title: The fracture strength by a torsion test at the implant-abutment interface.
abstract: BACKGROUND
  Fractured connections between implants and implant abutments or abutment screws are frequently encountered in a clinical setting. The purpose of this study was to investigate fracture strength using a torsion test at the interface between the implant and the abutment.
  
  
  METHODS
  Thirty screw-type implant with diameters of 3.3, 3.8, 4.3, 5.0, and 6.0 mm were submitted to a torsion test. Implants of each size were connected to abutments with abutment screws tightened to 20 N · cm. Mechanical stress was applied with a rotational speed of 3.6 °/min until fracture occurred, and maximum torque (fracture torque) and torsional yield strength were measured. The mean values were calculated and then compared using Tukey's test. The abutments were then removed, and the implant-abutment interfaces were examined using a scanning electron microscope (SEM).
  
  
  RESULTS
  No significant differences in mean fracture torque were found among 3.3, 3.8, and 4.3 mm-diameter implants, but significant differences were found between these sizes and 5.0 and 6.0 mm-diameter implants (p < 0.01). Concerning mean torsional yield strength, significant differences were found between 3.3, 3.8, and 4.3 mm-diameter and 5.0 and 6.0 mm-diameter implants (p < 0.01). Observations under the SEM showed that all the projections of the abutment corresponding to the internal notches of the implant body had been destroyed.
  
  
  CONCLUSIONS
  Smaller diameter implants demonstrated lower fracture torque and torsional yield strength than implants with larger diameters. In internal tube-in-tube connections, three abutment projections corresponding to rotation-prevention notches were destroyed in each implant.
authors.affiliation: Department of Crown and Bridge Prosthodontics, School of Life Dentistry at Niigata, The Nippon Dental University, 951-8580 1-8 Hamaura-cho, Chuo-ku, Niigata, Japan. fumi@ngt.ndu.ac.jp.
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Watanabe
authors.affiliation: Oral Implant Care Unit Niigata Hospital, The Nippon Dental University, 1-8 Hamaura-cho, Chuo-ku, Niigata, Japan.
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Hiroyasu
authors.affiliation: Oral Implant Care Unit Niigata Hospital, The Nippon Dental University, 1-8 Hamaura-cho, Chuo-ku, Niigata, Japan.
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Ueda
keywords: Abutment connection deformation; Implant-abutment interface; Mechanical load; Torque; Torsion test