Effect of 5 wt.% Nanohydroxyapatite Reinforcement on the Surface Microhardness of Nanohybrid and Microhybrid Resin Composites: An in vitro comparative Study

Abstract

Introduction: Advancements in restorative dentistry have increased the use of microhybrid and nanohybrid composites due to their strength and esthetics. The addition of nanohydroxyapatite (nHA) shows potential to further improve mechanical properties and bioactivity. Microhardness, which reflects resistance to wear, is crucial for restoration longevity; however, limited evidence exists comparing the effect of nHA on microhybrid and nanohybrid composites.

Objectives To evaluate and compare the surface microhardness of nanohybrid and microhybrid resin composites, both unmodified and modified with 5 wt% nanohydroxyapatite.

Methods: An in vitro experimental study was conducted on 20 samples, divided into four groups (n = 5): unmodified nanohybrid composite, nanohybrid composite modified with 5 wt% nHA, unmodified microhybrid composite, and microhybrid composite modified with 5 wt% nHA. Specimens were prepared using standardized Teflon molds and polymerized using a light-curing unit. Modified composites were obtained by incorporating 5 wt% nHA through a combination of manual and mechanical mixing. Following storage at 37°C for 24 hours, surface microhardness was assessed using a Vickers hardness tester. Statistical analysis was performed using one-way ANOVA followed by Tukey’s post hoc test (α = 0.05).

Results: A statistically significant difference in Vickers hardness was observed among the groups (p < 0.001), with nanohybrid composites demonstrating higher hardness values compared to microhybrid composites. The incorporation of 5 wt% nHA did not result in a statistically significant change in microhardness within the same composite category.

Conclusions: Nanohybrid composites exhibited superior surface microhardness compared to microhybrid composites. The type of composite material had a greater influence on hardness than the addition of nanohydroxyapatite.