Influence of prosthesis fit and the effect of a luting system on the prosthetic connection preload: an in vitro study

It was the aim of this study to evaluate the efficiency of a luting technique that is said to compensate for misfits of implant-supported prostheses by means of a combined screw retained-luted fixation of the prostheses to the supporting abutments.

One three-unit prosthesis was made on cylindric abutments, and one was made on conical abutments. Two more prostheses were made, one on the cylindric and one on the conical abutments, with the luting system. The preload was measured in different fit and misfit situations, with and without the use of the luting system. The preload is a combination of internal preload (positive axial forces), which is a clamping load that keeps the implant-prosthesis components together, and external preload (axial forces and bending moments), which is the result of a deformation of the implant-prosthesis complex during fixation caused by prosthesis misfit. The external preload on the supporting abutments after screw tightening the prostheses was used as an indicator for the quality of fit of the prostheses.

The axial forces were lower and the bending moments were higher in cases of misfit in comparison with the optimal fit situation. The luting system generally did not decrease the registered external preload. Except for one test condition, even higher bending moments were registered on the supporting abutments when the luting system was used.

For the prostheses evaluated in this study, the luting system was not effective in reducing the external preload on the supporting implants caused by prosthesis misfit. Although the luting system could compensate for visual misfit, it failed to really improve the load conditions of the supporting implants.