How do you fix a dent in a CD?

A retail scratch removed is an option that will buff the disc with a bit of water. Another option is to take Turtle Wax and buff the disc (using a piece of felt) surface to try and fill the scratch. If a scratch is deep enough it will damage the data layer of the disc and will likely not be recoverable. Also note that scratches on the TOP of the CD are more damaging then the bottom. There is a thicker protective layer on the bottom of the disc then on the top.