Experimental study of the removal force in tapered implant-abutment interfaces: A pilot study

Abstract

Conically tapered interface fits (TIF) provide a reliable and strong self-locking mechanism between a dental implant and its matching abutment. On occasion, it may be necessary to remove the abutment for maintenance purposes. The removal of an indexed implant with a TIF-type connection requires the application of a (removal) force to overcome the friction force due to preload. The purpose of this study was to measure the removal force needed to extract the abutment from the implant in TIF-type connections. A workbench was designed and built to measure the forces involved in the abutment removal process. Experiments were conducted to test the removal force (F(R)) for 20 conical interfaces specifically built for the study. The effects of the preload magnitude (F(P)) and the difference between the taper angles of the implant and the abutment (taper mismatch) were investigated experimentally and theoretically. A 2-way factorial ANOVA and regression analysis was used to evaluate the variability in the process and the influence of the 2 variables considered in the experiments (α=.05). Experiments revealed that the (F(R)-F(P)) ratio decreases with the preload F(P), whereas the influence of the taper mismatch cannot be clearly stated. The removal force increases with increasing preload and the F(R)-F(P) ratio varies widely. This variability is attributed to the variability of the friction coefficient, and it can influence implant-removal applications because the removal force can be, in some restorations, as large as 40% of the preload.