This question is very unclear:
-Are you asking whether its necessary to do research in college in order to be accepted to dental school?
-Are you asking whether you will be able to find a spot in a professor's lab to do research--your concern being that there are too many pre-dents that want to do research?
-Are you asking, statistically, whether there are a lot of pre-dents that do research at universities?
Either way the answer is "it depends"