Postgrad entry to Dent, Med or Vet is barkingly competitive and as you will already have a degree, usually doesnt get full funding. Its simply not a realistic option.
If you want to be a Dentist - DO DENTISTRY. If that involves working your socks off this year to get the grades you need and applying in a gap year, do it. It that involves resits, do it, If it involves reapplying three times, do it. Just dont do Biochem as an 'instead' until you have exhausted all other ways of doing Dentistry.