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OVERVIEW & SCRUTINY COMMITTEE – WATER FLUORIDATION BRIEFING AUGUST 2008

INTRODUCTION

Changes to the Water Act, enacted in 2003, have given Primary Care Trusts (PCTs) in the North West the opportunity to consider the possibility of water fluoridation as a method of reducing levels of dental caries (tooth decay) in the population.

Information has now been gathered for PCTs to enable them to decide whether they wish to request the North West Strategic Health Authority (SHA) to explore the possibility of water fluoridation. PCTs across the North West will now be taking the opportunity to engage with their key stakeholders to discuss this issue. At this stage this engagement will involve providing important updates on the decision making process involving PCTs and the SHA in the North West; sharing evidence; and seeking their views on the process by which each PCT will make a decision on whether to ask the SHA to explore the possibility of fluoridation.

The purpose of this paper is to summarise the circumstances relating to dental caries levels in the locality; describe the potential options to address these; to explain the legislative framework relating to water fluoridation; review contemporary guidance issued by the Department of Health; and to outline the decision making process involving each PCT in the North West. It is intended to support discussions to be held during the key stakeholder engagement phase.

Version 4 26-08-08 1 DENTAL CARIES IN BLACKPOOL

Dental caries is a common, preventable condition. It is a disease of the teeth in which micro-organisms convert sugar in the mouth to acid. This acid then erodes the teeth.

Average levels of caries prevalence (the number of individuals with one or more teeth affected by decay) and severity (the numbers of teeth affected by dental caries) in children in Blackpool as a whole are high compared with other areas in the North West, and fail to meet improvement targets set for 2003

Fig 1

5-year-old children's average tooth decay levels (dmft) and the percentage affected by tooth decay in 2005/06

(34%) Central & Eastern Cheshire 1.16 The percentage of children with one or more decayed, missing or filled teeth (35%) North Lancashire 1.28 is shown in brackets

(39%) Western Cheshire 1.38

(38%) Sefton 1.45

(39%) Warrington 1.54

(41%) Stockport 1.54

(40%) Trafford 1.59

(42%) Wirral 1.65

(42%) Cumbria 1.66

(45%) Liverpool 1.80

(45%) Central Lancashire 1.84

(46%) Bury 1.98

(47%) NORTH WEST 2.00

(50%) Halton & St Helens 2.09

(49%) Ashton, Leigh & Wigan 2.11

(47%) East Lancashire 2.13

(55%) Tameside & Glossop 2.24

(53%) Blackpool 2.27

(53%) Salford Teaching 2.42

(52%) Bolton 2.49

(53%) Oldham 2.60

(53%) Heywood, Middleton & Rochdale 2.68

(62%) Manchester 3.01

(62%) Knowsley 3.02

(63%) Blackburn with Darwen Teaching 3.21

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 3.25 3.50

Average dmft The Dental Observatory

Version 4 26-08-08 2 The proportion of children in Blackpool with dental decay at five years of age, measured in 2005/2006 is higher than the statistic for the North West and for England. This is illustrated in Figure Two.

Fig 2

Five year old children's average tooth decay levels (dmft) and the percentage affected by tooth decay in 2005/06 in the North West Local Authorities

(24%) Congleton 0.66 (26%) Crewe & Nantwich 0.77 The percentage of children with one or more (28%) Fylde 0.99 decayed, missing or filled teeth (34%) Vale Royal 1.14 is shown in brackets (32%) Ribble Valley 1.16 (32%) Chorley 1.21 (39%) Eden Valley 1.28 (34%) Lancaster 1.30 (38%) Chester 1.32 (33%) South Lakeland 1.36 (38%) Sefton 1.43 (40%) Wyre 1.45 (45%) Glossop 1.46 (38%) ENGLAND 1.47 (38%) Macclesfield 1.47 (39%) Warrington 1.54 (41%) Stockport 1.54 (40%) Barrow-In-Furness 1.59 (45%) Ellesmere Port & Neston 1.59 (40%) Trafford 1.62 (42%) Wirral 1.64 (42%) Carlisle & District 1.68 (46%) West Lancashire 1.78 (45%) Copeland 1.79 (45%) South Ribble 1.80 (46%) Liverpool 1.89 (46%) Bury 1.98 (47%) NORTH WEST 2.00 (51%) Halton 2.01 (49%) Allerdale 2.08 (49%) Wigan 2.11 (48%) Rossendale 2.12 (50%) St Helens 2.14 (53%) Blackpool 2.27 (53%) Hyndburn 2.30 (53%) Salford 2.42 (57%) Tameside 2.44 (50%) Burnley 2.45 (56%) Preston 2.46 (52%) Bolton 2.49 (54%) Pendle 2.53 (52%) Rochdale 2.56 (53%) Oldham 2.60 (61%) Manchester 2.92 (62%) Knowsley 3.02 (63%) Blackburn with Darwen 3.18

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75 Average dmft

Version 4 26-08-08 3 The consequences of suffering from caries for individuals and their families include severe pain, abscess formation, sleep loss for patients and parents or carers and behavioural problems. There may also be a need for extractions under general anaesthesia with its associated, potentially life-threatening risks. In 2005/2006 357 child residents of Blackpool were admitted to hospital for the extraction of teeth. Further, suffering from caries in childhood is the strongest predictor for suffering from caries in adulthood.

There are no local adult dental caries prevalence data available for Blackpool PCT. However, national data collected in the most recent UK Adult Dental Health Survey in 1998 suggest that, at local level there are likely to have been decreases in the levels of caries in adults since the 1970s. Notwithstanding the general reduction in caries prevalence across the country, marked regional differences were noted. For example, almost two-thirds (65%) of dentate adults in the North had at least one decayed or unsound tooth, compared with just over half of those living in the Midlands (52%) and the South (51%). This, added to the high levels of dental caries in children will mean that dental caries and its consequences will continue to affect a substantial proportion of the local population for the foreseeable future, unless additional preventive interventions are introduced.

Version 4 26-08-08 4 PREVENTING CARIES – THE OPTIONS

Fluoride has been the cornerstone of caries-preventive strategies for more than five decades. Fluoride acts principally topically. It prevents caries by acting in two main ways:

1. It reduces the loss of mineral from the tooth surface when it is under acid attack.

2. It repairs the damage caused by the caries process. As part of the repair process fluoride and makes the tooth more resistant.

There is a suggestion that fluoride also kills the bacteria that cause caries, but there is only weak evidence for this. It is important to note that fluoride has a caries-preventive effect on both children’s and adult’s teeth

There are a number of ways in which fluoride can be used to have a caries preventive effect. It may be present naturally, or can be added to drinking water, fluoride- containing salt, milk, toothpastes, mouth rinses, gels, varnishes and slow release devices are the modalities most used at present, either alone or in combination, to provide a predominantly topical caries preventive effect.

In addition to fluoride there are two other interventions which do not deliver fluoride that are commonly used in attempts to prevent caries. The first of these is the use of fissure sealants, which acts by physically protecting some vulnerable surfaces of teeth i.e. pits and fissures. The second is dental health education and promotion, which is intended to increase knowledge of caries-risk behaviour and attempts to improve dental health related behaviour.

As this paper principally relates to water fluoridation a summary of the evidence of the benefits and potential harms is given below. A more concise summary of each alternative intervention, the evidence of its effectiveness, and limitations is given below. A more comprehensive analysis of caries-preventive interventions can be found in a report prepared by the Office for Public Management in June 2008 which is discussed below. This has been the principal source of data for this section.

Water fluoridation

Version 4 26-08-08 5 Water fluoridation is the process of artificially topping up the natural fluoride in water to the level at which it can help to reduce tooth decay.

Gathering Evidence

The Department of Health commissioned York University to review the evidence of the safety and efficacy of fluoridation of drinking water (York Review). This was published in 2000. Details of the York Review objectives and findings can be found in Appendix One. When undertaking the review York Reviewers found little high quality research of relevance to their research questions. Having considered the findings of the York Review, the Government asked the Medical Research Council (MRC) to establish ways that the evidence for the benefits and disbenefits of fluoridation might be strengthened. The MRC reviewed the existing evidence, and considering the possibilities of adverse health effects, identified length of exposure may be relevant. The MRC acknowledged that whilst there had been over 40 years of exposure to artificially fluoridated water in Birmingham, other UK population groups had been exposed to naturally fluoridated water for considerably longer. To be confident that observations made on populations receiving naturally fluoridated water were applicable to the populations receiving artificially fluoridated water, on the recommendation of the MRC, the Department of Health commissioned a study into the bioavailability of fluoride in both artificially and naturally fluoridated water. This found no evidence of any differences between the absorption of fluoride ingested in artificially fluoridated drinking water and in drinking water in which fluoride was present naturally. Since this time a further review of evidence, commissioned by the Australian Government’s National Health and Research Council (Australian Review) has been undertaken which was published in December 2007.

Evidence of potential benefit

The York Reviewers were able to confirm that the best available evidence suggested that fluoridation of drinking water supplies does reduce caries prevalence and severity. The more recent Australian Review has not challenged this. It is noted that the review stresses that the degree to which caries is reduced is not definitive and reports a wide range of effectiveness both in terms of prevalence and severity. Available evidence also suggests that the more deprived an area, the greater the benefit derived from fluoridation on caries severity, whether it be natural or artificial.

The York Reviewers also found that caries prevalence rises following withdrawal of water fluoridation. These findings are supported by evidence from the North West,

Version 4 26-08-08 6 where there are three water treatment works that provide fluoridated water to the populations in their catchment areas. Hurleston supplies Nantwich and part of Crewe, whilst the two works in Cumbria together supply an area of West Cumbria which includes Workington and Whitehaven. Unlike the Cumbria schemes, the Hurleston scheme has been running since its inception in 1991.

The child population resident in Cheshire that has received an uninterrupted supply of fluoridated water have a significantly lower prevalence of caries compared with the population that have not. This was demonstrated across all socioeconomic groups. This effect was however not mirrored in the Cumbria child population that had been supplied with an interrupted supply of fluoridated water.

Evidence of potential harms

Considering potential harms, the York Review highlighted the association between water fluoridation and dental fluorosis 1 and estimated that at a concentration of 1 part per million (ppm), the prevalence of aesthetically objectionable fluorosis was estimated at 12.5%. During early fluoridation trials, it was found that 1ppm in temperate climates such as the UK gave a balance between minimising the risk of dental fluorosis whilst also giving major reductions in tooth decay.

Overall, no clear association between water fluoridation and incidence or mortality of bone cancers, thyroid cancer or all cancers was found. The studies examining other possible negative effects provided insufficient evidence on any particular outcome to permit confident conclusions.

Fluoridated salt

The caries-preventive effectiveness of fluoridated salt has not been studied in the UK. Nevertheless, studies carried out in other parts of the world demonstrate significant improvements in caries prevalence and severity. Given the risks for individuals in promoting the use of fluoridated salt, its use is not a viable option for a community programme.

Fluoridated milk

The majority of the relevant evidence finds that milk fluoridation schemes do reduce caries, but this reduction is not definitive. A recent study, carried out in Liverpool has

1 Dental fluorosis is a form of developmental defect of tooth enamel, which appears as markings on the surfaces of teeth. It is caused by excessive intake of fluoride when the teeth are developing. It varies from faint white flecks to more noticeable cream or brown stains with surface pitting. In most cases fluorosis is barely visible and only detectable by an expert..

Version 4 26-08-08 7 reported no significant benefits for primary dentition. The effectiveness of milk fluoridation schemes is heavily reliant on compliance at a number of levels.

Fluoride toothpaste

High quality evidence demonstrates that brushing with a suitable amount of an appropriate strength of fluoride toothpaste reduces caries in both the primary and permanent dentitions. The higher the fluoride concentration the better the effect. Caries prevention is also reliant on compliance. It is important that fluoride toothpaste is not ingested if fluorosis is to be avoided.

Fluoride varnish

Fluoride varnish is professionally applied. High quality evidence shows that it can substantially reduce caries in the primary and permanent dentitions as measured by both prevalence and severity. The effective use of fluoride varnishes requires compliance and regular attendance at dental services or the provision of a community- based scheme.

Fluoride tablets or drops

The use of fluoride tablets or drops can have a caries-preventive effect. They are not recommended for use in community schemes for a number of reasons including consent and compliance issues.

Fluoride mouth rinses

Fluoride mouth rinses have been shown to be an effective caries-preventive measure, and are recommended for use in the UK as part of an individual caries-preventive regime for those at high risk of developing caries. Their effectiveness is limited by compliance factors.

Fluoride gels and slow release devices

The use of fluoride gels and slow release devices (SRGs) and is targeted at high risk individuals. Fluoride gels are effective at reducing caries and SRGs can be more effective than water fluoridation, although this is due to the fact that they are targeted at high risk individuals rather than the general population. As these interventions are applied by a dental professional, they require regular attendance at dental services.

Version 4 26-08-08 8 Fissure sealants

High quality evidence has shown that that resin based fissure sealants are effective in preventing caries. As fissure sealants are applied by a dental professional, they require regular attendance at dental services.

Dental health education and promotion

There appears to be very little evidence on the caries-preventive effectiveness of dental health education and promotion. High quality evidence has shown that dental health education leads to improved knowledge levels and temporary improvements in oral health related behaviours.

Note

There are a number of interventions which can be implemented as part of a caries preventive regime for at both individual and population level. Some of these are already being used in schemes. This consideration of water fluoridation should be as an addition to these measures. It is noted that water fluoridation is the only community-based available option not requiring compliance at individual level.

Version 4 26-08-08 9 CONSIDERING WATER FLUORIDATION

PCTs are responsible for assessing the oral health needs of their population and for commissioning services or interventions required to address identified needs. In discharging their duty to improve oral health of their population, PCTs have been encouraged by the Chief Dental Officer to consider the option of fluoridating their water supplies.

Legislative framework

Arrangements for all the existing fluoridation schemes in the UK were made before 1985. In 1985 the ‘The Water (Fluoridation) Act 1985’ was passed and subsequently incorporated into ‘Water Industry Act 1991’. Part of this Act stated that, ‘Where a District Health Authority have applied in writing to a water undertaker for the water supplied within an area specified in the application to be fluoridated, that undertaker may, while the application remains in force, increase the fluoride content of the water supplied by the undertaker within that area’. Despite the policy intentions of successive UK Governments, because water undertakers did not feel equipped to make decisions on what they considered to be a public health issue, no new schemes were introduced under this legislation. This prompted amendments to the Water Industries Act 1991.

The Water Act 2003 amended Water Industries Act 1991 which now includes an obligation on water providers and reads as follows

“If requested in writing to do so by a relevant authority a water undertaker shall enter into arrangements with the relevant authority to increase the fluoride content in the water supplied by that undertaker to premises within the area specified in the arrangements”.

The relevant Authority in this case is a Strategic Health Authority(SHA)

In addition the Act also requires a relevant authority (SHA) to consult and ascertain opinion in accordance with regulations. These regulations are the Water Fluoridation (Consultation) Regulations 2005.

The Act also requires SHAs with fluoridation schemes to monitor their effects on the health of the population affected by the schemes and publish reports on their findings at four yearly intervals.

Version 4 26-08-08 10 Department of Health Guidance

In February 2008, the Chief Dental Officer for England circulated a document which included updated guidance on the respective roles of SHAs and PCTs in planning, consulting upon and implementing fluoridation schemes. It states that the legislation gives SHAs the executive role because water distribution systems are generally larger than areas covered by a single PCT.

The guidance says that after reviewing local oral health needs and considering the options for reducing tooth decay, the PCT may conclude that fluoridation of water could be the most effective solution to reducing the prevalence of dental disease and reducing inequalities in oral health. It is advised that the PCT may then approach the SHA in order to discuss the commissioning of a study from the water company to assess the technical feasibility and the cost of a fluoridation scheme. This is the stage that PCTs are about to embark upon in the North West.

North West Fluoridation Evaluation Group

Water flows in the North West are complex and span many PCT boundaries. As a consequence of the nature of these water flows in the region, the North West PCT Chief Executives (NW PCT CEOs) felt that the matter be best considered by the North West PCTs working together. They requested the establishment of a group to bring together information to support PCTs consideration of water fluoridation.

The North West Fluoridation Evaluation Group (NWFEG) was formed, funded by all 24 PCTs in the North West. The aim of the group was to assemble as much information and guidance as possible to allow individual PCTs to consider the relative merits and feasibility of fluoridation as one intervention aimed at improving dental health and dental health inequalities. The work has been conducted from a position of being neutral on fluoridation. It is now complete; the report has been released and is available on the Ashton Wigan and Leigh PCT website at www.alwpct.nhs.uk.

Version 4 26-08-08 11 NORTH WEST FLUORIDATION EVALUATION GROUP REPORT

The meeting of NW PCT CEOs received the report from the NWFEG on 27th June 2008. The report is comprehensive and covers the key areas that the PCT will need to consider when deciding whether to request the SHA to explore the possibility of fluoridation. It reiterates relevant parts of the guidance issued by the Chief Dental Officer in February 2008, and sets the context in terms relevant legislation and regional oral health. A review of the costs and benefits and risks of caries-preventive measures, commissioned from the Office of Public Management is included. These parts of the report are summarised above.

The remainder of the report addresses technical considerations, and outlines four possible schemes for the North West, with indicative costs. Sections on financial planning and recommendations are then presented.

United Utilities is the main operator of the water distribution system in the region. It operates upwards of 80 water treatment works of varying sizes throughout the North West of England. These plants supply almost the whole of the population of the North West SHA footprint with the exception of two small water zones, one near Chester and the other in Alston in Cumbria.

United Utilities does not supply water on the basis of PCT or SHA boundaries but on the basis of available reserves and gravity, so any fluoridation scheme is unlikely to deliver the optimal dose of 1ppm across a whole PCT area consistently for 365 days a year. The introduction of fluoridation at any given site is likely to miss out a number of desired target areas while also spilling over into other areas already enjoying relatively good dental health.

Four possible schemes involving groups of water treatment works have been identified in the North West on the basis of technical feasibility. These are:

1. a scheme for Greater Manchester and Merseyside (Figure Three)

2. a scheme for Greater Manchester and Merseyside, plus some other key locations (Figure Four) (includes Blackpool)

3. a scheme for almost the Whole Region (Figure Five)(includes Blackpool)

4. a scheme based on fluoridating most of the largest sites to take advantage of economies of scale (a. Woodgate Hill),(includes Blackpool) together with a sub-

Version 4 26-08-08 12 option (b. Watchgate) (includes Blackpool)adding a small number of sites in areas of particularly poor dental health (Figures Six and Seven)

Fig 3

Version 4 26-08-08 13 Fig 4

Version 4 26-08-08 14 Fig 5

Version 4 26-08-08 15 Fig 6

Version 4 26-08-08 16 Fig 7

Version 4 26-08-08 17 Costs

Indicative costs for each scheme are shown in Table 1

Table 1

The current guidance from the Department of Health on meeting the capital and revenue costs of any scheme states that:

‘Subject to the availability of funding, the Department will pay the capital costs of new schemes or the replacement of plant required to maintain existing schemes. SHAs should note that the fluoridation plant becomes an asset of the water company and is therefore excluded from the NHS capital charges arrangements.’

Therefore capital costs of any new scheme will not fall on SHA or PCT budgets. With regard to revenue costs for new schemes the guidance states that

‘The PCTs will have to reimburse the SHA for the recurring costs of the fluoridation scheme. PCTs may use funds allocated to them for primary care dental services to meet these costs’.

In principle, the allocation of costs to PCTs to reimburse the SHA for recurring costs would be calculated on a per capita receiving the benefit.

Version 4 26-08-08 18 PCT RESPONSIBILITIES – NEXT STEPS

The NWFEG report was also presented with an outline process, which lists both PCT and SHA responsibilities and timescales. This was considered by the SHA Board on 18 th July 2008 and has been published by the SHA.

PCT Board will need to decide whether it wishes to request the SHA to explore the possibility of fluoridation of public water supplies by 31st October 2008. The PCT Board will meet to consider this issue on the 10th September 2008. Should it wish the SHA to explore this issue, it will be required to express a view on the potential schemes presented in the report. Prior to consideration of fluoridation and the proposed schemes the PCT is engaging with key stakeholders to obtain their views as a contribution to the decisions to be made.

Version 4 26-08-08 19

PCT PROPOSED PROCESS

The process that the PCT will employ is diagrammatically illustrated in Figure Eight.

Fig 8

SHA Board North West Fluoridation Option Appraisal

y Agrees Steering Group (NWFOASG) established t i v

i Process and does further work to develop feasibility and t c Guidelines costs of a scheme based on the A

18.7.08 responses of PCTs at October A H S

PCT works with NWFOASG to refine possible scheme

T C P

/ Stakeholder Engagement r e

d Letters to councils Opportunity for stake holders to provide further l

o feedback and views h y

t Letters to professional bodies i e v k i t a t c

S A OSC 9/9/08 NWFEG Report

PCT y

t PCT PEC PCT Formal i

v Board paper i t

c Meeting Board Meeting Response to A

definitive scheme

T 13/8/08 10/9/08

C and decision to P request SHA to consult on it July Aug Sep Oct Nov Dec

Eric Rooney

Consultant in Dental Public Health

Version 4 26-08-08 20 APPENDIX ONE - THE YORK REVIEW OBJECTIVES AND FINDINGS

The York Reviews had five objectives, the findings are shown below. The reviewers considered evidence using quality criteria were based on a pre-defined hierarchy of evidence (A, B, and C), ‘A’ being the highest quality and ‘C’ the lowest quality.

Objective 1: What are the effects of fluoridation of drinking water supplies on the incidence of caries?

Results - Objective 1

A total of 26 studies of the effect of water fluoridation on dental caries were found. For this objective, the quality of studies found was moderate (no level A studies). A large number of studies were excluded because they were cross-sectional studies and therefore did not meet the inclusion criteria of being evidence level B or above. All but three of the studies included were before-after studies, two included studies used prospective cohort designs, and one used a retrospective cohort design. All before-after studies located by the search were included. The most serious defect of these studies was the lack of appropriate analysis. Many studies did not present an analysis at all, while others only did simple analyses without attempting to control for potentially confounding factors. While some of these studies were conducted in the 1940’s and 50’s, prior to the common use of such analyses, studies conducted much later also failed to use methods that were commonplace at the time of the study.

Another defect of many studies was the lack of any measure of variance for the estimates of decay presented. While most studies that presented the proportion of caries-free children contained sufficient data to calculate standard errors, this was not possible for the studies that presented dmft/DMFT scores. Only four of the eight studies using these data provided estimates of variance.

The best available evidence suggests that fluoridation of drinking water supplies does reduce caries prevalence, both as measured by the proportion of children who are caries free and by the mean change in dmft/DMFT score.

The studies were of moderate quality (level B), but of limited quantity. The degree to which caries is reduced, however, is not clear from the data available. The range of the mean difference in the proportion (%) of caries-free children is -5.0 to 64%, with a median of 14.6% (interquartile range 5.05, 22.1%). The range of mean change in dmft/DMFT score was from 0.5 to 4.4, median 2.25 teeth (interquartile range 1.28, 3.63 teeth). It is estimated that a median of six people need to receive fluoridated water for one extra person to be caries-free (interquartile range of study NNTs 4, 9).

The best available evidence from studies following withdrawal of water fluoridation indicates that caries prevalence increases, approaching the level of the low fluoride group. Again,

Version 4 26-08-08 21 however, the studies were of moderate quality (level B), and limited quantity. The estimates of effect could be biased due to poor adjustment for the effects of potential confounding factors.

Version 4 26-08-08 22 Objective 2: If water fluoridation is shown to have beneficial effects, what is the effect over and above that offered by the use of alternative interventions and strategies?

Results - Objective 2

To address this objective, studies conducted after 1974 were examined. While only nine studies were included for Objective 2, these would have been enough to provide a confident answer to the objective’s question if the studies had been of sufficient quality. Since these studies were completed after 1974, one might expect that the validity assessments would be higher than the earlier studies following the introduction of more rigorous study methodology and analytic techniques. However, the average validity checklist score and level of evidence was essentially the same for studies after 1974 as those conducted prior to 1974. Hence, the ability to answer this objective is similar to that in Objective 1.

In those studies completed after 1974, a beneficial effect of water fluoridation was still evident in spite of the assumed exposure to non-water fluoride in the populations studied. The metaregression conducted for Objective 1 confirmed this finding.

Objective 3: Does water fluoridation result in a reduction of caries across social groups and between geographical locations, bringing equity?

Results - Objective 3

No level A or B studies examining the effect of water fluoridation on the inequalities of dental health between social classes were identified. However, because of the importance of this objective, level C studies conducted in England were included. A total of 15 studies investigating the association of water fluoridation, dental caries and social class in England were identified. The quality of the evidence of the studies was low, and the measures of social class that were used varied. Variance data were not reported in most of these studies, so a statistical analysis was not undertaken.

There appears to be some evidence that water fluoridation reduces the inequalities in dental health across social classes in 5 and 12 year-olds, using the dmft/DMFT measure.

This effect was not seen in the proportion of caries-free children among 5 year-olds. The data for the effects in children of other ages did not show an effect. The small quantity of studies, differences between these studies, and their low quality rating, suggest caution in interpreting these results.

Objective 4: Does water fluoridation have negative effects?

Results - Objective 4

DENTAL FLUOROSIS Dental fluorosis was the most widely and frequently studied of all negative effects. The fluorosis studies were largely cross-sectional designs, with only four before-after designs. Although 88

Version 4 26-08-08 23 studies of fluorosis were included, they were of low quality. The mean validity score for fluorosis was only 2.8 out of 8. All, but one, of the studies were of evidence level C. Observer bias may be of particular importance in studies assessing fluorosis. Efforts to control for the effects of potential confounding factors, or reducing potential observer bias were uncommon. As there may be some debate about the significance of a fluorosis score at the lowest level of each index being used to define a person as ‘fluorosed’, a second method of determining the proportion ’fluorosed’ was selected. This method describes the number of children having dental fluorosis that may cause ‘aesthetic concern’.

With both methods of identifying the prevalence of fluorosis, a significant dose-response relationship was identified through a regression analysis. The prevalence of fluorosis at a water fluoride level of 1.0 ppm was estimated to be 48% (95% CI 40 to 57) and for fluorosis of aesthetic concern it was predicted to be 12.5% (95% CI 7.0 to 21.5). A very rough estimate of the number of people who would have to be exposed to water fluoride levels of 1.0 ppm for one additional person to develop fluorosis of any level is 6 (95% CI 4 to 21), when compared with a theoretical low fluoride level of 0.4 ppm. Of these approximately one quarter will have fluorosis of aesthetic concern, but the precision of these rough estimates is low. These estimates only apply to the comparison of 1.0 ppm to 0.4 ppm, and would be different if other levels were compared.

BONE FRACTURE AND BONE DEVELOPMENT PROBLEMS There were 29 studies included on the association between bone fracture and bone development problems and water fluoridation. Other than fluorosis, bone effects (not including bone cancers) were the most studied potential adverse effect. These studies had a mean validity score of 3.4 out of 8. All but one study were of evidence level C. These studies included both cohort and ecological designs, some of which included analyses controlling for potential confounding factors. Observer bias could potentially play a role in bone fracture studies, depending on how the study is conducted.

The evidence on bone fracture can be classified into hip fracture and other sites because there are more studies on hip fracture than any other site. Using a qualitative method of analysis (Figure 8.1), there is no clear association of hip fracture with water fluoridation. The evidence on other fractures is similar. Overall, the findings of studies of bone fracture effects showed small variations around the ‘no effect’ mark. A meta-regression of bone fracture studies also found no association with water fluoridation.

CANCER STUDIES There were 26 studies of the association of water fluoridation and cancer included. Eighteen of these studies are from the lowest level of evidence (level C) with the highest risk of bias. There is no clear association between water fluoridation and overall cancer incidence and mortality. This was also true for osteosarcoma and bone/joint cancers. Only two studies considered thyroid cancer and neither found a statistically significant association with water fluoridation.

Overall, no clear association between water fluoridation and incidence or mortality of bone cancers, thyroid cancer or all cancers was found.

OTHER POSSIBLE NEGATIVE EFFECTS

Version 4 26-08-08 24 A total of 33 studies of the association of water fluoridation with other possible negative effects were included in the review. Interpreting the results of studies of other possible negative effects is very difficult because of the small numbers of studies that met inclusion criteria on each specific outcome, and poor study quality. A major weakness of these studies generally was failure to control for any confounding factors.

Overall, the studies examining other possible negative effects provide insufficient evidence on any particular outcome to permit confident conclusions. Further research in these areas needs to be of a much higher quality and should address and use appropriate methods to control for confounding factors.

Objective 5: Are there differences in the effects of natural and artificial water fluoridation?

Results - Objective 5:

The assessment of natural versus artificial water fluoridation effects is greatly limited due to the lack of studies making this comparison. Very few studies included both natural and artificially fluoridated areas, and direct comparisons were not possible for most outcomes. No major differences were apparent in this review, however, the evidence is not adequate to make a conclusion regarding this objective.

Version 4 26-08-08 25

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