We wrote a blog about this on our website a few weeks ago and have lots of different toys on our site that may help.
Teething Puppies – Gizmo's Dog Shop
We have a mutt Cici who started grinding with her back teeth when she was getting them and we lost a lot of pillows, blankents, shoes and clothes because she would grind off whole chunks. The rope toys really help especially if they want to grind. as long as you train them that one is okay and the other isn't you should be fine.