The cost-effectiveness of fluoridating water supplies in New Zealand

Objective: Tooth decay has been substantially reduced in New Zealand, and t he difference in caries rates between fluoridated and non-fluoridated areas has narrowed. We investigated whether it is cost-effective to fluoridate w ater supplies that are now non-fluoridated. Methods: The net cost of fluoridation was based on the cost of fluoridating a water supply minus the averted costs of treating decay. A range of popul ation sizes was considered. The main analysis was conducted from a societal perspective, using a real discount rate of 5%. Fluoridation was assumed to occur continuously between the years 2000 and 2030. Other assumptions were a Maori population proportion of 15%, no new decay after age 34, and no fu rther dental cost savings after age 45. Information on averted decay in 4 t o 12 year old New Zealand children (29,000 receiving fluoridated water and 47,000 receiving nonfluoridated water) was available; information on averte d decay in adults was obtained from a study in the United States. Sensitivi ty analyses investigated the effects of varying the Maori population propor tion, the discount rate, and the number of fluoride injection sites. Results: Fluoridation was cost-saving (dental cost savings exceeded fluorid ation costs) for communities above about a thousand people. The true break- even community size may be lower. For smaller communities, fluoridation may be considered cost-effective depending on the non-monetised value assigned to an averted decayed surface. Conclusions and implications: Fluoridation remains very cost-effective, and is particularly so for communities with high proportions of children, Maor i, or people of low socio-economic status.