Eligibkity of BDS says that:

• The students, who have passed the 10+2 examination withscience streamand have had Physics, Chemistry and Biology and English in 12thstream, may go for the BDS course.

• It is the course which will be having hands on training in the field of dentistry for the duration of five years. The students will get the chance to interact with the patient and will get the practical knowledge of the diseases.

• The students have to score minimum50% marks(40% in the case of reserved category) in plus two and have to appear for an entrance examination conducted by the respective authorities.

So according to this you cant go for medical if you didnt had PCB in 12th.