Dr. Gary Slade of UNC School of Dentistry describes his study on the effects of fluoridation on dental caries in Australian adults and discusses implications for the U.S. population and cost-benefit calculations of community water fluoridation.
I’m Gary Slade. I’m a professor in the School of Dentistry at University of North Carolina at Chapel Hill. We did this study because there was a question in the Australian population that was begging to be answered. When we conducted our national dental health survey in 2004 there was this natural experiment regarding community water fluoridation and dental decay in adults. Fluoridation in Australia began only in the 1960s but in the very rapid space of about one decade the percentage of Australians with access to fluoridated water increased from 0 to about 65 percent so this natural experiment had four groups. Two of the groups were born before 1960. They’d had no experience of fluoride as children. They were not born with fluoride in drinking water but about half of them were exposed to fluoride as adults and a half of them were not. The younger cohort born 1960 or beyond, about a half of them were exposed to fluoride in drinking water for most of their lives but one half were not. So we conducted the studies because we wanted to determine not only if greater exposure to fluoride in drinking water was beneficial but secondly whether it was beneficial only for those who had grown up with fluoride. That’s the earlier younger generation. Or was it also beneficial for people born before 1960 who had not had fluoride when they were born.
We found preventive benefits of community water fluoridation in both cohorts for adults born before 1960 who had not had fluoridation as children. There was a ten to thirty percent reduction in levels of decay for people who live most of their lives in fluoridated areas compared to people who’d lived with little or no fluoridation. For the more recent generations born after 1960 there was a ten to twenty percent reduction in decay for that generation. Some of those people had lived all of their lives in fluoridated areas. In a strict scientific sense we can generalize the results only to the Australian population. However as a matter of sort of logical reasoning and extrapolation there are many similarities between that history in Australia and the history in the United States, particularly the rapid expansion of fluoridation and we know also the decay levels in adults by and large are fairly comparable between Australia and the United States. So the circumstances are fairly similar between the two countries in many respects, so it wouldn’t be unreasonable to expect a similar pattern and similar preventive effects of community water fluoridation in adults in the U.S.
Yes it does and there’s several ways to think about it. For example when we conducted this study in 2004, Australian population had about 16 million Australian adults and their average decay level was about 14. Now if you apply the same preventive benefit of about a twenty percent reduction that means that fluoride would be preventing something like 42 million decayed teeth in adults. The cost of fluoridating a water supply applies to an entire community so it makes sense that we should measure the benefits not only in children living in that community but for all children and adults. And in fact, Australian researchers, health economists, did a rigorous assessment of cost-effectiveness of water fluoridation. They found that whether or not adult benefits were factored in was critical. When benefits in reduced decay were also considered for adults they found that it was highly cost-effective to fluoridate even the smallest water supplies. In Australia, the national health the national oral health survey that we conducted face several challenges that is typical of population-based surveys. First we had to obtain a valid random sample of adults and get access to them so that we could interview them. We interviewed them first by telephone and then we wanted to dentally examine them. For researchers like us that creates a new requirement that we spend a good amount of time investigating potential bias because not everyone is going to take part in the study. In this paper we use some statistical methods to sort of ask the question what benefit would we have seen had everyone who we wanted to be in the study actually been in the study. That’s a statistical methodology that requires quite a bit of time and effort and skill, and it also requires us collecting data along the way, mindful of the fact that we will not have one hundred percent participation, mindful of the fact that we will have to analyze potential bias due to non-participation. There are challenges in a study like this where we have to inquire of people where they’ve been living. We had people do this at their home, in their own time with a self complete questionnaire. We didn’t want to try to rush this. I don’t think this is something you can rush and do over the telephone. It’s not a good method for that so we had this multi method of assessment in this survey. We had telephone interviews first of all. We followed it by dental examinations. We followed that by these questions done in the home where people were asked to recall where they had lived through their lives. We then had to map that information to existing records of water fluoridation in the places that they had lived and so we were reliant on having good public records that had been maintained and kept up to date about the fluoridation levels of communities in which those people had lived. And because it was a nationally representative sample, we had to know about fluoridation across the entire country. We found that water fluoridation was reducing decay significantly in adults. This means that fluoridation was having greater benefits in the population than many people previously had thought so communities can expect preventive benefits of water fluoridation to begin occurring as soon as they fluoridate.