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The aim of this study was to evaluate the biomechanical behavior, by means FEA, of maxillary central incisor with weakened roots restored with different posts, crowns and ferrule presence. A digital image of an intact maxillary central incisor section plane around the alveolar bone was obtained in order to build the model of sound tooth. A sound tooth and eight two-dimensional numerical models were generated from the protocol of image processing. The studied factors were: crown type - metal-ceramic crown (MC) and alumina-reinforced ceramic (CC); post type - glass fiber post (GFP) and cast post and core (CPC); and ferrule - absence of ferrule (AFE) and 2,0 mm ferrule (FE2). A 2N static and oblique load with a 135° inclination to the tooth longitudinal axis was applied at the level of palatal surface of the crown. The displacement was restricted and stress of tensile and compression within the tooth structure was recorded. Cast post and core models concentrated stresses in post dentin interface and glass fiber post models had homogeneous stresses distribution within the root dentin similar to sound tooth. The restorative complex GFP-CC concentrated higher stress in coping than GFP-MC, both models with or without ferrule. The ferrule presence improved the stress distribution regardless of the crown and post types. Therefore, cast post-and-cores concentrate too much stresses within a root dentin and post interface; glass fiber post has more homogeneous stress distribution in dentin than cast post-and-cores; the presence of 2 mm ferrule improves the mechanical behavior.

Abstract. In this paper a simulation of movements of lumbar spine is proposed by using a model with serially connected parallel manipulators. An analysis has been computed for the human spine structure and its movements, in order to simulate the motions and forces that actuate a spine specifically in the lumbar segment. A mechanical model has been designed with available identified parameters of human spine, by using characteristics of parallel manipulators and spring stiffness. This model is suitable to properly simulate the trunk behavior at macroscopic level but also the smooth behavior of intervertebral discs and actuating motions of muscles and tendons. Simulation results for spring actions and joints reaction forces can give an evaluation of the forces that intervertebral discs supports during motions of a real spine.