Generally with dentistry/medicine, I see that maths or physics do help alongside Chem and Bio but it's up to you because the science sector can mean anything!
Business or Geo is a bit strange?
If you think you have a rough idea of what you want to do, browse around the entry requirements for several different universities and what third subject they'd like. Better safe than sorry.
By the way as someone mentioned, Business is a soft subject, Economics is more respected.