Surface microhardness of nanohybrid and microhybrid composite resins light cured at different distances

Objective: This study aimed to compare the surface microhardness of a nanohybrid and a microhybrid resin composite light-cured at two different distances.Methods: A total of ۴۰ disc specimens were prepared for this in vitro experiment; ۲۰ from a nanohybrid composite resin (Filtek P۶۰; ۳M ESPE) and ۲۰ from a microhybrid composite resin (Filtek Z۲۵۰; ۳M ESPE). Each group was divided into two equal subgroups (n=۱۰), based on the distance between the light-curing device and the composite surface (either ۲ or ۴ mm). After ۲۴ hours of curing, the teeth underwent the microhardness test to determine the Vickers hardness number (VHN) at the surface. The data were subjected to statistical analysis using a two-way analysis of variance (ANOVA) at the significance level of P<۰.۰۵.Results: The nanohybrid resin composite showed higher microhardness values than the microhybrid resin at both ۲ mm and ۴ mm distances, although the difference between the two groups was only significant at the distance of ۴ mm (P = ۰.۰۱۷). No significant difference was observed in the nanohybrid composite resin between the two curing distances (P = ۰.۱۵۱). However, the hardness of the microhybrid composite decreased significantly with increasing the curing distance from ۲ to ۴ mm (P = ۰.۰۱۵).Conclusions: This study reveals that light-curing distance significantly affects the microhardness of microhybrid composite resin. The nanohybrid composite showed comparable hardness up to the distance of ۴ mm, indicating its suitability to be used in situations where a close curing distance cannot be achieved.

Keywords:

Composite resins , Curing lights , Hardness test , Microhybrid composite , Nanohybrid composite , Restorative treatment