Thesis (doctoral)--Lunds Universitet.

Thesis (doctoral)--Lunds Universitet.

Thesis (M.S.P.H.)--University of Michigan, 1942.

Thesis (M.P.H.)--University of Michigan, 1946.

Thesis (M.S.)--University of Michigan, 1995. / Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains vi, 47 p. : ill. (some col.) Vita. Includes abstract. Includes bibliographical references (p. 44-46).

High F- groundwaters occur in various parts of South Africa, namely, the larger part of the Karoo, Limpopo, North West and Northern Cape Provinces. The use of these waters for drinking purposes on continual basis can lead to fluorosis. Fluorosis is a debilitating disease caused by drinking water with F- concentrations higher than ca. 1 mg.L-1. The disease is characterized by mottled teeth in dental fluorosis and brittle bones in severe skeletal fluorosis. Solution to this problem involves the implementation of a method for F- removal from water. Defluoridation has become a widely practiced process worldwide due to the problem of fluorosis caused by the presence of F- in drinking waters. Methods such as adsorption, precipitation, ion exchange and membrane processes have been employed for F- removal. Adsorption techniques, in particular using activated alumina have proven successful in removing F- from water. However, this method can not always be used in rural areas because of high costs and technical requirements. In this study, locally available clays were studied as potential substrates for F- removal from water. The first part of the study focused on the explanation of mechanisms and the development of an adsorption model. The exchange of OH- by F- in the clay structure is the principal mechanism that takes place during adsorption. The change in pH during this exchange process was studied to support and verify the fluoride-hydroxide exchange mechanism. In the second part of the study, locally available South African clays were studied as possible adsorbents for F- removal from water. Clays containing aluminium and iron oxide surfaces proved to be useful substrates for F- adsorption. The adsorption of F- onto clay samples was found to be pH dependent. Maximum adsorption was achieved at pH 5 for aluminium oxide type sorbents and pH 4 for iron oxides types such as goethite. The effect of physical and chemical pretreatment improved the adsorption capacity of some clays. Coating clay samples with aluminium and iron oxides enhanced the adsorption capacity of clays. The last part of the study involves the development of a cost-effective and quick way to assess the performance of clays as adsorbents for F- removal using laboratory scale defluoridation columns. / Prof. P.P. Coetzee

The main drivers for this body of work were a systematic review on water fluoridation by the NHS Centre for Research Dissemination (known as the York Report) and a report by the Medical Research Council entitled 'Water Fluoridation & Health'. Both documents highlighted shortcomings in the evidence base on water fluoridation. Two major projects form the basis of this thesis in an attempt to address some of the issues raised. The first project in Chiang Mai, Thailand aimed to determine the ability of QLF to discriminate between populations with differing exposures to fluoride. Populations with differing exposures to fluoride were identified through the analysis of drinking water and cooking water. Subjects were examined for fluorosis with standardized photographs and QLF to evaluate software techniques for fluorescence image analysis. The results in Thailand demonstrated that QLF was able to discriminate between populations with differing exposures to fluoride in water to a similar degree to blinded, subjective clinical scoring. There was significant agreement between the two methods (ICC 0.65 Spearman's rho). However, confounding factors for QLF were found. The aim of the second project was to assess the use of blinded and objective methods for assessing caries and fluorosis in fluoridated Newcastle and non-fluoridated Manchester in northern England. This study involved clinical and intra-oral photographic caries examinations using ICDAS, together with standardized photography and QLF imaging for fluorosis examinations. The results in Newcastle and Manchester suggested that there were significantly lower levels of caries in the fluoridated population compared to the non-fluoridated population. For early caries (Newcastle mean DMFT 2.94[clinical]/2.51[photo], Manchester mean DMFT 4.48 [clinical]/3.44[photo]) and caries into dentine (Newcastle Mean DMFT 0.65[clinical]/0.58[photo], Manchester mean DMFT 1.07 [clinical]/0.98 [photo]). This was reflected as an increase in caries as the level of deprivation increased (confirmed through intra-oral photographic scoring). The reduction in caries levels was associated with increased levels of fluorosis in Newcastle. The prevalence of fluorosis from photographic scores in fluoridated Newcastle was 55%, in non-fluoridated Manchester it was 27%. In Newcastle, 48% of subjects had TF scores of 1 or 2 and 7.1% of subjects had TF scores of 3 or greater. QLF showed significant associations with the clinical scores for fluorosis (ICC 0.405 Kendall's tau) and suggested a fluorosis prevalence for TF 3 or greater of 19% in Newcastle and 10% in Manchester. The integration of technologies such as intra-oral photographs for blind caries scoring and QLF for the detection and objective quantification of fluorosis may still prove to be useful adjunctive tools when used alongside clinical indices. The data derived from the methodologies under investigation suggest a benefit in caries reduction from community water fluoridation and this may help to reduce inequalities in oral health by reducing the social gradient between deprivation and caries.

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published_or_final_version / abstract / Dentistry / Doctoral / Doctor of Philosophy