title: The transverse strength, reliability and microstructural features of four dental ceramics--Part I.
abstract: OBJECTIVE
  The flexural strength, reliability and microstructure of a heat pressed ceramic system (Empress) was evaluated in comparison with three current frit materials used in ceramic crown and inlay construction.
  
  
  METHODS
  Twenty bar specimens per material were constructed, overglazed and transverse tested at a crosshead speed of 0.5 mm/min. Etched and fractured bar specimens were viewed under a scanning electron microscope using secondary electron imaging.
  
  
  RESULTS
  Mean strengths (MPa +/- SD) were: Empress, 117.3 +/- 31.7; Cerinate porcelain, 118.2 +/- 8.7; Corum porcetain, 92.9 +/- 13.3; and Alpha porcelain, 60.9 +/- 10.1. Results were highly significant (P < 0.001) with differences between all groups (P < 0.05) except Cerinate porcelain and Empress (P > 0.05). Weibull analysis of the results provided m-values and the predicted strength at the 1 and 5% probabilities of failure. Microstructural examination using secondary electron imaging showed leucite crystals 1.6-3.5 microns and associated microcracking in Corum porcelain and leucite crystal clusters (1.5 microns) in Empress. Cerinate porcelain exhibited a uniform distribution of fine leucite crystals (1 micron). Spherical porosity combined with crack pore combinations were noted in Vita Alpha porcelain.
  
  
  CONCLUSIONS
  Empress glass ceramic was not stronger than Cerinate or more reliable than many of the frit materials. Uniform leucite distribution and fine crystal size may be associated with improved strength and reliability.
authors.affiliation: Royal London School of Medicine and Dentistry, UK.
authors.forename: M J
authors.initials: MJ
authors.lastname: Cattell
authors.forename: R L
authors.initials: RL
authors.lastname: Clarke
authors.forename: E J
authors.initials: EJ
authors.lastname: Lynch
mesh_terms: D000134:Acid Etching, Dental; D000538:Aluminum Silicates / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003442:Crowns; D003776:Dental Porcelain / Q000737:chemistry*; D005544:Forecasting; D007284:Inlays; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D016062:Porosity; D011336:Probability; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D000538:Aluminum Silicates; C085095:Cerinate; C075815:IPS-Empress ceramic; D003776:Dental Porcelain; C078519:leucite