title: Fracture load of ceramic restorations after fatigue loading.
abstract: BACKGROUND
  A clinician must decide what ceramic coping and veneer material to prescribe based on the amount of tooth reduction possible and the desired esthetic outcome of the restoration.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to compare the fracture strength of monolithic and bilayered lithium disilicate (IPS e.max) and zirconia (LAVA) crowns at clinically relevant thicknesses after load cycling.
  
  
  METHODS
  Crowns (n=8) were fabricated from 6 groups: 1.2-mm monolithic lithium disilicate, 1.5-mm monolithic lithium disilicate, 1.5-mm bilayered lithium disilicate with hand-layered veneer, 0.6 mm monolithic zirconia, 1.2-mm bilayered zirconia with hand-layered veneer, and 1.2-mm bilayered zirconia with milled veneer (dimension represents thickness at the occlusal pit). Crowns were cemented to identical milled resin dies with resin-modified glass ionomer cement. Cemented crowns were stored at 37°C for 24 hours and load cycled for 200,000 cycles at 25 N at a rate of 40 cycles/minute. The ultimate fracture load for each specimen was measured in a universal testing machine. Data were analyzed with a 1-way ANOVA and Tukey honest significant difference post hoc analysis (α=.05).
  
  
  RESULTS
  Mean ±SD fracture load values were 1465 ±330 N for monolithic lithium disilicate (1.2-mm thickness) and 2027 ±365 N (1.5-mm thickness) and 1732 ±315 N for bilayered hand-veneered lithium disilicate (1.5-mm thickness). Fracture loads were 1669 ±311 N for monolithic zirconia crowns (0.6mm thickness), 2625 ±300 N for zirconia milled-veneered (1.2-mm thickness), and 2655 ±590N for zirconia hand-veneered crowns (1.2mm thickness). One-way ANOVA showed a statistically significant difference among the groups (P<.01). Veneered zirconia crowns showed the highest fracture strength, 1.2-mm hand veneered zirconia was similar to that of 1.5-mm monolithic zirconia, and all other groups were not statistically different.
  
  
  CONCLUSIONS
  Crowns of 1.2-mm bilayered zirconia had higher fracture loads than 0.6-mm zirconia or 1.2-mm lithium disilicate monolithic crowns.
authors.affiliation: Postdoctoral student, Eastman Institute of Oral Health, University of Rochester, Rochester, NY.
authors.forename: Balasudha
authors.initials: B
authors.lastname: Baladhandayutham
authors.affiliation: Assistant Professor, Department of Biomaterials, University of Alabama at Birmingham School of Dentistry, Birmingham, Ala. Electronic address: nlawson@uab.edu.
authors.forename: Nathaniel C
authors.initials: NC
authors.lastname: Lawson
authors.affiliation: Professor, Division of Biomaterials, University of Alabama at Birmingham School of Dentistry, Birmingham, Ala.
authors.forename: John O
authors.initials: JO
authors.lastname: Burgess
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D002484:Cementation / Q000379:methods; D002516:Ceramics / Q000737:chemistry*; D017076:Computer-Aided Design; D003442:Crowns; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000295:instrumentation; D003801:Dental Veneers; D005899:Glass Ionomer Cements / Q000737:chemistry; D008422:Materials Testing; D017680:Potassium Compounds / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D015040:Zirconium / Q000737:chemistry
chemical_list: D000538:Aluminum Silicates; D003764:Dental Materials; D005899:Glass Ionomer Cements; D017680:Potassium Compounds; D019279:Resin Cements; C493120:lithia disilicate; D003776:Dental Porcelain; C016447:feldspar; D015040:Zirconium; C028541:zirconium oxide