I think they work. The amber has natural properties that are absorbed through the skin.
I stopped putting Harry's on him, and after a while (when his teeth started moving again) he was really bad. He used to be an awesome sleeper, and started suddenly screaming and standing up in his cot and not going to sleep. I put it back on him, and that night he went to sleep as usual!
Had a quick search and here's some good threads...
Teething necklaces
Teething necklaces???
Best amber teething necklace
Edited by arohanui