In vitro evaluation of the microhardness of conventional and bulk-fill resins based on the depth of light-curing and the curing unit.

Abstract

Background: To evaluate the microhardness of conventional and bulk-fill composite resins based on the depth of light-curing (2 mm and 4 mm) and the curing unit used (VALO Grand and BluePhase N G4 lamp).

Material and methods: Discs were fabricated using two bulk-fill resins: Beautifil Bulk (BB) and Filtek Bulk Fill (ZB); and two conventional resins: Beautiful II (BC) and Filtek Z350 XT (ZC). For the preparation, the light-curing depth was set at 2 and 4 mm, and the curing units used were VALO Grand and BluePhase N G4. Microhardness was measured using the Vickers test on light-cured samples under standardized conditions. Statistical analysis was performed using ANOVA and the Tukey test (p < 0.05).

Results: Significant differences were found between the groups, with the BB 4mm Valo group exhibiting the lowest microhardness values and significant differences compared to the others. Meanwhile, the 4 mm Bluephase ZC resin exhibited the highest microhardness values compared to the bulk-fill resin. At a thickness of 2 mm, the conventional resins showed similar values regardless of the polymerization source, except for BB, which performed better with the Valo unit. In addition, Valo demonstrated good performance with ZC at both thicknesses and results comparable to Beautifil II at 2 mm. Bluephase showed consistent values across all groups and depths, with superior performance when applied over ZC.

Conclusions: The results showed that the final microhardness of the restorative material is influenced by a combination of resin type, depth, and light-curing unit; the conventional composite resin that exhibited the highest microhardness values was ZC, light-cured using a Bluephase light source at a thickness of 4 mm, compared to the bulk-fill resin.