title: Abutment rotational displacement of external hexagon implant system under lateral cyclic loading.
abstract: OBJECTIVE
  This in vitro study investigated the effect of lateral cyclic loading with different load positions and periods on abutment rotational displacement (RD) of external hexagon implant system.
  
  
  METHODS
  Four groups of five implant assemblies each were used. Each assembly consisted of Brånemark System Mk IV implant (Nobel Biocare AB, Göteborg, Sweden), CeraOne abutment (Nobel Biocare AB), and a cement-retained casting. A cyclic load of 50 N was applied centrally and perpendicular to the long axis of the implant for groups A and B for 0.25 and 0.50 x 10(6) cycles, respectively, while for groups C and D, the same load was applied at 4-mm distance eccentrically for 0.25 and 0.50 x 10(6) cycles, respectively. The displacement was evaluated by hand drawing a longitudinal line across the implant-abutment interface. Before and after loading, the lateral distance between two reference points on the abutment and implant was measured under high resolution (x200) and the difference formed the RD value. The data were analyzed with one-way analysis of variance and compared with Tukey test (alpha=0.05).
  
  
  RESULTS
  Group D had the highest mean of RD value (55.00 +/- 1.871 microm), while group A had the lowest (2.800 +/- 0.837 microm). Groups A and B had a high statistically significant difference in RD values, as compared to groups C or D (p < .001). Moreover, group C had statistically significant difference from group D (p=.011). Conversely, no statistical significance was obtained when group A was compared with group B.
  
  
  CONCLUSIONS
  Within the limits of this in vitro study, the RD of the external hexagon joint components occurred significantly under eccentric lateral loading when compared to centric loading. The displacement increased significantly with longer period of eccentric lateral loading.
authors.affiliation: Department of Conservative Dentistry and Prosthodontics, Faculty of Dentistry, University of Jordan, Amman, Jordan. khraisat@lycos.com
authors.forename: Ameen
authors.initials: A
authors.lastname: Khraisat
authors.forename: Zaid H
authors.initials: ZH
authors.lastname: Baqain
authors.forename: Leena
authors.initials: L
authors.lastname: Smadi
authors.forename: Shuichi
authors.initials: S
authors.lastname: Nomura
authors.forename: Osamu
authors.initials: O
authors.lastname: Miyakawa
authors.forename: Ziad
authors.initials: Z
authors.lastname: Elnasser
mesh_terms: D000044:Dental Abutments; D003738:Dental Cements / Q000737:chemistry; D015921:Dental Implants; D017267:Dental Prosthesis Design; D019094:Dental Prosthesis, Implant-Supported; D019232:Dental Restoration Failure; D006801:Humans; D008422:Materials Testing; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D019415:Torque
chemical_list: D003738:Dental Cements; D015921:Dental Implants