My mother is a dental hygientist and says that reguardless of the age, thumb sucking causes teeth to buck forward, as do unorthadontic pacifiers. The shape of the noonie, or thumb, causes the "pallet", not the teeth themselves, to deform.
I mean, some people are cool with it, and some are strict. I am a strict one, only because i've seen horrible effects from it in the medical books. I mean it's baad.
Sucking can also cause a speech impediment for toddlers. Or cause them to speak less due to an object obstructing their mouth.
Now, to the moms who didn't use a noonie, kudos!!! Lol. My friend did that and her daughter doesn't suck a thumb or a doll. I couldn't imagine the sleepless nights because a baby just wanted to suck.
A noonie you can throw away after x amount of time. A thumb is on their hands *forever*!!!!!! There's no way you're going to be able to stop a baby from sucking a thumb as easily as a noonie. No way. It's their comforting tool.
Sarah