title: Mechanism of strength increase for a hydrothermal porcelain.
abstract: OBJECTIVE
  The objectives of this study were to verify the formation of a hydrolyzed surface layer on Duceram LFC, to determine the effects of such a layer on mechanical material properties, and to identify a specific mechanism responsible for any strength increase observed.
  
  
  METHODS
  Specimens were fabricated from dentin porcelain by a vibration blotting technique and were prepared to have either blunt or sharp surface flaws. Half of the specimens underwent accelerated aging. Specimens were fractured in three-point flexure to measure their strength, and fractographic analysis was used to determine fracture toughness and residual surface stress. Surface hardness and elastic modulus were measured using a microindentation method. Porcelain surface topography was examined using atomic force microscopy, and Fourier transform infrared spectroscopy was used to determine the composition of the surface layer.
  
  
  RESULTS
  The aging treatment modified the porcelain surface topography but did not create a layer with increased hydroxyl ion content. Porcelain strength increased upon aging, and the increase was proportional to initial flaw severity. The apparent fracture toughness of sharp flaw specimens increased to match that for specimens containing blunt flaws upon aging. Surface hardness and elastic modulus decreased upon aging.
  
  
  CONCLUSIONS
  Previous studies on the strength increase of hydrothermal porcelain were contradictory because a variety of specimen preparation procedures were used. This study resolves the apparent contradiction by determining the effect of specimen preparation on material strength.
authors.affiliation: Department of Biomaterials Science, Baylor College of Dentistry, TAMUS HSC, 3302 Gaston Avenue, Dallas, TX 75246, USA. jgriggs@tambcd.edu
authors.forename: Jason A
authors.initials: JA
authors.lastname: Griggs
authors.forename: Anil
authors.initials: A
authors.lastname: Kishen
authors.forename: Kim Nga
authors.initials: KN
authors.lastname: Le
mesh_terms: D000704:Analysis of Variance; D003776:Dental Porcelain / Q000138:chemical synthesis / Q000737:chemistry; D003799:Dental Stress Analysis; D004548:Elasticity; D006244:Hardness; D006868:Hydrolysis; D016014:Linear Models; D008422:Materials Testing; D018625:Microscopy, Atomic Force; D018583:Pliability; D017550:Spectroscopy, Fourier Transform Infrared; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength; D014867:Water
chemical_list: C095718:Duceram; D014867:Water; D003776:Dental Porcelain