Shrinkage stress of three composites under different polymerization methods

Abstract

ABSTRACT:The aim of this study was to evaluate the shrinkage stress of three composites under different polymerization methods: halogen conventional polymerization (G1), halogen "soft-start" polymerization (G2) and LED polymerization (G3). The composites tested were Filtek Z-100 (3M/ESPE), Filtek Z-250 (3M/ESPE) and Solitaire 2 (Heraeus Kulzer). For G1, an XL-3000 (3M/ESPE) curing unit with light intensity of 507 mW/cm 2 was employed. In G2, the same light unit was used, but with a reduced light intensity in the first 20 s (166 mW/cm 2 ). In G3, an Ultrablue I (DMC) LED curing unit with light intensity of 125 mW/cm 2 was used. The test was performed with a DL 2000 (EMIC) universal testing machine and two metallic molds with a 1 mm space between them. The composites were inserted in the space between the molds and light cured according to the protocols mentioned above. Stress was registered in different periods of time: 10, 20, 40, 60, 90 and 120 s. A significant linear increase of the shrinkage stress over time was observed, except for Z-100 in G2. Generally, LED polymerization (G3) reduced the generated stress when compared to conventional halogen polymerization (G1). In G3, the composite with the additional co-initiatior presented lower stress when compared to the other composites tested. The combination between composite and polymerization method produced different patterns of stress behavior. LED polymerization reduced the initial shrinkage stress of the three materials and was influenced by the presence of co-initiators in the composites. DESCRIPTORS: Composite resins; Dental stress analysis; Physical and chemical properties. RESUMO:O objetivo do presente estudo foi avaliar o estresse de contração de três resinas compostas sob diferentes métodos de fotoativação: fotoativação convencional halógena (G1), fotoativação "soft-start" halógena (G2) e fotoativação por LED (G3). As resinas compostas testadas foram a Filtek Z-100 (3M/ESPE), Filtek Z-250 (3M/ESPE) e Solitaire 2 (Heraeus Kulzer). Para G1, um aparelho fotoativador XL-3000 (3M/ESPE) com intensidade de 507 mW/ cm 2 foi empregado. Em G2, o mesmo aparelho foi utilizado, mas com a intensidade reduzida nos primeiros 20 s (166 mW/cm 2 ); em G3 foi utilizado um fotoativador LED Ultrablue I (DMC) com intensidade de 125 mW/cm 2 . O teste foi realizado com uma máquina de ensaio universal DL 2000 (EMIC) e duas matrizes metálicas com um espaço de 1 mm entre elas. A resina composta foi inserida no espaço entre as matrizes e fotopolimerizada de acordo com o protocolo supracitado. O estresse foi registrado nos diferentes períodos de tempo: 10, 20, 40, 60, 90 e 120 s. Um aumento linear significante do estresse de contração em relação ao tempo foi observado, exceto para a Z-100 em G2. No geral, a fotoativação por LED (G3) reduziu o estresse gerado em comparação com a fotoativação convencional halógena (G1). Em G3, a resina com co-iniciador na sua composição apresentou menor estresse em comparação com as outras resinas testadas. A combinação entre resina composta e o méto...

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