The influence of the parameters of annular layer which is removed in surgical LASIK and IntraLASIK correction of hyperopia on the changes of the stress-strain state of the cornea is analized. The elastic system cornea-sclera is presented as two conjugate transversely isotropic spherical segments loaded by internal pressure. In order to estimate changes of the intraocular pressure measurements obtained by Goldmann (GAT) and Maklakov (MAT) applanation tonometers after hyperopia surgery, the problem of deformation of the cornea under the load with a flat base is considered. A comparison of the results of two different operations and a comparison of two methods of measuring intraocular pressure for each of these operations is carried out using in all cases the same true intraocular pressure. As a result of the finite element simulation, it was found that reduction in the cornea thickness as a result of annular layer removing during hyperopia surgical correction reduces the flexural rigidity of the cornea and, as a consequence, leads to decrease in the intraocular pressure readings obtained by GAT and MAT. According to calculations, the changes in the intraocular pressure readings depend on the inner and outer diameters of the annular layer, on the depth of the ablation zone, and on the thickness of corneal flap. Nevertheless it was obtained than changes in the intraocular pressure readings obtained by MAT are significantly less than changes obtained by GAT. Numerical calculations have shown the advantage of the IntraLASIK refractive correction of hyperopia compared to the LASIK correction. Because of the fact that during the LASIK surgery the annular layer with smaller inner and outer diameters is ablated and thicker corneal flap is cut, larger deformations and displacements in the thinning region of the cornea, as well as greater decrease of the flexural rigidity of the cornea, have been observed.

Key words: intraocular pressure, hyperopia, applanation tonometry, LASIK surgery, IntraLASIK surgery.

This paper presents a 3D method of quantifying and analyzing the muscle forces and joint forces exerted on the mandible under loadings. The experimental protocol, the hypotheses, the writing and then the resolution of the equations system that is related to the static equilibrium of the mandible, are described and applied using data from four volunteers. A sensor was designed to simulate and register the bite force between two teeth, and was applied successively between two incisors, two premolars, and then two molars. Dissections were carried out to determine the contacts between the mandible condyles and the temporal bone and also the insertions of the jaw-closing muscles. The directions of the muscular forces were thus determined in a morphological coordinate system. Magnetoresonance imaging and electromyography data were used in vivo to evaluate the magnitudes of six muscle forces on each side of the face. The resolution of the equation system written to calculate the forces transmitted through the articular contacts was computer-assisted. For an identical loading applied successively to positions 31, 34 and 36, on the basis of twelve recordings, the results show that the sagittal components of the articular forces are strongly influenced by interdental distance. In position 31, the vertical component is thus multiplied by 1.65 while the interincisor distance increases from 5 to 15 millimeters. The magnitudes of the articular forces are strongly influenced by modifications of the mouth aperture and by the directions of the resulting muscular forces.

Key words: biomechanical characterization, muscle forces, joint forces, mechanical modelling, temporomandibular joint implant.

The paper deals with the problem of organization of walk of the active exoskeleton in regular flat mode of walk on a flat horizontal surface. It is assumed that the exoskeleton is equipped with two engines in the knee joints, and is controlled by human interaction by means of viscoelastic straps connecting of it to the machine at certain points of the body. Two types of control motors ideal torque and hydraulic motors are considered. The apparatus has sensors of interlink angles and angular velocities. In this paper, a system of dynamic equations is elaborated, describing the motion of exoskeleton in mode of single support foot under the influence of viscoelastic forces due to the straps and control torques. Walking mode is set by a human operator, and is supported through his own muscular efforts. Information about angles is read via sensors installed in the joints. On the basis of the full equations of the dynamics, the control of exoskeleton is designed that provides tracking of the desired motion in the knee joints with the required quality of transients. In the case of ideal simulation engine, it has proved the correctness of these algorithms and high precision of implementation defined gait (including the angular position of the exoskeleton body) and revealed a significant effect of damping coefficients and elastic straps. The study showed the possibility of selection of factors ensuring a comfortable motion for a human operator due to a sharp reduction of vibrations in the system. At the same time, a decrease in person energy, calculated by the criterion of biomechanical functional is observed. The model of the exoskeleton, which takes into account the dynamic properties of hydraulic cylinders and the geometry of their location is described they are also installed in the knee joints. Constructed control allows us to simultaneously realize the desired quality of desired angular movements in the knee joints, and the necessary efforts developed in the hydraulic drive. The simulation showed great influence of the gain of the process to ensure the stability of the computing process.

Key words: exoskeleton, contact points of the body and the machine, tracking the desired torque at the knees.

In this paper, we analyzed the parameters of the original design of non-removable bridge for replacement of the defect in side dentition complicated by secondary horizontal deformations. Traditional constructions of fixed bridges cannot be used at tilting the abutment teeth more than 30° without removing of tooth pulp and grinding of a significant layer of hard dental tissues. Application of the proposed construction of a bridge makes it possible to dissect the abutment teeth with minimal removal of hard tissues and eliminates removing of tooth pulp. Using the bridge for tilted abutment teeth with convergence more than 30° is achieved by connecting the parts of a non-removable bridge by two extra-coronary rail locks in the form of a tube with fastening and also by the occlusal pad at the distal support crown that properly distributes the masticatory loads in the surrounding tissues. The aim of the paper is to calculate the stress fields in the prosthesis at some characteristic masticatory loads and to assess necessary and sufficient strength of the material used for the prosthesis construction. The three-dimensional model was built for non-removable collapsible bridge for replace the missing first molar and second premolar, the static stress fields calculations were performed by the ANSYS software, and also the decrease in maximum stress was shown when using occlusal pad.

Key words: non-removable dental bridge, ANSYS, stress field, oclusal pad.

A mathematical model for analysis of displacements of a tooth root in the linear elastic periodontal membrane was developed in this study. Tooth root was assumed as rigid solid body and its outer surface was modelled as hyperboloid of two sheets. The initial motion was expressed with a combination of translational displacement and rotational angle. The total strain of periodontal tissue normal to the surface of the root was assessed in conjunction with the width of the periodontal ligament in this direction. Analysis of different types of initial tooth movements was made on the basis of determination of displacements along the helix axis and according to the helix equation. Tipping, rotational and translational movements of the tooth root were considered in the analysis. Visualisation of the initial displacement of the root during tipping motion was carried out considering the position of the helix axis and the trajectories of individual points of the root. Description of the rotational motion was performed using the axis of rotation. It was shown that translational displacement of the tooth can be affected by the load acting with an angle to the longitudinal axis of the tooth root. The analysis of the influence of the ellipse eccentricity in the cross-section of the root and a parameter of the root roundness on the value of load required for a given displacement of the tooth, as well as on the position of a root's centre of resistance was carried out. Coordinates of the centre of resistance analysed with the developed mathematical model and those analysed with finite element modelling were compared. The results can be used to predict and visualise the displacements of teeth, as well as assessment of the stress-strain state of periodontal ligament, and finding optimum load for orthodontic tooth movement.

Key words: periodontal ligament, tooth root, elliptical hyperboloid, initial displacements, center of resistance, helix.

The experience considered below gives the basis for laying out a complex of reconstructive surgery principles for elastic structures that have been injured all at once, and reveals the importance of biomechanical tension factor for the operational algorithm and techniques in microsurgery. Here, we present the method of increasing the number of satisfactory results in reconstructive surgery, based on the experience of replanting of large limbs’ segments in 153 patients. The method of mathematical modelling used for surgery led to a change in the sequence of operation steps, caused by the necessity to conduct certain measurements in the process of surgery and their computer processing. The obtained data was used to determine the length of transplant and other structures under reconstructions – nerves, blood vessels, sinew-muscle complex. It follows both from the mathematical formulas and surgical experience, that operations aimed at shortening an extremity should in certain cases include resection of the ends of bones and elastic structures. The success of the performed reconstructive operations was also due to organization and surgical methods: the operation involved two teams of surgeons  in order to minimize the time of reintroduction of the cut-off part into blood circulation system, doing provisional osteosynthesis, to be replaced in the early post-operation period, or in the end of operation, by the final variant of osteosynthesis, usually the apparatus one. Bathing with patient’s blood the cut-off segment during its introduction back  into blood circulation system was used to avoid the “inclusion syndrome”. The early psycho-physiological rehabilitation also produced positive effect. The follow-up was available for 131 patients: 19 results were excellent, 77 – good (the patients resumed their jobs),  35 – unsatisfactory.

Key words: trauma, transplant, blood vessels, nerves, sinews, elastic structures, tension, diastasis.

A comparative analysis of dynamics of the biomechanical properties of the vascular walls, skin and skeletal muscles of the lower extremities at an increase in the longitudinal dimensions of the tibia and femur in the process of natural growth in children and the surgical lengthening by the Ilizarov method 10–30 % of the original length was conducted. By using original methods, these properties of the arteries, skin, and muscles at 450 healthy people between the ages of 7 to 23 years and 197 patients with congenital shortening of the lower extremities were studied. It was shown that in healthy children proportionality between the increase in limb length and an increase in performance of the elastic properties of the walls artery was preserved up to 6 years, the skin – up to 10 years of age and skeletal muscles up to 18 years. Immediately after surgical limb lengthening, indicators of biomechanical properties of the skin and muscles became more of initial values, and muscle strength reduced. In the long-term period after the treatment, biomechanical performance of soft tissues was approaching the level of indicators specific to healthy children of the same age. However, the contractile ability of muscles was recovering relatively slowly and only later after the end of treatment. The pace of recovery depends on the limb lengthening and higher in younger patients.

Key words: tissue biomechanics, muscle transverse hardness, dynamometry, growth in children, lengthening limbs.