Influence of irradiation time on subsurface degree of conversion and microhardness of high-viscosity bulk-fill resin composites

Abstract

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.

Microhardness of Bulk-Fill Composite Materials

“…Namely, in the present study, the samples were grounded and polished, while in the previous study, the hemi-cylindrical molds were used without polishing and hardness testing was performed at the specimen outer resin-rich layer. Th is likely contributed to the lower microhardness values in the previous study 23 . Diff erent composite characteristics are aff ected by fi ller properties such as size, volume and weight.…”

“…Greater variations were not observed in the values on the surface and at 2 or 4 mm. In our previous study 23 , which investigated Knoop microhardness of high-viscosity bulk-fi ll materials, only 30-s irradiation with a similar light intensity was suffi cient to achieve 80% of maximum microhardness at 4-mm depth for QF and XTF, but not for TECBF. Th is diff erence could be explained by diff erent methodologies used.…”

Water sorption and solubility of bulk-fill composites polymerized with a third generation LED LCU

“…Regular bulk-fills do not need an additional capping layer and can be used as a singlestep filling material. 5,8 With the spread of photopolymerizable dental composites, significant advances have been made in light curing units (LCUs) used in polymerization processes. Recently, the incorporation of different photoinitiators has led to the development of third generation polywave LED LCUs.…”

Comparing depth-dependent curing radiant exposure and time of curing of regular and flow bulk-fill composites

“…Also, some studies used over or under exposure time. 3,6,13,14,15 According to Tarle et al, 16 minimum curing times recommended by the manufacturers is not adequate for placement of high-viscosity bulk-fill materials.…”