Effect of Age on Microhardness and Setting Time of Mineral Trioxide Aggregate
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Mineral trioxide aggregate (MTA) was first developed to be used as a perforation repair material. However, due to its various favorable properties, MTA's uses expanded to include use of the material as a root-end filling material, an apical barrier in apexification, and a capping material in vital pulp therapy. Recently at the University at Buffalo – School of Dental medicine, we encountered some cases where, upon reentry, the MTA has failed to set. Therefore the purpose of this study was to investigate whether the age of gray MTA (GMTA) may contribute to MTA's failure by comparing the setting time and microhardness of expired versus unexpired GMTA. For the microhardness, 10 samples of each cement were prepared following the manufacturer's instructions, placed into an appropriate plastic mold, and stored in an incubator at 37 °C and 95% humidity for 24 hours. All samples were loaded with an indenter with a weight of 500 g-f for 15 seconds at 5 random spots per disc. The average Vickers microhardness was calculated. The setting time was measured with a Gilmore needle apparatus. GMTA was mixed following the manufacturer's instructions, and placed into an incubator at 37 °C and 95% humidity for 30 minutes. The setting time was calculated in 30-minute intervals until the material was set. The test was repeated 3 times for each material. The mean microhardness was 32.27 for the unexpired GMTA, and 37.64 for expired GMTA. The difference was not statistically significant ( P = 0.245). The mean setting time was found to range from 240 to 270 minutes for both unexpired and expired GMTA. No significant difference was found between the two materials. The results indicated that age of MTA (expired) has no significant effect on the setting time and microhardness.