published_or_final_version / abstract / Dentistry / Doctoral / Doctor of Philosophy

Faculty of Science School of Geography,Achaeology and Enviromental Studies 9905929t thodgskiss@yahoo.com / This study was stimulated by questions that arose on the Middle Stone Age (MSA) tools from Sibudu cave, KwaZulu-Natal, South Africa. Many stone tools were found to have ochre traces or ochre plant resin traces on their proximal ends, as well as bending fractures on their laterals caused by hafting. This placement of ochre is unusual because it would be expected that ochre would be found on the working edges of the tools if they had been used to prepare ochre. A possible explanation is that the ochre is part of the hafting process and that ochre was used as an aggregate in the adhesive that held the stone tool to the haft. The question this research aims to answer is why ochre was used as an aggregate in plant resin instead of other easily acquirable substances, such as sand or ash. I have experimented with a variety of aggregates and then performed various activities with the hafted tools to test the strength and effectiveness of the different adhesive recipes. The chemical and physical properties of the ingredients used in the adhesives are also explored, together with principles of geological cementation and the methods involved in the creation of industrial concrete. Results of my replications are varied and they show that uncontrollable variables influence the resultant adhesive quality. Results contribute to understanding the uses and implications of the ochre on the MSA sites, and illuminate that people living in the MSA had an understanding of the best physical and chemical properties needed in adhesives, even though they could not have had an understanding of attributes like mineralogy and pH.

Magister Scientiae Dentium - MSc(Dent) / Restorative dentistry aims to replace lost or damaged tooth structure with durable and life-like alternatives. To accommodate the inherent limitations and weakness of the restorative materials, preparation techniques often require the sacrifice of healthy tooth structure to create enough restorative space. This can lead to weakening of the remaining tooth structure, with subsequent damage or catastrophic failure. When using indirect restoratives, the development of adhesive luting agents (adhesive cements) and stronger allporcelain restorations (lithium disilicate) has contributed to the development of “minimally invasive” preparation techniques and concepts such as cavity design optimization (CDO) and bio-substitution. With these techniques, resin materials are combined with ceramic restoratives in an attempt to not only produce strong restorations, but also increase the longevity of the remaining tooth. The clinician needs to therefore find the ideal preparation design that combine such materials to produces a clinically performing restoration while increasing the strength and longevity of the underlying tooth.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

The task of this thesis is to test different adhesives uses in electrical drives for high performance applications. The purpose is to investigate possible replacements to the current used adhesive which will be obsolete in short term. This task is approached by first doing a literature search for typical testing methods for adhesives and which ones are appropriate for Moog. Then, a test rig is designed to accomplish the tests. Finally, the tests are evaluated and analysed to find out the best replacement adhesive.

During the drying of a surface, the liquid evaporation acts to keep the temperature relatively constant, due to evaporative cooling. As the drying nears completion the liquid film begins to break, exposing areas that are no longer cooled through evaporation, which begin to heat. Although this heating can be measured with an Infrared (IR) camera, the sensitivity is often not sufficient to recognize the point at which the film breaks. Complicating the measurement is the changing emissivity that commonly occurs as objects dry. The sensitivity and emissivity issues can be addressed by analyzing the temperature in the area of interest and computing the coefficient of variance (COV) of the temperature. This technique is compared to temperature and standard deviation measurements made with an IR camera and the COV technique is shown to be superior for determining when the liquid film breaks. The film breakage point is found to vary with temperature and material roughness in two industrially significant applications: the drying of wood flakes and the drying of polymer films. Film breakage in wood flakes is related to detrimental finished quality problems and also to emission problems. The rate at which an adhesive dries affects the roughness of the polymer film and subsequently, the bond strength. The COV technique is used to predict the roughness of the finished polymer film. Use of the COV technique allows the drying of a liquid film to be visualized in a way that has been previously unreported.

Thesis (M.Sc.(Odontology))--University of Pretoria, 2009. / Includes bibliographical references (leaves 75-101).

Modern synthetic structural adhesives are finding a place in the drive to improve the fuel efficiencyof automobiles through weight reduction of the structure. One of the most important properties ofthe adhesives used in this type of joining is the fracture energy.A literature study is carried out to gain a broader understanding of the methods used for thedetermination of the fracture energy of adhesives. One of the most common experimental methodsrelies on the use of the Double Cantilever Beam (DCB) test specimen. International standards for theDCB test are studied. Prediction of the fracture energy using Linear Elastic Fracture Mechanics andthe J-integral approach, a closed form solution and finite element methods are also seen. Differencesin these methods are attributed in part to the nonlinear behaviour of the adhesive being studied. It isdecided to use the results of a non-standard DCB test and the 40% error calculated by a theoreticalstandard method as a point of reference.A comprehensive comparison of the American Society for Testing Materials (ASTM) and BritishStandard Institution (BSI) standards for the determination of the fracture energy of adhesives isundertaken. Limitations and overlaps in the standards are identified. A DCB specimen isrecommended and an experimental procedure that satisfies elements one or both standards issuggested along with several small additions such as using a wire to assist in the application of theadhesive and the use of cameras to track the crack growth. In addition, a new fixture to allow testingof the recommended DCB specimen according to the standards is designed and manufactured.Materials for the preparation of tests specimens are ordered and, based on available laboratorytime, a single DCB test specimen is made for the purposes of testing a rubber-based automotivestructural adhesive. The specimen is tested using the recommended experimental procedure usingthe new fixture. The data produced during the test are collected and interpreted using themethodology proposed in the BSI standard for the calculation of the fracture energy of the selectedrubber-based adhesive. Several challenges found during this process are identified. The fractureenergy determined from the standard-based experiment ranges from 140 J/m2 to 1380 J/m2depending on the methodology used.The values of the fracture energy determined from the standard-based DCB experiment are thencompared to the fracture energy seen with the nonstandard-based experiment and to the standardbasednumerical test seen in the literature. It is shown that when simple beam theory method isused the difference in the results found in the standard-based experiment and nonstandard-basedexperiment can be confirmed to lie within the 40% error observed in the literature.Finally, the contributions of the project are summarized and recommendations for future work aremade. In particular, the lack of information given in the BSI standard when calculating the fractureenergy and the need for multiple test specimens are required by the standard, must be addressed inorder to support the obtained results and conclusions.

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