THEORETICAL-STUDY OF THE EFFECTS OF TOOTH AND IMPLANT MOBILITY DIFFERENCES ON OCCLUSAL FORCE TRANSMISSION IN TOOTH IMPLANT-SUPPORTED PARTIAL PROSTHESES/

Statement of problem. Despite their mobility differences under occlusa l loads, a natural tooth and an implant are often used together to sup port fixed prostheses. In some situations, tooth/implant-supported par tial prostheses include cantilever extensions, especially in the poste rior region where the bone is inadequate for placement of an additiona l implant. Purpose. In this study, engineering beam theory was used to study the effects of the mobility differences between the implant and the tooth on the force and moment distribution, due to occlusal loads in tooth/implant-supported prostheses. Methods. The prosthesis was tr eated as a linear elastic beam and the supports were modeled as spring s with (vertical) translational and rotational stiffness. The bending moments and forces on the supports were calculated as functions of the : parameters that describe the geometry, position of the occlusal load , and stiffness ratios (namely, implant or tooth) of the springs. Resu lts. Bending moments on the supports were more sensitive to the relati ve rotational mobility between the supports and their individual value s than to the relative translational mobility. The moment at the impla nt was minimized when the supports had similar mobilities. A prelimina ry design concept was introduced and eliminated the moment at the impl ant without significantly increasing the magnitude of the moment at th e tooth. Cantilevering the prosthesis resulted in moderately increased bending moments and considerable tensile forces on the supports for a broad range of the parameters that describe the geometry and loading. Conclusions. From this simulation, it is suggest that cantilever exte nsions should be avoided or supported by a short implant, which will o nly restrain the vertical movement of the cantilever end.