The Effect of Layer Thickness and Light Intensity on the Degree of Conversion, Microhardness and Cytotoxicity of Bulk Fill Composite Resins

Objectives: The aim of this study was to evaluate the effects of polymerizing bulk fill composite resins at different thicknesses and different light intensities on the degree of conversion, microhardness and cytotoxicity of the composites.Methods: Two different bulk fill composite resins were used in this in vitro study: Sonic Fill 2, Filtek Bulk Fill. Samples prepared from both composites with a thickness of 2, 4 and 6 mm were polymerized in 2 different power modes. The degree of conversion, microhardness and cytotoxicity of these samples were measured.Results: As the layer thickness of the bulk fill composite resins increased, the degree of conversion of the lower surfaces of the composites decreased significantly (p <.05). When the lower and upper surface microhardness ratios of bulk fill composite resins were examined, 2 mm thick samples of both composites polymerized by both polymerization methods and 4 mm thick samples polymerized in standard power mode exceeded the acceptable threshold value of 0.80. According to the results of the WST-1 experiment; cell viability decreased as the layer thickness of bulk fill composites increased.Conclusions: The upper surface degree of conversion and microhardness values of the bulk fill composite resins examined were higher than the lower surface values. According to the results of the WST-1 experiment; as the layer thickness of the bulk fill composites increased, the cell viability decreased, the cytotoxic properties increased.