Led light effect on knoop microhardness of conventional composite resins and bulk fill

Objective: Evaluate the Knoop microhardness (KHN) of conventional and bulk fill composites light cured in different layers. Materials and Methods: Eighty specimens were prepared, of which forty in 8x2mm thickness and forty in 8x4mm thickness, according to the resins tested: Opus Bulk Fill (FGM); Filtek Bulk Fill (3M); Filtek Z350 XT (3M); Opallis (FGM). The material was prepared according to ISO 4049.The photoactivation was performed with the LED device for 40s. The specimens obtained were submitted to the Knoop microhardness test. Results: Thus, the values obtained were submitted to Kruskall Wallis test, followed by Dunn test, p <0.05. When evaluating the top and bottom surfaces, the top surfaces showed statistically superior results to the bottom surfaces in all resins. From the micro hardness of the 8x2mm samples evaluated, only Filtek Bulk Fill and Filtek Z350 XT resin had acceptable top / bottom ratio (≥0.8). Of the 8x4mm specimen only the validated bulk fill resins presented this acceptable microhardness ratio and were statistically similar to the 8x2mm base. Conclusion: It was observed that, according to the methodology used, only the bulk fill composite resins achieved an acceptable polymerization and microhardness at 4mm depth.