The resonance frequencies and mode shapes of dental implants: Rigid body behaviour versus bending behaviour. A numerical approach.

The purpose of this study was to evaluate the modal behaviour of the bone-implant-transducer (Osstell) system by means of finite element analyses. The influence of different parameters was determined: (1) the type of implant anchorage being trabecular, cortical, uni-cortical, or bi-cortical, (2) the implant diameter, (3) the length of the implant embedded in the bone, and (4) the bone stiffness. The type of anchorage determines the resulting modal behaviour of the implant-transducer system. A rigid body behaviour was found for a uni-cortical anchoring and for a homogeneous anchoring with low bone stiffness (< or =1000 MPa), whereas a bending behaviour was found for a homogeneous anchoring with a high bone stiffness (> or =5000 MPa) and for a bi-cortical anchorage. The implant dimensions influence the values for the resonance frequencies. Generally, an increase in implant diameter or implant length (in bone) results in higher resonance frequencies. This study also showed that resonance frequencies in case of rigid body behaviour of the implant-transducer system are more sensitive to changes in bone stiffness than resonance frequencies in case of bending behaviour. In conclusion, it seems that the Osstell transducer is suited for the follow-up in time of the stability of an implant, but not for the quantitative comparison of the stability of implants.