A friend of mine has a DVD with a crack "its a crack straight through it, about two centimeters on each side of the middle circle", he says.
I suggested toothpaste, will anything else work?
No it won't.
Any CD/DVD that is that structurally damaged is not suitable to put into your CD/DVD drive. Putting it risks the disk 'exploding' due to the rotation forces.
This in turn could result in your drive being rendered useless as well as your disk.
Toothpaste will supposedly help a scratched disc by buffing out some of the surface scratches.
I think your friend is out of luck in this case...