You know, I'm looking at that shot from the trailer of the Joker surrounded by knives and guns, and some of you are right. He really doesn't seem to have the grillz in that scene. Not only are they not darker and metallic, but they don't appear as large either. It almost looks like Leto's natural smile.
But then again it's a far-away shot, and even the best quality close ups are blurry enough to play tricks on the eyes, so I could be completely wrong.
It would be cool to see an evolution in the character's look.