Browse Articles

The article presents the technology and process, whereby a small-scale demonstration model and the real-scale prototype of vertical axis wind turbine blades are produced using rapid prototyping technology (3DP) and GFRP surface coatings, which help to improve the mechanical properties. In the end of the article the results of the production process and the advantages of combining these technologies are presented.

Explaining the phenomena occurring at the level of relative friction surfaces has become increasingly complex and often contradictory. Research over time has shown that the friction coefficient for a friction coupler is not a constant magnitude, as Amonton-Coulomb has stated, its values being dependent on a multitude of factors (normal load, slip rate, the nature of the material, the state of lubrication, etc.). The laws of the two are considered to be valid only under conditions of dry rubbing and elastic deformation of the surfaces in contact. The present paper proposes in the first part a study on the theoretical expression of the coefficient of friction. The experimental part of the paper highlights the variation of the coefficient of friction with the speed, loading and processing of the contact surface. It was made on a tribological stand of pin / disc type, and the coupler used was polymeric material called Turcit (for disc) / general purpose steel (for pine).

The aim of our study was to evaluate fracture resistance of the PMMA complete dentures and to make a comparison between the classic acrylic maxillary complete dentures and the metal-reinforced ones, in terms of fracture resistance during function and to compare the fracture pattern of the two groups of complete dentures. We used maxillary complete dentures made of heat-processed acrylate, 5 exclusively and 5 in which a metal-cast net in the form of a mesh was inserted after being casted, worn by patients for a period of 5 years. A bilateral progressive force was applied to the PM2-M1 area until the samples failed, recording the force value at which the first change occurred. A Universal Loading Machine was used. The results were analyzed using the ANOVA method. For the classic acrylic complete dentures group, the minimum fracture force value was 1060 N, the maximum fracture force value being 2443 N. For the reinforced complete dentures group, the minimum fracture force value was 3320 N, the maximum value being 3760 N. Statistical analysis of data using the ANOVA shows that the results are statistically relevant, with a p value of 0.000137 (p[0,05). All the dentures from the classic acrylic complete dentures group fractured presenting two or more fracture lines, most of them involving also fractures on the acrylic teeth and breaking into multiple pieces, while all the dentures from the reinforced complete dentures group fractured presenting one or two fracture lines, most of them without detachable fragments and involving also fractures on the acrylic teeth.

FDM is 3D printing technology using mainly PLA and ABS as filament materials. PP has close characteristics to PLA and, due to that, is a potential material for for deposition. Paper aims to analyse the behaviour of PP during heating cycle specific to 3D printing process. Macroscopic and microscopic analysis of the deposited strings have been performed. They revealed less stiffness of the PP deposition comparing to PLA, which is due to the lower viscosity of PP. DSC Thermal analysis has been done at it revealed a 30% higher heat flux in PP comparing to PLA and that increases its fluidity. It was recorded a difference between the elongation viscosity of the PP filament and the PP deposited by FDM process. After 5s the deposited PP proves higher values for the elongation viscosity. Dynamic shear rheology measurements the was applied on samples deformed under 210 kN at 190oC. It has been found that the PP requires lower storage energy and that means that it has a lower viscosity for the entire range of applied frequencies. In the same time, the complex viscosities prove different behavior. To improve the control of the deposition shape, it is necessary to reduce the extrusion temperature with 4-5%. That leads to economy in power consumption.

PLGA (poly-lactic-co-glycolic acid) nanoparticles represent an important synthetic biocomponent that has the potential to be a promising carrier of drugs, proteins, nucleic acids, due to its biodegradability and minimal side effects. The aim of our study was to observe the antioxidant effect of vitamin E loaded in PLGA nanoparticles administered over a period of 3 weeks in Wistar rats treated with a hypercaloric diet. Glutathione (GSH) and malondiadehyde (MDA) biomarkers determined from liver lysate were analyzed to evaluate the oxidative stress (OS) induced by the hypercaloric diet. The results of our study revealed a statistically significant increase for GSH and vitamin E in group 2 of Wistar rats receiving hypercaloric diet and a daily dose of vitamin E versus group 1 (p[0.005). The antioxidant effect of vitamin E was also observed by the statistically significant decrease of MDA in group 2 of Wistar rats compared with group 1. The daily dose of vitamin E has improved the liver redox status of group 2 Wistar rats.

The paper presents an analysis regarding the use of ERTALON 4.6 polyamide in high thermal shock systems. The behavior of ERTALON 4.6 polyamide mounted on high thermal shock systems was studied using high speed thermal imaging cameras. In the same time its mechanical proprieties were studied with the purpose to determine if it can withstand the stresses that occur during rifle firings.

Treatment of crown root fracture is complex and requires an accurate diagnostic and treatment plan. The purpose of this article is to report a case of a maxillary central incisor with a crown-root fracture with pulp exposure treated and rehabilitated with the preservation of pulp vitality using a micro-pulpotomy and pre-mixed bioactive endodontic cements followed by zirconia restauration, a bioinert ceramic material, milled using CAD/CAM technology. The preservation of pulp vitality using premixed bioceramic materials, ensures the continuation of dentinogenesis with its benefits, higher resistance of radicular walls against fracture, smaller diameter of apical foramen as well as creating conditions over time for a post retained crown with better aesthetic results.

The thermochemical stability of a MOL (mineral oil) electroinsulating mineral oil was studied by the gas chromatography technique, compared with a Voil (vegetable oil) electroinsulating fluid based on natural esters (oil), exposed to a longer (1000 hours) thermal treatment (110 ± 5 °C) in contact with the core transformer plate (silicon steel sheet) both blank and covered by immersion with three different types of lacquers (L-G epoxide, L-528 alkyl epoxy-melamine copolymer and L-S polyurethane). Experimentally it was noted that during the thermal treatment applied and in contact with the silicon steel sheet, the investigated oils have produced mainly C2H4, CH4 and H2. The total amount of flammable gases formed in Voil (vegetable oil) is about 7.5 time lower than in MOL. It has also been found that the lacquer coating of the silicon steel sheet does not change the mechanism of gas formation processes in the investigated oils, as well as the fact that the oxygen content of the investigated oils decreases monotonously during the thermal treatment applied due to either the formation of CO2 and CO and the oxidation processes of investigated lacquers.

The article presents a promising technology for medical applications - additive technology by thermoplastic extrusion. Some conceptual models for knee prostheses of different constructional forms have been made using FDM technology. Different materials, including biocompatible, were considered and different 3D printing equipment was used to choose the variant with the most optimal characteristics. These conceptual models can have various beneficial applications in medicine, improving the quality and functionality of personalized prostheses.

Periodontal diseases are inflammatory diseases that cause lesions of the dento-periodontal system and can even lead to the loss of teeth. A successful treatment of periodontal diseases includes procedures aimed at reducing inflammation, by mechanical and chemical means, which have the role to decrease the pathogenicity of microorganisms found in the bacterial plaque. The study was conducted on a group of 50 patients, of whom a control group of 25 patients followed conventional periodontal treatment, while the other 25 patients received magnesium-terpene therapy by using polymeric thermoforming mouth custom trays, along with conventional periodontal treatment. The statistical and clinical assessment of the study revealed the efficiency of the magnesium-terpene active gel for the treatment of periodontal disease.