Mechanical response of bone under short-term loading of a dental implant with an internal layer simulating the nonlinear behaviour of the periodontal ligament.

We consider a non-standard design for a fixed dental implant, incorporating a soft layer which simulates the presence of the periodontal ligament (PDL). Instead of being aimed at causing an a priori defined stress/strain field within the surrounding bone, upon loading, such a design simply tries to better reproduce the natural tooth-PDL configuration. To do this, the mechanical properties of the internal layer match those of the PDL, determined experimentally to be strongly nonlinear. Three-dimensional finite element analyses show that the presence of such a layer produces (i) a prosthesis mobility very similar to that of a healthy tooth, for several loading conditions, and (ii) a stress/strain distribution substantially different from that arising, upon loading, around a conventional implant. The lack of knowledge of the real mechanical fields existing, under loading, in the bone around a healthy tooth makes it very difficult to state that the stress distribution produced by the modified implant is "better" than that produced by the standard one. Nevertheless, the comparison of the results obtained here, with those of previous refined analyses of the tooth-PDL-bone system, indicates that the modified implant tends to produce a stress distribution in the bone, upon loading, closer to "natural" than that given by the standard one, within the limits imposed by the presence of threads coupling the implant with the bone.