Potential synergistic effects of a mixture of mineral trioxide aggregate (MTA) cement and Bacillus subtilis in dental caries treatment.

Bacillus subtilis is nonpathogenic in humans and produces a number of useful substances and, therefore, this bacterium is used in probiotic therapy. There have been trials of B. subtilis for patients with periodontitis, but not for patients with caries. Similarly, mineral trioxide aggregate (MTA) cement has been widely used for endodontic treatment, but there are few reports of its use for caries. Therefore, examinations were performed regarding the benefits of addition of B. subtilis to MTA cement for treatment of dental caries. Indirect pulp capping with a mixture of MTA cement and B. subtilis spore powder is effective for avoiding pulpectomy or tooth extraction in such cases (personal communication). This study was planned to examine the scientific basis of this clinical finding, with examination of possible synergistic effects of MTA cement and B. subtilis. From these experiments, the following five results were obtained: (1) B. subtilis did not proliferate in liquid-culture media at pH ≥10. (2) B. subtilis proliferated when mixed with MTA cement. (3) There was no significant difference in proliferation of B. subtilis under aerobic and microaerobic conditions. (4) B. subtilis exhibited antibacterial effects on Staphylococcus aureus and Lactobacillus casei. (5) MTA cement exhibited antibacterial effects on S. aureus and Streptococcus mutans, but not on B. subtilis. These results support the hypothesis that a combination of B subtilis and MTA cement is likely to be clinically useful for treatment of dental caries.