Research, Clubs, Leadership at School/ student Gov't, tutoring other students. Dental seminars, or continuing education type opportunities? Service learning? IDK just ideas
Most major cities have these programs. I am in one now and they are both clinical and investigative research. Its not dental but its medical and people love it regardless. Plus it gives you something to talk about why you don't want to be a MD.
Any type of school club will be good, especially if you can get some leadership experience. Find a charity or two that you like and volunteer for them. Participate in some type of sports or musical events. Having a job is a good EC. Research positions, internships, or TA positions would also be nice. Learning another language = FTW. Just find what you like and stick with 3 or 4 things, no need to accomplish it all!
A good app is well rounded in volunteering, shadowing hours, club participation, and other activities.