[Chemical change of calcium hydroxide contained in root canal filling materials in serum]

In the previous report we showed the conversion of calcium hydroxide contained in root canal filling materials to calcium carbonate by means of 4 weeks of subcutaneous implantation in rats. The purpose of this study was to discover if this reaction would take place in vitro as a chemical reaction and also to find out the rate of the conversion. The alteration of three materials. Vitapex, Calvital, calcium hydroxide, when in serum, was checked and the alteration of the latter two, when in the air, was checked. The solubility of calcium hydroxide in serum or distilled water was also determined. The results showed that calcium hydroxide was neutralized to calcium carbonate after several weeks in the serum. The conversion in the air was much slower than that in the serum. This means that calcium hydroxide will not change while in storage and when it has no contact with the tissue fluid. Calcium hydroxide was dissolved in both the serum and distilled water, but calcium carbonate was not. This fact suggests that calcium hydroxide neutralized to calcium carbonate by serum will cause little or no chemical irritation.