Papers by Author: Marian Miculescu

Abstract: In the present study, four different types of the commercial dental implants used as support for total/partial dental prosthesis have been investigated. Pure Ti and Ti6Al4V alloy, provided by four different manufactures, were chosen because these were the most used in dentistry market. The corrosion resistance was evaluated by using linear polarization technique, after recording the open circuit curves in Fusayama Meyer artificial saliva for 240 minutes. The corrosion tests in artificial saliva with pH 5.2 have shown that pure Ti exhibited a better behavior than the Ti alloy. This result can be explained by a higher stability of the passive thin layer of titanium oxide than the complex oxide layer formed on the Ti alloy surface.

Abstract: The need for reliable data on thermophysical properties of materials has increased continuously in the last period. The existing data, except for some pure elements or alloys and compounds, often unreliable, and in many cases the need for accurate and acceptable data, can only be achieved by measuring a given property. This paper focuses on elements of the used test methods associated with the description of the newly introduced parameter (effectiveness of dental coating). The selected method was the “pulse method” for determining thermal diffusivity (the method allows simultaneous determination of thermal diffusivity, specific heat capacity and thermal conductivity) directly applicable in the study of the thermal compatibility of metal-ceramic systems in dental applications.

Abstract: Although the literature describes many studies that attempt to define and interpret the interaction between the metal component and overlying sintered ceramic mass, researchers still have conflicting opinions. It is not yet fully understood the hybrid layer occurrence phenomenon that rises by diffusion at the sintering temperature between the compositional elements of the alloy and the ceramic mass. Also, there isn’t a standardized technology test for the compatibility between the alloy for this technology and a specific plating ceramic mass, from the strength of the bond between the two components at the interface point of view.This paper aims to present the composition, properties and the interaction between the two materials that participates in obtaining metal-ceramic fixed prostheses, and tries to expose a possible method for analysing the bonding strength and compatibility between dental alloys and ceramic masses. However, the mechanical surface contamination by the migration of the chemical elements it is possible, due to the mechanical stresses during cutting and polishing due to the hardness differences between the prosthesis components.Electron microscopy analysis allows the diffusion phenomenon evaluation and of the fact that the elements with reduced concentration within the ceramic have a higher diffusivity (Al as compared with Si), and that metallic elements diffuse in the ceramic mass. The extent of this interdiffusion is probably the degree of adhesion between the two components of the mixed metal-ceramic crown.

Abstract: The aim of the study is to highlight the influence of the cooling conditions on cortical bovine bones derived hydroxyapatite. Bone samples with thicknes of 50 mm were cut from the central part of the bovine femur with a jigsaw. Then, they were processed in order to remove all the proteins and collagen traces by boiling for 4 hours and heating and holding them at 450°C for 2 hours. They were heat treated at temperatures ranging from 1000° to 1300°C, being held for 3 hours and then rapidly cooled in air atmosphere or ice-water. A natural fracture of the samples appeared after the applied heat treatments, which allowed us to analyse the fragments without a further preparation. The morphological changes that occurred during the sample processing were highlighted using the scanning electron microscopy (SEM) techniques. The morphological changes occurred not only between the heat treated samples at different temperature, but also in samples cooled in different environments. Also, it was noticed that crystals sizes proportionaly increased with temperature, while the porosity considerably decreased and also a condensation of the porous matrix/structure appeared.

Abstract: Hydroxyapatite (HA) is one of the most common ceramic materials used for bone substitutions or reconstructions [1]. HA synthesis from natural sources is convenient relative to synthetic HA preparation while ensuring a similarity with viable bone tissue in terms of chemical composition and some other properties. One of the most important markers used for hydroxyapatite identification and differentiation from other calcium phosphates is the Ca/P ratio [2]. In order to perform a proper identification, this ratio should be evaluated with high accuracy, which involves a correct determination of the elemental concentrations. This study was made on a series of samples, derived from bovine osseous tissue, thermaly treated at 1000, 1100 and 1200°C. Establishing the influence of sample preparation on the Ca/P ratio assessment from the energy dispersion spectrometry (EDS) coupled with scanning electron microscopy determinations was intended. The samples were prepared by two completely different methods: mechanical fracture (without further preparation) and milling followed by homogenization. Regardless the sample preparation method, the analytical results represents the five measurements average performed on different spots.The EDS results showed that, within the same group, the compositional dissimilarities between the samples treated at different temperatures do not exceed 10% regardless of the sample preparation technique. For the same thermal treatment temperature, slight differences between the elemental chemical compositions of differently prepared samples were observed. The most important effect was a 20% decrease of the average Ca/P ratio for the samples prepared by milling and homogenization in regard to the mechanical fractured ones. Thereby, heat treated bovine bone samples’ milling and further homogenization for performing semi quantitative EDS analysis allows the Ca/P ratio assessment with a better accuracy.

Abstract: Push rod method for determining linear thermal expansion using vertical differential dilatometer was used in the study of the thermal compatibility of metal-ceramic systems for dental applications. The purpose of this study consisted in evaluating the effectiveness of dental coating by determining the ceramic metal bonding strength of metal-ceramic couples (Ni-Cr and Co-Cr alloy coated with dental ceramic) and correlation with the difference of linear thermal expansion coefficients of metals and ceramics.

Abstract: The implant surface morphology and microstructure significantly affect cells and tissue quantity formed at the interface. Therefore, the biocompatibility of an implant is just one of many parameters that influence tissue response to metallic implants. In order to understand the importance of the surface morphology and microscopic structures, we must retain first the main problem that limit the application and operation of metal implants - the lack of implant viable anchoring within the tissue. On this basis, experimental studies were carried out on implants having different microstructures and macrostructures that have been used in order to achieve a better long-term anchoring and stability of the implant support.

Abstract: Sintered ceramics and ceramic glasses are frequently used as biomaterials for dental restorations, usually for inlays, onlays, veneers, crowns or bridges. In this study we analyzed several types of ceramic-ceramic type prosthetic restorations in order to assess the types of defects that can lead to their failure. The research aim is to morphologically identify by scanning electron microscopy the main types of defects that lead to failure over time of ceramic-ceramic prostheses type. The type of failure registered were fracture of plating material (feldspatic porcelain) and fracture of entire structure (zirconia and feldspatic porcelain).

Abstract: In this paper we have focused on the study of the thermal expansion coefficient of a dental alloy, WBC, and its compatibility with a ceramic mass ,VITA VM 13, following thermal treatment according to the technological stages of production of a metal-ceramic prosthetic restoration.

Abstract: Among others, biomedical research is conducted for the systematic collection and analysis of data from which general conclusions can be drawn and which can increase the life quality of the patients. Given these issues, the aim of the research presented in this paper is to analyze the concentration of heavy elements from the human body, using complementary analysis methods, based on the energy dispersion spectrometry (EDS) technique.