Non- Carious Cervical Lesions: A Review

Non-carious cervical lesions (NCCL) are characterized by a loss of hard dental tissue near the cement-enamel-junction. Commonly, their shape is like a wedge with the apex pointing inwards. Other times, they appear as regular depressions, like a dome or a cup. Their etiology seems to be related to different factors: hexogen and endogen acids, mechanical abrasive action, tooth flexion under axial and non-axial loads. Moreover, it seems that a fundamental role is ascribable to tooth bending phenomena due to the strength components parallel or oblique to the occlusal level, which occur during the normal function as well as during Para functions. The frequent therapeutic failures are probably due to the same factors causing the onset of the original lesion. Several materials have been proposed to restore NCCL: amalgam (abandoned) glass-ionomer cements, composers, and composite resins. Early failures of these restorations have often been reported in the literature, probably due to the same factors which originally caused the lesions. Further investigations are required to determine more reliable restorative therapies.

Research of the Resistance of Reinforced Polymeric Composite Materials to Hydro-Abrasive Action

The results of the research of the resistance of reinforced polymeric composite materials to hydro-abrasive action are presented. Hydro-abrasive wear research was carried out on a specially developed device that makes it possible to study the wear resistance of materials and coatings under impact conditions of loosely suspended abrasive particles simulating the flow of a hydro-abrasive medium. Composites based on polyester resin and polyurethane reinforced with ultra-high molecular weight polyethylene (UHMWPE) fibers and glass fibers were chosen as the objects for the study. An analysis of the intensity and nature of wear of these composites in compared with structural steel, UHMWPE and polyurea was carried out.The analysis of the obtained research results shows that UHMWPEis the most resistant to hydro-abrasive effects. However, the high cost and variation of the traditional technology of manufacturing composite products using UHMWPE as a lining material shows the advantage of using composite materials reinforced with oriented UHMWPE fibers.

ZUR OKOLOGIE UND WUCHSFORM DER SAULENKORALLE DENDROGYRA CYLINDMS EHRENBERG BEOBACHTUNGEN IN DEN RIFFEN DER INSEL SAN ANDRÉS (KARIBISCHES MEER, KOLUMBIEN

Submarine observations around San Andres Island indicate that quiet backreef and leeward reef waters from 1 to 20 m deep, are the most favorable habitat for the pillar coral Dendrogyra cylindrus. It thrives even at the submarine terraces along the calm West coast of the Island, where abrasive action by coral fragments is heavy during occasional storm surges. Besides a few minor incrusting and hemispherical species, Dendrogyra seems to be the only major scleractinian to resist abrasion and break-down without permanent damage in this environment. Dendrogyra initiates colony growth with a broad incrustation followed by upgrowth of pillars. Unstable basement may cause tumbling of the whole coral and subsequent pillar growth at approximately right angles to old columns. This process may be repeated, resulting in the formation of a third generation of pillars.

Hydrophobic coatings based on SiO2

The method of conversion, properties and usage of hydrophobic coatings on the bases of silicon dioxide is presented in the article. These layers are formed by use the silanes which are not react with water. What is more, these layers could provide not only great resistance to the effect of water molecules, but also better resistance to the effect of abrasive action and hardness as well as keeping the top stair of the transparency. Uncomplicated methods such as zol-zel are used to settling these layers. There are methods of putting on the various surfaces, without necessity of usage specific and sophisticated technological solutions. As a transparent and simple to keep in the cleanness surfaces these layers found application in various field such as sport, motorization, building industry, optical system whether in our houses.

Modeling of Material Removal Rate in Micro-ECG Process

Microelectrochemical grinding (micro-ECG) is a variant of electrochemical grinding (ECG) process, in which material is removed by a combination of electrolytic dissolution and abrasive action that take place in a small interelectrode gap. This paper discusses analytical modeling of the material removal phenomenon in micro-ECG process to predict material removal rate. In the model, the phenomena, which contribute to the material removal in the process by electrolytic and abrasive actions, have been considered; these include streaming potential in the electrochemical action and shearing forces due to the flow of electrolyte through interelectrode gap and the abrasive action of grinding wheel. Two configurations of the process, viz., surface and cylindrical micro-ECG, have been modeled. The results have been validated by CFD simulation in the case of surface micro-ECG process, and specific experimentation in the case of cylindrical micro-ECG process.