Erosive demineralization of enamel by different acids at different pH

Objective: Investigation of enamel erosive capacity of different acids at varying pH. Methods: Bovine enamel specimens were wet ground (grit 4000) and eroded for 1-5 min with eight acids adjusted to either pH 2.0, 2.3 or 3.0: citric-(CA), maleic-(MA), lactic-(LA), tartaric-(TA), phosphoric-(PA), oxalic-(OA), acetic–(AA), hydrochloric acid (HCl). Constant pH was provided by high incubation volumes. Calcium (Ca) and phosphate (P) release were determined photometrically using arsenazo III (CA) and malachite-green (P). Additionally, amount of titratable acid in solutions was determined by titration with NaOH (1mol/l). Each subgroup contained 8 enamel specimens. Results: MA, LA, TA, AA and HCl caused linear release of Ca and P with time for all pH. Same was true for P-release induced by PA. Determination of P-release caused by PA and Ca-release induced by OX and CA were not possible, since OX and CA interfered with the calcium assay. P-release induced by OX was not linear with time. For all acids erosive mineral loss was pH-dependent. Ca-release varied between 28.6 ± 4.4 [nmol•mm^-2•min^-1](LA, pH 2.0) and 2.4 ± 0.7 (HCl, pH 3.0), P-release ranged between 17.2 ± 2.6 (LA, pH2) and 1.4 ± 0.4 (HCl, pH3.0). Significantly strongest dissolution of Ca and P at pH 2.0 and 2.3 was observed for LA (at pH 3.0: AA). HCl and MA led to lowest erosive effects. Regarding all solutions at all pH, only weak correlation was found between P/Ca-release and the amount of titratable acid (r=0.28). If correlation was carried out separately, there was a strong correlation for pH 3.0 (r=0.88), (pH 2.3: r= 0.42; pH 2.0: r= 0.39). Conclusions: Different acids show significantly different erosive capacity on enamel as determined by calcium and phosphate release. Erosive effect depends rather on pH than on amount of titratable acid during short time exposition at constant pH.