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Dental erosion is defined as irreversible loss of dental hard tissue due to chemical processes without the involvement of microorganisms. The aim of this study was to compare in vitro the erosive potential of two acidic sources and evaluate the effectiveness of treatments for prevention of dental erosion. To compare the acidic sources, crowns of 5 unerupted human third molars were sectioned in four, totalizing 20 enamel slabs. In the slabs, a test surface (window) of 3 x 3 mm was delimited. The specimens were submitted to erosive challenge into gastric juice (from endoscopy exam) (n=10), or orange juice (industrialized) (n=10), as follows: 5 minutes in 3 ml of acidic solution, rinse with distilled water and stored in artificial saliva for 3 hours. This cycle was repeated for four times a day during 14 days. Calcium (Ca) loss after acid exposure was determined by atomic emission spectroscopy. The presence of carbonate (CO) and phosphate (PO) in the specimens was evaluated before and after the erosive challenge by FT-Raman spectroscopy. To evaluate the treatments for prevention of dental erosion, forty enamel specimens of unerupted human third molars were distributed according to the following treatments (n=10): acidic phosphate fluoride gel (APF 1.23%), Nd:YAG laser (100 mJ, 1 W, 10 Hz), and the associations fluoride + laser and laser + fluoride. These treatments were applied 1 hour before the erosive challenge, which, in this phase was made with hydrochloric acid only (0.01 M/pH 2.2). The fluoride was applied on the enamel surfaces for 4 minutes. The irradiation of enamel surface was made in the contact mode after coating with a photo-activator. The associations were done using fluoride and laser like describe before. The Ca loss was determined by atomic emission spectroscopy and superficial roughness (Ra) was measured before and after the erosive challenge. In the comparison of the acidic sources, the mean loss of Ca were: 12.74 ± 3.33 mg/L Ca (gastric juice) and 7.07 ± 1.44 mg/L Ca (orange juice) (p=0.0003). The FT-Raman spectroscopy found no statistically significant difference in the ratio CO/PO after the erosive challenge. The CO/PO ratios values before and after the challenge were: 0.16/0.17 (gastric juice) (p=0.37) and 0.18/0.14 (orange juice) (p=0.16). In the evaluation of the treatments, the mean Ca loss were (mg/L): APF 1.707a (± 0.113), Nd:YAG 1.638a (±0.080), APF + Nd:YAG 1.385b (±0.078), Nd:YAG + APF 1.484b (±0.068). The mean initial roughness of specimens was 0.14 μm. After the erosive challenge the roughness showed a significant increase (p<0.01): APF 0.69bc (±0.091), Nd:YAG 0.87a (±0.119), APF + Nd:YAG 0.61c (±0.090) and Nd:YAG + APF 0.72b (±0.069). It was concluded that gastric juice has higher erosive potential to enamel than orange juice and the association between fluoride and laser was more efficient for the prevention of dental erosion than both methods separately. Key-works: Tooth erosion; Fluoride; Lasers; Prevention & control; Spectrometry; Spectrum analysis Raman; Tooth demineralization LISTA DE ILUSTRAÇÕES Figura 4.1 Corte do dente e obtenção de quatro fragmentos65 Figura 4.2 Espécimes de esmalte recobertos com esmalte cosmético formando janela de exposição65 Figura 4.3 Frasco “bronquinho” para coleta de suco gástrico67 Figura 4.4 Suco de laranja utilizado como fonte ácida de origem extrínseca68 Figura 4.5 Ciclo de desmineralização-remineralização70 Figura 4.6 Aparelhos utilizados para avaliação da perda de conteúdo mineral dos espécimes. AEspectrômetro de emissão atômica. BEspectrômetro FT-Raman73 Figura 4.7 Métodos de controle da erosão utilizados. AFlúor. BLaser Nd:YAG. 76 Figura 4.8 Rugosímetro78 Figura 4.9 Esquema da metodologia da segunda fase do experimento79 Figura 5.1 Gráfico da titulação do suco de laranja e suco gástrico81 Figura 5.2 Médias da intensidade dos picos antes e após ciclagem em suco gástrico83 Figura 5.3 Médias da intensidade dos picos antes e após ciclagem em suco de laranja84 Figura 5.4 Fotomicrografias da superfície dos espécimes (1 aumento 400x, 2 aumento 2000x). A Superfície após polimento para início da ciclagem. B Superfície após ciclagem em suco gástrico. C Superfície após ciclagem em suco de laranja 87 Figura 5.5 Comparação entre as médias de cálcio perdido dos grupos de métodos de controle da erosão e a análise estatística89 Figura 5.6 Médias e desvios-padrão da rugosidade superficial antes e após os métodos de controle da erosão e desafio erosivo, análise estatística 91 Figura 5.7 Fotomicrografias da superfície dos espécimes (1 aumento 400x, 2 aumento 2000x). A Superfície após aplicação de flúor e desafio ácido. B Superfície após irradiação com laser Nd:YAG e desafio ácido. C Superfície após aplicação de flúor + irradiação com laser de Nd:YAG e desafio ácido. D Superfície após irradiação com laser de Nd:YAG + aplicação de flúor e desafio ácido93 Quadro 4.1 Composição da saliva artificial69

Comparação do potencial erosivo de duas fontes ácidas sobre o esmalte e avaliação de métodos de controle da erosão dental