Universal Bulk-Fill Composites: An Investigation into the Efficiency of Rapid Curing with Reversible Addition–Fragmentation-Chain Transfer (RAFT)-Mediated Polymerisation

Novel universal bulk-fill composites with reversible addition-fragmentation chain-transfer (RAFT)-modulated polymerization continue the trend towards increasing simplification of the restoration process to facilitate the reconstruction of deep posterior restorations in 4 mm increments as well as anterior restorations through improved aesthetics. This study aims to assess the suitability of such materials for rapid curing (3 s) with high-radiant emittance in terms of degree of conversion (DC) and polymerization kinetics at relevant depths (2 mm vs. 4 mm). For this purpose, two newly introduced bulk-fill universal composites (Tetric^® plus Flow and Tetric^® plus Fill) were compared with already established fast-curing composites (Tetric^® Power Flow and Tetric^® Power Fill). DC was measured in real time over 300 s using ATR-FTIR spectroscopy. The temporal DC evolution was modelled using an exponential sum function. Novel bulk-fill composites showed DC results that were independent of the measured sample depth or curing mode. The polymerization kinetics of all composites are somewhat slower in the gel phase at moderate irradiance or when measured at deeper layers, but compensate for the differences in the glass phase, finally reaching equivalent DC values by the end of the 300-s observation period. These novel composites are therefore suitable for rapid curing (3 s) at high irradiance.