title: Influence of leucite content on slow crack growth of dental porcelains.
abstract: OBJECTIVE
  To determine the stress corrosion susceptibility coefficient, n, of seven dental porcelains (A: Ceramco I; B: Ceramco-II; C: Ceramco-III; D: d.Sign; E: Cerabien; F: Vitadur-Alpha; and G: Ultropaline) after aging in air or artificial saliva, and correlate results with leucite content (LC).
  
  
  METHODS
  Bars were fired according to manufacturers' instructions and polished before induction of cracks by a Vickers indenter (19.6N, 20s). Four specimens were stored in air/room temperature, and three in saliva/37 degrees C. Five indentations were made per specimen and crack lengths measured at the following times: approximately 0; 1; 3; 10; 30; 100; 300; 1000 and 3000 h. The stress corrosion coefficient n was calculated by linear regression analysis after plotting crack length as a function of time, considering that the slope of the curve was [2/(3n+2)]. Microstructural analysis was performed to determine LC.
  
  
  RESULTS
  LC of the porcelains were 22% (A and B); 6% (C); 15% (D); 0% (E and F); and 13% (G). Except for porcelains A and D, all materials showed a decrease in their n values when stored in artificial saliva. However, the decrease was more pronounced for porcelains B, F, and G. Ranking of materials varied according to storage media (in air, porcelain G showed higher n compared to A, while in saliva both showed similar coefficients). No correlation was found between n values and LC in air or saliva.
  
  
  CONCLUSIONS
  Storage media influenced the n value obtained for most of the materials. LC did not affect resistance to slow crack growth regardless of the test environment.
authors.affiliation: Department of Dental Materials, School of Dentistry, University of São Paulo, São Paulo, Brazil. paulofc@usp.br
authors.forename: Paulo F
authors.initials: PF
authors.lastname: Cesar
authors.forename: Fabiana N
authors.initials: FN
authors.lastname: Soki
authors.forename: Humberto N
authors.initials: HN
authors.lastname: Yoshimura
authors.forename: Carla C
authors.initials: CC
authors.lastname: Gonzaga
authors.forename: Victor
authors.initials: V
authors.lastname: Styopkin
mesh_terms: D000388:Air; D000465:Algorithms; D000538:Aluminum Silicates / Q000032:analysis / Q000737:chemistry*; D001031:Apatites / Q000032:analysis / Q000737:chemistry; D003776:Dental Porcelain / Q000032:analysis / Q000737:chemistry*; D005898:Glass / Q000032:analysis / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D012464:Saliva, Artificial / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors
chemical_list: D000538:Aluminum Silicates; D001031:Apatites; D012464:Saliva, Artificial; C506670:d.SIGN ceramic; C483027:vitadur alpha; D003776:Dental Porcelain; C078519:leucite; C058233:Ceramco