title: Fatigue strength of bilayered ceramics under cyclic loading as a function of core veneer thickness ratios.
abstract: BACKGROUND
  Minimal evidence is available concerning the appropriate thickness of each layer in bilayered ceramic systems.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to examine the effect of core-veneer thickness ratios on the fatigue strength of a bonded bilayered ceramic system.
  
  
  METHODS
  Specimens of Ivoclar Porcelain System (IPS) e.max lithium disilicate were fabricated with core/veneer thicknesses of 0.5/1.0 mm, 0.75/0.75 mm, 1.0/0.5 mm, and 1.5/0.0 mm. All specimens were cemented to bases of a dentin-like material. Each specimen was cyclically loaded by a 2-mm-diameter G10 piston in water. Loads ranging from 10 N to the target load were applied at a frequency of 20 Hertz for 500,000 cycles. If cracked, the next specimen was cycled at a lower load; if not cracked, at a higher load (step size of 25 N).
  
  
  RESULTS
  Mean and standard deviations of fatigue loads for the different core thicknesses were 0.5-mm core 610.94 N ±130.11; 0.75-mm core 600.0 N ±132.80; 1.0-mm core 537.50 N ±41.67; a Nd 1.5-mm core 501.14 N ±70.12. All veneered groups were significantly stronger than the full thickness group (ANOVA, P<.001; 95% post hoc). Cone cracking was observed only in the 2 thinner core groups (χ(2) test, P<.05), possibly indicating residual stresses.
  
  
  CONCLUSIONS
  Results indicate that the addition of veneering porcelain to lithium disilicate cores increases the fatigue strength of the biceramic system.
authors.affiliation: Resident, Department of Reconstructive Dentistry and Center for Biomaterials, University of Connecticut Health Center, Farmington, Conn.
authors.forename: Aurora Clark
authors.initials: AC
authors.lastname: Dibner
authors.affiliation: Professor, Department of Reconstructive Dentistry and Center for Biomaterials, University of Connecticut Health Center, Farmington, Conn. Electronic address: Kelly@uchc.edu.
authors.forename: J Robert
authors.initials: JR
authors.lastname: Kelly
mesh_terms: D002516:Ceramics / Q000737:chemistry*; D003776:Dental Porcelain; D003799:Dental Stress Analysis; D003801:Dental Veneers / Q000592:standards*; D019544:Equipment Failure Analysis; D006801:Humans; D008422:Materials Testing; D013314:Stress, Mechanical
chemical_list: D003776:Dental Porcelain