Issue 18

F. Felli et alii, Frattura ed Integrità Strutturale, 18 (2011) 14-22; DOI: 10.3221/IGF-ESIS.18.02 21 our tests). The failure of the screw causes the implant fixture to be subsequently broken due to the reduction of the resisting cross section. The SEM image (Fig. 13) shows the crack initiation site, the propagation area and the final rupture region. Figure 12 : Wohler diagram for screw type implant. Figure 13 : Wide angle SEM image of the fracture surface of the screw implant. C ONCLUSIONS wo dental implants are tested against fatigue by using different loading schemes. For the first implant (hollow cylinder with bored side surface) is selected a tensile cyclic stressing so that it is possible to simulate the tension stress, which actually occurs during mastication motion in a portion of the implant. The second implant is fatigue tested using a mixed loading scheme comprising all the mechanical stresses that can act on an implant during its service life. This composite load is constituted by compression/tension, bending, and torsion components. The performed tests are summarized in the Wohler-type diagrams that exhibit the static resistance, which can be assumed as the strength of the whole implant, and a fatigue limit, that is the load below which the implant could resist indefinitely or the limit load at which no damage can start. Moreover, the analysis on the hollow cylinder implant has provided other results: - the difference in air and saline solution tests is small. This can confirm the effectiveness of the titanium for the production of such implants. T