Lately, in orthodontic treatments, the use of transparent aligners for the correction of malocclusions has become prominent owing to their intrinsic advantages such as esthetics, comfort, and minimal maintenance. Attempts at improving upon this technology by varying various parameters to investigate the effects on treatments have been carried out by several researchers. Here, we aimed to investigate the biomechanical and clinical effects of aligner thickness on stress distributions in the periodontal ligament and changes in the tooth’s center of rotation. Dental finite element models comprising the cortical and cancellous bones, gingiva, teeth, and nonlinear viscoelastic periodontal ligaments were constructed, validated, and used together with aligner finite element models of different aligner thicknesses to achieve the goal of this study. The finite element analyses were conducted to simulate the actual orthodontic aligner treatment process for the correction of malocclusions by generating pre-stresses in the aligner and allowing the aligner stresses to relax to induce tooth movement. The results of the analyses showed that orthodontic treatment in lingual inclination and axial rotation with a 0.75 mm-thick aligner resulted in 6% and 0.03% higher principal stresses in the periodontal ligament than the same treatment using a 0.05 mm-thick aligner, respectively. Again, for both aligner thicknesses, the tooth’s center of rotation moved lingually and towards the root direction in lingual inclination, and diagonally from the long axis of the tooth in axial rotation. Taken together, orthodontic treatment for simple malocclusions using transparent aligners of different thicknesses will produce a similar effect on the principal stresses in the periodontal ligament and similar changes in the tooth’s center of rotation, as well as sufficient tooth movement. These findings provide orthodontists and researchers clinical and biomechanical evidence about the effect of transparent aligner thickness selection and its effect on orthodontic treatment.

Orthodontic treatment increasingly involves transparent aligners; however, biomechanical analysis of their treatment effects under clinical conditions is lacking. We compared the biomechanical efficacy and effectiveness of orthodontic treatment with transparent aligners and of fixed appliances in simulated clinical orthodontic treatment conditions using orthodontic finite element (FE) models. In the FE analysis, we used Model Activation/De-Activation analysis to validate our method. Fixed appliances and 0.75-mm and 0.5-mm thick transparent aligners were applied to a tooth-alveolar bone FE model with lingually-inclined and axially-rotated central incisors. Compared to the fixed appliance, the 0.75-mm and 0.5-mm transparent aligners induced 5%, 38%, and 28% and 21%, 62%, and 34% less movement of the central incisors and principal stress of the periodontal ligament and of the alveolar bone, respectively, for lingual inclination correction. For axial-rotation correction, these aligners induced 22%, 37%, and 40% and 28%, 67%, and 48% less tooth movement and principal stress of the periodontal ligament and of the alveolar bone, respectively. In conclusion, transparent aligners induced less tooth movement, it is sufficient for orthodontic treatment, but 0.5-mm aligners should be used for only mild corrections. Additionally, the Model Activation/De-Activation analysis method is suitable for FE analysis of orthodontic treatment reflecting clinical treatment conditions.

The purposes of this study are to establish and validate a finite element (FE) model using finite element analysis methods and to identify optimal loading conditions to simulate masticatory movement. A three-dimensional FE model of the maxillary and mandibular cortical bone, cancellous bone, and gingiva was constructed based on edentulous cone-beam-computed tomography data. Dental computer-aided design software was used to design the denture base and artificial teeth to produce a complete denture. Mesh convergence was performed to derive the optimal mesh size, and validation was conducted through comparison with mechanical test results. The mandible was rotated step-by-step to induce movements similar to actual mastication. Results showed that there was less than a 6% difference between the mechanical test and the alveolar bone-complete denture. It opened 10° as set in the first stage, confirming that the mouth closed 7° in the second stage. Occlusal contact occurred between the upper and lower artificial teeth as the mouth closed the remaining angle of 3° in the third stage while activating the masseter muscle. These results indicate that the FE model and masticatory loading conditions developed in this study can be applied to analyze biomechanical effects according to the wearing of dentures with various design elements applied.

본 연구는 SW교육을 통하여 길러질 수 있는 중학생의 핵심 역량을 분석하기 위하여 수행되었다. 2015년에 국가 교육 정책으로 시작된 SW교육은 2018년에 2015 개정 정보과 교육과정이 학교 현장에 적용되면서 본격적으로 확대되었다. 현재 SW교육은 초등학교에서는 실과 수업에서 17시간 이상, 중학교에서는 정보 수업에서 34시간 이상으로 편성되어 운영되고 있다. SW교육의 목적은 컴퓨팅 사고력을 가진 창의 인재 양성에 있으며, 핵심 역량은 컴퓨팅 사고력과 정보문화소양이다. 우리나라에서 SW교육이 전방위적으로 실행되면서, 교육 전문가들은 SW교육의 교육내용과 방법, 평가 방법 등에 관한 다양한 연구를 수행하고 있다. 이러한 흐름에 맞추어 본 연구는 정보 교육의 실행 첫해에 중학생을 대상으로 SW교육 역량을 평가하고 그 결과를 분석하였다. 본 연구에 참여한 대상은 2018년에 2015개정 정보과 교육과정에 따라 정보 교육을 받은 중학교 1학년 2,949명이다. 본 연구에서 사용한 평가도구의 내용은 자동판매기를 소재로 한 문제해결 과제이며, 총 13개의 5지 선다형 문항으로 구성되었다. 학생들의 정보 교과에 대한 흥미와 효능감 평가 도구는 5단계 라이커트 척도를 이용한 10개 문항으로 구성되었다. 전체 평가 시간은 약 50분 내외로 소요되었다. 그 결과, 중학교 학생들의 SW교육역량은 평균 5.45점(13점 만점)으로 조사되었다. 학습자 특성 변인에 따른 분석에서, 여학생이 남학생보다 더 높은 점수를 얻었다. 정보 교과에 대한 흥미와 효능감이 높은 학생들이 그렇지 않은 학생들보다 SW교육 역량이 더 높았다. 하지만, 교육 환경 변인에 따른 분석에서는 집단 간의 차이가 통계적으로 유의미하지 않았다. 이러한 결과를 바탕으로 후속 연구를 위한 시사점을 제시하였다.

Time-dependent force reduction may affect the biomechanical performance of thermoformed clear aligners. This proof-of-concept in vitro study compared initial and 7-day system-level 3D resultant forces of DURAN, ZENDURA FLX, and MESHEET under attachment-free and attachment-integrated conditions. Thirty independently fabricated aligners (n = 5 per condition) were tested on a rigid resin model with FDI tooth 11 positioned at 5° of labioversion. Forces were recorded at 1 Hz for 168 h under dry room conditions and summarized at 12 h intervals. Temporal series and group-level normalized decay were evaluated descriptively; no longitudinal inferential analysis was performed. Separate 3 × 2 two-way ANOVAs assessed absolute resultant force at 0 and 168 h. Higher endpoint forces were observed under the attachment-integrated condition in this experimental setup at 0 h [F(1,24) = 24.510, p < 0.001, partial η² = 0.505] and 168 h [F(1,24) = 7.175, p = 0.013, partial η² = 0.230]. However, because testing followed a fixed, nonrandomized sequence, the observed difference cannot be attributed exclusively to attachment condition. Material and interaction effects were not significant at either endpoint. Under the attachment-integrated condition, normalized decay was 51.4%, 48.2%, and 44.5%, while 168 h mean forces were 1.415, 1.664, and 1.558 N, respectively. These findings do not establish decay-rate differences, material superiority, equivalence, or clinical efficacy.