Dental Caries and Anti-Caries Activity
The human mouth is the most bacteria-crowded place in our body. Oral bacteria in dental plaque ferment sugars to produce a range of organic acids (lactic acid, propionic acid) that promote dissolution of tooth enamel leading to formation of dental caries.
Fluoride decreases demineralization of the enamel and promotes re-mineralization by physicochemical mechanisms. These well-established mechanisms are reviewed in Cerklewski (1997) and the papers cited therein.
The effects of fluoride on plaque bacteria involve inhibition of several enzymes, which limit the uptake of sugars and reduce the amount of acid produced (National Academy Press, 1999 and papers cited therein; also at http://www.nap.edu/books/0309063507/html/288.html).
In addition, recent evidence (Cox et al., 1999) demonstrates a direct influence of fluoride on the ability of caries-causing streptococci to colonize tooth enamel surfaces.
Streptococci, that cause caries, bind glucan on tooth enamel surfaces by means of glucan-binding molecules called lectins. Fluoride interferes with this specific binding and thus inhibits biofilm formation by the streptococci that demineralize the enamel.
The fluoride ion also inhibits chain formation (growth) in streptococci, and affects the physiological capabilities of the microorganism to metabolize sucrose (Embleton et al., 1998). However, these effects are manifested only at high fluoride concentrations, making the role of fluoride in mineralization the likely process for caries reduction.
The free fluoride ion has direct topical effects on the ability of tooth enamel to resist decay in erupted teeth. These effects have been categorized as:
- A reduction of the acid solubility of enamel
- Promotion of remineralization of incipient enamel lesions at the ultra-structural level
- Increasing the deposition of mineral phases of plaque, which may under acidic conditions increase remineralization and retard demineralization of the enamel surface
- Fluoride is incorporated into the hydroxyapatite in tooth enamel to increase the proportion of Fluoroapatite, which is less-easily dissolved by mouth acids than is hydroxyapatite, and therefore more resistant to decay (Public Health Service, 1991; Cerklewski, 1997).
The effectiveness of fluoride gel application
The effectiveness of fluoride gel application has been well established in caries prevention trials involving permanent teeth, and was recently confirmed by a meta- analysis of clinical studies. Marihno[1] showed that the overall caries-inhibiting effect of APF gel treatment was 21% (95%, CI = 14-28%). The main outcome of the meta analysis was caries increment measured by the change in decayed, missing, and filled permanent tooth surfaces (D(M)FS). The primary measure of effect was the prevented fraction (PF) that is the difference in mean caries increment between the treatment and control groups expressed as a percentage of the mean increment in the control group. Twenty-five studies were included, involving 7,747 children. For the twenty-three that contributed data for meta-analysis, the D(M)FS pooled prevented fraction estimate was 28 percent (95 percent CI, 19 percent to 37 percent; p < 0.0001). There was clear heterogeneity, confirmed statistically (p < 0.0001). Clear evidence of a caries-inhibiting effect of fluoride gel was found. The best estimate of the magnitude of this effect, based on the fourteen placebo-controlled trials, was a 21 percent reduction (95 percent CI, 14 to 28 percent) in D(M)FS.
Another meta-analysis was performed by Van Rijkom[2] on published data on the caries-inhibiting effect of fluoride gel treatment in 6- to 15-year-old children. The purposes of this meta-analysis were: (1) to calculate the overall caries-inhibiting effect of clinical fluoride gel treatment studies based on explicit selection criteria and (2) to explore factors potentially modifying the effect of fluoride gel treatment in caries prevention, concerning the baseline caries prevalence of the target population, the general fluoride regimen, and application features. The caries-inhibiting effect of fluoride gel application was assessed by the prevented fraction and the 'number needed to treat' (NTT). The overall prevented fraction of the fluoride gel treatment studies, indicating the reduction of caries incidence by fluoride gel treatment relative to the incidence in the control group, was 22% (95% CI = 18-25%). Multiple regression analysis showed no significant influence on the prevented fractions for the variables 'baseline caries prevalence', 'general fluoride regimen', 'application method', and 'application frequency'.
Olivier[3], in a 2-yr period, evaluated the efficacy of bi-annual APF gel topical applications without previous prophylaxis in reducing dental caries among high-risk children living in non-fluoridated communities. 488 children 6 yr old, presenting at least three cavities on proximal surfaces of their primary teeth, were randomly assigned to two groups. The experimental group received bi-annual topical APF gel applications and the control group received a placebo. All treatments were given at school without any prior tooth cleaning. The APF gel provided a 34.3% reduction in caries incidence (P-value = 0.03) among the children with 3-14 cavities on their primary teeth at the beginning of the study.
Kurkleva[4] examined the effect of fluoride gel on caries prevention of first permanent molars in the first year after eruption in a group of children with low risk caries. The study included 213 seven-year-old children from Plovdiv, Bulgary. In the experimental groups four applications with 0.42% fluoride gel were performed at three months intervals. At the end of the study period the prevalence rate of caries on teeth and on dental surfaces was higher in the control group (P < 0.001). Caries reduction in the experimental group was 73.81%.
[1] Marinho VC, Higgins JP, Logan S, Sheiham A (2003).
Systematic review of controlled trials on the effectiveness of fluoride gels for the prevention of dental caries in children. J Dent Educ 67:448-458.
[2] H. M. van Rijkom, G. J. Truin, M. A. van 't Hof. A Meta-Analysis of Clinical& Studies on the Caries-Inhibiting Effect of Fluoride Gel treatment.Caries Research 1998;32:83-92
[3] Olivier M, Brodeur JM, Simard PL. Efficacy of APF treatments without prior tooth cleaning targeted to high-risk children. Community Dent Oral Epidemiol. 1992 Feb;20(1):38-42.
[4] Kukleva M. Prevention of dental caries on the first permanent molars with fluoride gel in the first year after eruption. Folia Med 1998;40(4):60-4.