179 research outputs found
A Hemispherical Contact Model for Simplifying 3D Occlusal Surfaces
Statement of problem
Currently, dental articulators can recreate mandibular movements and occlusal contacts. However, whether virtual articulators can also provide information about occluding dental surfaces, functional movements, and the mandibular condyles is unclear. Purpose
The purpose of this in vitro study was to evaluate the occluding surfaces on dental casts obtained from a patient and approximate them to a hemispherical contact model. Both models were tested by digitizing the Dentatus ARL dental articulator. Material and methods
A combination of photogrammetry and structure from motion methods were used to scan a Dentatus ARL articulator and representative dental casts. Using computer-aided engineering and finite element analysis, contact points and action vectors to the forces on occluding surfaces and condyles were obtained for cast and hemispherical models. This experiment was performed using centric occlusion and 3 different condylar inclinations. The Kruskal-Wallis 1-way analysis of variance on ranks test was used to allow all pairwise comparisons between condylar inclination and mechanical action vector values in each location (α=.05). Results
Action vectors from the cast model and each location of the hemispherical model were calculated to show the mechanical consequences and the similarity among models. Overall, no significant differences were observed for action vectors (A20 versus A40 versus A60) at each location (dental cast/hemisphere, right condylar, and left condylar) in the analysis of dental casts and the hemisphere model (.382â€Pâ€.999). Conclusions
This study provided graphical information that may assist the dental professional in determining which occlusal contacts should be modified to attain condylar and balanced centric occlusion
Fractal and multifractal analysis of PET-CT images of metastatic melanoma before and after treatment with ipilimumab
PET/CT with F-18-Fluorodeoxyglucose (FDG) images of patients suffering from
metastatic melanoma have been analysed using fractal and multifractal analysis
to assess the impact of monoclonal antibody ipilimumab treatment with respect
to therapy outcome. Our analysis shows that the fractal dimensions which
describe the tracer dispersion in the body decrease consistently with the
deterioration of the patient therapeutic outcome condition. In 20 out-of 24
cases the fractal analysis results match those of the medical records, while 7
cases are considered as special cases because the patients have non-tumour
related medical conditions or side effects which affect the results. The
decrease in the fractal dimensions with the deterioration of the patient
conditions (in terms of disease progression) are attributed to the hierarchical
localisation of the tracer which accumulates in the affected lesions and does
not spread homogeneously throughout the body. Fractality emerges as a result of
the migration patterns which the malignant cells follow for propagating within
the body (circulatory system, lymphatic system). Analysis of the multifractal
spectrum complements and supports the results of the fractal analysis. In the
kinetic Monte Carlo modelling of the metastatic process a small number of
malignant cells diffuse throughout a fractal medium representing the blood
circulatory network. Along their way the malignant cells engender random
metastases (colonies) with a small probability and, as a result, fractal
spatial distributions of the metastases are formed similar to the ones observed
in the PET/CT images. In conclusion, we propose that fractal and multifractal
analysis has potential application in the quantification of the evaluation of
PET/CT images to monitor the disease evolution as well as the response to
different medical treatments.Comment: 38 pages, 9 figure
Dynamics of airflow in a short inhalation
During a rapid inhalation, such as a sniff, the flow in the airways
accelerates and decays quickly. The consequences for flow development and
convective trans- port of an inhaled gas were investigated in a subject
geometry extending from the nose to the bronchi. The progress of flow
transition and the advance of an inhaled non-absorbed gas were determined using
highly resolved simulations of a sniff 0.5 s long, 1 litre per second peak
flow, 364 ml inhaled volume. In the nose, the distribution of airflow evolved
through three phases: (i) an initial transient of about 50 ms, roughly the
filling time for a nasal volume, (ii) quasi-equilibrium over the majority of
the inhalation, and (iii) a terminating phase. Flow transition commenced in the
supraglottic region within 20ms, resulting in large- amplitude fluctuations
persisting throughout the inhalation; in the nose, fluctuations that arose
nearer peak flow were of much reduced intensity and diminished in the flow
decay phase. Measures of gas concentration showed non-uniform build-up and
wash-out of the inhaled gas in the nose. At the carina, the form of the
temporal concentration profile reflected both shear dispersion and airway
filling defects owing to recirculation regions.Comment: 15 page
Telemedicine using VoIP combined with a store and forward approach
Rural areas in South Africa have unique conditions such as remoteness and scarcity of reliable public facilities. Information and Communication Technologies (ICTs) introduced into these areas must be suitable for these conditions. Using a user-centred design approach based on Participatory Design and Action Research, we have developed a telemedicine application for a rural village in the Eastern Cape. This paper describes how we determined the requirements and design for the application and why we chose Voice over Internet Protocol (VoIP) combined with a store and forward approach to achieve our telemedicine goals. We present an overview of the methodology we are using, describe the software application we have developed and mention several challenges we have faced to date. Finally we conclude that VoIP and store and forward technologies are appropriate to the South African rural situation.Telkom, Siemens, THRIP, IDRC, SANPADDepartment of HE and Training approved lis
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