title: Depth-resolved Raman microprobe examination of a commercial dental porcelain exposed to a simulated oral environment.
abstract: OBJECTIVE
  The specific aims were investigation of the chemical transformations into the interior of a commercial dental porcelain upon exposure to a simulated oral environment and identification of structural alterations that contribute to the strengthening of the porcelain.
  
  
  METHODS
  Samples of a commercial dental porcelain, Duceram LFC, were exposed to refluxing dilute acetic acid for 0, 1, 5, 10, and 72 h to simulate exposure to the oral environment. The control and refluxed samples were examined using a depth-resolved Raman microprobe system covering the low (0-2550 cm-1) and high (2000-4000 cm-1) frequency ranges. Spectra were processed using exploratory factor analysis. Significant factors were retained, accounting for 99.999% of the variance.
  
  
  RESULTS
  The porcelain was found to be significantly depolymerized prior to acid-refluxing. Exposure to water and to acid resulted in the formation of a better-ordered region near the surface. In that region, three intermingled zones of chainlike metaborate and pyroborate, of boroxol rings, and of a mixture of borate and silicate tetrahedra were identified. The borate/silicate factor was dependent on refluxing time. Hydroxyl groups were detected in all of the samples, but no changes to the hydroxyl environment were noted until after 10 or more hours of refluxing. Then, molecular water and isolated hydroxyls/SiOH were detected. After 72 h, an additional unassigned factor around 2800-2950 cm-1 was noted.
  
  
  CONCLUSIONS
  Acid refluxing causes generation of ordered boron-containing species near the surface of the porcelain.
authors.affiliation: Department of Chemistry, Dental School, Ann Arbor, MI 48109-1055, USA.
authors.forename: N L
authors.initials: NL
authors.lastname: Jestel
authors.forename: M D
authors.initials: MD
authors.lastname: Morris
authors.forename: W J
authors.initials: WJ
authors.lastname: O'Brien
mesh_terms: D001896:Boron Compounds / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry*; D005898:Glass / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D017665:Hydroxyl Radical / Q000737:chemistry; D017655:Silicon Compounds / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D014867:Water / Q000737:chemistry
chemical_list: D001896:Boron Compounds; C095718:Duceram; D017655:Silicon Compounds; D014867:Water; D003776:Dental Porcelain; D017665:Hydroxyl Radical