How Fluoride Works

When acids are produced by the metabolization of carbohydrates by cariogenic bacteria, the pH of the plaque biofilm decreases. When it drops below 5.5, the result is enamel demineralization: the dissolution of tooth enamel hydroxyapatite (calcium and phosphate ions). Remineralization occurs when the minerals are reincorporated from an elevation of pH via buffering from saliva. If demineralization/remineralization successions are ongoing and there is no intervention, a subsurface caries lesion is the outcome. Cavitation, and even potential pulp involvement and tooth loss can follow.^36,41,42

Topical fluoride deters demineralization and enhances remineralization; when it is present in saliva and dental plaque, it replaces hydroxyapatite with fluorapatite, which is more resistant to dissolution in the presence of cariogenic acid challenges. The result is that incipient carious lesions are prevented or their growth reduced by the anticaries agent fluoride.^43,44

Figure 6. Demineralization/Remineralization.

Figure 6. Demineralization/Remineralization.

(A) Plaque acids cause a demineralized, sub-surface lesion. (B) Fluoride treatments remineralize the lesion with a more acid resistant fluorapatite mineral.

In a comprehensive evidence-based review of fluoride vehicles and strategies, O’Mullane et al. concluded, “Fluoride toothpaste is now the most widely used method for maintaining a constant low level of fluoride in the oral environment, and its widespread use is considered to have played an important role in the decline in dental caries in industrialized countries in recent decades.”⁴⁵ Fluoride incorporation in marketed dentifrices has become the norm, with 95% of commercially available toothpastes in many countries now containing it.⁴⁶ In the US, three different fluoride compounds are approved for usage in marketed dentifrices today as per the US monograph system, and these three are also the most frequently used globally: sodium monofluorophosphate (Na₂PO₃F “MFP”), sodium fluoride (NaF), and stannous fluoride (SnF₂). When formulated in a toothpaste correctly in the right concentration (1000-1500 ppm for over the counter pastes) and bioavailability, all have been shown in clinical trials to significantly reduce dental caries compared to a negative control.^47,48 Dental professionals generally recommend the twice daily use of an ADA-approved fluoride toothpaste.