They are suppose to be better because they are in your ear and they block out outside noise so well. Because of that you don't have to cut them up as loud. So they are better in that perpective because instead of having them at 100db (just an example number) you only have it at 50db. The closeness to your ear doesn't matter. What matters is how much db you are directing at your ear drum.
As for the sound getting stuck and vibrating back in forth against your ear drum, I can't say anything for sure on that. However it doesn't make sense to me. Sound is vibration. If the same vibrations were echoing in your ear you'd hear that. You'd hear the music echoing. Don't take my word on it. I'm no ear doctor. That just seems a little odd to me.
http://www.headwize.com/articles/hearing_art.htm
Some things on hearing loss related to head phones.
All I can tell you is that in ear canal phones are concidered safer that all other headphones. Mostly because the noise blocking. If you keep them at low levels (as you should with any head phones) they'll benifit you.
Ive read many differing opinions on canal earphones, such as the sony fontopia and the shure brand of earphones. I know not everyone likes them, and feel that they are uncomfortable, but I for one enjoy wearing them, and find them great.
The question I have is whehter or not canal earphones are actually much more likely to damage my ears because of the way they block your ear, or the proximity of the earphone. I have heard that because its closer to your ear, that may cause a problem. I have also heard that because it completely blocks the canal, the sound vibrations just bounce back and forth against your ear drums.
On the other hand, I have read that because they block out background noise so well, better than noise cancellation devices, most users dont even need to turn them up as loud to block out other noise, and hence are much better.
I am unclear as to whether or not the above mentioned problems are actually real, and should be a concern.
Any studies or facts that can be shown, or some sort of opinion would be greatly appreciated, thanks 
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