Well, lets see...
1) Use contractions in your quote, use "I'm" instead of "I am," if you don't use contractions is makes it sound like a robots is talking and the quote doesn't sound real.
2) as someone else said, don't list every specialty, say something like "general dentists and a variety of dental specialists."
3) Your last paragraph sounds like a listing of your EC section, you really don't need to put down everything you've done, maybe just one or two and relate them to why you want to be a dentist. That paragraph just seemed to drag on a bit.
4) Lastly, and I think the most important part, you're not really conveying why you want to be a dentists. You keep bringing up points, and then you talk about them a little bit, and THEN you kind of say how that original point makes you want to be a dentist, but in reading the entire thing, I can't really sum up why you want to be a dentist other than you don't want to do research for the rest of your life. Focus on this, it's what they're really looking for.
Ironically I had a very similar experience with a bike and I did a face plant and landed teeth first, haha.