Just as they say, NCERTs are must in NEET UG and you must understand the concepts, similarly Preclinical & Paraclinical subjects are must for NEET MDS and you must understand the concepts. They are not only required for NEET MDS but would be required life long. (eg: osmoregulation, anaemia, leukemia, inflammation, healing, neoplasia, cavity preparation, tooth embryology, drug interactions etc).
Trend now-a-days is to ask questions hugely from preclinical & Paraclinical subjects. Now when you start learning the medical and dental, Preclinical – Paraclinical subjects by heart and you start grasping the concepts, you are 50% done with the preparation. So learn them well.
Now most of the people generally start preparation from 3rd year onwards but I have talked with one of my senior who was all India under 15 ranker told me if someone learn the basics by heart then one year preparation during internship would be enough. And I agree with her.
BDS degree is important. Focus on it and you would be 50% done with your preparation.