surface stain you can remove by normal brushing....baking soda helps by acting as a abrasive
the strength of the strips are so weak that it can only bleach the surface stain
if the stain is deep inside the teeth.....go see a dentist
celeron 266MHz (Covington) @ 400MHz - power without L2 cache
i just went to the dentist yesterday... they said crest whitening strip is the best.. but because of a certain chemical that makes the strips, so if you use it too much it's not good for your teeth