Problem statement In restorative dentistry high degree of polymerization has great influence on the quality of luting cement. In dual cured composite resin luting materials the light activation is a key factor for a good degree of conversion of the monomers. This raises the question, how effective the latest generation of curing units can polymerize at shorter light activation and how effective they are at various thicknesses of the ceramic.
Objective The aim of the study was to investigate whether a significant difference in regard to the conversion rate of link Variolink®II after light curing through ceramic discs with different thicknesses and with different curing lights of the latest generation exist. Furthermore, it was analysed whether a significant difference occurs in the degree of conversion of Variolink®II after 20 s and 40 s light curing, respectively. In addition, the temperature produced by the curing devices was measured and statistically analysed.
Materials and Methods The residual monomer content of Variolink®II was determined by FTIR spectroscopy before and after polymerization through Vitabloc® Mark II ceramic discs of 2 mm, 3 mm and 4 mm thickness. The photopolymerization was carried out by the high-power LED curing lights Bluephase® 20i and FreeLight®2, the high-intensity QTH curing light Optilux®501 and the QTH curing light CuringLight XL 3000, for 20 s and 40 s, respectively. In 24 Groups, 16 samples each were measured at constant 37 degrees Celsius. Results When light cured for 20 seconds, Bluephase® 20i was able to sufficiently polymerize Variolink®II at 2 and 3 mm thickness, Freelight® 2 und Optilux®501 sufficiently polymerized at 2 mm. Below 4 mm thickness and 20 and 40 seconds light activation Optilux® 501 polymerized significantly lower than the other curing lights. 50% shorter polymerization time had a significant influence on the conversion at all ceramic thicknesses for almost all curing lights. The curing light Bluephase®20i achieved the highest degrees of conversion at all ceramic thick-nesses and curing times; however this was also accompanied with the highest increase in temperature.