How Deep Can High-Powered LED Curing Lights Cure Bulk-Fill Composites?

Objectives: Traditional light-cure composites must be placed in increments due to light attenuation with increasing depth; however, clinicians today have the option of bulk-fill materials and new high-powered LED lights which claim to cure faster and deeper. This study examines depth-of-cure by measuring hardness through depth of bulk-fill composites when cured with high-powered lights.
Methods: Three bulk-fill composites (Filtek One Bulk Fill, 3M Oral Care; Tetric EvoCeram Bulk Fill and Tetric Powerfill, Ivoclar Vivadent) were tested in combination with standard curing light (Demi Ultra, 1350 mW/cm², Kerr) or two LED curing lights with high power modes (Valo Grand, Xtra Power mode 3117 mW/cm², Ultradent; Bluephase PowerCure, Turbo mode 2435 mW/cm² and 3S mode 3344 mW/cm², Ivoclar Vivadent]). The composites were inserted in a plaster slot-mold (1.5mm wide, 2mm deep, 7mm long), covered with yellow glass, and light-cured from the slot opening using minimum time recommended by manufacturers (3, 5, 6, 10, or 20 sec). Vickers hardness (VHN) was measured after 24 hours in 1-mm increments over a length representing 5mm depth. Sample size was 10 per group. Hardness results were analyzed with one-way ANOVA and Student-Newman-Keuls post hoc test (significance 0.05).
Results: Hardness profiles showed differences in curing characteristics among the composites. Hardness decreased with depth in all bulk composites, with hardness less than 10% at 4mm depth. Filtek One Bulk Fill had the highest surface hardness regardless of the curing light. Filtek One cured by Demi Ultra for 20 sec was the only combination able to maintain a statistically consistent hardness from 0-1 mm.
Conclusions: Under the testing conditions, no combination of light and composite was capable of sufficiently curing bulk-fill composites up to 4mm. The combination Filtek One/Demi Ultra 20 sec and Tetric EvoCeram/Valo Xtra 6 sec provided the best hardness at 4mm.