This is a great use for Interface, which is Apex Dental Material's "super silane". "White Lines" are a problem with all composites except ones with very low shrinkage (Exquisite). They're caused when we cure composites too fast. Composites come as a paste and the molecules have single bonds between them. "Curing" changes the single bonds to double bonds to harden the paste. Double bonds are shorter than single bonds, so the paste shrinks as it hardens. The amount of shrinkage is built in to the material. We can't control that. But we can control the rate of shrinkage. If it shrinks really fast, our bonding systems are strong enough that they will pull the enamel crystals apart at the margin, creating the "white lines". We can slow down the rate of shrinkage by adding small amounts of light (the photo initiator is camphorquinone in the composite paste) over time, aka "pulse curing".
In this technique we are placing Interface on the "white line", letting it dwell for 10 seconds, then drying, adding a couple of coats of Surpass 2, drying that and adding Surpass 3 and curing that for 10 seconds. Watch the "white line" disappear.
The procedure is let Interface dwell for 10 secs, then dry it and add 2 coats of Surpass 2, dry that, add Surpass 3 and cure for 10 secs. This techniques cures white lines both on new restortions and on older ones.
Now if you want to avoid all this, get some Exquisite. It's a very low shrinkage, low stress composite. We have been bulk filling Exquisite up to 4 mm's and curing with our Valo light set on "XTRA POWER", which is 3200 mW/cm2, for 3 seconds. Regular power is 1000 mW/cm2. We're seeing absolutely zero "white lines" with this technique. After finishing/polishing we re-cure for 3 more seconds. There's more info about that technique here.