A Cochrane review included 25 studies with a total of 7 747 subjects. There is clear evidence of a caries-inhibiting effect of fluoride gel. The best estimate of the magnitude of this effect, based on the 14 placebo-controlled trials, is a 21% reduction (95% CI, 14 to 28%) in change in decayed, missing and filled tooth surfaces (D(M)FS).This corresponds to an NNT of 2 (95% CI, 1 to 3) to avoid 1 D(M)FS in a population with a caries increment of 2.2 D(M)FS/year, or an NNT of 24 (95% CI, 18 to 36) based on an increment of 0.2 D(M)FS/year.
Comment: The quality of evidence is downgraded by study limitations; more than 20% loss to follow up.