Survival of Four Conical Implant Abutment Connections After Removal of the Abutment Screw and Simulated Cyclic Loading: An In Vitro Comparative Study.

This in vitro study evaluated the mechanical behavior of different conical connection implant systems after abutment screw withdrawal. Four conical connection systems were selected based on different conical half-angles: Ankylos (5.7°), Cowell (7.0°), Straumann (7.5°), and Astra (11.0°). In each system, 5 implants and abutments were used (n = 5). According to the recommended value, each abutment screw was torqued to settle the abutment and then withdrawn through a predesigned hole of the cemented crown. The retentiveness of the abutment was evaluated by the following mechanical testing. All specimens were subjected to cyclic loading of 20-200 N, 30°, and 4-mm off-axis to the implant axis, for 106 cycles. The pullout forces and axial displacements of the abutments were measured. The data of the Cowell system was obtained from our previous work. All groups other than Astra group, in which abutment loosened after abutment screw withdrawal, passed the cyclic loading test. Straumann group demonstrated a significantly lower pullout force (27.4 ± 21.1 N) than Ankylos (160.1 ± 41.4 N) and Cowell (183.7 ± 30.5 N) groups. All groups showed abutment rebound after screw withdrawal except Straumann group. In addition, Ankylos, Cowell, and Straumann groups demonstrated axial displacement after cyclic loading. In terms of the retentiveness of the abutment after abutment screw withdrawal examined in this study, Ankylos and Cowell groups had much higher retentiveness than Straumann group, while Astra group had none. Conical angle could be a key design parameter to make abutment screw withdrawal after conical abutment settlement feasible, but more studies must be conducted for clinical application.

Different Conical Angle Connection of Implant and Abutment Behavior: A Static and Dynamic Load Test and Finite Element Analysis Study.

Dental implants are artificial dental roots anchoring prosthetic restorations to replace natural teeth. Dental implant systems may have different tapered conical connections. Our research focused on the mechanical examination of implant-superstructure connections. Thirty-five samples with 5 different cone angles (24°, 35°, 55°, 75°, and 90°) were tested for static and dynamic loads, carried out by a mechanical fatigue testing machine. Fixing screws were fixed with a torque of 35 Ncm before measurements. For static loading, samples were loaded with a force of 500 N in 20 s. For dynamic loading, the samples were loaded for 15,000 cycles with a force of 250 ± 150 N. In both cases, the compression resulting from load and reverse torque was examined. At the highest compression load of the static tests, a significant difference (p = 0.021) was found for each cone angle group. Following dynamic loading, significant differences (p < 0.001) for the reverse torques of the fixing screw were also shown. Static and dynamic results showed a similar trend: under the same loading conditions, changing the cone angle-which determines the relationship between the implant and the abutment-had led to significant differences in the loosening of the fixing screw. In conclusion, the greater the angle of the implant-superstructure connection, the smaller the screw loosening due to loading, which may have considerable effects on the long-term, safe operation of the dental prosthesis.

Optimization of the Conical Angle Design in Conical Implant-Abutment Connections: A Pilot Study Based on the Finite Element Method.

Conical implant-abutment connections are popular for their excellent connection stability, which is attributable to frictional resistance in the connection. However, conical angles, the inherent design parameter of conical connections, exert opposing effects on 2 influencing factors of the connection stability: frictional resistance and abutment rigidity. This pilot study employed an optimization approach through the finite element method to obtain an optimal conical angle for the highest connection stability in an Ankylos-based conical connection system. A nonlinear 3-dimensional finite element parametric model was developed according to the geometry of the Ankylos system (conical half angle = 5.7°) by using the ANSYS 11.0 software. Optimization algorithms were conducted to obtain the optimal conical half angle and achieve the minimal value of maximum von Mises stress in the abutment, which represents the highest connection stability. The optimal conical half angle obtained was 10.1°. Compared with the original design (5.7°), the optimal design demonstrated an increased rigidity of abutment (36.4%) and implant (25.5%), a decreased microgap at the implant-abutment interface (62.3%), a decreased contact pressure (37.9%) with a more uniform stress distribution in the connection, and a decreased stress in the cortical bone (4.5%). In conclusion, the methodology of design optimization to determine the optimal conical angle of the Ankylos-based system is feasible. Because of the heterogeneity of different systems, more studies should be conducted to define the optimal conical angle in various conical connection designs.