Biomechanical impact of different isthmus positions in mandibular first molar root canals: a finite element analysis.

OBJECTIVE: This study used image-based finite element analysis (FEA) to assess the biomechanical changes in mandibular first molars resulting from alterations in the position of the root canal isthmus. METHODS: A healthy mandibular first molar, characterized by two intact root canals and a cavity-free surface, was selected as the subject. A three-dimensional model for the molar was established using scanned images of the patient's mandibular teeth. Subsequently, four distinct finite element models were created, each representing varied root canal morphologies: non-isthmus (Group A), isthmus located at the upper 1/3 of the root (Group B), middle 1/3 of the root (Group C), and lower 1/3 of the root (Group D). A static load of 200 N was applied along the tooth's longitudinal axis on the occlusal surface to simulate regular chewing forces. The biomechanical assessment was conducted regarding the mechanical stress profile within the root dentin. The equivalent stress (Von Mises stress) was used to assess the biomechanical features of mandibular teeth under mechanical loading. RESULTS: In Group A (without an isthmus), the maximum stress was 22.2 MPa, while experimental groups with an isthmus exhibited higher stresses, reaching up to 29.4 MPa. All maximum stresses were concentrated near the apical foramen. The presence of the isthmus modified the stress distribution in the dentin wall of the tooth canal. Notably, dentin stresses at specific locations demonstrated differences: at 8 mm from the root tip, Group B: 13.6 MPa vs. Group A: 11.4 MPa; at 3 mm from the root tip, Group C: 14.2 MPa vs. Group A: 4.5 MPa; at 1 mm from the root tip, Group D: 25.1 MPa vs. Group A: 10.3 MPa. The maximum stress in the root canal dentin within the isthmus region was located either at the top or bottom of the isthmus. CONCLUSION: A root canal isthmus modifies the stress profile within the dentin. The maximum stress occurs near the apical foramen and significantly increases when the isthmus is located closer to the apical foramina.

Exergames improves cognitive functions in adolescents with depression: study protocol of a prospective, assessor-blind, randomized controlled trial.

BACKGROUND: Depression is a condition that imposes a significant disease burden, with cognitive impairment being one of its costly symptoms. While cognitive rehabilitation is crucial, it is also challenging. Although some studies have investigated the impact of exergames on cognitive function improvement, these have primarily focused on the elderly population, with limited attention given to individuals with depression. Consequently, this study aims to investigate the effects of exergames on cognitive functions in adolescents with depression and compare the effectiveness of exergames with traditional exercise. METHOD: The present investigation is a single-center randomized controlled trial that employs the ANOVA method to calculate the sample size using G*Power software, assuming a 25% dropout rate. The study enrolls fifty-four eligible patients with depression who are randomly allocated to one of three treatment groups: the exergames group, which receives standard treatment and exergames intervention; the exercise group, which receives standard treatment and traditional exercise intervention; and the control group, which receives standard treatment exclusively. The study provides a comprehensive regimen of 22 supervised exercise and exergame sessions over an 8-week period, with a frequency of twice per week for the initial two weeks and three times per week for the subsequent six weeks. The researchers gather cognitive, mood, and sleep metrics at the onset of the first week, as well as at the conclusion of the fourth and eighth weeks. The researchers employ a wearable device to track participants' heart rate during each intervention session and evaluate the Borg Rating of Perceived Exertion scale at the conclusion of each session. DISCUSSION: The findings from this study make several contributions to the current literature. First, this study comprehensively reports the efficacy of an exergames intervention for multidimensional symptoms in adolescents with depression. Second, this study also compares the efficacy of exergames with that of traditional exercise. These findings provide a theoretical basis for the use of exergames as an adjunctive intervention for depression and lay the groundwork for future research. TRIAL REGISTRATION: This trial is registered with the Chinese Clinical Trials Registry (Registration number: ChiCTR2100052709; Registration Status: Prospective registration;) 3/11/2021, URL:    http://www.chictr.org.cn/edit.aspx?pid=135663&htm=4 .

Driven dynamics in dense suspensions of microrollers.

We perform detailed computational and experimental measurements of the driven dynamics of a dense, uniform suspension of sedimented microrollers driven by a magnetic field rotating around an axis parallel to the floor. We develop a lubrication-corrected Brownian dynamics method for dense suspensions of driven colloids sedimented above a bottom wall. The numerical method adds lubrication friction between nearby pairs of particles, as well as particles and the bottom wall, to a minimally-resolved model of the far-field hydrodynamic interactions. Our experiments combine fluorescent labeling with particle tracking to trace the trajectories of individual particles in a dense suspension, and to measure their propulsion velocities. Previous computational studies [B. Sprinkle et al., J. Chem. Phys., 2017, 147, 244103] predicted that at sufficiently high densities a uniform suspension of microrollers separates into two layers, a slow monolayer right above the wall, and a fast layer on top of the bottom layer. Here we verify this prediction, showing good quantitative agreement between the bimodal distribution of particle velocities predicted by the lubrication-corrected Brownian dynamics and those measured in the experiments. The computational method accurately predicts the rate at which particles are observed to switch between the slow and fast layers in the experiments. We also use our numerical method to demonstrate the important role that pairwise lubrication plays in motility-induced phase separation in dense monolayers of colloidal microrollers, as recently suggested for suspensions of Quincke rollers [D. Geyer et al., Phys. Rev. X, 2019, 9(3), 031043].