Effect of Post-Process Curing and Washing Time on Mechanical Properties of mSLA Printouts

The article discusses the influence of the post-process on the mechanical properties of elements produced with the use of the mask stereolithography (mSLA) method. Printed samples were subjected to the following post-process steps: Washing and post-curing, at various times. Then, static tensile and static bending tests were carried out, as well as Shore D hardness measurements for the inner and surface part of the sample, as well as profilographometric analysis of the surface. The post-curing time has been found to strongly affect the tensile and bending strength of printouts, and to improve their surface quality. Washing has an ambiguous effect on the strength of the printouts, but, in the end, it was found that extended washing slightly reduces the strength. Washing significantly affects the quality of the printout surface. A washing time that is too short results in a surface that strongly resembles the printing process, with high roughness. Increasing the washing time to 10 min lowers the roughness by one order of magnitude. Post-curing has also been shown to be beneficial for the cured sample with the application of shielding water. This approach results in an improvement in the flexural strength of the printouts. In general, the obtained research results indicate that, for printouts with cross-sectional dimensions of several mm, the optimal washing time is no more than 10 min and the post-curing time is at least 30 min.     

原子吸收测钡法间接测定水中硫酸盐的研究

目的研究一种快速、准确、适合大批量测定水中硫酸盐的新方法。方法利用一定量的金属钡离子在酸性条件下沉淀水中的硫酸根离子。过滤后,用原子吸收分光光度法测定过剩的钡离子,间接测定水中硫酸盐的含量。结果该法通过优化实验条件,最低检出限为10mg/LSO42-,精密度CV=16%,回收率为88%～105%,适用于硫酸盐含量在10mg/L以上,且总硬度(以CaCO3计)在100度以下的水样,与铬酸钡比色法经过对比试验,结果无统计学意义。结论原子吸收测钡法间接测定水中硫酸盐操作简便、快速、结果准确,适合大批量水样检测。     

Calcium and magnesium in drinking water and risk of death from acute myocardial infarction in Taiwan

Many studies have examined the association between cardiovascular disease mortality and water hardness. However, the results have not been consistent. This report examines whether calcium and magnesium in drinking water are protective against acute myocardial infarction (AMI). All eligible AMI deaths (10,094 cases) of Taiwan residents from 1994 to 2003 were compared with deaths from other causes (10,094 controls), and the levels of calcium and magnesium in drinking water of these residents were determined. Data on calcium and magnesium levels in drinking water throughout Taiwan have been obtained from the Taiwan Water Supply Corporation. The control group consisted of people who died from other causes and the controls were pair matched to the cases by sex, year of birth, and year of death. The adjusted odd ratios (95% confidence interval) were 0.79 (0.73-0.86) for the group with water calcium levels between 25.1 and 42.4 mg/L and 0.71 (0.65-0.77) for the group with calcium levels of 42.6 mg/L or more. After adjustment for calcium levels in drinking water, there was no difference between the groups with different levels of magnesium. The results of the present study show that there is a significant protective effect of calcium intake from drinking water on the risk of death from AMI.     

Mechanical properties of resin cements with different activation modes

Dual-cured cements have been studied in terms of the hardness or degree of conversion achieved with different curing modes. However, little emphasis is given to the influence of the curing method on other mechanical properties. This study investigated the flexural strength, flexural modulus and hardness of four proprietary resin cements. Materials tested were: Enforce and Variolink II (light-, self- and dual-cured), RelyX ARC (self- and dual-cured) and C & B (self-cured). Specimens were fractured using a three-point bending test. Pre-failure loads corresponding to specific displacements of the cross-head were used for flexural modulus calculation. Knoop hardness (KHN) was measured on fragments obtained after the flexural test. Tests were performed after 24 h storage at 37 degrees C. RelyX ARC dual-cured showed higher flexural strength than the other groups. RelyX ARC and Variolink II depended upon photo-activation to achieve higher hardness values. Enforce showed similar hardness for dual- and self-curing modes. No correlation was found between flexural strength and hardness, indicating that other factors besides the degree of cure (e.g. filler content and monomer type) affect the flexural strength of composites. No statistical difference was detected in the flexural modulus among the different groups.     

Correlation Between the Depth of Invasion and Hardness of Resected Gastric Carcinoma Specimens Using a New Ultrasound Tactile Sensor

Abstract: We assessed the objective measurement of gastric wall hardness in gastric cancer specimens with a new tactile sensor. The basic principle of measuring hardness and/or softness of living tissue is based on changes in the frequency of the tactile sensor. The change in resonance frequency, Δf=fx-fo, is the difference between the frequency of the sensor in contact with the specimen, fx, and the non-contact frequency, fo. The change in resonance frequency increases as tissue hardness decreases. We measured hardness at 5 points in 13 fresh specimens obtained by gastrectomy and analyzed the histopathological features corresponding to each point. We found that the more deeply the tumor had invaded, the harder the cancerous areas tended to be as compared to normal areas. However, the hardness of gastric cancer areas was influenced not only by the depth of invasion, but also by tumor size, the presence of associated fibrosis within the lesion, and the tumor stroma quantity. Gastric wall hardness correlated with the depth invasion of lesions less than 40 mm in size, the absence of tumor fibrosis, and medullary type tumor extension.     

Chelating agents in root canal treatment: mode of action and indications for their use

Chelating agents were introduced into endodontics as an aid for the preparation of narrow and calcified root canals in 1957 by Nygaard-Østby. A liquid solution of ethylenediaminetetraacetic acid (EDTA) was thought to chemically soften the root canal dentine and dissolve the smear layer, as well as to increase dentine permeability. Although the efficacy of EDTA preparations in softening root dentine has been debated, chelator preparations have regained popularity recently. Almost all manufacturers of nickel–titanium instruments recommend their use as a lubricant during rotary root canal preparation. Additionally, a final irrigation of the root canal with 15–17% EDTA solutions to dissolve the smear layer is recommended in many textbooks. This paper reviews the relevant literature on chelating agents, presents an overview of the chemical and pharmacological properties of EDTA preparations and makes recommendations for their clinical use.     

Association between masticatory performance and maximal occlusal force in young men

The purpose of this study was to examine the relationship between masticatory performance and maximal occlusal force in dentate subjects, using test foods of varying hardness. Subjects were 20 young males with natural dentitions. Gummy jellies with two different degrees of hardness have been used as test foods to evaluate masticatory performance. Masticatory performance was evaluated by the increase of the surface area of expectorated pieces of comminuted gummy jelly that was calculated from the concentration of gelatin. Maximal occlusal force was measured with pressure sensitive sheets (DENTAL PRESCALE 50H R type). The results suggested that maximal occlusal force had a significant positive correlation to the masticatory performance both with soft gummy jelly and hard gummy jelly. The correlation coefficient (r) with hand gummy jelly tended to be larger than with soft gummy jelly.     

Cardiovascular mortality and morbidity in seven counties in Sweden in relation to water hardness and geological settings. The project: myocardial infarction in mid-Sweden.

An east-west regional gradient in cardiovascular mortality was found within seven counties in mid-Sweden during the years 1969-1983. The mortality differences were of considerable magnitude for ischaemic heart disease (IHD) as well as for stroke. In previous reports, in which the distribution of risk factors among middle-aged men was presented, the moderate variation among the communities could not explain the mortality variation. Water hardness has previously been reported to be inversely related to cardiovascular mortality in several countries. In this paper, water samples from all 76 communities in seven counties were analysed in relation to mortality rates from IHD and stroke for men and women. Water hardness (Ca+Mg and other minor constituents), and the sulphate and bicarbonate concentrations of the drinking water were inversely related to IHD as well as stroke mortality. The water factors were also inversely related to non-fatal IHD even when account was taken of the age variation and the traditional risk factors as measured by a postal questionnaire. Variation of the water factors accounted for 41% of the variation in IHD mortality rate and 14% of the variation in stroke mortality rate over the 76 communities.     

河南汝阳县农民高血压流行病学调查 河南汝阳县农民高血压流行病学调查

1987年3月对河南汝阳县15岁以上农民5177人进行高血压流行病学调查,结果查出确诊高血压522例,高血压标化患病率为8.48%,男、女性标化患病率分别为6.38%、10.45%。同时对男性进行吸烟习惯的调查,吸烟者标化患病率为7.64%,不吸烟者为6.07%,二组间差异非常显著(P<0.01),说明吸烟是高血压的危险因素之一。但各自然村饮用水水质总硬度与其高血压患病率之间无相关现象。     

Hardness Anisotropy of Acetaminophen Crystals

The anisotropy of acetaminophen hardness was demonstrated using both Vickers and Knoop indentation hardness measurements. Based on a model of Knoop hardness anisotropy proposed by Brookes et al. (1), it was concluded that plastic flow in acetaminophen crystals occurs primarily as a result of slip in the (010)(001) system. This conclusion was corroborated with the results of the Vickers indentation tests. The apparent brittleness of acetaminophen was rationalized because only one slip system appeared to be operative. Under these conditions generalized plastic flow cannot occur, since this requires the operation of at least five independent slip systems (2). The high stress concentrations that result from flow lead to fracture. Therefore acetaminophen is more precisely classified as being semiductile. When a material deforms plastically as a result of slip in only one slip system, considerable crystal realignment can occur during compaction. This in turn can facilitate capping during decompression and ejection, since the cleavage plane, (010), would become aligned with the direction of highest tensile stress.