What I have done in D-School was kept a list of patients that can show on very short notice. I have fit in many denture patients this way. The thing with dental school patient is that many of them are always avalible. If you suspect a patient is not going to show, call them half hour before appointment, if they cancel, go to short list and call in the quick fills. If they both show, do them both. Another thing is DONT DO ANYONE FAVORS. If they no show follow your school policy and boot them ASAP. Even if they do have endo or fix, boot them. You will never get your requirements by letting people walk over you.
I have recently change my policy. For now on, after the 1st broken appointment, patient will have to prepay for next vist up to $150. If the no show I keep the money as a appointment reservation fee.