Acid profile in carious dentin.

Organic acids in carious dentin from 69 permanent teeth were analyzed by gas chromatography. Lactate, acetate, propionate, and butyrate were detected in most samples, and limited amounts of isobutyrate, valerate, isovalerate, caproate, and isocaproate were occasionally detected. Lactate, acetate, and propionate were major acids and altogether accounted for about 90% of total acid in most samples of carious dentin. However, the proportion of these three acids varied among the samples. Some samples contained over 85% lactate, while others contained mainly acetate and propionate. A high percentage of acetate was usually accompanied by an appreciable amount of propionate. All seven samples in carious dentin under fillings or restorations had little lactate, but a high percentage of acetate plus propionate. The differences in acid profiles of carious dentin may reflect differences in the microbial ecology of carious dentin, and a stage of progress of dentin caries or a type of dentin caries.