Progression of the Erosive Lesion

The 3 stages in progression of an erosive lesion are initial surface softening, progressive loss of enamel and the creation of a lesion that involves dentin. By focusing on lesion progression models, the ability of a given therapy to protect against erosive progression can be determined. Two ways to help prevent dental erosion are to protect the tooth surfaces by, in effect, ‘galvanizing’ the surface with deposits that are acid-resistant, and/or to remineralize the surface between acid challenges. Superior efficacy for SnF₂ in reducing surface loss when measured in vitro, using microradiography (Figure 18) following several cycles of erosive challenges, immersion in saliva, and treatment with fluorides (Figure 19, Table 4) has been demonstrated in multiple studies. ^61-64

Figure 18. Microradiography is used to quantitatively measure tooth surface loss in vitro lesion progression models.

Figure 18. Microradiography is used to quantitatively measure tooth surface loss in vitro lesion progression models.

Adapted from: Eversole et al, 2014.⁶¹

Figure 19. Surface enamel loss with marketed dentifrices using a lesion progression model with microradiography.

Figure 19. Surface enamel loss with marketed dentifrices using a lesion progression model with microradiography.

Adapted from: Faller et al, 2011.⁶³

Reduced progression of erosive lesions has also been observed with stabilized SnF₂ toothpaste in situ compared with sodium fluoride toothpaste. In a study by Hooper and colleagues, the benefit of stannous fluoride increased over time (Figure 20).⁶⁵

Figure 20. Superior erosion protection was demonstrated for SnF₂ in an in situ human clinical study.

Figure 20. Superior erosion protection was demonstrated for SnF₂ in an in situ human clinical study.

Adapted from Hooper et al, 2007.⁶⁵

In a study by West et al (Figure 21), highly significant erosion protection benefits were found when comparing a stabilized SnF₂ dentifrice to a marketed dentifrice containing SMFP as the fluoride active and arginine bicarbonate.⁶⁹

Figure 21.

Figure 21.

Results from a human in situ clinical lesion progression study comparing a stabilized SnF₂ dentifrice versus a marketed dentifrice formulated with SMFP and arginine bicarbonate.⁶⁹

As noted earlier, many foods and beverages have a pH below 4.0 and are highly acidic (Table 2). Although pH values are not an absolute predictor of erosive potential, it is important to know the general pH values for different foods and beverages. It is also important to consider these values when performing erosion testing, as different pH values will result in different results. During an erosive acid challenge, the tooth starts to dissolve, in an effort to restore an equilibrium, by releasing calcium, phosphate and fluoride salts. At pH4, more than 90% of the fluoride salt released is present as fluoride ions, which protects the surface against demineralization. At a pH of 2, it is overwhelmingly hydrofluoric acid that is present, rather than fluoride ions; as a result, insufficient fluoride ions are present to protect the tooth surface, which leads to dissolution of the surface layer of the tooth. Stannous fluoride has been shown to provide unique protection against acids, particularly at a low pH (e.g., orange juice, ~2.6).^65,68,69

There are a variety of analytical methods, models and protocols that can be used to study erosion. Some measure lost mineral while others measure changes in the surface zone. Protocols differ depending on whether studies will be used to analyze the surface zone or to produce erosive lesions and measure effects on the progression of erosion. Depending on the method used, dramatic differences can be seen in the observed efficacy of various topical agents. Importantly, SnF₂ dentifrices, in particular stabilized SnF₂ dentifrices, have been demonstrated, using a wide range of both in vitro and in situ human clinical studies, to provide significantly greater erosion protection than other fluoride sources.^61-70