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

Abstract

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.

Keywords: FEA; conical angle; dental implants; dentistry; dynamic load; implantology; implant–abutment connection; screw loosening; static load; titanium implant.

Figure 1

Fatigue machine used during the experiments and the setup of the static load test. The loading head was perpendicular to the top surface of the implant head.

Figure 2

The schematic model of the 90° implant with dimensions (in mm).

Figure 3

Different meshing options (A: coarse; B: normal; C: finer) and the resulting stress distribution figures.

Figure 4

The line defined on the conical interface in the case of a 90° connection to assess mechanical stress.

Figure 5

The line defined on the implant side in the case of a 90° connection to assess mechanical stress.

Figure 6

Results of the static load tests. Representative load-compression graphs showed differences among different conical angle implants.

Figure 7

Compression rate (mean ± SEM) among different conical angle implants in the static load tests.

Figure 8

Irreversible vertical compression rate (mean ± SEM) among different conical angle implants and abutment connections.

Figure 9

Resilience and energy dissipation (mean ± SEM) among different conical angle implants and abutment connections.

Figure 10

The mean measurements for dynamic compression force among different conical angle implants for all 15,000 cycles.

Figure 11

Total vertical compression (mean ± SEM) among different conical angle implants at the 15,000th cycle.

Figure 12

The irreversible (permanent) deformation (mean ± SEM) among different conical angle implants in the implant–abutment system after the dynamic test.

Figure 13

Reverse torque (mean ± SEM) needed to roll apart the implant head and implant after the fatigue test among different conical angle implants.

Figure 14

(a–h). Finite element analyses of the mechanical stresses in case of compression at 24° (a–d) and 90° (e–h) conical angle implant and abutment model geometries.

Figure 14

(a–h). Finite element analyses of the mechanical stresses in case of compression at 24° (a–d) and 90° (e–h) conical angle implant and abutment model geometries.

Figure 15

The mechanical stress distribution along the selected line on the abutment and implant connection in the case of 24° (orange) and 90° (blue) conical angles.

Figure 16

The mechanical stress distribution along the implant height on the side in case of 24° (orange) and 90° (blue) conical angles.