Large‐scale bone mineral histomorphometry – report of a simplified technique

Karantzoulis V, Liapi C & Papaggelopoulos P
(2012) Histopathology
Large‐scale bone mineral histomorphometry – report of a simplified technique Aims: The aim of this study was the development of a simplified technique for bone mineral histomorphology on large undecalcified bone samples. Established techniques, such as undecalcified bone thin sectioning, ultrathin grinding, surface‐stained block grinding and micro‐computerized tomography (CT), are expensive, time‐consuming and put very high demands on equipment, safety standards, personnel and laboratory facilities. Methods and results: The method is based on the surface‐stained block‐grinding principle; however, its novelty lies in the selection of user‐friendly, safe and low‐cost materials, equipment and digitization techniques. We describe in detail the relevant steps, as well as many practical tips for their successful implementation: accurate bone cutting in thin sections with a customized arrangement on a commercial bandsaw, defatting with sodium hypochlorite, embedding in epoxy resin blocks at room temperature, silicon carbide paper grinding, von Kossa staining, flatbed scanner digitization and image processing. Conclusion: We believe that the proposed methodology could contribute to the expansion of the study of bone tissue, as it enables the rapid examination of bone specimens on a large scale with minimal laboratory requirements and consumables costs.     

Enamel gloss changes induced by orthodontic bonding

ABSTRACT

Objective: The purpose of this study was to assess enamel gloss changes induced by orthodontic bracket bonding with a light-cured composite or a light-cured resin-reinforced glass ionomer cement.

Setting: The Department of Biomaterials, School of Dentistry, National and Kapodistrian University of Athens, Greece.

Design: Laboratory study.

Methods: A total of twenty extracted upper human first premolars were included in this study and each tooth served as a control for itself. Their buccal surfaces were subjected to 60^o-angle gloss measurement (G%60) with a standardized and secure repeated analysis of the same site. After baseline evaluation, a bracket was bonded on the buccal surface of each tooth. Half of the specimens were bonded with acid-etching and a light-cured composite whereas the other half with a light-cured resin-reinforced glass ionomer cement without prior enamel conditioning. Gloss measurements were repeated after bracket debonding and removal of the composite/glass ionomer cement with an 18-fluted carbide bur. Gloss differences between the two measurement conditions (baseline and post-debonding) were analyzed through linear regression with standard errors derived using the bootstrap method. Level of significance was set at a?<?0.05.

Results: A statistically significant difference was detected between the tested groups for the outcome of interest. Teeth bonded with light-cured composite exhibited larger enamel gloss changes as compared to resin-reinforced glass ionomer cement (β?=?0.74; 95% CIs: 0.10, 1.38; p?=?0.02).

Conclusions: Bracket bonding with two common bonding protocols (acid-etching with a light-cured composite vs. no etching with resin reinforced glass-ionomer cement) and subsequently debonding and adhesive removal with an 18-fluted carbide bur induced enamel gloss changes.     

Mechanical and Tribological Behavior of Mechanically Alloyed Ni-TiC Composites Processed via Spark Plasma Sintering

Titanium carbide (TiC) reinforced nickel (Ni) matrix composites were processed via mechanical alloying (MA) followed by spark plasma sintering (SPS) process. Mechanical alloying has gained special attention as a powerful non-equilibrium process for fabricating amorphous and nanocrystalline materials, whereas spark plasma sintering (SPS) is a unique technique for processing dense and near net shape bulk alloys with homogenous microstructure. TiC reinforcement varied from 5 to 50 wt.% into nickel matrix to investigate its effect on the microstructure and mechanical behavior of Ni-TiC composites. All Ni-TiC composites powder was mechanically alloyed using planetary high energy ball mill with 400 rpm and ball to powder ratio (BPR) 15:1 for 24 h. Bulk Ni-TiC composites were then sintered via SPS process at 50 MPa pressure and 900–1200 °C temperature. All Ni-TiC composites exhibited higher microhardness and compressive strength than pure nickel due to the presence of homogeneously distributed TiC particles within the nickel matrix, matrix grain refinement, and excellent interfacial bonding between nickel and TiC reinforcement. There is an increase in Ni-TiC composites microhardness with an increase in TiC reinforcement from 5 to 50 wt.%, and it reaches the maximum value of 900 HV for Ni-50TiC composites.     

Characterization of W–Cr Metal Matrix Composite Coatings Reinforced with WC Particles Produced on Low-Carbon Steel Using Laser Processing of Precoat

The paper presents the study results of laser processing of precoat applied on C30 steel. The precoat consisted of powder mixtures with a binder in the form of water glass. Tungsten powder, chromium, and tungsten carbide (WC) were used to produce the precoat. The laser processing was carried out using a Yb:YAG disc laser with a rated power of 1 kW. Constant producing parameters (power of laser beam, 600 W; laser beam scanning rate, 400 mm/min) were applied. Chemical composition of the precoat was a variable parameter in coating production. A mixture consisting of 50% W and 50% Cr as a metal matrix was prepared. Subsequently, WC particles in weight ratios of 25%, 50%, and 75% were added to matrix. As a result, W–Cr metal matrix composite coatings reinforced with WC particles were formed. This study focused on investigation of microstructure, microhardness, phase, and chemical composition as well as corrosion and wear resistance, of the newly formed W–Cr/WC coatings. An instrumented nanoindentation test was also used in this study. As a result of laser beam action, the newly formed coatings had an interesting microstructure and good properties which were improved in comparison to substrate material. It is anticipated that the resulting coatings, depending on the treatment parameters (e.g., W–Cr/WC powder mixture) used, can be successfully applied to metal forming or foundry tools.     

Suppression of 3C-Inclusion Formation during Growth of 4H-SiC Si-Face Homoepitaxial Layers with a 1° Off-Angle

We grew epitaxial layers on 4H-silicon carbide (SiC) Si-face substrates with a 1° off-angle. The suppression of 3C-inclusion formation during growth at a high C/Si ratio was investigated, because a growth technique with a high C/Si ratio is needed to decrease residual nitrogen incorporation. 3C inclusions were generated both at the interface between the substrate and epitaxial layer, and during epitaxial growth. 3C-SiC nucleation is proposed to trigger the formation of 3C inclusions. We suppressed 3C-inclusion formation by performing deep in situ etching and using a high C/Si ratio, which removed substrate surface damage and improved the 4H-SiC stability, respectively. The as-grown epitaxial layers had rough surfaces because of step bunching due to the deep in situ etching, but the rough surface became smooth after chemical mechanical polishing treatment. These techniques allow the growth of epitaxial layers with 1° off-angles for a wide range of doping concentrations.     

Correlation between Defects and Electrical Performances of Ion-Irradiated 4H-SiC p–n Junctions

In this study, 4H-SiC p–n junctions were irradiated with 700 keV He⁺ ions in the fluence range 1.0 × 10¹² to 1.0 × 10¹⁵ ions/cm². The effects of irradiation were investigated by current–voltage (I–V) and capacitance–voltage (C–V) measurements, while deep-level transient spectroscopy (DLTS) was used to study the traps introduced by irradiation defects. Modifications of the device’s electrical performances were observed after irradiation, and two fluence regimes were identified. In the low fluence range (≤10¹³ ions/cm²), I–V characteristics evidenced an increase in series resistance, which can be associated with the decrease in the dopant concentration, as also denoted by C–V measurements. In addition, the pre-exponential parameter of junction generation current increased with fluence due to the increase in point defect concentration. The main produced defect states were the Z_1/2, RD_1/2, and EH_6/7 centers, whose concentrations increased with fluence. At high fluence (>10¹³ ions/cm²), I–V curves showed a strong decrease in the generation current, while DLTS evidenced a rearrangement of defects. The detailed electrical characterization of the p–n junction performed at different temperatures highlights the existence of conduction paths with peculiar electrical properties introduced by high fluence irradiation. The results suggest the formation of localized highly resistive regions (realized by agglomeration of point defects) in parallel with the main junction.     

Re-Melting Behaviour and Wear Resistance of Vanadium Carbide Precipitating Cr27.5Co14Fe22Mo22Ni11.65V2.85 High Entropy Alloy

High entropy alloys (HEAs) are among of the most promising new metal material groups. The achievable properties can exceed those of common alloys in different ways. Due to the mixture of five or more alloying elements, the variety of high entropy alloys is fairly huge. The presented work will focus on some first insights on the weldability and the wear behavior of vanadium carbide precipitation Cr_27.5Co₁₄Fe₂₂Mo₂₂Ni_11.65V_2.85 HEA. The weldability should always be addressed in an early stage of any alloy design to avoid welding-related problems afterwards. The cast Cr_27.5Co₁₄Fe₂₂Mo₂₂Ni_11.65V_2.85 HEA has been remelted using a TIG welding process and the resulting microstructure has been examined. The changes in the microstructure due to the remelting process showed little influence of the welding process and no welding-related problems like hot cracks have been observed. It will be shown that vanadium carbides or vanadium-rich phases precipitate after casting and remelting in a two phased HEA matrix. The hardness of the as cast alloy is 324HV0.2 and after remelting the hardness rises to 339HV0.2. The wear behavior can be considered as comparable to a Stellite 6 cobalt base alloy as determined in an ASTM G75 test. Overall, the basic HEA design is promising due to the precipitation of vanadium carbides and should be further investigated.     

Multilayer Diamond Coatings Applied to Micro-End-Milling of Cemented Carbide

Cobalt-cemented carbide micro-end mills were coated with diamond grown by chemical vapor deposition (CVD), with the purpose of micro-machining cemented carbides. The diamond coatings were designed with a multilayer architecture, alternating between sub-microcrystalline and nanocrystalline diamond layers. The structure of the coatings was studied by transmission electron microscopy. High adhesion to the chemically pre-treated WC-7Co tool substrates was observed by Rockwell C indentation, with the diamond coatings withstanding a critical load of 1250 N. The coated tools were tested for micro-end-milling of WC-15Co under air-cooling conditions, being able to cut more than 6500 m over a period of 120 min, after which a flank wear of 47.8 μm was attained. The machining performance and wear behavior of the micro-cutters was studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Crystallographic analysis through cross-sectional selected area electron diffraction patterns, along with characterization in dark-field and HRTEM modes, provided a possible correlation between interfacial stress relaxation and wear properties of the coatings. Overall, this work demonstrates that high adhesion of diamond coatings can be achieved by proper combination of chemical attack and coating architecture. By preventing catastrophic delamination, multilayer CVD diamond coatings are central towards the enhancement of the wear properties and mechanical robustness of carbide tools used for micro-machining of ultra-hard materials.     

On Investigating the Microstructural,Mechanical, and Tribological Properties of Hybrid FeGr1/SiC/Gr Metal Matrix Composites

In recent years, studies of different properties of hybrid metal matrix composites, as well as very detailed issues, have been published. In this article, ready-made iron, graphite, and silicon carbide powders were used to produce the base material and composites. An analysis of some microstructural and mechanical properties, as well as the tribological behavior of metal matrix composites (MMCs), based on FeGr1 sintered material with the single and hybrid addition of a silicon carbide and graphite was undertaken. During the study, the flexural and compressive strength of MMCs were analyzed and changes of the momentary coefficient of friction, the temperature of friction, as well as wear rates of the MMCs tested were monitored. Based on the results, it was revealed that wear rates decreased 12-fold in comparison to the base material when SiC or SiC + Gr were added. Further research into MMCs with ceramic particle additives is proposed.     

Wear Resistance Improvement of Cemented Tungsten Carbide Deep-Hole Drills after Ion Implantation

The paper is dedicated to the life prolongation of the tools designed for deep-hole drilling. Among available methods, an ion implantation process was used to improve the durability of tungsten carbide (WC)-Co guide pads. Nitrogen fluencies of 3 × 10¹⁷ cm⁻², 4 × 10¹⁷ cm⁻² and 5 × 10¹⁷ cm⁻² were applied, and scanning electron microscope (SEM) observations, energy dispersive spectroscopy (EDS) analyses, X-ray photoelectron spectroscopy (XPS) and Secondary Ion Mass Spectrometry (SIMS) measurements were performed for both nonimplanted and implanted tools. The durability tests of nonimplanted and the modified tools were performed in industrial conditions. The durability of implanted guide pads was above 2.5 times greater than nonimplanted ones in the best case, presumably due to the presence of a carbon-rich layer and extremely hard tungsten nitrides. The achieved effect may be attributed to the dissociation of tungsten carbide phase and to the lubrication effect. The latter was due to the presence of pure carbon layer with a thickness of a few dozen nanometers. Notably, this layer was formed at a temperature of 200 °C, much smaller than in previously reported research, which makes the findings even more valuable from economic and environmental perspectives.