Hii!
If you are talking about applying in to BDS course after completing your graduation, then let me tell you that the eligibility criteria for BDS course states that the candidate must have completed class 12th with atleast 50% marks in PCB and English subject combinations from a recognised Board of Education. The admission are provided based on NEET UG entrance exam. So, basically you will be doing graduation all over again after you complete bsc zoology course. The choice remains on you. Post graduation courses aren't provided directly.
Hope you understand.
Good luck!