Osseointegration of a 3D Printed Stemmed Titanium Dental Implant: A Pilot Study

In this pilot study, a 3D printed Grade V titanium dental implant with a novel dual-stemmed design was investigated for its biocompatibility in vivo. Both dual-stemmed (n = 12) and conventional stainless steel conical (n = 4) implants were inserted into the tibial metaphysis of New Zealand white rabbits for 3 and 12 weeks and then retrieved with the surrounding bone, fixed, dehydrated, and embedded into epoxy resin. The implants were analyzed using correlative histology, microcomputed tomography, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The histological presence of multinucleated osteoclasts and cuboidal osteoblasts revealed active bone remodeling in the stemmed implant starting at 3 weeks and by 12 weeks in the conventional implant. Bone-implant contact values indicated that the stemmed implants supported bone growth along the implant from the coronal crest at both 3- and 12-week time periods and showed bone growth into microporosities of the 3D printed surface after 12 weeks. In some cases, new bone formation was noted in between the stems of the device. Conventional implants showed mechanical interlocking but did have indications of stress cracking and bone debris. This study demonstrates the comparable biocompatibility of these 3D printed stemmed implants in rabbits up to 12 weeks

Correlative Spectromicroscopy and Tomography for Biomedical Applications involving Electron, Ion, and Soft X-ray Microscopies

Many important scientific and technical problems are best addressed using multiple, microscopy-based analytical techniques that combine the strengths of complementary methods. Here, we provide two examples from biomedical challenges: unravelling the attachment zone between dental implants and bone, and uncovering the mechanism of Alzheimer's disease. They combine synchrotron-based scanning transmission X-ray microscopy (STXM) with transmission electron microscopy ((S)TEM), electron tomography (ET), EELS tomography, and/or atom probe tomography (APT). STXM provides X-ray absorption based chemical sensitivity at mesoscale resolution (10–30 nm), which complements higher spatial resolution electron microscopy and APT

Evaluations of People Depicted With Facial Disfigurement Compared to Those With Mobility Impairment

There are few extant studies of stereotyping of people with facial disfigurement. In the present study, two experiments (both within-participants) showed positive evaluations of people depicted as wheelchair users and, from the same participants, negative evaluations of people with facial disfigurements, compared to controls. The results of Experiment 2 suggested that implicit affective attitudes were more negative toward people with facial disfigurement than wheelchair users and were correlated with evaluation negativity. Social norms were perceived to permit more discrimination against people with facial disfigurement than against wheelchair users. These factors could help to explain the evaluative differences between the two disadvantaged groups

The Effect of Particle Surface Area to Volume Ratio on Ion Release from CoCr Spheres

In 2005, over 200,000 Americans underwent a hip arthroplasty, the replacement of a hip joint with an artificial prosthesis. Of these arthroplasties, metal-on-metal type implants represent an increasing usage percentage. Metal-on-metal implants are selected largely for their low volumetric wear rate, durability, and resistance to corrosion. In spite of these advantages, little is known concerning the long-term consequences of heavy metal alloy use in the body, although early research indicates potentially carcinogenic results. This thesis is a preliminary investigation into these long term effects and their root causes. An improved comprehension of the corrosion kinetics and the rate of ion production from the high surface energy wear debris released by implant articulation can assist in illustrating the relative clinical significance of exposure to these metallic bodies over time. This thesis primarily focuses on developing a test methodology for the detection and analysis of ion dissociation in simulated body fluids. In order to validate this test methodology, the ion dissociation rates and surface characteristics of several predetermined diameters of cobalt chromium alloy spherical particles were analyzed. The effect of changing particle diameter, and thus surface area to volume ratio, on ion dissociation rate was determined to be significant when not affected by localized agglomeration. Additionally, preferential corrosion of cobalt within individual grains was observed and correlated to elevated cobalt concentrations in the electrolyte. These results suggest that ion dissociation kinetics for true wear particles can be determined through the refinement and application of the methodology developed

The impact of rising Ni and V impurity levels in smelter grade aluminium and potential control strategies

The technology for controlling smelter metal impurities post reduction has steadily improved. For example, control of sodium has seen the reduction and, in some plants, the elimination of chlorine gas from the casthouse. However, changes in the purity of cell feed materials such as anodes are giving rise to new challenges in impurity control; vanadium and nickel levels are an emerging problem. This paper briefly reviews the important impurities and their effects on downstream casting, forming and final application properties. Particular emphasis is given to nickel and vanadium. Strategies for controlling these impurities are also discussed and areas where new technology is needed are also highlighted. In some cases it is not known what the tolerable limits of impurities are. There are a plethora of metal refining techniques used in the extraction of other metals which could be investigated for the control of impurities in smelter grade aluminium

The downstream consequences of rising ni and v concentrations in smelter grade metal and potential control strategies

Technology for controlling smelter metal impurities post reduction has steadily improved. For example, control of sodium has seen the reduction and in some plants elimination of chlorine gas. However, changes in the purity of cell feed materials such as anodes are giving rise to new challenges in impurity control; vanadium and nickel levels are an emerging problem. This paper briefly reviews the important impurities and their effects on downstream casting, forming and final application properties. Particular emphasis is given to nickel and vanadium. Strategies for controlling these impurities are also discussed and areas where new technology is needed are also highlighted. In some cases it is not known where the tolerable limits of impurities are. There are a plethora of metal refining techniques used in the extraction of other metals which can be investigated for control of impurities in smelter grade aluminum

Stress induced defect formation in DC cast magnesium alloys

The horizontal direct chill (HDC) casting process is emerging as an attractive production route for magnesium remelt ingot. The CRC for Alloy and Solidification Technology (CAST) has performed significant development work to facilitate HDC casting of magnesium and its alloys. This paper reports the results of a study of the defects that may form during HDC casting of pure magnesium and alloy AZ91. Depending on the operating conditions and alloy cast, the ingot may sometimes display surface cracks and classic centreline DC casting hot cracks. The formation of these defects restrics productivity and casting quality and may also represent a significant safety hazard during HDC casting or in remelting the magnesium ingot. It is shown that both surface cracks and hot tears are related to the rupture of the partially solidified material as a consequence of the development of excessive stresses during casting. The process behaviour in terms of heat flow, sump profile and solidification mode has therefore been determined to enable the identification and prediction of the root causes of these defects during HDC casting of both pure magnesium and AZ91 under different casting conditions. Inspection of the cracks indicates that they have both formed while the alloy was in a partly solidified condition. The mechanisms leading to stress development in the ingot are discussed and related to the development of strength in the mushy zone during solidification