Fracture Resistance of Roots Obturated with Resilon and EndoREZ with Self-Adhesive Root Canal Sealers

<sec> <title>Objective:</title> This laboratory study aimed to evaluate the effect of self-adhesive root canal sealers on the fracture strength of root canals filled with Resilon or EndoREZ. </sec> <sec> <title>Materials and Methods:</title> A total of eighty extracted mandibular premolar teeth were selected in this in-vitro study. All teeth were instrumented using a crown-down technique by FlexMaster rotary NiTi files. Specimens were divided into 4 test groups (n = 20) according to the sealer material: RS; RealSeal, RSS; RealSeal SE, MS; MetaSeal, and CG; (control group) zinc oxide eugenol-based sealer. Each main group was distributed into two subgroups (n = 10) according to the filling material either Resilon or EndoREZ and gutta-percha (n = 20) in the control group. Each root was mounted in acrylic resin blocks and subjected to fracture in a universal testing machine. The load values at root specimens fractured were registered in Newton’s and the data were analyzed using two-way analysis of variance and the Tukey HSD test (α = 0.05). </sec> <sec> <title>Results:</title> The two-way analysis of variance analysis indicated that the filling material had a significant effect on the fracture strength of endodontically treated teeth (p < 0.05) but not the sealer materials (p≥.05). Higher mean fracture strength was recorded in MetaSeal and Resilon group (1281.90±200.34 N) and lower mean fracture strength was shown in RealSeal and EndoREZ group (847.55±191.04 N). </sec> <sec> <title>Conclusion:</title> Self-adhesive (fourth-generation) resin sealers increased the fracture strength of root teeth more than self-etching (third-generation) root canal sealers when used with EndoREZ points. </sec>

Fracture Resistance in Non-Vital Teeth: Absence of Interproximal Ferrule and Influence of Preparation Depth in CAD/CAM Endocrown Overlays—An In Vitro Study

There is ample evidence to support the use of endocrowns to restore endodontic teeth. However, the influence of the position of the interproximal margins on fracture strength has not yet been studied. The aim was to determine the relationship between the apicocoronal position of the interproximal restorative margins and fracture resistance in nonvital teeth restored with CAD/CAM endocrown overlays. Forty extracted human maxillary premolars were prepared for endocrown overlay restorations without ferrule on the interproximal aspects and classified according to the position of the interproximal restoration margins in relation to the alveolar crest: 2 mm (group A), 1 mm (group B), 0.5 mm (group C), and 0 mm (group D). Fracture strength was measured using a universal testing machine applying a compressive force to the longitudinal tooth axis. Group A had a mean fracture resistance of 859.61 (±267.951) N, group B 1053.9 (±333.985) N, group C 1124.6 (±291.172) N, and group D 780.67 (±183.269) N, with statistical differences between groups. Group C had the highest values for fracture strength compared to the other groups (p < 0.05). The location of the interproximal margins appears to influence the fracture resistance of CAD/CAM endocrown overlays. A distance of 0.5 mm between the interproximal margin and the alveolar crest was associated with increased fracture resistance.

Layer-dependent Fracture Strength of Few-layer WS2 Induced by Interlayer Sliding: A Molecular Dynamics Study

Understanding the relationship of interlayer interaction with mechanical properties and behaviors of two-dimensional layered materials (2DLMs) is critical in favoring the development of related nanodevices, nevertheless, still challenging due to the difficulties in experiments. In this work, nanoindentation simulations on few-layer WS2 were conducted by varying tip radius, suspended membrane radius and membrane size using molecular dynamics simulation. Consistent with our previous experimental results, few-layer WS2 exhibited layer-dependent reduction in fracture strength owing to the uneven stress distribution among individual layer induced by interlayer sliding under out-of-plane deformation. Besides, apparent curve hysteresis was observed due to interlayer sliding in the supported region when large tip radius and membrane radius were employed. However, instead of the supported part, the interlayer sliding within the suspended part resulted in the reduced fracture strength with the increase of layer number. These findings not only provide an in-depth comprehension on the influence of interlayer sliding on the fracture strength of few-layer WS2, but also suggest that the role of interlayer interaction should be seriously considered during nanodevice design.

A Study on the Fiber YAG Laser Welding of 304L Stainless Steel

This work aims to optimize the main YAG fiber laser parameters to weld 304L stainless steel plates of 3 mm thick. Different laser powers (2500, 2000, and 1500 W) and speeds (60, 40, and 20 mm/s) were used and merged in heat input, maintaining the defocusing distance at –2 mm to get full penetration. The weld quality and the effect of the laser heat input on the microstructures of the weld and heat-affected zones were investigated. Besides, the fracture strength of the welded joints and hardness distribution through the cross-sections were evaluated. The weld width has a direct relationship with heat input. The laser power of 2800 W produced full penetration joints without any macro defects while reduction in laser power pronounced partial penetration defects. The size of the heat-affected zone in all the processing parameters was very small. The microstructure of the weld zone shows columnar dendrite austenite grains with small arm spacing in most of the welded zone. The size of the dendrites became finer at lower heat input. At a higher heat input, a reasonable amount of lathy equiaxed grains with some delta ferrite occurred. A small amount of delta ferrite was detected in the heat-affected zone, which prevented the crack formation. The hardness of the weld metal was much higher than that of the base metal in all processing parameters and it has a reverse relationship with the heat input. The fracture strength of the welded joints was very close to that of the base metal in the defect-free samples and it increased with decreasing the heat input.

Study on the Distribution of Frictional Forces on Z-Yarn Continuous Implanted Preforms and Its Application

In order to improve the quality and efficiency of the Z-directional 3D preform forming, the Z-yarn friction force distribution model of the preform and its wear mechanism were investigated. Designed the tensile force measuring device of the replacement guide sleeves,the measured tensile force is equivalent to the Z-yarn friction force. Found that the frictional force was proportional to the number of preform layers, the frictional force applied to the one preform decreased from the corner, edge, sub-edge and middle in order. Established BP neural network model to predict the friction at different positions of preform with different layers, the error is within1.9%. The wear of Z-yarn was studied at different frictional positions and after different times of successive implantation into the preform, showed that with the increase of the number of Z-yarn implantation and the friction force, the amount of carbon fiber bundle hairiness gradually increase, and the tensile fracture strength damage of the fiber is increasingly affected by the friction force,and in the corner position of the preform, when the number of implantation is 25 times, the fiber fracture strength will occur non-linearly and substantially decreased, in order to avoid fiber fracture in the implantation process, the Z-yarn needs to be replaced in time after 20~25 times of continuous