Graphene oxide and graphite filled polyester composites were prepared by using conventional melt-mixing methods in order to improve tribological performance of polyester. It was investigated friction stability, microhardness, friction coefficient, and specific wear rate of the composites in details. It was found that the presence of graphite and graphene oxide influenced friction coefficient and wear rate of the composites. Graphene oxide decreased wear rate with increasing of test speed and graphite decreased wear rate for composite for all speeds. Tribological performance of the polyester/graphene composites is mainly attributed to bigger thermal conductivity for graphene, which can easily dissipate the heat which appears during the friction process at bigger forces. The positive influence of graphite on coefficient of friction (COF) of the composites is the result of the clivage of graphite layers during the loadings due to van der Waals weak bonds between the graphite layers.
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Materials based on acrylic resins are commonly used in dental practice. These are obtained through various technologies, which determine the chemical, physical and biological properties of the final product, which can influence the inflammatory processes in the periodontal tissue. To evaluate the effects of these materials, we identified the concentrations of TGFb1 and IL8 in crevicular fluid in 23 patients with temporary dentures made of polymethyl methacrylate by two polymerization methods: (1) a product processed immediately prior to application, wherein the polymerization of the material occurs in the oral cavity; and (2) a product processed in the dental laboratory from a prepolymerized block (block-type PMMA), and applied directly into the patient’s mouth. The results of our study revealed a significant correlation between the IL-8 inflammation marker and the clinical parameters in the periodontal tissue exposed to the polymerization of the material in the oral cavity.
This paper presents the development and characterization of polymer composites based on natural rubber, crosslinked using two types of vulcanization systems, as follows: the classical method using sulfur and curing accelerators and the method using peroxide in the presence of a polyfunctional monomer - trimethylolpropanetrimethacrylate. The composites were made with 0 parts to 100 parts rubber (phr) and 40 phr filler content. The physical-mechanical characteristics of resulting composites depend on the crosslinking method and on the composition. The mechanical parameters of materials were derived by processing the transmissibility curves, derived for samples with known dimensions and density. The main vibration frequencies and the quality factor, derived in the vicinity of resonances, allow to derive the elasticity and internal damping of materials.
The main aim of this study was to prepare and characterize polymeric nanoparticles containing two cardiovascular active pharmaceutical ingredients: valsartan (VAL) and amlodipine besylate (AML). Six formulations were evaluated with different ratios of AML:VAL:PLGA (1:16:17, 1:16:34, and 1:16:51) and different stirring speed (1200 and 2400 rpm). Encapsulation efficiency (EE, %) and particle size analyses were performed to characterize and optimize the formulation. All loaded nanoparticles showed a high EE (%), nano-size, negative x-potential and a high homogeneity.
Utilization of computer-aided design/computer-aided manufacturing (CAD/CAM) rapidly increases in dental medicine. Making of computer-engineered complete denture is based on scanning of patient data, designing of prosthesis and milling or rapid prototyping. This is digital denture, term that includes innovative devices, software programmes and corresponding materials. Industrially polymerized cross-linked polymethyl methacrylate (PMMA) is the material used for fabrication of digital denture. The aim of this study is to analyze the different cross-linked PMMA used for fabrication of CAD/CAM complete denture.
The study aimed to assess the changes of the surface roughness induced by some acidic beverages on indirect restorative materials by using profilometry. Twenty samples of three composite resins (Ceramage, SR Adoro, Luna-Wing) and three ceramics (IPS In Line, Hera Ceram, Reflex Dimension) immersed in three acidic beverages (Red Bul, wine, Coca Cola), for 5 minutes, three times daily, 14 days. The control samples were immersed in artificial saliva during the study periode. After the end of the erosive cycles and before to determine the surface roughness of the samples in the study groups, all the samples were immersed in artificial saliva for 18 hours. The surface roughness was determined in relation to the baseline surface using profilometer Perthometer_M1 (Mahr Gottingen GmbH, Germany). The immersion of the indirect restorative materials tested in the three acidic beverages lead has resulted to changes in their surface roughness. The most aggressive was wine, followed by Coca Cola, and Red Bull.
This paper presents the results of the experimental researches obtained in the three-point test of the glass-fiber-reinforced polymeric composites. Mathematical modeling of experimental results was performed using a virtual instrument (VI) developed in the graphical programming language called LabVIEW. In order to process the experimental data and display the results, the virtual instrument (VI) allows both the reading of experimental data from a saved text file from the same folder as the current VI file and the direct entry of experimental values into a control element disposed on its front panel. The virtual instrument described in this article is part of a more complex project used for the mathematical modeling of the experimental data obtained in determining the physic-mechanical characteristics of glass fiber randomly reinforced polymeric composites.
The aim of the study was to measure the goniometric differences of the knee and hip joints and the changes regarding the features of fitness balls by taking into consideration its circumference and the vertical and horizontal diameters under the action of the body weight. The outcomes of the study have resulted in the creation of a table with reference values regarding the size of fitness balls in relation to the height and body mass index of the subjects.
The present paper deals with a comparative study on the influence of two different bioplasticizers: acetyl tributylcitrate (ATBC) and LAPOL108 on the mechanical and antimicrobial properties of poly(lactic acid) PLA containing 1 wt.% chitosan. PLA based biocomposites were investigated by means of processing behavior, FT-IR spectroscopy, DSC analysis, tensile and barrier properties, migration in food simulants and antifungal activity. Based on the obtained results it can appreciated that the properties of the PLA based biocomposites could be appropriate for designing flexible or rigid food packaging depending of the bioplasticizer used.
Possible causes of microleakage and microfractures of dental fillings are often in the center of many academic research and investigations. Some authors found that one important cause of microleakage is the contraction/ shrinkage of the filling materials during polymerization. The purpose of this study is to demonstrate that microcracks and consequent microleakage is influenced by mechanical stresses occurring inside of dental filling materials and at the interface of the dental cavities and dental filling materials. We also tried to evaluate the deformation of some dental filling material types during mechanical loading. Cylindrical specimens were made of different types of dental filling materials, namely microhybrid composites and glass ionomer cement. Some extracted teeth were prepared with class II cavities, and filled. The lateral swelling of the tested specimens and the deformation of the filled teeth during vertical axial loading was measured with an optical method, ESPI/ Shearography.Of the tested specimen, the least deformable dental filling materials were the composite materials. During occlusal vertical loading of the filled teeth, there were found that mechanical stresses were different inside of the filling material than inside of the walls of the dental tissues, mechanical stressed being concentrated at the restoration interface. The ESPI/Shearography meth ode proved to be very useful for investigation in this field. Due to mechanical stresses accumulating at the interface of the dental filling material and the walls of the dental cavity, it is possible that later microcracks to appear due to masticatory forces.