Tooth decay rates throughout the western world have declined at a steep rate over the past 50 years, irrespective of whether a country fluoridates its water or not. This fact has invited scrutiny into the necessity and effectiveness of water fluoridation, particularly in light of the discoveries that (1) fluoride’s primary benefit to teeth comes from topical, not systemic application; and (2) unlike the research on topical fluoride products, such as toothpaste, there has never been a “randomized controlled trial” to scientifically demonstrate fluoridation’s benefits.
The need for a serious reappraisal of water fluoridation’s alleged benefits is further underscored by a series of large-scale studies that have sharply contradicted the findings of the studies that launched fluoridation. These studies, including from United States, Australia, Canada, and New Zealand, have repeatedly been unable to detect significant differences in tooth decay when using the “Decayed, Missing or Filled Teeth” (DMFT) measure of decay. As noted by Dr. Mark Diesendorf:
“[R]esults of recent large-scale studies in at least three countries show that, when similar communities are compared and the traditional DMFT index of dental caries is used, there is no detectable difference in caries prevalence. This has been demonstrated for schoolchildren in the major cities of New Zealand, Australia, the US and elsewhere.”
SOURCE: Diesendorf, M. et al. (1997). New Evidence on Fluoridation. Australian and New Zealand Journal of Public Health. 21: 187-190.
Because of the difficulty of detecting differences in tooth decay when using DMFT as the metric, most studies on fluoridation now use a more sensitive measure of tooth decay called “Decayed, Missing or Filled Tooth Surfaces” (DMFS). However, even where modern studies detect differences in DMFS between fluoridated and non-fluoridated areas, the differences are generally trivial.
In the largest dental study in the United States, for example, the average difference in tooth decay was just 0.6 tooth surfaces, which is less than 1% of the 100+ tooth surfaces in a child’s mouth. (Brunelle & Carlos 1990). Studies from Australia have found even less flattering results, with one large study finding no difference in DMFS, and others finding differences of just 0.12 to 0.3 tooth surfaces. (Spencer 1996). As noted in one recent review:
“For the past 50 years, CWF [community water fluoridation] has been considered the most cost-effective measure for the control of caries at the community level. However, it is now accepted that systemic fluoride plays a limited role in caries prevention. Several epidemiologic studies conducted in fluoridated and nonfluoridated communities clearly indicated that CWF may be unnecessary for caries prevention, particularly in the industrialized countries where the caries level has become low.”
SOURCE: Pizzo G, Piscopo MR, Pizzo I, Giuliana G. 2007. Community water fluoridation and caries prevention: a critical review. Clinical Oral Investigations 11(3):189-93.
For those looking for detailed discussions of some of the modern studies, you can find analyses of the following papers by clicking on the respective links: Levy (2009); Armfield & Spencer (2004); Brunelle & Carlos (1990), and Yiamouyiannis (1990).
Tooth Decay Rates vs. Total Fluoride Intake:
For a detailed discussion of the “Iowa Fluoride Study,” click here.
“These findings suggest that achieving a caries-free status may have relatively little to do with fluoride intake, while fluorosis is clearly more dependent on fluoride intake.”
SOURCE: Warren J, et al. (2009). Considerations on optimal fluoride intake using dental fluorosis and dental caries outcomes: A longitudinal study. Journal of Public Health Dentistry 69:111-15.
“This study reports changes in non-cavitated tooth surface diagnoses after a 4-year period… No fluoride, socioeconomic status or beverage variables were significantly associated with lesion progression.”
SOURCE: Warren JJ, Levy SM, Broffitt B, Kanellis MJ. (2006). Longitudinal study of non-cavitated carious lesion progression in the primary dentition. Journal of Public Health Dentistry 66(2):83-7.
“A Bayesian survival analysis is presented to examine the effect of fluoride-intake on the time to caries development of the permanent first molars in children between 7 and 12 years of age using a longitudinal study conducted in Flanders… Our analysis shows no convincing effect of fluoride-intake on caries development.”
SOURCE: Komarek A, et al. (2005). A Bayesian analysis of multivariate doubly-interval-censored dental data. Biostatistics 6:145-55.
Tooth Decay Rates vs. Fluoride Level in Water Supply:
A) U.S. Studies:
“For children’s dental health measures, it was found that fluoridation rates were not significantly related to the measures of either caries or overall condition of the teeth for urban or rural areas.”
SOURCE: Hendryx M, et al. (2011). Water fluoridation and dental health indicators in rural and urban areas of the United States. West Virginia Rural Health Research Center. Available at: http://wvrhrc.hsc.wvu.edu/docs/2011_fluoridation_final_report.pdf
“Greater toothbrushing frequently was significantly associated with fewer new non-cavitated caries, while gender, exam variable, and composite water level were not significantly associated with new non-cavitated caries. . . . Gender, SES, tooth brushing frequency, and composite water fluoride level were not significantly associated with new cavitated caries.”
SOURCE: Chankanka O, et al. (2011). Longitudinal associations between children’s dental caries and risk factors. Journal of Public Health Dentistry 71(4):289-300. [See discussion of study]
“Greater toothbrushing frequency was significantly associated with not having new cavitated caries, while gender, age at mixed dentition exam, and composite water fluoride level were not significantly associated with having or not having new cavitated caries. . . . A higher composite water fluoride level was significantly associated with not having new cavitated caries in girls (OR = 0.88, P = 0.08); however, it was not significantly associated with caries incidence in boys.”
SOURCE: Chankanka O, et al. (2011). Mixed dentition cavitated caries incidence and dietary intake frequencies. Pediatric Dentistry 33(3):233-40. [See discussion of study]
“This study assessed the relationship between dental caries and fluorosis at varying fluoride levels in drinking water. Methods: Subjects were followed from birth with questionnaires every 3-4 months to gather information on fluoride intake. 420 study subjects received dental examinations at age 5 on primary teeth and at age 9 on early-erupting permanent teeth… Conclusions: Fluorosis prevalence increased significantly with higher water fluoride levels; however, caries prevalence did not decline significantly.”
SOURCE: Hong L, Levy S, Warren J, Broffit B. (2006). Dental caries and fluorosis in relation to water fluoride levels. ADEA/AADR/CADR Conference, Orlando Florida, March 8-11, 2006. http://iadr.confex.com/iadr/2006Orld/techprogram/abstract_73811.htm [See discussion of study]
“Water fluoridation status of the children’s area of residence did not have a significant effect on Early Childhood Caries (ECC) at the 0.1 level of significance in the unadjusted logistic regression analysis, nor was it found to be a confounder of the effect of race/ethnicity on ECC prevalence in the multivariable model.”
SOURCE: Shiboski CH, et al. (2003). The association of early childhood caries and race/ethnicity among California preschool children. Journal of Public Health Dentistry 63(1):38-46.
“Higher fluoride proportions appeared to be associated with lower dfs + DFS, with an estimated difference between fluoridated and non-fluoridated groups of 0.65 decayed or filled surfaces per child, but this association was not statistically significant. The effects of fluoridation on the other outcomes were small and not statistically significant.”
SOURCE: Leroux BG, Maynard RJ, Domoto P, Zhu C, Milgrom P. 1996. The estimation of caries prevalence in small areas. J Dent Res. 75(12):1947-56.
“Data from Head Start surveys show the prevalence of baby bottle tooth decay is about three times the national average among poor urban children, even in communities with a fluoridated water supply.”
SOURCE: Von Burg MM et al. (1995). Baby Bottle Tooth Decay: A Concern for All Mothers. Pediatric Nursing 21: 515-519.
“Children attending centers showed no significant differences [in baby bottle tooth decay] based on fluoride status for the total sample or other variables.”
SOURCE: Barnes GP, et al. (1992). Ethnicity, location, age, and fluoridation factors in baby bottle tooth decay and caries prevalence of head start children. Public Health Reports 107: 167-73.span>
“An analysis of national survey data collected by the National Institute of Dental Research (NIDR) concludes that children who live in areas of the U.S. where the water supplies are fluoridated have tooth decay rates nearly identical with those who live in nonfluoridated areas.”
SOURCE: Hileman, B. (1989). New Studies Cast Doubt on Fluoridation Benefits. Chemical & Engineering News. May 8. [See discussion of study]
“We found that caries prevalences do vary between the geochemical regions of the state. In the total sample, however, there were no significant differences between those children drinking optimally fluoridated water and those drinking suboptimally fluoridated water.”
SOURCE: Hildebolt CF, et al. (1989). Caries prevalences among geochemical regions of Missouri. American Journal of Physical Anthropology 78:79-92.
B) Australian Studies:
“A less unexpected result of this study, given the findings for the deciduous dentition, was the lack of a significant relationship between consumption of nonpublic water and caries experience in the permanent dentition across any of the differing conditions of access to fluoridated tap water. Earlier research using these data on South Australian children had noted the small absolute mean number of permanent tooth surfaces upon which caries was prevented by exposure to fluoridated water supplies. The benefit was considerably less than noted for the deciduous dentition, and was smaller in South Australia than another comparison state, Queensland. Slade et al. suggested that these results reflected the lower caries experience of children in their permanent dentition, the possible impact of fissure sealants and the possible operation of a halo effect in South Australia. Although the halo effect would be expected to pertain to deciduous as well as to permanent teeth, the lower caries experience in permanent teeth may make the halo effect more of a problem in obtaining significant results in the permanent dentition than in the deciduous dentition. Against this background it was not unexpected that the association for exposure to nonpublic water was not strong, or statistically significant, for the permanent dentition.”
SOURCE: Armfield JM, Spencer AJ. 2004. Consumption of nonpublic water: implications for children’s caries experience. Community Dentistry & Oral Epidemiology 32:283-296. [See discussion of study & excerpts]
“lifetime exposure to fluoridation is associated with average reductions of 2.0 dmfs and between 0.12 and 0.30 DMFS per child compared with non-exposed children.” (Note: There are over 100 tooth surfaces in a child’s mouth. Out of these 100 tooth surfaces, this study found children with lifetime exposure to fluoridation had only 0.12 to 0.30 less surfaces with decay than children in non-fluoridated areas.)
SOURCE: Spencer AJ, et al. (1996). Water fluoridation in Australia. Community Dental Health 13(Suppl 2):27-37.
C) Canadian Studies:
“[S]urvey results in British Columbia with only 11 per cent of the population using fluoridated water, show lower average DMFT rates than provinces with 40-70 percent of the population drinking fluoridated water. How does one explain this?… [S]chool districts recently reporting the highest caries free rates were totally unfluoridated.”
SOURCE: Gray, AS. (1987). Fluoridation: Time for a New Base Line? Journal of the Canadian Dental Association. 10: 763-765.
D) New Zealand Studies
“I obtained the national figures on tooth decay rates of five-year-olds from our dental clinics which had served large numbers of these children from the 1930s on . They show that tooth decay had started to decline well before we had started to use fluorides (Fig. 1). Also, the decline has continued after all children had received fluoride all their lives, so the continuing decline could not be because of fluoride. The fewer figures available for older children are consistent with the above pattern of decline . So fluorides, while possibly contributing, could not be the main cause of the reduction in tooth decay.”
SOURCE: Colquhoun J. 1997. Why I changed my mind about fluoridation. Perspectives in Biology and Medicine 41(1):29-44. [See paper]
“Recent studies and reports agree that the differences in dental decay prevalence between fluoridated and non-fluoridated areas in New Zealand are small. For 12- and 13-year old children nationally the percentages who were caries-free in each kind of area differed by only 1 or 2 per cent, and were often higher in the non-fluoridated part of a health district.”
SOURCE: Colquhoun, J. (1987). Child Dental Health Differences in New Zealand.Community Health Studies 6: 85-90.
“In this study in oral epidemiology, officially collected statistics are presented which show that, 15 yr after fluoridation commenced in Auckland, New Zealand, there was still a significant correlation between dental health of children and their social class. They also show that treatment levels have continued to decline in both fluoridated and unfluoridated areas, and are related to social class factors rather than to the presence or absence of water fluoridation… When the socioeconomic variable is allowed for, dental health appears to be better in the unfluoridated areas.”
SOURCE: Colquhoun J. (1985). Influence of social class and fluoridation on child dental health. Community Dentistry and Oral Epidemiology 13:37-41.
E) Studies Elsewhere (Finland, Germany, Ireland, Iran, Mexico)
“The results of the dental examinations of 9,555 pupils (6 or 7 years old) of the first classes of all 63 primary schools in the Landkreis Mayen-Koblenz from 5 years are compared to the fluoride content of the drinking water. The data show no obvious correlation between dental health and fluoride concentration for any of the dental health parameters investigated. However, in spite of the low geographic resolution of social parameters, there was a notable connection between dental health status and sociodemographic indicators for the respective region. DISCUSSION: 30 years after the study by Einwag in the same region, the natural fluoride content of drinking water either had no influence on dental health at all, or this influence is so diminutive that it is exceeded by far by sociodemographic factors.”
SOURCE: Steinmeyer R. (2011). [Influence of natural fluoride concentration in drinking water on dental health of first class pupils in an area with enhanced fluoride content at the beginning of the 21st century]. Gesundheitswesen. 73(8-9):483-90.
“We found no significant relationship between fluoride exposure and dental caries experience in the permanent dentition.”
SOURCE: Vallejos-Sanchez AA, et al. (2006). Cross-Sectional analysis of dental caries in children with mixed dentition. ADEA/AADR/CADR Conference, Orlando Florida, March 8-11, 2006. http://iadr.confex.com/iadr/2006Orld/techprogram/abstract_73452.htm
“In the present study, fluoridated water did not seem to have a positive effect on dental health, as it might have been expected in a community with the respective caries prevalence.”
SOURCE: Meyer-Lueckel H, et al. (2006). Caries and fluorosis in 6- and 9-year-old children residing in three communities in Iran. Community Dentistry and Oral Epidemiology 34:63-70.
“In lifetime residents of fluoridated areas 47% had evidence of erosion; in 21% erosion had progressed to the dentine or pulp. The corresponding figures in non-fluoridated areas were 43% and 21% respectively… Levels in fluoridated and non-fluoridated areas were similar. ”
SOURCE: Harding MA, et al. (2003). Dental erosion in 5-year-old Irish school children and associated factors: a pilot study. Community Dental Health 20(3):165-70.
“[E]ven a longitudinal approach did not reveal a lower caries occurrence in the fluoridated than in the low-fluoride reference community.”
SOURCE: Seppa L. et al. (2002). Caries occurrence in a fluoridated and a nonfluoridated town in Finland: a retrospective study using longitudinal data from public dental records. Caries Research 36: 308-314.
“There was no statistically significant difference between DMFT in municipalities of the same size, regardless of the presence or absence of fluoride in the water supply…”
SOURCE: Sales-Peres SH, Bastos JR. (2002). [An epidemiological profile of dental caries in 12-year-old children residing in cities with and without fluoridated water supply in the central western area of the State of Sao Paulo, Brazil]. Cadernos de Saude Publica 18: 1281-8.