Non-Fluoride Trace Metals in Drinking Water and Oral Health Outcomes: A Scoping Review of Global Evidence

Abstract

Background/Objectives: The impact of non-fluoride trace metals (NFTMs) in drinking water on oral health remains an under-explored area of environmental health. This scoping review maps global evidence on the associations between non-fluoride trace metals (NFTMs) in drinking water and oral health outcomes, such as dental caries, enamel hypoplasia, and periodontal diseases. Methods: A systematic search of electronic databases including PubMed, Scopus, Web of Science, and Embase was executed to identify peer-reviewed observational and experimental studies published within a 10-year window between January 2015 and December 2025. Data extraction captured geographic settings, target populations, specific metal exposures, oral health assessment indices, and observed health parameters. Results: A total of 20 studies met the inclusion criteria, consisting of 16 cross-sectional studies, 2 case–control studies, 1 prospective cohort study, and 1 experimental laboratory evaluation. Heavy metals such as lead (Pb), cadmium (Cd), and arsenic (As) were frequently associated with elevated risks of dental caries and structural enamel defects, such as demarcated opacities. Conversely, elements like molybdenum (Mo) demonstrated potential inverse, protective associations with caries prevalence. Most of the evidence relies on cross-sectional designs, which limits the ability to infer temporal pathways or direct biological causation. Conclusions: The mapped literature indicates that non-fluoride trace metals in drinking water are associated with shifts in oral health outcomes. However, substantial heterogeneity in exposure pathways, geographic variability, and the lack of standardized mixture-risk assessments limit definitive conclusions. Future prospective epidemiological tracking and standardized multi-metal exposure models are required to clarify these environmental pathways.