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Title: Application of X-Ray Scanning Microradiography to the Study of Caries-like Lesions in Enamel and Hydroxyapatite Model Systems
Author: Bollet-Quivogne, Frederic-Remy-Gaston
ISNI:       0000 0001 3469 1637
Awarding Body: Queen Mary, University of London
Current Institution: Queen Mary, University of London
Date of Award: 2007
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The mechanisms leading to enamel caries and lesions in hydroxyapatite (HAP) pellets systems are poorly understood. The kinetics of enamel and HAP demineralisation are usually controlled by surface reactions, but the surface layer retention suggests that diffusion in and out of the dissolving solid affects the kinetics of caries-like lesions formation. This project aimed at gaining some understanding of the physico-chemical processes occurring during caries lesion formation. Mineral loss was quantified l)'Sing X-ray scanning microradiography which provided precise and repeatable measurements. The use of a solid-state photon detector allowed photon energy discrimination, so that a near monochromatic beam could be used. In the first study, enamel and HAP samples were submitted alternately to a demineralising buffer and water with switching periods from 0.5 to 4 h. Mean rates of demineralisation decreased as the switching period increased, suggesting that demineralisation conditions within the solid persisted for a time after switching to water. A mathematical model was developed to fit the results. In the second study, HAP sections were separated from the demineralising buffer by an aqueous column 0 to 0.9 cm long. The rate of demineralisation decreased as the length increased, suggesting outward diffusion of dissolved HAP controlled the kinetics of demineralisation. Mathematical modelling based on Fick's diffusion supported this interpretation of the experimental results. The third study focused on the demineralising behaviour of points at increasing depths below the HAP surface. This showed that mineral redeposition occurred near the solid surface. In the last study, samples were submitted to demineralising buffers (same pH) with increasing ionic strength (increase of inert electrolytes concentration). The rate of demineralisation increased with the ionic strength while the surface layer formation was significantly suppressed. This suggests that coupled diffusion between inflow of acid and outflow ofdissolution products is important in surface layer formation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available