The impact of the downward adjustment of fluoride concentration in the Malaysian public water supply on dental fluorosis and caries

In Malaysia, the public water supply has been artificially fluoridated since 1972 at an optimum level of 0.7 ppm fluoride as a public health measure to control dental caries. However, concerns arose that a fluoride concentration of 0.7 ppm was too high given increasing exposure to other sources of fluoride. That prompted a downward adjustment of the fluoride concentration from 0.7 to 0.5 ppm in 2005. In addition to Malaysia, there has recently been a movement towards the downward adjustment of fluoride concentration in the water in the United States, Hong Kong, Singapore and Ireland. However, little is known about the impact of such adjustments on oral health. This thesis aimed to evaluate the outcome of the downward adjustment of fluoride concentration in the Malaysian public water supply from 0.7 to 0.5 ppm in relation to dental fluorosis and dental caries. Two projects were conducted. The first project comprised a systematic review to critically appraise the literature on stopping the addition of fluoride or reducing the level of fluoride in public water supply on dental caries and fluorosis. This review highlighted the gaps in knowledge and several methodological issues such as lack of examiner blinding and control of confounders. The second project was a cross sectional survey involving life-long residents aged 9 and 12 year-olds in fluoridated and non-fluoridated areas in Malaysia (n=1155). In the fluoridated area, children aged 12 years and 9 years were exposed to 0.7 and 0.5 ppmF respectively at the times when maxillary central incisors enamel developed. Fluoride exposures were assessed by questionnaire. Standardized photographs of maxillary central incisors were blind scored for fluorosis using Dean’s Index. Caries prevalence was examined using ICDAS-II criteria. The key findings indicated that the change in fluoride iv level from 0.7 to 0.5 ppm has reduced fluorosis and maintains caries preventive effect. The change in fluoridation concentration has also had a significant impact on caries prevalence at different thresholds of severity. The findings support the policy initiative of a lower fluoride concentration in the Malaysian public water supply. It also highlights the need for modification of oral health advice with regards to fluoride exposure in maximising caries prevention while minimising fluorosis