Letter to Editor Efficacy of Fluoride Toothpaste Over Time

This paper reports on an assessment of the total fluoride and the total soluble fluoride in different top-selling brands of toothpastes in Brazil. The authors rightly state that the concentration of soluble fluoride in toothpaste determines its anti-caries efficacy and that at least 1000 ppm of soluble fluoride are necessary for a toothpaste to have an anti-caries effect (1). According to the paper, four of the five toothpastes analyzed were NaMFP toothpastes and one was a NaF toothpaste. The results of the analysis, undertaken within the product’s expiry dates, revealed that the NaF toothpaste contained similar amounts of soluble fluoride as compared to the total fluoride content. In contrast, the four NaMFP toothpastes contained notably less soluble fluoride than the total fluoride content; the soluble fluoride fraction being on average about 80% that of the total fluoride (but still above the 1000 ppm of soluble fluoride required for anti-caries efficacy). Based on the samples analyzed, the authors rightly conclude that “the top-selling Brazilian toothpastes presented available (soluble) fluoride concentration to control caries”.Another recent study by Carrera et al. (2) on total and soluble fluoride content in toothpastes purchased in a chain of drugstores in Chile and analyzed within the product’s expiry date, came to similar conclusions regarding the anti-caries efficacy of the toothpastes analyzed. Of the 18 toothpastes analyzed only one contained less than 1000 ppm total soluble fluoride. However, only four of the toothpastes analyzed in Chile were NaMFP, while the others were NaF with silica. Two of the four NaMFP toothpastes had a reduced soluble fluoride fraction of about 70% and only one contained less than the required 1000 ppm of soluble fluoride. All NaF toothpastes contained soluble fluoride similar to the total amount of fluoride. While the analyses of fluoride toothpaste in the two papers were undertaken within the expiry date, no information was provided as to the age of the toothpastes at the time of analysis. This differs from the paper from de Oliveira Conde et al. (3), where the initial analysis of toothpastes was undertaken more than two years before the expiry date (defined by ISO to be three years after the date of production). The age of toothpastes is a point of serious concern since a recent paper on soluble fluoride in toothpastes purchased in different countries shows that toothpastes using a NaMFP formulation have considerably reduced fractions of soluble fluoride, in many cases far below the required 1000 ppm of soluble fluoride (4). Most of these toothpastes analyzed had no information on the package regarding production date or expiry date, the latter being a requirement of the ISO (5). Previous studies on the soluble fluoride content of toothpastes revealed a considerably reduced concentration of soluble fluoride for NaMFP toothpastes as well as a gradual decrease over time (3,4).We are concerned that the data presented on total soluble fluoride in toothpastes in Brazil (1) and Chile (2) might not be totally representative of the true situation in these countries since the toothpastes were purchased in supermarkets or in a chain of drugstores where the turnover time is most likely to be short. De Oliveira Conde et al. (3), analyzing fluoride toothpaste in Manaus, Brazil, estimated the time that toothpastes stay in a supermarket to be approximately three months. Toothpastes sold by smaller shops, drugstores or on markets, as well as those sold in more remote regions of these countries are more likely to have much longer turnover time. If this is the case then it is quite possible