Hardening of GI-Based Restoratives with LED curing

Objective: To evaluate degree of hardening of GI-based restorative materials using two second-generation LED and one QTH light curing units (LCUs). Methods: Four restorative materials: Z-250 (composite, 3M-ESPE), Beautifil (giomer, Shofu), Dyract-AP (poly-acid-modified composite, Dentsply) and Fuji-II-LC (RMGI, GC Corp) with shade A3.5 were tested. Three LCUs: Astralis 3 (QTH, Ivoclar-vivadent), Blue phase (LED, Ivoclar-Vivadent) and Radii (LED, SDI) were used. Fifteen disc specimens 3.5 mm in diameter and 2 mm thick were prepared using specially-constructed moulds from each material. Specimens were irradiated from top surface only to a similar energy density equivalent to 14 J/CM. Microhardness measurements were then performed using a Vickers indenter. For each specimen three indentations were made for top surface and three for bottom following 15 min of dark storage. Measurements were repeated at 24h and 7days of dark storage. Mean VHNs and SD of top and bottom surfaces of all specimens were calculated. Relative hardness numbers (RH), that is mean hardness of bottom surfaces divided by mean hardness of top surfaces, were also calculated for each test group. Data were statistically-analyzed with MANOVA. Results: At 15 min Z-250 had VHNs that were 50% higher than those of the other restoratives. Top surfaces of Z-250, Beautifil and Dyract-AP were significantly harder than bottom (P<0.05) with all LCUs and at all time intervals. However, for Fuji II LC, mean VHNs of bottom surfaces were significantly higher than those of top (P<0.05). Blue phase LCU was the only LCU that resulted in RH values above the critical 80% level with all tested materials at all time intervals. At 7-days Fuji-II-LC was the only GI-based restorative that exceeded the 80% RH with all LCUs. Conclusions: One LED LCU (Blue phase) resulted in RH values which were consistently within the desired level of 80% + with all tested restoratives.