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Lignin, a natural renewable material, was incorporated in a series of polydimethylsiloxane/silica composites. Besides the effect as bulk filler, the presence of lignin determines the change of some properties among them being surface properties that were evaluated by contact angle and water sorption measurements. The contact angles were determined in static regime by using the sessile drop technique. Dynamic water vapour sorption was applied to register the sorption/desorption isotherms and kinetic curves. The sorption type and maximum vapour sorption capacity were evaluated based on these data. The results were correlated with the composition of the prepared materials. Keywords: surface properties; siloxanes; composites; lignin

Organic biopolymers are a source of raw material for agriculture, whereas the composition of protein wastes provides sufficient elements to improve the composition and remediation of degraded soils and plants by exploiting elements, such as nitrogen, calcium, magnesium, sodium, potassium etc. From processing one tone of raw hide, 75% is discarded, of which 50% could be further used as organic fertilizer. Protein biopolymers were obtained by means of an innovative enzymatic procedure for waste processing. In combination with polyacrylamide, acrylic, maleic, cellulose, starch etc. are used in the agricultural field. We characterize the protein biopolymers by specific morpho-structural analysis methods (UV-Vis, IR spectroscopy, thermal analyses, X-ray diffraction, microscopy).The novelty of this work is the biochemical combination process of synthetic polymers with organic biopolymers from tanneries with viable and interesting applications in agriculture. Keywords: biopolymer, protein wastes, tannery, soil, structural analysis

Functionalized dental implants represent an advanced approaching in implantology, aiming to improve the biointegration and the long-term success of surgical procedures. In this article are reported the synthesis of hydroxyapatite (HA) and Poly(methyl methacrylate) (PMMA) thin films on metallic substrates – used as dental implant-type structures – by pulsed laser deposition (PLD) method. Plasma and plume evolution of ablated HA and PMMA species was registered through optical analyze by fast CCD camera. Numerical simulation performed using a simple hydrodynamic model properly reproduce this type of plasma behaviour. SEM-EDAX measurements were performed assessing the apatitic-type structure of the prepared films along with their satisfactory mechanical adhesion. Keywords: synthetic polymer, pulsed laser deposition, hydrodynamic model

The use of the acrylic resins in the dental technique was a very important gain for the manufacturing and treatment of dentures and during the years new materials and technologies have appeared on the market, promising a better quality. Full-denture casting currently represents a technological alternative. The casting system we tested usually uses reversible hydrocolloids for investing wax patterns, and has certain advantages. Thermoplastic materials are used more and more widely in the technology of complete or removable partial dentures due to their superior qualities. Thermoplastic resins are suitable for manufacturing a wide range of removable partial dentures without metallic structure, in optimal conditions of biocompatibility, by injection. Our aim is to compare thermopolimerysable acrylic resins, manufactured using the classic technology with cast full dentures and injected thermoplastic resins. Keywords: thermopolimerisable acrylic resin, thermoplastic resin, molding-injection devices, casting, full dentures

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