Study on quantitative analysis of bracket-induced nonlinear response of labio-cheek soft tissue during the orthodontic process / 生物医学工程学杂志

In the orthodontics process, intervention and sliding of an orthodontic bracket during the orthodontic process can arise large response of the labio-cheek soft tissue. Soft tissue damage and ulcers frequently happen at the early stage of orthodontic treatment. In the field of orthodontic medicine, qualitative analysis is always carried out through statistics of clinical cases, while quantitative explanation of bio-mechanical mechanism is lacking. For this purpose, finite element analysis of a three-dimensional labio-cheek-bracket-tooth model is conducted to quantify the bracket-induced mechanical response of the labio-cheek soft tissue, which involves complex coupling of contact nonlinearity, material nonlinearity and geometric nonlinearity. Firstly, based on the biological composition characteristics of labio-cheek, a second-order Ogden model is optimally selected to describe the adipose-like material of the labio-cheek soft tissue. Secondly, according to the characteristics of oral activity, a two-stage simulation model of bracket intervention and orthogonal sliding is established, and the key contact parameters are optimally set. Finally, the two-level analysis method of overall model and submodel is used to achieve efficient solution of high-precision strains in submodels based on the displacement boundary obtained from the overall model calculation. Calculation results with four typical tooth morphologies during orthodontic treatment show that: ① the maximum strain of soft tissue is distributed along the sharp edges of the bracket, consistent with the clinically observed profile of soft tissue deformation; ② the maximum strain of soft tissue is reduced as the teeth align, consistent with the clinical manifestation of common damage and ulcers at the beginning of orthodontic treatment and reduced patient discomfort at the end of treatment. The method in this paper can provide reference for relevant quantitative analysis studies in the field of orthodontic medical treatment at home and abroad, and further benefit to the product development analysis of new orthodontic devices.

Non-linear Finite Element Analysis of Trans-Tibial Residual Limb and Prosthetic Socket / 医用生物力学

Objective To study the load transfer mechanics between residual limb and prosthetic socket, as well as stress distributions below the residual limb, so as to provide a theoretical basis for designing and optimizing of prosthetic socket and improving the wearing comfort. Methods Aiming at compression-release stabilization （CRS）, the finite element software ABAQUS was used to analyze the stress distribution at the interface between the residual limb and CRS socket. The soft tissues were defined using the Mooney-Rivlin function. The interface pressures and shear stresses between the residual limb and CRS socket during mid-stance were obtained. A three-dimensional finite element model of the patellar tendon bearing (PTB) socket was established, and the results were compared. Results The interface pressures between the residual limb and CRS socket were mainly distributed at lateral tibia, media tibia and popliteal depression regions, which were similar to the main force regions of PTB socket. The mean interface pressures on the end of stump for CRS socket was increased by 19 kPa over PTB socket. Conclusions CRS socket had better breathability and reasonable stress distributions. The stress distribution of biomechanical interface was different due to the different shapes of socket. Therefore, the optimization of prosthetic socket can help to improve the wearing comfort of prosthetic limbs.