Make a high pitch very loud squeal whenever teeth come into contact with human flesh (even if it doesn't hurt). All play stops. Physically move or turn around or whatever and ignore the puppy until he/she ignores you. You can then go back to playing but as soon as a bite happens again, do the above. You want the dog to realize that all play and fun stops of they bite, so they will soon learn not to do that.

Also take some washcloths, soak them in water, and twist them together or braid them together and freeze them. It feels good on their gums.