title: Studies on the influence of fluoride on the equilibrating calcium phosphate phase at a high enamel/acid ratio.
abstract: Data obtained in a previous study suggested that brushite is the solubility-determining phase when enamel is first exposed to acid solution in a series of repeated equilibrations. Fluoride in solution might be expected to inhibit brushite formation, and experimental studies at low solid/solution ratio support this. We have now re-examined the effect at a very high ratio, in an attempt to mimic what happens in an enamel caries lesion. Powdered enamel was repeatedly exposed to HCl solution, 10-70 mmol/l, containing 2 ppm F, for 24 h, initially in a ratio of 1 g/3 ml. Ion activities were determined after 20 min and 24 h and potential plot diagrams constructed. In early repetitions the -log (Ca2+) (OH-)2 vs. -log (H+)3(PO4(3-)) points tended to follow the brushite line, rather than the hydroxyapatite (HAp) line which one would expect if enamel behaved as pure HAp. Solution F was below measurable limits after 20 min and F then had little influence on the brushite equilibrating phase. In later (> 13) repetitions, points fell closer to the HAp line, with or without F added to the acid solution. However, added F, which was not then completely removed from solution, caused the slope of the regression line through the points to approach the Ca/P ratio of HAp, and therefore may have had a small effect in reducing the brushite phase. It is concluded that high solid/solution ratio, a previously neglected factor in enamel dissolution studies, has a profound effect in increasing the manifestation of a brushite surface phase and reducing the inhibitory effect of F on this phase.
authors.affiliation: Dental Research Unit, Health Research Council of New Zealand, Wellington.
authors.forename: E I
authors.initials: EI
authors.lastname: Pearce
authors.forename: M J
authors.initials: MJ
authors.lastname: Larsen
authors.forename: T W
authors.initials: TW
authors.lastname: Cutress
mesh_terms: D001031:Apatites / Q000737:chemistry; D002118:Calcium / Q000737:chemistry; D002126:Calcium Hydroxide / Q000737:chemistry; D002130:Calcium Phosphates / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003731:Dental Caries / Q000378:metabolism; D003743:Dental Enamel / Q000737:chemistry*; D003747:Dental Enamel Solubility; D017886:Durapatite / Q000737:chemistry; D005459:Fluorides / Q000737:chemistry*; D006801:Humans; D006851:Hydrochloric Acid / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry
chemical_list: D001031:Apatites; D002130:Calcium Phosphates; D010710:Phosphates; D017886:Durapatite; C025105:fluorapatite; C494366:calcium phosphate, dibasic, dihydrate; D002126:Calcium Hydroxide; D005459:Fluorides; D006851:Hydrochloric Acid; D002118:Calcium