Impact of downward adjustment of water fluoride concentration on dental caries and fluorosis

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James, Patrice
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University College Cork
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Introduction: Community water fluoridation (CWF) was initiated in Ireland in 1964 at a concentration of 0.8 to 1 ppm fluoride. In 2007, in the context of ongoing reductions in dental caries with increasing prevalence and severity of dental fluorosis, water fluoride concentration in Ireland was adjusted to 0.6 to 0.8 ppm with the aim of reducing the prevalence and severity of dental fluorosis while maintaining reductions in dental caries. Aim: To determine the difference in dental caries and fluorosis levels following downward adjustment of CWF concentration. Methods: Ethical approval was obtained from the Clinical Research Ethics Committee (CREC) of the Cork Teaching Hospitals. A before and after study compared dental caries and fluorosis in random samples of 8-year-olds in Dublin (n=707) and Cork-Kerry (n=1,148) in 2016-17 with 8-year-olds in Dublin (n=679) and Cork-Kerry (n=565) in 2002. Dentinal caries experience in primary teeth (d3vcmft(cde)) and fluorosis in permanent teeth (Dean’s Index, whole mouth score) were clinically measured by trained and calibrated dentists. Standardised oral photographs were taken (8 seconds drying) for children in Cork-Kerry in 2016-17 and 2002. Fluorosis (Thylstrup-Fejerskov (TF) Index) in permanent maxillary central incisors was scored from the photographs in duplicate by two trained and calibrated dentists, blind to fluoridation status and year, with disagreements resolved by consensus. Person-level TF score was the highest score in the central incisors. Children were categorised as having lifetime or no exposure to CWF (Full-CWF/No-CWF). Effect of examination year on dental caries prevalence (d3vcmft(cde) > 0) and severity (mean d3vcmft(cde) among children with caries experience) and fluorosis prevalence (Dean’s ‘very mild’ or greater, TF 1 or greater and TF 2 or greater) were evaluated using multivariable regression controlling for the effects of other explanatory variables. Additional multivariable regression analyses evaluated the effect of CWF on dental caries prevalence and severity and fluorosis prevalence in 2002 and 2016-17, before and after the downward adjustment, respectively. Results: After controlling for the effects of other explanatory variables, children in Cork-Kerry in 2016-17, with lifetime exposure to CWF at 0.6 to 0.8 ppm fluoride, had lower caries prevalence (56% vs. 65%) and severity (mean d3vcmft(cde) 3.7 vs. 4.2) in primary teeth than their counterparts with No-CWF. Among children with Full-CWF, there was no statistically significant difference in caries prevalence or severity between 2002 and 2016-17. In 2016-17, caries prevalence was 55% in Dublin (Full-CWF) and 56% in Cork-Kerry (Full-CWF) and mean d3vcmft(cde) among children with caries was 3.4 and 3.7, respectively. Among children with No-CWF, caries severity was less in 2016-17 (mean 4.2) than 2002 (mean 4.9) (P = 0.039). The difference in caries severity between children with Full-CWF and No-CWF was less in 2016-17 than 2002 (Interaction P = 0.013), suggesting a reduced benefit for CWF in 2016-17. In 2016-17, fluorosis prevalence (Dean’s Index) was 18% in Dublin (Full-CWF) and 12% in Cork-Kerry (Full-CWF). Fluorosis was predominantly ‘very mild’ with no statistically significant difference between 2002 and 2016-17. Fluorosis prevalence in permanent maxillary central incisors was predominantly TF 1 and TF 2 and was lower in Cork-Kerry in 2016-17 than in 2002 at both case definitions. Among children with Full-CWF, prevalence of TF 1 or greater was 40% in 2016-17 and 75% in 2002 (OR 0.24, 95% CI [0.17, 0.34], P < 0.001) and prevalence of TF 2 or greater was 15% in 2016-17 and 27% in 2002 (OR 0.50, 95% CI [0.33, 0.75], P = 0.001). At both time points, fluorosis prevalence measured using Dean’s Index and the TF Index was higher among children with Full-CWF than their counterparts with No-CWF (2002 and 2016-17, P < 0.001). Conclusion: There was no reduction in fluorosis prevalence measured clinically using Dean’s Index in 2016-17 compared with 2002. However, fluorosis prevalence in the aesthetically important maxillary central incisors measured blind to year and fluoridation status from oral photographs was reduced following downward adjustment of water fluoride concentration. Based on the cross-sectional comparison of children with Full-CWF and No-CWF in 2016-17, the lower concentration of 0.6 to 0.8 ppm fluoride is an effective caries-preventive measure. However, the before and after study indicated that downward adjustment of water fluoride concentration may have reduced the caries-preventive effect of CWF in primary teeth. Further research is needed to evaluate the impact of the downward adjustment on dental caries in permanent teeth of children and adults with CWF.
Dean's Index , Thylstrup and Fejerskov Index , Dental caries , Water fluoridation , Dental fluorosis , Prevalence , Downward adjustment , DMF index
James, P. M. 2022. Impact of downward adjustment of water fluoride concentration on dental caries and fluorosis. PhD Thesis, University College Cork.
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