title: D90: The Strongest Contributor to Setting Time in Mineral Trioxide Aggregate and Portland Cement.
abstract: BACKGROUND
  The setting times of commercial mineral trioxide aggregate (MTA) and Portland cements vary. It was hypothesized that much of this variation was caused by 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 characterized by their percentile equivalent diameters (the 10th percentile, the median, and the 90th percentile [d90], respectively). Setting time data were received from manufacturers who performed indentation setting time tests as specified by the standards relevant to dentistry, ISO 6786 (9 respondents) or ISO 9917.1 (1 respondent), or not divulged to the authors (1 respondent). In a parallel experiment, 6 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 American Society for Testing and Materials C 191. Cumulative heat release was measured using isothermal calorimetry to assess the reactions occurring during the setting of these pastes. In all experiments, linear correlations were assessed between setting times, heat release, and the 3 particle size parameters.
  
  
  RESULTS
  Particle size varied considerably among MTA cements. For MTA cements, d90 was the particle size characteristic showing the highest positive linear correlation with setting time (r = 0.538). For Portland cement, d90 gave an even higher linear correlation for the initial setting time (r = 0.804) and the final setting time (r = 0.873) and exhibited a strong negative linear correlation for cumulative heat release (r = 0.901).
  
  
  CONCLUSIONS
  Smaller particle sizes result in faster setting times, with d90 (the largest particles) being most closely correlated with the setting times of the samples.
authors.affiliation: UQ Oral Health Centre, School of Dentistry, University of Queensland, Herston, Queensland, Australia. Electronic address: w.ha@uq.edu.au.
authors.forename: William N
authors.initials: WN
authors.lastname: Ha
authors.affiliation: Materials and Structural Systems Division, Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland.
authors.forename: Dale P
authors.initials: DP
authors.lastname: Bentz
authors.affiliation: UQ Oral Health Centre, School of Dentistry, University of Queensland, Herston, Queensland, Australia.
authors.forename: Bill
authors.initials: B
authors.lastname: Kahler
authors.affiliation: UQ Oral Health Centre, School of Dentistry, University of Queensland, Herston, Queensland, Australia.
authors.forename: Laurence J
authors.initials: LJ
authors.lastname: Walsh
mesh_terms: D017607:Aluminum Compounds / Q000737:chemistry*; D017610:Calcium Compounds / Q000737:chemistry*; D003738:Dental Cements / Q000737:chemistry*; D004338:Drug Combinations; D006801:Humans; D008422:Materials Testing; D010087:Oxides / Q000737:chemistry*; D010316:Particle Size; D017640:Silicates / Q000737:chemistry*; D013997:Time Factors
chemical_list: D017607:Aluminum Compounds; D017610:Calcium Compounds; D003738:Dental Cements; D004338:Drug Combinations; D010087:Oxides; D017640:Silicates; C086631:mineral trioxide aggregate
keywords: Hydration; Portland cement; mineral trioxide aggregate; particle size; root canal filling materials; setting time