Browse Articles

Low-volume production components represent a possibility to create prototypes from the same process and materials that someone use for the final product and to bring new products to market instead of waiting for final components to arrive from the machine shop. Additive FDM create geometrical products through the deposition of ABS (Acrylonitrile-Butadiene-Styrene) filaments layer by layer satisfying this necessity. Since the specialized literature offers little information on the properties of such plastic materials, in this paper the authors present some experimental procedures in order to evaluate the elastic and mechanical properties of such a plastic material. The specimens have been printed on a 3D “ULTIMAKER –2” printer. Keywords: Acrylonitrile-Butadiene-Styrene, Fused Deposition Modeling, 3D printing, integrated software home manufaturing

The puropose of this paper was the approaching the patology of the oral mucosa in older patients, induced by acrylic resins in removable dentures. Prosthetics resolves many problems in older adults (mastication, aesthetics, phonation, etc.) but the wearing of dentures has consequences on all the living tissues in contact with them. The reactions of buccal mucosa are the result of mechanic irritations, plaque build-up and of toxic and/or allergic action of the denture materials, therefore the field cannot be neglected. An essential aspect of the clinic goal of removable prosthetic restorations is the consistency between the biomaterials used, their biological integration, the approached technological line, and the particularity of the prosthetic field of the older patient. Keywords: oral mucosa, acrylic resins, removable dentures, irritating toxic phenomena, biocompatible

The viscous flow over a shrinking permeable sheet with partial slip is investigated. The flow is governed by a third-order nonlinear differential equation and heat transfer by a second-order differential equation. The equations of motion are solved analitically by Optimal Homotopy Perturbation Method (OHPM). This procedure is highly efficient and it controls the convergence of the approximate solutions. A few examples are presented, showing the exceptionally good agreement between the analytical and numerical solutions. OHPM is very efficient in practice, ensuring a very rapid convergence after only one iteration. Keywords: Optimal homotopy perturbation method, viscous flow, partial slip, shrinking sheet,heat transfer

Gingival enlargement is also known as gingival hyperplasia or hypertrophy and it is an abnormal overgrowth of gingival tissues. This type of lesions can be produced by a large group of pathologic processes. The most common are the reactive hyperplasia which develops in response to a chronic tissue injury that stimulates an excessive tissue repair response. Often, dental prosthesis have been reported to cause this type of lesions due to a mechanical chronic irritation or by a reaction of the oral tissue to substances released into the oral environment by the materials used in manufacturing this type of prosthesis. One of these substances is the methylmethacrylate (PMMA), a widely used in dentistry. The first step in treatment of these lesions is the removal of the irritative factor which sometimes can lead to healing depending on the type of lesion. The challenge is to differentiate a lesion caused by a mechanical irritation from a lesion in which the cytotoxicity of PMMA may be the cause. Often, surgery is the only treatment option for the first situation. When we have an irritative reaction and a cytotoxicity reaction, we must treat them both. Keywords: methylmethacrylate, acrylic resin, TNF alfa, citotoxicity

The medical industry has greatly benefited from the aid of various additive manufacturing (AM) technologies, especially for applications that include the fabrication of bespoke implants and guides, devices and surgical instruments. Manufacturing functional prototypes that can behave as close as possible to the final product is a key factor in developing successful anatomically compliant medical products. The current research is intended to evaluate the optimum AM technology to fabricate medical prototypes with thin wall structures, destined for anatomical functional tests and surgical practitioner feedback. The main criteria of evaluation were: speed of fabrication from *.STL file to final prototype, mechanical characteristics and manufacturing costs. Keywords: bespoke medical prototype, optimum additive technology, functional simulations, anatomical thin structures

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

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

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

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

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