Evaluation of Stress and Strain Magnitude in Tapered and Cylindrical Implant Surrounding Bone, Used for Restoration of Mandibular Teeth: Finite Element Analysis in All-on-Four Concept.

The prevalence of the elderly population increased in the 20th century, as described in the World Health Organization 2004 Annual Report. The use of tilted implants parallel to the anterior wall of the maxillary sinus or the mental foramen/inferior alveolar nerve has been proposed for the treatment of the atrophic edentulous ridge. The aim of this study was to evaluate stress and strain magnitude in tapered and cylindrical surrounding bones. A 3D finite element model of an edentulous mandible was constructed. Two models of implants were used: cylindrical and tapered BEGO Semados RI Implants. Four implants were inserted between the bilateral mental foramen according to All-on-Four concept, and a mandibular bar was designed to use with the All-on-Four bar supported models. A vertical and 30 degree vertical load of 100 N was applied to both cylindrical and tapered implants models. Strain and stress were analyzed with ANSYS software (ANSYS R18.0). The maximum stress and strain were applied in all axes for the posterior man-dibular areas in the crestal region of the bone, and for the anterior areas at the intraosseous contact site. Also, the stress and strain of the bone under force in all axes in all areas for tapered implants is less compared to that for cylindrical implants. We found that the highest rate of bone resorption occurs in the posterior areas near the junction of the fixture with the abutment of implant, and in the anterior areas near the end of the fixture of implant. Still, more research on the subject is needed.