Volume 49, Issue 2

Abstract: The objective of this study is to compare the results obtained while determining the amount of residual monomer in three samples of acrylic resin in the first 24 hours after getting done the prostheses in the dental lab with the results of patch-tests performed on three subjects, after they have worn dentures for three months. Keywords: patch-test, acrylic resin, residual monomer, allergenic potential

Abstract: When making a denture, a removable partial prosthesis or a removable orthodontic appliance, long term preservation of structure and function require that potential irritating effects are kept at minimum. Polymer manufacturing technology with optimal properties and the material type are essential for a successful treatment. Increasing the biomechanical comportment of polymeric materials implies fiber reinforcing. The different fibers reinforcing products made very difficult the evaluation of their performances and biomechanical properties analysis. The aim of this study was to assess the quality of various polymeric materials used in dental technology and to validate the en face OCT defectoscopic evaluation of polymeric dental prostheses by using scanning electron microscopy (SEM). SEM investigations evidenced the nonlinear aspect of the interface between the polymeric material and the fiber reinforcement and materials defects in some samples. The advantages of the OCT method consist in non-invasiveness and high resolution. In addition, en face OCT investigations permit visualization of the more complex stratified structure at the interface between the polymeric material and the fiber reinforcement. Keywords: polymeric materials, defectoscopy, en face optical coherence tomography, scanning electron microscopy

Abstract: The use of fine fiber has become an important design tool for filter media. Nanofibers-based filter media have some advantages such as lower energy consumption, longer filter life, high filtration capacity, easier maintenance, lower weight compared to other filter media. The nanofibers based filter media made up of fibers with diameters ranging from 100 to 1000 nm were conveniently produced by electrospinning technique. Typically filter media are produced with a layer of fine fibers that can be used lonely or as a component in a media structure. The fine fiber increases the efficiency of filtration by trapping small particles which increases the overall particulate filtration efficiency of the structure. Improved fine fiber structures have been developed in this study in which a controlled amount of fine fiber is placed on both sides of the media to result in an improvement in filter efficiency and a substantial improvement in lifetime. In this research, regenerated silk fibroin obtained from industrial silk wastes and polyacrylonitrile (PAN) fibers was used to produce filter. Characteristics such as fibers diameter and its distribution, porosity and thickness of nanofiber filters obtained in lab were examined by Scanning Electron Microscopy (SEM) and analysed using image processing algorithms. Keywords: electrospinning, nanofilter, image processing, Fourier Transform, porosity

Abstract: Dental restoration materials act as a local irritating factor superimposed to the bacterial factors, and the inflammatory and immune response of the marginal periodontal tissue leads to replacement of the functional structures with granulation tissue that continues to grow in size, while the subgingival dental plaque is heading to the lateral and apical areas. We evaluated morphologically and immuno-histochemically the marginal periodontium adjacent to the fixed metallic-alloyed prostheses (Cr-Ni), composite resins (Cromasit) and ceramic (Vita-Ceram), but also some of the patients with periodontitis which were not associated with prosthetic devices. By the morphological analysis of the periodontal components we reported structural microscopic alterations closely correlated with macroscopic changes observed during clinical examination. We observed a direct relationship between the proportion of inflammatory infiltrate / collagen fibers according to the type of material adjacent to the periodontal tissue. By immunohistochemical evaluation we observed that regeneration and re-epithelizing process appear to be delayed by: persistent inflammatory infiltrate in the epithelial spurs, the presence of fibrinous exudate, fibro-purulent and blood cells on the surface of mucosa. Immunohistochemical investigation in marginal periodontitis watched the evaluation of the immunoreactivity in the periodontal morphological substrates toward the proliferation markers of the gingival epithelium (Ki-67), as well as the mesenchymal reactions specific to the healing process in periodontal lesions (CD -31). The morpho-pathological changes of the periodontal tissue are more profound in the presence of the dental prostheses than in the patients without any such devices and also the regenerative epithelial capacity of the damaged periodontium is more reduced in patients with prostheses than in those without. Keywords: dental materials, parodontium, imunohistochemistry, morphopathology

Abstract: The article presents and discusses experimental data regarding synthesis and characterization of epoxy resins modified with glycols of different molecular weight, synthesized in a 2: 1 molar ratio resin / glycol. The synthesis of epoxy resins modified with glycols was examined by using the spectrophotometer (FT-IR methods) against analytical (chemical) methods, by determining the content of the epoxy groups in time. Furthermore, in order to determine the influence of the glycol nature on the characteristics of the resulted resins, they were cured by using an aromatic polyamine hardener such as 4.4’-diaminodiphenylmetane (DDM), and the resulted epoxy resins were characterized by using both conventional mechanical analyses and the dynamic mechanical analyses (DMA). From the DMA determinations we noticed that resin flexibility increases in the same time with the polieteric chain length. Keywords: epoxy resin, glycol, glass transition, dynamical properties, mechanical properties

Abstract: Optical coherence tomography is a new noninvasive investigation method with various applications in dentistry and orthodontics respectively. The intra-oral OCT investigation opens a totally new perspective on the investigation of orthodontic bonding. Polymeric orthodontic brackets (Damon Clear) were bonded on the teeth of the upper arch of a patient following the manufacturer instructions with a light-curing orthodontic adhesive (Blugloo). After bonding the teeth were examined by spectral OCT in order to examine the interface formed by the enamel, orthodontic resin and the bracket. Several images were obtained. Intra-oral OCT is a method of great potential and real benefits in elaborating a prognosis on the clinical durability of bonded polymeric brackets. Keywords: spectral optical coherence tomography, orthodontic bonding, orthodontic adhesives, polymeric brackets

Abstract: The fundamental assumptions of the traditional deterministic linear models are those of continuous and differentiability of physical quantities involved in drug release processes. However, these assumptions are in reality contrary to the evidence given by the complexity of the drug release process. Thus, we will consider that, at mesoscopic scale, the drug release mechanisms are based on the assumption that the drug particle movements take place on continuous, but non-differentiable curves (fractal curves), for which a Weibull type equation results. In this approach, analyzing some experimental data, information on the drug release mechanism and system complexity are obtained. Keywords: fractal, drug release mechanism, polymers microparticles, mesoscopic scale

Abstract: A new set of molecularly imprinted polymers (MIPs), based on acrylonitrile: methacrylic acid (AN:MAA) matrix, selective for diosgenin, was synthesized and characterized. The target molecule, diosgenin, is an important anticancer and antileukemia bioactive compound. The phase inversion method, an emerging and insufficient studied preparation method, was used to prepare 0.5 mm spherical MIPs. Three copolymers of acrylonitrile with methacrylic acid were synthesized by radical copolymerization: AN:MAA 90:10, 80:20 and 70:30 and used for diosgenin imprinting. The imprinted materials were analysed by elemental analysis (EA), attenuated total reflectance infrared spectroscopy (ATR FT-IR), RAMAN spectroscopy, size exclusion chromatography (SEC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and batch rebinding tests. The affinity for the template, expressed as the imprinting factor IF, decreases in the order MIP-AN:MAA-80:20 ] MIP-AN:MAA-90:10 ] MIP-AN:MAA-70:30, meaning that -COOH functional groups have an important role in the imprinting process. Too much methacrylic groups, however, do not exhibit the highest affinity, maybe due to the steric obstruction of methyl groups and to a less stability of the structure by decreasing the AN ratio. Keywords: molecular imprinting, diosgenin, phase inversion, acrylic copolymers, MIPs

Abstract: This paper presents a usage method of wood waste as sawdust resulting from sawing processes, by achieving hybrid composite materials consisting of epoxy resin reinforced with flax weave fabrics and wood particles. Mechanical characteristics obtained from tensile testing of the material on both directions of the natural fibres weave fabric used as reinforcement are also presented here. New lignocellulosic composite has application to automotive interior components industry, furniture with complex shapes, etc. Keywords: wood sawdust, hybrid composite, weave fabrics, natural fibres, tensile tests, automotive applications

Abstract: We deduced the equation of motion for free vibrations using Mohr-Maxwell method, considering that the bar is requested to bending by the inertial forces and by the damping forces. We experimentally obtained the dynamic response for sandwich bars with polypropylene honeycomb core, which have the exterior layers made of epoxy resin reinforced with steel fabric. In addition, we determined the damping coefficients per unit mass and per unit length of the bar, for bar with core thicknesses equal to 10, 15 , 20 mm; width of 40 and 60 mm, and the free length of embedded bar equal to 200, 250, 300 and 350 mm. For each type of bar studied, we determined the relationships of exponential type for the calculus damping coefficients (mentioned above), according to the free length of the embedded bar. Keywords: sandwich beam, damping factor, polypropylene honeycomb, free vibrations

Abstract: The purpose of this paper is to show the possibility of finding the location and to describe internal discontinuities in plates made of plastic materials using non-destructive evaluation methods. Their effect on the mechanical behaviour is also evaluated by means of numerical calculus. The technique of computer tomography („CT”) is used as a non-destructive evaluation method whereas the numerical calculus is realized by the finite element method. Keywords: computer tomography, discontinuity, finite element analysis

Abstract: The paper refers to the new approach in bone grafting: biomaterials. Many artificial bone substitute materials are currently available for use in orthopaedic trauma surgery. The selection of these materials is more and more difficult as many bone substitute products are now available for use and this method led to a new approach, although the autologus bone grafting still represents the “gold standard” in bone reconstruction surgery. Keywords: bone grafting, biomaterials, reconstruction, fracture