title: Influence of firing time and framework thickness on veneered Y-TZP discs curvature.
abstract: OBJECTIVE
  The objective of the present work was to study the curvature of very thinly, veneered Y-TZP discs of different framework thicknesses submitted to different firing times.
  
  
  METHODS
  Fifteen 20-mm-wide Y-TZP discs were produced in three different thicknesses: 0.75, 1, 1.5mm. One disc from each group was left unveneered while the others were layered with a 0.1mm veneering ceramic layer. All discs underwent five firing cycles for a total cumulative firing time of 30 min, 1, 2, 5 and 10h at 900°C. The curvature profile was measured using a profilometer after the veneering process and after each firing cycle respectively. A fitted curve was then used to estimate the, curvature radius. The coefficient of thermal expansion (CTE) measurements were taken on veneering, ceramic and Y-TZP beam samples that underwent the same firing schedule. Those data were used to calculate the curvature generated by CTE variations over firing time.
  
  
  RESULTS
  All bilayered samples exhibited a curvature that increased over firing time inversely to framework thickness. However non-veneered samples did not exhibit any curvature modification.
  
  
  CONCLUSIONS
  The results of the present study reveal that even a very thin veneer layer (0.1mm) can induce a significant curvature of Y-TZP discs. The dilatometric results showed that Tg and CTE, variations are not sufficient to explain this curvature. A chemical-induced zirconia volume, augmentation located at the framework sub-surface near the interface could explain the sample, curvature and its increase with firing time.
authors.affiliation: Unité de Recherches Biomatériaux Innovants et Interfaces (URB2I-EA4462), Université Paris Descartes, Sorbonne Paris Cité, Faculté de Chirurgie Dentaire, Paris, France. Electronic address: bjak@wanadoo.fr.
authors.forename: Boris D
authors.initials: BD
authors.lastname: Jakubowicz-Kohen
authors.affiliation: Unité de Recherches Biomatériaux Innovants et Interfaces (URB2I-EA4462), Université Paris Descartes, Sorbonne Paris Cité, Faculté de Chirurgie Dentaire, Paris, France.
authors.forename: Michaël J
authors.initials: MJ
authors.lastname: Sadoun
authors.affiliation: INSA-LYON, UMR CNRS 5510 MATEIS, 20 Avenue Albert Einstein, 69621 Villeurbanne Cedex, France.
authors.forename: Thierry
authors.initials: T
authors.lastname: Douillard
authors.affiliation: Unité de Recherches Biomatériaux Innovants et Interfaces (URB2I-EA4462), Université Paris Descartes, Sorbonne Paris Cité, Faculté de Chirurgie Dentaire, Paris, France; Department of Fixed Prosthodontics, Institute of Dentistry, University of Liège Hospital (ULg CHU LIMARC), 45 Quai G. Kurth, Liège, 4020, Belgium.
authors.forename: Amélie K
authors.initials: AK
authors.lastname: Mainjot
mesh_terms: D003801:Dental Veneers; D006358:Hot Temperature; D008422:Materials Testing
keywords: Firing time; Profilometry; Residual stress; Thickness; Veneering ceramic; Zirconia