Yeah, not to worry. Definately with an 18AA and 18PAT (or maybe 1 -2 points lower) will get you in to most private schools. Well reounded individuals and those who can demonstrate their interest in dentistry is very important. Be sure to have hobbies!! Take up some manual ones like ceramics, painting, drawing, mechanics.....they love to see that you have manual dexterity. Also, research the schools before you apply...see what they like. i know Tufts for example is big on volunteering your time, so they would want to see your dedication to the less fortunate.
On a side note: I had research experience as well as TA experience as an undergrad, and worked part time throughout school. Therefore I didn't have that much time to volunteer. When I went to the interview at tufts they asked me about my volunteering....I told them the little i did plus the fact that I really couldn't do that much being that I was working and doing research.
So do well on the DAT, and spice your application up by taking on other activities.
Good luck!