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 2 mm 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 manufacturerʹs 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 (2 mm thickness, 40 s), 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 (10–20 s). 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 10 s exposure time for all materials except Ceram X Mono (20 s). Significance When incrementally exposed, all resin composites investigated were polymerized sufficiently at a maximum of 20 s exposure time.