Effects of pH and Mixing Agents on the Temporal Setting of Tooth-colored and Gray Mineral Trioxide Aggregate

The purpose of this study was to test the compressive strength of white mineral trioxide aggregate (WMTA) and gray mineral trioxide aggregate (GMTA) when mixed with sterile water or local anesthetic and exposed to an acidic environment. A total of 248 samples of WMTA and GMTA were mixed and placed in phosphate-buffered saline (PBS), at pH 5.0 or 7.4, for a period of 7 or 28 days. When WMTA and GMTA were mixed with local anesthetic, the following were observed: 1) pH 5.0 caused a significant decrease in compressive strength (p < 0.0001); 2) WMTA was significantly stronger than GMTA (p < 0.0001); and 3) more time in PBS (total 28 days) caused a significant decrease in compressive strength (p < 0.001). There were no consistent differences in compressive strength for WMTA or GMTA when mixed with sterile water. Variability of results suggests both types of MTA be mixed with sterile water in acidic and neutral environments.