Polymerisation Kinetics of Simplified Universal Bulk-Fill Composite

Objectives: This study investigated the real-time polymerisation properties of a novel, simplified universal bulk-fill composite containing reversible addition-fragmentation chain transfer (RAFT).
Methods: Five bulk-fill composites were tested: new universal composites Tetric Plus (T+; Ivoclar) and Tetric Plus Flow (T+flow; Ivoclar); predecessors Tetric PowerFill (PFill; Ivoclar) and Tetric PowerFlow (PFlow; Ivoclar) and Ecosite Bulk Fill (DMG) as a control without RAFT. The specimens were 0.1- or 4-mm thick and were polymerised with Bluephase PowerCure for 3s (3047 mW/cm²), 10s (1187 mW/cm²) or 20s (1203 mW/cm²). Uncured specimens (n=6) were placed over the Fourier transform infrared spectrometer with attenuated total reflectance and light cured. The spectra were recorded during and after light curing for the first 5 minutes. The degree of conversion (DC_5min), maximum reaction rate (R_max), time to reach R_max (t_max) and kinetic parameters a, b, c and d were calculated. The results were analysed using one-way ANOVA and Tukey post-hoc test (p<0.001).
Results: At 0.1 mm, the highest DC showed PFlow (68.50±0.20%) and Ecosite (69.99±3.02%) for 20s polymerisation, followed by T+Flow, T+ and PFill. At 4-mm depth, the following DC_5min order was identified: PFlow>T+Flow>T+>PFill>Ecosite. Ecosite had the lowest DC_5min (40.71±1.45%) for 3s at 4-mm. The DC_5min and R_max at 4-mm were significantly lower than at 0.1-mm for all materials and polymerisation protocols tested. 3s polymerisation accelerated the R_max of all materials at both depths, but had no effect on t_max, except for Ecosite at 4-mm. T+ and T+Flow had higher “a” and lower “c” parameters for 3s polymerisation than PFill and PFlow, respectively. For all materials tested, except for the control Ecosite with 3s and 10s polymerisation, the DC_5min ratio 4-mm/0.1-mm was above 80%.
Conclusions: New simplified universal composite T+ has a higher DC_5min and improved polymerisation kinetics than its predecessor PFill. 3s curing is not recommended for materials without RAFT agents.
This work was supported by the Croatian Science Foundation under the project number HRZZ-IP-2024-05-2884.