Methods: Cells were exposed to blue light respecting clinically relevant distance (lamp tip to cells), durations and curing programs :
- for the PAC unit (Flipo®/Lokki) : 9 mm, program 3 (1500 mW/cm²) for 12 s,
- for the LED unit (Bluephase®/Ivoclar-Vivadent) : 9 mm, program LOP (650 mW/cm²) for 20 s and program HIP (1100 mW/cm²) for 60 s. Cell morphology and viability were assessed respectively by means of scanning electron microscopy and MTT assay. Light intensities and thermal emission were also measured using a radiometer (Cure Rite®/Dentsply) and a thermocouple (model K-type/Anritsu).
Results: No differences were observed between cells exposed to the PAC light and those exposed to the LED light concerning cell morphology but cell viability was greater (34%) for HGF exposed to the PAC light. In the experimental conditions (different irradiation durations and curing programs) :
- even if light intensity delivered by the PAC unit was the most important (at 9 mm : 488 mW/cm² vs for LED unit 61 mW/cm² for LOP program and 140 mW/cm² for HIP program), energy transmitted to cells (intensity x duration) was much lower than the one transmitted to cells exposed to LED light (respectively 5.86 J/cm² and 9.62 J/cm²),
- temperature rise was lower using the PAC unit (below 0.5 °C) than using the LED unit (3.5 °C).
Conclusion: A high-intensity emitted for a short time (PAC unit), and thus, a low light energy and a low temperature rise, appeared to be more beneficial to cell viability than a low intensity emitted for a great duration (LED unit).