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The complex microstructure and properties of dental enamel have been studied for decades using a variety of quantitative and qualitative techniques in order to gain a greater depth of understanding behind the chemical and physical processes that are associated with the formation and destruction of this biological apatite. Dental enamel is composed of highly ordered carbonated hydroxyapatite crystals which, together with its small organic component, are responsible for its mechanical strength, allowing it to serve its functional purpose. Environmental changes at any stage of the biomineralisation process or post eruption can disrupt the orientation and alter the structure and function, which can have detrimental clinical effects. The aim of this study is to understand and characterise the structural and crystallographic properties of disrupted enamel, and compare this to healthy unaffected tissue. Enamel affected by the genetic disorder, Amelogenesis Imperfecta, alongside enamel disrupted by dissolution and caries were studied using Synchrotron X-ray diffraction, 3D X-ray Microtomography, and Scanning Electron Microscopy techniques to relate these features to the clinically observed characteristics; to the chemistry; and to the known genetics of the tooth. Synchrotron radiation was used to map changes in preferred orientation, while the corresponding mineral density distributions were seen by using an in house developed, non-destructive microtomography system. Structural information on dental enamel at the crystallographic and micron length scales can benefit a variety of different disciplines. This project has the potential to inform early diagnosis, develop a tool for an early recognition of progressive or highly variable medical conditions, and design potential treatment regimes. The comparison of affected enamel to that of healthy enamel will provide a unique opportunity to identify the developmental pathways required for normal tooth development and give insights into the basic principles underlying mammalian biomineralisation.

Human deciduous and permanent enamel samples were simultaneously exposed to 0.1 M acetic acid pH 4.0 solution with an increasing calcium and phosphate concentration. Demineralisation rates at each calcium and phosphate increment were measured by scanning microradiography (SMR) to monitor in real-time the demineralisation trend. No significant differences (p > 0.05) were observed between baseline demineralisation rates of each enamel type. Similarities in the demineralisation trend as a function of increasing calcium and phosphate concentration were also observed. SMR detected a halt in demineralisation rate at 30 mM and 32.5 mM calcium concentration for permanent and deciduous enamel equilibrium between the solution and enamel samples had been achieved. Comparisons of the SMR data with a speciation software program indicated the solubility product of deciduous and permanent enamel is 121 in pH 4.0 and 25 ⁰C conditions. X-ray Microtomography (XMT) results of the mineral concentrations of each enamel type showed no significant differences (p > 0.05) and Confocal laser scanning microscopy (CLSM) image analysis of rhodamine B dye infiltration showed no significant differences between the interprismatic regions of each enamel type (p >0.05), complementing the SMR data. Permanent enamel exhibited significantly larger prism head diameters near to the surface of enamel compared to near the EDJ, whereas prism head diameters in deciduous enamel remained relatively constant throughout enamel. Thus the high caries incidence rates amongst children may be due to a lower level of protection offered by saliva and the oral environment of a child compared to an adult rather than the structure and the physical chemistry of the tissue itself.

Thesis (M.D.S.) - University of Hong Kong, 1993. / Includes bibliographical references (leaf 143-154). Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

abstract / Dentistry / Doctoral / Doctor of Philosophy

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