1H-NMR analysis of microbial-derived organic acids in primary root carious lesions and saliva

Abstract

In addition to lowered pH values, the molecular profile and concentrations of microbial-derived organic acids in carious dentin are important demineralization parameters involved in the induction, development and progression of dental caries. High-resolution proton ((1)H) NMR spectroscopy was employed to examine the organic acid status of primary root carious lesions. (1)H-NMR analysis of post-neutralized perchloric acid extracts of active carious lesions revealed that at an operating frequency of 600 MHz, the (1)H-NMR-detectable organic acid composition of carious dentin samples (mean molecular percentage content +/- standard error; the mean molecular percentage content is defined here as the mean of the concentration of each (1)H-NMR-visible organic acid/anion expressed as a percentage of total (1)H-NMR-detectable organic acid/anion level in each sample) was acetate 51 +/- 2%, formate 37 +/- 2%, lactate 5 +/- 1%, propionate 3 +/- 0.8%, pyruvate 2.4 +/- 0.3%, n-butyrate 1.2 +/- 0.2%; succinate 0.1 +/- 0.1%; iso-butyrate, n- and iso-valerate, and n- and iso-caproate (total) <0.2%. Further components detectable included alanine, glycine, choline, phosphorylcholine, trimethylamine oxide, methanol, glycolate and assorted saccharides. In view of their high dissociation constants (K(a)), our results demonstrate that formic and pyruvic acids (K(a) = 1.77 x 10(-4) and 3.20 x 10(-3) mol/dm(3), respectively) contribute substantially to the decreased pH values associated with active caries lesions (cf. lactate K(a) = 1.40 x 10(-4) mol/dm(3)), and hence the pathogenesis of primary root caries.