Curing Depth of a New Fiber-reinforced Flowable Composite.

Objectives: Although the use of classical crowns supported by posts remains widespread in dentistry, their invasiveness has been largely criticized. As an alternative, conservative approach of using short fibre-reinforced composites (SFRCs) as post-core foundations have been proposed. However, the question whether the light-cured SFRC composite could have an adequate curing depth. The aim of this study was to analyze the depth of cure of a new SFRC flowable composite (everX Flow, GC Corporation) assessed by surface microhardness (VH) and degree of conversion (DC%) through different thicknesses. In addition, the curing depth was also measured under more clinically relevant conditions, inside prepared root canals.
Methods: Cylindrical test specimens (Ø5 mm) were produced from both everX Flow and the conventional bulk-fill flowable composite (SDR⁺, Dentsply-Sirona). For each material, five different incremental thicknesses (3, 4, 5, 6 and 7 mm) were considered (n=4). The specimens were prepared in Teflon molds that are open at the top and bottom sides and cured for 10 s by applying the curing unit (D-Light Pro, GC Corporation) on the specimens’ top surface. Root canals of human teeth were prepared, materials were applied and polymerized (40 s) into the canals in bulk (n=3). After that, the specimens were ground with a silicon carbide paper with a grit size of 2000 and 4000, and then stored dry at room-temperature for 24 h. DC% was determined by FTIR-spectrometry and a Vickers indenter was used for testing VH. Statistical analysis was carried using ANOVA (p<0.05) followed by Tukey post hoc test.
Results: everX Flow composite presented higher DC% and VH compared to SDR⁺ composite (ANOVA, p<0.05) at different thicknesses. SDR⁺ presented drastic decrease of VH values after 4 mm depth inside root canal, while for everX Flow this was beyond 8 mm.
Conclusions: Flowable SFRC composite (everX Flow) revealed extended depth of cure at simulated root canal which indicates its potential use as post/core treatment.