Browse Articles

Due to the multitude of restorative materials on the today market, the studies presented in this paper come to make some contributions regarding the evaluation of biomaterials in terms of resistance to the wear process, the factors influencing the tribological behaviour of hard structures and restorative dental biomaterials in the oral environment. Keywords: composite materials, tribology, wear, dental medicine

In the idea of improving the performances of both full and removable partial dentures, new materials and technologies are coming on the market, promising a better quality. 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, we have manufactured several removable partial dentures without metallic structure. Full denture casting currently represents a technological alternative. The casting system we tested, usually uses reversible hydrocolloids for investing wax patterns. Besides the system’s own advantages, the authors also noticed certain errors consecutive to casting, materialized in lack of substance and the development of porosities on the mucosal facets of the complete denture bases. Keywords: removable partial dentures, thermoplastic materials, molding-injection devices, casting, full dentures, errors

The paper is focused on the behavioural simulation of the intraocular organic lenses, defined by geometric characteristics (the accumulation radius, thickness and diameter) [1] and material characteristics, for a certain incident wavelength [2]. The simulation provides a picture of the ray-tracing for the second and third reflection/refraction. At the same time, the user can display the print of a ray on a normal plane related to optical axis direction. The authors designed the simulation program, aimed to evaluate the wounded through the multiple reflections in the spectre available for chosen material. Thus the disparity of a certain parameter will influence the transference through lenses for some radiation or spectre. The paper is designed to be used in optics, to shape the refractive components, and can predict the useful diameter of lenses, diaphragms or aperture stop. Keywords: organic optical glass, optical layout, multiple reflections, imaging

In order to point out the intrinsic peculiarities of thermorheodynamical behaviour of solid-like polymer materials, the framework of a Zener - Arrhenius model is considered, the frequency or/and temperature dependences being approached in the case of strain-controlled conditions. The complete set of the explicit general relations providing the characteristic thermorheodynamical quantities (the storage, loss and absolute moduli, as well as the loss factor, and the corresponding storage, loss and absolute compliances) is presented in terms of meaningful rheological parameters including the low - and high frequency limit values of the storage modulus, and the appropriate relaxation time. The underlying analytical relations are given in forms suitable for direct numerical simulation of both isothermal frequency - dependence, and well as of isochronal temperature - dependence circumstances. Keywords: analytical relations, characteristic thermorheodynamical quantities, strain-controlled conditions, Zener - Arrhenius model, isothermal and isochronal circumstances

The present study is focused on a multidisciplinary research, regarding the durability of complete dentures realised from light curing UDMA resins. Absence of methyl, ethyl, propyl or butyl monomers from their composition is responsible for their good utilization, because they do not generate contact allergies. For testing there was used Eclipse Prosthetic Resin System (DENTSPLY International Inc. - DeguDent GmbH, Hanau Germany), which consists of: Base Plate, Set-Up and Contour Resins. Using the technology recommended by the producer, there were realized nine samples, which were mechanically tested with Zwick Roel equipment. A pair of finite prostheses, realized with the help of this system, was used by finite elements method (3D scanning, software Pixform Pro Program, program CAD – Ansys Workbench (ANSYS Multiphysics) or ABACUS / CAE version 6.6.1). Static analyses for stress and strain were based on „reverse engineering” method. In the end, experiment certification took place also through fatigue tests (Walter-Bai Dynamic Testing Machine). The following mechanical parameters were determined after testing: Young’s modulus of elasticity: 2908.45 MPa, ultimate tensile strength Rm= 59.49 MPa; total elongation At= 4.582 %, at a medium force value of 1203N. Stress and strain analysis of the denture subjected to different loadings, was revealed through chromatic spectres on denture virtual models. The warm colours indicate the areas with problems. By finite elements method one can realize noninvasive numerical procedures, which reveal the risk areas that can lead to dentures’ fracture; thus, one can correct and improve the complete dentures quality. Following the fatigue tests, we may consider that mechanical properties of Eclipse allow a five years warranty for complete denture. Key words: complete dentures, light curing resins UDMA, finite elements analysis, fatigue

PEHD plastic materials are more and more used in applications. Their possible physical and chemical changes, depending on the temperature changes and time, in a given atmosphere, can be made by simultaneous measurement of the sample mass and its temperature. It is achieved by the use of thermogravimetry (TG). The thermogravimeter Mettler Toledo presents thermograms or thermogravimetric curves as well as their differentials. Results obtained in this way can be starting points for next researches. Keywords: PEHD, thermogravimetry, thermogravimetric differentials, quantitative analysis

When great damages occur on gas-pipes, a quick intervention is often needed, as close to the place of damage as it can be. That is the reason why recently it has more and more been used a procedure of squeezing the pipe using a squeeze-off tool and thus stopping the flow. After the damage has been removed, the deformed pipe returns to the original shape by using re-rounding clam and the flow is established again. After the above-described process, the pipe is permanently deformed, as far as shape and thickness are concerned. The size of the deformation is important for the assessment of further use of the existing pipes or for determining the parameters for the newly-projected pipes. So far, the researches have been dealing with the hydrostatic and stress states after the squeezing of the pipe. The subject of this research is the decrease of the pipe thickness after the squeezing, and the goal is to help the designers of distributive plastic gas-pipes to determine the pipe wall thickness, as well as to help the managers of distributive networks so that they would know what happens to the existing gas-pipes after the intervention on the pipe. Keywords: sqeeze – off tool, polyethylene gas pipe

The paper presents results on wear after testing a class of composites (PA +1% black carbon and different 5 concentrations of micro glass spheres) and discussions about damaging processes within the superficial layer, grouped in two categories: one favouring the material remove and the other the reduction of wear intensity. The analysis points out that tribological behaviour should be interpreted only by putting together information about wear, friction, temperature in contact, pair of materials in contact in order to obtain sustainable results that could be useful in engineering design. Keywords:micro-nano particles, polyamide, wear, IR thermogravimetric, SEM

Conformational parameters, and free and Van der Waals volume values for a group of polymers containing methylene bridges, some of them having methyl substituents as well, have been calculated and correlated with physical properties such as solubility, glass transition and decomposition temperature, tensile stress and dielectric constant which were measured for these polymers. Thus, it was shown that conformational rigidity determines the packing of macromolecules in solid state, and therefore the free volume, and glass transition temperature and dielectric constant. The presence of methyl substituents and other flexible groups such as isopropylidene, carbonyl or hexafluoroisopropylidene has a more complex effect on the values of mechanical properties. Keywords: polyimides, thin films, conformational parameters, glass transition, dielectric constant

This work aims to present the optimization of the design of a plastic part manufactured at Accurate Machine and Tool Ltd. Canada, by using Moldflow [1] combined with the optimization method developed by Dr. Genichi Taguchi. The method uses statistical principles and involves reducing the variation in a process through robust design of experiments. The experimental design proposed by Taguchi uses orthogonal arrays to organize the parameters affecting the process and the levels at which they should be varied; it allows for the collection of the necessary data to determine which factors most affect product quality with a minimum amount of experimentation, thus saving time and resources. Moldflow allows part designers and mold makers to predict the manufacturability and quality of their design during preliminary product development stages. It helps to select the best injection gates configuration, as well as the values of mold temperature (Tw), melt temperature (Tm) and an optimized body shape for a part in order to minimize variability in a key performance measure. This presentation discusses the application of these tools on a real life production of the parts. Using this method, with a modest number of simulations runs, the resultant savings are significant. The part has the weight reduced from 0.03lb for the initial part to 0.022lb. On this one design alone it is saved 27% of the material for each part. Keywords: polymers, injection molding, design, optimization, Taguchi Method