Russian Journal of Biomechanics

Finite element modelling is the commonly used methodology for the analysis of stress concentration within tooth components. The main limitation of the technique is oversimplifications are usually required due to the complex conditions at which oral structures operate. Therefore, the aim of this study is to examine how assumptions and modelling practices, related to the internal tooth structure, material properties and loading conditions, affect the mechanical response within dental models. This was achieved by developing a generalised mandibular first molar tooth model and by performing an in-silico parametric study.

In this paper, a mathematical model describing the deviation of the medical steel needle when it moves in the phantom of soft tissues (human tissues). This model will expect for use in the operational mode, where high precision positioning of the tip of the needle is necessary. The needle have asymmetric tip and because when the needle moves, it to deviate from rectilinear motion. Thus, by inserting and rotating the needle around its axis, it is possible to move the tip of the needle along a predetermined path. Consequently, having developed the model with its help, it will be possible to track the movement of the needle in the tissues or to predict optimal puncture points. The general formulation of the problems is considered and one of the sub-tasks is solved, as well as the available calculation of the needle tip deflection during the translational movement in a homogeneous material. The article shows the model used and the simulation results for different material densities and different needle tip angles. Comparison of the experimental data with the results obtained in the calculation using the proposed model is given.

The aim of this work was to study the features of microstructure and mineral saturation in the focus of artificially (in vitro) created demineralized tooth enamel with the use of computer microtomography. The method of microtomography implemented with the help of an X-ray computer installation Nikon Metrology XT H 225, provided the possibility of certification of macro- and microstructure of small samples of human teeth in vitro, without breaking the integrity, special preparation and preliminary destruction of objects, in a relatively short time. A multilevel analysis based on visual-instrumental (ICDAS criteria), stereomicroscopes (Olympus SZX-16; Olympus DP-73; Olympus Stream Motion v.1.8) and microtopographical assessment of teeth with artificially (in vitro) created focal demineralization of enamel using original technique (patent of Russian Federation No. 172561 and No. 171409 from 16.12.2016) allowed to obtain three-dimensional information on the nature of simulated lesions of the enamel, confirmed the high sensitivity and specificity of the experimental model of primary caries. The algorithm of qualitative and quantitative analysis of computer tomograms of teeth includes 3D-reconstruction of the tooth and the focus of demineralized enamel with the assessment of volume characteristics, safety of the structure, etc.; morphometric analysis of the linear dimensions and geometric characteristics of the lesions of enamel and their individual zones; determination of mineral density in different areas of the lesion by reference densitometry. Artificial enamel caries clinically corresponded to ICDAS (2), according to the microtomography data represented an X-ray diffuse structural heterogeneous lesion center of triangular shape, with a depth of 423.8 ± 107.4 µm, with a multi-level loss of mineral saturation, most pronounced in its Central zones (1.47-1.86 ± 0.17 g/cm3). The use of the method of computer microtomography and the developed model of artificial enamel caries for the assessment of mineral saturation of the demineralization focus in vitro during the approbation of various means and methods of prevention and treatment of early stages of dental caries is promising.

The aim of this work was to study the primary and secondary stability of dental implants, installed with the use of pre- and postoperative laser therapy by special device B-CureLaserDentalPro , using the method of frequency-resonance analysis. Photobiostimulation effects of low-level laser therapy device B-CureLaserDentalPro is demonstrated on the example of harmonization of the formation of the bone-implant complex. The blind randomized comparative placebo controlled prospective study determined that the professional and individual use of a 5th generation diode laser with a wavelength of 808 nm, a power of 250 mW, a pulse frequency of 14 kHz, a defocused beam of 4.5 1.0 cm, a power flux density of 14.4 J/min at peak (3.2 J/cm2 per min) at the stages of preoperative preparation and postoperative follow-up of dental implantation provides full-fledged osseointegration of implants with secondary stability indicators ( ISQ 2), determined by the frequency-resonance method (Osstell ISQ ), ensuring timely functional loading of the implant with a permanent orthopedic design with a long-term favorable prognosis of treatment. Intragroup and all individual indicators of secondary stability of implants in the combination of dental implants with pre-and postoperative irradiation of periimplant tissues with a defocused beam B-CureLaserDentalPro met the criterion of excellent, exceeding the initial stability by 14.6%, whereas in control observations full-fledged osseointegration with significantly ( p < 0.001) less (by 5.9%) relative to the baseline increase in the value of ISQ 2 was noted in 96.5%, and patients with failure of loss of implant in 3.5% of cases.

The Poisson's ratio (coefficient of transverse deformation) plays an important role in the deformation behavior of materials. Along with the Young's module, it constitutes a pair of independent and most informative material constants of solids. For hard tissues of the tooth (enamel and dentin), the Poisson's ratio should correspond to the Poisson's ratio of restorative materials in order to avoid overstresses at the boundary of the sections restorative material-enamel and restoration material-dentin. In addition, the value of the Poisson's ratio affects the deformation strength of enamel and dentin, namely, crack resistance, when they occur in a stress-strain state. In this paper, the orientational dependence of the Poisson's ratio of teeth dentin on the basis of matrices of elastic constants and the compliance coefficients of hexagonal crystals, such as crystals of dentine hydroxyapatite, was obtained for the first time. The results of calculating the Poisson's ratios of dentin as a crystalline system with a hexagonal structure are presented in the form of tables and diagrams in the polar and Cartesian coordinate systems. The minimum and maximum coefficients for the corresponding directions of the longitudinal and transverse deformations in the crystallographic coordinate system are also calculated. It is shown that the maximum value of the Poisson's ratio of dentin (0.53) is greater than the upper limit for the Poisson's ratio of isotropic materials, including known restoration materials, which in some cases may reduce the quality of restorations. It is noted that a similar analysis can be performed for tooth enamel.