Failure Probability, Stress Distribution and Fracture Analysis of Experimental Screw for Micro Conical Abutment

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.

Influence of Implant-Abutment Contact Surfaces and Prosthetic Screw Tightening on the Stress Concentration, Fatigue Life and Microgap Formation: A Finite Element Analysis

“…When comparing the mechanical responses of the models, it was possible to observe that the external hexagon platform showed a higher stress concentration, when the axial walls were in contact with the abutment. This validates, as reported in previous studies, that this region has the areas of plastic deformation when an excessive load was applied in this implant system [10,35]. Therefore, more contact between the implant and the abutment, with a higher number of surfaces contacting each other, will increase the stress in this region.…”

Survival Analysis and Torque Loosening of Experimental Screw After Mechanical Performance for Micro Conical Abutment

“…According to previous studies (Peixoto & Almas, 2016;Melo-Filho et al), the screw stress peaks were concentrated in the first threads of the prosthetic screw, due to the high flexural movement of the screw when subjected to preload or during mastication. This shows that the correct screw geometry and the combination of materials can be important for the stress distribution in the screw Melo-Filho et al).…”

“…Although the abutment screw fracture is not most recurrent mechanical problem (Eckert & Wollan, 1998), it is important to highlight that when it occurs, there is great difficulty in removal, which can lead to loss of the implant (Satwalekar et al, 2013;Schmage et al, 2014;Shah & Lee, 2016). The ideal geometry of the screw should provide a favorable design for the removal of the broken parts (Melo-Filho et al, 2019). In this way, the ideal geometry of the abutment screw containing a thinner portion in the screw's neck, can direct the fracture to a more external region, easier to remove (Siamos et al, 2002;Melo-Filho et al).…”

“…The ideal geometry of the screw should provide a favorable design for the removal of the broken parts (Melo-Filho et al, 2019). In this way, the ideal geometry of the abutment screw containing a thinner portion in the screw's neck, can direct the fracture to a more external region, easier to remove (Siamos et al, 2002;Melo-Filho et al). Research on torque mantainance during fatigue and survival rates are needed whenever the design is modified.…”

Effect of Titanium Hardness on the Integrity and Stress Concentration of External Hexagon Dental Implants

“…The increase in the use of single implants has resulted in several studies, and the most reported biomechanical complications are the precision fit between the implant and abutment (Tribst et al, 2021), deformations of the hexagon surface (Romero et al, 2000;Renner, 2000;Khraisat et al, 2004;Segundo et al, 2007;Melo-Filho et al, 2019;Rodrigues et al, 2020), the rotational freedom between implant fixation and abutment (Bambini et al, 2005), dimensional changes and machining tolerances on prosthetics connections (Schulte, 1994;Malaguti et al, 2011), loosening or fracture of prostheses screws (Chen et al, 2021).…”