title: Effect of water exposure on the fracture toughness and flexure strength of a dental glass.
abstract: OBJECTIVE
  The low fusing dental glass (Duceram LFC) has been advertised as presenting a superior chemical resistance and augmented strength after 16h exposure to water or 4% acetic acid. The purpose of this study was to evaluate the effect of prolonged exposure to water on two mechanical properties (fracture toughness and flexure strength) of LFC.
  
  
  METHODS
  Disks and bars were mirror polished and annealed prior to aging in: (1) air (control), (2) water for 24h at 80 degrees C and (3) water for 8 weeks at 80 degrees C. Fracture toughness (K(Ic)) was determined by indentation fracture (IF) and indentation strength (IS) using a 19.6N Vickers indentation load. Flexure strength values were obtained from three-point bending at 0.1mm/min. Statistical analysis was performed using the Weibull distribution, Tukey and Bartlett tests (P<0.05).
  
  
  RESULTS
  Both techniques (IS and IF) showed a significant improvement in the K of Duceram LFC after 8 weeks in water (0.88 and 1.14MPa m(0.5)) as opposed to the 24-h values both in water and air (0.77-0.78MPa m(0.5)). However, for flexure strength the Weibull characteristic (S(0)) and the m parameter did not change significantly with water storage (S(0)=90-100MPa, Weibull m =7-8).
  
  
  CONCLUSIONS
  The increase in toughness of Duceram LFC after aging in water is an interesting and favorable observation for a restorative material exposed to the oral environment. Nevertheless, in comparison with other contemporary ceramics, the toughness of this LFC remains in the range of soda-lime-glass or classic feldspar porcelains.
authors.affiliation: Department of Prosthodontics, School of Dental Medicine, University of Geneva, Geneva, Switzerland. susanne.scherrer@medecine.unige.ch
authors.forename: S S
authors.initials: SS
authors.lastname: Scherrer
authors.forename: I L
authors.initials: IL
authors.lastname: Denry
authors.forename: H W
authors.initials: HW
authors.lastname: Wiskott
authors.forename: U C
authors.initials: UC
authors.lastname: Belser
mesh_terms: D019342:Acetic Acid / Q000737:chemistry; D000388:Air; D000538:Aluminum Silicates / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D003775:Dental Polishing; D003776:Dental Porcelain / Q000737:chemistry*; D005898:Glass / Q000737:chemistry*; D006244:Hardness; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D018583:Pliability; D017680:Potassium Compounds / Q000737:chemistry; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D014867:Water / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D003764:Dental Materials; C095718:Duceram; D017680:Potassium Compounds; D014867:Water; D003776:Dental Porcelain; C016447:feldspar; D019342:Acetic Acid