Hello aspirant, 

Kindly mention the state you are talking about, I'll answer you the generalization points with reference being Mumbai city. So the general marks range for BDS admission ends around at 485-495. This year with increased competition cutoff may rise, but anything above 500 is going to be safe. Rest is all about luck and fate. The state merit rank and the state you reside in will decide the different cutoffs of different states. 

Hope this helps..