Location of Streptococcus mutans in the dentinal tubules of open infected root canals.

Seventy-six teeth from open canals were extracted to prepare serial longitudinal sections. The sections were made from apical portions of the teeth and stained. Ninety similar teeth were extracted to prepare dentinal splinters with files from the enlarged infected canal. The splinters were spread on a selected medium to grow S. mutans. S. mutans was detected in 48.7% of the 76 teeth examined. The distance of invasion of S. mutans in the dentinal tubules revealed by immunofluorescence averaged 509 micrometer from the canal wall and reached 1150 micrometer, depending on the serogroups of S. mutans. Unidentified germs in the sections which were demonstrated by Gram's stain invaded further than S. mutans. The frequency of appearance of the serogroups of S. mutans was 32.6% (d), 27.9% (c), 24.4% (a), and 15.5% (b).