title: Environmental scanning electron microscopy connected with energy dispersive x-ray analysis and Raman techniques to study ProRoot mineral trioxide aggregate and calcium silicate cements in wet conditions and in real time.
abstract: BACKGROUND
  ProRoot mineral trioxide aggregate (MTA) and calcium silicate cements are able to set in a moist environment. The aim of the study was to examine the surface structure and composition of a cement paste under wet conditions and in real time during setting by environmental scanning electron microscopy connected with energy dispersive x-ray analysis (ESEM-EDX) and micro-Raman techniques.
  
  
  METHODS
  White ProRoot MTA and experimental white tetrasilicate cement (wTC) and wTC containing bismuth oxide (wTC-Bi) were studied. Cement disks were analyzed 10 minutes after powder-liquid mixing (freshly prepared samples) and after immersion in Dulbecco phosphate-buffered saline at 37 degrees C for 24 hours (24-hour-aged samples).
  
  
  RESULTS
  Freshly prepared wet cements at ESEM-EDX exposed an irregular surface (displaying calcium, silicon, aluminum, chlorine reflexes, and bismuth traces in MTA and wTC-Bi) with needle-like and cubic-hexagonal shaped crystals. Aggregates of spheroidal Ca-P-rich crystals (spherulites) appeared on the surface of 24-hour-aged samples. The starting unhydrated powders displayed the typical Raman bands of Portland cement components: alite, belite, and calcium sulfate (only as anhydrite in MTA and as both anhydrite and gypsum in wTC and wTC-Bi). MTA powder showed higher amount of calcium carbonate and lower quantities of anhydrite and higher crystallinity of the silicate component, leading to a slower hydration reaction. Products/markers of hydration reactions were present on fresh samples; ettringite formed on the surface of all the cements; calcium hydroxide (portlandite) was detected only on the surface of wTC, but no conclusion can be drawn on wTC-Bi and MTA because of the interference of bismuth oxide. Calcium phosphate and calcite/aragonite bands were detected on all 24-hour-aged cements; portlandite was no longer detected on wTC.
  
  
  CONCLUSIONS
  ESEM and micro-Raman are powerful and suitable techniques to investigate endodontic calcium silicate hydrated cements in real time and in their humid state without inducing artifacts by sample preparation. The formation of apatite spherulites on calcium silicate cements might have clinical relevance.
authors.affiliation: Laboratory of Biomaterials and Oral Pathology, Endodontic Clinical Section, Department of Odontostomatological Science, Alma Mater Studiorum - University of Bologna, Bologna, Italy. mgiovanna.gandolfi@unibo.it
authors.forename: Maria Giovanna
authors.initials: MG
authors.lastname: Gandolfi
authors.forename: Kirsten
authors.initials: K
authors.lastname: Van Landuyt
authors.forename: Paola
authors.initials: P
authors.lastname: Taddei
authors.forename: Enrico
authors.initials: E
authors.lastname: Modena
authors.forename: Bart
authors.initials: B
authors.lastname: Van Meerbeek
authors.forename: Carlo
authors.initials: C
authors.lastname: Prati
mesh_terms: D017607:Aluminum Compounds / Q000737:chemistry; D001031:Apatites / Q000737:chemistry; D001729:Bismuth / Q000737:chemistry; D017610:Calcium Compounds / Q000737:chemistry; D003738:Dental Cements / Q000737:chemistry; D004338:Drug Combinations; D008855:Microscopy, Electron, Scanning / Q000379:methods; D010087:Oxides / Q000737:chemistry; D012184:Retrograde Obturation / Q000379:methods; D012387:Root Canal Filling Materials / Q000737:chemistry*; D012823:Silicate Cement / Q000737:chemistry; D017640:Silicates / Q000737:chemistry; D013052:Spectrometry, X-Ray Emission; D013059:Spectrum Analysis, Raman / Q000379:methods; D014867:Water / Q000737:chemistry; D017155:Wettability
chemical_list: D017607:Aluminum Compounds; D001031:Apatites; D017610:Calcium Compounds; D003738:Dental Cements; D004338:Drug Combinations; D010087:Oxides; D012387:Root Canal Filling Materials; D017640:Silicates; C472247:accelerated Portland cement; C086631:mineral trioxide aggregate; D014867:Water; D012823:Silicate Cement; C033301:bismuth oxide; D001729:Bismuth