Avaliação da resistência coesiva e da microdureza de uma resina composta polimerizada com fontes de luz halógena e LED / Evaluation of tensile strength and microhardness of a photo polymerizing resin composite, cured with light curing units - halogen and LED

RESUMO

O presente estudo teve como objetivo avaliar a resistência coesiva, por meio do teste de tração, de uma resina composta fotopolimerizável (Z250 - 3M/ESPE) com variação de espessura do material, utilizando aparelhos de lâmpada halógena (Curing Light 2500 - 3M/ESPE - CL) e do tipo LED (Ultraled - Dabi-Atlante - UTL e UltraBLue - DMC - UB3 e UB6) com diferentes densidades de potência (130mW/cm2, 300mW/cm2 e 600 mW/cm2), assim como a influência do tempo de ativação (20s, 40s e 60s) e, adicionalmente, relacionar essa resistência com a microdureza na porção correspondente à região de fratura do material. Foram estabelecidos 24 grupos (n=10), sendo utilizadas duas matrizes de aço segmentadas, com espessuras de 1 e 2mm para a obtenção dos espécimes. Posteriormente, os corpos-de-prova foram submetidos ao teste de tração na Máquina Universal de Ensaios Kratos,utilizando-se a célula de carga de 50g e velocidade de 0,5mm/min. Os valores de resistência à tração foram obtidos em kgf/cm2 e transformados em MPa. Para o teste de microdureza, as mesmas matrizes foram utilizadas para confecção dos espécimes (24 grupos com n=5), analisando-se a dureza na interface correspondente à área de união. O teste de microdureza Knoop foi realizado com auxílio do Microdurômetro Shimadzu HMV-2, com carga estática de 50g por 30s.

ABSTRACT

The aim of this study was to evaluate the tensile strength, through tensile tests, of a photopolymerizable composite resin (Filtek Z250 - 3M/ESPE), with variation of material's thickness, using an halogen light curing unit (Curing Light 2500 - /ESPE - CL) and two light emitting diodes units (Ultraled - Dabi/Atlante- UL; Ultrablue IS - DMC - UB3 and UB6) with different power densities (130, 300, 600 and 40mW/cm2), as well as the influence of activation times (20, 40 and 60s) and, additionally, relate this data with the Knoop microhardness in that area corresponding to the fracture region of material. A number of 24 groups were stablished and a set of stainless matrix composed by two parts was used, with thickness of 1 and 2mm, to obtain the specimens. Next, the specimens were submitted to tensile tests in a Universal Testing Machine (Kratos), using a crosshead speed of 0,5mm/min and a 50Kg load cell until fracture. Tensile strength values were calculated in kgf/cm2 and translated into MPa. To microhardness test, the same matrix was used to obtain the specimens (24 groups - n=5), analyzing the hardness in the surfaces exposed and non-exposed to the light source. The Knoop microhardness test was made using a Shimadzu HMV-2 Microhardness Tester, at a static load of 50g at 30 seconds. The values obtained were submitted to three-way ANOVA and for individual comparison a Tukey test was applied with a 0.05 significance level. The results showed that, with regard to individual performance of light curing units studied, there was similarity in tensile strength to the different activation times evaluated (20, 40 and 60s), both to 1mm of thickness as 2mm; (2) Composite resin showed superior tensile strength to 2mm thickness, while with respect to microhardness at the area corresponding to union interface, the values were higher when specimens with 1mm thickness were tested, demonstrating that a higher hardness does not implies superior tensile strength;