Abstract
The aim of this study was to evaluate the failure probability of two types of abutment screws after compressive load and to analyze the stress distribution with finite element method. Sixty (60) single-tooth implant restorations were assembled on titanium implants (e-fix, A.S. Technology - Titanium Fix). The groups were divided into Conventional screw (Screw neck 1.5 ø mm) and Experimental screw (Screw neck constricted with 1.2 ø mm). Specimens were subjected to single load to failure with compressive test according ISO 14801. The fractured specimens were subjected to stereomicroscopy for measurement of remaining screws inside the implant and characterization of fracture origin. Representative specimens were analyzed by scanning electronic microscopy. For finite element method (FEM), an identical 3D model of the two in vitro test groups were used with similar conditions (30º, 100 N load). The stress in the abutment screw was analyzed by von-Mises criteria. The results of strength means were 4132.5 ± 76 MPa and 4528.2 ± 127.2 for conventional and experimental groups, respectively. During microscopy, the mean (mm) of the remaining screw piece inside the implants were 0.97 ± 0.23 and 1.32 ± 0.12 for conventional and experimental groups, respectively. In FEM, the conventional group showed stress concentered in an unfavorable region (peak of 39.23 MPa), while the experimental group showed more stress areas but less concentration than the conventional group (36.6 MPa). In using the tested experimental geometry, the abutment screw can have its strength improved, and the origin of failure can be more favorable to clinical resolution.
Highlights
The region most susceptible to fracture in an abutment screw is located at the junction between the threads and the neck [1]
The geometry is abruptly altered in this region, and small equiaxial depressions visible by electron microscopy are formed during fracture of the material [1]
The present study evaluated an experimental geometry for abutment screws (Figs. 1 and 2), performing the failure probability, stress distribution and fracture origin characterizations
Summary
The region most susceptible to fracture in an abutment screw is located at the junction between the threads and the neck [1]. The geometry is abruptly altered in this region, and small equiaxial depressions visible by electron microscopy are formed during fracture of the material [1]. Another concern for the clinician is regarding maintenance of the torque during installation of the prosthetic components; since the screws of the abutment may be subject to loosen under fatigue [2]. This can be minimized, for example, by using thicker screws with an apical indexer [2]. The strength is directly connected to stress dissipated onto the body of the screw during masticatory load, and through finite element analysis method it is possible to observe that larger screws are less susceptible to reach critical fracture when compared with smaller diameter screws [4]
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