不同表面处理对LAVA树脂纳米瓷剪切强度的影响

目的 研究不同处理方式对树脂纳米瓷(LAVA Ultimate)与树脂水门汀粘接后剪切强度的影响。方法 本次实验分为喷砂实验和粘接实验两部分。将LAVA Ultimate切削成大小约 6 mm×6 mm,高度约为2 mm的样本80片,依照不同的喷砂时间和喷砂气压随机分为4组,每组10个试件,使用3M Single Bond Universal+3M RelyX Ultimate与纳米树脂柱粘接后在万能试验机上测试断裂载荷,计算剪切强度,选出最高组。同等喷砂条件下40个样本随机分为A(Single Bond Universal(3M)+RelyX Ultimate(3M)) ,B (Porcelain Primer(Bisco)+ All-bond Universal(Bisco)+RelyX Ultimate(3M))与纳米树脂柱进行粘接。粘接后再分成两个亚组,分别进行冷热循环5 000次和恒温水浴24 h。在万能试验机上测试断裂载荷,计算剪切强度,采用单因素方差分析对数据进行统计分析。结果 单因素方差分析结果表明不同喷砂条件的分组对剪切强度差异有统计学意义(第2组和第4组)(P=0.037);冷热循环后,A组和B组试件的剪切强度均有明显下降(P=0.003,P<0.01);A、B组不同粘接方式的剪切强度差异无统计学意义(P=0.062,P=0.671)。结论 0.2 MPa压力下喷砂14 s可明显提高树脂纳米瓷与树脂水门汀的剪切强度;冷热循环会明显降低剪切强度;粘接方式对剪切强度无明显影响。     

The Microstructural Evolution and Mechanical Properties of Zr-Based Metallic Glass under Different Strain Rate Compressions

In this study, the high strain rate deformation behavior and the microstructure evolution of Zr-Cu-Al-Ni metallic glasses under various strain rates were investigated. The influence of strain and strain rate on the mechanical properties and fracture behavior, as well as microstructural properties was also investigated. Before mechanical testing, the structure and thermal stability of the Zr-Cu-Al-Ni metallic glasses were studied with X-ray diffraction (XRD) and differential scanning calorimeter. The mechanical property experiments and microstructural observations of Zr-Cu-Al-Ni metallic glasses under different strain rates ranging from 10⁻³ to 5.1 × 10³ s⁻¹ and at temperatures of 25 °C were investigated using compressive split-Hopkinson bar (SHPB) and an MTS tester. An in situ transmission electron microscope (TEM) nanoindenter was used to carry out compression tests and investigate the deformation behavior arising at nanopillars of the Zr-based metallic glass. The formation and interaction of shear band during the plastic deformation were investigated. Moreover, it was clearly apparent that the mechanical strength and ductility could be enhanced by impeding the penetration of shear bands with reinforced particles.     

Effect of pulsatile swirling flow on stenosed arterial blood flow

The existence of swirling flow phenomena is frequently observed in arterial vessels, but information on the fluid-dynamic roles of swirling flow is still lacking. In this study, the effects of pulsatile swirling inlet flows with various swirling intensities on the flow field in a stenosis model are experimentally investigated using a particle image velocimetry velocity field measurement technique. A pulsatile pump provides cyclic pulsating inlet flow and spiral inserts with two different helical pitches (10D and 10/3D) induce swirling flow in the stenosed channel. Results show that the pulsatile swirling flow has various beneficial effects by reducing the negative wall shear stress, the oscillatory shear index, and the flow reverse coefficient at the post-stenosis channel. Temporal variations of vorticity fields show that the short propagation length of the jet flow and the early breakout of turbulent flow are initiated as the swirling flow disturbs the symmetric development of the shear layer. In addition, the overall energy dissipation rate of the flow is suppressed by the swirling component of the flow. The results will be helpful for elucidating the hemodynamic characteristics of atherosclerosis and discovering better diagnostic procedures and clinical treatments.     

The effect of thermal cycling on the bovine dentine shear bond strength of current adhesive systems

The aim of this study was to evaluate the effect of thermal cycling on shear bond strength to bovine dentine of four current adhesive systems. Forty bovine incisors were ground flat with #600-grit silicon carbide paper to obtain superficial coronal dentine surfaces. Three one-bottle (etch and rinse) adhesive systems (Single Bond, Bond 1, One Step), and one self-etching primer adhesive system (Clearfil Liner Bond 2V) were evaluated. Dentine was conditioned and bonded with the adhesive systems tested according to the manufacturers' instructions. A cylindrical teflon mould (3 x 4 mm) was placed over the bonded area (to eliminate the bonded surface) and filled with composite resin. For each adhesive system the filling composite used was from the same manufacturer. Ten specimens were prepared for each material and all specimens were conditioned at 37 degrees C for 24 h. Five specimens of each material (half of the specimens) were thermocycled at 5000 cycles (at 5, 37, 55 and 37 degrees C) with a dwell time of 15 s and bonds were stressed in shear at a rate of 0.5 mm min(-1) until failure. Data were analysed by one-way anova and Student-Newman-Keuls rank test (alpha=0.05). Statistical analysis revealed that thermal cycling significantly (P < 0.05) reduced the bond strengths of all adhesive systems. Bond strengths prior to thermocycling were not significantly different (P > 0.05), except for One Step which revealed the lowest bond strength, and varied from 22.5 +/- 3.34 to 10.98 +/-0.87 MPa. After thermal cycling, the bond strengths ranged from 9.35 +/- 1.13 to 6.06 +/- 1.77 MPa. Failures after testing and prior to thermal cycle were most commonly adhesive failures between the bonding resin and dentine associated with partial cohesive failures in the adhesive resin (type 2). Adhesive failures between bonding resin and dentin (type 1) after thermocycling were most commonly seen.