Citation: Bagegni, A.; Weihrauch, V.;
Vach, K.; Kohal, R. The Mechanical
Behavior of a Screwless Morse Taper
Implant–Abutment Connection: An
In Vitro Study. Materials 2022, 15,
3381. https://doi.org/10.3390/
ma15093381
Academic Editor: Eugenio
Velasco-Ortega
Received: 13 February 2022
Accepted: 4 May 2022
Published: 8 May 2022
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Article
The Mechanical Behavior of a Screwless Morse Taper
Implant–Abutment Connection: An In Vitro Study
Aimen Bagegni
1,
*, Vincent Weihrauch
1
, Kirstin Vach
2
and Ralf Kohal
1
1
Medical Center–University of Freiburg, Center for Dental Medicine, Department of Prosthetic Dentistry,
Faculty of Medicine, University of Freiburg, Hugstetter Straße 55, 79106 Freiburg, Germany;
vincent.weihrauch@uniklinik-freiburg.de or vincentweihrauch@googlemail.com (V.W.);
ralf.kohal@uniklinik-freiburg.de (R.K.)
2
Medical Center–University of Freiburg, Institute of Medical Biometry and Statistics, Faculty of Medicine,
University of Freiburg, 79106 Freiburg, Germany; kv@imbi.uni-freiburg.de
* Correspondence: aimen.awad.bagegni@uniklinik-freiburg.de or a.bagegni@gmail.com;
Tel.: +49-761-2704-8470
Abstract:
The use of screwless Morse taper implant–abutment connections (IAC) might facilitate the
clinician’s work by eliminating the mechanical complications associated with the retention screw. The
aim of this study is to evaluate the effect of artificial chewing on the long-term stability of screwless
Morse taper IACs. Thirty-two implant abutments restored with an upper central incisor zirconia
crown were used and divided into four groups according to the implant–abutment assembling manner
(C1,H: screw retained (20 Ncm); C2: tapped; or C3: torqued (20 Ncm; the screws were removed before
the dynamic loading)). All specimens were subjected to a cyclic loading (98 N) for 10 million chewing
cycles. The survived samples were exposed to a pull-off force until failure/disassembling of the
connection. All the samples revealed a 100% survival. Regarding the pull-off test, the screw-retained
internal hexagonal IAC revealed significantly higher resistance to failure/disassembling (769.6 N)
than screwless conical IACs (171.6 N–246 N) (p < 0.0001). The retention forces in the Morse taper
groups were not significantly different (p > 0.05). The screw-retained hexagonal IAC showed the
highest retention stability. The screw preload/retention in the conical IAC was lost over time in the
group where the screws were kept in place during loading. Nevertheless, the screwless Morse taper
IACs were stable for an extended service time and might represent a valid form of treatment for
single-tooth replacement.
Keywords: screwless; implant–abutment connection; conical; Morse taper; pull-off force
1. Introduction
The success of an implant treatment depends on the successful osseo- and soft tissue
integration of the implant and also on the stability of the restoration (i.e., the implant–
abutment–crown complex) [
1
–
6
]. Moreover, implant–abutment connections are considered
a key factor of a successful implant therapy since they directly influence the long-term
stability of the systems [
7
]. They represent the central stress resistance points of oral im-
plants, as they must counteract the maximal and permanent masticatory forces. There are
data that suggest that external implant–abutment connections are combined with higher
rates of technical complications compared with internal connections [
8
–
10
]. However, a
recent systematic review [
8
] reported a technical complication rate of 10.1% for internal
implant–abutment connections and 12.4% for external implant–abutment connections.
These differences between internal and external connections did not reach statistical signifi-
cance (p = 0.431) [8].
Abutments serve as a link, connecting the oral implant and the prosthetic super-
structure, and they are usually screw-retained to the implant. They can be customized or
Materials 2022, 15, 3381. https://doi.org/10.3390/ma15093381 https://www.mdpi.com/journal/materials
