Foot internal stress distribution during impact in barefoot running as function of the strike pattern.

The aim of the present study is to examine the impact absorption mechanism of the foot for different strike patterns (rearfoot, midfoot and forefoot) using a continuum mechanics approach. A three-dimensional finite element model of the foot was employed to estimate the stress distribution in the foot at the moment of impact during barefoot running. The effects of stress attenuating factors such as the landing angle and the surface stiffness were also analyzed. We characterized rear and forefoot plantar sole behavior in an experimental test, which allowed for refined modeling of plantar pressures for the different strike patterns. Modeling results on the internal stress distributions allow predictions of the susceptibility to injury for particular anatomical structures in the foot.

Non-linear finite element model to assess the effect of tendon forces on the foot-ankle complex.

A three-dimensional foot finite element model with actual geometry and non-linear behavior of tendons is presented. The model is intended for analysis of the lower limb tendon forces effect in the inner foot structure. The geometry of the model was obtained from computational tomographies and magnetic resonance images. Tendon tissue was characterized with the first order Ogden material model based on experimental data from human foot tendons. Kinetic data was employed to set the load conditions. After model validation, a force sensitivity study of the five major foot extrinsic tendons was conducted to evaluate the function of each tendon. A synergic work of the inversion-eversion tendons was predicted. Pulling from a peroneus or tibialis tendon stressed the antagonist tendons while reducing the stress in the agonist. Similar paired action was predicted for the Achilles tendon with the tibialis anterior. This behavior explains the complex control motion performed by the foot. Furthermore, the stress state at the plantar fascia, the talocrural joint cartilage, the plantar soft tissue and the tendons were estimated in the early and late midstance phase of walking. These estimations will help in the understanding of the functional role of the extrinsic muscle-tendon-units in foot pronation-supination.

Stresses and Strains Analysis Using Different Palatal Expander Appliances in Upper Jaw and Midpalatal Suture.

Rapid maxillary expansion (RME) is the technique of increasing the transverse dimension of the upper jaw using lateral forces applied by palatal expander. Usually, this palatal appliance is anchored on posterior teeth. The purposes of this computer simulation study were to analyze the stress and strain distribution generated in the maxilla, mainly in midpalatal suture (MPS), during RME by tooth-borne and bone-borne expanders and to study the correlation between mechanical strain and Wolff's Law. The analysis was performed with finite element models developed based on Cone Beam computed tomography (CT). To simulate the expansion load, displacements were applied concerning one (0.125 mm) and three (0.375 mm) activations in the medial sides of the tooth-borne expander, and one activation (0.125 mm) for miniscrews (MSIs) in transverse and lateral direction. It was observed that to obtain approximately the same spacing in the MPS activating once the expander with bone support, three activations for the tooth-borne were necessary. However, the strain level caused by bone-borne expansion, when applying a single activation, reached 900 and 5000 µÉ›, with peaks up to 20 000 µÉ›, in a region very close to the MSIs. Comparing the results, bone-borne appliance anchorage in the palatine bone is more effective than tooth-borne expander. Nevertheless, the stresses and strains increased significantly in the entire jaw when the bone-borne expander is used.

A method for obtaining a three-dimensional geometric model of dental implants for analysis via the finite element method.

PURPOSE: The aim of the study was to present a methodology of development of a virtual 3-dimensional dental implant model for analyses via the finite element method. MATERIALS AND METHODS: A set, consisting of a dental implant and abutment, was embedded in acrylic resin for subsequent metallographic grinding and polishing. After the evidentiation of the internal geometry of the implant, the specimen was treated in a sputter for observation using scanning electron microscopy (SEM). The SEM image was transported to computer-aided design software by which all details of the implant were measured. With the measures obtained, the geometry was reproduced with 3-dimensional modeling software. Finally, the model was imported into finite element method analysis software with which it was discretized, generating a mesh. RESULTS: A model with the accurate geometry of the implant was developed. A mesh of 297,600 elements and 490,045 nodes was generated. An aleatory acceleration simulation was performed to test the mesh, and no errors were identified. CONCLUSION: The developed methodology generated a precise dental implant model, which can be applied in different finite element method simulations.

Analytical and numerical analysis of human dental occlusal contact.

The knowledge of contact forces in teeth surfaces during mastication or para-functional movements can help to understand processes related to friction and wear of human dental enamel. The development of a numerical model for analysis of the occlusal contact between two antagonistic teeth is proposed, which includes three basic steps: the characterisation of the surface roughness, its homogenisation using an assumed distribution function and the numerical determination of the resulting forces. Finite element strain results for the main different asperities are statistically combined, deriving the predicted macroscopic behaviour of the interface. Axisymmetric and 3D numerical models with an elasto-plastic constitutive law are used to simulate micro-indentations and micro-contacts, respectively. The contact is allowed to occur locally in planes not necessarily parallel to the surface's mean plane, a problem for which there is no analytical solution. The three identified parameters, homogenised surface hardness (3.68 GPa), surface yield stress (3.08 GPa) and static friction coefficient (0.23), agree with the experimental values reported in the literature.