Charles Younes

Surface properties of titanium and zirconia dental implant materials and their effect on bacterial adhesion

OBJECTIVES Zirconia ceramic material has been widely used in implant dentistry. In this in vitro study the physiochemical properties of titanium and zirconia materials were investigated and the affinity of different bacteria to different materials was compared. METHODS Disc samples with different surface states were used: polished partially stabilized zirconia (PZ), titanium blasted with zirconia (TBZ), titanium blasted with zirconia then acid etched (TBZA), and polished titanium (PT) as a control. Surface topography was examined using scanning electron microscopy and profilometry. Contact angle, surface free energy (SFE), surface microhardness and chemical composition were determined. Disc samples were separately incubated with Streptococcus mitis and Prevotella nigrescens, either with or without pre-coating with human saliva, for 6h and the surface area covered by bacteria was calculated from fluorescence microscope images. RESULTS PZ and TBZ exhibited lower surface free energy and lesser surface wettability than PT. Also, PZ and TBZ surfaces showed lower percentage of bacterial adhesion compared with control PT surface. CONCLUSIONS The zirconia material and titanium blasted with zirconia surface (TBZ surface) showed superior effect to titanium material in reducing the adhesion of the experimented bacteria especially after coating with saliva pellicle. Modifying titanium with zirconia lead to have the same surface properties of pure zirconia material in reducing bacterial adhesion. SFE appears to be the most important factors that determine initial bacterial adhesion to smooth surface.

Comparison between magnetic force microscopy and electron back-scatter diffraction for ferrite quantification in type 321 stainless steel

Several analytical techniques that are currently available can be used to determine the spatial distribution and amount of austenite, ferrite and precipitate phases in steels. The application of magnetic force microscopy, in particular, to study the local microstructure of stainless steels is beneficial due to the selectivity of this technique for detection of ferromagnetic phases. In the comparison of Magnetic Force Microscopy and Electron Back-Scatter Diffraction for the morphological mapping and quantification of ferrite, the degree of sub-surface measurement has been found to be critical. Through the use of surface shielding, it has been possible to show that Magnetic Force Microscopy has a measurement depth of 105-140 nm. A comparison of the two techniques together with the depth of measurement capabilities are discussed.

Essential oils and zirconia dental implant materials.

PURPOSE This study was conducted to evaluate the effectiveness of natural antimicrobial agents in reducing biofilm development on different titanium and zirconia dental implant materials in vitro using a constant depth film fermentor (CDFF). MATERIALS AND METHODS Contact angles and surface free energy were determined for all surfaces. Biofilms were grown on disks of polished partially stabilized zirconia, titanium blasted with zirconia, titanium blasted with zirconia and acid-etched, and polished titanium using a CDFF to simulate oral cavity conditions. Antimicrobials (cinnamon oil, clove oil, chlorhexidine gluconate, or 0.5% Tween 80) were pulsed twice daily to the biofilm to mimic application in the oral cavity. Samples were taken after 6, 24, and 48 hours. Serial dilutions were made and plated onto agar. Bacterial colonies were counted to determine colony-forming units/mL. RESULTS Treatment of different implant material surfaces with the various antimicrobial agents led to significant increases in wettability and free energy on all surfaces. All surfaces showed a remarkable decrease in bacterial adhesion in the first 2 days in a relatively similar manner, with significant reduction in most of them, particularly after 48 hours. CONCLUSIONS Functionalization of different dental implant material surfaces with essential oils resulted in immediate and ongoing antibacterial and antiplaque activities, and this antibacterial effect was enhanced with increased plaque age. Differences in the type of material seemed to have little effect on bacterial adhesion after treatment with antimicrobial agents. Expansion of this work with in vivo studies and clinical trials would be valuable.

The effect of the microscale distribution of boron on the yield strength of C-Mn steels subjected to neutron irradiation

Abstract The presence of B as an impurity in C–Mn steel and weld metal can have a significant effect on the mechanical properties of these materials depending upon whether this element is present as the free atomic species or incorporated within particular microstructural features such as grain boundaries, inclusions or precipitates. This is important in the case of the steel plates and weld metals used for the construction of nuclear pressure vessels where irradiation, with a contribution from thermalised neutrons to the fast neutron spectrum, can lead to transmutation of the B. In this work we examine the distribution of B within the microstructure of a range of C–Mn steels and weld metals containing 1 ppm ≤ boron ≤48 ppm using low and high resolution microanalytical techniques. These results are compared with measured tensile and hardness properties. The distribution of the impurity B within the microstructure and the measured changes in the yield strength of these C–Mn steels following neutron irradiation are discussed. The measured changes in the yield strength are addressed using models that describe the displacement damage arising from several sources. In particular the contribution of neutron irradiation damage from B transmutation to the irradiation strengthening is related to the bulk B content and its distribution to inclusions and carbide precipitates in the overall microstructure.

The Effect of Different Surface Modifications on Titanium Dental Implant Surface Characteristics and Bacterial Adhesion

Purpose: The presented work was to evaluate the effect of different surface modifications on the physiochemical characteristics of titanium surfaces, and to examine the influence of these modifications on bacteria adhesion with and without saliva coating. Materials and Methods: Pure polished titanium discs were subjected to various surface treatments. Surface topography was examined. Contact angle, surface free energy, crystalline phase, chemical composition, roughness, and microhardness were also evaluated. Titanium discs were incubated with a suspension of each of the chosen bacteria for 6 hours and the percentage of area covered by the bacteria was calculated using fluorescence microscope images. Results: A significant difference was found in contact angle measurements with a wide variation in most of the measured physiochemical properties between the modified surfaces. A significant reduction was observed in bacterial adhesion to surfaces with high surface hydrophobicity and low surface free energy after coating with saliva. Conclusions: Physiochemical properties of titanium can be altered depending on the type of modification, and most of the modifications to a titanium surface increase its hydrophobicity and decrease its surface free energy. Increased surface hydrophobicity along with decreased surface free energy leads to decrease bacterial adhesion to titanium surface after coating with saliva. Keyword: Dental implant, bacteria, titanium, surface modification, physiochemical characteristics, surface free energy

A Microstructural Sensitivity Study of 316H Austenitic Stainless Steel to Inter-Granular Creep Fracture

A preliminary sensitivity examination of the ductility exhaustion based creep damage prediction model, currently used in the R5 high temperature assessment procedure, showed that material property inputs had significant effects on damage prediction. In the present work, the link between the microstructural factors and the susceptibility to inter-granular high temperature creep failure is considered. The latter was judged to be associated with the low creep ductility. Here, the longitudinal section of a creep specimen and the fracture surface were examined. Auger electron spectroscopy was used to investigate the grain boundary composition in this specimen, which failed after a creep test of 1038h at 550°C under a triaxial stress state. The present results demonstrate that there is a possibility to correlate the susceptibility to high temperature inter-granular fracture from the low temperature fracture investigations. Finally, the susceptibility of the pre-treated 316H stainless steel to inter-granular high temperature failure and the contribution to the creep damage model are briefly discussed.

Surface and bulk analysis of metal-organic chemical vapor deposition-derived superconducting Tl2Ba2Ca2Cu3Ox thin films by Auger electron spectroscopy

Abstract The surface and bulk chemical compositions of as-deposited and annealed superconducting Tl 2 Ba 2 Ca 2 Cu 3 O x thin films have been analyzed by Auger electron spectroscopy (AES). These films are prepared on yttria-stabilized zirconia single-crystal substrates by a combination of metal-organic chemical vapor deposition (MOCVD) and thallium vapor diffusion. BaCaCuO films are first prepared by MOCVD. Thallium is then incorporated into these films by annealing in the presence of a mixture of oxides (Tl 2 O 3 , BaO, CaO and CuO) of a specific composition. The as-deposited BaCaCuO films are found to be free of carbon in the interior region. AES depth-profiling experiments reveal consistent atomic homogeneity throughout both the as-deposited BaCaCuO films and the Tl vapor-diffused superconducting films. Apparent intergrowth observed at the substrate-film interface may be due to surface roughness.