title: Acidic pH weakens the microhardness and microstructure of three tricalcium silicate materials.
abstract: OBJECTIVE
  To investigate the microhardness and microstructural features of three tricalcium silicate materials: mineral trioxide aggregate (MTA), Endosequence Root Repair Material Putty (ERRM Putty) and Endosequence Root Repair Material Paste (ERRM Paste), after exposure to a range of acidic environments in comparison with intermediate restorative material (IRM).
  
  
  METHODS
  Endosequence Root Repair Material Putty (Brasseler, Savannah, GA, USA), ERRM Paste (Brasseler, Savannah, GA, USA), MTA (ProRoot; Dentsply Tulsa Dental, Johnson City, TN, USA) and IRM (Dentsply Caulk, Milford, DE, USA) were set in cylindrical rubber moulds as four groups containing twenty specimens each. Fifteen specimens per each material were randomly distributed into three groups (n = 5) to be exposed to butyric acid buffered at three different pH levels (5.4, 6.4 and 7.4) for 7 days. The remaining five specimens were exposed to distilled water as a control group. The surface microhardness after exposure either to acid or to water was measured after 7-days at 37 °C. The morphology of the internal microstructure was observed using a scanning electron microscope (SEM). Two-way univariate analysis of variance (anova) was applied to evaluate the Vickers microhardness value (VHN).
  
  
  RESULTS
  The microhardness values of the materials were significantly higher in the neutral environment of butyric acid at pH 7.4 compared to those in the acidic condition of pH 5.4 for all groups (P < 0.001). MTA, ERRM Putty and ERRM Paste had higher microhardness values than IRM at all pH levels (P < 0.001). Specimens exposed to distilled water displayed significantly higher microhardness values than those values obtained in the presence of butyric acid buffered to all pH levels (P < 0.001). A more porous microstructure was observed following exposure to butyric acid at pH 5.4 than at pH 7.4. Several types of crystalline structures were formed by recrystallization, especially at pH 7.4 in all groups except for IRM.
  
  
  CONCLUSIONS
  The microhardness values of ERRM Putty, ERRM Paste and MTA were reduced in an acidic environment, which resulted in these materials having more porous and less crystalline microstructures. MTA seems the most suitable material for application to an area of inflammation where a low pH value may exist.
authors.affiliation: Division of Endodontics, Department of Oral Biological & Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, BC, Canada; The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) & Key Laboratory of Oral Biomedicine Ministry of Education, School & Hospital of Stomatology, Wuhan University, Wuhan, China.
authors.forename: Z
authors.initials: Z
authors.lastname: Wang
authors.forename: J
authors.initials: J
authors.lastname: Ma
authors.forename: Y
authors.initials: Y
authors.lastname: Shen
authors.forename: M
authors.initials: M
authors.lastname: Haapasalo
mesh_terms: D000143:Acids / Q000737:chemistry*; D017610:Calcium Compounds / Q000737:chemistry*; D006245:Hardness Tests; D006863:Hydrogen-Ion Concentration; D008855:Microscopy, Electron, Scanning; D012387:Root Canal Filling Materials / Q000737:chemistry*; D017640:Silicates / Q000737:chemistry*
chemical_list: D000143:Acids; D017610:Calcium Compounds; D012387:Root Canal Filling Materials; D017640:Silicates; C506393:tricalcium silicate
keywords: butyric acid; microhardness; microstructure; mineral trioxide aggregate; root repair material