Minimal exposure time of different LED-curing devices.

Objectives: The purpose of the study was to investigate the shortest possible exposure time of different LED-curing devices for five different resin composites in a clinically relevant in vitro-model, where a 7 mm distance from the light guide tip to the bottom side of the cavity was compiled.

Methods: Resin composite samples (Tetric EvoCeram A3, Filtek Supreme XT A3B, Premise A3, CeramX Mono M5, QuiXfil) were filled in three increments of 2mm thickness each in stainless steel moulds (Ø=5 mm, h=6 mm, n=9). The samples were incrementally exposed to different blue LED-curing devices (Bluephase, Bluephase C8, Bluephase 16i/Ivoclar Vivadent, L.E. Demetron II/sds Kerr, Elipar FreeLight 2/3M ESPE, Smartlite PS/DENTSPLY, Translux Power Blue/Heraeus) according to the manufacturer's recommendations at a distance of 7 mm from the bottom of the cavity to simulate a class II-curing situation. Surface hardness was measured (Zwick Z2.5/TS1S) 10 min post-exposure at the bottom surfaces of the resin sample. A bottom/top-surface hardness ratio of 80% of a reference sample (2mm thickness, 40s), was defined as clinically acceptable for safe curing. A descriptive statistical analysis was carried out.

Results: The curing devices Bluephase, Bluephase C8, Smartlite PS and Translux Power Blue could cure all composite resins investigated sufficiently in the exposure time recommended by the manufacturers (10-20s). The curing device Bluephase 16i and L.E. Demetron II only cured the composite Quixfil sufficiently in the exposure time recommended by the manufacturer. FreeLight 2+ allowed a 10s exposure time for all materials except Ceram X Mono (20s).

Significance: When incrementally exposed, all resin composites investigated were polymerized sufficiently at a maximum of 20s exposure time.