Effect of time and pH on physical-chemical properties of orthodontic brackets and wires.

OBJECTIVE: To test the hypothesis that treatment time, debris/biofilm, and oral pH have an influence on the physical-chemical properties of orthodontic brackets and arch wires. MATERIALS AND METHODS: One hundred twenty metal brackets were evaluated. They were divided into four groups (n  =  30) according to treatment time: group C (control) and groups T12, T24, and T36 (brackets recovered after 12, 24, and 36 months of treatment, respectively). Rectangular stainless-steel arch wires that remained in the oral cavity for 12 to 24 months were also analyzed. Dimensional stability, surface morphology, composition of brackets, resistance to sliding of the bracket-wire set, surface roughness of wires, and oral pH were analyzed. One-way analysis of variance, followed by a Tukey multiple comparisons test, was used for statistical analysis (P < .05). RESULTS: Carbon and oxygen were shown to be elements that increased expressively and in direct proportion to time, and there was a progressive increase in the coefficient of friction and roughness of wires as a function of time of clinical use after 36 months. Oral pH showed a significant difference between group T36 and its control (P  =  .014). CONCLUSIONS: The hypothesis was partially accepted: treatment time and biofilm and debris accumulation in bracket slots were shown to have more influence on the degradation process and frictional force of these devices than did oral pH.

Nanohybrid versus nanofill composite in class I cavities: margin analysis after 12 months.

This study evaluates the margin of a nanofill, a nanohybrid, and a conventional microhybrid composite in restorations in occlusal cavities of posterior teeth after 12 months. Forty-one patients, each with three molars affected by primary caries or the need to replace restorations, participated in this research. The teeth were restored with a nanofill (Filtek Z350), a nanohybrid (Esthet-X), and a microhybrid as a control (Filtek Z250). Ten patients were selected randomly, and the three restorations were molded with a low-viscosity polyvinyl siloxane material. The molds were poured with epoxy resin, gold-sputter coated, observed by scanning electron microscopy, and classified as: "perfect margin," "marginal irregularity," "marginal gap," "marginal fracture," or "artifact." For statistical analysis, the Wilcoxon and Friedman nonparametric tests and paired-samples t-test were used (significance level of 5%). The performance of the three materials was compared after 1 week and 12 months. No statistically significant differences were detected for all criteria (P > 0.05). When each composite was compared over time, statistically significant differences were found for the criterion, perfect margins (Esthet-X and Filtek Z350, P < 0.05). The materials performed satisfactorily over the 12-month-observation period, but all composites under investigation showed a certain amount of deterioration relating to marginal quality over time.

Avaliação do Efeito Erosivo em Microscopia Eletrônica de Varredura e Propriedades Físico-Químicas de Bebidas Gaseificadas de Baixa Caloria / Evaluation of the Erosive Effect in Scanning Electron Microscopy and Physicochemical Properties of Low-Calorie Carbonated Beverages

Objetivo: Avaliar o pH, a quantidade de Sólidos Solúveis Totais (°Brix), condutividade elétrica e a superfície do esmalte bovino submetido à ação de bebidas gaseificadas de baixa caloria, em Microscopia Eletrônica de Varredura (MEV). Material e Métodos: Os produtos utilizados foram: Aquarius Fresh® limão, H2OH!® limão, Aquazero® limão, Viver light® limão, Coca-cola® (controle positivo) e água deionizada (controle negativo). A avaliação do pH foi realizada mediante o uso de phmetro digital, a condutividade elétrica foi determinada por meio de um condutivímetro de bancada e para a quantificação do °Brix utilizou-se um refratômetro específico de campo. Para cada análise foram feitas três aferições e calculou-se a média aritmética. A superfície adamantina foi confeccionada a partir da exodontia de incisivos hígidos de maxilares bovinos de animais destinados ao abate, obtendo-se ao final, blocos de esmalte de 3x3mm (n=12) que foram submetidos ao contato por 5 minutos com as bebidas e em seguida lavados e armazenados para posterior análise em MEV. Resultados: Os valores de pH variaram de 2,56 (controle positivo) a 6,00 (controle negativo), estando as demais bebidas abaixo do pH 3,46. Os resultados para condutividade elétrica variaram de 001mS.cm -¹ (controle negativo) a 1071 mS.cm -¹ (Coca-Cola® ). Com relação aos °Brix, todas as bebidas, com exceção da Coca-Cola® (6,5°Brix) tiveram valor 0°Brix. Observou-se que as bebidas analisadas revelaram-se potencialmente erosivas. A superfície do esmalte exposto às bebidas gaseificadas apresentou características microestruturais indicativas de erosão. Conclusão: As bebidas gaseificadas analisadas se revelaram potencialmente erosivas para a superfície adamantina exposta, por um curto período de tempo, à ação destes produtos, não apresentando potencial cariogênico.

Objective: To evaluate the pH, the amount of total soluble solids (°Brix), electrical conductivity and the surface of bovine enamel, by Scanning Electronic Microscopy (SEM), subjected to the action of low- calorie soft drinks. Materials and Methods: The products tested were: Aquarius® Fresh lemon, H2OH!® lemon, Aquazero® lemon, Viver Light®lemon, CocaCola® (positive control) and deionized water (negative control). The pH evaluation was performed by using digital pHmeter. Electrical conductivity wa s determined by a workbench conductivimeter and for quantification of °Brix was used a specific refractometer of . For each analysis were made three measurements and the arithmetic mean was calculated. The adamantine surface was made from the extraction of healthy maxillary incisors from bovine animals for slaughter, resulting in the end, in 3x3mm enamel blocks (n = 12), which were submitted to contact for 5 minutes with the drinks and then washed and stored for subsequent analysis by SEM. Results: The pH values tranged from 2.56 (positive control) to 6.00 (negative control), while the remaining beverages showed pH bellow than 3.46. The results for electrical conductivity ranged from 001 mS.cm-¹ (negative control) to 1071 mS.cm- (Coca-Cola®). Considering the TSS, all beverages had a value of 0° Brix, excepting Coca-Cola® (6.5° Brix). It was observed that the beverages analyzed proved to be potentially erosive. The enamel surface exposed to fizzy drinks had microstructural features indicative of erosion. Conclusion: Fizzy drinks analyzed have proved to be potentially erosive for the adamantine surface exposed for a short period of time to the action of those products, presenting no cariogenic potential.