Penetration of dentine by three oral bacteria in vitro and their associated cytotoxicity.

Three common oral bacteria, namely Streptococcus sanguis, Actinomyces viscosus and Corynebacterium spp. were studied with regard to their ability to penetrate etched and unetched dentine and for their effect on underlying cell cultures. The test organisms were grown in cylinders above dentine slices 100 and 500 microns thick for 72 hours. The slices were in contact with tissue culture medium covering a layer of fibroblasts. Penetration of 100 microns slices was most rapid with S. sanguis, followed by A. viscosus and Corynebacterium. The pattern was similar but slightly delayed when 500 microns slices were used, but in most cases penetration had occurred by 72 hours. The presence of a smear layer had no effect on the results obtained. Following penetration, cell destruction was most extensive with S. sanguis, the most cytotoxic organism, followed by Corynebacterium and A. viscosus. In the limited number of dishes where no penetration occurred there was little effect on cell numbers.