Transparency Transition: A New Option For Bulk Filling Composites

Objectives: Bulk filling composites guarantee a layer thickness of at least 4 mm. To obtain this layer thickness, these composites have a high transparency to secure the curing at the bottom of the filling. Because of the high transparency, the aesthetics of these fillings are limited. A new method to get an aesthetic filling with high curing depth is transparency transition during curing. The uncured composite has a high transparency; during curing the transparency decreases because of change in the refractive index of the monomer matrix. A composite with this new technology (Tetric EvoFlow Bulk Fill) is compared with other flowable bulk filling composites on the market. The change of transmission of light through the composite during curing and the transparency of the composite before and after curing were measured.
Methods: 5 different flowable bulk composites were evaluated: Tetric EvoFlow Bulk Fill TEF (Ivoclar Vivadent), SDR (Dentsply), Venus Bulk Fill (Haraeus Kulzer), X-tra base (Voco), and Filtek Bulk Fill Flowable Restaurative (3M/Espe). To measure the light transmission, the entrance of an Ulbrichts sphere was covered with a cylinder (Ø = 6 mm, h = 4 mm, n = 5) and filled with the composites. The bottom surface was lined with transparent matrix tape. The radiometric signal was recorded during curing of the composites with a Bluephase style (Ivoclar Vivadent) for 10 s or 20 s. For the measurement of the transparency of the uncured composite, a bulb (20x20x1 mm, n=3) was filled; for the cured composite, a disc (Ø = 20 mm, h = 1 mm, n = 3) was polymerized (2x3min Spektramat). Both were measured in the Spectrophotometer Minolta CM-5.
Results: All composites showed a change in transparency and light transmission during polymerization. TEF is the only composite which showed a reduction in transparency and light transmission during curing.
Conclusions: With an optimized selection of filler and monomers, bulk composites with tooth-like transparencies are possible.