Objective: To evaluate in vitro the formation of calcium carbonate (CaCO3) in calcium hydroxide pastes as well as their pH, using five different vehicles. Method: Calcium hydroxide p. a. and the following anesthetic vehicles were used: Scandicaine (3% mepivacaine without vasoconstrictor), Mepiadre (2% mepivacaine with 1: 100,000 epinephrine), Alphacaine (2% lidocaine with 1:100,000 epinephrine) and Novocol (2% lidocaine with 1:2,500 phenylephrine) and milliQ distilled water (Millipore) as a control. Eppendorf tubes containing the calcium hydroxide p. a. (0.8 g) were placed in a stirrer (Phoenix AP 56) and the solvents were added (0.8 mL) until obtaining uniform paste that were stored at 37 degrees +/- 1 degrees C. Each anesthetic solution formed a group (n=9) that was analyzed in three moments: initial (time 0), 7 days and 14 days. The amount of CaCO3 in the pastes was measured by titration (0.1 N of H2SO4) and the pH of the anesthetic solutions and pastes was measured with a pH-meter (Micronal). Analysis of variance and Schefee's multiple-comparison test were used to evaluate the obtained data among the time points for each group and among the groups at each time point. Results: The pH of the pastes ranged from 12.46 to 12.88 immediately after mixing. The control group presented the highest percentage of CaCO3 after 14 days of storage, while Novocol and Alphacaine presented higher CaCO3 formation at time 0 and after 7 days. The remaining groups (Scandicaine and Mepiadre) did not present statistically significant differences between the evaluated time points. However, comparison of the groups at the same time point showed that only Novocol exhibited a statistically significant alteration at 7 days. Conclusion: The pH of the pastes was high (from 12.46 to 12.88) immediately after mixing and that CaCO3 formation occurred in the pastes regardless of the employed vehicle.
