The effect of three rotational speed settings on torque and apical force with vortex rotary instruments in vitro

Introduction

Both the number of rotations in curved canals and torque are related to fracture resistance of nickel-titanium rotaries via the respective mechanisms of brittle and flexural failure. Increased rotational speed (rotations per minute [RPM]) may lead to higher cutting ability and could overcompensate for increased fatigue. The impact of three RPM settings on peak torque (Nmm) and apically directed force (N) during root canal preparation were investigated in vitro.

Methods

S-shaped canals in plastic blocks (n = 12/group) were instrumented with Vortex rotaries (Dentsply Tulsa Dental, Tulsa, OK) sizes #15 to 30 with a .04 taper. Rotaries were used in a manufacturer-recommended sequence: #30, 25, and 20 in a crown-down approach progressively deeper into the canal, #15 to the working length, and apical enlargement with sizes 20 and 25 to WL. A total of 216 preparation procedures were performed using a custom testing platform. RPM was set at 200, 400, or 600; automated axial feed mirrored clinical handling, resulting in two in-and-out movements, each to preset insertion depths. Torque and apical force were continuously recorded and peak values statistically contrasted using analysis of variances.

Results

No file fractures were observed in any of the three experimental groups. Peak torques and forces varied by instrument size and were highest at 200 RPM for all sizes; torque and force were reduced by 32% and 48%, respectively, at 400 RPM (P < .001). Increasing RPM to 600 did not result in further reductions. The number of discernible peaks for torque (threshold: 0.3 Nmm) and force (threshold: 0.2 N) significantly decreased from 200 RPM to 400 RPM and did not decrease further with 600 RPM.

Conclusions

Under the present experimental conditions, rotational speed had a significant impact on preparation with Vortex rotaries, with instruments at 400 RPM generating less torque and force compared with 200 RPM.     

INAUGURAL ARTICLE by a Recently Elected Academy Member:Helicity and singular structures in fluid dynamics

Helicity is, like energy, a quadratic invariant of the Euler equations of ideal fluid flow, although, unlike energy, it is not sign definite. In physical terms, it represents the degree of linkage of the vortex lines of a flow, conserved when conditions are such that these vortex lines are frozen in the fluid. Some basic properties of helicity are reviewed, with particular reference to (i) its crucial role in the dynamo excitation of magnetic fields in cosmic systems; (ii) its bearing on the existence of Euler flows of arbitrarily complex streamline topology; (iii) the constraining role of the analogous magnetic helicity in the determination of stable knotted minimum-energy magnetostatic structures; and (iv) its role in depleting nonlinearity in the Navier-Stokes equations, with implications for the coherent structures and energy cascade of turbulence. In a final section, some singular phenomena in low Reynolds number flows are briefly described.This inaugural article, although long delayed, is now fortuitously quite timely for various reasons. First, helicity in fluid dynamics is a measure of the knottedness and/or linkage of the vortex lines of a flow (1), invariant under ideal-fluid Euler evolution. Knotted vortices were first conceived by Lord Kelvin (then Sir William Thomson) in 1868 (2), but have only recently been unambiguously observed: a vortex in the form of a trefoil knot has been generated in a remarkable experiment by Kleckner and Irvine (3) by means of an ingenious technique that can in principle be adapted to generate vortices of arbitrarily linked or knotted form. The possible existence of knotted vortices is therefore no longer a matter of mere speculation!Second, helicity has long been known to be of crucial importance in turbulent dynamo theory—the theory of the spontaneous growth of a magnetic field in a conducting fluid in turbulent motion. The associated chirality of the flow is responsible for the α-effect (4), which is a crucial ingredient of the dynamo process in stars and planets. The von Karman sodium (VKS) experiment (5) developed in France over the last decade has at last provided convincing evidence for a turbulent dynamo mechanism that undoubtedly involves this α-effect in conjunction with differential rotation and strong diffusive processes.Third, the process of magnetic relaxation of a knotted magnetic flux tube in a perfectly conducting fluid under the topological constraint of invariant helicity leads in a natural physical way to the concept of the energy spectrum of knots and links (6). The minimum energy configurations obtained by this procedure are, with certain qualifications, essentially the same as the ideal or tight knot configurations introduced by Katritch et al. (7) which minimize the length-to-diameter ratio of knotted tubes. Tight knots have found wide application in polymer physics and molecular biology, as discussed in recent workshops of the Isaac Newton Institute for Mathematical Sciences (8, 9), and huge progress has been made in determining all tight configurations for links and knots up to 9 and 10 crossings, respectively (10). In particle physics, a striking correlation has been noted between the knot/link energies and the mass/energies of glueballs in the quark–gluon plasma (11); the subject has perhaps come full circle since the time of Kelvin!The time is therefore ripe to review some of the salient features of these and related phenomena in which helicity plays a central role, and I take this welcome opportunity to do so. I include also, at the suggestion of a referee of this article, a section on certain structures that can arise in flows that are dominated by viscosity, and that nevertheless exhibit structures of nontrivial topology.     

Left ventricular blood flow patterns at rest and under dobutamine stress in healthy pigs

Intracardiac blood flow patterns are affected by the morphology of cardiac structures and are set up to support the heart's pump function. Exercise affects contractility and chamber size as well as pre‐ and afterload. The aim of this study was to test the feasibility of four‐dimensional phase contrast cardiovascular MRI under pharmacological stress and to study left ventricular blood flow under stress. 4D flow data were successfully acquired and analysed in 12 animals. During dobutamine infusion, heart rate and ejection fraction increased (82 ± 5 bpm versus 124 ± 3 bpm/46 ± 9% versus 65 ± 7%; both p < 0.05). A decrease in left ventricular end‐diastolic volume (72 ± 14 mL versus 55 ± 8 mL; p < 0.05) and end‐systolic volume (40 ± 15 mL versus 19 ± 6 mL; p < 0.05) but no change in stroke volume were observed. Trans‐mitral diastolic inflow velocity increased under dobutamine and the trajectory of inflowing blood was directed towards the anterior septum with increased inflow angle (26 ± 5°) when compared with controls (15 ± 2°). In 5/6 animals undergoing stress diastolic vortices developed later, and in 3/6 animals vortices collapsed earlier with significantly smaller cross‐sectional area during diastole. The vorticity index was not affected. Under the stress condition direct flow (% ejection within the next heart beat) increased from 43 ± 6% to 53 ± 8%. 4D MRI blood flow acquisition and analysis are feasible in pig hearts under dobutamine‐induced stress. Flow patterns characterized by high blood velocity and antero‐septally oriented diastolic inflow as well as decreased ventricular volumes are unfavourable conditions for diastolic vortex development under pharmacological stress, and cardiac output is increased by a rise in heart rate and directly ejected left ventricular blood volume.     

上肢涡流水疗法治疗上肢烧伤术后疤痕增生的回顾性研究

目的探究上肢涡流水疗法治疗上肢烧伤术后疤痕增生患者的临床疗效。方法回顾性分析于我院2016年12月~2018年12月接受治疗的98例上肢烧伤术后疤痕增生患者的临床资料,并根据其治疗方法进行分组,其中对照组48例予以压力疗法、超声波治疗等常规治疗,观察组50例在对照组基础上给予上肢涡流水疗法进行治疗。比较两组患者治疗前及治疗3个月后的瘢痕状况、上肢功能及生活质量变化情况。结果治疗3个月后,两组患者柔软度、血管分布、厚度、色泽得分及总分均较治疗前显著下降(P均<0.05),且观察组明显低于同期对照组(P<0.05);治疗3个月后,两组患者上肢FMA及MI得分均较治疗前显著提升(P均<0.05),且观察组明显高于同期对照组(P<0.05);治疗3个月后,两组患者生活质量各项评分均较治疗前显著升高(P均<0.05),且观察组明显高于对照组(P<0.05)。结论在常规治疗的基础上采用上肢涡流水疗法可有效促进上肢烧伤术后疤痕增生患者的上肢功能恢复,还可改善日常生活能力。     

震荡法在纠正EDTA依赖的假性血小板减少中的应用

目的:评估震荡法纠正EDTA依赖的假性血小板减少(EDTA-dependent pseudothrombocytopenia,EDTA-PTCP)的可行性。方法:收集140例EDTA-PTCP血标本,比较震荡前后全自动血细胞分析仪血小板计数检测结果,同时进行外周血涂片以观察血小板分布情况。结果:140例EDTA-PTCP血标本中,93例外周血涂片显示震荡后血小板聚集明显减少,血小板计数中位数为184×10~9/L,与震荡前(33×10~9/L)差异有统计学意义(P0.05);另47例为未完全解聚标本血小板计数中位数为48×10~9/L,与震荡前(39×10~9/L)差异无统计学意义。140例EDTA-PTCP标本中,震荡前后其他参数差异均无统计学意义。20例正常抗凝血标本震荡前后各项参数差异均无统计学意义。结论:震荡法可纠正多数EDTA-PTCP,是一种简单、有效的方法,可以提高检测效率,减轻患者痛苦。     

无创性定量左室心腔内涡流的方法及临床应用

定量观察左室腔内涡流,可以评价左室的收缩功能和舒张功能。涡流的形态及位置随心功能减低而发生变化。已经证实,MRI及超声心动图均能够准确观测左室内的涡流。虽然观测方法仍存在一些局限性,借助声学造影的超声心动图方法是能够用于临床的最为准确有效的技术。该方法利用声学微泡流动与涡流的一致性特征对心室重构及心肌做功进行定量研究。敏感参数包括涡流深度比(0.482±0.06)、长度比(0.467±0.05)、宽度比(0.128±0.06)、球形指数(3.66±0.6)、相对强度比(2.10±0.8)、涡流的相对强度(1.19±0.5)和脉动相关系数(1.31±0.5);舒张早期涡流半径(3±1mm)、舒张早期充盈血流前锋速度Vp(47±6cm/s)及Vp/E(0.59±0.07)。但是,由于临床试验研究对象的例数较少,临床应用效果仍缺乏相应的循证医学的依据。