If you could get 400+ in NEET 2020 then there is so many chances of you getting BDS . As you are from OBC it is also a key factor for you. For your knowledge I am sharing you link of last two years cut off for  BDS https://www.google.com/amp/s/medicine.careers360.com/articles/neet-cut-off/amp

Hope it may help you

Hello,

semester question paper are official documents are kept under the university under which your college is affiliated. If you are studying in a university then your university will have those documents. These are internal matters and is not disclosed or shared in public. Ask to your teacher on the respective subject, he/she may help you to give if they have. if they don't have then they will guide you how to prepare for semesters.

ask your seniors who you are familiar with. else read the materials and notes given to you by the teacher and other resources. Those will be enough to appear the semester.

Hope it helps!