Yes, it definitely hurts you having an active FB in the short term applying to dental schools. In case you've been living under the rock politically for 10 years, academic institutions and faculty are heavily, heavily liberal on social and fiscal ideas - and issues have become so emotionally charged in this country that people make large assumptions about your character, and your "fit" for being a dental professional, based on statements or beliefs that may have differed from their's. Answer yourself this: after all these years of hard work, is that undeserved judgment worth being viewed in a negative light? Is an attack on your character or qualifications as a dentist worth that extra status post on your belief system or that argument you had with friends online? Just remember that you don't have autonomy in your outward beliefs when it comes to an admissions committee - they are looking for you to say what they want to hear with respect to what they believe is "proper" for dentistry. Don't be naive.
I would heavily advise against you posting any statuses or thoughts on political or social issues during your cycle *especially* if they're against the grain. We live in a hyper-emotional, PC culture that hypocritically judges you if you don't believe what media or "progressivism" spits back at you, that it's not even worth posting anything at all.
If you must have a FB to connect, I would make sure during your cycle to have deleted all statuses, link shares, or pictures that are incriminating to you. In fact, I would delete all newsfeed-based grinds on your timeline and keep the FB as shortly professional as possible. The less others in position of decision-making and pre-judgment have access to you, the better off you'll be in this process.
Please, please, please trust me when I say that adcoms are looking for any reason to deny applicants these days, especially students who fall into majority subsets - there are so many more applications that they have to find ways to draw lines in the sand somewhere. Facebook, Twitter, and Instagram are so much more destructive in this modern day for people involved in evaluations for jobs and admissions that it's pointless to be active on it.