Dental erosion has been defined as a chemical process that involves the dissolution of enamel and dentine by acid(s) not derived from bacteria when the surrounding aqueous phase is under-saturated with tooth mineral. Clinically however, dental erosion hardly ever occurs exclusively from the other modes of tooth wear such as abrasion and attrition. Hence the term erosive wear has been proposed and used to describe erosion-facilitated wear.With the prevalence of erosive wear being reported to be on the rise among children and adolescents in many countries, a plethora of oral health products such as dentifrices and mouth rinses had been put forward with claims of increasing the resistance of the enamel and / or dentine from being demineralised. However, the efficacy of these oral health products is still widely questionable as the studies carried out were mainly in vitro and / or in situ studies and the contradictory results were reported by different groups of researchers.The above mentioned discrepancies are often due to non-standardised in vitro and in situ study designs of erosion studies. Parameters such as type of acid used, concentration of acid used, duration of acid exposure, inclusion or exclusion of abrasion in the study model, ex vivo or in vivo acid challenge, ex vivo or in vivo treatment with oral health product and the nature of pellicle on the specimen are often varied.The availability of an detection tool which could be used to measure demineralisation on natural tooth surface in vivo would exclude many of the inevitable variability in in situ and in vitro study design, such as the simulation of the intra oral conditions in which the erosion challenge and intervention take place and the nature of the pellicle formed on the specimens. Hence with an in vivo detection tool, it is hopeful that the efficacy of any interventions would be evaluated more accurately and its results expounded to a wider context. It would be useful if the tool was sensitive to the very early stages of the erosion process as this would entail shorter and more economical study designs. Arising from the problems discussed above, potential non-invasive assessment methods that could be used clinically to measure demineralisation were explored and it was found that two optical methods, Optical Coherence Tomography (OCT) and Quantitative Light-induced Fluorescence (QLF) were potential methods for the tasks.The studies described in this thesis were divided into three main big sections; the first being the in vitro validation work of the two optical methods (Chapter 5 and 6), the second, validation of these methods in situ (Chapter 7) and finally the assessment of the efficacy of a high fluoride dentifrice on early enamel erosion using these two methods (Chapter 8).In the in vitro validation (Chapter 5), it was demonstrated that both QLF and OCT were able to detect erosion-interval related changes in natural surface samples eroded with orange juice for 60 minutes. However, results of Multiple Linear Regression and Paired t test suggest that QLF was more sensitive than OCT in the detection of demineralisation changes in this particular experimental setting. QLF demonstrated a R2 value of 0.590 while the best of the OCT outcome measure demonstrated a R2 value of 0.319.Further in vitro study (Chapter 6) was performed to explore the use of a moistened-exposed surface as a reference method for both OCT and QLF as it was felt that it would be beneficial if a coated reference area which posts as an additional step for error could be done away with. Results of this study showed that the moistened-exposed surface could be used a reference method for QLF only but not for OCT. Furnished with the findings of the above mentioned in vitro validation studies, an in situ validation of both the optical methods was performed (Chapter 7). It was found that OCT and QLF were able to longitudinally measure in situ demineralisation on polished and natural surfaced enamel which were subjected to 150 minutes of in vivo exposure to orange juice. Similar to the results of the in vitro study, QLF was found to be more sensitive than OCT in the detection of demineralisation changes on natural surfaced enamel. The last in situ study (Chapter 8) was to evaluate whether there was a protective effect of treating human enamel with a high-concentrated fluoride dentifrice during an active erosion phase and whether OCT and QLF were able to detect the protective effect. It was found that treating natural surface enamel with a 5000ppm NaF dentifrice increased its resistance against concurrent in vivo erosive challenge with an orange juice challenge. QLF was able to detect the protective effect of the 5000ppm NaF dentifrice on natural surface enamel against early in vivo erosion with an orange juice challenge regime while OCT did not.

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