Key Points
Question What is the association between systemic fluoride exposure and dental fluorosis?
Findings This cross-sectional study of 2995 children and adolescents found that higher fluoride levels in water and plasma were associated with dental fluorosis.
Meaning These findings suggest that public health policy related to water fluoride levels and fluoridation should consider balancing caries prevention with dental fluorosis risk.
Importance While the effects of fluoride on health have been widely researched, fewer high-quality studies examine the association of fluoride levels in water and dental fluorosis.
Objective To investigate the association between fluoride exposure from drinking water and dental fluorosis.
Design, Setting, and Participants This cross-sectional study used the 2013-2014 and 2015-2016 National Health and Nutrition Examination Survey (NHANES) data (January 1, 2013, through December 31, 2016). NHANES uses a complex sampling technique to develop nationally representative sample estimates of the US population that consists of interviews and physical assessments. Children and adolescents aged 6 to 15 years were included because NHANES contains their data for all 3 forms of fluoride measures: plasma fluoride levels, water levels of fluoride, and dietary fluoride supplementation. Data were analyzed from January 1 to April 30, 2023.
Exposures Water and plasma fluoride levels were measured by laboratory personnel. Dietary fluoride supplement data were self-reported.
Main Outcomes and Measures The Dean’s Fluorosis Index was used to evaluate fluorosis status for each tooth. The dental fluorosis severity value was based on the second most affected tooth. Independent variables included plasma and water fluoride concentrations and dietary fluoride supplementation. An independent samples t test was used to compare fluoride exposures between groups, and Pearson correlation assessed the association between plasma and water fluoride levels. To assess whether fluoride exposures were associated with dental fluorosis, logistic regression analyses were conducted.
Results There were 1543 participants in the 2013-2014 NHANES cycle (weighted proportion male, 51.9%; mean [SD] age, 11.0 [2.7] years) and 1452 in the 2015-2016 cycle (weighted proportion male, 52.6%; mean [SD] age, 11.1 [2.8] years). A weighted 87.3% exhibited some degree of fluorosis in the 2013-2014 cycle and 68.2% in the 2015-2016 cycle. After adjusting for covariates in the 2015-2016 cycle, both higher water and plasma fluoride concentrations were associated with higher odds of dental fluorosis: adjusted odds ratios [AORs], 2.378 (95% CI, 1.218-5.345]) for water fluoride and 1.568 (95% CI, 1.038-2.499) for plasma fluoride. Fluoride supplements were not significantly associated with dental fluorosis: AOR, 0.741 (95% CI, 0.367-1.408).
Conclusions and Relevance The findings of this cross-sectional study suggest that exposure to higher concentrations of fluoride in water and having higher plasma levels of fluoride were associated with a greater risk of dental fluorosis. Further research can help policy makers develop policies that balance substantial caries prevention with the risk of dental fluorosis.
EXCERPTS:
In this cross-sectional study of a nationally representative population of US children and adolescents aged 6 to 15 years, we found that compared with the reference groups of 0.30 mg/L or less for fluoride water concentration and a plasma level of 0.30 umol/L or less, higher levels of fluoride in plasma and water were independently associated with an increased risk of dental fluorosis. These findings are consistent with previous studies that found dental fluorosis might occur even with low levels of fluoride exposure from water.18,19 To reduce the effects of water fluoridation, the DHHS and policy makers may need to reconsider current recommendations for water fluoridation. In addition, it was not surprising that children who used fluoride supplements experienced lower water fluoride concentration exposures than those who did not take any fluoride supplements. It was reassuring that in this group, fluoride supplements were not associated with an increased risk of dental fluorosis, since these findings were not statistically significant. This finding may support the American Dental Association’s recommendation that children at high risk for cavities with low fluoride levels in their drinking water can safely benefit from fluoride supplements.20
Another key finding was that the overall prevalence of fluorosis for both the 2013-2014 cycle (87.3%) and 2015-2016 cycle (68.2%) was greater than the 23% prevalence reported in 2004 by the Centers for Disease Control and Prevention.21 While the prevalence may seem surprisingly high, it parallels an upward trend identified by Wiener et al,22 who reported an increase of 31.6% in fluorosis prevalence in adolescents aged 16 and 17 years between 2001 to 2002 and 2011 to 2012. Our results also align with those of Neurath et al,23 who found large increases in both the prevalence and severity of fluorosis over a 26-year period, peaking at a prevalence of 65% in 2011 to 2012. One reason for the increase in fluorosis prevalence may be the wider use of fluoride toothpaste and dental fluoride treatments. In contrast, 1 possible explanation for the decline in prevalence between the 2013-2014 and 2015-2016 cycles seen in this study may be the 2015 recommendation by the DHHS to lower water fluoride concentrations from 1.2 to 0.7 mg/L to minimize the risk of dental fluorosis.12 This policy change is also consistent with the lower plasma fluoride levels seen in the 2015-2016 group. However, the full effect of the 2015 recommendation may not be evident until later NHANES cycles since some 2015 enrollees may have been exposed to higher fluoride concentrations when their permanent teeth were forming. Additional studies examining whether this decline persists will be important for assessing the new recommendation’s impact on fluorosis.
The finding that well over half of the study group had some degree of fluorosis suggests that strategies to reduce the prevalence of dental fluorosis may be of value. However, when policies to reduce dental fluorosis are considered, the flip side is the potential loss of cavity protection. As policy makers weigh this balance, it should be noted that Do and Spencer24 did not find a negative association between mild dental fluorosis and the perception of dental appearance, self-rated oral health, or child or parent perceptions about their oral health. Similarly, another study25 reported no negative effects on oral health–related quality of life with mild fluorosis and even some suggestion of enhanced oral health–related quality of life with mild fluorosis.
Strengths and Limitations
A strength of this study is its generalizability to the childhood population in the US. However, several limitations need to be considered. First, this study was cross-sectional rather than longitudinal, and while it demonstrates an association between fluoride exposure and fluorosis, this does not necessarily mean causation. Having a longitudinal study would allow for observation of the effect of fluoride over a longer period. Additionally, measuring fluoride levels in drinking water and plasma at a single time point might not accurately reflect exposure levels in the years when the permanent teeth of the participants were forming. The data for individuals who are ingesting tap water and were not reported may also contribute to the exposure levels. Receiving a fluoride supplement was a self-reported variable from the parents, and the use of questionnaires are subject to recall bias and misreporting. Furthermore, fluoride supplement use did not include information such as the length of use and the fluoride dose.
In this cross-sectional study of 2995 participants using data obtained from the 2013-2014 and 2015-2016 NHANES cycles, exposure to higher concentrations of fluoride in water and having higher plasma fluoride levels were associated with a greater risk of dental fluorosis. In the 2013-2014 cycle, 87.3% of children exhibited some degree of dental fluorosis and 68.2% in the 2015-2016 cycle, a reduction that may be due to the 2015 DHHS recommendation to lower water fluoride concentrations. Further research is needed to assess the new fluoridation standard and to incorporate fluoride exposures from dietary fluoride supplements, topical fluoride application, fluoride toothpaste, fluoridated water, and natural products without fluoride to help policy makers balance caries prevention with dental fluorosis.
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THE FULL-TEXT STUDY IS ONLINE AT
https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2806509
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