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1.
《Dental materials》2022,38(5):778-788
ObjectivesTo evaluate two-body wear (2BW) and three-body wear (3BW) of different CAD/CAM and direct restorative materials against zirconia using a dual-axis chewing simulator and an ACTA wear machine.Methods3 CAD-CAM resin-based composite or polymer infiltrated ceramic network blocs, 1 lithium disilicate CAD-CAM ceramic (LS2), 3 direct resin composites, amalgam and bovine enamel were tested. For 2BW, 8 flat specimens per material were produced, grinded, polished, stored wet (37 °C, 28d) and tested (49 N, 37 °C, 1,200,000 cycles) against zirconia. For 3BW, specimens (n = 10) were stored accordingly, and tested against a zirconia antagonist wheel (3Y-TZP, d = 20 mm, h = 6 mm; 200,000 cycles, F = 15 N, f = 1 Hz, 15% slip) in millet seed suspension. Wear resistance was analysed in a 3D optical non-contact profilometer, measuring vertical wear depth and volume loss for 2BW and mean wear depth and roughness (Ra) for 3BW. Vickers hardness (15 s, HV2) was measured. Statistical analysis was performed using non-parametric tests (Mann-Whitney-U test, p < 0.05).Results2BW and 3BW have a different impact on material surfaces. Similar wear resistance was observed for direct and indirect resin based materials with analogous filler configurations in both methods. Bovine enamel exhibited the best wear resistance in 2BW, but the least wear resistance in 3BW against zirconia. Regarding 2BW, a direct/indirect composite material pair of the same manufacturer showed the significantly highest mean volume losses (2.72/2.85 mm³), followed by LS2 (1.41 mm³). LS2 presented the best wear resistance in 3BW (mean wear depth 2.85 µm), combined with the highest mean Vickers hardness (598 MPa). No linear correlation was found between Vickers hardness and both wear testing procedures. The zirconia antagonists showed no recordable signs of wear.SignificanceDental restorative materials behave differently in 2BW and 3BW laboratory testing. Vickers hardness testing alone cannot hold for a correlation with wear behavior of materials. Micromorphological investigation of material composition can reveal insights in wear mechanisms related to variations in filler technologies.  相似文献   
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Objectives

The aim of this study was to develop a high-fidelity minimally invasive mitral valve surgery (MIMVS) simulator.

Methods

The process of industrial serial design was applied based on pre-set requirements, acquired by interviewing experienced mitral surgeons. A thoracic torso with endoscopic and robotic access and disposable silicone mitral valve apparatus with a feedback system was developed. The feedback system was based on 4 cameras around the silicone valve and an edge detection algorithm to calculate suture depth and width. Validity of simulator measurements was assessed by comparing simulator-generated values with measurements done manually on 3-dimensional reconstructed micro-computed tomography scan of the same sutures. Independent surgeons tested the simulator between 2014 and 2018, whereupon an evaluation was done through a questionnaire.

Results

The feedback system was able to provide width and depth measurements, which were subsequently scored by comparison to pre-set target values. Depth did not significantly differ between simulator and micro-computed tomography scan measurements (P = .139). Width differed significantly (P = .001), whereupon a significant regression equation was found (P < .0001) to calibrate the simulator. After calibration, no significant difference was found (P = .865). In total, 99 surgeons tested the simulator and more than agreed with the statements that the simulator is a good method for training MIMVS, and that the mitral valve and suture placement looked and felt realistic.

Conclusions

We successfully developed a high-fidelity MIMVS simulator for endoscopic and robotic approaches. The simulator provides a platform to train skills in an objective and reproducible manner. Future studies are needed to provide evidence for its application in training surgeons.  相似文献   
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BackgroundVirtual environments (VE) are increasingly used in rehabilitation settings for gait training, and positive effects are reported. However, little is known about how walking under environmental constraints and solving motor tasks in fully immersive VEs impact gait patterns.Research QuestionHow are gait patterns in healthy adults impacted by walking under environmental constraints and solving motor tasks on a treadmill, in a fully immersive VE?Methods29 healthy adults (age: 28.9±4.8 yrs) were included. Basic gait parameters (step length, cadence, walk ratio) and gait variability in the anteroposterior, mediolateral and vertical directions were measured using an inertial sensor attached to the lower back. A familiarisation treadmill walk >2 min was performed, followed by 200 m familiarisation walk in the VE with no task or environmental constraints The participants were then exposed to height, two grabbing tasks, a balancing task and narrow-path walking. Gait patterns were captured for 15–25 seconds during each of the conditions. The Simulator Sickness Questionnaire was completed before and after the session.ResultsGait regularity decreased when solving all the motor tasks, and under all the environmental constraints, except when being familiarised to height exposure, where regularity returned to pre-exposure levels. Step length and walk ratio decreased, and cadence increased during height exposure and while performing the grabbing tasks and the balancing task. The different tasks and environments appeared to have specific impact on gait patterns. There was no increase in simulator sickness symptoms.SignificanceGait patterns were impacted by solving motor tasks, and by environmental constraints, in healthy young adults, suggesting increased need for balance control. We suggest that VE-training on a treadmill holds potential for improving gait and balance control.  相似文献   
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体外磨损试验(ISO 14242)基于良好的实验室控制条件和操作规范模拟人体行走步态的关节承受载荷和运动角度范围,广泛用于比较髋关节假体不同材料、假体设计的耐磨损性能。本文基于体外磨损试验和临床磨损评价的研究文献,介绍体外磨损标准试验方法及其在髋关节设计开发中的应用,探讨体外磨损标准方法的局限、研究进展以及未来发展方向。  相似文献   
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目的:探讨MatriXX 2D矩阵电离室和X线模拟定位机应用于挡铅射野质量保证的方法及可靠性.方法:用MatriXX 2D矩阵电离室测得挡铅射野的形状和大小,应用Matlab编程绘制出治疗计划系统(treatment plan system,TPS)中相对应的射野的形状和大小;利用X线模拟定位机拍摄出射野挡铅的验证片并通过计算机上的RT PACS获取保存,对尺寸较大的射野,使用Photoshop图像处理软件合成出包含挡铅射野全部信息的验证片;从TPS调出相对应的包含挡铅射野信息的数字重建影像(digital reconstruction radiography,DRR).分别比较2对图片包含的射野信息.结果:对60个所测挡铅射野和计划射野进行比较,发现2种射野的形状总体上相符,3种方式的误差分别为(1.71±0.84)、(2.32±0.31)和(2.89±0.47)mm.结论:利用MatriXX 2D矩阵电离室和X线模拟定位机进行挡铅射野质量保证,简单易行、快速有效,能够满足放疗质控中对射野挡铅的要求.  相似文献   
9.

Objective

Secondary caries lesions next to direct restorations are associated with the restoration material and the integrity of the tooth-restoration-interface (presence of interfacial gaps) as well as the application of masticatory forces. It remains unclear if this is true for indirect restorations. We aimed to evaluate secondary lesions next to conventionally-cemented partial gold (PG) and adhesively-cemented partial ceramic (PC) restorations, placed with or without interfacial gaps.

Methods

In human molars, standardized two-surfaced cavities were prepared. Four groups (restoration material + cementation strategy) were compared: (1) gold + glass ionomer cement (Degudent/Ketac Cem), (2) lithium disilicate ceramic + self-adhesive resin cement (IPS e.max Press/RelyX Unicem 2), (3) lithium disilicate ceramic + self-etch adhesive + resin cement (IPS e.max Press/Adhese Universal/Variolink Esthetic DC), (4) lithium disilicate ceramic + etch-and-rinse adhesive + resin cement (IPS e.max Press/Syntac/Variolink Esthetic DC). Half of the restorations received a simulated interfacial gap (mean gap height was 237 μm), while the other half did not (n = 12/group). Specimens were submitted to a Lactobacillus rhamnosus-monospecies-biofilm-model with concomitant cyclic loading for 10 days. Mineral loss (ΔZ) of enamel-surface-lesions (ESL) and dentin-wall-lesions (DWL) was analyzed using transversal microradiography.

Results

For ESL, neither the presence of an interfacial gap nor the restoration material nor the cementation strategy had a significant influence on ΔZ (p > 0.05/Generalized Linear Modelling). For DWL, ΔZ was significantly higher beneath restorations with interfacial gaps (p = 0.003/GLM); the restoration material and cementation strategy did not have a significant influence (p > 0.05).

Significance

The presence of interfacial gaps, but not the restoration material or cementation strategy determined secondary caries lesions next to indirect restorations in vitro.  相似文献   
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