It mostly depends on what college you want to go to (because for some colleges you need specific grades to get into specific courses). It also very much depends on what you want to do when you leave school.
What do you want to do at uni? I might be able to suggest some courses?
For dentistry, I highly suggest chemistry and biology or maths as they are the requirements to study it at uni. Chemistry is a must for medincine and dentistry. I also suggest you pick two more easier A levels which you know you will be able to pass
They are the same types of courses I am considering, for most of those you will need chem and bio, you may possibly also need maths. If you pick them three try and pick a fourth which you will enjoy or one that you'll find quite easy because the three i have suggested are quite difficult (or so i have been told).
Maths and physics are quite different even though physics involves maths, for a course such as the ones you have mentioned I would go with maths, i think. I do not think that universities will require you have an a-level in physics for the courses you have chosen.