BDS

Both are interdisciplinary courses. You will face a lot of difficulties since both are of entirely different subjects. But if you interest, you can go for astrophysics.

You can consider following courses:
B.Pharma (Bachelor of Pharmacy)
Physiotherapist
B.Sc Nursing
B.Sc Biotech
B.Sc. Radiography
BE in Environmental Engineering
B.Sc Operation Theatres
B.Sc Speech therapy

No, this totally depends on your interest. But in general, BDS is a little tough.
Good luck.

Go for MS abroad, having more value than in India.

The Master of Science in Forensic Science program in Modi University is designed to service the needs of both practicing professionals and full-time students who desire an advanced program of study in forensic science. The master's program is an exciting and innovative curriculum that offers students hands-on training in crime scene investigation techniques and crime laboratory methodologies.
B.Sc in Forensic Science, Physics, Chemistry, Maths, Botany, Zoology, Microbiology, Biochemistry, Engineering or Pharmacy with minimum 55% marks.
For more visit: http://www.modyuniversity.ac.in

No, you cannot get any government college in Tamilnadu. Your NEET marks are too low.

Hi PRADYUMN,
Yes, you can do M.Sc. In astrophysics after completing your graduation in BDS. But you should not have any backlogs of previous degree at the time of admission.
Best of luck.

If you have done BDS, then why you are going for such courses you can easily go for some healthcare management courses for a brighter career ahead. For more choices you can go for Masters Courses.