Relative hardness of composite restoratives polymerized with high-intensity LED lights

Objective: Relative hardness (RH) is considered a reliable indirect measure for degree of monomer conversion of resin composites. The aim of this study was to determine RH of composite restoratives polymerized with 2 new high-intensity LED-lights. Methods: Disc specimens 2 mm thick and 4 mm diameter were prepared from 3 composites; Z-100 (3M/ESPE), Filtek-LS (LS) (3M/ESPE), TPH (Dentsply). Specimens were polymerized for 20s and 40s using conventional LED light (DEMI, Kerr - 900-1000 MW/cm2); 5s and 10s using high-intensity LED light (Mini-LED Super-Charged, Acteon - 2,200 MW/cm2); and 7s using another high-intensity LED light (Mini-LED Auto Focus, Acteon - 2,200 Mw/cm2). Light was applied only at upper surfaces. Specimens were stored in dark in incubator at 37°C for 24h. Microhardness measurements were then made on upper and lower surfaces of each specimen. A hardness tester with Knoop indenter and 50g load was used. Four indentations were made on upper surface and corresponding four were made on lower surface of each specimen. RH ratios, means and standard deviations (SDs) were calculated and data statistically-analyzed with ANOVA and Tukey's tests. Results: Means and SDs of RH ratios for 20s DEMI polymerization cycle were: .85(.04), .78(.04) and .69(.02) for Z-100, TPH and LS, respectively. For 40s DEMI polymerization cycle RH ratios were: .89(.02), .82(.02) and .80(.03) for Z-100, TPH and LS, respectively. When Mini-LED Super-Charged was used for 5s ratio were: .84(.02), .76(.02) and .69(.04) for Z-100, TPH and LS, respectively; while for 10s cycle ratios were: .91(.03), .81(.01) and .78(.03) for Z-100, TPH and LS, respectively. For 7s Mini-LED Auto Focus RH ratios were: .84(.02), .77(.03) and .75(.02) for Z-100, TPH and LS, respectively. ANOVA revealed significant differences among the means (p<.05). Conclusions: One high-intensity LED light resulted in reducing polymerization time by 50% for RH ratio above 80%. Acknowledgements: Acteon, 3M/ESPE.