As características protectoras das superfícies de aços revestidos com zinco (imersão a quente ou electrodeposição) são geralmente intensificadas através da passivação por crómio hexavalente (Cr6+). Porém, por ser este um elemento tóxico, vários estudos visando a substituição do procedimento de cromatização vêm sendo realizados. As resinas de silicone, devido a propriedades como dureza, resistência química e aderência, podem vir a ser um excelente substituinte ao processo de cromatização. Neste trabalho, filmes de silicone obtidos pela hidrólise e subsequente condensação do tetraetoxisilano (TEOS) em presença de Polidimetilsiloxano (PDMS - OH) e de uma resina de silicone comercial foram aplicados em aço galvanizado e aço electrodepositado com ZnFe. A composição estudada foi 45% PDMS - 40% TEOS - 15 % Resina. O revestimento foi então avaliado através de Espectroscopia de Impedância Electroquímica, em solução de NaCl 3%. A evolução do comportamento frente à corrosão do sistema de revestimento foi investigada de forma temporal, verificando-se a influência dos diferentes componentes na resposta electroquímica do filme. Os dados obtidos pela Espectroscopia foram modelados através de um circuito equivalente, permitindo a obtenção dos parâmetros electroquímicos para o sistema avaliado. Os resultados obtidos mostram que o comportamento dos filmes de silicone é dependente do tipo de revestimento metálico que foi aplicado no aço. Maiores valores para |Z| foram obtidos para os filmes aplicados sobre o aço galvanizado, sendo este valor pouco alterado com o tempo de imersão.

Corrosion properties of galvanized steels are generally increased through a passivation processes with Cr6+ resulting in the formation of a passive layer. However, these kinds of chromates are toxic and environmentally legislation prohibits pre-treatments with chromates. As a consequence alternative pre-treatments have been studied along of last decades. Thus, alternative coatings of silicone resins due to their specific properties, such as hardness, chemical resistance and hydrofobicity, can be a viable substitute. In the present work silicon films obtained by hydrolysis and posterior condensation of tetraethoxysilane (TEOS) in presence of Poli(dimetilsiloxane) (PDMS - OH) and a commercial silicone resin, in a sol-gel process conditions, were applied on galvanized steel and on steel electroplated with a ZnFe alloy. The composition studied was 45%PDMS - 40% TEOS - 15% Resin. The film corrosion protection properties were evaluated by Electrochemical Impedance Spectroscopy (EIS) in a NaCl 3% solution at different immersion times. EIS experimental data were fitted to an equivalent circuit from which the electrochemical parameters were obtained. Results show that the overall performance of the coatings system appears to be highly dependent on the metallic coating kind applied to the steel. The better results in terms of impedance |Z|were obtained in coatings applied over galvanized steels, these impedance values showing a stable behaviour with immersion time increasing.

Chromatation pre-treatments have been widely used to improve galvanized steel corrosion resistance. However, due to the high toxicity of chromate ions, chromatation pre-treatments tend to be banned and, in last years, alternative coating systems are under investigation. Recently, polysiloxanes have been developed for application as coatings. Among them, and due to their specific properties, such as hardness, chemical resistance and hydrophobicity, silicone resins may be considered as promising substitutes for chromatation pre-treatments. In this work silicone films, obtained from the hydrolysis of a methoxy functional silicone reactive intermediate, were applied on galvanized steel and on steel electroplated with a ZnFe alloy. Electrochemical techniques were used to characterize the degradation behavior of the samples. These consisted on the monitoring of the open circuit potential (OCP), and on the potentiodynamic polarization of the samples, which was performed in a 3% NaCl aqueous solution. Additionally, electrochemical impedance spectroscopy (EIS) was used as a complementary technique for the evaluation of the corrosion mechanisms of the coating system. SEM and EDS were employed to inspect the surface of the samples before and after the electrochemical tests. EIS data was fitted to an equivalent circuit from which the electrochemical parameters were obtained. Results show the protective character of the resin films, when compared with uncovered specimens. The capacitance of the films increased with the immersion time, in accordance to the behavior expected for an organic film. The overall performance of the coating systems appears to be highly dependent on the type of metallic coating applied to the steel. During the first three days of immersion the coatings applied upon galvanized steel showed larger |Z| values when compared with those applied to the electroplated steel, indicating a superior corrosion resistance of the former. However, after that time, an abrupt drop of |Z| is observed in the film applied on galvanized steel. In comparison, the coating system involving ZnFe alloy evidences a better stability throughout the immersion time.

In Europe, in the late seventies, Lurh, Spiessel, Schilli and Champy, among others developed and popularized internal fixation with plates and screws with the aim of avoiding the need of maxillomandibular fixation in the treatment of maxillofacial injuries and deformities. In this paper the need to remove this materials after the consolidation time is discussed. There are some adverse circumstances that oblige the surgeon to remove the hardware like, palpation, exposure, migration, locally infection or thermal intolerance. This paper presents a retrospective study of thirty-six patients who underwent Le Fort osteotomy at the Department of Oral and Maxillofacial Surgery in Vall d'Hebron Hospital. Also, a review of the complications derived from the hardware material is presented. After a minimum follow-up of 30 months the following results were observed: only 4 of the 160 installed miniplates had to be removed. The low incidence of complications does not justify the systematic removal of ostheosynthesis material in this group of patients.

Se evaluaron retrospectivamente un total de 36 pacientes sometidos a osteotomía de LeFort I. En 21 de estos pacientes (8 hombres y 13 mujeres con edad media 20,8 años) se realizaron osteotomías estándar con corrección del defecto con miniplacas en forma de «L», usando en 11 casos miniplacas 2,0 y el resto 1,5. Se sometieron a los 15 pacientes restantes (8 hombres y 7 mujeres con edad media 39,6 años) a osteotomía segmentada sagital para el abordaje lesiones de la base del cráneo, colocando en todos ellos miniplacas de 2,0. Después de un seguimiento mínimo de 30 meses se llegaron a los siguientes resultados: De un total de 160 miniplacas colocadas ( 84 en grupo estándar y 76 en osteotomías de abordaje neuroquirúrgico) se retiraron sólo 4 de estas miniplacas, 2 de ellas por palpación intraoral y 2 por exposición. Por todo lo expuesto y en comparación con otras series concluimos que la baja incidencia de complicaciones derivadas del material de osteosíntesis no justifica su retirada sistemática en las osteotomías de maxilar superior.