Cut offs change every year depending on various factors such as no.of Candidates appearing for the exam, no.of Candidates qualified, top NEET score and difficulty of the exam. You haven't mentioned your Category. BDS seats are filled through 15% All India Counselling and 85% State Counselling. Now not all the Top Dental Colleges are in the same State which means for the Colleges that are not in your State, you have to appear for All India Counselling. Then the cut offs will be relatively higher. All in all, to speak in generic terms, if you belong to General Category, you will need atleast 550 and if you belong to Reserved Categories, you will need 500.