title: Correlation between fracture toughness and leucite content in dental porcelains.
abstract: OBJECTIVE
  To determine the correlation between fracture toughness and leucite content in dental porcelains. The mechanisms by which leucite influences the fracture toughness of dental porcelains were also investigated.
  
  
  METHODS
  Six porcelains were tested: A (Ceramco I/Dentsply), B (Ceramco II/Dentsitply), C (Finesse/Dentsply), D (d.Sign/Ivoclar), Cb (Cerabien/Noritake) and V (Vitadur Alpha/Vita). Bar-shaped specimens were produced, and their fracture toughness was determined by means of the single-edge precracked beam (SEPB) method. The test consisted of fracturing the specimen after a precrack was generated by a bridge-anvil device. KIc was calculated based on fracture force and size of the precrack. Microstructural analysis and determination of the leucite volume fraction were performed on polished specimens etched with 2% HF for 15s by means of scanning electron microscopy. Fractographic analysis was performed on fracture surfaces.
  
  
  RESULTS
  Porcelains A and B presented the highest leucite contents (22%) and similar KIc values (1.23 and 1.22 MPa m1/2, respectively), significantly higher than the other materials. Porcelains C and D presented similar K(Ic) values (0.81 and 0.93 MPa m1/2, respectively), but different leucite contents (6 and 15%, respectively). Porcelain D presented higher KIc compared to porcelains Cb and V (0.71 and 0.75 MPa m1/2, respectively), which presented similar values and the lowest leucite contents (0%). Fractographic analysis showed that porcelains with higher leucite content presented higher incidence of crack deflection.
  
  
  CONCLUSIONS
  For the materials evaluated in this study, the leucite content was directly related to KIc. The main toughening mechanism observed was crack deflection around leucite particles and clusters.
authors.affiliation: Department of Dental Materials, School of Dentistry, University of São Paulo, Brazil. paulofc@usp.br
authors.forename: Paulo F
authors.initials: PF
authors.lastname: Cesar
authors.forename: Humberto N
authors.initials: HN
authors.lastname: Yoshimura
authors.forename: Walter G
authors.initials: WG
authors.lastname: Miranda Júnior
authors.forename: Cristina Y
authors.initials: CY
authors.lastname: Okada
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D006244:Hardness; D008422:Materials Testing / Q000379:methods; D013314:Stress, Mechanical
chemical_list: D000538:Aluminum Silicates; D003776:Dental Porcelain; C078519:leucite