Issue 18

F. Felli et alii, Frattura ed Integrità Strutturale, 18 (2011) 14-22; DOI: 10.3221/IGF-ESIS.18.02 16 work the authors tried to replicate this loading condition to verify possible behaviour similarities between the retrieved implants and the laboratory tested samples. After the experiments performed with the bore cylinder type, which demonstrated a similarity of failure mode between retrieved and tested implants, another kind of dental prosthetic implant has been tested. For these implants, more recent than the previous ones, there was no availability of implants broken "in situ". Thus, a finite element analysis was required to assess the most stressed area of the implant under mastication-like loading scheme. After fatigue testing, aim of this work was to verify whether fatigue failures occurred in the regions suggested by FEA. Further studies on these implants concerned other aspects, involved in the component failure, such as loosening of screws and flexural deformation. This paper, for the first implant, aims at comparing service failure and simulated failure behaviour to build up a valid testing method and to estimate the fatigue limit under which the implant could resist indefinitely. As far as the second implant is concerned the aim of the work is to provide information on its fatigue behaviour in order to provide a possible fatigue limit under loading conditions similar to those involved in the actual mastication. M ATERIALS AND METHODS Implants he tested implants belong to two different types: - Titanium (grade 2, according to the ASTM F-67 standards) hollow cylinder with holes on the side surface to promote osseointegration with the bone tissue (Bonefit hollow cylinder, ITI). - Screw implant (Branemark system, Nobelbiocare) with threaded fixture in titanium (grade 2) with chemically etched and anodic passivated surface; titanium abutment and connecting screw, Cr-Co alloy dental capsule with hemispherical profile, coated with dental ceramic. In Figs. 1 and 2 the two types of implants and their dimensions expressed in millimeters are reported. Figure 1 : Hollow cylinder type implant. Figure 2 : Screw type implant. Mechanical stress Implants are tested under fatigue loading in different ways. The first implant (hollow cylinder) is subjected to tensile stress while the second one (screw type) is dynamically loaded with a complex stress system of compression-bending-torsion loads similar to the one that takes place in the actual mastication action. T