Background:
Monomer to polymer conversion of resin-based composites (RBCs) is initiated by photo-initiators, which are in turn activated by light energy from light-curing units (LCUs). The degree of conversion (DC) partially depends on the compatibility of photo-initiator absorption and LCU emission spectra. White shades of RBCs may contain 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), a photo-initiator which requires energy <420 nm, which may not be provided by some LCUs.
Aim:
To ascertain if DC (%) of a RBC containing TPO (Vit-l-escence (Ultradent Products)) and a non-TPO control material (Herculite XRV Ultra (Kerr Italia)), is influenced by curing with a polywave or monowave light-emitting diode LCU.
Method:
Samples of each material (n=3) were prepared in moulds (5x2 mm), and cured with polywave bluephase®G2 (Ivoclar-Vivadent), polywave Valo (Ultradent Products) or monowave bluephase® (Ivoclar-Vivadent). Top and bottom surface DC of each sample was determined using micro-Raman spectroscopy and mean DC (+/-SD) calculated. Data was analysed in Minitab 16 (Minitab Inc.) at α = 0.05.
Results:
i. Herculite (non-TPO) polymerised with the monowave LCU, resulted in highest DC (65.5%), which was significantly greater than any other RBC/LCU combination (p<0.001).
ii. There was no significant difference in DC of Vit-l-escence polymerised with either monowave or polywave LCUs (p>0.05).
iii. There was no significant difference in DC for top and bottom surfaces of either material irrespective of LCU (p>0.05).
Conclusion(s):
DC of a non-TPO material may be higher with a monowave LCU. DC of a RBC containing TPO does not appear to be influenced by the type of LCU.