Surface roughness and microhardness of bulk-fill and low-stress restorative composites

Objectives: The aim of this in vitro study was to compare the surface roughness and microhardness of bulk-fill and low-stress nano-filled and nano-hybrid restorative composites with a conventional microhybrid composite.
Methods: Two nanohybrid bulk-fill composites; Sonic Fill (Kerr; SF), Tetric N-Ceram Bulk-Fill (Ivoclar/Vivadent; TB), one nano-filled bulk-fill composite; Filtek Bulk Fill (3MESPE; FB), two low-stress nanohybrid composites; Kalore (GC; K) and Charisma Diamond (Hereaus; CD) and a reference conventional microhybrid composite (Filtek Z250; Z250) were tested. A total of 100 composite discs, 20 from each material (6x4 mm), were prepared using teflon molds and then polymerized with a LED curing unit (Demi Ultra, Kerr) according to the manufacturer's instructions. Following storage in distilled water for 24 hours at 37^°C, the specimens in each composite group were randomly divided into two groups (n=10) according to the tested parameters. Surface microhardness (HV) of the specimens was determined using a digital microhardness tester (Buehler) while surface roughness (Ra) was evaluated after wet polishing of the specimens with the two step polishing system Enhance/POGO (Dentsply) with a profilometer (Perthometer M1 Mahr). Data were statistically analyzed with one way ANOVA and post hoc Tukey’s tests (p<0.05).
Results: Different superscript letters in each row indicate significant differences at (p<0.05).
Conclusions: Conventional microhybrid composite created smoother surfaces than the nano-filled and nano-hybrid bulk-fill and low-stress composites. Within the class of bulk-fill and low-stress composites microhardness showed large differences which were similar or lower than the microhybrid composite.