A new study (1), published in the October issue of Community Dentistry and Oral Epidemiology, has cast yet further doubt on one of the long-standing beliefs in fluoride research. The study, which examined tooth decay and dental fluorosis rates in two areas of Ethiopia, found that as the severity of dental fluorosis increased, so too did the rate of tooth decay.
According to the authors, “Independent of the fluoride concentration in drinking water, caries prevalence increased consistently with increasing severity of dental fluorosis in the second molars, first molars, premolars and canines.” (1)
Dental Fluorosis: Reducing the Mineral Content of Teeth
On the face of it, this finding isn’t entirely surprising. After all, dental fluorosis refers to a “mineralization defect” in teeth which results in an increased “porosity” of the enamel. (2)
“Hypoplasia”, a term often used to describe the appearance of dental fluorosis, is a condition marked by “thin enamel” and “enamel deficiency.” Mosby’s Medical Dictionary defines hypoplasia as an “incomplete or underdeveloped organ or tissue, usually the result of a decrease in the number of cells.” See: http://tinyurl.com/438bz and http://tinyurl.com/4kxvl. (Hypoplasia in teeth can be caused by other factors besides fluoride, such as malnutrition in childhood. See: http://tinyurl.com/6a6z4 )
In dental fluorosis, the enamel has been found to have a “decreased mineral content” (3), and, more specifically, a “decrease in calcium content.” (4) In light of this decrease in mineral content, it would seem an apparent anomaly if fluorosed teeth were actually stronger and not weaker than normal teeth. Think for instance of bones. If a bone becomes thinner, and more porous, one would reasonably assume that the bone has become more prone to fracture, not less. At the very least, one would not expect the bone to have become stronger.
In reviewing the scientific literature on dental fluorosis, one is tempted to make a similar assumption with fluorotic teeth – although it‚s unclear at what stage of severity the thinning could be significant enough to increase decay.
Similarities between Dental Fluorosis & Early Stages of Tooth Decay?
It is interesting to note that when dental fluorosis was first being investigated in the first half of the 20th century, several scientists commented on the similarities between the appearance of fluorotic teeth and teeth with the early stages of caries (decay).
According to a 1936 review by H.T. Dean, “the histologic picture of mottled enamel disclosed no essential difference from that of incompletely calcified forming enamel, or enamel showing the early stages of caries.” (5)
Dean also commented on findings which indicated that “the permeability of mottled enamel is comparable to that of… enamel affected by caries.” (5)
But, nonetheless, the view (6) that won out in the public health community by the second half of the 20th century, is the view that largely remains until this day: namely, that teeth with dental fluorosis – no matter how severe – are stronger and more resistant to decay. The orthodoxy is that “although unsightly, these teeth rarely have any dental caries.” See: http://tinyurl.com/6ccth
Recent Findings Challenge Orthodoxy
This view, however, has come under increasing scientific challenge over the past 30 years, as other researchers, from other countries, have begun to investigate the issue for themselves. And, contrary to the early research from the US, this newer research has often found that dental fluorosis makes teeth more prone, not less prone, to tooth decay (1, 7-14).
As with the new study mentioned above (1), a 2002 study by a research team in Sri Lanka, reported:
“caries prevalence and the mean caries experience were significantly higher in children with (dental fluorosis) than in those without.” (7)
Similarly, a 1997 study from a team in Sudan reported:
“analyses based on children in the 2.5 ppm area alone, showed significantly higher DMFT (Decayed, Missing, and Filled Teeth) by increased severity of dental fluorosis.” (8)
Earlier, a team from Israel ˆ in two separate papers looking at two separate age groups (9, 10) – reported:
“A statistically significant positive association was found between caries prevalence and fluorosis; the more caries experienced, the more severe the fluorosis level.” (10)
Earlier yet, Dr. Arvid Carlsson (a recent winner of the Nobel Prize in Medicine) reported on findings from Sweden which showed:
“more severe degrees of enamel fluorosis are associated with an abnormally high incidence of caries… There is thus no doubt that a high degree of enamel fluorosis causes an increased tendency to caries.” (14)
In addition to these findings, a series of recent papers have also reported that tooth decay rates may actually increase as the fluoride level in the water increases (15-18). For example:
In 2002, a research team in Tanzania reported:
“subjects in the high-F (fluoride) and urban Arusha municipality were at a significantly higher risk of dental caries than children in the low-F (fluoride) areas.” (15)
In 2001, a research team in South Africa reported:
“Significantly (P < 0.01) more children had decayed teeth in the high F (fluoride) area than in the other two areas. The results suggest a positive association between high F levels in the drinking water and dental caries.” (16)
And perhaps most comprehensively, a research team in India (summarizing 30 years of observation) reported:
“Our findings indicate that dental caries was caused by high fluoride and low dietary calcium intakes, separately and through their interactions. Dental caries was most severe and complex in calcium-deficient children exposed to high intakes of endemic fluoride in drinking water.” (17)
US orthodoxy beginning to change?
While it still remains unclear from the above studies at what stage dental fluorosis – and fluoride exposure – may weaken teeth, it appears that at least some members of the public health community in the United States are beginning to acknowledge that – at least in its moderate/severe forms – dental fluorosis may increase decay (19, 20).
According to a recent review from Steven Levy, a prominent researcher in the US:
“With more severe forms of fluorosis, caries risk increases because of pitting and loss of the outer enamel.” (19)
A similar statement was made in a 2003 review from the US Agency for Toxic Substances and Disease Registry (ATSDR). Citing the work of Mann (9,10) and Driscoll (11), ATSDR stated:
“In more severely fluorosed teeth, the enamel is pitted and discolored and is prone to fracture and wear. Several studies have found significant increases in the number of decayed, missing, or filled tooth surfaces in children with severe dental fluorosis.” (20)
The Most Damning Blow?
Another important, and perhaps the most damning, finding for the ‘fluorosis makes teeth stronger’ orthodoxy has been the finding, now acknowledged by the Centers for Disease Control (CDC), that fluoride incorporated within the tooth‚s enamel does not increase a tooth‚s resistance to decay. Here, for instance, is the most recent statement from the CDC on the matter:
“The prevalence of dental caries in a population is not inversely related to the concentration of fluoride in enamel, and a higher concentration of enamel fluoride is not necessarily more efficacious in preventing dental caries.” (21)
The significance of this concession from the CDC is that it negates a key purported mechanism by which dental fluorosis was assumed to reduce decay: namely, via an increased incorporation of fluoride within the internal structure of the tooth during the early years of life (22).
Today, of course, the notion that fluoride‚s primary benefit comes via ingestion – and the subsequent build-up of fluoride within the tooth – is largely refuted by the dental research community (but less so by individual practicing dentists, who may find it difficult to let go of notions learned in dental school (23)).
The current consensus by the research community, as reiterated recently by researchers Levy & Warren, is that:
“fluorides work primarily by topical means through direct action on the teeth and dental plaque. Thus ingestion of fluoride is not essential for caries prevention” (24).
The CDC has also acknowledged this point, stating in 1999 that:
“laboratory and epidemiologic research suggests that fluoride prevents dental caries predominately after eruption of the tooth into the mouth, and its actions primarily are topical for both adults and children” (25).
Hence, fluoride’s “primary benefit” is now believed to come from direct application of fluoride to the outside of teeth, not from accumulation within the teeth via ingestion. Thus, a principal means by which fluorosis was believed to make teeth stronger for life (via internal accumulation of fluoride), is now considered mostly insignificant in protecting against decay (21, 22, 25-26), and, based on the findings discussed above (1, 7-18), may actually make teeth weaker instead.
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3) DenBesten PK, Crenshaw MA. (1984). The effects of chronic high fluoride levels on forming enamel in the rat. Archives of Oral Biology 29: 675-9.
4) Susheela AK, Bhatnagar M. (1999). Structural aberrations in fluorosed human teeth: Biochemical and scanning electron microscopic studies. Current Science 77: 1677-1680.
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