Effects of different alveolar bone finite element models on the biomechanical responses of periodontal ligament / 生物医学工程学杂志

In the study of oral orthodontics, the dental tissue models play an important role in finite element analysis results. Currently, the commonly used alveolar bone models mainly have two kinds: the uniform and the non-uniform models. The material of the uniform model was defined with the whole alveolar bone, and each mesh element has a uniform mechanical property. While the material of the elements in non-uniform model was differently determined by the Hounsfield unit (HU) value of computed tomography (CT) images where the element was located. To investigate the effects of different alveolar bone models on the biomechanical responses of periodontal ligament (PDL), a clinical patient was chosen as the research object, his mandibular canine, PDL and two kinds of alveolar bone models were constructed, and intrusive force of 1 N and moment of 2 Nmm were exerted on the canine along its root direction, respectively, which were used to analyze the hydrostatic stress and the maximal logarithmic principal strain of PDL under different loads. Research results indicated that the mechanical responses of PDL had been affected by alveolar bone models, no matter the canine translation or rotation. Compared to the uniform model, if the alveolar bone was defined as the non-uniform model, the maximal stress and strain of PDL were decreased by 13.13% and 35.57%, respectively, when the canine translation along its root direction; while the maximal stress and strain of PDL were decreased by 19.55% and 35.64%, respectively, when the canine rotation along its root direction. The uniform alveolar bone model will induce orthodontists to choose a smaller orthodontic force. The non-uniform alveolar bone model can better reflect the differences of bone characteristics in the real alveolar bone, and more conducive to obtain accurate analysis results.

The Extra-Oral Measuring Technique of Initial Restoring Force Produced by Orthodontic Archwire Based on Dental Model / 医用生物力学

Objective To realize the extra-oral measurement of initial recovery force produced by orthodontic wire using simulated dental model. Methods A clinical patient was selected as the study objective, and maxillary dental models, which were in accordance with the real dentition of patient, were fabricated by three-dimensional printing. An orthodontic force measuring system was constructed using Nano17 F/T mechanical sensors to measure the initial recovery forces on two maxillary central incisors, which were produced by a standard circle Ni-Ti wire with the diameter of 355.6 μm after the archwire was assembled on the dental model. Results Central incisor 21 suffered a lager initial orthodontic force compared with incisor 11, and the force systems on two incisors were both adverse to tooth ideal movement, therefore, an assistive device was necessary to improve force status of the teeth. When the orthodontic treatment plan was optimized, a satisfactory result was obtained after 18 months of treatment. Conclusions Force systems caused by orthodontic wire and exerted on the teeth could be accurately measured using the simulated dental model of patient, so as to predict the teeth moving type, and improve teeth treatment plan on this basis. The extra-oral measuring technique of orthodontic force provides an important reference for clinical orthodontic treatment, and creates a novel idea for the optimal design of orthodontic plan.