For the purpose of erosion prevention the present study aimed to compare the efficacy of two biomimetic products and a fluoride solution to optimize the protective properties of the pellicle. After 1 min of in situ pellicle formation on bovine enamel slabs, 8 subjects adopted CPP-ACP (GC Tooth Mousse), a mouthwash with hydroxyapatite microclusters (Biorepair), or a fluoride based mouthwash (elmex Kariesschutz) for 1 min each. Afterwards, samples were exposed in the oral cavity for 28 min. Native enamel slabs and slabs exposed to the oral cavity for 30 min without any rinse served as controls. After oral exposure, slabs were incubated in HCl (pH values 2, 2.3, and 3) for 120 s and kinetics of calcium and phosphate release were measured photometrically; representative samples were evaluated by SEM and TEM. The physiological pellicle reduced demineralization at all pH values; the protective effect was enhanced by fluoride. The biomimetic materials also reduced ion release but their effect was less pronounced. SEM indicated no layer formation after use of the different products. However, TEM confirmed the potential accumulation of mineral components at the pellicle surface. The tested products improve the protective properties of the in situ pellicle but not as effectively as fluorides.

For the purpose of erosion prevention the present study aimed to compare the efficacy of two biomimetic products and a fluoride solution to optimize the protective properties of the pellicle. After 1 min of in situ pellicle formation on bovine enamel slabs, 8 subjects adopted CPP-ACP (GC Tooth Mousse), a mouthwash with hydroxyapatite microclusters (Biorepair), or a fluoride based mouthwash (elmex Kariesschutz) for 1 min each. Afterwards, samples were exposed in the oral cavity for 28 min. Native enamel slabs and slabs exposed to the oral cavity for 30 min without any rinse served as controls. After oral exposure, slabs were incubated in HCl (pH values 2, 2.3, and 3) for 120 s and kinetics of calcium and phosphate release were measured photometrically; representative samples were evaluated by SEM and TEM. The physiological pellicle reduced demineralization at all pH values; the protective effect was enhanced by fluoride. The biomimetic materials also reduced ion release but their effect was less pronounced. SEM indicated no layer formation after use of the different products. However, TEM confirmed the potential accumulation of mineral components at the pellicle surface. The tested products improve the protective properties of the in situ pellicle but not as effectively as fluorides.

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.

Dental erosion is a result of the demineralization of enamel surface by the action of acids that soften it, and it may affect bracket adhesion to enamel. This research aimed to assess the effect of the application of aluminum oxide sandblasting and aluminum oxide discs on bond strength of metal brackets rebonded on artificially eroded enamel. Fifty-four crowns of bovine incisors were divided into group functions: Control (artificial saliva), Ox Al (aluminum oxide sandblasting), and SL (aluminum oxide discs Sof-Lex Pop On, 3M ESPE). The crowns were fixed in PVC tubes and enamel surface was flattened with carborundum discs (#320, 600, and 1200 Al2O3 discs; Buehler, Lake Bluff, IL, USA) in metallographic polisher (APL4, Arotec). Knoop microhardness was assessed for the standardization of enamel surfaces (HMV-2000; Shimadzu Corporation, Tokyo, Japan). Next, Ox Al and SL teeth were subjected to the erosive action, submerged in Coca-Cola™ for 1 minute, 3x a day for 7 days. Kirium metal brackets, specific for upper right central incisors, slot 022, Roth prescription (3M/Abzil, São José do Rio Preto, São Paulo, Brazil) were bonded on the buccal aspect of teeth. Shear strength was measured with a universal testing machine EMIC (DL200, EMIC, São José dos Pinhais, Paraná, Brazil) at speed of 0.5 mm/min. The Adhesive Remnant Index (ARI) was performed in samples after shear through a magnifying glass (10x). Kolmogorov-Smirnov, Levene, and homoscedasticity tests were used, as well as ANOVA, for the assessment of microhardness and shear strength. The three groups presented no significant differences for microhardness and shear, but the control group had the highest microhardness mean. There were no statistically significant differences among the three groups for shear bond strength (p=0.163). However, the Ox Al group showed higher values for bond strength. The assessment of ARI of groups showed statistically significant difference when comparing the Control group with Ox Al and SL groups. The ARI values showed the prevalence of ARI 3 (50%) for the control group, followed by ARI 4 (22%) and 5 (22%). For Ox Al and SL, ARI 1 and 2 prevailed. The use of aluminum oxide sandblasting and aluminum oxide discs did not increase bond strength of brackets when they were bonded on artificially eroded enamel. The Adhesive Remnant Index indicated that eroded teeth present higher resin adhesion to enamel. / O objetivo desta pesquisa foi avaliar o efeito da aplicação do microjateamento de óxido de alumínio e de discos de óxido de alumínio na resistência adesiva de braquetes metálicos recolados em esmalte erodido artificialmente. Cinquenta e quatro coroas de incisivos bovinos foram divididas em função dos grupos: Controle (Saliva Artificial), Ox Al (Microjateamento com óxido de alumínio) e SL (discos de óxido de alumínio (Sof-Lex Pop On, 3M ESPE). As coroas foram fixadas em tubos de PVC e a superfície do esmalte foi planificada com discos de carborundum (numerações 320, 600 e 1200 discos de Al2O3; Buehler, Lake Bluff, IL, USA), em Politriz Metalográfica (APL4, Arotec). A microdureza Knoop foi aferida para padronização das superfícies de esmalte (HMV-2000; Shimadzu Corporation, Tokyo, Japan). Após aferição os dentes de OxAl e SL foram submetidos ao desafio erosivo, submersos em Coca-Cola® por 1 minuto, 3X ao dia, por 7 dias. Foram colados braquetes metálicos Kirium específicos para incisivos centrais superiores direitos, slot 022”, prescrição Roth [(3M/Abzil, São José do Rio Preto, São Paulo, Brasil)] na face vestibular do dente. A força de cisalhamento foi mensurada por meio de uma máquina de teste universal EMIC (DL200, EMIC, São José dos Pinhais, Paraná) com velocidade 0,5mm/min. O Índice de Remanescente Adesivo (IRA) foi obtido nas amostras utilizando-se lupa (10X). Foram aplicados os testes de Kolmogorv-Smirnov, de Levene e a homocedasticidade e ANOVA para avaliação da microdureza e força de cisalhamento. Não houve diferenças estatisticamente significantes entre os três grupos quando avaliadas microdureza (p=0,163). Porém, ao avaliar o IRA entre grupos, houve diferença estatisticamente significativa ao comparar o grupo Controle com o OxAl e SL. Sendo a prevalência de IRA 3 (50%) para o grupo controle, seguido de IRA 4 (22%) e 5 (22%), respectivamente. Para OxAl e SL, IRA 1 e 2 prevaleceram. Concluiu-se que o uso de microjateamento de óxido de alumínio e discos de óxido de alumínio não aumentaram positivamente a resistência adesiva dos braquetes quando colados em esmalte erodido artificialmente. O índice de remanescente adesivo indicou que dentes erodidos apresentam uma maior adesão da resina ao esmalte.