What makes them different from regular toothbrushes (even electric powered ones) and do they work as well as they claim? (eg. whiter teeth within 28 days, as well as all the other benefits)
take a look at the site http://www.sonicare.com
for the "how" .I've been using one for eight years now and I get better dental checkups and my teeth feel cleaner also I get less gum disease. Before that, I used a normal electric toothbrush. I haven't noticed a great difference in whiteness, but my teeth are not naturally very white and I don't smoke, drink black coffee or strong tea and only drink red wine occasionally. IMHO they do make it easier to clean teeth properly.
I bought an 'Ultrasonex' toothbrush for my wife for Christmas and she feels that it's a lot more thorough, more powerful and your teeth feel cleaner. Also, they actually do look whiter. She's only used them for a month so I'm a believer - it is definitely revolutionary!