title: Comparison of fracture resistance of pressable metal ceramic custom implant abutments with CAD/CAM commercially fabricated zirconia implant abutments.
abstract: BACKGROUND
  The adequacy of the strength of dental zirconia abutments under heavy occlusal load conditions is questionable, with degradation of the mechanical properties of zirconia having been reported. Therefore, some alternatives must be considered.
  
  
  OBJECTIVE
  The purpose of this study was to determine the efficacy of fabricating pressable metal ceramic custom implant (Pr) abutments, and to evaluate the fracture resistance of these abutments.
  
  
  METHODS
  Two groups of implant abutment specimens were fabricated (n=10). The experimental group consisted of Pr abutments, and the control group consisted of CAD/CAM-designed zirconia-based ceramic (Zr) abutments. For the experimental group, custom metal abutments were cast using a compatible metal alloy (Lodestar); this was followed by injection molding with lithium disilicate pressable ceramic (IPS e.max Press) around the metal column of the custom implant abutment. For the control group, 10 specimens were fabricated from CAD/CAM-designed zirconia abutments (Procera Zirconia). Following scanning, all-ceramic crowns with the average dimensions of a human central incisor were fabricated for the experimental and control abutments (n=20) using lithium disilicate pressable ceramic (IPS e.max Press). Each crown was cemented to the implant abutments with a resin luting agent (Variolink II). The crown-abutment test specimens were fixed to titanium implant analogs and placed in a test stand at 30 degrees from the vertical axis of the specimens in a computer-controlled universal testing device. The independent t test was used to detect if the mean values of the fracture load differed significantly (alpha=.05) between the 2 groups.
  
  
  RESULTS
  The mean (SD) fracture load was significantly higher in the Pr group (901.67 (102.05) N) than in the Zr group (480.01 (174.46) N, P<.005).
  
  
  CONCLUSIONS
  This study found that Pr abutments are stronger than Zr abutments.
authors.affiliation: Department of Prosthodontics, Yonsei University, School of Dental Medicine, Seoul, Korea. drsungtaekim@gmail.com
authors.forename: Sungtae
authors.initials: S
authors.lastname: Kim
authors.forename: Hyeong-Il
authors.initials: HI
authors.lastname: Kim
authors.forename: Jane D
authors.initials: JD
authors.lastname: Brewer
authors.forename: Edward A
authors.initials: EA
authors.lastname: Monaco