Penn isn't just into academics and test scores, although those will get your foot into the door. They're looking for people with unique experiences who are ambitious and really value Penn but are also in a way laidback. Not much I can say about research, volunteering, etc. Just as long as you have one or two good ECs, that should be good. Research isn't necessary. I would say shadow a lot of dentists and maybe become more active in a dental office or lab of some sort (but it's not necessary).