Effect of Zirconia and Alumina Fillers on the Microstructure and Mechanical Strength of Dental Glass Ionomer Cements.

BACKGROUND: Glass-ionomer cements perform a protective effect on the dentin-pulp complex considering the F ions release and chemical bonding to the dental structures. On the other hand, those materials have poor physic-mechanical properties in comparison with the restorative resin composite. The main aim of this work was to evaluate the influence of zirconia and/or alumina fillers on the microstructure and strength of a resin modified glass-ionomer cement after thermal cycling. METHODS: An in vitro experimental study was carried out on 9 groups (n = 10) of cylindrical samples (6 x 4 mm) made from resin modified glass-ionomer (Vitremer, 3M, USA) with different contents of alumina and/or zirconia fillers. A nano-hybrid resin composite was tested as a control group. Samples were mechanically characterized by axial compressive tests and electron scanning microscopy (SEM) coupled to energy dispersive X-ray spectrophotometry (EDS), before and after thermal cycling. Thermal cycling procedures were performed at 3000, 6000 and 10000 cycles in Fusayama´s artificial saliva at 5 and 60 (o)C. RESULTS: An improvement of compressive strength was noticed on glass-ionomer reinforced with alumina fillers in comparison with the commercial glass ionomer. SEM images revealed the morphology and distribution of alumina or zirconia in the microstructure of glass-ionomers. Also, defects such as cracks and pores were detected on the glass-ionomer cements. The materials tested were not affected by thermal cycling in artificial saliva. CONCLUSION: Addition of inorganic particles at nano-scale such as alumina can increase the mechanical properties of glass-ionomer cements. However, the presence of cracks and pores present in glass-ionomer can negatively affect the mechanical properties of the material because they are areas of stress concentration.

Contaminação das águas subterrâneas por nitrato em Presidente Prudente - SP, Brasil / Nitrate contamination in grounwater in Presidente Prudente-SP, Brazil

A pesquisa teve como objetivo delimitar zonas de contaminação das águas subterrâneas por nitrato na área urbana de Presidente Prudente-SP, Brasil, verificar a sua possível relação com a expansão da urbanização e apontar prováveis causas do fenômeno a ser caracterizado. Os trabalhos executados incluíram a consulta aos arquivos do Instituto Adolfo Lutz com referência a análises físico-químicas de águas subterrâneas, alocalização dos pontos de coleta de amostras pelo sistema de coordenadas UTM, o tratamento geoestatístico dos dados das análises por meio do Programa Surfer-Surface Mapping System, com a interpolação por Krigagem linear. Este mapeamento realça a localização da contaminação em áreas bem definidas, estando os poços contaminados em zona inscrita na área de ocupação urbana anterior ao ano de 1962. Como fontes da contaminação, a pesquisa executada distingue o vazamento de esgoto doméstico, a lixiviação de fossas e a lixiviação de depósitos variados de resíduos sólidos. Os resultados das análises evidenciam também a resina de troca iônica, cujo emprego se tem mostrado eficiente