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The polysiloxane networks have been prepared by means of hydrosilylation reaction of poly(dimethyl, hydrogen-methyl)siloxanes (HlPDMS) containing Si–H groups and siloxane copolymers named VlPDMS and VcPDMS containing Si-CH=CH2 functional groups. The structure of the siloxane copolymers was determined from 1H-NMR and FT-IR spectra analyse and the characterization of the siloxane copolymers was performed by gel permeation chromatography (GPC), viscosity and determination of the content of functional groups. The mechanical properties of the newly obtained networks were determined by physico-mechanical measurements, dynamic mechanical analysis (DMA), and differential scanning calorimetry (DSC). Keywords: polysiloxane, hydrosilylation crosslinking, polymer networks

A series of thermotropic liquid crystalline phosphorus-containing copolyesters was prepared by polycondensation reaction starting from various ratios of 2-(6-oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl)-1,4-benzene diol, 1, terephthaloyl bis-(4-oxybenzoyl-chloride), 2, and, 1,12-dodecanediol, 3. The molar ratio of aromatic bisphenol to aliphatic diol was varied in order to generate copolyesters with tailored physico-chemical properties. The chemical structure of the synthesized polymers has been confirmed by Fourier transform infrared and 1H NMR spectroscopy. The phase transitions of the phosphorus-containing copolyesters have been investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction measurements, structure–properties relationships being established and discussed. Keywords: phosphaphenanthrene; phase transitions; structure-property relations

The objective of the present study was to check the debonding strength in four types of orthodontic adhesives frequently purchased at present in our country: Ortho-Loc, Transbond XT, Tranasbond Self Etching Primer and Grengloo. For this study forty patients with integral maxillary arches and minor dental-maxillary abnormalities were selected and further randomly divided into four groups (one for each adhesive), each group being bonded with Resolve® Classic Bracket-type metal brackets. After one month, during which the brackets were subjecte to the action of oral factors, they were debonded using the force measurement FK model of the SAUTER device. There were no signficant differences between the four types of adhesives, nevertheless, the highest values were obtained for Transbond XT. All four types of adhesives were within the clinically acceptable interval being able to be safely used by clinicians. Key words: orthodontic adhesives, brackets, self-etching, debonding strengths

In this paper we determine a field of stress, which verifies the Cauchy equations of equilibrium, the conditions of continuity on the surfaces between layers, and boundary conditions, for a sandwich bar, with symmetrical distribution of layers, subject to traction. We have considered the relationships, previously obtained, for a composite bar built of three layers. Using a mediation formula for deformations and stress, we obtained a new formula for calculating the longitudinal elasticity modulus, in the case in which the constituent materials have different coefficients of transversal contraction. We realized the experimental measurements for test samples from polyesteric resin, reinforced with woven of fibers glass, carbon and glass-carbon. Keywords: composite materials, characteristic curve, elasticity modulus

The major interest of practitioners for FRC dental restorations derives from the biological traits of this technique. The study concerned the biomechanical behaviour of polyethylene fiber reinforced composites. The experimental determination of the maximum pressure force that can be supported by a FRC fixed prosthetic restoration has also been targeted (Construct - Premise Indirect). For this purpose two samples have been used, each been made of a FRC restoration resin bonded to two lateral teeth which are fixed in a plaster block. The 2 samples differ by the fiber width and by the thickness of the veneer composite. The 2 samples have been tested with static short duration loads on a testing machine. It has been observed that both samples had a perfect elastic behaviour for force under 280N (sample 1) and 360N (sample 2). The maximum flexural stresses as a result of the load are 102.77MPa for the first pontic and 92.5MPa for the second one. The persistence of the fiber allows maintaining the bridge under certain conditions and for a certain period of time. If the stress increases the restoration is destructed (the force has to be almost doubled before the important displacement could lead to the fracture of the bridge). In a clinical situation this reversible and cost effective procedure, which is minimally invasive, aesthetically and biologically desirable offers a viable alternative to conventional replacement of lost teeth. Keywords: FRC, polyethylene fiber, prosthetic restoration

This paper presents a numerical simulation for metal sheet bending with elastic pads made of silicone rubber reinforced with different ratios of very small glass fibers. Experimental tests were performed (traction and compression), in order to determine some characteristics for the materials and the results were used in the simulation program. A correction for the geometry of the punch, a prediction diagram for springback angle and the evolution of the force developed by the punch are also presented Keywords: numerical simultation, silicon rubber, glass fibers, finite elements

The work presents the experimental determination of the transverse contraction coefficient í (Poissson’s ratio) for three kinds of composite materials. For this purpose, it was used the digital image correlation method that is an optical method for the measuring of the deformations. The composite materials were made of the same epoxy resin but the reinforcement was different: reinforcement with glass fabric; reinforcement with oak wood flour; reinforcement both with oak wood flour and with glass fabric (hybrid composite material). The specimens were subject to tensile test and during the test, it was used the system Aramis 2M for image acquisition and their post-processing to determine both the longitudinal strain ex (axial strain) on the direction of tensile loading and transversal strain ey on the direction of the specimen width. The variations of the transverse strains ey as a function of the axial ones for each specimen were graphycal lyrepresented. Then, the experimental data were approximated by linear regression that is by linear functions. The slopes of the straight lines represent Poisson’s ratio n. It was found that the adding of the oak wood flour as filling material in case of the composite materials reinforced with glass fabric, leads to the increasing of the Poisson’s ratio n . Keywords: composite material, wood flour, tensile test, Poisson’s ratio

The aim of the present study was to synthesize and characterize some bioconjugated systems based on dendritic polymers and paclitaxel. Three types of polyamidoamine dendrimers (PAMAM) with amine terminated groups and different generations (PAMAM-G1-NH2, PAMAM-G4- NH2, PAMAM-G6-NH2) were used as polymeric hosts. The bioconjugated systems were characterized using FT-IR Spectroscopy and thermogravimetrical analysis. Keywords: dendrimers, paclitaxel, FTIR spectroscopy

The objective of this paper was to review the acrylic based resins biodegradation phenomena. The general objectives are based on multidisciplinary research of biomaterials used in dental medicine. For this analysis, different types of polymers were evaluated for water absorption and mechanical strength degradation caused by exposure to saliva. Two sets of 10 specimens were prepared from the analyzed materials according to manufacturer recommendations. The mechanical properties determined on wet samples were lower than those of samples from the same materials, tested dry. Difference between the mechanical properties determined in wet and dry was higher for those materials in which the degree of water absorption was higher. This indicates a clear influence of saliva on the biodegradation of these materials. Key words: dental polymer, mechanical properties, saliva

This paper presents the results of the experimental researches regarding the influence of the composition of some film-forming polymeric products for the protection of concrete on certain of their characteristics. Thus, there have come into prominence the film-forming products based on acrylic resins with superior characteristics by comparison to the film-forming products based on acrylic-styrene resins. Keywords: film-forming product, acrylic polymers, concrete, covering system, acrylic-styrene polymers