Fatigue lifetime of reduced-diameter implants placed in different bone models

Objectives: This study assessed the fatigue lifetime of reduced-diameter implants placed in either bovine rib or polymer-based bone model. Methods: Bovine ribs were classified according to the criteria proposed by Lekholm and Zarb and were analyzed for bone fraction. Fourteen dental implants (3.25 mm in diameter x 15 mm in length) were placed in bovine ribs used as a bone model. They were subjected to resonance frequency analysis. Stainless steel loading hemisphere caps were bonded on the abutments position at 30-degree angle and with a moment arm of 11 mm. Accelerated life testing using the step-stress method was conducted at 2 Hz with a stress ratio of 0.1 until fracture on a servohydraulic load frames machine (MTS). Results were compared with those of a previous study wherein implants were placed in a polymer-based bone model. Fatigue lifetime statistics (characteristic lifetime and Weibull modulus) of physical specimens were estimated in a reliability analysis software (ALTA PRO). Fractured specimens were examined under an electron scanning microscope to determine the failure mode. Result: The implants exhibited high stability quotient values (75.07 +/- 3.81). Implants placed in bovine ribs showed better data dispersion and longer fatigue lifetime than those placed in polymer-based bone models, with no significant difference between groups. All fractures occurred in the implant body near the bone level and were indicative of fatigue fractures. Significance: Bovine ribs appear to be a more suitable material for accelerated life testing than the polymer-based material because of better data dispersion.