Effects of ceramic shade and thickness on the micro-mechanical properties of a light-cured resin cement in different shades

Abstract

Objective. The aim of this study was to evaluate the micro-mechanical properties of a light-cured resin cement in four different shades when polymerized through a leucite-reinforced glass-ceramic in different shades and thicknesses. Materials and methods. A light-cured resin cement in four different shades (HV+1, HV+3, LV-1 and LV-3) was selected for this study. The specimens were cured by using a LED-unit (Bluephase®, IvoclarVivadent) for 20 s under a leucite-reinforced glass-ceramic (IPS Empress® CAD, IvoclarVivadent) in two different shades (A1 and A3) of different thicknesses (1 and 2 mm). Specimens cured directly, without an intermediate ceramic, served as control. The specimens were stored after curing for 24 h at 37°C by maintaining moisture conditions with distilled water. Micro-mechanical properties (indentation modulus, E; Hardness, HV; creep, Cr) of the resin cements were measured with an automatic microhardness indenter (Fisherscope H100C, Germany). Twenty groups were included (n = 3), while 10 measurements were performed on each specimen. Data were statistically analyzed by using one-way ANOVA and Tukey’s post-hoc test, as well as a multivariate analysis to test the influence of the study parameters. Results. Significant differences were observed between the micromechanical properties of the tested resin cements (p < 0.05). The resin cement shade showed the highest effect on the micromechanical properties (Partial-eta squared (η_P²)-E = 0.45, η_P²-HV = 0.59, η_P²-Cr = 0.29) of the resin cement, followed by ceramic thickness (η_P²-E = 0.38, η_P²-HV = 0.3, η_P²-Cr = 0.04) and ceramic shade (η_P²-E = 0.2, η_P²-HV = 0.26). Conclusions. Resin cement shade is an important factor influencing the mechanical properties of the material. Light shades of a resin cement express higher E and HV as well as lower Cr values compared with the darker ones.     

Development of a new niobium-based alloy for vascular stent applications

This study was performed in order to develop a new stent material that would provide reduced MR image artifact compared to current stent materials. Alloy design rationale is initially presented and following this the development of a Nb–28Ta–3.5W–1.3Zr alloy is described, including the manufacture of stent tubing. Tensile testing of this new alloy showed that it had approximately twice the yield strength of current Nb–1Zr material with a 25% higher elastic modulus. The new alloy was also confirmed to have suitably low magnetic susceptibility. Mechanical testing of demonstration coronary stents made from the new alloy were shown to have acceptable compression strength and elastic recoil performance. It is concluded that this new Nb–28Ta–3.5W–1.3Zr alloy is a practical candidate stent material for both coronary applications and peripheral uses such as carotid or intracranial stenting, where reduced MR image artifact would be beneficial.     

Tensile properties of human knee joint cartilage: I. Influence of ionic conditions, weight bearing, and fibrillation on the tensile modulus

The flow-independent (intrinsic) tensile modulus of the extracellular matrix of human knee joint cartilage has been measured for normal, fibrillated, and osteoarthritic (removed from total knee joint replacements) cartilage. The modulus was determined in our isometric tensile apparatus and measured at equilibrium. We found a linear equilibrium stress-strain behavior up to approximately 15% strain. The modulus was measured for tissues from the high and low weight-bearing areas of the joint surfaces, the medial femoral condyle and lateral patello femoral groove, and from different zones (surface, subsurface, middle, and middle-deep) within the tissue. For all specimens, the intrinsic tensile modulus was always less than 30 MPa. Tissues from low weight-bearing areas (LWA) are stiffer than those from high weight-bearing areas (HWA). The tensile modulus of the ECM correlates strongly with the collagen/proteoglycan ratio; it is higher for LWA than for HWA. Osteoarthritic cartilage from total knee replacement procedures has a tensile stiffness less than 2 MPa.     

Structural and mechanical remodelling of the common bile duct after obstruction

Biliary obstruction in man, most often caused by cholelithiasis, induces remodelling of the bile ducts. Obstruction-induced structural remodelling of the common bile duct (CBD) has been previously described. The mechanical changes that accompany the structural remodelling, however, have not been studied in detail. The aim of this study is to quantify the structural and mechanical changes in the CBD at different time intervals after acute obstruction. The CBD was ligated in the pig, near the duodenum, and studied after 3 h, 12 h, 2 days, 8 days and 32 days (n=5 in each group). One additional animal in each group was sham-operated. At each scheduled time, the CBD was mechanically tested in vitro with a computer-controlled volume infusion system to study the pressure-volume relationship of the CBD segment. A video camera provided simultaneous measurements of the outer dimensions of the CBD at the various pressures. The diameter and wall thickness of the CBD increased about three-fold in the 32-day group compared to the sham group (P < 0.001). The circumferential stress-strain relationship differed between groups (P < 0.001); it was shifted to the right, indicating softening, in the 3-h, 12-h, and 2-day groups and to the left, indicating stiffening, in the 8-day and 32-day group, compared to the sham group. The longitudinal stress-strain curves were all shifted to the left of the circumferential stress-strain curves (P < 0.05). The collagen area increased during obstruction (P < 0.001) but no correlation between the size of the collagen area and the biomechanical parameters was found. A practical implication of the present study serves as a warning to surgeons. A reduction in the wall stiffness in the first several days of obstruction along with an increased duct diameter and a decreased wall thickness suggest that operative procedures such as suturing, anastomosis and procedures related to ERCP must be performed with special care to avoid damage to the CBD.     

实时剪切波弹性成像评价先天性肌性斜颈胸锁乳突肌

目的 应用实时剪切波弹性成像（SWE）技术评价先天性肌性斜颈（CMT）患儿胸锁乳突肌（SCM）。方法 对130例初诊CMT患儿进行二维超声检查,根据二维超声表现确定其二维分型（Ⅰ~Ⅳ型）,采用SWE测量患侧、健侧SCM弹性模量平均值（E_mean）;对患侧二维超声表现分型与E_mean进行相关性分析;运用ROC曲线计算各型的E_mean截断值。结果 CMT患儿各二维超声表现分型健侧与患侧SCM的E_mean差异有统计学意义（P<0.05）。各二维超声表现分型与患侧E_mean呈正相关（r_s=0.76,P<0.05）。利用ROC曲线获得Ⅰ~Ⅳ型E_mean截断值分别为15.35 kPa、29.60 kPa、38.05 kPa及47.80 kPa。结论 SWE技术可客观量化显示SCM硬度,评估CMT患儿胸锁乳突肌纤维化严重程度,具有较高临床价值。     

超声弹性成像技术评估卒中后痉挛研究进展

超声弹性成像（UE）为新型超声诊断技术，通过直接测量弹性模量反映肌肉硬度变化，近年来逐渐用于定量评估卒中后痉挛（PSS）程度及指导治疗PSS。本文对UE评估PSS研究进展进行综述。     

组织工程化骨修复材料的弹性模量测定及其临床意义

目的对组织工程化骨形成蛋白-脱钙骨基质颗粒-骨水泥复合材料进行弹性模量测定并探讨其临床意义。方法提取牛骨形成蛋白(bBMP)并进行成骨诱导活性测定,制备人的异体脱钙骨基质颗粒(DBM),将bBMP与DBM以1:25的质量比复合后,再与骨水泥(BC)按0:10,4:6,5:5,6:4和7.5:2.5的质量比进行复合,对所得的骨形成蛋白-脱钙骨基质颗粒-骨水泥复合材料进行弹性模量测定,并与正常人成年男性的股骨、股骨下端松质骨的弹性模量相比较。结果对测定结果进行统计学分析,含bBMP-DBM复合物75%的复合材料的弹性模量与正常成年男性股骨下端松质骨的弹性模量差异无显著性意义,P<0.01,其余各组两两比较均差异有显著性意义,P>0.01。结论含bBMP-DBM复合物75%的复合材料与成年男性股骨下端松质骨的弹性模量相接近,用其修复靠近关节面附近骨缺损可有效的防止关节的退行性变。     

脱细胞猪角膜的制备及其生物学性能观察

目的制备脱细胞猪角膜（DPC）并观察其生物学性能。方法用高渗盐溶液浸泡、低浓度酶消化、冻干的方法制备DPC。对比观察DPC、人羊膜（HAM）、兔角膜（RC）的光学特性和机械强度,阿贝折射仪测量折射率,PE分光光度计测量透射率,小型英斯特朗仪测量抗拉强度和弹性模量。结果折射率DPC为1.331 3、HAM为1.332 2、RC为1.334 0;透射率DPC为70%、HAM为72%、RC为92%;抗拉强度DPC为2.4 mPa、HAM为3.6mPa、RC为4.5 mPa;弹性模量DPC为3.8 mPa、HAM为0.78 mPa、RC为5.3 mPa。三种材料的折射率相比,P〉0.05;DPC与HAM的透射率相比,P〉0.05;三种材料的抗拉强度和弹性模量相比,P均〈0.05。结论成功制备了DPC,DPC具备与HAM相似的光学特性,DPC有其自身独特的力学特性,能耐受手术缝合。