The study aimed to quantify the excess risk of interaction between high free sugars (sugars) intake and lack of exposure to water fluoridation on child dental caries. Data from the Australian National Child Oral Health Study, a population-based survey of 24,664 children aged 5 to 14 y, were collected using parental questionnaires and oral epidemiological examinations by trained examiners. Information on socioeconomic status, dental health behaviors, and dental service use was used as covariates. The number of servings of sugars-containing foods and drinks consumed in a usual day was assessed as the main exposure, categorized into 5 groups. Residential history was used to calculate lifetime exposure to fluoridated water (LEFW), categorized as low (<25%), medium (25% to <75%), or high (75%-100%). Caries prevalence (dmfs/DMFS >0) and experience (dmfs/DMFS) in the primary (ages 5-10 y) and permanent (ages 8-14 y) dentitions were the main dependent variables. The association of sugars intake and LEFW with each outcome was estimated in multivariable log-Poisson regression models with robust standard error estimation, adjusted for covariates. The relative excess risk due to interaction (RERI) between sugars intake and LEFW was estimated. Strong positive gradients in all outcomes were observed across sugars intake groups. Relative to the lowest intake group, the 3 highest intake groups had significantly higher adjusted prevalence ratios for having caries and higher adjusted mean ratios of caries experience in both dentitions, after controlling for all covariates. LEFW strongly and consistently attenuated the effects of all levels of sugars intake on the outcomes. RERI estimates indicated that a combination of lack of exposure to fluoridated water and high sugars intake resulted in greater excess risk of primary and permanent caries than if there was no interaction. Evidently, children with high sugars intakes and low exposure to water fluoridation are at disproportionately higher risk of dental caries.

*Original abstract online at https://pubmed.ncbi.nlm.nih.gov/33899569/