Physical and mechanical characterization and the influence of cyclic loading on the behaviour of nickel-titanium wires employed in the manufacture of rotary endodontic instruments

AIM: To analyse the influence of cyclic loading on the mechanical behaviour of nickel-titanium (NiTi) wires employed in the manufacture of ProFile rotary endodontic instruments. METHODOLOGY: Nickel-titanium wires, 1.2 mm in diameter, taken from the production line of ProFile rotary endodontic instruments before the final machining step, were tensile-tested to rupture in the as-received condition and after 100 load-unload cycles in the superelastic plateau (4% elongation). The wires were characterized by X-ray energy-dispersive spectroscopy, X-ray diffraction and by differential scanning calorimetry and compared with new size 30, .06 taper ProFile instruments. The fracture surfaces of the wires were observed by scanning electron microscopy. RESULTS: The mechanical properties of the as-received wires, their chemical composition, the phases present and their transformation temperatures were consistent with their final application. Only small changes, which decreased after the first few cycles, took place in the mechanical properties of the cycled wires. The stress at maximum load and the plastic strain at breakage remained the same, while the critical stress for inducing the superelastic behaviour, which is related to the restoring force of the endodontic instruments, decreased by approximately 27%. CONCLUSIONS: The mechanical behaviour of the NiTi wires was modified slightly by cyclic tensile loading in the superelastic plateau. As the changes tended towards stabilization, the clinical use of rotary NiTi ProFile instruments does not compromise their superelastic properties until they fracture by fatigue or torsional overload, or are otherwise discarded.     

Influence of different periodontal curette grips on the outcome of mechanical non-surgical therapy

AIM: To determine to whether successful scaling and root planing (SRP) depends upon the grip used on the periodontal curette. METHODS: The hand grips used by dentists for holding periodontal curettes were examined and the dentists were allocated to one of two matched groups, one in which they used a modified pen grip, the other in which they did not. Using a split-mouth technique, patients scheduled for SRP had one quadrant treated by a dentist from each group. Instrument application force was recorded as were periodontal measures at operation and 3-months later. RESULTS: During scaling, forces reached a mean of 0.77N in dentists using a curette with a non-pen grip and 0.54N in those using a pen grip and during root planing, 0.93N and 0.64N respectively. These forces were statistically significantly different between the two groups. Pocket depth reduction in teeth treated by the two groups was similar but attachment levels were statistically significantly different. CONCLUSIONS: Instrument grip had a significant effect on response to SRP, suggesting that dentists using a modified pen grip achieved better clinical results.     

臭氧老化作用对SY-28硅橡胶机械性能的影响

目的：评估臭氧老化作用对SY-28硅橡胶机械性能的影响。方法：按照国家标准，对SY-28和MDx-4-4210硅橡胶臭氧老化前后的扯断强度、扯断伸长率、永久变形率（3min后）、撕裂强度、硬度（邵氏A）进行测试，并对其老化性能加以评价。结果：经臭氧老化作用处理，SY-28硅橡胶的永久变形率和邵氏硬度优于MDX-4-4210硅橡胶：扯断强度、扯断伸长率和撕裂强度与MDX-4-4210硅橡胶相似。结论：SY-28硅橡胶机械性能优良，同时具有良好的耐臭氧老化性能。     

Effect of Heat Treatment on Joint Properties of Laser-Welded Ag-Au-Cu-Pd and Co-Cr Alloys

PURPOSE: This study investigated the effect of heat treatment on the strengths of laser-welded cast Ag-Au-Cu-Pd and Co-Cr alloys. MATERIALS AND METHODS: Cast plates of Ag-Au-Cu-Pd (Ag) and Co-Cr (Co) alloys were prepared. After polishing the surfaces to be welded, the plates were matched and butted Ag to Ag (Ag/Ag), Co to Co (Co/Co), and Ag to Co (Ag/Co) and welded using Nd:YAG laser at a pulse duration of 10 ms, spot diameter of 1 mm, and voltage of 200 V. Five specimens were prepared for each experimental condition by bilaterally welding them with five spots. The Ag/Ag, Ag/Co, and control Ag underwent two heat treatments-softening (ST) and hardening (AH). A group of as-cast specimens serving as controls was not given either heat treatment. The failure load and percent elongation were measured at a crosshead speed of 1.0 mm/min. RESULTS: The fracture resistance of Co/Co was similar to that of the control Co, while the fracture resistance of Co/Ag was significantly lower than that of both like alloy pairings for all heat-treating conditions. The control Ag had greater fracture resistance after AH and lower fracture resistance after ST. The AH treatment increased the fracture resistance, and the ST treatment decreased the fracture resistance of both Ag/Ag and Co/Ag, although not significantly. The percentage of elongation appeared to positively correlate with the fracture resistance results. CONCLUSIONS: The results obtained in this study indicated that the age-hardening heat treatment increased the weld strength between the paired Au-Ag-Cu-Pd alloys and between the Au-Ag-Cu-Pd and Co-Cr alloys.     

机械压应力下骨硬化蛋白对成牙骨质细胞功能影响及机制的体外研究

目的 探究骨硬化蛋白（SOST）对处于机械压应力中的永生化成牙骨质细胞（OCCM-30）的功能影响及其相关的机制。方法 用不同浓度SOST培养液（0、25、50、100 ng·mL ^-1）处理细胞后依靠四点弯曲细胞力学加载器对细胞加载大小为2 000 μstrain、频率是0.5 Hz的单轴压应力6 h,用免疫印迹法检测β-连环蛋白（β-catenin）、磷酸化的细胞信号转导分子p-smad1/5/8、细胞信号转导分子smad1/5/8的蛋白水平;用碱性磷酸酶（ALP）活性检测法检测ALP活性;用荧光实时定量PCR检测核心结合蛋白因子2（Runx-2）、骨钙素（OCN）、骨涎蛋白（BSP）以及细胞核因子κB受体活化因子（RANKL）、骨保护因子（OPG）的表达。结果 p-smad1/5/8随着SOST浓度增加,呈减低的趋势,而β-catenin、smad1/5/8未有显著差异性。在仅对细胞加力时ALP活性降低,随SOST浓度升高,ALP活性逐渐发生下降,Runx-2、OCN和BSP的表达也都呈现降低趋势,RANKL的表达随着SOST增加而升高,OPG则随之下降。结论 压应力下,SOST的升高会对骨形态发生蛋白（BMP）/smad 通路产生抑制作用,对β-catenin表达未产生明显改变。外源性SOST对于BMP存在反馈性的负向调节作用。压应力下SOST对OCCM-30的矿化功能是抑制的,其机制或许是一方面利用BMP信号通路对成骨相关因子Runx2、OCN、BSP等实现下调,另一方面提高了与破牙骨质有关分子 RANKL/OPG的比率。     

SY-28、SY-20和MDX4-4210硅橡胶机械性能的对比测定

目的:对比SY-28、SY-20和MDX4-4210硅橡胶的机械性能。方法:以MDX4-4210硅橡胶为对照,对SY-28、SY-20硅橡胶扯断强度、扯断伸长率、永久变形率(3分钟)、撕裂强度、硬度(邵氏A)进行测试,对其机械性能加以评价,并进行统计学分析。结果:SY-28硅橡胶的扯断伸长率、撕裂强度和邵氏硬度优于MDX4-4210硅橡胶;扯断强度和永久变形率与之相似。SY-20硅橡胶的邵氏硬度优于MDX4-4210硅橡胶;扯断强度、扯断伸长率、永久变形率和撕裂强度与之相似。结论:①SY-28、SY-20硅橡胶可以满足颌面软组织缺损赝复材料的机械性能要求。②在硬度上,SY-28硅橡胶适合用于耳、鼻等缺损的修复;SY-20硅橡胶适合颌面部软组织缺损的修复。③应用硅橡胶并用技术弥补现有硅橡胶的性能缺陷,可以获得更适合临床应用的硅橡胶赝复材料。     

Laboratory strength of glass ionomer cement, compomers, and resin composites

PURPOSE: The study evaluates the compressive, flexural, and diametral tensile strengths of 8 core build-up materials from different material classes (highly viscous glass ionomer cement, autocured resin composite, and compomers). MATERIALS AND METHODS: All materials were manipulated according to the manufacturers' recommendations for use as core materials. At a temperature of 23.0 +/- 1.0 degrees C the properties of compressive, diametral tensile and flexural strength were determined using a universal testing machine at 15 minutes, 1 hour, and 24 hours after material preparation. Using one-way analysis of variance (ANOVA), multiple mean value comparisons were performed to determine significant differences (p< or =.05) between the core restoration materials. RESULTS: The values for compressive strength varied from 40.3 +/- 5.2 MPa (compomer) to 237.4 +/- 37.3 MPa (autocured resin composite) for the 3 measurement times. At 15 minutes, 1 hour, and 24 hours after first mixing, the ANOVA showed significant differences (p < or =.05) between the resin composite Core Paste and all of the other materials. Diametral tensile strengths ranged from 5.5 +/- 1.1 MPa for glass ionomer cement to 39.1 +/- 2.9 MPa for composite core material. Three-point flexural strength showed values ranging from 12.1 +/- 2.5 MPa for glass ionomer cement to 92.1 +/- 9.7 MPa for compomer between the 3 measurement times. CONCLUSIONS: Setting time influences the mechanical properties of the materials tested in this study. Autopolymerizing resin composite Core Paste demonstrated greater compressive and flexural strengths at the 3 measurement times than the other materials tested. Reinforced composites, in comparison to the autocured resin composites, yielded no improvement in tensile strength. Flexural and tensile strengths of the glass ionomer cement were lower than those of autocured resin composites and compomers.     

聚氨酯凝胶预聚物对传统树脂基质体积收缩的影响及对其综合性能的改善作用

合成一种光反应性聚氨酯（PU）凝胶预聚物IBGBMA,并探讨其对传统树脂基质体积收缩和机械性能的影响。     

基于雷泰医疗多模态智能直线加速器VenusX的验收测试

目的对雷泰医疗新型推出的医用直线加速器VenusX的各项技术指标进行临床验收测试,评估其临床应用的精确性、有效性及安全性。方法参考国家相关标准规定与方法,对VenusX的辐射安全、机械精度、射束性能及影像系统进行质量检测与评估。结果各项技术指标均符合相关标准要求:辐射安全项目正常有效;等中心大小0.5 mm、机架旋转角度0.3°、数字化光距尺精度1 mm、治疗床旋转角度0.5°、治疗床各方向误差≤1 mm,光栅叶片到位精度和重复性优于标准;剂量稳定性优于相关标准;MV-EPID中心到位精度0.4 mm、到位重复性精度0.2 mm、摆位精度0.5 mm;kV-EPID中心到位精度0.3 mm、到位重复性精度0.2 mm、摆位精度0.1 mm。结论VenusX作为一款国产多模态智能医用直线加速器,各项参数指标优于验收标准,证明其设备安全性、精确性和有效性均符合国家相关标准并满足临床要求。