Effects of torque cycles on implant prosthetic screws, a comparative study between hexagonal and square screws

During the rehabilitation procedures with implant supported prosthesis, the prosthesis are installed and removed a few times until the end of the treatment. Thus, the objective of this study was to evaluate the deformations of the square and hexagonal screw fitting, facing the torque cycles. 42 screws (21 hexagonals and 21 squares) were analyzed for external hexagonal implants (4.1 mm of platform), subdivided into 4 groups (n=5), according to the number of torque cycles: GI = 5 cycles; GII = 10 cycles; GIII = 20 cycles; GIV=30 cycles. Then, the screws were photographed (under optical microscope for 5 times) to assess the affected areas using the Image J Software. In addition, images were performed using the Scanning Electron Microscopy (470x). The data were analyzed in the non-parametric statistical analysis, using the Wicolson-Mann-Whitney test, with a significance level of 5%. It was observed that the most common damages were caused by the plastic transformation of the material in the contact region. The square screws showed greater wear in their fitting, compared to the hexagonal screws in all groups. Based on these results, it is recommended for square screws the maximum of 5 cycles and the hexagons, it can reach up to 10 cycles.