changing from water fluoridation to alternatives was considered by Professor Clarkson and acknowledged that there are a number of factors to be considered.

Caries levels had decreased, alternative sources of fluoride are available, water consumption patterns may be changing and sometimes there are difficulties maintaining the current level of fluoride in the water.

However, fluorosis is increasing but it appears that it is due to causes other than consumption of fluoridated water. (10, 13, 14)

Professor Clarkson made the following recommendations:

  • Maintain water fluoridation
  • Monitor levels in the water
  • Ensure technical standards
  • Monitor fluorosis levels
  • Research changes in water consumption
  • Evaluate the concentration range of fluoride in different regions and countries
  • Appropriate labelling of bottled water to show fluoride content. (In the United States most bottled waters have a fluoride level of < 0.3 mg / litre.)

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Salt Fluoridation

Fluoridated salt has been used in many countries since the 1950s: Switzerland, France, Costa Rico, Jamaica, Germany and South America.

A concentration of 200 mg Fluoride / kg may be regarded as a minimum when several types of salt are fluoridated (domestic and salt for bakeries, restaurants and other large kitchens), but twice this concentration may be appropriate when only domestic salt is fluoridated.

The effectiveness was illustrated with results of studies of dental caries (as measured by DMFT) in 12 year old children.

Country

Baseline Studies

Follow-up Studies

% Caries Reduction

Year

DMFT - 12

Year

DMFT - 12

Colombia

1964

6.7

1972

3.5

48

Costa Rico

1988

8.4

1996

4.8

49

Jamaica

1987

6.7

1995

1.1

83

Hungary

1966

8.2

1982

3.3

60

Mexico

1989

5.5

1999

-

-

Switzerland

1975

7.5

1983

3.4

51

As in the case of water fluoridation, the World Health Organisation has laid down a number of requirements for salt fluoridation to be commenced.

  • Water fluoridation is not possible due to multiple sources posing economic obstacles
  • Predominantly low levels of fluoride in the drinking water
  • Lack of political will for water fluoridation
  • Centralized salt production
  • The technical operations should be robust and monitored
  • Correct labelling of salt packages showing fluoride concentration

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Fluoridated Milk Schemes

New community milk schemes have been introduced in Bulgaria, Chile, China, Russia and in the United Kingdom, in which 5 mg fluoride are added to 1 litre of milk. Each child is given 200 ml of fluoridated milk every day for about 200 days a year. While results of these schemes have been encouraging, it is a limited public health measure.

Fluoridated Sugar

Further research is required on fluoridated sugar.

Fluoride Supplements

Fluoride supplements have limited application as a public health measure. Their use is associated strongly with the development of fluorosis.

Original dosage schedules were incorrect as they were calculated in an attempt to duplicate the fluoride intake of people receiving optimally fluoridated water. New schedules will take 7 to 10 years to assess.

In general, a dose of 0.5 mg / day should only be prescribed for children at risk in non-fluoridated areas, and starting only at age three years. The tablets should be chewed or sucked slowly and parents should be informed of the risks of overdosing.

Professor Clarkson made the point that any recommendations on the use of fluoride supplements rather than water fluoridation, the inconsistent effectiveness and definite risk of fluorosis must be balanced against the demonstrated effectiveness of water fluoridation and the low risk of fluorosis and that in his view perhaps the use of supplements should be eliminated completely.

Fluoride Toothpastes

There is high quality evidence available that brushing with a fluoridate toothpaste will reduce the incidence of dental caries. Well conducted 2 – 3 year clinical trials have demonstrated a 15 to 30% reduction in caries. Twice daily brushing maintains the level of fluoride in the saliva.

Standard toothpaste contains 1000 to 1100 ppm of Fluoride and is effective in reducing caries. A higher concentration (1500 ppm F.) has a slight advantage. Lower concentrations (250 ppm F.) have shown poor results; the effectiveness of toothpaste with 500 – 550 ppm F. has not been fully established.

Recommendations

Label containers

ppm F

Dispensers

Limit amount of paste

Brush twice daily

All individuals

Under 6 years

Pea sized portion

Supervised brushing

Clarify rinsing

Spit or rinse gently

Research

Low concentration – 550 ppm – children

High concentration – 1500 ppm – adults

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Topical Fluoride

Finally, Professor Clarkson dealt with the various methods of topical use of fluoride.

Professionally or individually applied gels or solutions.

Fluoride Gels

Fluoride gels are used in mouth trays, which allow the entire mouth to be treated in a single application. The professionally applied gels have a fluoride concentration up to 970 19,400 ppm F, while gels for individual application have a lower fluoride concentration (1000 to 5000 ppm).

Fluoride Varnishes

Fluoride varnishes are applied with brushes, a number of times a year, and have comparable caries-reduction benefits to other forms of topical fluorides.

Fluoridated materials

:Fluoride has been incorporated into dental materials such as amalgam, dental cements, composites and fissure sealants. The release of fluoride from these materials is short-lived, exhibiting a burst effect. There is some evidence that glass isomer cements and restorations have a sustained fluoride release and further research is warranted. Slow release fluoride devices have also been developed which may have a role in special needs patients.

Fluoride rinsing

Fluoride mouth rinsing is a widely used caries-preventive public health method. It can be used on an individual basis and in school-based programmes. Rinses for daily use contain 230 ppm of fluoride while rinses for weekly or fortnightly use contain 900 ppm. Fluoride rinsing is contraindicated in children under the age of 6 years, but is recommended for school children in low fluoride communities, bearing in mind the cost of implementing this measure and the caries status of the community.

Professor Clarkson concluded his talk by referring to the proceedings of an international workshop, attended by dental experts from throughout the world, which looked at the future research requirements on fluoride (15) and summarised his recommendations as follows:

  • The optimal intake of fluoride must be determined
  • All aspects of water fluoridation must be monitored
  • Intake of fluoridated toothpastes must be controlled in young children
  • Additional fluoride systems can be used for high risk individuals but must be well controlled
  • While levels of fluorosis in Ireland are low, they must nonetheless be well monitored
  • Ongoing research is required into all aspects of fluoride use.

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Presentation by Professor Hannu Hausen

Professor Hausen, Professor of Community Dentistry, University of Oulu, Finland delivered a presentation entitled ‘Experience of Water Fluoridation in Finland’.

He introduced his presentation by providing some background information on Finland and its oral health services.

Finland is a sparsely populated Nordic country with a population of approximately 5 million. It has been an independent country since 1917 and has been a member of the European union since 1995. (16) Health care is organised by local authorities, and services are mainly funded from tax revenues. Private sector health care supplements the services provided by the public sector.

Oral health care services are provided by both the public and private sectors. In 1972 the Primary Health Care Act obliged municipalities to organise oral health services for their populations.

As a result of this oral health care must be offered to:

  • Persons born in 1956 or later
  • Students
  • People who have had head or neck radiotherapy and to
  • War veterans

Most health centres offer oral health care also to special groups regardless of age (pregnant women, war veterans, people with an intellectual disability, people in receipt of social allowance and patients with serious general diseases).

However, because of economic constraints, some municipalities (mostly big towns) have restricted the number of groups entitled to care. Adults use mostly private dental services.

While public dental services are free of charge for all children and adolescents under the age of 19 years, child dental care starts before the child is born and includes considerable emphasis on disease prevention.

Manpower in oral health services has grown steadily during the last three decades and is now one of the highest per person in the world. There is on average one dentist for every 1000 inhabitants, which compares with one dentist for every 2,100 inhabitants in Ireland.

Professor Hausen described the effects of fluoridation in Finland. In general the natural fluoride content of the drinking water in Finland is low, but there are some areas with high natural fluoride levels.

At present water is not artificially fluoridated in Finland. The city of Kuopia, in central Finland, was fluoridated from 1959 until 1992, when it was discontinued following strong opposition from different civic groups. It was the only area in the Nordic countries ever to have artificially fluoridated water.

The main body of the presentation dealt with a review of different approaches to caries prevention among Finnish children and adolescents from the late 1950's until the present day. One of the earliest manifestations of fluoride-based caries prevention in Finland was water fluoridation in Kuopio, mid-eastern Finland that started in 1959. Professor Hausen regretted the fact that its effect was not evaluated properly from the very beginning. Since the middle of 1960’s, however, the average DMFT score among 7-year-olds in Kuopio was clearly lower than it was in Jyväskylä, a fairly similar nearby town with no water fluoridation. Ten years later the figures in Kuopio and Jyväskylä were equal, and since then there has been no systematic difference between the towns. These comparisons were based on data extracted from the patient records of public dental clinics (17) For 13-15-year-olds, the average DFS figure in 1973 was clearly lower in Kuopio than in Jyväskylä, but in 1982 no difference between the towns could be found in the study where a trained examiner examined the subjects.(18) The fluoridation in Kuopio was stopped in 1992 following opposition from civic groups.

Since then the occurrence of caries has not increased in Kuopio despite the fact that it was not compensated by increasing the use of other means of caries prevention. (19, 20) It seems apparent that at present the Finnish children and adolescents would not benefit much from the introduction of new water fluoridation programs. Professor Hausen made the point that this is due to the minor marginal utility of water fluoridation among a population that is exposed to a lot of other caries preventive measures and that there is ample evidence, however, that water fluoridation still works in countries where the level of other caries preventive efforts is lower.

In the 1960’s, fortnightly fluoride mouth rinsing programs were started in many communities, and in the 1970’s practically all schoolchildren took part in a fluoride-rinsing program or were exposed to some other means of topical fluoride, and the dental profession believed strongly in the beneficial effects of these efforts. According to a study by Tiainen and Ainamo however, children having participated in such a program for three years in the City of Vantaa, southern Finland, did not have less caries than comparable children who had received regular dental care only.(21) At that time practically no one could believe that the result was true. Afterwards, it seems likely that the result was due to a decreased marginal utility of fortnightly mouth rinsing in a situation where the use of fluoridated toothpastes was increasing rapidly. In the 1990’s, practically all communities in Finland had stopped fluoride mouth rinsing programs and replaced them with measures that were thought to be more effective, above all fluoride varnish applications and sealants.

Today the marginal utility of even fluoride varnish applications and sealants among the contemporary Finnish children and adolescents seems minor. According to an observational time-series study caries frequency in Kuopio and Jyväskylä was not higher in 1995 than in 1992 despite the fact that the average number of fluoride varnish applications and sealants was clearly lower in the three-year-period preceding 1995 than the corresponding period preceding 1992. (19, 20, 22) On the other hand, the three-year caries increment among children with high caries risk in a randomized clinical trial performed in the City of Vantaa between 1994 and 1997 was equal among children having received very intensive prevention and children who had received basic prevention only. (23) The intensified prevention included among other things decisively more fluoride varnish applications and sealants than the basic prevention did. While Professor Hausen found it difficult to point out any single factor responsible for the decreasing marginal utility of fluoride varnish and sealants in Finland, the use of fluoridated toothpastes has continued to increase, and the use of xylitol-containing products is increasing all the time. On the other hand, the yearly per capita consumption of candy increased by two kilograms between the beginning of 1990’s and 2000’s.

Between the middle 1970’s and the end of 1980’s, the average DMFT of Finnish 12-year-olds decreased steadily. Since the beginning of 1990’s no decreasing trend has been observed. It seems likely that in Finland the trend cannot be turned downwards by relying only on preventive measures that increase the resistance of the teeth. In countries, where the circumstances differ from those in Finland, the marginal utility of the above preventive measures can still be substantial.