I'm afraid I can't help with a topic idea, however I would like to ask:
What other AS courses are you taking? If you are only taking two other courses, then please reconsider EPQ. This is as most uni's will NOT accept it on it's own, or even in combination with other A-levels. This means it will look 'nice' sure. But will it benefit you?
If taken as a 4th or 5th AS then fair enough. But again, if you are looking at doing dentistry at Degree level, bear in mind how incredibly high the entrance grades are. If this would take valuable time from you, that would be better spent on your other subjects, to get the grades needed, then don't take this project. The number of people taking this course is decreasing each year, as uni's are not interested in it.
If you are 100% confident you can get 3 very strong grades in 3 relevant A-levels, and do this, then good luck and I hope you find a subject you are interested in to write the essay on ^^