Dušan Németh

Finite element analysis of stress distributions in mono- and bi-cortical dental implants.

The finite element analysis (FEA) of the stress distribution in the mono- and bicortically fixed implants subjected to 3-axial loading was performed and verified experimentally on a model mandible to evaluate the benefits of each type of fixation from the viewpoint of the compressive stress reduction in the cortical part of atrophied mandible. The analysis revealed that the highest compressive stresses in the cortical bone are generated at the edge of the cortical bone where the highest torque from the implant is acting. The most effective way to reduce the maximum level of compressive stresses in the cortical bone and in the implant is the recession of the implant thread slightly below the surface of the cortical bone. Shortening of the intraosseal length of the implant and/or thinning of the upper cortical bone result in a substantial increase of the maximum compressive stresses. The comparison of FEA and model experiments suggests that bicortical fixation is the most efficient in the fresh implants and the advantage of bicortical fixation compared to monocortical fixation decreases with time due to osteointegration, possibly as a result of gradual suppression of sliding between the bone and implant during loading.

The Effect of the Cortical Bone Thickness on the Stress Distribution in Dental Implants by FEM

The stress distribution in cortical bone and dental implant has been modeled by finite element method (FEM) using linear static analysis in the case of monocortical and bicortical fixation of a real dental implant for three cortical bone thicknesses: 2 mm, 2.5 mm, 4 mm. The analysis revealed that the highest stresses in the cortical bone and in the implant after three-axial loading are localized at the edge of the cortical bone near the implant neck where bending moment is the highest. An increase of the maximum stresses has been observed with the decrease of the intraosseal length of the implant and cortical bone thickness.

Cracking in Brittle Coatings during Nanoindentation

The FIB/SEM investigations of the microstructure changes in the hard brittle W-C based coating deposited on softer steel substrate after nanoindentation tests revealed that a set of approximately equidistant circular cracks forms in the coating in a sink-in zone around the indent and single cracks appear under the indenter tip. Finite element modeling (FEM) indicated development and concentration of the highest principal tensile stresses in the sink-in zone and in the zone below the indenter, which are considered to be the reason for the experimentally observed cracking. The distance from the indenter tip to the first circular crack combined with the calibration curve obtained from the FEM of the location of tensile stress maxima in sink-in zone can be used as a simple method for the determination of the strength of the studied coatings.

Modeling of Stress Distribution in Dental Implant in Frontal Part of Mandible

The aim of this work is the modeling of the stress distribution in cortical and trabecular bone of model frontal part of mandible by FEM analysis using linear static methods applying monocortical and bicortical fixation of dental implant. Depending on the position of the screw thread with regard to the bone surface, three different cases were simulated: exactly on the bone surface, 1,5 mm above and 0,5 mm below the surface of the cortical bone. It was found out that the stress field in the cortical part and the implant are considerably lower in the case of slightly recessed position in contrast with the above and normal position of the implant in both, monocortical and bicortical fixations. However, bicortical fixation in this case generates slightly lower stress field in the bone and implant parts than in monocortical fixation. Monocortical fixation is otherwise slightly more favorable from the viewpoint of maximum stresses in the bone in the case of exact and above positions of the implant.