The influence of stiffness of implant-abutment connection on load-deflection ratios of a screw-retained stiff cantilever beam. 3-D measurements in vitro.
OBJECTIVE
The purpose of this in vitro study was to investigate the influence of degree of stiffness of implant-abutment connection of a Brånemark implant system on load- deflection ratios in three dimensions of the beam-end of a screw-retained stiff cantilever beam when subjected to vertically directed loads.


METHODS
Two different implant-abutment connections were tested; welded and screw-retained. One of the abutments (EsthetiCone 2.0; Nobel Biocare AB) was screwed with a torque force of 20 N cm and then laser welded around its entire periphery to one of two Brånemark implants (welded unit). This unit and the other implant were tightly screwed into each of two pre-threaded holes in a steel plate so that the implants became submerged in the plate. The remaining abutment was thereafter screwed to its implant with a torque force of 20 N cm (screw-retained unit). A cantilevered gold beam of 6 mm height and width comprising a gold cylinder (Nobel Biocare AB) was attached to each abutment with a slotted, flat headed, prosthetic gold screw (torque force 10 N cm). A force transducer, synchronized with a 3-D motion analysis system, was glued on the upper surface of each beam-end 19.4 mm from the implant, to register the loads transferred from a specially built loading device. The beam-ends were stepwise subjected to vertically directed loads from 14.9 to 40.3 N and the vertical and horizontal deflections of the beam-ends were registered with the 3-D motion analysis system.


RESULTS
For load 14.9-40.3 N the vertical (z-axis) deflections of the beam-end were for the welded implant-abutment connection reduced with 18-46% compared with the screw-retained unit. After maximal loading (40.3 N) the horizontal counter-clockwise rotation of the beam around the screw joints (y-axis rotations) was reduced with 61% for the welded connection. The horizontal movements of the beam-end along the x-axis (x-axis deflections) were reduced with 49% at maximal loading.


CONCLUSIONS
It was concluded that increased implant-abutment stiffness will substantially reduce both vertical and horizontal deflections of a screw-retained stiff cantilever beam subjected to vertically directed loads.
The Institute for Postgraduate Dental Education, Department of Periodontology, Jönköping and Institute for Clinical Sciences, Department of Biomaterials, Göteborg University, Göteborg, Sweden.
Björn
B
Cassel
Dan
D
Lundgren
Dan
D
Karlsson
D000044:Dental Abutments; D059605:Dental Implant-Abutment Design; D015921:Dental Implants; D019094:Dental Prosthesis, Implant-Supported; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000379:methods*; D006047:Gold Alloys / Q000737:chemistry; D066298:In Vitro Techniques; D008422:Materials Testing; D013499:Surface Properties; D019415:Torque
D015921:Dental Implants; D006047:Gold Alloys