Australian Dental Journal

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1 Australian Dental Journal The official journal of the Australian Dental Association Australian Dental Journal 2015; 60: doi: /adj The effect of lifetime fluoridation exposure on dental caries experience of younger rural adults LA Crocombe,* DS Brennan,* GD Slade, JF Stewart,* AJ Spencer* *Australian Research Centre for Population Oral Health, School of Dentistry, The University of Adelaide, Adelaide, South Australia, Australia. Centre for Rural Health, The University of Tasmania, Hobart, Tasmania, Australia. Department of Dental Ecology, UNC School of Dentistry, The University of North Carolina, Chapel Hill, North Carolina, USA. ABSTRACT Background: The aim of this study was to confirm whether the level of lifetime fluoridation exposure is associated with lower dental caries experience in younger adults (15 46 years). Methods: Data of the cohort born between 1960 and 1990 residing outside Australia s capital cities from the Australian National Survey of Adult Oral Health were analysed. Residential history questionnaires were used to determine the percentage of each person s lifetime exposure to fluoridated water (<50%/50+%). Examiners recorded decayed, missing and filled permanent teeth (DMFT). Socio-demographic variables, periodontal risk factors, and access to dental care were included in multivariable least-squares regression models. Results: In bivariate analysis, the higher level of fluoridation category had significantly lower DMFT (mean 6.01 [SE = 0.62]) than the lower level of fluoridation group (9.14 [SE = 0.73] p < 0.01) and lower numbers of filled teeth (4.08 [SE = 0.43], 7.06 [SE = 0.62], p < 0.01). In multivariate analysis, the higher number of full-time equivalent dentists per people was associated with a lower mean number of missing teeth (regression coefficient estimate = 1.75, p = 0.03), and the higher level of water fluoridation with a lower mean DMFT ( 2.45, p < 0.01) and mean number of filled teeth ( 2.52, p < 0.01). Conclusions: The higher level of lifetime fluoridation exposure was associated with substantially lower caries experience in younger rural adults, largely due to a lower number of filled teeth. Keywords: Allied health, dental health, health outcomes research, oral epidemiology, rural health. Abbreviations and acronyms: DMFT = decayed, missing and filled permanent teeth; FTE = full-time equivalent; NSAOH = National Survey of Adult Oral Health. (Accepted for publication 31 March 2014.) INTRODUCTION The oral health status of Australian adults residing outside capital cities is poorer than that of people living in capital cities. 1 Roberts-Thomson and Do 2 reported that people residing outside capital cities were more likely to suffer complete tooth loss, to have an inadequate dentition (less than 21 teeth), and to have more missing teeth than capital city residents. They also suffered from a higher dental caries experience, with a higher percentage of people having untreated coronal dental caries and a higher mean dental caries experience. However, periodontal pocketing, clinical attachment loss, and self-rated oral health did not significantly differ inside and outside capital city areas. Similarly, oral health-related quality of life (as measured by the mean OHIP-14 score) did not vary between inside and outside capital cities areas. Although clinical oral health as measured by dental caries experience and the mean number of missing teeth has improved in most areas of Australia, the gap in clinical oral health between non-capital city than capital city areas did not reduce between and People living in rural areas are more likely to have a lower socio-economic status, 4 and a marked socioeconomic inequality in oral health exists in Australian adults. 5 The supply of dental services tends to be lower outside of major cities, 6 with fewer preventive services and more dentures provided. 7,8 The capital city/ non-capital city divide in clinical oral health persisted after controlling for socio-demographic status, preventive dental behaviours, and access to dental care. 9 Water fluoridation is less common in areas outside capital cities than in capital city areas. 10 Research is needed that includes lifetime water fluoridation expo Australian Dental Association

2 Dental care access and rural clinical oral health sure. This study aimed to determine whether lifetime water fluoridation was associated with better clinical oral health in non-capital city residents born between 1960 and This is important because over recent years, fluoridation has been removed from, or not added to, water supplies in some rural areas of Queensland and New South Wales. 11 Policymakers need to know if these decisions will lead to poorer rural clinical oral health in the future. MATERIALS AND METHODS The birth cohort from the National Survey of Adult Oral Health (NSAOH) was used to ascertain the clinical oral health of Australian non-capital city residents. NSAOH used a clustered stratified random sampling design to select a representative sample of persons aged 15 years or more. Survey participants were interviewed by telephone and those who had one or more natural teeth were asked to attend a nearby dental clinic where standardized oral epidemiological examinations were conducted by one of 30 dentist examiners trained in the survey methods. At the completion of the clinical examination, participants were given a pamphlet explaining that a questionnaire, from which was obtained information such as socio-economic status and dental visiting behaviour, would be mailed to their homes. Australian postcodes were used to create two groups based on the Australian Bureau of Statistics postcode geographic classification: capital city ( metropolitan stratum) and remainder of state ( exmetropolitan stratum) with the ex-metropolitan stratum group born between 1960 and 1990 being used in this study. The Australian Capital Territory was defined as a single metropolitan stratum. In the Northern Territory, ex-metropolitan postcodes were limited to the regional centres of Alice Springs, Katherine, Tennant Creek and Nhulunbuy. The survey was reviewed and approved by The University of Adelaide s Human Research Ethics Committee. Full details of sampling, examination protocol and survey participation have been described in previous research. 13 A cohort born between 1960 and 1990 was used because the oldest people in this cohort were 46 years of age at the time of the survey, 12 thereby removing any DMFT ceiling effect 14 and to ensure that enough people with varying lifetime fluoridation coverage were obtained. The DMFT ceiling effect describes the situation whereby the DMFT does not increase beyond a certain age. Fluoridation commenced in 1964 in Canberra, Hobart and Townsville, Sydney and Perth in 1968, Adelaide in 1971, Darwin in 1972 and Melbourne in Oral health status The number of decayed, missing and filled permanent teeth (DMFT Index; the missing teeth component included only teeth which had been lost due to pathology such as caries or periodontal disease) was used to indicate a person s lifetime experience of dental caries. The number of decayed permanent teeth enabled inferences to be made about the burden of untreated disease and the number of missing and filled permanent teeth indicated patterns of dental treatment. Lifetime exposure to fluoridated water To calculate lifetime exposure to fluoridated water, 15 residential locations were matched to water supplies in every year, coding fluoride concentrations as: (a) <0.3 ppm F = 0; (b) 0.3 <0.7 ppm F = 0.5; and (c) 0.7 ppm F = 1.0. The number of years at each concentration was multiplied by the concentration. The products were summed and divided by the person s age to yield the person s proportion of lifetime exposure to the equivalent of 1 ppm F in drinking water (hereafter lifetime fluoridation exposure ). The sample was dichotomized by lifetime fluoridation exposure (<50%, 50%+) to obtain similar and sufficient numbers in each group. Putative confounders Putative confounders were selected on the basis of having been shown in previous studies to be associated with oral health: age, gender, 19,20 country of birth, 18 socio-economic status, 5,21 brushing with fluoride toothpaste, 22 using sugar-free gum. 23 Smoking 24,25 and diabetes 26 were included as putative confounders because they are associated with tooth loss, and hence could influence both DMFT via the missing tooth component of the index. Although the current evidence is unable to answer the question of whether regular interdental cleaning provides a benefit above and beyond brushing with fluoride toothpaste, 27 interdental cleaning was included as a putative confounder because it is currently recommended by dental professionals to maintain good oral health. 28 Socio-demographic characteristics Age was split into three groups of 15 25, and years. Country of birth was dichotomized into Australia or overseas. Socio-economic status was measured by education and level of income. The highest level of education was trichotomized into Degree/Teacher/Nursing, 2015 Australian Dental Association 31

3 LA Crocombe et al. Trade/Diploma/Certificate and no Post-Secondary school education. Total annual household income was divided into low if less than $30 000, high if equal to or over $60 000, and middle if in between these amounts. Preventive dental behaviours Oral hygiene behaviours were the number of times brushed (twice+ per day, less than twice per day), used mouthrinse last week (yes/no), used sugar-free gum last week (yes/no) and regular interdental cleaning (at least daily, less than daily, not regularly). The toothbrushing dichotomy was used because people have been recommended to brush at least twice daily. 29 Periodontal risk factors Two periodontal risk factors were included in the analysis because they may explain some of any differences in numbers of missing teeth. These were the presence of diabetes (yes/no) and smoking (current/ past/never smoked). Data analysis Data were weighted by age, gender and regional location to generate all statistics, thereby producing population estimates for the target population of dentate Australians aged 15 years or more. Categorical variables were summarized as percentages, while ordinal and continuous variables were summarized as means. The dependent variables were compared by regional location, socio-demographic variables, periodontal risk factors, preventive dental behaviours, access to dental care variables and lifetime exposure to fluoridated water. Bivariate analysis was undertaken to identify and describe associations between the outcome variables and main explanatory variables and to find potential confounders. Variables that were statistically associated with both the explanatory (lifetime fluoridation exposure) and at least one of the outcome variables were considered to be confounders. A multivariate analysis was then undertaken with the dental caries clinical measures as dependent variables. SUDAAN (Research Triangle Institute, Research Triangle Park, NC, USA) was used to adjust for complex analytical design, to weight for sampling probability and non-response. Proc Surveyreg provided hypothesis tests for the model effects and for linear combinations of the regression parameters. Access to dental care Access to dental care was measured using questions that assessed whether the participants were eligible for public dental care, the number of full-time equivalent (FTE) locally based dentists (50+ per people/under 50), whether they had a lot of difficulty in paying a $100 dental bill, the average time between dental visits (12 months or less, over 12 months), the usual reason for dental visits (check-up/problem), and whether they had avoided or delayed dental treatment because of cost (yes/no). In Australia socio-economically disadvantaged adults are eligible for public-funded dental care, but the rationing of resources has led to disadvantaged adults being more likely to receive treatment for acute dental problems 30 than preventive/routine care. The number of locally based dentists per head of population was included as an access to dental care variable because even though people may have the financial means and the incentive to access regular and preventive dental care, they may not be able to access dental care if there are not enough local dentists to provide that care. People who have difficulty paying a $100 dental bill would be unable to afford routine dental care, and avoiding or delaying dental treatment because of cost was a barrier to receipt of dental care. 31 RESULTS The sample had 466 respondents, born between 1960 and 1990 and residing outside Australia s capital cities, approximately half of whom had 50+% or less than 50% lifetime fluoridation exposure respectively (Table 1). Over two-fifths (42.5%) of the sample was aged years, with the rest evenly divided between the year (28.2%) and year age groups (29.2%). Approximately half (49.8%) were female and the majority (91.1%) were born in Australia. About one-fifth (19.2%) had an annual household income under $ per annum ($30 <$ %, $ %), and nearly half (46.7%) did not have a post-secondary education (Degree/ Teacher/Nurse 24.1%, Trade/Diploma/Certificate 29.1%). Mean DMFT Index was 7.49 (SE = 0.54), the largest component of which was filled teeth (mean number of decayed teeth 0.74 (0.95), missing teeth 1.26 (0.16), filled teeth 5.49 (0.43)). Over half brushed their teeth two or more times per day (52.1%), or used a mouthrinse at least daily (61.1%), did not use chewing gum in the previous week (64.9%) and only 14.3% used interdental cleaning at least daily (less than daily = 41.3%, not regularly = 44.4%). Few respondents had diabetes (2.9%) and fewer than one-fifth smoked (17.0%, past smoker 21.6%, never smoked 61.4%). Under a quarter of the respondents were eligible for public dental care (22.6%), few respondents (3.3%) were located where there were 50+ FTE dentists per population, and one-fifth (20.1%) had a lot Australian Dental Association

4 Dental care access and rural clinical oral health Table 1. Categorical lifetime fluoride exposure, putative confounders and dental caries measures Variables Dental caries measures DMFT Decayed teeth Missing teeth Filled teeth mean SE mean SE mean SE mean SE Lifetime fluoride exposure <50% 9.14* % * 0.43 Socio-demographic characteristics Age years 2.71* * * years years Gender Male Female Annual household income <$ * * * $30-<$ $ Highest qualification Deg/Teach/Nurs 7.19* * 0.57 Trade/Dip./Cert No Post Sec. Ed Country of birth Australia Not Australia Oral hygiene Times brushed Twice+ per day <2 per day Used rinse in last week Did rinse Did not rinse Used gum last week Did * Did not Regular interdental cleaning At least daily 9.08* * 0.70 Less than daily Not regularly Periodontal disease risk factors Diabetes Yes 13.28* * * 1.48 No Smoking Current smoker * Past smoker Never smoked Access to dental care Eligibility for public care Eligible Not eligible FTE dentists per head 50+/ * 2.60 <50/ Diff. pay $100 dental bill A lot * None - a little Av. time between visit 12 mths or less 6.97* * 0.29 >12 months Usual reason dental visit Check-up * * Problem Avoided/delay due to cost Yes 9.38* * * 0.59 No *p < SE = Standard error of the mean. of trouble paying a $100 dental bill. Under a half (43.8%) visited a dentist at least annually, approximately one-half (51.7%) usually visited a dentist for a check-up rather than a problem, and approximately one-third (34.9%) responded that they avoided or delayed dental care due to cost. The higher lifetime fluoridation exposure category had a significantly and substantially lower DMFT and a significantly lower number of filled teeth (Table 1). There was not a significant difference in the mean number of decayed teeth or the mean number of missing teeth. The putative confounders that significantly differed between the two lifetime fluoridation exposure groups were highest qualification and FTE dentists per people. Highest qualification was associated with the DMFT and filled teeth, and FTE dentists per people with filled teeth (Table 2). Though age, annual household income, diabetes and usual reason for visiting were not significantly associated with lifetime fluoridation exposure, it was decided to include them in the regression because they play an important role with dental caries measures. 16, Australian Dental Association 33

5 LA Crocombe et al. Table 2. Putative confounders and lifetime fluoridation exposure Putative confounders Lifetime fluoride exposure <50% 50+% n* Col % n* Col % p Socio-demographic variables Age 15 <25 years <35 years <45 years Gender Female Male Annual household income <$ $30 <$ $ Highest qualification Deg/Teach/Nurs Trade/Dip./Cert No Post Sec. Ed Country of birth Australia Not Australia Oral hygiene Times brushed Twice+ per day <2 per day Used rinse in last week Did rinse Did not rinse Used gum last week Did Did not Regular interdental cleaning At least daily Less than daily Not regularly Periodontal disease risk factors Diabetes Yes No Smoking Current smoker Past smoker Never smoked Access to dental care Eligibility for public care Eligible Not eligible FTE dentists per head 50+/ <0.01 >50/ Diff. pay $100 dental bill A lot None - a little Av. time between visit 12 mths or less >12 months Usual reason dental visit Check-up Problem Avoided/delay due to cost Yes No *n was not weighted to the Australian population. The DMFT Index and the mean number of filled teeth were significantly lower in the higher lifetime fluoridation exposure cohort than the lower lifetime fluoridation exposure cohort (Table 3). Age was significantly associated with all four dental caries measures, annual household income with DMFT and mean number of missing teeth, the highest level of education and diabetes with mean number of decayed teeth, and FTE dentists/ population with the mean number of missing teeth. The analyses were re-run using the lifetime fluoridation exposure as a continuous variable and similar associations were observed (DMFT: Est 0.03 p < 0.05; Decayed teeth: 0.00 p = 0.77; Missing teeth: 0.00, p = 0.87, Filled teeth: 0.03 p < 0.01). DISCUSSION Younger adults who resided in non-capital city areas who have a higher lifetime fluoridation exposure had a substantially lower dental caries experience and fewer filled teeth than younger adults who resided in non-capital city areas who have a higher lifetime fluoridation exposure. This is an important finding, particularly as some rural municipalities in New South Wales and Queensland are removing fluoride from their water supplies. The finding means that we can expect higher than necessary dental caries experience and filled teeth in areas without fluoridation and areas removing fluoride from their water supplies. McDonagh et al. 32 suggested that cessation of fluoridation Australian Dental Association

6 Dental care access and rural clinical oral health Table 3. Multivariate models for dental caries measures with socio-demographic, periodontal risk factors and access to dental care Variables Dental caries measures DMFT Decayed teeth Missing teeth Filled teeth Est.* p Est. p Est. p Est. p Socio-demographic characteristics Age (25 35 years, ref: years) 2.90 < <0.01 Age (35 45 years, ref: years) 8.01 < < <0.01 Annual Income ($ $59 999, ref:<$30 000) Annual Income ($ , ref: <$30 000) Education (Trade/Dip/Cert, ref: No Post Sec) Education (Deg/Teach/Nur, ref: No Post Sec) < Periodontal disease risk factors Diabetes (Yes, Ref:No) Access to dental care FTE dentists/ (<50, ref: 50) Usual reason visit (Check-up, ref: Prob.) Fluoridation (50%, ref: <50%) 2.45 < <0.01 *Est. = Regression coefficient estimate. R 2 = 0.35 Model p < 0.01 R 2 = 0.11 Model p < 0.01 R 2 = 0.15 Model p < 0.01 R 2 = 0.35 Model p < 0.01 resulting in a narrowing of the difference in caries prevalence between the fluoridated and nonfluoridated populations. The fact that similar findings were obtained when using the lifetime fluoridation exposure as a continuous variable was a sensitivity analysis and validity check. The FTE dentists/ population being significantly associated with the mean number of missing teeth suggests that increasing the number of dentists or other dental clinicians will result in fewer extracted teeth, but this is an expensive option. Although the costs of establishing, maintaining and operating a fluoridation plant may be high, particularly in more rural or remote areas, Cobiac and Vos 33 concluded that given the substantial dental health disparities and inequalities in access to dental care that currently exist for more regional and remote communities, there is good justification for extending coverage to include all Australians, regardless of where they live, despite less favourable cost-effectiveness. They further found that extending the coverage of public water supply fluoridation to all communities of at least 1000 people will result in cost savings to the health sector. Similar findings have been published in New Zealand. 34 The findings of this study support those found in a review by Rugg-Gunn and Do 35 who found water fluoridation to be substantially effective in caries prevention and also Griffin s et al. 36 systematic review which concluded water fluoridation reduced caries by 27% in adults. In Australia, Slade et al. 15 found that exposure to water fluoridation was associated with lower dental caries experience in adults who were born before and after widespread implementation of fluoridation. In a cross-sectional study involving Australian Army recruits, a dose response relationship suggested benefits of lifetime exposure to fluoridated drinking water through young adulthood. 37 Similarly, Mahoney et al. 38 found the degree of lifetime exposure to fluoridated drinking water was inversely associated with DMFT in a dose response manner in an adult military population. Looking at the limitations of this study, the use of a dichotomization to define regional location may not be sensitive enough to capture differing levels of rural exposure. This study excluded people without a landline, making it more likely to exclude some groups of people over others, e.g. Aboriginals and Torres Strait Islanders. Cause and effect cannot be obtained from cross-sectional surveys such as the NSAOH. The FTE dentists/ population and diabetes variables were based on small numbers in some cells, and hence these findings should be interpreted with some caution. Data on fluoride toothpaste or fluoride mouthrinsing exposure was not available, but there was no significant difference in toothbrushing or mouthrinsing frequency between the two lifetime fluoridation exposure cohorts. The DMFT index has inherent problems as a measure of dental caries experience. For example, it suffers from its mixing of disease and treatment, 39 and is based on the assumption that all filled teeth were carious prior to filling which may lead to an overestimation of the caries experience as expressed by the filled teeth component of the DMFT. 40 The oldest people in this cohort were under 45 years of age, thus negating the DMFT ceiling effect 41 whereby a participant s DMFT Index cannot go above a maximum value because all susceptible teeth have already decayed, or been extracted or filled. The DMFT Index 2015 Australian Dental Association 35

7 LA Crocombe et al. does not account for teeth lost for reasons such as periodontal disease, but tooth loss due to periodontal disease would only be a small factor in people aged under 45 years. We investigated decayed, missing and filled teeth components of the DMFT Index individually to ascertain which component factor of the index had the largest effect in its difference between the two lifetime fluoridation exposure cohorts. A major strength of this study was that NSAOH is only the second nationwide oral health survey held in Australia, had a large sample size, and the degree of nonparticipation bias was small. 13 There was a mix of naturally occurring optimal fluoride levels and that obtained through community water fluoridation programmes and that no differentiation was made in the analysis. Higher than necessary dental caries experience and filled teeth can be expected in areas without fluoridation and areas removing fluoride from their water supplies which will lead to increased costs when budgets are limited. Further research needs to be undertaken to see whether the findings are consistent between regional areas of Australia, or with the inclusion of other factors such as psychosocial factors, attitude to health, or whether similar findings are found with oral health-related quality of life. CONCLUSIONS Higher lifetime fluoridation exposure was associated with substantially lower caries experience in younger adults in rural areas of Australia, largely due to a lower number of filled teeth. ACKNOWLEDGEMENTS Organizations that supported the National Survey of Adult Oral Health were the National Health and Medical Research Council (Nos , , ); the Australian Government Department of Health and Ageing Population Health Division; the Australian Institute of Health and Welfare; Colgate Oral Care; the Australian Dental Association; and the US Centers for Disease Control and Prevention. REFERENCES 1. Australian Institute of Health and Welfare. Geographic variation in oral health and use of dental services in the Australian population AIHW Dental Statistics and Research Unit Research Report No. 41. AIHW Cat. no. DEN 188. Adelaide: AIHW, Roberts-Thomson K, Do L. Oral health status. In: Slade GD, Spencer AJ, Roberts-Thomson KF, eds. Australia s dental generations. The National Survey of Adult Oral Health Canberra: Australian Institute of Health and Welfare, 2007: Crocombe LA, Stewart JF, Barnard PD, Slade GD, Roberts- Thomson KF, Spencer AJ. 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