Volume 52, Issue 2

Abstract: In this paper, the elasto-plastic and viscoelastic properties of two grades of polyethylene are investigated by cylindrical macro-indentation. Indentation tests, including relaxation tests, are performed with a cylindrical indenter having a flat-tip diameter of 1 mm. The bulk properties, such as the indentation modulus and the yield stress, are extracted from the indentation stress-displacement curves. The indentation relaxation data of polyethylene are analyzed using the steady-state creep model and the generalized Maxwell model. Based on experimental data and the Prony series model, equilibrium stress, relaxation ratio and relaxation time are determined, while the creep exponent and the characteristic relaxation time are estimated using the steady-state creep model. Keywords:cylindrical macro-indentation, relaxation tests, steady-state creep model

Abstract: Recently, there is market need to develop technologies focused on manufacturing custom and unique parts. Additive Manufacturing technologies create geometrical parts layer by layer and satisfy this necessity. In this article we try to establish a set of rules to be followed in FDM - Fused Deposition Modeling 3D printing process using ABS (Acrilonitril-Butadien-Styren) type plastic materials. The objects have been printed on a 3D “Ultimaker –2” printer. ABS (Acrilonitril-Butadien-Styren) filament was used to print the objects. The article also refers to printing constraints generated by the machine work load limitations and the extruded material. Keywords: Acrilonitril-Butadien-Styren, Fused Deposition Modeling, 3D printing

Abstract: The paper presents the results obtained by the authors in the research of the mechanical behaviour variation of the polymeric reinforced with protein fibers composite (CFP) depending on the reinforcing material concentration in the elastomeric matrix. The determination of the mechanical behavior variation depending on the reinforcing material concentration is important not only to establish a convenient concentration to obtain some mechanical properties required in any field of application, but for obtaining an optimal method of choice of some values in its concentration, so that the composite material to satisfy a certain property (value) or even a number of mechanical properties. Keywords: CFP, variation, mechanical properties, reinforcing concentration

Abstract: The electrochemical characteristics of polytetrafluoroethylene (PTFE) coating produced on NiTi orthodontic wires were investigated. Electrochemical impedance spectroscopy (EIS) and linear potentiodynamic polarization (LPP) techniques in the conventional three-electrode configuration was employed to test the PTFE-coated NiTi wire during their exposure to artificial saliva. For comparative purpose the same electrochemical measurements were performed on uncoated NiTi wire. In addition, scanning electron microscopy (SEM) was employed to observe the surface morphology of both uncoated and PTFE-coated NiTi wires after LPP in artificial saliva. It was found that the PTFE-coated NiTi wire had a lower corrosion rate (corrosion and passive current density), about one order of magnitude lower than the uncoated NiTi substrates. The NiTi substrate was actually passive in these experimental conditions. The EIS interpretation was performed in two-layer model of the coated sample. The corrosion mechanism for the PTFE-coated NiTi wires arises from electrolyte penetration in the pore of the PTFE deposits. Keywords: PTFE-coated NiTi wire, artificial saliva, EIS, LPP, SEM

Abstract: The third part of the study is oriented toward emphasizing the effect of aggressive media on mechanical behaviour of orthodontic systems. As the incisive teeth are suffering the largest loads during feeding this study is focused on accidental failure of incisive-bracket systems after their use in a manner not recommended by doctors. As in the previous two articles the bovine rib is used to simulate the teeth but in this case the orthodontic systems are tested in aggressive conditions meaning the systems are employing to bite from apples considering that the apples are containing enough acids to chemically affect the bond between incisive and bracket – one hand and, on the other hand, they are enough hard peeled in order to mechanically load the orthodontic system. Another aspect concerns with the fact that apples are most eaten fruits in Romania, especially in schools, and being about kids a failure of orthodontic system caused by inattention is more probable. Forty teeth were prepared for this study and twenty of them were new while the other twenty were used before for other studies and the brackets were newly mounted. The number of bites was set after an analysis regarding the human feeding behaviour namely by considering that a normal person or a normal kid might eat three apples a day. The shear strength of orthodontic system was determined in accidental conditions if the system did not fail during the biting part of tests. Keywords: orthodontics, adhesive, bracket, shear strength

Abstract: Natural polymers, or polymers derived from living creatures, are of great interest in the biomaterials field. Collagen is the most widely found protein in mammals (25% of our total protein mass!) and is the major provider of strength to tissue. The paper presents a study regarding obtaining and characterization of biocomposite based on vinyl-acrylic copolymers as latexes and collagen polypeptides, in the following variants: blends, intermolecular complexes and interpenetrated polymeric structures. The present work discusses the results obtained on the rheological behaviour of the fluid mixtures. Regression analysis of the experimental rheological data illustrates that the latex of vinyl-acrylic copolymer is characterized by a second-order polynomial model, while the composites including collagen hydrolysates are preferentially fitted with third-order polynomial model. It has been proved the influence of the molecular weight and the concentration of collagen hydrolysate aqueous solutions on the viscosity and flowing index of polymer mixture in fluid state. Keywords: biocomposite, collagen, blends, acrylic biopolymer

Abstract: The paper presents the technological steps to obtain new electrodes, made by Cu-Zn alloy, coated with one flux layer, which may be used to welding-brazing of thin plates from ferritic steels, with applications in automotive industry. The experiments realised for elements casting, was made on induction furnace, and the production technology of experimental batch for flux coated electrodes, begins with the elaboration of the alloy and his casting. The obtained electrodes have low production costs and good welding properties. Keywords: electrodes, welding-brazing; flux; galvanized steel

Abstract: The dimensional changes of the materials used for bite registrations are critical for the accuracy of the records meant for programming the dental articulators. The purpose of this study was to determine the long-term dimensional changes of three bite registration materials. We selected two polyvinyl siloxanes and a bis acrylate-based material. The study was carried out in a semi-adjustable articulator. The data were collected by a photo camera in standardized conditions and then analyzed using an appropriate program and statistical analysis. We did not find significant long-term dimensional changes of the used materials. In the limits of this study we concluded that the polyvinyl siloxane, as well as the bis acrylate based bite registration materials are accurate enough to provide reliable records to program the semi-adjustable articulators. Keywords: polyvinyl siloxane, bis acrylate, bite registration, dimensional changes

Abstract: In this work the properties of PDLC film based on block copolymer film are presented. The FTIR; phase transition temperature properties are studied in order to see the absorption of block copolymer with the LC. Optical microscopic work showed the increase in droplet size with the increase in block copolymer contents. It is found absorption of block copolymer does not increase linearly with the increase in its contents. Moreover a decrease in refractive index is observed with the increase in block copolymer contents. The decrease in refractive index of block copolymer with temperature is interesting for thermo-optical and electro-optical devices simultaneously. Keywords: Polymer Dispersed Liquid Crystal (PDLC); Phase separation; Liquid Crystal (LC): FTIR spectroscopy

Abstract: In Pediatric practical dentistry, beside the great variety of direct dental restoration materials the dentist must take into account several factors such as morpho-structural particularities of temporary teeth, the clinical situation, physician performance, behavioural features of children and last but not least the quality of the chosen material. Thus, we investigated the behavior of glass ionomers cements in occlusal stress by determining their mechanical properties. The study aims to determine the vertical compressive strength values, which is one of the mechanical properties of filling materials, the strength of materials being useful in the research of occlusal forces exerted on the future restorations. We had used two glass ionomer cements and a resin modified glass ionomer cement, which then we have tested them to obtain comparative data of the resistance for vertical compression. Keywords: glass ionomers cements, mechanical properties, vertical compression, temporary teeth

Abstract: The computerized technologies and equipment for obtaining nanofibers impose high training, a large interdisciplinary substantiation, capacity for data storage, memorizing, easy usage, selectivity, fiability, stability, reduced time for analizing / processing of the technological parameters. That is why the computerized electrospinning equipment and technologies for obtaining nanofibers are possible candidates to carry out these requirements owing to the fact that they present both the proper selectivity / sensibility and the increased processing /determining /intervening speed by using the computerized control. This paper aims to present the operation and aplication of equipment for obtaining polimeric nanofibers by electrospinning technology. The designing and accomplishing of the suggested electrospinning equipment has been aimed to obtain a modular system which should allow the control of the technological parameters by means of the computer. Thus, the multitude of the parameters which influence the process of electrospinning, can be independently and automatically varied. The obtained nanofibers were studied by scanning electron microscope. Keywords: nanofibers, equipment, technology, modular conception, electrospinning

Abstract: Plastination suits very good for 3D reconstruction and morphometric measurements. Digital representation of anatomical features has provided a useful source of data for computer-based instructional development. The validation of 3D reconstructions and measurements needs a thoroughly knowledge about shrinkage. The aim of this paper is to determine the average slice shrinkage rate occurring during sheet plastination (E12 and P40). Fresh human brain slices for P40, pelvis slices for the standard E12 technique and a shoulder tissue block for the E12 thin slice technique were used for this study. In order to determine the shrinkage rate, the slice areas were measured before and after plastination for al samples. For the E12 thin slice technique, the shoulder tissue block was measured before and after plastination and a volumetric shrinkage rate was determined. The shrinkage rate was for P 40 technique 5.74%, for standard E12 technique 6.54% and for the E12 thin slices technique 6.23%. Therefore, plastinated slices showed a decreased shrinkage rate and fit best for research purposes. All shrinkage rates were under 10%, so we believe that every shrinkage below this value is appropriate and actually is fitted for a correct plastination procedure. Keywords: plastination, polymer E12, polymer P40, shrinkage

Abstract: The surgical approach of the skull base pathology is in a state of constant development. The advancement of the ablative techniques forced the development in the field of reconstructive surgery of the skull base as well. The goal of the reconstructive surgery of the postablative defect of the skull base is to create a stable, watertight limit between the endocranian and the sinusal cavities. New reconstructive materials and adhesives were developed. The purpose of this article is to critically analyze the use of the mixture between the polyethylene glycol ester and trilysine amine solution as a sealant and adhesive in the reconstructive surgery of the skull base. Keywords: polyethylene glycol ester, trilysine amine solution, skull base, reconstructive surgery

Abstract: Statistical copolymers N-isopropylacrylamide (NIPAM) – 5,6-benzo-2-methylene-1,3-dioxepane (BMDO) with different compositions were prepared by RAFT polymerization and characterized by 1H NMR, GPC and DSC analyses. Their solid-state thermal degradation was investigated for the first time by TGA, showing that the presence of the BMDO units within the PNIPAM chain decreased the thermal stability of the copolymer. In the case of higher BMDO content copolymers the onset decomposition temperature was lower even than that of PBMDO, and also a multistep decomposition process was noticed. The evolution of the global activation energy of the degradation process as a function of degradation conversion was determined by means of the Kissinger-Akahira-Sunose isoconversional method. Keywords: N-isopropylacrylamide; 5,6-benzo-2-methylene-1,3-dioxepane; copolymer; thermosensitive; thermal degradation; Kissinger-Akahira-Sunose isoconversional method

Abstract: Many studies are concerning with impact properties of composite materials because their large usage in aero-spatial, automotive, marine and sport industry. As the use of composites is continuously increasing the need for more valuable materials becomes essential in designing and producing such materials for a growing market. It is well known that thermoplastic matrix composites show better impact resistance than the thermoset matrix materials but their forming technology is more expensive. This study was designed to analyse the impact behaviour of fabric reinforced thermoset polymer matrix composites with an emphasis on structure of reinforcement. The matrix is an epoxy resin (Epiphen RE4020 – DE 4020, Bostik) while the used fabrics are of carbon fibres, aramid, fibres and glass fibres. Low velocity tests were performed on materials, according to ISO N-6603, and the results were inspected by tomography. Keywords: epoxy resin, fabrics, impact tests

Abstract: Obstructive sleep apnoea (OSA) is the most common sleep-related breathing disorder that is increasingly recognized as a serious public health issue. The treatment management is determined by the severity of the syndrome. Oral appliances (OAs) are increasingly advocated as a treatment option for mild/moderate obstructive sleep apnoea (OSA). The aim of this paper was to present the two main treatment solutions for OSAS through custom oral appliances made in dental laboratory and to systematically review the available studies in the literature on the efficacy of OAs. Keywords: Obstructive sleep apnea, Oral Appliances, Heat-curing Acrylic resins, Mandible advancement device, Thermoforming method

Abstract: The aim of the current study was to obtain materials presenting a large scale of applications (polyurethane adhesives and foams) through a one-pot synthesis starting from post-consumer poly(ethylene terephthalate) (PET) bottles. The PET depolymerization was carried out using diethylene glycol (DEG) and catalyst (zinc acetate) in a microwave reactor. Using the obtained depolymerization mixture, different polyurethane adhesives or foams formulations were developed. The adhesives mechanical properties were tested affording samples with tensile shear resistance suitable for commercialization. The polyurethane foams testing confirmed the obtaining of rigid structure with good thermal insulation properties. Keywords: PET, microwaves, adhesives, polyurethane foams, one-pot synthesis

Abstract: Crown preparation and wax pattern technique are two key factors for the success of a cemented restoration. A poor marginal fit is the main cause of plaque penetration and leakage of oral liquids enhancing thus caries and periodontal disease [1, 2] The present study compares the marginal fit of full metallic crowns restoring caries free extracted molars using different types of marginal preparation as well as different wax-up techniques. The marginal gap was analyzed using scanning technique with an electronic microscope before and after in vitro cementation in several points for every surface of each tooth. Data were statistically analyzed and compared. The scanning technique enhances measurements of the marginal gap without sectioning and provides an objective evaluation of preparation and cementation techniques. Keywords: scanning electron microscopy, marginal gap, crowns, wax pattern techniques, marginal preparation techniques

Abstract: The fabrication of adsorbent textile fiber materials is of great scientific and industrial interests. In this work a new procedure for fabrication of an anionic compounds adsorbent based on polypropylene nonwoven has been described. Because of using atmospheric pressure plasma as a surface specific pretreatment, the described procedure can be considered as a convenient method without affecting the bulk properties of the fibers. Atmospheric pressure air plasma was used to produce peroxide groups on the surface of polypropylene fibers. Grafting of acrylic acid (AA) was followed to create carboxyl groups on the fibers surfaces and finally the grafted polypropylene fiber samples were aminated using diethylene triamine (DETA) to convert carboxyl groups to amine groups. The effects of various experimental conditions: such as the time for plasma treatment, monomer concentration, temperature and reaction time were investigated. The surface morphology of the fibers was evaluated by SEM. To determine the nitrate and phosphate adsorption on the modified fibers, UV-VIS spectrophotometer was used. Fiber samples modified under optimized conditions showed a high ability to adsorb nitrate and phosphate ions from aqueous media. Keywords: polypropylene, Ion adsorption, Plasma treatment, nitrate, phosphate, acrylic acid

Abstract: In order to assess in vitro biomechanical behaviour of dental implants, numerous experimental methods can be used. In our experiment, we use dental implants inserted into the artificial jaws, made of ABS plastic material and Araldite D, and we chose the VIC method (Video Image Correlation), spatial version (3D), to monitor the deformation field of area surrounding implant. For both experiment types, with ABS mandible or Araldite D sheet, the results were similar and controllable. Authors are confident with this technique and hope that experimental methods will serve as a database for research in this area. Keywords: dental implants, biomechanics, ABS, Araldite D

Abstract: Hybrid inorganic/organic films composed of an polyoxometalate (POM) (iron(III)-trisubstituted Keggin polyoxomolybdates, PFe3Mo9) and a non-conducting polymer [(poly(ortho-phenylenediamine)) or a conducting polymer (poly(1,8-diaminonaphtalene)) were synthesized by electropolymerization from aqueous solution on the surface of a graphite electrodes. Cyclic voltammetry gave evidence of a redox behaviour of the PFe3Mo9, irrespective of the type of polymer used for POM immobilization into the composite matrix. Keywords: polyoxometalate, electropolymerization, hydrogen peroxide, glucose

Abstract: Renal parenchyma is served by a complex vascular-ductal system formed by renal artery (RA), renal vein (RV) and the pyelocaliceal system (PCS) continued by ureter. In the training of medical students and residents, the study of the interrelations of the elements of intraparenchymatous branches of the RA, RV tributaries, and PCS, as well as the analysis of renal corrosion casts is superior because it allows simultaneous analysis of the three vascular-ductal systems of the kidney. The present study examines the most favourable order of plastic mass injection for obtain good quality renal corrosion casts. There were used 36 kidneys from 18 domestic pigs, divided into three groups, to whom the vascularductal elements were injected with plastic (Technovit 7143), with different order of injection: the first group - with injection in order: PCS, RV and RA; the second group - with injection in order: PCS, RA and RV; the third group - with injection in order: RA, RV and PCS. Most affected by vascular compression were the renal vein and its intraparenchymatous tributaries. The most favourable order of plastic mass injection for obtain good quality renal corrosion casts by ex-situ injection is: RA, RV and PCS. Keywords: corrosion casts, pig kidney; pyelocaliceal system; renal artery; renal vein; training

Abstract: This paper presents our experiments on obtaining and characterizing polymeric composites based on wood sawdust and natural rubber. Natural rubber was crosslinked both through a classic method – using benzoyl peroxide at high temperature, and an unconventional method at room temperature – electron beam irradiation. Physico-mechanical properties such as hardness, modulus at 100% elongation and tensile strength indicate a significant improvement as a result of adding wood sawdust to blends. Better results have been obtained using crosslinking by electron beam irradiation. The crosslinking rates of samples, measured using the Flory-Rehner equation increase as the amount of wood sawdust in blends increases and as the electron beam irradiation dose increases. The swelling parameters of samples significantly depend on the amount of wood sawdust in blends, because the latter has hydrophilic characteristics. Key-words: natural rubber, wood sawdust, irradiation, physico–mechanical characteristics, crosslink density, swelling parameters

Abstract: The bond strength of the root canal sealers to dentin and core material seems to be a very important property for maintaining the integrity and the seal of root canal filling. This in vitro study aimed to evaluate and compare the bond strength of three different root canal sealers. Forty five extracted single-root human teeth were prepared using ProTaper system. Teeth were divided into three groups (n=15) for obturation using AH Plus, RealSeal and a new, experimental endodontic sealer containing hydroxyapatite. Each tooth was obturated using warm vertical condensation technique in the apical third and gutta-percha injection in the middle and coronal thirds of the root canal. All teeth were sectioned transversally at the apical and middle thirds into 1 mm thick discs. Push-out tests were performed using a universal mechanical testing machine (Lloyd Instruments – LR5k plus). The maximum load at failure was recorded and divided by the area to obtain the bond strength in MPa. Using a stereomicroscope (STEMI 2000 C Zeiss, Jena, Germany), at a magnification of 20x, the interface where the obturation failure occurred was identified. Statistical analysis was performed and the result showed non significant differences between the three endodontic sealers at each level obturation. Also, the stereomicroscopic analysis showed a good adhesion to dentin for all sealers. The experimental sealer adhesion is comparable to that of the two consecrated materials. Keywords: push-out test, bond strength, endodontic sealer, root canal obturation

Abstract: Profiled steel sheeting dry board (PSSDB) consists of steel sheeting that are connected to a dry board using self-drilling and self-tapping screw to form a light composite structure. This study focuses on PSSDB that uses 12 M geopolymer concrete infill with half-sized dry-board infill (GPCHB). The detected weakness of the profiled steel sheeting on this PSSDB system is due to the relatively easy occurrence of local buckling on its structure as it reaches an ultimate load, especially on the top flange. This study aims to analyze the relationship between stiffness and deflection at the mid-span of PSSDB systems using different parameters. Results show that the panel with 12 M GPCHB has 107% and 40% increase in rigidity compared with those of the control (without infill) and full board normal concrete panels, respectively. Mid-span deflection is also reduced to 52%. In conclusion, stiffness increases and deflection decreases when 12 M GPCHB is used in the panel. Keywords: composite structure, geopolymer concrete, weakness, local buckling, stiffness

Abstract: Film forming polymer solutions for skin wound dressing were developed and characterized. Film forming solutions were prepared by adding polyvinyl alcohol (PVA) and poly (hydroxy) urethane (PHU) in different proportions into a well tolerate volatile solvent. The formulations were in vitro evaluated according to five criteria. Two formulations have proved the ability to form polymeric film. Evaluation of the tensile strength, contact angle and swelling index were made for these formulations. The results showed a positive response of the formulations to be used for skin wound dressing. Keywords: integrity on skin, swelling index, tensile strength, surface polarity

Abstract: The challenge of the chondral lesions treatment has been considerably answered with the development of non-cellular scaffolds. Among the most frequently used, the scaffolds based on Hyaluronic Acid and, respectively, collagen derived polymers are the subject of our comparative research. The present paper highlights some particularities related to their intrinsic physical properties such as adhesiveness, microstructure and cellular permeability and concludes that the two alternatives present qualitatively similar outcome and effectiveness. Keyword: hyaluronic acid polymer scaffold, collagen scaffold, chondral lesions, osteoarthritis

Abstract: The mechanism of action and adverse reactions of 52 mg levonorgestrel-releasing intrauterine system and also level of pain during the insertion and techniques of anesthesia or analgesia for this procedure have been well documented. On the opposite pole the 13.5 levonorgestrel-releasing intrauterine system has been recently launched in Europe. To our knowledge there are no studies correlating the device design and biomaterials, mechanism of action, surgical technique and level of pain during the insertion of levonorgestrel-releasing intrauterine systems. This study was undertaken in order to determine whether there is a different level of pain during the insertion of 52 mg levonorgestrel-releasing intrauterine system compared to 13.5 mg levonorgestrel-releasing intrauterine system, considering the mechanism of action and the structural and dimensional discrepancies between the two intrauterine devices. Keywords: Levorgestrel-releasing intrauterine systems, device design, mechanism of action, level of pain during the insertion

Abstract: The liver segmentation is determined by the distribution of the vascular and ductal hepatic elements; from this, the hepatic portal vein (HPV), the central element of liver afferent pedicle, is the most important. The posterior branch (PB) is serving right lateral division (RLD) of the liver and presents the lowest morphological variability. On a total of 125 pieces of liver corrosion casts, one examined the intraparenchymal distribution of portal PB and the segmentation of RLD. Regarding the intraparenchymal distribution of the branches in the RLD of the liver, we showed four distinct morphological types: Type I (77.6% of cases) in which the PB bifurcate symmetrically in branch of segments VI and branch of segment VII; Type II (8.8% of cases) in which the PB bifurcate in branch of segment VII and an inferior branch, that bifurcate branch of segment VI and branch of segment VIA; Type III 12.8% of cases) in which the PB bifurcate in branch of segment VI and a superior branch, that bifurcate in branch of segment VII and branch of segment VIIA; Type IV (0.8% of cases) in which the PB trifurcate in branch of segment VI, branch of posterior intermediate segments, and branch of segment VII. Knowledge of these morphological types of portal PB is important for clinical and surgical practice. Keywords: corrosion casts; hepatic portal vein; posterior branch; variability; morphological typologies

Abstract: Fiber reinforced composites (FRC) are used in periodontal therapy for stabilization of mobile teeth with compromised bone support. The type of fiber and the type of composite have a great influence on mechanical properties of FRC. The specimens made of different FRC systems were subject to a three-point bending test. The results indicate that the specimens which exerted the best ratio between high deflection, low flexural modulus and medium flexural strength have the best indications to be used in periodontal therapy. Regarding the fracture pattern, the FRC recommended for splinting are those that separate in two discrete parts while maintaining an intact polyethylene fiber. This aspect allows intraoral repairs, increasing the life-span of the periodontal splints. Keyword: fiber reinforced composite, periodontal splint, three-point bending test

Abstract: The purpose of this study is to assess the effects of artificial saliva with different pH on the wearing of glass ionomer cements. We used three types of glass ionomer cements and three immersion environments. We have prepared a total of 96 samples. We used 6 artificial saliva samples for each environment. Each sample was immersed in the storage solution to a specific pH. Storage solution was changed on days 1, 7, 14 and 28. Glass ionomer cements are influenced by the storage media, showing significant changes in the case of an acidic environment (in our case, artificial saliva with different pH). As long as the material is tolerated and protected by the tooth structure, resistance to abrasion will be satisfactory. Keywords: glass ionomer cements, pH, artificial saliva, wearing