I wouldn't sharpen any knife with my teeth. It wold simply wear down the protective enamel too fast.
If your serated knives are so dull as to be ineffective, then by all means, run them accross a sharpening steel first, since it doesn't remove metal. That may be all they need. If they actually need to be sharpened, go ahead and put then against a wet stone, as to have them professionally sharpened would probably cost you more than the knife is worth. They may not be as serrated, but they will be sharper.
Others may disagree with me, but that's my advise.
Seeeeeeya; Chief Longwind of the North