Dundee don’t look at GCSEs so if you are predicted AAA at the end of year 12 and have a good UKCAT score you can apply there.
Manchester want 6 As/7s at GCSE to include science and they are not lenient in this matter.
Cardiff also want As for science at GCSEs.
Unfortunately resits are not looked at for Dentistry.
May I recommend you take the UKCAT in the summer, if you do well you can apply for gateway at Dundee and possibly some foundation years for medicine. If not, Dentistry is not the only profession out there, there is also Dental hygiene and therapy and dental technician along with dental nursing. Also, if you have the funds available you can do Dentistry in Europe ( Bulgaria. Hungary or Romania) - However you can’t get student loans for this at they would take over 7 years as you have to do a years work in their country and then do a years conversion course.
Another good if you are very passionate about Dentistry is to do a Dental hygiene or nurse undergraduate and then do a Dental Postgraduate after the degree( this is 8 years though!!!)
Please let me know what you think about the given choices... there are many more.