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Fluoride gel and caries

The prevalence of caries in children in many countries in Western Europe and North America has declined dramatically in the last few decades. Reasons for this include the widespread use of fluoride toothpastes, and, in some cases, fluoridation of water supplies.

Additional use of fluoride gels with high fluoride contents has been one method of reducing tooth decay. These gels use higher concentrations and different formulations of fluoride from those found in most toothpastes. There are various forms of application, applied by individuals or by professionals, at a frequency from once a day to once a year. And they are used in populations with caries prevalence which might be low or very high.

Is the use of fluoride gels effective, and what amongst all these factors is important? A new meta-analysis [1] gives some answers.


The review sought randomised studies in populations representative of the general population on fluoride gels applied to permanent teeth of children aged six to 15 years. Only English and German studies published between 1965 and 1995 were used, and only MEDLINE searched.


Twenty-four studies were found, with a wide variation in the number of decayed, missing and filled surfaces (DMFS) at baseline (means 0.8 to 10.1) and application frequency (1 to 360 times per year). Follow-up periods were 1.5 to 3 years (median 3 years). Studies were large, with only a three studying fewer than 200 children.

The overall caries-inhibiting effect was 22% (95% CI 18 to 25%). This was a consistent effect at all levels of incidence of DMFS, as the L'Abbé plot shows. There was no effect of type of gel, or number of applications.

The most interesting part of the paper was the calculation of numbers needed to treat at various levels of background prevalence, using the consistent 22% effect.
Background caries incidence (DMFS/year) NNT for one year treatment (95% CI)
0.25 18 (16 to 22)
0.50 9.1 (7.8 to 11)
1.00 4.5 (3.9 to 5.4)
1.50 3.0 (2.6 to 3.6)


The NNT is low at high DMFS incidence for even one year of treatment, and there is an interesting discussion in the paper about how this could impact on cost-effectiveness strategies for reducing tooth decay in children. It might well make it easier to justify targeting efforts into areas of high prevalence, perhaps as part of a health improvement programme. It is also great to see dentists using NNTs.

Bandolier consults a wise old dentist, who makes the point that the issue of caries in children is not the only topic about which we need information on fluoride gels. There is a second wave of tooth problems in the elderly, and determining whether fluoride gels are useful in this setting is a priority. So far searching for a review has brought nothing forth, but perhaps young, keen, research dentists know of one.


  1. HM van Rijkom, GJ Truin, MA van't Hof. A meta-analysis of clinical studies on the caries-inhibiting effect of fluoride gel treatment. Caries Research 1998 32: 83-92.

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