title: Flexural strength and reliability of monolithic and trilayer ceramic structures obtained by the CAD-on technique.
abstract: OBJECTIVE
  To evaluate the flexural strength, Weibull modulus, fracture toughness, and failure behavior of ceramic structures obtained by the CAD-on technique, testing the null hypothesis that trilayer structures show similar properties to monolithic structures.
  
  
  METHODS
  Bar-shaped (1.8mm×4mm×16mm) monolithic specimens of zirconia (IPS e.max ZirCAD - Ivoclar Vivadent) and trilayer specimens of zirconia/fusion ceramic/lithium dissilicate (IPS e.max ZirCAD/IPS e.max CAD Crystall./Connect/IPS e.max CAD, Ivoclar Vivadent) were fabricated (n=30). Specimens were tested in flexure in 37°C deionized water using a universal testing machine at a crosshead speed of 0.5mm/min. Failure loads were recorded, and the flexural strength values were calculated. Fractography principles were used to examine the fracture surfaces under optical and scanning electron microscopy. Data were statistically analyzed using Student's t-test and Weibull statistics (α=0.05).
  
  
  RESULTS
  Monolithic and trilayer specimens showed similar mean flexural strengths, characteristic strengths, and Weibull moduli. Trilayer structures showed greater mean critical flaw and fracture toughness values than monolithic specimens (p<0.001). Most critical flaws in the trilayer groups were located on the Y-TZP surface subjected to tension and propagated catastrophically. Trilayer structures showed no flaw deflection at the interface.
  
  
  CONCLUSIONS
  Considering the CAD-on technique, the trilayer structures showed greater fracture toughness than the monolithic zirconia specimens.
authors.affiliation: Graduate Program in Dentistry, Federal University of Pelotas, Rua Gonçalves Chaves 457, 96015-560 Pelotas, RS, Brazil. Electronic address: gabybasso@yahoo.com.br.
authors.forename: G R
authors.initials: GR
authors.lastname: Basso
authors.affiliation: Graduate Program in Dentistry, Federal University of Pelotas, Rua Gonçalves Chaves 457, 96015-560 Pelotas, RS, Brazil.
authors.forename: R R
authors.initials: RR
authors.lastname: Moraes
authors.affiliation: Post-graduate Program in Dentistry, Dental School, University of Passo Fundo, Passo Fundo, RS, Brazil.
authors.forename: M
authors.initials: M
authors.lastname: Borba
authors.affiliation: Department of Biomedical Materials Science, University of Mississippi Medical Center, Jackson, MS, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Griggs
authors.affiliation: Post-graduate Program in Dentistry, Dental School, University of Passo Fundo, Passo Fundo, RS, Brazil.
authors.forename: A
authors.initials: A
authors.lastname: Della Bona
mesh_terms: D002516:Ceramics / Q000737:chemistry*; D017076:Computer-Aided Design; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D013499:Surface Properties; D015040:Zirconium / Q000737:chemistry*
chemical_list: C520133:IPS e.max CAD LT; C493120:lithia disilicate; D003776:Dental Porcelain; D015040:Zirconium; C028541:zirconium oxide
keywords: Dental ceramics; Flexural strength; Fractography; Monolithic and trilayer structures