UCSF

Introduction

The aims of this study are (1) to explore whether Bacillus subtilis is capable of precipitating calicite in extracted human teeth in vitro and (2) to observe whether Bacillus subtilis is capable of strengthening and decreasing the set time of Portland cement.

Materials and Methods

Dentin defect was simulated by placing indents on dentin blocks. The dentin blocks were divided into four groups- one experimental (B. subtilis culture in Luria Bertani (LB) broth + calcium chloride) and three controls. All samples were evaluated under light microscopy after one-, two-, and three-weeks of exposure.

Portland cement blocks were made by mixing the following liquids with Portland cement: experimental group - B. Subtilis and LB + calcium chloride, group A - B. Subtilis with LB, group B - LB, group C - LB + calcium chloride, and group D - water. Set time was evaluated at 1, 3, 6, 12, and 24 hours. After 24 hours, samples were subjected to new microhardness indentations. Indents were measured under light microscopy.

Results

Minimal deposition was observed in all samples after 1 and 2 weeks of exposure. However, the indents in the experimental group after three weeks of exposure appeared to be completely filled. This was confirmed with Micro CT scans.

Samples where Portland cement was mixed with water were set at 6 hours. The experimental group samples were set at 12 hours and Group A samples were partially set at 12 hours. Groups B and C were not set at 12 hours. Portland cement mixed with water showed the highest microhardness but significant difference was only observed between Groups D and C.

Conclusions

We found minimal deposition of calcite except filling of all microhardness indents in one of the week three experimental samples (B. subtilis with LB + calcium chloride). In the second part of the experiment, we found the addition of LB medium significantly delayed the set time compared to water but the addition of B. subtilis and calcium in LB reduced the set time compared to LB alone. Furthermore, B. subtilis had no effect on the hardness of the Portland cement.