Abstract
Purpose The aim was to evaluate the effect of different metallic alloys used in the manufacture of retention screws for universal cast to long abutment (UCLA) abutments for external hexagon (HE) and Morse taper (MT) connection implants, as well as of mechanical cycling on torque maintenance and fracture resistance through electromechanical fatigue testing by mastication followed by compression testing. Methods Sixty implants were used, 30 MT and 30 HE, with their respective titanium UCLA abutments and retention screws of 5 different materials (n = 6): Ti cp grade 2, Ti cp grade 4, Ti cp grade 4 hard, Ti grade 5—Ti6Al4V and surgical steel (DSP® Biomedical). The assemblies were positioned in an electromechanical masticatory fatigue testing machine. The fracture strength test was performed by compression testing in a universal testing machine EMICDL-200. Results The cycled screws and new screws of each alloy group for each connection type were evaluated, obtaining the maximum force (FM), in order to verify the effect of mechanical cycling. The data were tabulated and submitted to appropriate statistical analysis (α = 0.05). Conclusion It was concluded that for the MT, the alloy with the best performance was steel, both in the maintenance of torque and in the compression test, and cycling negatively influenced the maintenance of preload for this connection. The alloy material did not influence torque maintenance for HE. The new screws that were subjected to EMIC showed higher strength. The alloy with the lowest strength was Ti grade 2.
Highlights
Despite being a consolidated technique [1], implant-supported prostheses are still susceptible to biomechanical failures and complications [2, 3], those that interfere with the stability of the interface region between the implant, abutment, cylinder, and retention screw
Objectives and Hypothesis is research evaluated the effect of 5 different types of metals used in the manufacture of retention screws (Ti cp grade 2, Ti cp grade 4, Ti cp grade 4 hard, Ti grade 5—Ti6Al4V, and surgical steel) of universal cast to long abutment (UCLA) abutments for external hexagon and Morse taper implants on torque maintenance, before and after electromechanical fatigue testing by mastication, as well as their fracture resistance by compression testing. e null hypothesis of this study was that the different materials analyzed, the mechanical cycling, and the type of connection would not influence the torque maintenance and the fracture resistance of the retention screws in the different connections
The implants received the UCLA metal prosthetic abutments, and the retention screw referring to each group and over them a hemispherical device, on which loading was given, ensure the application of the load in the longitudinal axis, according to the Technical Standard ISO 14801 of 2016
Summary
Despite being a consolidated technique [1], implant-supported prostheses are still susceptible to biomechanical failures and complications [2, 3], those that interfere with the stability of the interface region between the implant, abutment, cylinder, and retention screw. E connection between the prosthetic pillar and the implant by means of a retention screw is called screwed connection, and the tightening force exerted on the screw is called torque [6, 7]. Once applied, it develops a compressive force between the parts that holds the components together, called preload [7]. There is an incidence of loads on the prosthetic structure, and these external forces, when higher than the preload value, can lead to loosening or even fracture of the screw [8, 9]. The most significant factor that gives the screw good qualities is its composition, since the frictional resistance between the implant internal threads and the screw threads, composed of two different metals, can limit the preload leading to fracture [12]
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