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Biomedical subjects

A Harrison

Publications and source records attributed to A Harrison.

At least 307 records · Page 17Linked to original sources
PubMedDate not supplied

The role of virtual reality technology in the assessment and training of inexperienced powered wheelchair users.

PURPOSE: The current paper provides quantitative and qualitative data concerning the application of two virtual environments to the assessment and training of inexperienced powered wheelchair users, both in terms of the ability to control the chair accurately without hitting objects in the environment (manoeuvrability) and in terms of being able to find ones way around a complex environment without becoming lost (route-finding). METHOD: Six novice powered wheelchair users participated in the project, completing either the manoeuvrability or route finding components of the study. Performance measures were taken in real life pre and post training and throughout virtual reality sessions. Participants also completed a questionnaire regarding the aesthetics of the virtual environments and aspects of the powered wheelchair simulation. RESULTS: The participants rated the aesthetics of the virtual environments positively and engaged well with the virtual system. However, they found the manoeuvrability tasks considerably more difficult in virtual reality (VR) than in real life. Some difficulties with controlling the simulated wheelchair were apparent. Some improvements on virtual and real life manoeuvrability tasks and route finding were noted following conventional and virtual training. CONCLUSIONS: The study indicated that the two virtual environments represent a potentially useful means of assessing and training novice powered wheelchair users. The virtual environments however must become less challenging if they are to represent a motivating and effective means of improving performance. Further development of the way in which wheelchair movement is controlled and simulated represents a key element in this multi stage project.

Adult↗
PubMedDate not supplied

Lung function in young persons after spinal fusion for scoliosis.

The long-term changes in vital capacity and in total lung capacity after spinal fusion for 43 scoliotic patients are described. The values recorded were seldom lower after surgery but did not show any marked subsequent increases with patient growth. Subsequent increases in volumes are less marked in the group of patients with paralytic scoliosis. These findings suggest that the psychological advantages of improving the patient's appearance by surgery and of preventing any respiratory condition from worsening may be achieved, although the total capacity and vital capacity are not much improved by spinal fusion.

Adolescent↗
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Endothelial nitric oxide synthase: correlation with histologic grade, lymph node status and estrogen receptor expression in human breast cancer.

Nitric oxide is produced by several isoenzymes which are present in many different tissues. We have recently reported the presence of inducible nitric oxide synthase in a breast cancer cell line. The purpose of this study was to examine the distribution of endothelial nitric oxide synthase (eNOS) in a series of human breast tumours. Immunohistochemical investigations demonstrated immunolabelling of tumour cells with the primary antibody, bovine endothelial anti-nitric oxide synthase. Although there was no correlation between eNOS staining and tumour size, there was a significant (p < 0.005) negative correlation (rho = -0.65) between the percentage of tumour cells staining positive for eNOS and the histologic grade of the tumour; there was also a significant (p < 0.05) negative correlation (rho = -0.40) between the percentage of tumour cells staining positive for eNOS and the number of positive lymph nodes. A significant (p < 0.005) positive correlation (rho = 0.63) between the percentage of tumour cells staining positive for eNOS and estrogen receptor (ER) expression by the tumour was also observed. In conclusion, our results demonstrate that eNOS is expressed by human breast tumours and that its presence negatively correlates with histologic grade and lymph node status and positively correlates with ER expression.

Animals↗
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Unidentified coryneform bacterial strain from cases of polyarthritis in chickens: phenotype and fatty acid profile.

We report isolation of a strain of fermentative coryneform bacteria from an outbreak of polyarthritis in chickens. This strain could not be assigned to any recognized bacterial taxon because its peculiar phenotype is not yet reported. The strain possessed phenotypic characteristics and fatty acid profile similar to Erysipelothrix but, on the other hand, exhibited temperature-dependent motility like Listeria. We found no evidence of either Mycoplasma synoviae or Chlamydia infection. Details of the phenotype and fatty acid profile of the isolate and measures undertaken to contain the outbreak have been described.

Actinomycetales↗
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The application of an Actel field programmable gate array in the design of an ECG RR interval recorder.

Field Programmable Gate Arrays (FPGAs) allow digital circuitry to be integrated on to a single device without the long time penalty incurred with mask programmable Application Specific Integrated Circuits (ASICs). This makes FPGA technology an attractive option to engineer involved in designing digital circuitry where space is at a premium. Furthermore, the relatively low cost of FPGAs at low volume, compared to mask programmable ASICs make them an excellent prototyping option for designers who are considering low cost volume production with mask programmable ASICs. There are several different types of FPGAs available which thus creates confusion for prospective users uncertain of their relative benefits. This paper serves as an introduction to FPGA technology and the stages involved in implementing a design, via the application of an Actel FPGA to the development of an ambulatory long term electrocardiogram (ECG) based RR interval recorder.

Biomedical Engineering↗
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Methods used to select artificial anterior teeth for the edentulous patient: a historical overview.

PURPOSE: Selecting artificial teeth for a denture is complex when there are no remaining natural teeth and no pre-extraction records. The aim of this paper is to review the methods used to select artificial anterior teeth for the endentulous individual. MATERIALS AND METHODS: The review takes account of the majority of papers published during the last 100 years and is organized according to the methods used for determining artificial tooth form. RESULTS: Several factors have been proposed as aids for artificial tooth selection, and numerous methods have been devised for the evaluation of reliable esthetic factors in determining artificial tooth form. CONCLUSION: To date, no universally reliable method of determining tooth form has been found. The Williams classification (1914) is the most universally accepted method of determining anterior tooth form.

Denture Design↗
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The effect of chopped poly(methyl methacrylate) fibers on some properties of acrylic resin denture base material.

PURPOSE: The fracture of acrylic resin dentures remains an unresolved problem. Over the years, various approaches to strengthening acrylic resin have been suggested, including modifying or reinforcing the resin. The aim of this study was to investigate the effect of chopped poly(methyl methacrylate) (PMMA) fibers on some properties of acrylic resin denture base material. MATERIALS AND METHODS: PMMA in the form of fibers 0.75 mm in diameter and 5 mm in length was added to acrylic resin denture base material in various percentages to form a composite material. The influence on doughing and manipulation times and transverse strength was examined. The results were subjected to statistical analysis using a one-way analysis of variance and, where appropriate, the Scheffé test. RESULTS: The results showed that the doughing time was decreased by the addition of fibers, with the manipulation and setting times showing inconsistent changes. There was a significant difference between the materials in terms of the transverse strength. When the amount of PMMA fibers in the acrylic resin was increased, there was a decrease in the modulus of rupture and a decrease in the modulus of elasticity. The differences were shown to be statistically significant in some groups. CONCLUSION: The doughing time was decreased by the addition of fibers, while the manipulation and setting times showed inconsistent changes. The incorporation of chopped, randomly oriented PMMA fibers into acrylic resin had no advantage over the unmodified polymer in terms of strength and cannot be recommended as a reinforcing agent for acrylic resin denture base material.

Acrylic Resins↗
PubMedDate not supplied

The effect of a hydroxyapatite-reinforced polyethylene stress distributor in a dental implant on compressive stress levels in surrounding bone.

This study investigated various designs of stress breakers incorporated into the dental implant using 3-D finite element analysis. These designs employed hydroxyapatite-reinforced polyethylene (HRP), a material capable of inducing osseointegration. The most successful design was that of a dental implant with a peripheral HRP component that was in direct contact with the bone surrounding the neck of the implant. This design lowered the compressive stress values in bone around the neck of the implant. Attempts were also made to optimize this design.

Alveolar Process↗
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Roughness of denture materials: a comparative study.

PURPOSE: Surface properties of denture materials are of clinical importance since they may affect plaque accumulation and staining. This in vitro study investigated the roughness of 20 commercially available denture materials. MATERIALS AND METHODS: Four denture base resins, nine hard lining materials, and seven soft denture lining materials were evaluated for roughness. Roughness measurements were made using a Mitutoyo Surftest SV-400, and the mean arithmetic roughness values (Ra) obtained were used for the comparisons. RESULTS: The overall Ra values ranged from 0.7 to 7.6 microns. The denture base materials group exhibited Ra values from 3.4 to 7.6 microns, whereas the hard liners were from 0.7 to 4.4 microns. The autopolymerized and visible light-cured soft liners presented Ra values from 0.7 to 3.5 microns, while the heat-cured soft liners ranged from 3.5 to 4.0 microns. CONCLUSION: The roughness exhibited by all of the materials tested (Ra values greater than 0.7 micron) indicates that there is a possibility for plaque accumulation, since 0.2 micron is considered the threshold below which no further bacterial adherence can be expected.

Acrylic Resins↗
PubMedDate not supplied

Effect of the addition of poly(methyl methacrylate) beads on some properties of acrylic resin.

PURPOSE: There have been numerous attempts to improve the mechanical properties of acrylic resin. However, the fracture of dentures is still an unresolved problem. The potential advantage of self-reinforcement should be improved mechanical properties over the amorphous random polymer. This study investigated the addition of poly(methyl methacrylate) (PMMA) beads in a variety of percentages on a range of mechanical properties of PMMA denture base acrylic resin. MATERIALS AND METHODS: The transverse and impact strengths and hardness of acrylic resin specimens stored in water for periods of 1 week and 6 months prior to testing were investigated. RESULTS: The results showed that for specimens stored for 1 week, the addition of up to 25% beads produced a significant increase in the modulus of elasticity. Addition of 5% beads produced a slight but nonsignificant increase in the modulus of rupture, although additions of increasing percentages produced a decrease in the modulus of rupture. The impact strength was increased for 5% to 25% beads and decreased for 40% beads. The hardness showed only small changes. For specimens stored in water for 6 months, the modulus of rupture decreased with increasing percentages of beads. The addition of beads up to 10% significantly increased the modulus of elasticity. There was no significant increase in impact strength but a significant increase in hardness for 5% beads. CONCLUSION: The addition of PMMA beads to acrylic resin did not produce a substantial improvement in the mechanical properties and cannot be recommended as a method of reinforcement in its present form.

Acrylic Resins↗
PubMedDate not supplied

An investigation of self-reinforced poly(methyl methacrylate) denture base acrylic resin using scanning electron and atomic force microscopy.

PURPOSE: The aim of this study was to examine the interfacial region of poly(methyl methacrylate) (PMMA) reinforced with untreated and surface-treated PMMA fibers in both chopped and continuous form using scanning electron and atomic force microscopy. MATERIALS AND METHODS: Acrylic resin specimens incorporating untreated and surface-treated (with butadiene styrene latex emulsion) PMMA fibers were examined using a scanning electron microscope and an atomic force microscope. RESULTS: There was evidence of random arrangement of untreated and surface-treated chopped fibers throughout specimens with areas of dense fiber aggregation and other areas containing few or no fibers. For the untreated and surface-treated fibers in continuous forms (a single and 2 unidirectional layers), there was evidence of fiber displacement and buckling, together with variation in interfiber spacing. For the specimens containing surface-treated continuous fibers in a cross-ply arrangement that had demonstrated a substantial improvement in the modulus of rupture, there was no evidence of fiber buckling, and the layer of butadiene styrene was consistently thin and even in comparison to weaker specimens. CONCLUSION: The thickness of the rubber layer and the fiber arrangement (in terms of fiber displacement and interfiber spacing) may be important factors in the success of the reinforcement.

Acrylic Resins↗
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Measurements of dimensional accuracy using linear and scanning profile techniques.

Various measurement methods have been described for the determination of dimensional accuracy and stability of denture base materials. This investigation introduces a computerised coordinate measuring machine (CCMM) and compares it with two methods routinely used for assessment of the accuracy of fit of denture base materials. The results demonstrate that the three methods (digital calipers, optical comparator, and CCMM) are acceptable for linear measurement. The CCMM was also used in its scanning mode to define and to quantify the contour changes of the resin bases. The advantages of the CCMM become apparent when two-dimensional changes require assessment.

Acrylic Resins↗
PubMedDate not supplied

Finite element analysis of the stress-concentrating effect of fraenal notches in complete dentures.

Based on clinical experience and empiricism, it was postulated that fraenal notches and midline diastemas lead to fracture of complete dentures. This study used finite element stress analysis to investigate the stress-concentrating effect of a fraenal notch with and without a midline diastema. It was found that a large fraenal notch resulted in high stress levels and that these stresses were augmented more by a narrow median diastema than its wider counterpart.

Dental Stress Analysis↗
PubMedDate not supplied

Soft lining materials in prosthetic dentistry: a review.

Although soft lining materials are widely used in prosthetic dentistry, their properties are far from ideal. This paper presents a review of these materials, including their historical development, clinical indications, ideal properties, and limitations. Examples of the three basic types are given together with their typical compositions. It is evident that further research and development is necessary to achieve a material with optimum properties.

Denture Liners↗
PubMedDate not supplied

Computer-aided learning in prosthodontics.

Interactive video is computer-aided learning illustrated by still or moving video pictures. First introduced for the study of pathology, its application and potential in prosthodontics is reported in this article. Partial denture design was chosen as the first subject, since the systematic approach concept could easily be established by dividing the subject into five units that could individually be expanded and tested. Students are generally enthusiastic about computer-aided learning and there is considerable potential to further develop this type of learning process.

Audiovisual Aids↗