Shakedown, self-stresses, and unilateral contact in a dental implant problem

Some issues related to the low-cycle fatigue failure of dental implants, subjected to cyclic axial and transverse loads, are studied by means of Finite Element shakedown analyses. The unilateral contact conditions existing at the interfaces between the various parts of the implant, which depend on the degree of tightening of the internal screw connecting the abutment to the fixture of the implant, make it impossible to apply in a straightforward way the classical shakedown theorems. We illustrate a way of reasoning which allows the combination of shakedown analyses results with considerations about the contact conditions. Shakedown envelopes associated to several values of the internal screw tightening can be constructed; these suggest that a common implant design is not fully safe against cyclic loading conditions.