Bone Stress Analysis in All-on-Four"" Implantation for Completely Edentulous Mandibles""

The aim of this thesis is to evaluate the von Mises stress in the peri-implant bone of an “All-on-four” implant supported prosthesis through finite element analysis using different types of bone, implant types, posterior implant angle and implant lengths under three kinds of mastication force. 　　“All-on-four” is a kind of implant protocol that inserts four implants between the mental foramina in placing a fixed prosthesis on an edentulous mandible. However, different treatment alternatives with various implant designs and surrounding conditions were performed in an edentulous mandible. Two 3D models of a human edentulous mandible were generated by CT scanner, one representing slight atrophy and the other representing moderate atrophy. Each mandibular bone has two bone types showing different biomechanical features, based on various patients physiological and pathological conditions. Two types of implant: NobelActive and NobelSpeedy with three different lengths (long/medium/short) were used. The two anterior implants were inserted in a parallel manner and the two distal implants were placed axially or tilted 30 degrees in each model. Three loading conditions (55 N / lateral incisor, 65 N / canine and 150 N / left second molar) were considered, and von Mises stress values in the peri-implant bone were determined. 　　Based on information and the stress distribution from finite element analysis of prosthesis supported by four implants, we are able to offer clinical dentists and patients suggestions regarding which kind of implant protocol may be more favorable under differing patients’ conditions, so as to avoid potential bone resorption, which may then facilitate bone deterioration during the treatment.