title: Particle size changes in unsealed mineral trioxide aggregate powder.
abstract: BACKGROUND
  Mineral trioxide aggregate (MTA) is commonly supplied in 1-g packages of powder that are used by some clinicians across several treatments against the manufacturer's instructions. ProRoot MTA cannot be resealed after opening, whereas MTA Angelus has a resealable lid. This study assessed changes in particle size distribution once the packaging had been opened.
  
  
  METHODS
  Fresh ProRoot MTA and MTA Angelus powder were analyzed by using laser diffraction and scanning electron microscopy and compared with powder from packages that had been opened once and kept in storage for 2 years. The ProRoot packet was folded over, whereas the MTA Angelus jar had the lid twisted back to its original position.
  
  
  RESULTS
  After 2 years, ProRoot MTA powder showed a 6-fold increase in particle size (lower 10% from 1.13 to 4.37 μm, median particle size from 1.99 to 12.87 μm, and upper 10% from 4.30 to 34.67 μm), with an accompanying 50-fold change in particle surface area. MTA Angelus showed only a 2-fold increase in particle size (4.15 to 8.32 μm, 12.72 to 23.79 μm, and 42.66 to 47.91 μm, respectively) and a 2-fold change in particle size surface area.
  
  
  CONCLUSIONS
  MTA reacts with atmospheric moisture, causing an increase in particle size that may adversely affect the properties and shelf life of the material. Smaller particles have a greater predisposition to absorb moisture. Single-use systems are advised.
authors.affiliation: University of Queensland School of Dentistry, Brisbane, Queensland, Australia.
authors.forename: William N
authors.initials: WN
authors.lastname: Ha
authors.affiliation: University of Queensland School of Dentistry, Brisbane, Queensland, Australia.
authors.forename: Bill
authors.initials: B
authors.lastname: Kahler
authors.affiliation: University of Queensland School of Dentistry, Brisbane, Queensland, Australia. Electronic address: l.walsh@uq.edu.au.
authors.forename: Laurence James
authors.initials: LJ
authors.lastname: Walsh
mesh_terms: D017607:Aluminum Compounds / Q000737:chemistry*; D017610:Calcium Compounds / Q000737:chemistry*; D003461:Crystallography / Q000379:methods; D004338:Drug Combinations; D004349:Drug Packaging / Q000379:methods; D004356:Drug Storage / Q000379:methods; D006801:Humans; D007834:Lasers; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D010087:Oxides / Q000737:chemistry*; D010316:Particle Size; D012031:Refractometry; D012387:Root Canal Filling Materials / Q000737:chemistry*; D017640:Silicates / Q000737:chemistry*; D013227:Steam; D013997:Time Factors
chemical_list: D017607:Aluminum Compounds; D017610:Calcium Compounds; D004338:Drug Combinations; D010087:Oxides; D012387:Root Canal Filling Materials; D017640:Silicates; D013227:Steam; C086631:mineral trioxide aggregate
keywords: Laser diffraction; mineral trioxide aggregate; particle size; pre-hydration; single-use applications