This report describes the clinical and technical aspects in the oral rehabilitation of an edentulous patient with knife-edge ridge at the mandibular anterior edentulous region, using implant-retained overdentures. The application of computer-aided design and computer-aided manufacturing (CAD/CAM) in the fabrication of the overdenture framework simplifies the laboratory process of the implant prostheses. The Nobel Procera CAD/CAM System was utilised to produce a lightweight titanium overdenture bar with locator attachments. It is proposed that the digital workflow of CAD/CAM milled implant overdenture bar allows us to avoid numerous technical steps and possibility of casting errors involved in the conventional casting of such bars.
The effect of solid solution treatment on semisolid microstructure of Zn-22Al with developed dendrites was investigated. Zn-22Al is a zinc-based alloy with aluminium as its main alloying element. Producing Zn-22Al product by semisolid metal processing (SSM) offers significant advantages, such as reduction of macrosegregations, porosity and low forming efforts. Meanwhile, thermal and microstructure analyses of Zn-22Al alloy were studied using differential scanning calorimeter (DSC) and Olympus optical microscope. Solidus and liquidus of the alloy can be determined by DSC analysis. In addition, changes to the microstructures in response to solid solution treatments were also analyzed. The major effort of all the semi-solid technologies is the generation of small and spherical morphologies. Prior to the generation of spherical morphologies, the fine grains should be first produced. The as-cast samples were isothermally held at 315°C, ranging from 0.5 to 5 hours before they were partially re-melted at semisolid temperature of 438°C to produce solid globular grains structure in liquid matrix. The results indicated that a non-dendritic semisolid microstructure could not be obtained if the traditionally cast Zn-22Al alloy with developed dendrites was directly subjected to partial remelting. After solid solution treatment at 315°C, the black interdendritic eutectics were dissolved and gradually transformed into ß structure when the treatment time was increased. The microstructure of the solid solution treated sample changed into a small globular structure with the best shape factor of 0.9 and this corresponded to 40±16µm when the sample was treated for 3 hours, followed by directly partial remelting into its semi solid zone.
Titanium alloy (e.g. Ti-6Al-4V) has an excellent combination of properties. However in many cases,
the application is limited because of the poor wear property. In this work, a surface modification
(plasma nitriding) is carried out to improve the surface properties of Ti-6Al-4V, as a treatment prior to a hardcoating deposition, leading to a duplex coating system. This is an effort to improve the surface and near surface property of Ti-6Al-4V. Plasma nitriding is performed utilizing microwave plasma method in 25% Ar- 75% N2 atmosphere at temperatures of 600°C and 700°C for different processing times (1, 3 and 5 hours). The phase and microstructure of plasma nitrided substrate were characterized by using X-ray diffraction (XRD) and Scanning electron microscopy (SEM). The plasma nitrided Ti-6Al-4V properties (surface roughness, surface hardness and case depth) were determined using profilometer and microhardness, respectively. Results obtained showed a significant increase on the surface hardness of Ti-6Al-4V. This is due to the formation of TiN and Ti2N phases in the form of compound layer. Besides, it shows that the diffusion of nitrogen into the Ti-6Al-4V substrate produces case depth up to 130 µm and this contributes to the improvement of the near surface hardness due to the changes in the microstructures. It was also found that the surface hardness and surface roughness increased with the increases in the process temperature and times.
It is the aim of all clinicians to accomplish biological tooth movement, which implies the use of low, continuous force. Constant unrelented search for a better wire, which can deliver optimal orthodontic force, has led to the invention of a lot of orthodontic wires such as Stainless steel, Beta Titanium, Nickel Titanium and multi stranded wires. In this study, the loading and unloading properties of 0.016 inch, 0.016x0.022 inch and 0.017x0.025 inch dimensions of stainless steel, conventional NiTi, Super elastic NiTi, and TMA arch wires were determined by means of a modified three point bending test for two inter bracket widths of 5 mm and 6.5 mm for deflection of 1 to 3 mm. The applied forces dependence on cross-sectional size differs from the linear-elastic prediction in super elastic NiTi wires. The stainless steel wires had the highest force values on all the three dimensions and cross section. On loading and unloading, TMA wires had force values in-between stainless steel, conventional NiTi and super elastic NiTi. The conventional NiTi had much lower force values compared to stainless steel and TMA and were linearly progressing compared to Super elastic NiTi. On loading and unloading the super elastic NiTi had force values in the range of conventional NiTi and had constant forces on higher deflection. The studies showed that the force value was comparatively higher in 5 mm inter bracket width than the 6.5 mm inter bracket width for all the cross section and dimension of wires.
The corrosion behaviour of ternary aluminium alloy sacrificial anodes with small amount addition of tin as depassivating element in natural seawater was studied by means of conventional DC electrochemical measurements. Metallurgical microscope was employed in order to observe the changing of microstructure caused by tin present in ternary alloys. The relationship between microstructure and electrochemical results was examined and particular attention paid to the cause of the electrochemical efficiency of anode performance. The results indicate that the proper precipitates uniformly distributed of tin are influence on improving electrochemical performance of alumnium alloy anode.
Synthesis and characterization of supported metal-based oxygen carriers were carried out to provide information related to the use of oxygen carriers for chemical looping combustion processes. The Cu, Co, Fe, Ni metals supported with Al2O3, CeO2, TiO2, ZrO2 were prepared using the wetness impregnation technique. Then, the X-ray Diffraction (XRD) characterization of oxidized and reduced samples was obtained and presented. The kinetic analysis using Thermogravimetric analyzer (TGA) of the synthesized samples was conducted. The kinetics of reduction reaction of all samples were estimated and explained.
Corrosion prevention in biomaterials has become crucial particularly to overcome inflammation and allergic reactions caused by the biomaterials' implants towards the human body. When these metal implants contacted with fluidic environments such as bloodstream and tissue of the body, most of them became mutually highly antagonistic and subsequently promotes corrosion. Biocompatible implants are typically made up of metallic, ceramic, composite and polymers. The present paper specifically focuses on biocompatible metals which favorably used as implants such as 316L stainless steel, cobalt-chromium-molybdenum, pure titanium and titanium-based alloys. This article also takes a close look at the effect of corrosion towards the implant and human body and the mechanism to improve it. Due to this corrosion delinquent, several surface modification techniques have been used to improve the corrosion behavior of biocompatible metals such as deposition of the coating, development of passivation oxide layer and ion beam surface modification. Apart from that, surface texturing methods such as plasma spraying, chemical etching, blasting, electropolishing, and laser treatment which used to improve corrosion behavior are also discussed in detail. Introduction of surface modifications to biocompatible metals is considered as a "best solution" so far to enhanced corrosion resistance performance; besides achieving superior biocompatibility and promoting osseointegration of biocompatible metals and alloys.
The aluminium-silicon (Al-Si) based on Metal Matrix Composites (MMCs) is widely used in lightweight
constructions and transport applications requiring a combination of high strength and ductility. A grain
refinement plays a crucial role in improving characteristics and properties of Al alloys. In this investigation,
titanium diboride (TiB2) and scandium (Sc) inoculants were added to the Al-Si alloys for grain refinement of
an alloy. In this investigation, the corrosion resistance rate of Al-Si cast alloy reinforced by TiB2 and Sc were
measured by potentiostat (AUTOLAB) instrument. The aim of this research is to investigate the corrosion
rate for Al-Si-TiB2-Sc composites that immersed in different concentration of acidic solutions. Besides, the
immersion time of acidic solutions also was investigated. All the samples were prepared accordingly for
ASTM standard by the composition of 6.0 wt% TiB2 and 0.6wt% Sc. All the samples undergo cold mounting
technique for easy handling on corrosion tests. Then the samples were immersed in two different
concentrations acidic medium solutions, which were 0.1.and 1.0 M hydrochloric acids (HCl). The corrosion
rate also was investigated for immersion samples of 1.0 M HCl for 21 days. From the results obtained, added
TiB2 and Sc onto Al-Si alloy gave the better properties in corrosion resistance. Corrosion rates to reduce when
the samples were immersed in a lower concentration of acidic medium, 0.1 HCl. However, there are some
significant on the result but it still following the corrosion rates trend. Thus, improvements to reinforcement
content need to be done in further research to cover the lack of this corrosion rates trend.
Duplex stainless steels (DSSs) are complex materials and they have been widely used in the marine environment and gas industries, primarily offering a better resistance of pitting corrosion and good mechanical properties. In the present work, the effects of heat treatment on duplex stainless steel (DSS) weld overlay samples that were heat treated at three different temperatures, namely 350 °C, 650 °C, and 1050 °C, and followed by air cooling and water quenching were studied. Stress relief temperature at 650 °C had induced sigma phase precipitation in between delta ferrite and austenite (δ/γ) grain boundaries, resulting in the loss of corrosion resistance in the weld metal. Interestingly, post weld heat treatment (PWHT) test samples that were reheated to solution annealing temperature had shown no weight loss. The ferrite count determination in the region of weld metal overlay increased at hydrogen relief and decreased at stress relief temperatures due to slow cooling, which is more favorable to austenite formation. The amount of ferrite in the weld metals was significantly reduced with the increment of solution anneal temperature to 1050 °C because of sufficient time for the formation of austenite and giving optimum equilibrium fraction in the welds.
Automobile, aerospace, and shipbuilding industries are looking for lightweight materials for cost effective manufacturing which demands the welding of dissimilar alloy materials. In this study, the effect of tool rotational speed, welding speed, tilt angle, and pin depth on the weld joint were investigated. Aluminum 5052 and 304 stainless-steel alloys were joined by friction stir welding in a lap configuration. The design of the experiments was based on Taguchi's orthogonal array for conducting the experiments with four factors and three levels for each factor. The microstructural analysis showed tunnel defects, micro voids, and cracks which formed with 0° and 1.5° tilt angles. The defects were eliminated when the tilt angle increased to 2.5° and a mixed stir zone was formed with intermetallic compounds. The presence of the intermetallic compounds increased with the increase in tilt angle and pin depth which further resulted in obtaining a defect-free weld. Hooks were formed on either side of the weld zone creating a mechanical link for the joint. A Vickers hardness value of HV 635.46 was achieved in the mixed stir zone with 1000 rpm, 20 mm/min, and 4.2 mm pin depth with a tilt angle of 2.5°, which increased by three times compared to the hardness of SS 304 steel. The maximum shear strength achieved with 800 rpm, 40 mm/min, and a 4.3 mm pin depth with a tilt angle of 2.5° was 3.18 kN.
Fixed orthodontic treatment requires the use of orthodontic brackets and archwires in order to correct malocclusions. The objective of this study was to evaluate the pattern of orthodontic material usages i.e. bracket and archwire among Malaysian orthodontists. A self-administered questionnaire was distributed to members of the Malaysian Association of Orthodontist. Data entry and statistical analysis was done using SPSS version 15.0. Descriptive statistics were used for analysis. Means and standard deviations were calculated for continuous variables, frequency and percentages for categorical variables. Thirty-four orthodontists responded to the survey, with 76% (n=26) were female and the mean age was 43.31 years (SD 8.76). Most respondents used conventional metal brackets (60%, n=60) and most bracket prescription used was MBT (56%, n=19). At levelling stage, most respondents used nickel titanium archwire (84.5%, n=47). Stainless steel archwire was the most favourable choice for retraction/space closure stage (73.9%, n=34). At finishing, most respondents (60.4%, n=29) preferred to use stainless steel wire in their cases. As a conclusion, specific types of orthodontic materials were preferred and used by Malaysian orthodontists in delivering orthodontic treatment.
Nitridation behaviour of Al-Mg-Si alloys was studied as a function of temperature by means of thermogravimetry method. A reactive gas, N2-4%H2 at a rate of 10 ml/min was purged into the thermogravimetry analyser chamber. The Al alloys were heated from 25oC to 625oC at the heating rate of 15oC/min and then reduced to 3oC/min until it reached 1500oC. It was found that by varying the amount of Mg and Si in Al-Mg-Si alloys significantly influenced the growth of the composites. A differential thermogravimetric curve shows the Mg containing alloys experienced many steps of chemical reactions. This indicates that besides AlN presence as a major phase, other compounds also exist in the final product. The X-ray diffraction results confirmed the existence of oxide phases such as a-Al2O3, MgAl2O4 and MgO in addition to residual Si and Al metal. The presence of oxide compounds is believed to be due to the reaction between the alloying elements and residual oxygen gas left in the reaction atmosphere. It was also found that Si could play a role in promoting the weight gain of the composite produced. The heating rate has also a profound effect on the weight gain, whereby higher heating rate resulted in low yielded of AlN during the nitridation reaction of the Al-Mg-Si alloys.
Anticorrosion potential of mangrove tannins on aluminium alloys AA6061 in NaCl solution has been studied using potentiodynamic polarisation method and scanning electron microscopy (SEM). The study was carried out in different pH of corrosive medium in the absence and presence of various concentrations of tannin. The corrosion inhibition behaviour of the mangrove tannin on AA6061 aluminium alloy corrosion was found to be dependant on the pH of NaCl solution. Our results showed that the inhibition efficiency increased with increasing tannins concentration in chloride solution at pH 6. Treatment of aluminium alloy 6061 with all concentrations of mangrove tannins reduced the current density, thus decreased the corrosion rate. Tannins behaved as mixed inhibitors at pH 6 and reduction in current density predominantly affected in cathodic reaction. Meanwhile, at pH 12, addition of tannins shifted the corrosion potential to more cathodic potentials and a passivating effect was observed in anodic potentials. SEM studies have shown that the addition of tannins in chloride solution at pH 12 reduced the surface degradation and the formation of pits.
Annealing temperature plays an important role in the formation of an Au-Ga eutectic alloy. The effects of the annealing temperature on gold nanoparticles colloid and substrate surface were studied using AFM, FE-SEM and TEM. At 600oC, the layer of gold colloids particle formed an island in the state of molten eutectic alloy and absorbed evaporated metalorganics to formed nanowire (NW) underneath the alloy. Pit formed on the substrate surface due to the chemical reactions during the annealing process have an impact on the direction of growth of the NW. Without annealing, the NW formed vertically on the GaAs (100) surface. The growth direction depends on the original nucleation facets and surface energy when annealed. When annealed, the wire base is large and curved due to the migration of Ga atoms on the substrate surface towards the tip of the wire and the line tension between the substrate surface and gold particle.
Feedstock preparation, as well as its characterization, is crucial in the production of highly sintered parts with minimal defect. The hard metal powder - particularly, cemented carbide (wc-co) used in this study was investigated both physically and thermally to determine its properties before the mixing and injection molding stage. Several analyses were conducted, such as scanning electron microscopy, energy dispersive X-ray diffraction, pycnometer density, critical powder volume percentage (cPvP), as well as thermal tests, such as thermogravimetric analysis and differential scanning calorimetry. On the basis of the CPVP value, the feedstock, consisting of wc-co powder, was mixed with 60% palm stearin and 40% polyethylene at an optimal powder loading, within 2 to 5% lower than the CPVP value. The CPVP spotted value was 65%. The feedstock optimal value at 61% showed good rheological properties (pseudoplastic behavior) with an n value lower than 1, considerably low activation energy and high moldability index. These preliminary properties of the feedstock serve as a benchmark in designing the schedule for the next whole steps (i.e. injection, debinding and sintering processes).
In the recent years, electronic packaging provides significant research and development challenges
across multiple disciplines such as performance, materials, reliability, thermals and interconnections.
New technologies and techniques frequently adopted can be implemented in soldering alloys of
semiconductor sectors in terms of optimisation. Wetting contact angle or wettability of solder alloys
is one of the important factors which has got the attention of scholars. Hence in this study, due to the
remarkable similarity over classical solder alloys (Pb-Sn), Bi-Ag solder was investigated. Data were
collected through the effects of aging time variation and different weight percentages of Ag in solder
alloys. The contact angle of the alloys with Cu plate was measured by optical microscopy. Artificial
neural networks (ANNs) were applied on the measured datasets to develop a numerical model for further
simulation. Results of the experiments and simulations showed that the coefficient of determination (R2
)
is around 0.97, which signifies that the ANN set up is appropriate for the evaluation.
Dental plaque has a harmful influence on periodontal tissue. When a porcelain restoration is fabricated and refinishing of the glazed surface is inevitable, the increase in surface roughness facilitates the adhesion of plaque and its components. The aim of this in vitro study was to evaluate the effect of surface roughness of glazed or polished porcelain on the adhesion of oral Streptococcus mutans.
OBJECTIVE: To compare the clinical performance of nickel titanium (NiTi) versus stainless steel (SS) springs during orthodontic space closure.
DESIGN: Two-centre parallel group randomized clinical trial.
SETTING: Orthodontic Department University of Manchester Dental Hospital and Orthodontic Department Countess of Chester Hospital, United Kingdom.
SUBJECTS AND METHODS: Forty orthodontic patients requiring fixed appliance treatment were enrolled, each being randomly allocated into either NiTi (n = 19) or SS groups (n = 21). Study models were constructed at the start of the space closure phase (T0) and following the completion of space closure (T1). The rate of space closure achieved for each patient was calculated by taking an average measurement from the tip of the canine to the mesiobuccal groove on the first permanent molar of each quadrant.
RESULTS: The study was terminated early due to time constraints. Only 30 patients completed, 15 in each study group. There was no statistically significant difference between the amounts of space closed (mean difference 0.17 mm (95%CI -0.99 to 1.34; P = 0.76)). The mean rate of space closure for NiTi coil springs was 0.58 mm/4 weeks (SD 0.24) and 0.85 mm/4 weeks (SD 0.36) for the stainless steel springs. There was a statistically significant difference between the two groups (P = 0.024), in favour of the stainless steel springs, when the mean values per patient were compared.
CONCLUSIONS: Our study shows that stainless steel springs are clinically effective; these springs produce as much space closure as their more expensive rivals, the NiTi springs.
The composite reinforcement technique has been used clinically to salvage damaged root-filled teeth compromised by caries, trauma, developmental abnormalities, internal resorption and iatrogenic causes. This clinical case report describes the use of the technique to reattach a fractured fragment in a compromised endodontically treated root besides reinforcing it for continued function in the mouth. Factors of clinical importance related to this additional application; including reattachment of tooth fragments, post crown retention, coronal microleakage and fracture resistance and strength, are also briefly discussed.
Matched MeSH terms: Metal Ceramic Alloys/chemistry
Denture marking is accepted as a means of identifying dentures and persons in geriatric institutions, or post-mortem during war, crimes, civil unrest, natural and mass disasters. Labelling on the acrylic resin component of the denture can easily be damaged or destroyed by fire but on cobalt-chromium components it would be more resistant. A copper vapour laser (CVL) can be used to label the cobalt-chromium components of dentures and metal restorations easily, and legibly, and miniaturised for the incorporation of more personal particulars necessary for the identification of the deceased person. The CVL beam is focussed by its optics and delivered to the material surface by the two-axis scanner mounted with mirrors. A personal computer controls the movement of the scanner and the firing of the CVL. The high peak power of the pulsed CVL is focussed to very high energy density producing plasma ablation of the alloy surface. Very fine markings of a few microns width can be produced enabling the storage of detailed information of the deceased person on a metal surface for the purpose of rapid identification.