title: The influence of multiple firing on thermal contraction of ceramic materials used for the fabrication of layered all-ceramic dental restorations.
abstract: OBJECTIVE
  During the production of layered all-ceramic restorations transient and/or residual thermal stresses may be formed which may affect a restoration's longevity. The aim of this study was to evaluate the influence of multiple firings on the thermal behavior of veneering porcelains and a ceramic core.
  
  
  METHODS
  The materials tested were: Empress 2 Core, Empress 2 Veneer and Eris glass-ceramics, Carrara Vincent and an experimental leucite-based veneering porcelain, Vitadur-Alpha aluminous porcelain, and two porcelains designed for titanium (i.e. Duceratin Dentine and Enamel). The thermal contraction coefficient of the materials was measured by means of dilatometery. The thermal contraction coefficient was measured during cooling and calculated over the temperature range of 450-20 degrees C by linear regression. One and two-way analysis of variance together with Tukey post-hoc tests were used as statistical analysis.
  
  
  RESULTS
  Repeated firing affects the thermal contraction coefficients of Empress 2 Veneer, Carrara Vincent porcelain and the experimental porcelain. The thermal contraction coefficients of Empress 2 Core were significantly different from Vitadur-Alpha, Carrara Vincent, experimental porcelain, and Duceratin porcelains. The contraction coefficients of Empress 2 Veneer and Eris were closest to that of Empress 2 Core.
  
  
  CONCLUSIONS
  The Empress 2 Core and Eris glass-ceramics, the aluminous porcelain and Duceratin porcelains showed better thermal stability after repeated firing than leucite porcelains. It can be concluded that due to the thermal stability of glass-ceramic materials, layered all-ceramic restorations of these materials may perform better.
authors.affiliation: Department of Dental Materials Science, ACTA, Louwesweg 1, 1066 EA Amsterdam, The Netherlands. g.isgro@acta.nl
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Isgrò
authors.forename: Cornelis J
authors.initials: CJ
authors.lastname: Kleverlaan
authors.forename: Hang
authors.initials: H
authors.lastname: Wang
authors.forename: Albert J
authors.initials: AJ
authors.lastname: Feilzer
mesh_terms: D000538:Aluminum Silicates; D000704:Analysis of Variance; D002516:Ceramics; D003735:Dental Casting Technique; D003776:Dental Porcelain; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis; D003801:Dental Veneers; D006358:Hot Temperature; D016014:Linear Models; D018020:Lithium Compounds; D008422:Materials Testing; D016876:Metal Ceramic Alloys
chemical_list: D000538:Aluminum Silicates; C503162:Carrara Vincent; C098572:Duceratin Porcelain; C118557:Empress 2; C500744:Eris ceramic; D018020:Lithium Compounds; D016876:Metal Ceramic Alloys; C483027:vitadur alpha; D003776:Dental Porcelain; C078519:leucite; C023506:Glass ceramics