Dental Fluorosis Incidence in New Zealand

Dental fluorosis is a defect in tooth enamel caused by fluoride poisoning of the body cells that make the tooth enamel. It appears as discolouration of the tooth, from white flecks to brown or black staining in advanced cases. It is the first sign of fluoride poisoning of children while their teeth are forming. The US National Research Council’s 2006 report identified a number of studies linking dental fluorosis with other more serious adverse health effects. Two studies have been conducted in NZ since 2000 – the Auckland study 2008 and the Southland study 2005.

The Auckland Study 2008

Prevalence of enamel defects and dental caries among 9-year-old Auckland children. Schulter PJ, Kanagaratnam S, Durward CS, Mahood R NZ Dental Journal December 2008 (p145-152) Summary This study found that water fluoridation increases the incidence of dental fluorosis, but has no lasting benefit in reducing tooth decay. The study concluded that there had not been a significant increase in fluorosis incidence since the 1980s (which was already 3 times higher than predicted when fluoridation was first proposed). The levels reported then were around 25% to 28% (Colquhoun, 1985). Dental fluorosis incidence

  • 29.1% of fluoridated children had dental fluorosis compared with 14.7% of unfluoridated children
  • Diffuse opacities (dental fluorosis) were the predominant tooth defects

Tooth decay rates

  • There was no difference in tooth decay rates in the permanent teeth (this differs from the Southland study, but at age 9 there is often an apparent benefit, likely due to delayed tooth eruption caused by fluoridation, that disappears by age 12 to 15 – see Armfield and Spencer, 2004)
  • There was no statistically significant difference in tooth decay rates in deciduous (“baby”) teeth based on affected tooth surfaces (dmfs score)
  • Fluoridated children had less tooth decay in deciduous teeth on a per tooth basis (dmft) and number of children caries free (62% v 55%)

The study noted that:

  • international research shows that the increase in dental fluorosis levels is directly related to total fluoride intake, and detectable even at small differences in intake
  • the swallowing of fluoride toothpaste by very young children (perhaps 50% of that placed on the toothbrush) is a risk factor (note – the Ministry of Health, NZ Dental Association, and Plunket advocate practices that significantly increase the amount of fluoride swallowed by young children)
  • the effect of fluoride in (allegedly) reducing tooth decay is primarily due to topical effect after the tooth has erupted (i.e. not from swallowing it).
  • fluoride tablets taken before tooth eruption have little effect on tooth decay but “present a clear risk for fluorosis”.

Method This study examined 310 fluoridated and 302 unfluoridated children, based on current fluoridation status. About half the children had intermittent residence in fluoridated areas, and some were unknown. It is not stated when the exposure occurred, even though international studies show that it is the time of exposure that is critical in causing fluorosis – the first 6 months is most critical if bottle fed, with reducing but significant risk up to age 4. The 2005 Southland study also showed a higher incidence of fluorosis in those who had lived in fluoridated areas up to age 4. The study did not separate out those who had had lifelong exposure to fluoridation, though it utilised a complex statistical modelling to counteract, in part, this shortfall. We do not consider the other “justifications” tenable if the purpose was to determine the effects of water fluoridation. Socio economic status was determined by the school decile rating, rather than the SES status of each child. Although this approach is not considered appropriate, the results suggest it has not significantly impaired the study. There was a significant difference in SES status between fluoridated and unfluoridated children (the unfluoridated children has the lower SES status, which international studies show is the main factor in higher levels of tooth decay). Many of the first molar permanent teeth, at higher risk of decay than other teeth, were fissure-sealed. This would corrupt the caries results, but, if so, seems to demonstrate that fissure-sealing is a more effective method of caries prevention than fluoridated water.

The Southland Study 2005

Enamel defects and dental caries among Southland children Mackay T D, Thomson W M, NZ Dental Journal 101, No. 2, June 2005  (p35-43) Key findings from this study were as follows. Dental fluorosis incidence

  • There were no socioeconomic differences in relation to dental fluorosis
  • The prevalence of diffuse opacities (and therefore the overall prevalence of any defect) was higher amongst those who continuously resided in fluoridated areas up to the age of 4. (Note: This should be read in conjunction with the 2008 Auckland study, which did not consider the age of exposure)

Tooth decay rates

  • Socioeconomic status (SES) did not affect tooth decay rates (note: international studies show that SES is the main determinant of dental health/ tooth decay. See in particular Armfield and Spencer 2004)
  • There was no benefit from fluoridation to the deciduous (“baby”) teeth
  • There was no benefit to permanent teeth in the initial results.  Following furtehr data manipulation, it was claimed that those 9 year olds who lived all their lives in fluoridated areas had half the decay (equating to ½ a filling) than those who had never lived in a fluoridated area. This finding conflicts with the 2008 Auckland study, which found no such benefit. However, at age 9 there are few permanent teeth, and they have had only brief exposure to decay, as noted in the Auckland study. 12 years old is the WHO-prescribed age for examining permanent teeth effects. International studies show there is often an apparent benefit at younger ages, likely due to delayed tooth eruption caused by fluoridation, but which disappears by age 12 to 15 – see Armfield and Spencer (2004); Newbrun (1989).

Implications of increased dental fluorosis The study notes that “the clinical… and public health significance of [diffuse opacities (i.e. dental fluorosis) remains unclear”. In other words, we do not know what associated health risks there may be! The US National Research Council Review, published in 2006, found a number of studies linking dental fluorosis to other adverse health effects. Method 436 children between the ages of 9 and 10 were examined. 137 children had not lived in fluoridated communities (but may have been given fluoride tablets – the analysis does not control for this; 116 had intermittent residence in fluoridated communities; and 183 had always lived in fluoridated communities. Socioeconomic status was determined by the school decile rating, rather than the SES status of each child. This approach is not considered appropriate. It is not clear from the results whether this has had a significant impact. Although a range of intersecting population characteristics was recorded, individual analysis tables look at only one factor at a time. These results are therefore meaningless, as a correlation between high decile and fluoridation status, for example, precludes any conclusion as to which factor was relevant. The fact that high decile children had the highest rates of dental fluorosis suggests there was such a correlation. The use of fluoride tablet would be exclusively among non-fluoridated children (including, possibly, intermittently fluoridated). Without controlling for this in each set of results, an “unfluoridated” child becomes a “fluoridated” child for analytical purposes. The authors conducted a multivariate analysis for permanent tooth decay only. This approach is intended to find a common factor giving rise to results. There are many ways of conducting such an analaysis. It is not possible to determine whether the particular approach used was appropriate or not without the raw data. On the face of it, it appears that the data may have been manipulated to show a desired result when that result was not shown by standard analysis. As the saying goes “you can ‘prove’ anything with statistics.” Overall, we feel compelled to recommend that their conclusions be viewed with extreme caution without an independent statistical analysis being available.