Comparison between all-on-four and all-on-six treatment concepts and framework material on stress distribution in atrophic maxilla: A prototyping guided 3D-FEA study.

We evaluated two treatment concepts for the rehabilitation of moderate atrophic maxilla with dental implants (all-on-four and all-on-six) and the effect of framework material on the stress distribution of implant-support system. A three-dimensional finite element model based on a prototype was built to simulate an entirely edentulous maxilla with moderate sinus pneumatization that was rehabilitated with a full-arch fixed dental prosthesis. Four standard implants were positioned according to the all-on-four concept and four standard implants and two short implants were placed according to the all-on-six concept. Three framework materials were evaluated: cobalt-chrome (CoCr), titanium (Ti) and zirconia (Zr), totalizing six groups. A unilateral oblique force of 150N was applied to the posterior teeth. The von Mises (sigmaVM), maximum (sigmamax) and minimum (sigmamin) principal stress and displacements were obtained. All-on-six showed smaller sigmamin, sigmaVM and sigmamax values on the cortical bone, implants and trabecular bone, respectively. All-on-four exhibited higher displacement levels. Ti presented the highest stress values on the cortical bone, implants, abutments, prosthetic screws and displacement levels. In conclusion, the all-on-six approach and framework stiffer materials showed the most favorable biomechanical behavior. However, the stress values did not exceed the bone resistance limits for both treatment concepts.