To ensure an adequate clinical composite filling light source for photopolymerization is of great importance. In everyday clinical conditions commonly used unit for polymerization of composite material is halogen curing unit. The development of new blue superbright light emitting diodes (LED) of 470 nm wavelengths comes as an alternative to standard halogen curing unit of 450-470 nm wavelengths. The purpose of this study was to compare the degree of conversion (DC) and temperature rise of four hybrid composite materials: Tetric Ceram, Pertac II, Valux Plus and Degufill Mineral during 40 s illumination with standard halogen curing unit Heliolux GTE of 600 mW cm(-2) intensity, Elipar Highlight soft-start curing unit of 100 mW cm(-2) (10 s) and 700 mW cm(-2) (30 s) intensity and 16 blue superbright LED of minimal intensity of 12 mW cm(-2) on the surface and 1 mm depth. The results revealed only a little bit higher DC values in case of polymerization with even 66 times stronger halogen curing units which showed twice higher temperature than blue diodes. Temperature and DC obtained are higher on the surface than on 1 mm depth regardless on the light source used.

OBJECTIVES To evaluate the influence of irradiation time on degree of conversion (DC) and microhardness of high-viscosity bulk-fill resin composites in depths up to 6 mm. MATERIALS AND METHODS Four bulk-fill materials (Tetric EvoCeram Bulk Fill-TECBF; x-tra fil-XF; QuixFil-QF; SonicFill-SF) and one conventional nano-hybrid resin composite (Tetric EvoCeram-TEC) were irradiated for 10, 20, or 30 s at 1,170 mW/cm(2). DC and Knoop microhardness (KHN) were recorded after 24-h dark storage at five depths: 0.1, 2, 4, 5, and 6 mm. Data were statistically analyzed using ANOVA and Bonferroni's post-hoc test ( = 0.05). RESULTS With increasing bulk thickness, DC and KHN significantly decreased for TEC. TECBF and SF showed a significant decrease in DC and KHN at 4-mm depth after 10-s irradiation, but no decrease in DC after 30-s irradiation (p > 0.05). XF and QF demonstrated no significant DC decrease at depths up to 6 mm after irradiation of at least 20 s. At 4-mm depth, all materials tested achieved at least 80 % of their maximum DC value, irrespective of irradiation time. However, at the same depth (4 mm), only XF and QF irradiated for 30 s achieved at least 80 % of their maximum KHN value. CONCLUSIONS Regarding DC, the tested bulk-fill resin composites can be safely used up to at least 4-mm incremental thickness. However, with respect to hardness, only XF and QF achieved acceptable results at 4-mm depth with 30 s of irradiation. CLINICAL RELEVANCE Minimum irradiation times stated by the manufacturers cannot be recommended for placement of highviscosity bulk-fill materials in 4-mm increments. Conclusions: Regarding DC, the tested bulk-fill resin composites can be safely used up to at least 4-mm incremental thickness. However, with respect to hardness, only XF and QF achieved acceptable results at 4-mm depth with 30 s of irradiation.Clinical relevance: Minimum irradiation times stated by the manufacturers cannot be recommended for placement of high-viscosity bulk-fill materials in 4-mm increments.

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