The following is quoted from the Fluoride Free NZ FANNZ.ORG.NZ:
The truth about decay ratesI was kindly sent these Graphs of Waikato and Taranaki decay rates. These show that there actually is no real difference in decay rates between the fluoridated and non-fluoridated areas.
In the Taranaki data we see the balance tipping over to the non-fluoridated areas now that New Plymouth has become non-fluoridated since 2010.
Rural populations tend to have more decay than urban populations, presumably because of access to dental care and it is usually the rural parts of a region that are non-fluoridated. The Taranaki data highlights how when the urban area is non-fluoridated that the decay rates tip in favour of the non-fluoridated population.
Hopefully more graphs for other areas where there is both fluoridated and non-fluoridated populations will be provided in the future too.