Comparative Evaluation of the Effect of Two Different Ultrafast Curing Exposure Durations on the Surface Hardness of Bulk‑Fill Composite: An In Vitro Study

Abstract

Introduction: Bulk-fill composite resins were introduced to address the shortcomings of conventional composites, including limited depth of cure and polymerization shrinkage. Recently, high‑intensity ultrafast curing protocols have been introduced to reduce clinical chairside time. However, concerns remain regarding their influence on polymerization efficiency and mechanical properties.

Objectives: To evaluate the impact of two ultrafast curing times on the surface hardness of bulk-fill composite resin in comparison with the conventional curing method.

Methods: Thirty standardized specimens of bulk‑fill composite resin were prepared using a custom Teflon mold (10 mm diameter × 2 mm thickness). Samples were randomly divided into three groups (n=10): Group I – ultrafast curing for 1 second, Group II – ultrafast curing for 3 seconds, and Group III – conventional curing for 20 seconds. Specimens were finished, polished, and stored for 24 hours before evaluation. Surface microhardness was assessed using a Vickers microhardness testing device. Statistical analysis was carried out with SPSS software version 21, employing the Kruskal–Wallis test followed by post-hoc pairwise comparisons.

Results: Mean microhardness values were highest in Group III (256.48±8.92 VHN), followed by Group II (105.60±2.69 VHN) and Group I (62.80±1.70 VHN). A statistically significant difference was noted among all the groups (p < 0.001).

Conclusions: Conventional curing demonstrated significantly higher surface hardness compared to ultrafast curing modes. Adequate curing time remains essential for achieving optimal polymerization and mechanical strength of bulk‑fill composite restorations.