Tomografía computarizada y sólidos virtuales para obtener modelos biomecánicos computacionales / Computed tomography and virtual solids to obtain computational biomechanical models

Uno de los padecimientos más comunes de los huesos es la fractura, definida como la pérdida de la continuidad del material óseo. Implantes y prótesis son utilizados para tratar algunas de ellas. Actualmente, antes de usar uno de estos dispositivos, se prueban modelos virtuales de los mismos utilizando un programa de diseño asistido por computadora. Para dichas pruebas, se requieren también modelos virtuales de los huesos. Los modelos óseos son obtenidos aplicando técnicas de segmentación de imágenes a las tomografías computarizadas (TC). Este trabajo presenta un procedimiento para la obtención de modelos biomecánicos hueso-implante a partir de las TCs y sólidos virtuales, teniendo en cuenta la estructura real de los huesos, compuesta de tejido cortical y trabecular. Para realizar los análisis de verificación del procedimiento se utilizó un modelo de un implante DHS y de una prótesis de cadera(AU)

One of the most common bone conditions is fracture, defined as the loss of the continuity of the bone material. Implants and prostheses are used to treat some of them. Currently, before using one of these devices, virtual models are tested using a computer-aided design program. For these tests, virtual models of the bones are also required. Bone models are obtained by applying image segmentation techniques to computed tomography (CT). This paper presents a procedure for obtaining biomechanical bone-implant models from the CTs and virtual solids, taking into account the real structure of the bones, composed of cortical and trabecular tissue. A DHS implant model and a hip prosthesis were used to perform the procedure verification tests(AU)

Load response of the natural tooth and dental implant: A comparative biomechanics study

PURPOSE: While dental implants have displayed high success rates, poor mechanical fixation is a common complication, and their biomechanical response to occlusal loading remains poorly understood. This study aimed to develop and validate a computational model of a natural first premolar and a dental implant with matching crown morphology, and quantify their mechanical response to loading at the occlusal surface. MATERIALS AND METHODS: A finite-element model of the stomatognathic system comprising the mandible, first premolar and periodontal ligament (PDL) was developed based on a natural human tooth, and a model of a dental implant of identical occlusal geometry was also created. Occlusal loading was simulated using point forces applied at seven landmarks on each crown. Model predictions were validated using strain gauge measurements acquired during loading of matched physical models of the tooth and implant assemblies. RESULTS: For the natural tooth, the maximum vonMises stress (6.4 MPa) and maximal principal strains at the mandible (1.8 mε, −1.7 mε) were lower than those observed at the prosthetic tooth (12.5 MPa, 3.2 mε, and −4.4 mε, respectively). As occlusal load was applied more bucally relative to the tooth central axis, stress and strain magnitudes increased. CONCLUSION: Occlusal loading of the natural tooth results in lower stress-strain magnitudes in the underlying alveolar bone than those associated with a dental implant of matched occlusal anatomy. The PDL may function to mitigate axial and bending stress intensities resulting from off-centered occlusal loads. The findings may be useful in dental implant design, restoration material selection, and surgical planning.

Personalized biomechanical modeling of prostate deformation based on elastography for MRI three-dimensional transrectal ultrasound(TRUS)image registration / 中华超声影像学杂志

Objective To evaluate the clinical significance of personalized biomechanical modeling of prostate deformation based on ultrasound elastography for magnetic resonance imaging(MRI)-transrectal ultrasound(TRUS)image registration.Methods A total number of 5 patients and 1 commercial prostate phantom were imaged via transrectal ultrasound elastography,3D-TRUS and MRI from June 2016 to December 2016.A personalized biomechanical model via the patient-specific ultrasound elastography was made for the deformable registration of prostate MRI and 3D-TRUS images.The registration accuracy was evaluated by the target registration error(TRE)and also the t-test was conducted to validate the statistical significance of our results.Results All the 5 sets of patient data as well as the phantom data were successfully registered.The TRE value of the phantom data was 1.65 mm.The mean TRE value of 5 patients was 1.31 mm,compared with the 2.52 mm TRE value of the registration method without patient-specific biomechanical properties via elastography,was approximately 48% lower(P <0.05).Conclusions Personalized biomechanical modeling of prostate deformation based on ultrasound elastography for MRI-TRUS image registration possesses important clinical significance and is a promising way to provide more quality guidance and improve the accuracy of prostate biopsy.

ANÁLISIS BIOMECÁNICO DE LA EPIFISIOLISIS DE LA CABEZA FEMORAL: COMPARACIÓN ENTRE FÉMURES SANOS Y ENFERMOS

En este trabajo se desarrolla un análisis por elementos finitos cuyo objetivo principal es determinar las diferencias de tensiones en la placa de crecimiento que se producen entre fémures sanos, con epifisiolisis unilateral y con epifisiolisis bilateral, para evaluar sus posibles causas. Se elaboraron los modelos de elementos finitos correspondientes a 45 pacientes. Los resultados mostraron un patrón de esfuerzos similar en todos los grupos de fémures y, además, la aparición de tensiones mayores en el grupo con epifisiolisis con respecto al grupo control. Se observó también que el valor del ángulo axial-fisis dependía significativamente del tipo de fémur analizado, y, además, una mayor influencia de los factores geométricos en la incidencia de la enfermedad, en comparación con la del índice de masa corporal.

In this work, a finite element analysis (FEA) is accomplished to study the differences of stresses in the growth plate, that are produced in healthy and unhealthy femurs, and to evaluate the possible causes of this illness. Finite element models of 45 patients were developed. The results demonstrated a similar pattern of stresses in all the groups of femurs and also the appearance of greater stresses in the group with slipped capital femoral epiphysis than in the control group. It was also observed a strong dependency on the value of the axial-fisis angle from the group of femur analyzed and a bigger influence of the geometric factors than of the body mass index, in the incidence of the illness.

A finite element analytical model of multiloop edgewise arch wire / 解放军医学杂志

Objective To construct a finite element analytical model of multiloop edgewise arch wire(MEAW),and study its mechanical characteristics.Methods Three-dimensional(3D) model of dentition-bracket-arch wire was set up in an initial graphics exchange specification(IGES) format complex by Pro/E software.The multiloop edgewise arch wire was spliced on the lower dentition.After dividing the arch wire and brackets with quarter-tetrahedron element method,the model was analyzed by ANSYS(an engineering simulation software).Results The finite element analytical model of multiloop edgewise arch wire was successfully built up.Based on the model,when multiloop edgewise arch wire was subjected to a heavy strength in certain parts(such as tooth 3,4),the anti-force strength on the other brackets(such as tooth 1,2,5,6,7) was not so heavy.The subjected strength was light and soft,especially on the first molar.Conclusion The results suggest that the finite element analytical model of multiloop edgewise arch wire built up in the experiment may be used to study the integrated mechanical characteristics,reveal the orthodontic specialty,and discuss the orthodontic mechanisms of multiloop edgewise arch wire techniques.