Hi,

The correct and up to the marked answer is not there for this. I can only suggest you something. 

Well as private colleges have no central quota..so all seats will be filled on the basis of your state rank...so cutoff for private BDS will depend upon your state...
As there are so many Private dental colleges these days so obviously cutoff will be quite low compare govt college cutoff..so I think if your score is 425 or higher, u will get a decent college and rest depend upon your state as some states like Karnataka, Tamilnadu, Andhra have many colleges so cutoff will be low but in North states it will be higher.

Hope this helps you in anyway.