Common Fluorides

Fluoride can be delivered from several different fluoride molecules. The three most popular sources of fluoride globally, which are all accepted by the US FDA as clinically effective, are (figure 3):

• stannous fluoride (SnF₂)

• sodium fluoride (NaF)

• sodium monofluorophosphate (Na₂PO₃F)

The efficacy of fluoride as a caries preventive agent depends largely on its concentration and availability in the oral fluids to affect the demineralization/remineralization balance. Over the years, hundreds of clinical studies have been conducted to test the efficacy of fluoride dentifrices in caries prevention. In general, across all fluoride types, these studies show approximately a 25% reduction in caries over a nonfluoridated control dentifrice.²⁸

1. Stannous fluoride. Stannous fluoride (SnF₂; also called tin fluoride) is highly reactive, and the challenge was finding an abrasive system that had low enough reactivity with fluoride to maintain the bioavailability of the fluoride. The formulation included 0.454% stannous fluoride and the abrasive calcium pyrophosphate was marketed as Crest^® with Fluoristan^®. While stannous fluoride also has the potential to deliver benefits related to the antibacterial properties of the ingredient, this early formulation only delivered an anticaries benefit based on the action of fluoride. In the 1990s, manufacturers developed methods to stabilize stannous fluoride formulations that deliver the antibacterial benefit of the ingredient as well.^29,30

2. Sodium fluoride. Sodium fluoride (NaF) is a fluoride salt commonly used in dentifrices and oral rinses. Sodium fluoride delivers a highly reactive fluoride ion; therefore, formulation chemistry with a compatible abrasive is critically important for achieving the anticaries benefit. The earliest fluoride dentifrices, formulated with NaF and calcium abrasives, provided essentially no anticaries efficacy.^31,32 In the early 1980s, silica abrasives that were compatible with sodium fluoride became available and allowed dentifrices with NaF to be developed; these formulas were tested and proven to be clinically effective against caries.^33,34

3. Sodium monofluorophosphate. Sodium monofluorophosphate (SMFP) was introduced into Colgate’s first fluoridated dentifrice and allowed this brand to obtain the ADA Seal of Acceptance for cavity protection in 1968 (Figure 10).³⁵ Unlike sodium fluoride, SMFP is not an ionic fluoride salt, but rather a covalently bound compound that requires enzymatic activation by a salivary enzyme (alkaline phosphatase) to release bioavailable fluoride (Figure 10).³⁶ Because of this lower reactivity, SMFP is compatible with more abrasives than other fluoride sources.³⁵

   Figure 10. Colgate^® with SMFP.

   

   Figure 10. Colgate^® with SMFP.

   Figure 11. Enzymatic activation of SMFP.

   

   Figure 11. Enzymatic activation of SMFP.

   The covalent bond of SMFP must be broken to release fluoride for bioavailability.