Editorial Type:
Article Category: Research Article
 | 
Online Publication Date: 14 Sept 2023

Survival of Four Conical Implant Abutment Connections After Removal of the Abutment Screw and Simulated Cyclic Loading: An In Vitro Comparative Study

PhD,
PhD,
MS,
PhD,
PhD, and
DrMedDent
Page Range: 393 – 400
DOI: 10.1563/aaid-joi-D-22-00037
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This in vitro study evaluated the mechanical behavior of different conical connection implant systems after abutment screw withdrawal. Four conical connection systems were selected based on different conical half-angles: Ankylos (5.7°), Cowell (7.0°), Straumann (7.5°), and Astra (11.0°). In each system, 5 implants and abutments were used (n = 5). According to the recommended value, each abutment screw was torqued to settle the abutment and then withdrawn through a predesigned hole of the cemented crown. The retentiveness of the abutment was evaluated by the following mechanical testing. All specimens were subjected to cyclic loading of 20–200 N, 30°, and 4-mm off-axis to the implant axis, for 106 cycles. The pullout forces and axial displacements of the abutments were measured. The data of the Cowell system was obtained from our previous work. All groups other than Astra group, in which abutment loosened after abutment screw withdrawal, passed the cyclic loading test. Straumann group demonstrated a significantly lower pullout force (27.4 ± 21.1 N) than Ankylos (160.1 ± 41.4 N) and Cowell (183.7 ± 30.5 N) groups. All groups showed abutment rebound after screw withdrawal except Straumann group. In addition, Ankylos, Cowell, and Straumann groups demonstrated axial displacement after cyclic loading. In terms of the retentiveness of the abutment after abutment screw withdrawal examined in this study, Ankylos and Cowell groups had much higher retentiveness than Straumann group, while Astra group had none. Conical angle could be a key design parameter to make abutment screw withdrawal after conical abutment settlement feasible, but more studies must be conducted for clinical application.

Figure 1.
Figure 1.

Assembly of the test specimen, setup of the cyclic test, and setup of the pullout test. (a) The test specimen comprising a crown, an implant–abutment complex, and a stainless steel form was subjected to cyclic loading of 20–200 N at 30° to the long axis and 4.0 mm off-axis to the center of the implant–abutment complex. (b) The test specimen assembly was aligned along the long axis of the specimen with the indenter of the crosshead at 30° through the fixation of the custom-made holder. (c) The test specimen assembly was fixed to another custom-made holder after the cyclic test. The holder was designed as 2 separate parts with the upper component fixing the neck of the abutment and the lower component fixing the stainless steel form of the test specimen. The force required to disengage the abutment was measured.


Figure 2.
Figure 2.

Schematic of axial displacement measurement in three stages. (a) Differences in the total length of the implant–abutment complex were calculated as axial displacement in stage 1 (screwing for abutment settlement) and stage 2 (abutment screw withdrawal). (b) The difference in the total length of the test specimen was calculated as axial displacement in stage 3 (cyclic loading).


Figure 3.
Figure 3.

Study design.


Contributor Notes

Corresponding author, e-mail: mlhsu@nycu.edu.tw
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