hi negar,
i agree with stanford fencer...i think that when compared to GPA/DAT and your dental experience, extracurriculars and leadership fall lower on the totem pole. during my interview at ucla, my interviewers spent most of the time talking about my experiences in the dental office--have some specific examples of what you liked, what inspired you, what goes on in the dental environment that you have exposed yourself to. be prepared to talk about what you wrote in your personal statement, being that they did refer to it during the interview. it has already been said so many times that it might sound like a cliche, but i cannot stress how true it is--just be sincere and honest...treat the interview as a chance for them to get a real idea of what your personality is like and a chance for you to get a feel of how you would like going to that school.
since you have not yet taken your DAT's...just focus on that...study hard, do well and you'll see that your hard work will not go wasted. if you have limited time, it's more worthwhile to spend it studying for the DAT than to find a leadership position at this time. that's just my 2 cents...good luck!
-wasabi007