Volume 51, Issue 3

Abstract: The specific parameters describing the flows of Bingham type rheological fluids through a circular pipe, under the action of a pressure gradient in the direction of the movement are established, using the Non-Standard Scale Relativity Theory approach. In such context, an analytical solution and a numerical application (for KELTAN 4200 — an etilene-co-propilene copolymer) are obtained. The friction effort has two components, one of specific fluid gliding, the other of shearing, depending on transverse speed gradient. In the central area of the fluid movements a particles agglomeration (fluid stopper) occurs, defined by a constantly moving structure. Keywords: rheology, friction effort, polymers, fluid stopper, speed

Abstract: Shape memory alloys are often used in applications where corrosion resistance property is very important. We can obtain a thin polymer layer using pulsed laser deposition on a nitinol wire with many applications in medical field. The polymer and the shape memory element with a non-metallic thin layer on the surface were analyzed by structural and chemical point of view using scanning electrons microscopy and X-ray dispersive energy analyze. Thermal insights were realized using a differential scanning calorimeter to analyze the polymer behaviour before and after deposition process. Preliminary results on the deposition set-up and the physico-chemical properties of the thin layer are presented and discussed below. Keywords: Shape memory alloys, thin polymer layer, pulsed laser deposition, PMMA

Abstract: In the following work a correlation was inferred of the effects of material behaviour in different zones of the extruder screw channel with a number of process parameters. Calculus of the average temperature variation of the processed material with length and depth of the screw channel allows effective positioning of intense mixing zones, resulting in enhanced melt thermal homogeneity and product quality. Relationships for the flow-rate of the feeding zone, the specific power and the efficiency of the extrusion process allow the overall performance calculus of the extruder. To increase process efficiency one must reduce the heat loss, Ql which results in energy savings and the decrease of thermal pollution of the environment. It becomes thus possible to replace a certain number z of actual extruders with diameter D, each with a total installed power Nt,1 and flow-rate Gm,1, with a single extruder of the same diameter D assuring a flow-rate Gm = z . Gm,1 and whose total installed power is Nt [ z . Nt,1. Heat lost through the external surface of the heating system of z extruders (z . Q1,l) is higher than that of a single modern extruder. Consequently, process efficiency in the up-graded extruder is higher than that of the extruders, resulting in diminished energy related expenses and cost of the mass unit of extruded product along with less environment pollution. Keywords: extrusion process; extruder performance; output; extruder efficiency; thermal pollution; energy

Abstract: This paper tackles a ligno-cellulosic composite, whose basic matrix is made out of hemp hurds and mineral binders, as regards the percentage participation of the hurds in the structural stability and thermal-transfer capacity, for a plate- or block-shaped product. The studies, corroborated with laboratory research, aim at ascertaining the use of these products both as lining and as filling material, in the sandwich-type structures, in civil engineering; the materials basis specific to constructions can thereby be achieved, in a wide range, in terms of the thermal-insulation capacity and, implicitly, of the energetic consumption typical of civil, industrial, agro-zootechnical engineering. Keywords: hemp hurds, mineral binders, thermal conductivity

Abstract: An important desirable effect of endodontic therapy is to induce the repair of periradicular tissues and to stimulate the cementogenesis. Endodontic perforations interfere with these goals, therefore, the discovery of an ideal material for perforations repair, with high biocompatibility, has become a necessity. The study is based on the comparative analysis of the biochemical profile of the animals implanted with three materials used in endodontics, at 7, 30 and 60 days after intervention, for Ca, P and Mg evaluation. Keywords: stomatognathic system homeostasis, biocompatibility, biochemical profile, Ca, P and Mg evaluation, biomaterials, dental treatments

Abstract: One of the aspects determining the speed rate, and therefore the economic viability, of an injection molding process is the efficiency of the heat transfer between the injected part and the mold. The quicker the temperature of the part drops below the threshold value at which it can be ejected from the mold, the sooner the mold can be closed and the injection of next part can begin. In this article is presented the solution to the highly constrained structural design optimization problem of maximizing the heat exchange surface area of the cooling system of an injection mold, an exercise aimed at increasing the speed of an existing molding system. The author described how a systematic design search via an evolutionary heuristic specifically designed for such highly constrained design problems can yield substantial increases in cooling area, while allowing the relatively straightforward implementation of the constraints that ensure the functionality of the system. Keywords: Evolutionary optimization, Injection molding process, Punctuated equlibrium, Cooling system

Abstract: Geopolymer has good bonding structure of amorphous inorganic polymer which has excellent bonding agent properties and shows high bond strength in an early stage. Therefore, inorganic material like geopolymer which have advantages in previous research and has potential in replacing the organic materials in coating application. The chemical composition of the geopolymer materials which were metakaolin, ground granulate blast slag (GGBS) and fly ash contain mostly Silica (Si) and Aluminium (Al) which were possible source material for the manufacture of geopolymer coating. Based on Si:Al ratio and water:cement ratio were the important factor in the process of geopolymer coating which Si:Al of 3.5 and water:cement ratio of 0.25 gave the best result in strength in geopolymer coating. The common techniques for coating method that have been used were brush, spraying and dipping. From previous research, coating method influenced the greater result in fire proofing materials and high temperature. For compositions with Si:Al = 2.5 the adhesive strength was > 3.5 MPa while for Si:Al=1 and 2 only weak adhesion to the metal substrates was achieved in metakaolin based geopolymer coating. Fly ash geopolymer coating has improved the compressive strength of the coatings materials as high as 40 MPa with the high sintering temperature, 1500°C. Thermal expansion measurements in metakaolin geopolymer coating of the Si:Al = 2.5 composition revealed expansion of up to 6% at 800 °C, while for Si:Al = 1 and Si:Al = 2 compositions up to 4% shrinkage was observed. Keywords: Alkali Activated Binder, coating, geopolymer, XRF, XRD, SEM

Abstract: Polyurethanes are used in many areas of bioengineering as they are biocompatible and present various mechanical properties according to the needs of each application. Necuron is a polyurethane that has been valued in many areas of industry. This paper presents compressive and three point bending testing done on three types of Necuron (840, 1020, 1300) with the purpose of evaluating its mechanical properties in order to use Necuron as a new material for transtibial prostheses. Results have shown Necuron 1300 to be a good candidate to fulfill this goal. Still there is need of further experimental programs to obtain reliable statistical information regarding the mechanical properties of Necuron. Keywords: Necuron, compression, bending, transtibial prostheses

Abstract: The aim of this study is to determine the bonding resistance of orthodontic brackets in accidental conditions i.e. bites from very hard materials which may occur in a normal activity. Many studies had been developed concerning the integrity of orthodontic systems and the strength of various pairs of brackets and adhesives in controlled conditions. In orthodontics many patients were returning to treatment, especially in the period immediately after the installation of orthodontic system as a result of failure of brackets. This failure is a consequence of patients’ natural habits on biting food despite medical recommendations. For this study bovine rib bone were used to simulate the human tooth and a certain pair adhesive-bracket. Pretests were developed in order to identify the behaviour of organic material and the results were satisfying. Unlike other studies in this study the shear resistance of the adhesive was analyzed using an universal testing machine with a load on the bracket. Since the study concerns with accidental detachment of the bracket the experimental parameters were set as close to the natural conditions. The results are encouraging the development of further studies on various pairs adhesive-bracket using bovine bone as human teeth simulator since its results are fitting data reported by other authors following numerical or empirical studies on human teeth. The use of bovine bone ensures the reproduction of the tests without having the care of teeth collection. Keywords: orthodontics, adhesive, bracket, shear strength

Abstract: The aim of this study is to analyze the stress generated by the shrinkage of lutting materials in restorative therapy with indirect composite inlays; we follow the way of the tension transmission from the lutting material to the restoration and to the dental tissues. In our study it was used a virtual construction of an upper first molar, created with the Finite Element Method. Our conclusions demonstrate that the shrinkage of the lutting resin influence the fracture resistance of the restored teeth, and, of course, the longevity of the indirect inlays. Keywords: indirect inlays, composite shrinkage, polymerization stress, prosthesis structure, dental treatment

Abstract: Removable partial dentures are widely and successfully used in the rehabilitation of partial edentulous patients. These types of dentures can be made from PMMA (poly methyl methacrylate resin) or polyamides, both types of materials having their advantages and disadvantages. Evaluation of these removable partial dentures is accurate only if are considered all the parameters. Computer-Aided Engineering (ANSYS) software is used with a 3D Computer-Aided Design (3D CAD) solid geometry and simulates the behaviour of solid bodies under thermal or structural loading conditions. ANSYS automated the Finite Element Analysis (FEA) technologies and deliver the results listed. All considered criteria materialized by Numerical Simulation concept serve as guides for a qualitative evaluation of known design requirements. Keywords: PMMA, ANSYS, 3D CAD, FEA

Abstract: The aim of this study was to evaluate the effects of one in-office and two home bleaching agents on the surface roughness of a hybrid, microhybrid and nanohybrid composite resin. Three composite resins (Valux Plus, 3M ESPE, Filtek Z 250, 3M ESPE, and Herculite XRV Ultra, Kerr) and three bleaching agents (Opalescence PF, Ultradent Products, Perfect Bleach, Voco, and Perfect BleachOffice +, Voco) were chosen for this study. Twenty eight samples of each composite resin were prepared and were equally split in 4 groups: 7 samples were stored in distilled water (control group), 7 samples were subject to 17% carbamide peroxide gel (Perfect Bleach) action for 3 h a day, 7 days, 7 samples were subject to 15% carbamide peroxide gel (Opalescence PF) action for 3 h a day, 7 days and 7 samples were subject to 35% hydrogen peroxide gel (Perfect BleachOffice +) action two times for 15 min . After cleaning the samples were submitted to roughness evaluation using atomic force microscopy (AFM). Bleaching agents that contain 35% hydrogen peroxide and 17% or 15% carbamide peroxide increased the composite resins surface roughness. The hybrid resin recorded the highest roughness after bleaching, followed in descending order by microhybrid and nanohybrid composite resins. Keywords: bleaching agent, composite resin, roughness evaluation, carbamide peroxide, atomic force microscopy

Abstract: The aim of the present paper was to investigate the chemical corrosion in various solutions, of a commercial resin based restorative nano-filled composite. 20 samples of a nanocomposite Filtek Supreme XT (3M ESPE) were immersed for 30 days in Ringer (physiological solution), Fusayama artificial saliva, and Afnor artificial saliva. After that, they were examined by scanning electron microscopy and energy-dispersive X-ray spectroscopy. It resulted that the corrosion is mainly due to the pitting, micrometric holes being observed. Also, preferred directions of corrosion resulted, as consequence of micro-scratches formation during the samples preparation. The oxygen content generally increased due to the oxides formation, while carbon, silicon and zirconium normalized atomic percents decreased, showing the corrosion both of the polymeric matrix and of the filler particles. Micro-holes size statistics revealed quantitatively the degree of corrosion and agrees well with the changes of chemical composition. Keywords: nanofilled composite, pitting corrosion, artificial saliva

Abstract: The aesthetic composite inlay or ceramic ones are useful for restoring posterior teeth affected by decay processes. The choice of the inlay type can sometimes be a challenge for the dentist. The aim of this study is to identify the optimal type of an inlay used for second-class cavities that can assure a good long-term prognosis of dental restoration. In order to achieve this study, it was performed a 3D analysis of stresses recorded in a premolar restored with a composite inlay and a ceramic inlay, the simulation being done by finite elements method (FEM) using ANSYS program. The study results showed that stresses registered in the tooth restored through ceramic inlay are more favourable than those recorded in the case of the tooth restored with composite inlay. Keywords: dentistry, restoration, FEM, composite material, tooth-restoration

Abstract: Facial epistasis represent facial prosthetic components made of acrylic or silicone plastics, which have no other function than to rebuild the lost region of the face in order to partially restore the physiognomy. A mandatory step in the manufacturing process of epistasis is represented by fingerprinting the tissue defect and the entire facial region and making a study model as basis for designing the epistasis . Keywords: facial episthesis, prosthetic components, acrylic or silicone plastics

Abstract: Metal-composite crowns or metal-polymeric crown are an intermediary option from the mechanical and esthetical characteristics between acrylic resin and ceramic materials. Same as in the case of other types of fix partial dentures, the esthetic veneer may present fissures or fractures. The replacement of a fix partial denture is time consuming and involves high costs. In specific clinical cases, the metal-composite fix partial dentures can be repaired with plastic materials like diacrylic composite resin. Metal-acrylic and metal-ceramic fix partial dentures can also take advantage of the diacrylic composite resin in similar situations- fracture. The repairing maneuver can be considered temporary for a longer period of time. The key of reparation’s success is the interface integrity between the two materials. Imagistic investigation methods, like Atomic Force Microscopy gives important information about the surface roughness of different materials. The purpose of the present study is the investigation of the new interface obtained after the direct reparation of metal-composite crowns with diacrylic composite resins. Keywords: crown, acrylic resins, ceramic materilas

Abstract: This paper is about obtaining polyolefin composites with antibacterial properties for the manufacture of hollow blown bodies (vials, bottles, jars) used for the packaging of medical products, cosmetics and food. As main polymer, it was used polypropylene, and as biocide active agent, it was used silver chloride deposited on a support of titanium dioxide or of silica. Antimicrobial silver was added as a premix, using for this purpose the co-polymer ethylene-1-octene. Hollow bodies were obtained by extrusion-blowing and were tested for their mechanical properties and biocompatibility. Keywords: polypropylene, co-(ethylene-1-octene), hollow blown bodies, extrusion

Abstract: The utilization of waste rubber powder in polymer matrices provides an attractive strategy for polymer waste disposal. In this study lead free composite material samples for anti– radiation purposes were produced. To attain this goal, 15 wt. % of recycled acrylonitrile-butadiene rubber (NBRr) were added to Naturalrubber (NR) to prepare the composite’s matrix part. Then the matrix was incorporated with various hard materials wastes such as iron particulates, iron fillings and slags brought from different industry zones. The amounts of the added particulates were ranged from 15–75 wt%. All fabricated samples were assessed for their anti-radiation attenuation properties. The attenuation measurements were performed using gamma spectrometer of NaI (Tl) detector. The utilized radiation sources comprised 137Cs and 60Co radioactive elements with photon energies of 0.662 MeV for 137Cs and two energy levels of 1.17 and 1.33MeV for 60Co. Likewise theHalf-Value Layer (HVL) and the mean free paths (Mfp) for the tested samples were obtained. The aim of this work is to investigate the effects of the waste loading rates, the particulate types and their dispersive manner within the rubber blends on the attenuation coefficients. The maximum linear attenuation coefficient (m)was attained for rubber incorporates iron particulates wastes of 65 wt. %. They were of 0.0510± 3.2123 ×10-3for 137Cs and 0.0346± 6.973×10-3and 0.0182±1.297×10-3 for 60Cofor the energies of 0.662, 1.17and 1.33 MeV respectively. A Significant improvement of attenuation performance was achieved by 25%–30% for rubber samples incorporate iron particulate. The tested samples were examined using different techniques, metallographic facilities, optical microscopy, scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR) Spectroscopy, and hardness and measurement facilities. The microstructure, homogeneity, particulate dispersion, porosity and structure defects, and the mechanical properties of the fabricated samples were studied and evaluated. Keywords: Attenuation coefficient, radioactive, wastes iron filings, NR/NBRr blends, SEM, NaI (Tl), steel slag

Abstract: This paper is aimed to the identification of the plastics used in the insulation of the conductors and the electrical cables and depending on their characteristics , the influence exercised on power losses in the dielectric of the cables . Solid organic synthetic insulating materials that are used in electrotechnics , represents a sensitive group larger than natural materials . According to current statistics , it is clear that solid synthetic materials are implemented in a majority share in achieving equipment and electrical installations insulation being in the configuration of generation, transmission and distribution of electricity systems. Keywords: plastic , polyvinylchloride , insulation, electrical cable , thermal stability

Abstract: During the daily activity the orthodontic systems are suffering various loadings which together with saliva lead to a depreciation of bonding material which is used to fix the brackets on the dental surfaces. For this study human incisive shaped bovine bone were used to simulate mastication in a media consisting in a mixture of sesame, poppy and sunflower seeds and water. The aim is to compare the shear resistance of the bond with the one evaluated for fresh mounted brackets. Also a qualitative analysis is aimed based on micro photos took before and after bracket debonding. There are not rare the cases when patients are returning to doctor immediately after orthodontic system installation despite the medical advice because it is almost impossible to inhibit natural habits developed. In the first period after the installation of the orthodontic systems the reflex of biting the food is present in all the cases and that produces the detachment of the incisive bonded brackets. However during the mastication components of the food are interacting with the brackets generating local loads over the brackets themselves and also over the bonding material which can be a polymer or a composite. These loadings together with the ones meant by the doctor are producing in time small fractures and cracks at the bonding level with consequences on shear resistance of brackets on the tooth. Keywords: orthodontics, adhesive, bracket, shear strength

Abstract: To achieve a modeling of the epithesis as close as possible to the lost organ, information on its size and shape can be registered by using computed tomography and 3D reconstruction. This paper aims to investigate to what extent the recording geometry of facial regions using computed tomography and identify on the sections of computed tomography the contour of the region to be reconstructed for virtual modeling of future silicone epithelium can be achieved. The results were obtained by applying the algorithm described in C + + program and contour detection in computed tomography images recorded preoperatively in patients who were to receive resection surgery of a facial region followed by reconstruction of the defect by facial epithesis. Keywords: acrilic resins, contour detection

Abstract: The poly (vinyl butyral)/silica (PVB/SiO2) composite fibers were produced by the electrospinning process. The experiments were performed with the PVB solution in concentration of 10 wt.% where ethanol was used as the solvent. The silica nanoparticles were added into the solution in different content of 1, 3 and 5 wt.% SiO2. The PVB fibers with 50 wt.% SiO2 nanoparticles were deposited on p-aramid fabrics which were coated with PVB solution. The effect of the processing parameters on the morphology of PVB/SiO2 composite fibers was analysed. Mechanical properties of the p-aramid fabrics were tested by dynamic mechanical analysis (DMA). Keywords: electrospinning, electrospun composite fibers, silica nanoparticles, p-aramid fabrics

Abstract: Polyelectrolyte multilayers composed of chitosan and poly(acrylic acid) were constructed onto silicon wafers from solutions of different concentrations of polymer and NaCl. To modulate the film properties, the multilayers were subject to three post-treatment strategies: (i) immersion in an aqueous solution with pH = 2.4 for 1 min, followed by a 15 s immersion step in water and drying at 80 oC for 60 min; (ii) immersion for 30 min in water and (iii) immersion in an aqueous solution with pH = 2.4 for 5 min, followed by immersion for 1 min in water and thermal treatment at 120 oC for 60 min. The changes of the film morphology, thickness, and wetting state as a function of deposition conditions and post-treatment strategies used were followed by atomic force microscopy, spectroscopic ellipsometry and contact angle measurements. Keywords: polyelectrolyte multilayer; chitosan; poly(acrylic acid); post-treatments

Abstract: The purpose of this study was to evaluate colour changes of aesthetic fixed prosthetic restoration materials, when these materials are exposed to a drink rich in colorants, in this case, cola, coffee and red wine. For the study were required 18 fixed partial dentures: 6 integral polymeric dentures, 6 metal-polymeric dentures and 6 metal-ceramic dentures. To verify the colour there were used: VITA EASYSHADE spectrophotometer and the VITA shade for ceramic restorations. Following the results obtained, it was concluded that prosthetic composite resin changes quickly their colour, compared to the ceramic. Also, the liquid that affect the most in changing the colour of this material is coffee. Keywords: composite resin, colour change, aesthetic restorative materials

Abstract: Polysomnography is a new and innovative test used for the diagnosis of sleep disorders. It offers the possibility to identify and to early treat important diseases which can lead sudden to death in children and adults too. The portable monitor simplifies the procedure and it permits to monitor the patients at home. Obesity is the most powerful and the only reversible risk factor for obstructive sleep apnea. This condition is one of the most serious problem of the 21st century. It can appear like common obesity caused by an increased food intake and it is also part of some rare genetic syndromes. Prader Willi Syndrome is a genetic disorder caused by an abnormality on the 15th chromosome. It is the most common known genetic cause of life-threatening obesity in children. The study aims to describe sleep disorders in patients diagnosticated with this genetical syndrome. The evaluated patients associated a characteristically phenotype for Prader Willi Syndrome with unrest sleep and they had no treatment before. A high number of obstructive sleep apneas and rapid eye movement sleep alteration was registered. Breath and cardio-vascular pathological changes were also identified. Large fluctuations in heart rate and relatively long duration of low oxygen saturation was threatening patients life and nasal continuous airway pressure was needed in order to reverse respiratory and cardiovascular symptoms. Keywords: polysomnography, obstructive sleep apnea, sleep disorders, Prader Willi Syndrome

Abstract: Dental composite resins already have a history and a vast use in dentistry. In vivo and in vitro research gave precise directions and indications but the tests are not completely relevant. Different clinical parameters cannot be reproduced by in vivo and in vitro research. The evolution of dental materials leads to the use of nano materials. For the present study, were used human extracted teeth on which were prepared class I cavities. For half of the samples had been used normal adhesive and composite resin and for the second group was used nanomaterials- a ferric nanoparticles modified dental adhesive was used and then filled with the same resin composite material. The interfaces generated by hard dental tissue and classical adhesive and adhesive made from nano-particles were investigated through micro-CT imagistic investigation method. With the software VGStudio MAX the 3D reconstruction of the constituents were made. Micro-CT using the synchrotron technology and 3D reconstruction offers important details and of high quality of investigated area. All the samples were imagistic investigated through, X-ray, SEM and EDAX technologies. Each investigation method spotted the defects of the investigated area according to its limitation. Keywords: composite resin, dental adhesive, feeric nanoparticles, micro-CT, X-ray, SEM, EDAX

Abstract: This article presents a benchmark between Dissipative Particle Dynamics (DPD) thermostat and Standard Molecular Dynamics (MD) simulations for three different systems: a water cube, a small dipalmitoylphosphatidylcholine (DPPC) bilayer in water, and a large DPPC bilayer in water. The DPPC phospholipids’ molecule consists of a hydrophilic head and two hydrophobic tails. The molecular dynamics simulations results for the three above systems as function of number of cores are shown. Keywords: molecular dynamics, thermostats, friction

Abstract: The paper describes the components of an artificial intelligence based system intended to control the manufacturing processes of composite materials with polymeric matrix. Based on previous results in which neural networks were trained initially with simulated data and then continued to acquire experimental values over Internet for refining their knowledge, the system includes updated state-of-the-art data acquisition components, improved statistical data processing capabilities and the ability of real-time controlling the manufacturing equipment. Keywords: composite materials, polymeric matrix, artificial intelligence