Influence of irradiation time on subsurface degree of conversion and microhardness of high-viscosity bulk-fill resin composites
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/cm2. 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 (α = 0.05).
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.
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.
Minimum irradiation times stated by the manufacturers cannot be recommended for placement of high-viscosity bulk-fill materials in 4-mm increments.
KeywordsBulk-fill resin composites Degree of conversion Microhardness Depth of cure Irradiation time
This investigation was supported by the authors’ institutions and the Croatian Science Foundation. Dental companies Ivoclar Vivadent (Schaan, Liechtenstein) and Dentsply DeTrey (Konstanz, Germany) are gratefully acknowledged for the generous donation of the resin composite materials used in this study.
Conflict of interest
The authors declare that they have no conflict of interest.
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