Fluoreto presente em águas de abastecimento, pode ser determinado por titulação condutométrica, usando-se La(NO3)3 como titulante. O método proposto no presente trabalho exige a separação prévia de fluoreto da amostra, por destilação a 135ºC. O pH do destilado é ajustado entre 5,5 - 6,0; etanol é adicionado até atingir-se a proporção de 50%, titulando-se a solução resultante com La(NO3)3. Nessas soluções, fluoreto nas concentrações de 500 ppb e 2,0 ppm podem ser determinadas com precisões de 5% e 4%, respectivamente. Amostras naturais foram analisadas condutometricamente pelo método proposto, potenciometricamente com eletrodo íon seletivo de fluoreto, obtendo-se resultados compatíveis. / Fluoride ions in drinking water can be easily determined by condutometric titraction using La(NO3)3 as titrant. The sample must be destilled in H2S04 previously to separate the fluoride ions, at 1350 C. The destillated, in 50% ethanol is titrated with La(NO3)3 In these conditions, fluoride ions at the concentrations of 500 ppb and 2,0 ppm are determined with accuracy of, respectively, 5% and 4%. Natural samples of drinking water were analysed by this method and by the ion-selective method, with agreement among the results.

Este estudo objetivou estabelecer condições de irradiação com o laser de Er,Cr:YSGG (de comprimento de onda de 2.79 µm) que propiciassem modificações no esmalte dental e aumentassem sua resistência à desmineralização, associadas ou não à aplicação tópica de flúor fosfato acidulado (FFA). Fluências laser de 2,8 J/cm², 5,6 J/cm² e 8,5 J/cm² foram selecionadas, as quais foram associadas com a aplicação prévia de substância fotoabsorvedora (pasta de pó de carvão) e então com aplicação de FFA posteriormente às irradiações. Inicialmente, foram avaliadas as alterações morfológicas, as modificações na temperatura superficial e os aumentos na temperatura intrapulpar decorrentes das irradiações. Posteriormente, as amostras tratadas foram submetidas a uma ciclagem de pH com duração de 10 dias. Após a produção das lesões de mancha-branca, foi avaliada a perda mineral e as quantidades de flúor fracamente ligado e fortemente ligado. Todas as soluções desmineralizantes e remineralizantes foram avaliadas com relação ao seu conteúdo de cálcio, fósforo inorgânico e flúor. Os dados foram avaliados quanto à normalidade e homogeneidade de sua distribuição para que pudesse ser escolhido o teste estatístico mais adequado, considerando o nível de significância de 5%. As fluências selecionadas promoveram superfícies ablacionadas; as fluências de 5,6 J/cm² e 8,5 J/cm² promoveram aumentos de temperatura superficial superiores a 110º C. A análise da temperatura intrapulpar revelou que as fluências escolhidas não aumentaram as temperaturas pulpares acima do limite estabelecido para pulpite. A pasta de pó de carvão não promoveu modificações morfológicas ou alterações significativas nas temperaturas pulpares; entretanto, aumentou as temperaturas superficiais durante as irradiações. Apenas a irradiação laser sob fluência de 8,5 J/cm² diminuiu significativamente a perda mineral quando comparado ao grupo sem tratamento; embora a associação da pasta de carvão + irradiação laser a 2,8 J/cm² + aplicação de FFA tenha apresentado o menor valor de perda mineral de todos os grupos de tratamento deste estudo, tal valor não diferiu estatisticamente daquele obtido quando apenas o FFA foi aplicado (grupo controle positivo). A análise de flúor fracamente ligado revelou que a irradiação laser proporcionou maior formação e retenção do fluoreto de cálcio formado após aplicação de FFA, provavelmente devido à ablação do esmalte, enquanto que a análise de flúor total mostrou não haver diferenças na quantidade de fluorapatita formada após a irradiação laser quando comparado às amostras não-irradiadas. A avaliação das soluções desmineralizantes e remineralizantes evidenciou não haver diferenças significativas nas concentrações de cálcio e fósforo inorgânico entre as amostras irradiadas ou não irradiadas; contudo, a determinação de flúor nestas soluções mostrou diferenças expressivas no conteúdo de flúor, sugerindo que a irradiação laser pode favorecer a uma maior formação de fluoreto de cálcio. De acordo com os resultados deste estudo, pode-se concluir que a irradiação laser proporciona maior retenção de fluoreto fracamente ligado formado no esmalte decorrente da aplicação tópica de flúor; entretanto, a associação dos tratamentos não proporcionou maior efeito na redução da desmineralização do esmalte do que o efeito da aplicação tópica de FFA isoladamente. / This study aimed to stablish irradiation conditions of Er,Cr:YSGG laser (wavelength of 2.79 µm) which could propitiate changes on human dental enamel and increase its resistance to demineralization, when associated or not with topical application of acidulated phosphate fluoride (APF). Fluences of 2,8 J/cm&sup2, 5,6 J/cm&sup2 e 8,5 J/cm&sup2 were selected; they were associated or not with previous application of a photoabsorber (coal paste) and then APF was applied or not after laser irradiation. In a first step, the morphological findings, the surface temperatures, and the pulpal temperatures were evaluated during laser irradiation. After that, the treated samples were submitted to a a ten-day pH-cycling model. After producing the incipient white-spots lesions, the following aspects were evaluated: the mineral loss, the loosely bound fluoride and the firmly bound fluoride. All the demineralizing and remineralizing pH-cycling solutions were evaluated with respect to their calcium (Ca), inorganic phosphorous (Pi) and fluoride (F-) concentrations. The data had their normality and homogeneity distribution statistically evaluated, and it was chosen an appropriated statistical test for each performed analysis according to the obtained results, considering 5% significant level. The fluences selected for this study created ablated surfaces; the fluences of 5.6 J/cm&sup2 and 8.5 J/cm&sup2 promoted increments in surface temperature above 110º C. The intrapulpal temperature changes revealed that laser irradiation did not increase the pulpal temperatures above the critical threshold for induction of pulpitis. The coal paste did not promote any changes on surface morphology or in the intrapulpal temperature changes; however, this paste increased the surface temperatures during laser irradiation. Only laser irradiation at 8.5 J/cm&sup2 was able to decrease the mineral loss when compared to the no-treatment group; although the association of coal paste + laser at 2.8 J/cm&sup2 + APF application presented the lesser mineral loss of all treatment groups of this study, this value was not statistically different than those revealed in the FFA group (positive control). The analysis of loosely bound fluoride revealed that laser irradiation was able to retain the calcium fluoride formed after APF application due to the ablation process, while the analysis of firmly bound fluoride showed no differences in fluorapatite quantities formed after laser irradiation when compared to the non-irradiated samples. The evaluation of demineralizing and remineralizing pH-cycling solutions evidenced no significant differences in calcium or inorganic phosphorous concentrations between lased or unlased samples; however, the fluoride determination exposed important differences on fluoride contents, which suggested that laser irradiation could induce a higher calcium fluoride formation. According to the results of this study, it was possible to conclude that the laser irradiation can propitiate, on enamel, higher loosely bound fluoride retention formed by topical application of fluoride; however, the association of treatments did not increased the effect obtained by APF application alone on enamel demineralization.

Estudos têm avaliado a eficiência de diferentes tipos de laser no aumento da resistência ácida e na redução da solubilidade do esmalte dentário. O objetivo do presente estudo clínico longitudinal foi avaliar o comportamento do laser de CO2 associado, ou não, à aplicação tópica de fluoreto acidulado na prevenção de lesões de cárie em fossas e fissuras de primeiros molares permanentes parcialmente irrompidos. Foram selecionadas 61 crianças de alto risco a cárie dentária, de 6 a 8 (7,1 ± 0,8) anos de idade, apresentando os quatro primeiros molares permanentes parcialmente irrompidos e hígidos. Cada primeiro molar recebeu aleatoriamente um dos tratamentos avaliados nas fossas e fissuras: (L) - laser de CO2 (0,066J/cm2); (FL) - gel fluoretado acidulado a 1,23% e laser de CO2 (0,066J/cm2); (V) - verniz fluoretado a 5%; (S) selante (controle). Os dentes foram avaliados aos 3, 6, 12 e 18 meses após a realização dos tratamentos, por meio de exame visual direto e avaliador calibrado e \"cego\" aos tratamentos (Kappa 0,70). Foi utilizado o indíce ICDAS-II para avaliação da manutenção da higidez, presença de lesão de mancha branca ativa e de lesões cavitadas em esmalte e/ou dentina. Para avaliação da retenção do selante, foram utilizados os critérios visuais modificados de Yildiz et al. (2004). Foi aplicada a análise de sobrevida de Kaplan-Meyer. O hazard ratio dos tratamentos foram estimados utilizando-se shared frayilt models com distribuição gama, considerando-se o paciente como conglomerado. O modelo também evidenciou que a correlação intra-paciente foi significante (p = 0,0022), com covariância de 0,8425 (erro padrão = 0,3208). Clinicamente, não houve diferença significante entre os tratamentos (L), (LF) e (V) após 18 meses de avaliação. Para o tratamento (S), observou-se a maior taxa de desenvolvimento de lesões de cárie. Após análise longitudinal de 18 meses, pode-se concluir que a aplicação do laser de CO2, independentemente do uso associado ao fluoreto, foi eficiente na prevenção de lesões de cárie em fossas e fissuras de molares parcialmente irrompidos, em crianças de alto risco à cárie. / Studies have evaluated the efficiency of different laser systems in increasing strength and reducing the acid solubility of dental enamel. The aim of this longitudinal clinical study was to evaluate the CO2 laser combined or not to the topical application of acidulated fluorides in preventing caries in pits and fissures of partially-erupted first permanent molars. It were selected 61 children at high caries-risk, with 6-8 (7.1 ± 0.8) years old, with the four first permanent molars partially erupted and healthy. Each first molar randomly received one of the tested treatments in pits and fissures: (L) - CO2 laser (0.066 J/cm2), (FL) - acidulated fluoride gel 1.23% and CO2 laser (0.066 J/cm2) (V) - 5% fluoride varnish, (S) - sealant (control). The teeth were evaluated at 3, 6, 12 and 18 months after treatment, through direct visual examination and by a calibrated operator blinded to the treatments (Kappa 0.70). The ICDAS-II index was used to assess the soundness of tooth structure, presence of white spot lesions and cavitated enamel and/or dentin lesions. The Yildiz et al. (2004) visual modified criteria was used to evaluate the retention of sealant. The Kaplan-Meyer survival analysis was used. The hazard ratio of the treatments was estimated using frayilt shared models with gamma distribution, considering the patient as a conglomerate. The model also showed that intra-patient correlation was significant (p = 0.0022), with covariance of 0.8425 (standard error = 0.3208). Clinically, there was no significant difference between (L), (LF) and (V) treatments after 18 months of evaluation. For (S) treatment, there was a higher rate of caries development. After long-term analysis of 18 months, it can be concluded that the application of CO2 laser, regardless of use with fluoride, was effective in preventing caries in pits and fissures of partially-erupted molars in children at high caries-risk.

A aplicação do laser sobre o esmalte associada ou não a aplicação tópica de fluoreto têm demonstrado aumentar sua resistência à ação de ácidos. O presente estudo teve como objetivo avaliar o efeito da irradiação laser de alta potência associada à aplicação de fluoretos sobre o esmalte dentário submetido à erosão e/ou abrasão dentária. Para tal, 184 blocos de esmalte foram selecionados pela microdureza de superfície (SMH inicial) e foram divididos em 8 grupos com 23 espécimes cada (3 foram utilizados para realização da biópsia básica da superfície de esmalte dentário, 10 foram submetidos à erosão e os outros 10 à erosão associada à abrasão): G1- sem tratamento (controle); G2- tratamento com flúor fosfato acidulado (1,23% F) por 4 min; G3- verniz fluoretado; G4- irradiação com laser Nd:YAG (56,6 J/cm2); G5- aplicação de flúor fosfato acidulado e posterior irradiação com laser Nd:YAG (56,6 J/cm2); G6- aplicação de flúor fosfato acidulado e prévia irradiação com laser Nd:YAG (56,6 J/cm2); G7- aplicação de verniz fluoretado e posterior irradiação com laser Nd:YAG (56,6 J/cm2); G8- aplicação de verniz fluoretado e prévia irradiação com laser Nd:YAG (56,6 J/cm2). Após os tratamentos, os blocos submetidos à ciclagem erosiva sofreram 4 imersões diárias em bebida ácida com pH 2,6, 0,32 ppm F (Coca-Cola Company, Spal, Porto Real, RJ, Brasil), por 2 min, seguida pela imersão em solução remineralizadora por 2 h, durante 5 dias. Nos blocos submetidos à erosão associada à abrasão, uma vez ao dia após cada ciclo, os espécimes foram submetidos à abrasão com 40 ciclos de escovação simulada com força de 2,5 N. Os blocos de esmalte foram avaliados por meio da perfilometria. Os resultados foram submetidos à ANOVA a um (biopsia básica) e dois critérios (perfilometria) e Teste de Tukey (p<0,05). Todos os grupos de tratamento promoveram menor desgaste dentário em relação ao controle, sendo que entre eles, a irradiação laser promoveu o pior resultado (p<0,05). Os grupos de tratamento com fluoreto resultaram em maior concentração de flúor no esmalte na biopsia básica (p<0,05). Em todos os grupos estudados, a erosão promoveu menor desgaste dentário quando comparada a erosão associada à abrasão (p <0,05). Conclui-se o laser apresenta efeito preventivo menor que os fluoretos, quando se trata de erosão associada ou não à abrasão. Além disso, quando a irradiação laser é associada a aplicação de fluoretos não há efeito sinérgico. / The laser application on enamel associated or not to the topic fluoride have been showed to increase the resistance to acid action. This study aimed to evaluate the effect of high intensity laser irradiation submitted to dental erosion and/or abrasion. Hence, 184 enamel samples were selected by surface microhardness (initial SMH) and then divided into 8 groups with 23 specimens each (3 were selected to routine biopsy of enamel surface, 10 submitted to erosion procedure and another 10 were submitted to erosion associated to abrasion): G1 without treatment (control group); G2 treated with acidic phosphate for 4 min (1.23% F); G3 fluoride varnish; G4 - irradiation with Nd:YAG laser (56.6 J/cm2) ; G5 - acidic phosphate fluoride with posterior irradiation with Nd:YAG laser (56.6 J/cm2) ; G6 application of acidic phosphate fluoride with previous irradiation of Nd:YAG laser (56,6 J/cm2); G7- application of fluoride varnish with posterior laser irradiation with Nd:YAG laser (56,6 J/cm2); G8- application of fluoride varnish with previous irradiation of Nd:YAG laser (56,6 J/cm2). After the treatments, the samples were submitted to erosive cycling with 4 diary immersions in acidic beverages with pH 2.6, 0.32 F ppm (Coca-Cola Company, Spal, Porto Real, RJ, Brasil) for 2 min followed by remineralized solution for 5 days. To groups submitted to erosive associated to abrasion, once a day after each cycling, the specimens were submitted to abrasion with 40 simulated brushing cycles with power of 2.5 N. The enamel samples were evaluated by profilemetry. The results were submitted to one way ( routine biopsy) and two way (profilometry) ANOVA and Tukey test (p < 0.05). All the groups demonstrated a wear dental decrease in relation to control group, and among them, the laser irradiation promoted the worst outcome (p < 0.05). The groups related to fluoride resulted in increase concentration of fluoride in the enamel routine biopsy (p<0,05). To all groups, the erosion promoted a decrease of dental wear when compared to erosion associated to abrasion (p < 0,05). It can be concluded that the laser presented a minor preventive effect when compared to fluoride treatment, when is related to erosion associated or not to abrasion. Furthermore, when irradiation is associated to fluoride application there was not a synergic effect.

O presente trabalho teve como objetivo avaliar in vitro o efeito de diferentes densidades de energia da irradiação com lasers de CO2 e Nd:YAG sobre o esmalte e dentina quando submetidos a erosão (fase 1) e depois avaliar o efeito do melhor parâmetro associado ao fluoreto na diminuição da erosão dentária, quando aplicados sobre esmalte e dentina hígidos e previamente erodidos (fase 2). Além disso, na fase 1 foi avaliado o efeito do recobrimento das estruturas dentárias com pigmento (corante foto absorvente) no desempenho do laser de Nd:YAG. Na fase 1, 130 blocos de esmalte e 130 blocos de dentina (dente bovino), foram igualmente e aleatoriamente divididos em 13 grupos (n = 10): C- sem tratamento (controle), Nd1 e Nd5- irradiação com laser Nd:YAG (42,45 J/cm2), Nd2 e Nd6- irradiação com laser Nd:YAG (56,6 J/cm2), Nd3 e Nd7- irradiação com laser Nd:YAG (84,9 J/cm2), Nd4 e Nd8- irradiação com laser Nd:YAG (99,05 J/cm2), CO1 - irradiação com laser CO2 (esmalte: 7,2 J/cm2; dentina: 3,6 J/cm2), CO2 - irradiação com laser CO2 (esmalte: 14,4 J/cm2; dentina: 7,2 J/cm2), CO3 - irradiação com laser CO2 (esmalte: 21,4 J/cm2; dentina: 10,7 J/cm2) e CO4 - irradiação com laser CO2 (esmalte: 28,8 J/cm2, dentina: 14,4 J/cm2). Nos grupos Nd5-9 foi feita aplicação de corante a base de carvão antes da irradiação com laser Nd:YAG. Antes da irradiação os blocos tiveram 2/3 de suas superfícies protegidas com esmalte cosmético para realização da perfilometria. Após a irradiação, os blocos foram submetidos à ciclagem erosiva, composta por 4 imersões diárias em bebida ácida por 2 minutos, seguida pela imersão em saliva artificial por 2 h, durante 5 dias. A perda de esmalte e dentina foram avaliados por meio da perfilometria após a aplicação do laser e após o 1º e 5º dia de ciclagem erosiva. Na segunda fase foi utilizado o grupo que obteve o melhor resultado numérico ou estatístico quanto à diminuição do desgaste. Assim 120 blocos de cada tipo de substrato foram divididos em 12 grupos (n = 10): C - controle sem erosão prévia; C+EP - controle com erosão prévia; Nd:YAG - irradiação com laser Nd:YAG (esmalte: 56,6 J/cm2 e dentina: 42,45 J/cm2); EP+Nd:YAG - erosão prévia seguida da irradiação com laser Nd:YAG; F - aplicação de AmF (1% F); EP+F - erosão prévia e posterior aplicação de AmF (1% F); Nd:YAG+F - irradiação com laser Nd:YAG e posterior aplicação de AmF (1% F); EP+Nd:YAG+F - erosão prévia seguida da irradiação com laser Nd:YAG e posterior aplicação de AmF (1% F); CO2 - irradiação com laser CO2 (esmalte: 28,6 J/cm2 e dentina: 10,7 J/cm2); EP+CO2 - erosão prévia seguida da irradiação com laser CO2; CO2+F - irradiação com laser CO2 e posterior aplicação de AmF (1% F); EP+CO2+F - erosão prévia seguida da irradiação com laser CO2 e posterior aplicação de AmF (1% F). Assim como na 1ª fase, antes da irradiação, os blocos foram protegidos (2/3) e após os tratamentos, os blocos foram submetidos à ciclagem erosiva previamente descrita. Os blocos foram avaliados por perfilometria como descrito. Os resultados foram submetidos à ANOVA ou Kruskal Wallis e Teste de Tukey (p<0,05), sendo que os dois tipos de lasers foram avaliados separadamente. Os diversos parâmetros do laser Nd:YAG não apresentam efeito preventivo em relação à erosão dentária independentemente do corante foto absorvente. Para o CO2 apenas as densidades de energia de 28,8 J/cm2 para o esmalte e 10,7 J/cm2 para a dentina apresentaram este efeito. A estrutura dentária previamente erodida resulta em maior desgaste quando comparada à estrutura hígida. A utilização de fluoreto na maioria das situações apresentou efeito preventivo em relação à erosão, no entanto a associação do fluoreto ao laser não apresentou efeito sinérgico, tendo sido observada uma diminuição do efeito preventivo do fluoreto. Considerando esses resultados, para os pacientes com risco de erosão dentária, a aplicação de fluoreto ainda é o tratamento com melhor resultado preventivo em relação à erosão dental. / This study aimed to evaluate the in vitro effect of different irradiation power densities of CO2 and Nd:YAG lasers on enamel and dentine when eroded (phase 1). To evaluate the effect of fluoride associated with the best parameter of laser able to reduce dental erosion considering sound and previously eroded enamel and dentine (phase 2). Furthermore, in phase 1 the application of an absorbing photo dye was evaluated on the performance of Nd:YAG. In phase 1, 130 enamel blocks and 130 dentine blocks, were equally and randomly divided into 13 groups (n = 10): C -untreated (control), Nd1 and Nd5 - irradiation with Nd:YAG laser (42.45 J/cm2), Nd2 and Nd6 - irradiation with Nd:YAG laser (56.6 J/cm2), Nd3 and Nd7 - irradiation with Nd:YAG laser (84.9 J/cm2), Nd4 and Nd8 - irradiation with Nd:YAG laser (99.05 J/cm2), CO1 - CO2 laser irradiation (enamel: 7.2 J/cm2; dentine: 3.6 J/cm2), CO2 - CO2 laser irradiation (enamel: 14.4 J/cm2; dentine: 7.2 J/cm2), CO3 - CO2 laser irradiation (enamel: 21.4 J/cm2; dentine: 10.7 J/cm2) and CO4 - CO2 laser irradiation (enamel: 28.8 J/cm2, dentine: 14.4 J/cm2). In groups Nd5 to 9 coal-paste dye was applied before Nd:YAG laser irradiation. Before irradiation 2/3 of the blocks surfaces were protected with nail varnish for performing the profilometry. After irradiation, the blocks were submitted to four erosive 2-min cycles, followed by immersion in artificial saliva for 2 h for 5 days. Enamel and dentine losses were evaluated by profilometry after laser application and after 1 and 5 days of erosive cycling. In the second phase, the group that obtained the best numerical or statistical result was used. So 120 enamel and dentine blocks were divided into 12 groups (n = 10): C - control without prior erosion; C+EP - control with prior erosion; Nd:YAG - laser irradiation with Nd:YAG (enamel: 56.6 J/cm2 and dentin: 42.45 J/cm2); EP+Nd:YAG - prior erosion followed by Nd:YAG irradiation; F - AmF (1% F) application; F+EP - erosion prior subsequent AmF (1% F) application; Nd:YAG+F - irradiation with Nd:YAG laser and subsequent AmF (1% F) application; EP+Nd:YAG+F - prior erosion followed by Nd:YAG irradiation and subsequent AmF (1% F) application; CO2 - CO2 laser irradiation (enamel: 28.6 J/cm2 and dentin: 10.7 J/cm2</sub); EP+CO2 - prior erosion followed by CO2 laser irradiation , F+CO2 - CO2 laser irradiation and subsequent AmF (1% F) application; F+EP+CO2 - erosion prior CO2 laser irradiation and subsequent AmF (1% F) application. As in stage 1, before irradiation, the blocks were protected (2/3) and after the treatments, the blocks were subjected to erosive cycling as previously described. The dental loss was evaluated by profilometry as described. The lasers were analyzed separated. The results were submitted to ANOVA or Kruskal Wallis (as passed or not in the normal curve) and Tukey test (p<0.05). The various parameters of Nd:YAG laser did not present effect in relation to dental erosion regardless of the use of photo absorbent dye. In relation to CO2 laser only the energy densities of 28.8 J/cm2 for enamel and 10.7 J/cm2 for dentin showed some preventive effect. The previously eroded substrate resulted in greater wear when compared to sound one. Generally, fluoride had some preventive effect against erosion. However, the combination of fluoride to the laser showed no synergistic effect, since it was observed a decrease in fluoride preventive effect. Considering these results, for patients at high risk for dental erosion, application of fluoride is still the best preventive treatment.

A incidência de lesões dentais não cariosas vem aumentando nos últimos anos, entre outros fatores devido a mudanças de hábitos alimentares da população, assim como ao aumento na freqüência de indivíduos que apresentam distúrbios gastro-esofágicos ou doenças como bulimia. Esse estudo teve como objetivo avaliar se o laser de CO2 associado ou não ao flúor poderia prevenir a erosão ácida causada por ácido cítrico em esmalte. 10 voluntários participaram desse estudo in situ e cruzado, onde 4 tratamentos foram testados: G1 controle, sem tratamento; G2 irradiação com laser de CO2 através dos parâmetros: 0.3J/cm2-5s-226Hz; G3 aplicação tópica de flúor (1.25% - 3 minutos); G4 aplicação tópica de flúor + laser de CO2). Durante cada tratamento os voluntários utilizaram durante o dia e noite, exceto durante as refeições e higiene bucal, dispositivo palatino removível contando amostras de esmalte bovino esterilizadas. A desmineralização das amostras foi realizada através da imersão do dispositivo palatino contendo as amostras em 80 ml de ácido cítrico (0.05M pH 2.3) durante 20 minutos 2 vezes ao dia (entre 6:00 e 9:00 horas a primeira imersão e entre 18:00 e 21:00 horas na segunda imersão). Durante toda a pesquisa a higiene bucal foi realizada pelos voluntários com pasta dentifrícia sem flúor e sem o dispositivo palatino in situ. Antes e durante os tratamentos o intervalo de 7 dias foi mantido. Duas amostras foram coletadas do dispositivo palatino de cada voluntário nos dias 1, 3 e 5 (n=20/dia/tratamento). A perda de estrutura foi medida utilizando-se um perfilômetro digital. Mensurações da quantidade de flúor através da técnica de biópsia e espectroscopia de fluorescência de Raios-X por energia dispersiva (EDX) e análises morfológicas foram realizadas nos grupos nos dias 1, 3 e 5. Nos testes realizados in vitro, os mesmos tratamentos foram realizados durante os mesmos tempos, no entanto, ao invés das amostras estarem presas ao dispositivo palatino na cavidade bucal dos voluntários, as mesmas foram armazenadas em água deionizada em temperatura ambiente (n=12/dia/tratamento). Os resultados mostraram que os grupos laser e flúor + laser apresentaram uma redução significante (p<0.05) na perda de estrutura de esmalte em todos os tempos tanto no modelo in situ quanto in vitro. O grupo flúor apresentou uma redução significativa apenas no modelo in vitro (p<0.05). A análise por EDX mostrou que o grupo flúor + laser apresentou um aumento significativo quantidade de flúor comparado aos outros grupos, assim como as mensurações de flúor através da técnica de biópsia revelaram que apenas no dia 1 os grupos flúor + laser e flúor apresentaram uma quantidade significativa de flúor (p<0.05). A irradiação com laser de CO2 com os parâmetros de baixa fluência (0.3J/cm2, 5s e 226Hz), associada ou não ao flúor, deixou a superfície de esmalte mais resistente a erosão do causada por ácido cítrico tanto in situ quanto in vitro. / Dental erosion is increasing as consequence of changing habits from the population, as well as increase of prevalence gastric reflux or vomiting. The possibility of making dental enamel more resistance to erosion is the objective of this study. 10 volunteers participated in the in situ study, in a crossover design with 4 treatments (G1 control, no treatment; G2 CO2 laser irradiation; 0.3J/cm2-5s-226Hz; G3 topical fluoride treatment 1.25% - 3 min; G4 - CO2 laser + fluoride treatment). For each treatment the volunteers used palatal appliances containing fixed sterilized bovine enamel samples during day and night except for meals. For erosive demineralization the mouth appliances were immersed extra-orally in 80ml of 0.05M citric acid (pH 2.3) for 20 minutes twice daily. Individual oral hygiene was performed with fluoride-free products and without the appliance in situ. Before and between the treatment periods, a 1 week wash out period was included. Two samples were collected from the appliances for analysis on days 1, 3 and 5 (n=20/day/treatment). Surface loss was measured by digital profilometer. Additional fluoride measures, morphological analyses and EDX analyses were performed. For the in vitro model all the procedures were repeated, but instead of maintaining the samples in oral cavity, they were maintained for the same time in deionized water (n=12/day/treatment) and the surface loss was analyzed by digital profilometer. The results showed that the groups laser and fluoride + laser presented significant lower surface loss in all times both in situ and in vitro models. Fluoride presented significant surface loss only in the in vitro model. The EDX analysis, showed that fluoride + laser group presented significant more fluoride than the others groups, and the fluoride measurements of the samples showed that only in the first day the groups fluoride and fluoride + laser presented significant more fluoride that the other groups. CO2 laser irradiation at 0.3J/cm2 (5s, 226Hz) associated or not with fluoride decreases enamel erosive surface loss caused by citric acid, in situ and in vitro.

Natural materials can be used to remove water contaminants by applying proper physical, chemical, and biological water treatment processes. This study involves using natural materials, as they are considered to be more environmentally benign and cost-effective than synthetic materials. This dissertation concentrates on monitoring five major water quality parameters—ammonia, fluoride, turbidity, pH, and fecal indicator bacteria (FIB) —in two major applications where clean water is needed. The focus is on meeting the water quality requirements for each contaminant. The overall objective of this study is to control the levels of ammonia in aquaculture wastewater, and adjust fluoride, turbidity, pH, and FIB in drinking water by using natural materials. To accomplish this objective, this dissertation study is divided into two parts. Part I is about ammonia removal in aquaculture wastewater. Zeolite was the representative natural material that was used in this study. The methodologies presented include ion exchange and chemical neutralization processes. Part II is about fluoride, turbidity, pH and fecal indicator bacteria control in drinking water. Pumice stone was used in this study. The methodologies utilized in this work include biofiltration and adsorption. In Part I, the methods of ion exchange and chemical neutralization as a function of ammonia removal efficiency, toxicity, and daily cost were compared. All these methods were found to remove ammonia by a simple drop-off system. Chabazite, a natural zeolite, was the ion exchanger source. Similarly, we compared the effectiveness of commercialized neutralizers versus a novel neutralizer prepared for this work. The ion exchanger (chabazite) had the highest ammonia removal in freshwater, but no significant ammonia removal in seawater was observed after in-vivo trials. However, for commercial water neutralizers, the in-vivo trials showed that they are not able to control ammonia levels in either freshwater or seawater. The novel neutralizer was found to have higher ammonia removal efficiencies in both freshwater and seawater. In terms of toxicity, the AmmoSorb can be considered non-toxic. To safely use the novel neutralizer, it is recommended to control its daily dose at 1 g/L/day followed by a two-thirds volume of water change every day. A comprehensive cost analysis also showed that the novel neutralizer was the least expensive ammonia remover. In Part II, drinking water was treated by a bench-scale biosand filter system that included different filtration technologies, biological disinfection, and adsorption. The filtration technologies analyzed in this work include Aluminum Oxide Coated Pumice (AOCP) and sand. The AOCP also works as adsorption media to remove fluoride in water. As results, the AOCP imbedded biosand filter (BSF) can efficiently control fluoride, turbidity, and pH level to meet the WHO standards. In addition, the exhausted BSF can be regenerated by recoating the pumice with additional layers of aluminum oxide. The fluoride, turbidity, pH, as well as fecal indicator bacteria levels controlled by the regenerated BSF also meet the WHO standard for about one-month operation. The overall contribution of this research is providing new methods to treat water at an affordable cost and an easy operational procedure with potential health benefits to the specific applications that require ammonia, fluoride, turbidity, pH, and E. coli levels to be controlled.

Master of Science / Department of Geology / Saugata Datta / Elevated concentrations of arsenic (As) and fluoride (F) have been documented within the volcano-sedimentary aquifers of the Independence Basin Aquifer System in Guanajuato, Mexico which lies in the Mesa Central (MC) physiographic province on the northern edge of the Trans Mexican Volcanic Belt (TVMB). The geogenic sources of these contaminants are not well understood. This study adds to the existing record of the distribution of As and F contamination in the major aquifers of the basin by analyzing 24 water samples from five urban and rural areas. The mean As and F concentrations in the Cuenca Alto Rio Laja (CARL) aquifer on the western side of the basin were ~10 µg/L (median = 36 µg/L) and ~0.5 mg/L (median = 0.8 mg/L), respectively. In contrast, the mean As and F concentrations in the Laguna Seca (LS) aquifer on the eastern side of the basin were ~44 µg/L (median = 11 µg/L) and ~5.8 mg/L (2.6 mg/L), respectively. The high sodium, alkalinity, and low calcium concentrations observed in both aquifers are typical for fractured acid volcanic geothermal systems which have been observed in many Mexican states. Boron, lithium, and groundwater temperature showed positive correlations with As (R2 = 0.47, 0.68, and 0.55) and F (R2 = 0.31, 0.73, and 0.57) concentrations. These trace elements and elevated groundwater temperatures are indicators of water with hydrothermal origins. The drill cuttings from two boreholes ~500 m in depth were analyzed by X-ray diffraction, petrographic, and elemental analysis. This work revealed that the volcanic rocks of the CARL aquifer are primarily comprised of plagioclase, quartz, potassium-feldspar, calcite, volcanic glass, apatite, and iron oxyhydroxides. Additionally, there are layers of volcanic rocks comprised of pyroxene, plagioclase, quartz; amphibole, biotite, and apatite. The sedimentary rocks of the LS aquifer are comprised primarily of plagioclase, potassium feldspar, muscovite, biotite, volcanic glass, apatite, calcite, and quartz. These sedimentary rocks were deposited on volcanic rocks comprised of plagioclase, pyroxene, quartz, calcite, apatite, olivine, amphibole, hematite, chlorite, biotite, and ilmenite. To determine source zones the distribution of leachable F from the drill cuttings of both boreholes was examined through batch reactors. The leached F concentration profile revealed that the upper 140 m and lower 400 m of the western and eastern sides of the basin were the dominant source zones of leachable F. Overpumping in the IBAS has caused water table levels in this aquifer the decline over time. As these groundwater wells continue to be constructed to deeper depths to reach groundwater the release of As and F from these sources and the mechanisms controlling As and F from these subsurface lithologies needs to be understood. The release of both As and F from the rocks of the western and eastern side of the basin at 400 to ~500 m depths were examined through pH-adjusted batch reactors with groundwater from the CARL which contained initial As and F concentrations of ~7.9 µg/L and ~0.8 mg/L; respectively. The dissolution of F-bearing minerals and adsorption reactions with iron oxyhydroxides display a dominant control on the changes in As and F concentrations in the groundwater of the CARL aquifer. At pH 5, the rocks from the 400 – 500 m depth within the CARL aquifer reduced the initial concentrations of As and F to values of ~5.8 µg/L and ~0.5 mg/L, respectively, after 200 hours. Whereas at a pH of 9 these rocks leached F increasing its concentration to ~0.9 mg/L. The As concentration was reduced to ~6.3 µg/L. In contrast to the CARL aquifer rocks, the rocks of the LS aquifer released F at all three pH values as F-bearing minerals dissolved. Alongside F-bearing mineral dissolution, adsorption on to iron oxyhydroxide surfaces could be occurring as F concentrations continuously decreased after 50 hours of reaction. The As concentrations in the rocks from the 400 – 550 m depths of the LS aquifer released minor amounts of As at pH 7 and 9, increasing the concentration slightly until 50 hours of reaction. During the remaining 150 hours of reaction the As concentrations displayed a continuous decrease in concentration. At pH 5, however, As concentrations decreased to ~5.7 µg/L after 200 hours of reaction. The spatial and kinetic leaching patterns observed in this study, combined with the mapping of known As- and F-bearing minerals within major rock aquifer groups on the east and west side of the basin, will suggest initial release or mobilization mechanisms to future researchers. The mechanisms of initial release and transport of As and F through aquifers of the Independence Basin should be studied through a combination of laboratory experiments and reactive flow and transport modeling to determine the migration of As and F from source rocks to groundwater wells.

Les batteries tout-solides à ions fluorures reposent sur l'échange réversible d'ions F- entre un métal et un fluorure métallique au travers d'un électrolyte solide. Ces dispositifs électrochimiques peuvent théoriquement permettre l'obtention de fortes densités énergétiques, bien supérieures à celles des batteries conventionnelles Li-ion commerciales. En conséquence, les batteries à ions F- suscitent un fort engouement. Dans ce contexte, une partie de nos travaux ont portés sur le développement d'une cellule permettant d'évaluer leurs performances. De plus, les propriétés électrochimiques de l'électrolyte solide LaF3 dopé BaF2, La1-xBaxF3-x, ont fait l'objet d'une attention particulière. Finalement, les changements structuraux s'effectuant au sein des électrodes lors des cycles de charge/décharge ont été étudiés afin de mieux comprendre les mécanismes électrochimiques mis en jeu. / Solid-state fluoride-ion batteries rely on the reversible exchange of the F- ion between a metal and a metal fluoride through a solid electrolyte. These electrochemical devices can theoretically reach energy densities superior to conventional Li-ion commercial batteries. Consequently, fluoride-ion batteries can be seen as a new promising chemistry generating a growing interest. In this context, a part of our work has been dedicated to the development of a cell allowing the evaluation of their electrochemical performance. Moreover, particular attention was given to the electrochemical properties of the solid electrolyte, BaF2-doped LaF3, La1-xBaxF3-x. Finally, the structural changes taking place at the electrodes upon charge/discharge were studied in order to gain insight into the electrochemical mechanisms involved in these devices.

South Africa is the second largest producer of zircon (ZrSiO4) in the world, Australia being the largest. Zircon is notorious for its chemical inertness. Extreme processing conditions such as alkaline fusion (NaOH at 600 °C or Na2CO3 at 1200 °C) are used to extract the zirconium values from the mineral. The purpose of this study was to investigate the use of microwave digestion as an alternative process, and to determine the parameters for this technique for the digestion of zircon with ammonium acid fluoride (AAF) under various conditions. Ammonium acid fluoride is more convenient and safer to use than conventional fluorination methods such as HF and F2. In this study zircon was treated with ammonium acid fluoride (NH4F∙1.5HF) by means of microwave assisted digestion. Reaction times ranged from 10 to 330 minutes at temperatures between 100 °C and 240 °C. Successive microwave digestion steps, interrupted by an aqueous wash procedure, resulted in a >99 % conversion of zircon to the water soluble intermediates (NH4.)3ZrF7 and (NH4)2SiF6. XRD and Raman spectroscopy confirm that zircon was the major phase present in the insoluble fraction of the product after washing. Arrhenius rate laws are derived for both reaction control (progressively shrinking particle) and diffusion control by the product layer. Both models show reasonably good agreement with the experimental data, but diffusion control was accepted as the most probable. The derived diffusion coefficient corresponds to a solid-liquid case. Copyright / Dissertation (MSc)--University of Pretoria, 2013. / Chemical Engineering / unrestricted