For Dentistry, Unis will not 'have spaces left' to fill via Clearing.
In order to avoid having to organise and reassemble the whole complicated MMI entourage in the middle of Clearing, if they have any spaces they may accept a few 'near-miss' Firm applicants and/or use applicants from a waiting list - those they interviewed earlier in the year but who just missed the necessary interview score for an offer at that Uni and crucially, are not now holding another Dentistry offer anywhere else. These people will have already been told they are on a waiting list and may get a phone call on Results Day.
You can, of course, check websites on Results Day and even phone Unis if you want to - but the response will be a big fat No.