Bacterial invasion of non-exposed dental pulp

Anaerobic procedures were adopted to demonstrate the early bacterial invasion of non-exposed dental pulps, and to isolate and identify the bacteria. Of 19 freshly extracted teeth which originally exhibited deep dentinal lesions, clinical examination and electric pulp testing showed that nine of them had no pulpal exposure. Thus the pulps of these teeth were covered by clinically sound dentine beneath the carious lesion. Bacteria were found to have invaded the pulps of six of these nine teeth. The predominant bacteria were obligate anaerobes belonging to the genera Eubacterium, Propionibacterium and Actinomyces. Other obligate anaerobes were Lactobacillus, Peptostreptococcus, Veillonella and Streptococcus. The bacterial composition resembled that of the deep layers of dentinal lesions described previously, suggesting that the bacteria isolated in this study had passed through some individual dentinal tubules, to invade the dental pulp.