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.

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An in vitro method for the cytotoxicity testing of endodontic materials is described which aims to simulate the clinical situation. Materials can be tested in the presence or absence of a compacted layer of dentine chips mimicking the periapical dentine plug. A total of twelve materials were tested. In the absence of dentine, Kloroperka, Biocalex, Diaket and Endomethasone were slightly cytotoxic; AH26 with and without silver, Sealapex, Tubliseal and Kerr's pulp canal sealer were moderately cytotoxic, while Forfenan, Spad and Kri paste were strongly cytotoxic. In the presence of dentine the cytotoxicity of these materials was considerably reduced, with the exception of Endomethasone, Forfenan, Spad and Kri paste. The method provides a satisfactory alternative to implantation testing and is an inexpensive and reproducible test system in which dentine can be incorporated.