The cost-effectiveness of fluoridating water supplies in New Zealand

Objective: Tooth decay has been substantially reduced in New Zealand, and the difference in caries rates between fluoridated and non-fluoridated areas has narrowed. We investigated whether it is cost-effective to fluoridate water 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 population 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 further dental cost savings after age 45. Information on averted decay in 4 to 12 year old New Zealand children (29,000 receiving fluoridated water and 47,000 receiving non-fluoridated water) was available; information on averted decay in adults was obtained from a study in the United States. Sensitivity analyses investigated the effects of varying the Maori population proportion, the discount rate, and the number of fluoride injection sites. Results: Fluoridation was cost-saving (dental cost savings exceeded fluoridation 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.