Novel Ball Head Screw and Screwdriver Design for Implant-Supported Prostheses With Angled Channels: A Finite Element Analysis
The primary objective of this study was to design the optimal geometry of a novel screwdriver, create the grooves on a ball head screw, and demonstrate its resistance to a torque of up to 40 Ncm at angulations of 0°, 15°, and 30° by using nonlinear finite element analysis. A secondary objective was to create a foolproof, easily recognizable system. The grooved ball head screw and geometry of the screwdriver, functioning from an angulation of 0° to 30°, was generated using Pro-ENGINEER Wildfire 5.0 software. Static structural analyses among bodies in contact were performed at different angles of 0°, 15°, and 30° at a torque of 20 Ncm and 40 Ncm using nonlinear finite element simulation by means of ANSYS 12.0. The maximum stress supported by the ball head screw and screwdriver was similar at 20 Ncm and 40 Ncm. Although greater deformations were found at 40 Ncm, these were small and might not affect the performance of the system. Further, the rupture torque value for the M2 connection was 55 Ncm for 0° and 30°, and 47.5 Ncm for 15°. Numerical simulation showed that the ball head system design can achieve the mechanical strength requirements expected for screws used in implant-supported restorations at an angulation of up to 30°. Finite element analysis showed this novel ball head screw and screwdriver system to be a good solution for angled screw channels in implant-supported prostheses.
Figure 1. Screw and screwdriver design. Left: ball screw head; Right: screwdriver. Figure 2. Optimal geometry of the screw and screwdriver. Left: diagram of force and linear speed. Due to the radial contact surfaces, the transmission angle is 0°. Right: angles influencing angular misalignment.
Generation of the final geometry. Step 1: The screwdriver geometry was generated. Step 2: The generation method was used to create a geometry that includes all the possible positions of the screwdriver around a spherical screw head from 0° to 30°. Step 3: The negative part of the generated groove was cut, obtaining the positive part of the generated groove. Step 4: The geometry obtained in Step 3 was used to make a cut to the sphere to obtain the final screw head geometry. Step 5: The screw head was attached to the body of the screw.
Final geometry of the screw and screwdriver. Left: final geometry of the screw head. Right: final geometry of the screwdriver.
Different meshes for the screw and screwdriver generated for each inclination angle to increase accuracy. Left: sphere used to refine the mesh around the contact point at an inclination angle of 15°. Middle: screw and screwdriver mesh. Right: refinement of the screw mesh at the contact point.
Stress distribution for each inclination. Von Miss equivalent stresses at 0°, 15°, and 30° and at 40 Ncm torque. At 20 Ncm, the stress distribution was similar; however, the absolute stress values were different.
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