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D90: The strongest contributor to setting time in MTA and Portland Cement



William Ha, Dale P. Bentz, Wyatt Kahler, Laurence Walsh


Introduction: The setting times of commercial mineral trioxide aggregate (MTA) and Portland cements vary. It was hypothesized that much of this variation was due to differences in particle size distribution. Methods: Two gram samples from 11 MTA-type cements were analyzed by laser diffraction to determine their particle size distributions (d10, d50 and d90). Setting time data were received from manufacturers who performed indentation setting time tests as specified by the standards relevant to dentistry, ISO 6786 (n=9) or ISO 9917.1 (n=1), or not divulged to the authors (n=1). In a parallel experiment, six samples of different size-graded Portland cements were produced using the same cement clinker. The measurement of setting time for Portland cement pastes was performed using ASTM C 191. Cumulative heat release was measured to assess the reactions occurring during the setting of these pastes. In all experiments, linear correlations were assessed between setting time, heat release and the three particle size parameters. Results: Particle size varied considerably among MTA brands. For MTA, d90 was the particle size characteristic showing the strongest positive linear correlation with setting time (r=0.554). For Portland cement, d90 gave a strong positive linear correlation for initial setting time (r=0.804), for final setting time (r=0.873) and a very strong negative linear correlation for cumulative heat release (r=0.901). Conclusion: Smaller particle sizes result in faster setting times with the 90th percentile (the largest particles) governing the setting times of the samples.
Journal of Endodontics


Hydration, mineral trioxide aggregate, particle size, portland cement, root canal filling material, setting time.


Ha, W. , Bentz, D. , Kahler, W. and Walsh, L. (2015), D90: The strongest contributor to setting time in MTA and Portland Cement, Journal of Endodontics, [online],, (Accessed April 24, 2024)
Created April 14, 2015, Updated October 12, 2021