title: Effect of pH on physical properties of two endodontic biomaterials.
abstract: OBJECTIVE
  To compare the surface microhardness, setting time, and elemental and topographic changes of mineral trioxide aggregate (MTA) and calcium-enriched mixture (CEM) in contact with acidic, neutral, and alkaline solutions.
  
  
  METHODS
  For evaluating 24-h and 28-day surface microhardness using Vickers test and initial setting time using Gillmore apparatus, glass molds were filled manually or ultrasonically, either with CEM or MTA and randomly immersed in solutions with acidic, neutral, and alkaline pH (5.4, 7.4, and 9.4, respectively). Topographic changes of the samples as well as energy dispersive X-ray spectra were examined using the scanning electron microscopy.
  
  
  METHODS
  Data were analyzed using the Kruskal-Wallis, Mann-Whitney, Wilcoxon, one- and two-way ANOVA, Tukey's post hoc, and t-tests.
  
  
  RESULTS
  After 28 days, there was an increase in the microhardness for all samples (without statistical significance [P > 0.05]), except for the samples of CEM in acidic environment (P > 0.05). The setting time of MTA samples was statistically higher than CEM samples (P ≤ 0.001). The setting time of both biomaterials was significantly higher in acidic pH than other groups (P ≤ 0.005). Surface topography and elemental constituents of biomaterials were altered in different solutions.
  
  
  CONCLUSIONS
  The surface microhardness, setting time, and elemental and topographic properties of MTA and CEM were affected by different solutions. CEM exhibited quicker setting time than MTA; however, acidic solution negatively influenced both of them.
authors.affiliation: Department of Endodontics, Dental Branch, Islamic Azad University, Tehran, Iran; Dental Research Center, Research Institute of Dental Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Pooneh
authors.initials: P
authors.lastname: Mohebbi
authors.affiliation: Iranian Center for Endodontic Research, Research Institute of Dental Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Saeed
authors.initials: S
authors.lastname: Asgary
keywords: Biomaterials; calcium-enriched mixture; endodontics; hardness; mineral trioxide aggregate; pH; ultrasonics