title: New insights into structural alteration of enamel apatite induced by citric acid and sodium fluoride solutions.
abstract: Attenuated total reflectance infrared spectroscopy and complementary scanning electron microscopy were applied to analyze the surface structure of enamel apatite exposed to citric acid and to investigate the protective potential of fluorine-containing reagents against citric acid-induced erosion. Enamel and, for comparison, geological hydroxylapatite samples were treated with aqueous solutions of citric acid and sodium fluoride of different concentrations, ranging from 0.01 to 0.5 mol/L for citric acid solutions and from 0.5 to 2.0% for fluoride solutions. The two solutions were applied either simultaneously or consecutively. The citric acid-induced structural modification of apatite increases with the increase in the citric acid concentration and the number of treatments. The application of sodium fluoride alone does not suppress the atomic level changes in apatite exposed to acidic agents. The addition of sodium fluoride to citric acid solutions leads to formation of surface CaF2 and considerably reduces the changes in the apatite P-O-Ca framework. However, the CaF2 globules deposited on the enamel surface seem to be insufficient to prevent the alteration of the apatite structure upon further exposure to acidic agents. No evidence for fluorine-induced recovery of the apatite structure was found.
authors.affiliation: Institute of Mineralogy and Petrology, Department of Earth Sciences, University of Hamburg, Grindelallee 48, D-20146 Hamburg, Germany.
authors.forename: Xiaojie
authors.initials: X
authors.lastname: Wang
authors.forename: Arndt
authors.initials: A
authors.lastname: Klocke
authors.forename: Boriana
authors.initials: B
authors.lastname: Mihailova
authors.forename: Lubomira
authors.initials: L
authors.lastname: Tosheva
authors.forename: Ulrich
authors.initials: U
authors.lastname: Bismayer
mesh_terms: D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002124:Calcium Fluoride / Q000737:chemistry / Q000378:metabolism; D002327:Cariostatic Agents / Q000494:pharmacology*; D019343:Citric Acid; D003743:Dental Enamel / Q000737:chemistry* / Q000378:metabolism; D017886:Durapatite / Q000737:chemistry* / Q000378:metabolism; D005459:Fluorides / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D008855:Microscopy, Electron, Scanning; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D010758:Phosphorus / Q000737:chemistry / Q000378:metabolism; D012969:Sodium Fluoride; D012996:Solutions / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D014077:Tooth Erosion / Q000139:chemically induced / Q000473:pathology / Q000517:prevention & control; D014867:Water / Q000737:chemistry
chemical_list: D002327:Cariostatic Agents; D012996:Solutions; D014867:Water; D010758:Phosphorus; D019343:Citric Acid; D012969:Sodium Fluoride; D017886:Durapatite; D002124:Calcium Fluoride; D005459:Fluorides; D010100:Oxygen; D002118:Calcium