title: Stress analysis of two methods of ceramic inlay preparation by finite element.
abstract: OBJECTIVE
  Ceramic inlays are bonded to tooth structure with resin cements. During the resin cement setting, shrinkage stress develops at the interfaces. During tooth preparation, the undercut areas formed due to the different patterns of caries progression can either be blocked out before taking impression with suitable cement such as glass ionomer cement, or before making the final restoration in the laboratory. Then, the relieved space will be filled with luting cement in clinic. The aim of this study was to compare these two methods of undercut filling in term of stress distribution in the ceramic inlay.
  
  
  METHODS
  An axisymmetric finite element analysis was performed to study the stress distribution during inlay cementing. The solid model was generated from a longitudinal section of maxillary premolar in which a class I cavity with 60 degree undercut at the preparation wall and 20 degree divergence of the vertical walls was prepared. A thermal model was used to simulate the polymerization shrinkage of the resin cement. Finite element analysis was carried out in ANSYS environment.
  
  
  RESULTS
  Filling the undercut by glass ionomer cement decreased the stress concentration at the ceramic/cement interface. The dominant normal stress at the tooth cement interface in absence of glass ionomer cement was tensile with maximum of 30 Mpa. Using glass ionomer, cement developed stresses with different compressive and tensile signs. With increasing the thickness of resin cement (100 µm, 150 µm, 200 µm), the stress increased.
  
  
  CONCLUSIONS
  Cements with minimum shrinkage and as thin layer as possible should be used. Filling the undercut with glass ionomer cement decreases the stress. Other experimental and clinical studies must follow this research.
authors.affiliation: Department of Operative Dentistry, Dental School, Islamic Azad University, Khourasgan Branch, Iran.
authors.forename: Leila
authors.initials: L
authors.lastname: Pishevar
authors.forename: Maryam
authors.initials: M
authors.lastname: Ghavam
authors.forename: Ahmadreza
authors.initials: A
authors.lastname: Pishevar
mesh_terms: D002516:Ceramics; D003799:Dental Stress Analysis / Q000379:methods*; D020342:Finite Element Analysis