Performance of RAFT-based and conventional bulk-fill composites cured with conventional and high irradiance photocuring: a comparative study.

Background: Understanding the impact of advanced photocuring and composite formulations for clinical outcomes and restoration durability. This study evaluated the degree of conversion (DC), polymerization shrinkage strain, and flexural properties (Flexural strength and modulus) of conventional and RAFT-based bulk-fill resin composites cured with conventional and high-irradiance ultra-fast photocuring.

Methods: A total of 80 specimens of a RAFT-based bulk-fill resin composite (Tetric PowerFill, TP, Ivoclar Vivadent AG Bendererstrasse 2 9494 Schann/Liechtenstein) and a conventional bulk-fill composite (Tetric N-Ceram, TN, Ivoclar Vivadent AG 9494 Schaan/Liechtenstein) were cured using two protocols: high irradiance ultra-fast mode (2700 mW/cm² for 3 s) and conventional mode (900 mW/cm² for 20 s). The DC was measured using FTIR Spectroscopy(Thermo-Nicolet 67,000, USA), and the polymerization shrinkage strain was quantified with a polyimide-backed electrical resistance strain gauge using a strain meter (PCD-300A Kyowa-Electronic Instruments Co, LTD, Tokyo, Japan). Flexural strength σ_f (MPa) and modulus E_f (MPa) were assessed using 3-point loading in a universal testing machine (Instron 3365, Norwood, MA, USA, with a maximum load capacity of 5 kN) immediately after curing and after thermal aging (10,000 cycles). Results were analyzed using multi-factorial ANOVA with a significance level set at (p ≤ 0.05).

Results: The DC for TP showed no significant differences between curing modes, with values of 57.82% in fast mode and 55.3% in conventional mode. Similarly, its mechanical properties remained relatively consistent, with σf measuring 121.66 MPa in fast mode and 137.5 MPa in conventional mode, while the Ef was 6078.50 MPa and 6167.26 MPa, respectively. In contrast, TN exhibited a lower DC in fast curing (50.27%) compared to conventional curing (61.5%). However, its mechanical properties remained nearly unchanged, with σf recorded at 135.34 MPa in fast mode and 137.26 MPa in conventional mode, and Ef at 6356.54 MPa and 6857.2 MPa, respectively. Moreover, TP showed greater resistance to mechanical property degradation after thermal aging compared to TN.

Conclusions: The RAFT-based bulk-fill composite performed comparably to the conventional composite in both curing modes while demonstrating greater durability. However, fast curing of the conventional bulk-fill composite resulted in unacceptable properties, underscoring the importance of selecting appropriate materials and curing protocols to ensure long-lasting restorations.