after 2nd pu we will do MBBS first &then BDS

Hi

No, it's not like that.

This is because,

There is no need to do MBBS for doing BDS as you can directly do  BDS after your 2nd PU or class 12th.

Actually,
Admission in both BDS and MBBS is through the same entrance examination i.e neet, you can directly do BDS or MBBS after your 12th through Neet and to be eligible for appearing in NEET examination you need to fulfill its eligibility criteria provided below:-

*Neet 2021 eligibility  criteria says that, to be eligible  one must be either appearing for the class 12th board examination 2021 or one must have passed 12th board examination with physics, chemistry ,biology/biotechnology and English and must have got at least  50  % in aggregate of PCB  i.e Physics, Chemistry and Biology/Biotechnology  in 12th examination  if belongs to general category , or   at least  40%  in aggregate of PCB if belongs to  Obc/ Sc /st category  , or at least 45 % in aggregate of PCB in case of general pwd candidates to be eligible.

Also,
* to be eligible for neet 2021 one has to be at least 17 years old or more by  31st  December 2021

So, if you fulfill these criteria then you can appear in NEET examination and then can get admission in MBBS or BDS on the basis of rank / marks obtained by you in NEET examination.

For detailed information about neet examination eligibility go through our page for which link is provided below; -

https://medicine.careers360.com/articles/neet-eligibility-criteria

Thank you