Load Fatigue Performance of Conical Implant-Abutment Connections

Conical-abutment connections for platform-switching have been recently introduced in implant systems. Objectives: Load-fatigue performance of 3 conical-abutment systems and their corresponding abutments were investigated. Methods: Regular diameter implants of Dentsply/Friadent Ankylos(AK), Keystone Dental Primaconnex(PC) and Straumann(ST) Bone-Level systems were tested with their corresponding titanium(Ti) and zirconia(Zr) abutments at manufacturers' recommended torque. n=5 for each test-group. A rotational load-fatigue machine applied sinusoidally varying tensile-compressive 21N load to specimens at a 45⁰ angle, producing an effective bending moment of 35Ncm at 14Hz frequency. The number of cycles to failure was recorded with upper limit set at 5x10⁶ cycles. Results: The AK Ti group had 4 abutment fractures(80%) at a level 0.5mm below the platform with concurrent screw fracture(CSF). AK Zr group had 5 abutment fractures(100%) 0.5mm below the platform level with CSF. PC Ti group had 4 samples with screw fracture and 1 sample with implant neck fracture and CSF. PC Zr group had 5 abutment fractures(100%) just below the screw-head seat. ST Ti group had 5 abutment fractures(100%) just above the internal screw thread. ST Zr group had no failures in 4 out of 5 samples and 1 failure(20%) just below the screw-head. 2-Way ANOVA revealed significant differences between systems. Post-hoc tests showed that ST group was significantly different from the AK or PC groups. Subsequent 1-way ANOVA for Ti abutments showed that there was no difference between systems. 1-way ANOVA for Zr abutments showed that the ST group was significantly different from the AK and PC groups. Conclusions: Ti conical-abutments appear to have poorer load-fatigue performance compared with earlier studies of external-hexagon connections. Zr conical-abutments load-fatigue performance varied and seemed to be system dependant. Many of the conical-abutments in both the Ti and Zr groups fractured within the implant and removal was difficult.