Influence of the Height of the External Hexagon and Surface Treatment on Fatigue Life of Commercially Pure Titanium Dental Implants

Purpose: This study evaluated the effect of external hexagon height and commonly applied surface treatments on the fatigue life of titanium dental implants. Materials and Methods: Electropolished commercially pure titanium dental implants (seven implants per group) with three different external hexagon heights (0.6, 1.2, and 1.8 mm) and implants with the highest external hexagon height (1.8 mm) and different surface treatments (electropolishing, grit blasting with aluminium oxide, and acid etching with sulfuric acid) were tested to evaluate their mechanical fatigue life. To do so, 10-Hz triangular flexural load cycles were applied at 37°C in artificial saliva, and the number of load cycles until implant fracture was determined. Tolerances of the hexagon/abutment fit and implant surface roughness were analyzed by scanning electron microscopy and light interferometry. Transmission electron microscopy and electron diffraction analyses of titanium hydrides were performed. Results: First, the fatigue life of implants with the highest hexagon (8,683 ± 978 load cycles) was more than double that of the implants with the shortest hexagons (3,654 ± 789 load cycles) (P .02). Second, the grit-blasted implants had the longest fatigue life of the tested materials (21,393 ± 2,356 load cycles), which was significantly greater than that of the other surfaces (P .001). The compressive surface residual stresses induced when blasting titanium are responsible for this superior mechanical response. Third, precipitation of titanium hydrides in grain boundaries of titanium caused by hydrogen adsorption from the acid solution deteriorates the fatigue life of acid-etched titanium dental implants. These implants had the shortest fatigue life (P .05). Conclusions: The fatigue life of threaded root-form dental implants varies with the height of the external hexagon and/or the surface treatment of the implant. An external hexagon height of 1.8 mm and/or a blasting treatment appear to significantly increase fatigue life of dental implants. Keywords: acid etching, dental implants, fatigue, grit blasting, mechanical properties, titanium