Introduction

Resin composites offer aesthetic and adhesive advantages, but polymerization efficiency can be affected by tip distance and photoinitiator compatibility. This study evaluated the effect of increasing curing distances of a polywave light curing unit (LCU) on microhardness of bulk-fill composites with different photoinitiator systems. This in vitro study aimed to evaluate and compare the sorption and solubility of a contemporary light-cured resin luting cement with those of resin-modified glass ionomer and self-adhesive resin luting cements, when immersed in distilled water and artificial saliva.

Material and methods

Standardized cylindrical specimens (4 mm thick × 4 mm in diameter) were prepared and light-polymerized using a polywave LCU at 0 mm, 2 mm, 4 mm, and 6 mm distances. Samples (n = 80) were divided randomly into two equal groups (n = 40 per group), depending on the type of photoinitiator present in the composite: camphoroquinone (CQ)-containing composite, SDR Plus Bulk Fill Flowable (n = 40), and composite containing a combination of CQ and Ivocerin, i.e., Tetric N-Ceram (n = 40). Vickers microhardness (VHN) was measured on top and bottom surfaces after 24 hours of dark storage. Data were analyzed using ANOVA and independent t-test (p < 0.05).

Results

Tetric N-Ceram showed significantly higher microhardness values than SDR at all distances. Increasing tip distance led to a reduction in VHN for both materials, more markedly in SDR. The difference in microhardness between top and bottom surfaces was non-significant for Tetric N-Ceram at all distances tested. However, for SDR, the difference in microhardness between top and bottom surface was significant at tip distances of 4 mm and 6 mm.

Conclusions

Curing tip distance negatively affects microhardness in bulk-fill composites. Tetric N-Ceram outperformed SDR when cured with polywave LCU.