title: Critical bending moment of implant-abutment screw joint interfaces: effect of torque levels and implant diameter.
abstract: OBJECTIVE
  Critical bending moment (CBM), the moment at which the external nonaxial load applied overcomes screw joint preload and causes loss of contact between the mating surfaces of the implant screw joint components, was measured with 2 types of implants and 2 types of abutments.
  
  
  METHODS
  Using 4 test groups of 5 implant-abutment pairs, CBM at the implant-abutment screw joint was measured at 25%, 50%, 75%, and 100% of the manufacturer's recommended torque levels. Regular Platform (RP) Nobel Biocare implants (3.75 mm diameter), Wide Platform (WP) Nobel Biocare implants (5.0 mm diameter), CeraOne abutments, and Multiunit abutments were used. Microstrain was measured as loads were applied to the abutment at various distances from the implant-abutment interface. Strain instrumentation logged the strain data dynamically to determine the point of gap opening. All torque applications and strain measurements were repeated 5 times.
  
  
  RESULTS
  For the CeraOne-RP group, the mean CBMs were 17.09 Ncm, 35.35 Ncm, 45.63 Ncm, and 62.64 Ncm at 25%, 50%, 75%, and 100% of the recommended torque level, respectively. For the CeraOne-WP group, mean CBMs were 28.29 Ncm, 62.97 Ncm, 92.20 Ncm, and 127.41 Ncm; for the Multiunit-RP group, 16.08 Ncm, 21.55 Ncm, 34.12 Ncm, and 39.46 Ncm; and for the Multiunit-WP group, 15.90 Ncm, 32.86 Ncm, 43.29 Ncm, and 61.55 Ncm at the 4 different torque levels. Two-way analysis of variance (ANOVA) (P < .001) revealed significant effects for the test groups (F = 2738.2) and torque levels (F = 2969.0).
  
  
  CONCLUSIONS
  The methodology developed in this study allows confirmation of the gap opening of the screw joint for the test groups and determination of CBM at different torque levels.
  
  
  CONCLUSIONS
  CBM was found to differ among abutment systems, implant diameters, and torque levels. The torque levels recommended by the manufacturer should followed to ensure screw joint integrity.
authors.affiliation: Department of Restorative Dentistry, Faculty of Dentistry, National University of Singapore, Republic of Singapore.
authors.forename: Ban Fui
authors.initials: BF
authors.lastname: Tan
authors.forename: Keson B
authors.initials: KB
authors.lastname: Tan
authors.forename: Jack I
authors.initials: JI
authors.lastname: Nicholls
mesh_terms: D000704:Analysis of Variance; D000044:Dental Abutments; D015921:Dental Implants; D017267:Dental Prosthesis Design; D004548:Elasticity; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D018583:Pliability; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry; D019415:Torque
chemical_list: D015921:Dental Implants; D006047:Gold Alloys; D014025:Titanium