Microbiological studies of carious dentine from human teeth with irreversible pulpitis.

Aerobic and anaerobic cultures were made from 29 extracted teeth with irreversible pulpitis to identify the predominant flora in different parts of deep carious lesions. Most isolates were Gram-positive rods, in which lactobacilli were the most frequent organisms, then other Gram-positive, non-branching rods. Gram-positive cocci were the next most common; only a low number of Streptococcus mutans was recovered. Two types of carious lesions were found, one with high numbers of lactobacilli, the other with low. In the 15 lesions with high numbers, lactobacilli constituted 91.9% of the total flora at the pulpal site and gradually decreased in number as the sampling moved away from the pulp. Strep. mutans and alpha-haemolytic streptococci were not recovered from pulpal or deep carious sites in this group. In the 14 lesions with low numbers of lactobacilli, the flora was diverse. Gram-positive cocci, anaerobic Gram-positive non-branching rods, branching rods and/or Bacteroides were the main isolates in a few of this group.