The aim of this study was to develop a three-dimensional (3D) finite element model (FEM) of the first maxillary premolar in order to compare the stress profiles in the buccal and palatal cervical regions. The 3D geometry of the tooth was reconstructed, the solid model was transferred into a finite element program where a 3D mesh was created, and the stress distribution analysis was performed. Two typical cases have been considered: the tooth under normal occlusion (case I) and the tooth under malocclusion (case II). In case I, larger compressive stresses were found in the cervical enamel and dentine. Tensile stresses were found in the fissure system, adjacent area, and at the vestibular surface of the buccal cusp. The peak values for the principal stress ranged from -259 to +2.25 MPa in the cervical areas. In the case II, larger compressive stresses were found in the palato-cervical enamel and dentine. Tensile stresses were found inside the enamel in the fissure system, adjacent area, at the vestibular surface of the buccal cusp, and in the bucco-cervical enamel. The peak values for the principal stress ranged from -501.947 MPa in palatal region to +82.4 MPa in the buccal region This study implies a role of occlusal forces in development of non-carious lesions. In the case of malocclusion, tensile stresses generated on the cervical areas were higher compared with the stresses generated in the case of normal occlusion and it is probably capable of producing non-carious cervical lesion.

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a b s t r a c tThe subject of this paper is numerical prediction of bird strike induced damage in real aeronautical structures using highly detailed finite element models and modern numerical approaches. Due to the complexity of today's aeronautical structures, numerical damage prediction methods have to be able to take into account various failure and degradation models of different materials. A continuum damage mechanics approach has been employed to simulate failure initiation and damage evolution in unidirectional composite laminates. Hashin's failure initiation criteria have been employed in order to be able to distinct between four ply failure modes. The problem of soft body impacts has been tackled by applying the Coupled Eulerian Lagrangian technique, thereby avoiding numerical difficulties associated with extensive mesh distortion. This improvement in impactor deformation modelling resulted in a more realistic behaviour of bird material during impact. Numerical geometrical and material nonlinear transient dynamic analyses have been performed using Abaqus/Explicit. The main focus of the work presented in this paper is the application of the damage prediction procedure in damage assessment of bird impact on a typical large airliner inboard flap structure. Due to the high cost of gas-gun testing of aircraft components, experimental testing on the real flap structure could not have been performed. In order to evaluate the accuracy of the presented method, the bird and composite damage model have been validated against experimental data available in the literature.

The objective of this research was to develop a technique that would allow three-dimensional imaging of root canals utilizing computer image processing. Ten single-rooted permanent human teeth with mature apices were analysed. The teeth were decoronated and fixed on boards with the long axis of the root perpendicular to the board. The cross-sectioning started at the root apex and continued in the coronal direction, roughly perpendicular to the long axis of the ++root. The samples were divided into two groups. The first five samples were sectioned 15 times, each section being 0.5-mm thick, in order to obtain the three-dimensional reconstruction of the root and the root canal. The root apex of each sample was cross-sectioned 19 times and each section was 0.2-mm thick. After each section, the root canal contour was defined utilizing the calibrated net with coordinate system in the ocular of the stereomicroscope. The coordinates of the root canal cross-section contour thus determined, together with the value of the thickness of each cut, were relevant input data for the reconstruction of the root canal cross-sections, longitudinal sections and for the final three-dimensional rebuild of the root and the root canal model. this technique appears to be highly accurate in determining the anatomy of the root canal system and may also be applied in other fields of dental research.

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