Effect of loading frequency on cyclic fatigue lifetime of a standard-diameter implant with an internal abutment connection

Objective To investigate the effect of loading frequency on the fatigue lifetime of one standard-diameter titanium dental implant system. Methods Thirty-six titanium dental implant specimens (Bone Level RC, Straumann) were assembled following manufacturer's instructions and torqued into cylindrical holder blocks following the apparatus specified by the ISO 14801 test standard. Stainless steel loading hemispheres were bonded on the abutments with a moment arm of 11mm. The holder blocks had layers of differing stiffness to simulate human jaw bone. Constant-stress fatigue lifetime testing was conducted at two frequencies (2Hz and 15Hz) with a stress ratio of 0.1 until fracture in deionized water at 37°C on servo-hydraulic load frames (MTS). The fractured specimens were retrieved and examined using fractographic technique to determine the failure mode. The lifetime data were fit to a general log-linear regression model. Results The coefficient for the load amplitude term of the regression model indicated that increasing load amplitude had a statistically significant negative effect on the fatigue lifetime. The coefficients for the cyclic frequency term and the load-frequency interaction term were not significantly different from zero, which indicated that increasing loading frequency did not have an influence on the number of cycles to failure. Fractographic analysis showed that all specimens exhibited an identical combined fracture of abutment and abutment screw adjacent to the bone level. Significance Higher loading frequency at least up to 15Hz may be used for future studies of some implant systems to improve the efficiency of fatigue testing.