title: Stability of implant-abutment interface with a hexagon-mediated butt joint: failure mode and bending resistance.
abstract: BACKGROUND
  Clinical data showed that the external hexagon implant system with a gold abutment screw has reduced the problem of screw loosening or fracture. However, the behavior of the implant-abutment joint components with respect to unfavorable bending force is still unclear.
  
  
  OBJECTIVE
  This study investigated the joint instability and bending resistance of a single-tooth external hexagon implant system after lateral cyclic loading.
  
  
  METHODS
  Fifteen implant assemblies (Nobel Biocare, Göteborg, Sweden) were divided equally into three groups: A, B, and C. Each assembly consisted of a Brånemark System Mk IV implant (4 x 10 mm) mounted in a brass block, a CeraOne abutment (3 mm), and an experimental cement-retained superstructure. For group A, a centric lateral cyclic load of 50 N was applied for 1.0 x 10(6), whereas for group B, the same load was eccentrically applied for 1.0 x 10(6) cycles. Group C, the control, was not loaded. After cyclic loading, specimens were mounted in a universal testing machine, and the yield and bending strengths were measured (kg). The external hexagon surface texture was examined using a secondary electron microscope. The data were analyzed with one-way analysis of variance and compared by the Tukey test (alpha = .05).
  
  
  RESULTS
  For all test specimens, the abutment screw was plastically bent in the unthreaded portion. Group B had a significantly lower mean yield and bending strengths than group C (p = .005 and .010, respectively). Post-cyclic loading photographs showed that group B implants had marked burnishing around the hexagon corners. The bending force abraded both corner areas of the hexagon surface but left the middle area nearly intact for all tested groups. However, group B had the significantly lowest mean abraded area.
  
  
  CONCLUSIONS
  Within the limits of this study, eccentric rather than centric lateral cyclic loading negatively affected the resistance of the implant-abutment joint to static bending.
authors.affiliation: Department of Conservative Dentistry and Prosthodontics, Faculty of Dentistry, University of Jordan, Amman. khraisat@lycos.com
authors.forename: Ameen
authors.initials: A
authors.lastname: Khraisat
mesh_terms: D000044:Dental Abutments; D003738:Dental Cements / Q000737:chemistry; D019250:Dental Implants, Single-Tooth; D017267:Dental Prosthesis Design; D017268:Dental Prosthesis Retention; D019094:Dental Prosthesis, Implant-Supported; D019232:Dental Restoration Failure; D004577:Electron Probe Microanalysis; D006047:Gold Alloys; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D003738:Dental Cements; D006047:Gold Alloys