Method: One gram samples of MTA Angelus, BO and three types of PC (raw, sub-14μm and sub-8μm for the largest particles in the 90thpercentile) were placed into distilled water mixed with 1g/L sodium hexametaphosphate undergoing continuous ultrasonic agitation, and immediately analysed using laser diffraction particle size analysis with a Malvern MicroPlus analyser. The nonlinear least squares method determined the PSD constituents in MTA in accordance to the library of the four pure standards.
Result: MTA Angelus had a bimodal PSD with the two maxima located at 9μm and 30.53μm. These correspond to the BO modal particle size of 10μm and the PC modal particle size of 19.31μm. There were no PC particles sub-14μm or sub-8μm in this commercial MTA product.
Conclusion: When assessing the particle size distribution of MTA, the smaller particles in the bimodal distribution are BO and the larger ones are PC. This needs to be considered when exploring methods such as ball milling to lower the mean particle size of MTA.