title: Comparison of chamfer and deep chamfer preparation designs on the fracture resistance of zirconia core restorations.
abstract: OBJECTIVE
  One of the major problems of all-ceramic restorations is their probable fracture under occlusal force. The aim of the present in vitro study was to compare the effect of two marginal designs (chamfer and deep chamfer) on the fracture resistance of all-ceramic restorations, CERCON.
  
  
  METHODS
  This in vitro study was carried out with single-blind experimental technique. One stainless steel die with 50' chamfer finish line design (0.8 mm deep) was prepared using a milling machine. Ten epoxy resin dies were prepared. The same die was retrieved and 50' chamfer was converted into a deep chamfer design (1 mm). Again ten epoxy resin dies were prepared from the deep chamfer die. Zirconia cores with 0.4 mm thickness and 35 µm cement space were fabricated on the epoxy resin dies (10 chamfer and 10 deep chamfer samples). The zirconia cores were cemented on the epoxy resin dies and underwent a fracture test with a universal testing machine and the samples were investigated from the point of view of the origin of the failure.
  
  
  RESULTS
  The mean values of fracture resistance for deep chamfer and chamfer samples were 1426.10±182.60 and 991.75±112.00 N, respectively. Student's t-test revealed statistically significant differences between the groups.
  
  
  CONCLUSIONS
  The results indicated a relationship between the marginal design of zirconia cores and their fracture re-sistance. A deep chamfer margin improved the biomechanical performance of posterior single zirconia crown restorations, which might be attributed to greater thickness and rounded internal angles in deep chamfer margins.
authors.affiliation: Associate Professor, Department of Prosthodontics, Dental School, Islamic Azad University, Tehran, Iran.
authors.forename: Ezatollah
authors.initials: E
authors.lastname: Jalalian
authors.forename: Roghayeh
authors.initials: R
authors.lastname: Rostami
authors.forename: Berivan
authors.initials: B
authors.lastname: Atashkar