You should be able to get a replacement. Just when you tell why you want a replacement leave out the scratches. Only tell them about the dust and dead pixels. Apple won't give you a replacement because of scratches. Its not their fault that your phone got scratched but it could be their fault that you have dead pixels and dust under the screen.
I got a replacement phone for a crack in the plastic even though there were scratches all over the back. I'm sure you would recieve a replacement as well.