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Risk-Benefit Balance in the Use of Fluoride among Young ChildrenAustralian Research Centre for Population Oral Health, School of Dentistry, The University of Adelaide, Australia 5005 Correspondence: * corresponding author, loc.do{at}adelaide.edu.au
This study aimed to evaluate the risk-benefit balance of several fluoride exposures. Fluoride exposure history of randomly selected children was collected for calculation of exposure to fluoridated water, toothpaste, and other fluoride sources. We evaluated the risk-benefit balance of fluoride exposure by comparing dental fluorosis on maxillary central incisors, recorded at the time of the study with the use of the Thylstrup and Fejerskov Index, and deciduous caries experience, recorded at age six years, of the same group of South Australian children who were from 8 to 13 years old in 2002–03. Population Attributable Risk for fluorosis and Population Prevented Fraction for caries were estimated. Fluorosis prevalence was found to be 11.3%; caries prevalence, 32.3%; mean dmfs, 1.57 (SD 3.3). Exposure to fluoridated water was positively associated with fluorosis, but was negatively associated with caries. Using 1000-ppm-F toothpaste (compared with 400- to 550-ppm-F toothpaste) and eating/licking toothpaste were associated with higher risk of fluorosis without additional benefit in caries protection. Evaluation of the risk-benefit balance of fluoride exposure provides evidence to assist in the formulation of appropriate guidelines for fluoride use.
Key Words: fluoride • fluorosis • caries • risk-benefit balance • children
The use of fluoride for promoting oral health has always involved a balance between the protective benefit against caries and the risk of developing fluorosis. Monitoring fluoride exposure in childhood continues to be important in preserving the effectiveness of fluorides in caries prevention, while limiting the risk of fluorosis. Fluoride exposure during the first few years of life has a potential bidirectional association with oral health. On the benefit side, early fluoride exposure protects newly erupting deciduous teeth, creating a "biologically friendly" oral environment. It is suggested that this deciduous caries protection is an important outcome of early fluoride exposure per se, and is a predictor of later permanent caries experience (Li and Wang, 2002; Skeie et al., 2006). On the risk side, early exposure to fluoride is a risk factor for fluorosis (Fejerskov et al., 1994). The current generation of children is exposed to numerous fluoride sources, each of which has an unknown balance of benefit and risk. Identifying and maintaining an effective balance of the caries-protective benefit and the fluorosis risk are crucial to the confidence of the dental profession and the population in the use of fluoride. Epidemiological evaluation of the risk and benefit balance is often based on measurement of the hazardous and protective impact of an exposure (in this case, fluoride exposure) (Spassof, 1999). At the population level, the hazardous impact [where Relative Risk (RR) > 1] can be measured as Population Attributable Risk (PAR), which defines the proportion of cases (children with fluorosis) attributed to the exposure in the population. The protective impact (RR < 1) can be measured as Population Prevented Fraction (PPF), which defines the proportion of cases (children with caries) prevented by the exposure in the population. These impact indicators are of interest in epidemiological evaluation, because they measure the absolute impact of an exposure on a disease or condition in a population (Rose, 1994). This study aimed to evaluate the balance of benefit and risk of several fluoride exposures among South Australian children.
The study was nested in a large-scale population-based study, the Child Oral Health Study (COHS), conducted in 2002–04 among South Australian children attending the School Dental Service (SDS). The study design and data collection process have been detailed elsewhere (Do and Spencer, in press). Three sources of data were collected for each child: fluoride exposure history from the COHS questionnaire collected in 2002–03, caries experience from SDS-archived clinical records, and fluorosis experience collected in 2003–04. Caries experience data were extracted from SDS-archived clinical records (APPENDIX). For the purpose of this study, we used data recorded at the first available dental visit after a child turned six years old. We used only caries experience on deciduous molars and canines to calculate the prevalence of caries and dmfs score among the children when they were six years of age.
A fluoride exposure history of each child was collected through a 12-page self-administered parental questionnaire (Do and Spencer, in press). Percent lifetime exposure to fluoridated water for the birth-to-age-three-years period was estimated and used to categorize children into three groups: having 0% lifetime, > 0 & COHS participants in South Australia, who were born in 1989–94 inclusive (from 8 to 13 years old at the time of the study), and whose questionnaire and clinical caries data were available, were invited to be examined for fluorosis at their local SDS clinic. One calibrated dentist (LGD) conducted all the examinations using the Thylstrup and Fejerskov Index (Fejerskov et al., 1988) under standard clinical conditions. Permanent teeth were cleaned and dried with compressed air and scored for fluorosis. For this analysis, a case of fluorosis was defined as having a Thylstrup & Fejerskov (TF) Fluorosis Index score of 2+ on one or both maxillary central incisor. Children’s front teeth were photographed with a clinical digital camera. The maxillary central incisors were scored according to the TF Fluorosis Index, based on the photographs after the fieldwork completion, so that intra-examiner reliability could be calculated. The absolute agreement was above 80%, and the kappa scores ranged from 0.74 to 0.79 for each and both central incisors combined. We re-weighted the data to adjust for different sampling ratios and age and sex distribution. The weights were used in the analysis to produce representative estimates for the South Australian child population. Caries experience, recorded when a child was six years old, and fluorosis prevalence, recorded at the examination in 2003–04, were compared between and among groups with different levels of fluoride exposure in bivariate analyses. The case definition of caries for multivariate logistic regression models was the prevalence of caries at age six years, and the case definition of fluorosis was having a TF Fluorosis Index score of 2+ on one or both maxillary central incisors. We used fluoride exposures to generate logistic regression models for the fluorosis prevalence at the time of the study and the caries prevalence at age six years, with the significance level set at 0.05. All fluoride exposures in early childhood were included in the models, because all can theoretically be a risk factor for fluorosis and a protective factor for caries. Sex, birth cohorts, parental education, and household income were also included in the models. Estimates of those logistic regression models were used to estimate Population Attributable Risk (PAR) for fluorosis and Population Prevented Fraction (PPF) for caries, according to a method presented in the medical literature (Bruzzi et al., 1985). This method has previously been used in fluorosis research (Riordan, 1993; Pendrys, 2000). The number of potentially affected children was calculated as a function of PAR and PPF and the prevalence of fluorosis and caries. Ethics approval was obtained from the University of Adelaide Ethics Committee. Informed parental consent was received for use of caries data and for the children’s participation in the fluorosis examination.
A total of 677 children participated in the study (Table 1  ). A quarter of the children had been exposed to fluoridated water over half of their first three years, while another quarter had no exposure. Nearly half of the children commenced fluoridated toothpaste use before 19 months, but some 23% commenced it after 30 months of age. Two-thirds of the children reportedly used a children’s 400- to 550-ppm-F toothpaste. Half of the children reportedly had an eating/licking toothpaste habit.
A TF Fluorosis Index score of 2+ was observed on the maxillary central incisors of 57 children (11.8%). Among those, 48 had the same fluorosis scores on contralateral teeth. A TF Fluorosis Index score of 3 was the highest severity score observed. A TF Fluorosis Index score of 1 (visible only after teeth were dried) was observed in another 11.6%. A total of 603 (89%) children had had an archived clinical examination at age six years [mean age, 6.3 yrs (SD 0.4)]. The prevalence of deciduous caries was 32.3%, with a mean dmfs of 1.6 (SD 3.3).
Exposure to fluoridated water from birth to age three years was significantly associated with the prevalence of fluorosis and caries, in both bivariate (Table 2
Age when fluoridated toothpaste use began was also associated with both fluorosis and caries (Table 2  ). Commencing toothbrushing after 30 months was not related to significantly lower fluorosis prevalence, but was related to significantly higher caries prevalence and severity, compared with starting brushing before 30 months in either bivariate (Table 2) or multivariate analysis (Table 3). Commencing fluoride toothpaste use in the 19- to 30-month period was not associated with higher caries experience, compared with earlier commencement (Table 2).
The use of a children’s 400- to 550-ppm-F toothpaste when toothpaste use started was associated with a significantly lower prevalence of fluorosis. However, using this type of toothpaste was not associated with a significantly higher caries prevalence, in both bivariate (Table 2
The impact measures on fluorosis and caries of South Australian children are presented for fluoride exposures in Table 4
PAR estimates for fluorosis of several patterns of fluoridated toothpaste use ranged from 27 to 44% (Table 4 ). The use of standard 1000-ppm-F toothpaste was responsible for 27% of fluorosis cases, or 30 cases per 1000 children, compared with the use of children’s 400- to 550-ppm-F toothpaste. This exposure was not associated with a significant PPF against caries. Having an eating/licking toothpaste habit was attributed to 44% of fluorosis cases (50 cases/1000 children), without a significant association with caries at age 6 years. Swallowing slurry after brushing was attributed to 33% of fluorosis cases. Commencing toothpaste use before 30 months of age was not associated with a significantly higher risk of fluorosis compared with later commencement. However, that pattern was attributed to fewer caries cases at age 6 years (29%, or 95 cases/1000 children).
It is believed that this paper is the first study reporting the impact measurements (PAR and PPF) of fluoride use for both fluorosis and caries in the same children. Findings of this study can help evaluate the impact of fluorides. The study used population data specific for South Australian children. Therefore, generalizability of the study findings is dependent on each population’s fluoride exposure profile, oral health status, and SES. This study used complex data collection procedures. Retrospective and concurrent data were collected on inter-related aspects of oral health and their contributory factors. The comprehensive questionnaire collected fluoride exposure history, to facilitate estimation of fluoride exposures that could be related to both fluorosis and caries prevalence. Recall error is an inherent limitation of retrospective research. The COHS questionnaire was carefully designed to minimize such error. We tested the reliability of recalled data by comparing estimates of this sample with the whole COHS sample in South Australia. The fluoride exposure data of this study sample were similar to those reported by the parent COHS sample (unpublished), and by a study in Western Australia (Riordan, 2002). The examiner was blind to the questionnaire’s data at the examination, but not blind to a child’s current residence. However, current residence was not used as a direct explanatory factor. Although strongly related, current residence did not always reflect the exposure to fluoridated water during the birth-to-three-years age period used in this study. Caries data were collected by 31 uncalibrated clinicians. However, the clinicians used uniform manuals to perform the examinations. Also, analyses were based on the presence/absence of cavitated caries experience (either filled or not), which is reliable (Rugg-Gunn et al.,1976). Caries experience at age six years was used for the analysis, to coincide with the time when most children start enrolling in the SDS. Caries on deciduous molars and canines was used because anterior teeth were exfoliating, and permanent caries experience was negligible at age six. Fluorosis experience on maxillary central incisors at ages 8 to 13 yrs was used because all children would have those teeth present. Although limiting the observation to those teeth might underestimate the prevalence of fluorosis, maxillary central incisors are more appropriate, because they are developed (hence, at risk) during the first few years of life, when the issue of risk and benefit of fluoride exposure is most critical. Also, maxillary central incisors are the most observable teeth, given that the effect of mild fluorosis is esthetic. Future plans with the sample will focus on collection and analysis of data on fluorosis and caries in all permanent teeth. The risk-benefit balance of community water fluoridation has long been established. Water fluoridation has been hailed as one of the 10 most successful public health achievements for its benefit in preventing caries (CDC, 2001). Such a benefit of water fluoridation has often been found associated with a risk of fluorosis (Ismail et al., 1990; Szpunar and Burt, 1990; Riordan and Banks, 1991; Spencer et al., 1996; Mascarenhas, 2000). This study reported unadjusted and adjusted estimates of risk and benefit of exposure to fluoridated water. There was a significant association of exposure to fluoridated water with both fluorosis and caries among the same children. This suggests that a balance between the risk and benefit of exposure to fluoridated water already exists at the current level of fluoridation. A significant deterioration of child oral health would occur if exposure to fluoridated water was reduced or eliminated in Australia. Potential impact of any such change should always be carefully evaluated. Unlike water fluoridation, risk and benefit of toothpaste use can be dependent on patterns of its use and the oral health status of the children using it. The efficacy of fluoridated, as compared with non-fluoridated, toothpaste in the prevention of caries has been clearly established (Marinho et al., 2003). However, fluoridated toothpaste is one of the main sources of fluoride intake, thus contributing to a risk for fluorosis (Levy et al., 2001, 2003). Since almost all the children in this study population used fluoridated toothpaste, it was impossible to compare fluoridated toothpaste use with that of non-fluoridated toothpaste. However, components of fluoridated toothpaste use might still be modified to create a more favorable risk and benefit balance. Those components were: age when the use of toothpaste began, type of toothpaste, after-brushing routine, and an eating/licking toothpaste habit. These findings suggested that there was an opportunity to refine fluoridated toothpaste to lower the risk of fluorosis without significantly reducing its effectiveness in caries prevention. The measures might include encouraging commencement of toothpaste use in the 19- to 30-month age period, use of 400- to 550-ppm fluoridated toothpaste when toothpaste use starts, encouraging spitting after brushing, and (especially) preventing an eating/licking toothpaste habit in young children. Appropriate recommendations for toothpaste use and their timely dissemination to the public, especially parents of young children, would shift the balance toward more protection from caries without the unnecessary risk of fluorosis. Such recommendations are pertinent, given the significant risk of fluorosis attributable to those components of fluoridated toothpaste use. To conclude, water fluoridation and the patterns of fluoridated toothpaste use can have different risks and benefits for oral health. Appropriate guidelines that are based on the evaluation of the risk and benefit of each component of fluoride exposure can lead to a more beneficial outcome.
The study was supported by the University of Adelaide, by a National Health and Medical Research Council Project Grant, by an Australian Dental Research Foundation grant, and by the South Australian Dental Service. Professors John W. Stamm and Andrew J. Rugg-Gunn and two anonymous Reviewers are acknowledged for their highly constructive comments.
A supplemental appendix to this article is published electronically only at http://www.dentalresearch.org. Received for publication November 24, 2005. Revision received March 14, 2007. Accepted for publication April 15, 2007.
Journal of Dental Research, Vol. 86, No. 8,
723-728 (2007) This article has been cited by other articles:
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ABSTRACT
INTRODUCTION
50% lifetime, and > 50% lifetime exposure. Age when fluoridated toothpaste use began, and patterns of toothbrushing practice when toothpaste use began were collected and used in the analysis (APPENDIX). 
