title: Effect of nano silica on setting time and physical properties of mineral trioxide aggregate.
abstract: BACKGROUND
  Mineral trioxide aggregate (MTA) has been widely used in all fields of endodontics. One of the major drawbacks of this material is the long setting time. MTA is primarily composed of type 1 Portland cement and bismuth oxide. In cement, nanoscale SiO2 behaves as a filler to improve microstructure and to accelerate hydration process. The aforementioned reaction is also expected in MTA because of the same structure. Thus, the aim of this study was to evaluate the effect of addition of nano-SiO2 to MTA on the setting time and its physical properties.
  
  
  METHODS
  Two concentrations (8% and 10%) of nano-SiO2 were added to the white MTA powder. After mixing with water, the setting time, compressive strength, and flexural strength were investigated and compared with pure MTA.
  
  
  RESULTS
  With the addition of 8% and 10% of nano-SiO2 to the MTA, the setting time of both mixtures decreased significantly (P < .05). However, the compressive strength (after 1 day and 1 week) and flexural strength increased; this was not significant (P > .05). There was no significant difference between MTA mixed with 8% and 10% nano-SiO2 in setting time, compressive strength, and flexural strength (P > .05).
  
  
  CONCLUSIONS
  The addition of 8% and 10% of nano-SiO2 to MTA accelerated the hydration process, reduced the setting time, and had no adverse effect on the compressive and flexural strength of MTA.
authors.affiliation: Dental Research Center, Faculty of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Majid
authors.initials: M
authors.lastname: Akbari
authors.forename: Seyed Mojtaba
authors.initials: SM
authors.lastname: Zebarjad
authors.forename: Behnam
authors.initials: B
authors.lastname: Nategh
authors.forename: Armita
authors.initials: A
authors.lastname: Rouhani
mesh_terms: D065966:Absorption, Physicochemical; D017607:Aluminum Compounds / Q000737:chemistry*; D017610:Calcium Compounds / Q000737:chemistry*; D055598:Chemical Phenomena; D019245:Compressive Strength; D004338:Drug Combinations; D006244:Hardness; D006801:Humans; D006813:Humidity; D008422:Materials Testing; D053758:Nanoparticles / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D018583:Pliability; D012387:Root Canal Filling Materials / Q000737:chemistry*; D017640:Silicates / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D013314:Stress, Mechanical; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D017607:Aluminum Compounds; D017610:Calcium Compounds; D004338:Drug Combinations; D010087:Oxides; D012387:Root Canal Filling Materials; D017640:Silicates; C086631:mineral trioxide aggregate; D014867:Water; D012822:Silicon Dioxide
keywords: Compressive strength; MTA; flexural strength; nano-SiO2; setting time