Maxillary All-on-Four™: FEM Analysis of Load Distribution According to Prosthesis Stiffness UNIVERSITY OF TURIN ITALY SAMIR S1, CACCIABUE PG2*, MENICUCCI G2, MANZELLA C2, BIGNARDI C1, CAROSSA S2 . 1Department of Mechanical and Aerospace Engineering, Politecnico di Torino eng.shadysamir@hotmail.com 2Department of Surgical Science, Prosthodontic Section - C.I.R. - Dental School, University of Turin paolacacciabue@gmail.com Objectives: The purpose of this study was to analyse, by a Finite Element Method (FEM), the load distribution to the prosthesis, implants, sponge and cortical bone, in an immediately loaded maxillary fixed bridge on four implants, when three different thicknesses of the resin bridge incorporate a 2mm thick titanium framework.(Fig.1) Material and Method: A FEM was created using different softwares ( Mimics, Rhinoceros, Abaqus) (Fig.2) in order to get a 3D model analysed by FEM from a patient’s CBCT. Three different thicknesses of the resin prosthesis were investigated (3.6 mm, 4.8 mm, 6 mm) each one with and without a titanium framework reinforcement.(Fig.3) Different static loads simulating normal and para-function were applied over different area (​​ 36mm2 )of the bridge: 200N and 500N on the distal cantilever 200 N on the anterior area, between the two central implants.(Fig.4) The stress induced inside the prosthesis, the implants, and the peri-implant sponge and cortical bone, was investigated. Fig.1 A) cortical bone B) sponge bone C) implant D) prosthesis E) metal framework Fig.2 FEM contours Results: The insertion of a titanium framework inside the prosthesis (Fig.5): a) reduces the stress peak in the prosthesis itself and in the cortical and sponge bone. Also the resin thickness contributes, at a lower extent, to reduce the stress transmitted to the prosthesis and the peri-implant bone. b) increases, on the contrary, the maximum stress inside the implants and in particular (+ 50%) when the resin is thinner. This mechanical behaviour keeps the same trend under every loading condition.   The stress value ​upon the resin, particularly when it is thin and without the metallic framework reinforcement, is very close to the resin fracture load. The maximum stress reached inside the implants, with the metallic framework reinforcement, is very far from the implant fracture load. Fig.3 prosthesis thickness with and without framework Fig.4 Static load Fig.5 Results Conclusions: When loading a fixed bridge on four implants, especially under immediate loading condition, the insertion of a titanium framework in the prosthesis improves the load distribution and reduces the maximum stress transmitted to the bone and the prosthesis itself. These data confirm that immediate splinting of the implants by means of a metallic-reinforced fixed provisional prosthesis might protect the bone-implant interface from adverse loading and improve healing condition. However, it must be considered that stiffening of the prosthesis always increases the stress concentration inside the implants.