Enamel Erosion Inhibition Studied using White Light Interferometry

Objective: To monitor and quantify the effect, in vitro, of a dietary acid challenge on the surface topography of human enamel, and determine the result of pretreatment with an anti-erosion sodium fluoride toothpaste (Sensodyne Pronamel™) on this effect. Methods: Polished human enamel specimens were divided into one of four treatment groups: i) no treatment, ii) toothpaste treatment, iii) toothpaste treatment followed by erosive challenge or iv) erosive challenge alone. During the toothpaste treatment, specimens were incubated for 2 mins in agitated 1:3 w/w toothpaste:deionised water slurries. During the erosive challenge, the enamel was immersed in 1.0% citric acid, pH 3.8 for 5 min. Surface topography was investigated using a White Light Interferometer (ADE PhaseShift MicroXAM), which benefits from nanometer height resolution and rapid data acquisition from a wide range of sample areas. Results: Measurement of Ra (surface roughness) and Rz (ten point height) values from enamel treated with acid alone vs untreated control specimens showed that the acidic challenge significantly increased the surface roughness of the specimens, by an approximate factor of four. Pre-treatment with the anti-erosion sodium fluoride toothpaste markedly reduced this effect, and the increase in surface roughness on acid challenge in this case was minimal. Conclusion: This study has shown that exposure of human enamel to citric acid leads to a marked increase in the surface roughness of the biomineral. Pre-treatment with the anti-erosion sodium fluoride containing toothpaste significantly decreased this effect. White Light Interferometry is a sensitive, fast and convenient technique for monitoring changes in the enamel surface after exposure to citric acid.