Abstract High levels of shrinkage stress caused by volumetric variations during the activation process are one of the main problems in the practical application of composite resins. Objective The aim of this study is to reduce the shrinkage stress and minimize the effects caused by composite resin volumetric variation due to the photopolymerization. In this way, this work proposes a systematic study to determine the optimal dimming function to be applied to light curing processes. Material and Methods The study was performed by applying mathematical techniques to the optimization of nonlinear objective functions. The effectiveness of the dimming function was evaluated by monitoring the polymerization shrinkage stress during the curing process of five brands/models of composites. This monitoring was performed on a universal testing machine using two steel bases coupled in the arms of the machine where the resin was inserted and polymerized. The quality of the composites cured by the proposed method was analyzed and compared with the conventional photoactivation method by experiments to determine their degree of conversion (DC). Absorbance measurements were performed using Fourier-transform infrared spectroscopy (FT-IR). A T-test was performed on DC results to compare the photoactivation techniques. We also used scanning electron microscopy (SEM) to analyze in-vitro the adhesion interface of the resin in human teeth. Results Our results showed that the use of the optimal dimming function, named as exponential, resulted in the significant reduction of the shrinkage stress (~36.88% ±6.56 when compared with the conventional method) without affecting the DC (t=0.86, p-value=0.44). The SEM analyses show that the proposed process can minimize or even eliminate adhesion failures between the tooth and the resin in dental restorations. Conclusion The results from this study can promote the improvement of the composite resin light curing process by the minimization of polymerization shrinkage effects, given an operational standardization of the photoactivation process.

Um novo sensor baseado em nanotubos de carbono de paredes múltiplas modificado com bastões de SnO2 foi desenvolvido para a determinação eletroquímica de levofloxacino. A morfologia, a estrutura, e o comportamento eletroquímico do eletrodo compósito foram caracterizados por microscopia eletrônica de varredura, energia dispersiva de raios X e voltametria cíclica, respectivamente. Voltametria de pulso diferencial em solução tampão fosfato pH 6,0 permitiu a aplicação de um método para determinar níveis de levofloxacino em um intervalo de 1,0-9,9 µmol L-1, com limite de detecção calculado em 0,2 µmol L-1 (72,0 mg L-1).

A new sensor based on multi-walled carbon nanotubes modified with SnO2 rods for the electrochemical determination of levofloxacin has been investigated. The morphology, the structure, and the electrochemical performance of the composite electrode were characterised by scanning electron microscopy, energy dispersive X-ray spectroscopy, and cyclic voltammetry, respectively. Differential pulse voltammetry in phosphate buffer solution at pH 6.0, allowed the application of a method to determine levofloxacin levels in a range of 1.0-9.9 µmol L-1, with a limit of detection calculated at 0.2 µmol L-1 (72.0 mg L-1).

Thiol-functionalised silica films were deposited on various electrode surfaces (gold, platinum, glassy carbon) by spin-coating sol-gel mixtures in the presence of a surfactant template. Film formation occurred by evaporation induced self-assembly (EISA) involving the hydrolysis and (co)condensation of silane and organosilane precursors on the electrode surface. The characterization of such material was performed by IR spectroscopy, thermogravimetry (TG), elemental analysis (EA), atomic force microscopy (AFM), scanning electron microscopy (SEM) and cyclic voltammetry (CV).

O desempenho do eletrodo de pasta de carbono (EPC) modificado com a sílica SBA-15 nanoestruturada organofuncionalizada com benzotiazol-2-tiol na determinação de íons Cd(II) em águas naturais é descrito, baseado no processo de DPASV. O Cd(II) apresentou um pico de oxidação por volta de -0,85 V (vs. ECS) em tampão fosfato (pH 3,0). Os melhores resultados obtidos foram com as seguintes condições otimizadas: amplitude de pulso 100 mV, 2 min de tempo de acumulação, velocidade de varredura 10 mV s-1 em solução tampão fosfato pH 3,0. Usando tais parâmetros observou-se uma resposta linear para o Cd(II) no intervalo de 1,00 a 10,0 <FONT FACE=Symbol>´</FONT> 10-6 mol L-1 com limite de detecção de 4,5 <FONT FACE=Symbol>´</FONT> 10-7 mol L-1. Cd(II) foi adicionado em amostras de águas naturais e determinado com recuperação média de 96,4% em concentrações da ordem de 10-6 mol L-1.

The performance of a carbon paste electrode (CPE) modified with SBA-15 nanostructured silica organofunctionalised with 2-benzothiazolethiol in the determination of Cd(II) ions in natural water is described, based in a DPASV procedure. The Cd(II) oxidation peak was observed around -0.85 V (vs. SCE) in phosphate buffer (pH 3.0). The best results were obtained under the following optimised conditions: 100 mV pulse amplitude, 2 min accumulation time, 10 mV s-1 scan rate in phosphate buffer pH 3.0. Using such parameters a linear dynamic range from 1.00 to 10.0 <FONT FACE=Symbol>´</FONT> 10-6 mol L-1 Cd(II) was observed with limit of detection 4.5 <FONT FACE=Symbol>´</FONT> 10-7 mol L-1. Cd(II) spiked in a natural water sample was determined with 96.4% mean recovery at µmol L-1 level. The results indicate that this electrode is sensitive for determination of Cd(II). Interference of some divalent cations were also evaluated.