Shortest exposure time possible with LED curing lights

To investigate the shortest exposure time of different light emitting diode (LED)-curing devices for different resin composites in a clinically relevant laboratory model.

Nine LED curing devices (Bluephase, Bluephase 16i, Bluephase G2, Bluephase 20i/Ivoclar Vivadent, DEMI/sds Kerr, Elipar FreeLight 2, Elipar S10/3M ESPE, Radii plus/SDI, mini LED Autofocus/Satelec) were investigated to polymerize Tetric EvoCeram (TEC) and Filtek Supreme XT B (FS) in the shades A1, A2, A3, A3.5, and A4. The Bluephase 20i was investigated in its high power and turbo modes. Stainless steel molds (Ø = 5 mm, h = 6 mm, six resin composite test samples per curing device, material, and shade) were filled in three increments of 2 mm thickness each and incrementally exposed with the light guide tip in a 7 mm distance from the bottom side to simulate a Class II curing situation. Surface hardness was measured 10 minutes post exposure at bottom surfaces of resin samples (n=3 per sample). A bottom/top-surface hardness ratio of 80% of a reference surface hardness cured at a zero-distance (40 seconds) was defined as clinically acceptable for safe curing. A statistical analysis (Excel) was carried out.

To ensure a ratio in surface hardness of at least 80% the minimal exposure time(s) were: Elipar FreeLight 2, DEMI: TEC and FS: 10 seconds for all shades, except DEMI FS A4: 20 seconds. Elipar S10: 10 seconds for both, TEC and FS shades A2-A4 but 5 seconds for shades A1. Bluephase, Bluephase 16i and Bluephase G2: FS: 10 seconds for shades A1-A3.5; 20 seconds for shade A4. TEC: Bluephase: A1-A3.5: 10 seconds, A4: 20 seconds. Bluephase 16i: A1-A3: 10 seconds; A3.5 + A4: 30 seconds. Bluephase G2: A1-A3: 10 seconds; A3.5 + A4: 20 seconds. Bluephase 20i-HIP: 10 seconds for all shades of TEC and FS, Bluephase 20i-Turbo: 10 seconds for all shades of TEC but 5 seconds for all shades of FS: Radii plus: TEC A1-A3: 10 seconds; A3.5+A4: 20 seconds. FS A1, A2 and A4: 10 seconds; A3+A3.5: 20 seconds. Mini LED Autofocus: TEC A1, A3, A3.5: 10 seconds; A2: 15 seconds; A4: 20 seconds. FS A1: 5 seconds; A2-A4: 10 seconds. In its turbo mode with a 5-second exposure time, the Bluephase 20i was able to polymerize all shades of FS, but not of TEC. For the Elipar S10 and the Mini LED Autofocus this was also possible for the A1 shade of FS; for Elipar S10 additionally for TEC. The higher power of the Bluephase G2 and the S10 LED allowed the use of an enhanced light guide tip diameter while the exposure time was not affected compared to their predecessors equipped with an 7.5 or 8 mm light guide tip diameter respectively. Nevertheless, 10 seconds should be the minimal exposure time recommended for lighter shades under optimal circumstances.