Evaluation of the depth of cure and surface microhardness of various bulk fill composite resins polymerized with different light sources

Aim: To compare the the microhardness of composite sample with different thickness following polymerization with different light sources. For this purpose, the microhardness values of the top and bottom surfaces of the composite samples were measured and the microhardness of composites at different depths were compared using the values obtained from the top and bottom surfaces. Materials & Methods: Effectiveness of cure sources was determined by measuring the top and bottom surface hardness (VHN) of 4 and 2-mm composite specimens. One microhybrid composite (Z250, shade A2) as control group and two bulk fill composite (SDR bulk fill composite and Tetric evoceram bulk fill composite) were used to prepare 10 samples for a total of 120 samples. The samples were made up in 8 mm diameter circular black polypropylene molds, with 4 and 2mm thickness. Each sample was prepared in the same manner by the same operator and cured maintaining a distance of 2mm between the specimen and light tip. After 24 hours' storage in distilled water , Vickers micro-hardness measurements were obtained on both sides of the samples, with a load of 50 grams for 10 seconds. Three indentations were performed on each surface of each sample and the Vickers hardness values were obtained. Data analysis: Two Way Anova test was used, for the evaluation of the effect of different material, application thickness of the material and also the type of light curing device on the hardness ratio means. In comparison, the parameters between more than two groups, One-way Anova Test; and during the determination of the group that caused the differences Tukey HDS test was used. Also, in comparison the parameters between the two groups, Student t test was used.Significance was evaluated on the level of p < 0,05. Result: When halogen light was used, statistically significant differences were found between the hardness ratio means of the materials which had 2 mm thicknesses(p = 0,015; p <0,05) and statistically significant differences were found between the hardness ratio means of the materials which had 4 mm thicknesses (p = 0,001; p <0,01) When LED light unit was used, no statistically significant differences were found between the hardness ratio means of the materials which had 2 mm thicknesses but statistically significant differences were found between the hardness ratio means of the materials which had 4 mm thicknesses (p = 0,001; p <0,01) Conclusion: All composites with 2 mm or 4 mm thickness (except Tetric Evo Ceram 2 mm) when cured with LED showed lower hardness ratio means than the materials cured with halogen light