What wad cutoff for BDS last year
Your Question is incomplete as you have not mentioned whether you are talking about AIQ, State Quota or any other private Deemed University. Also you have not mentioned your state. So I can give you a rough idea about all these.
Last Year 2017 AIQ cutoff was around 480 till the seats had not reverted back to State Quota.
For State Quota, it depends on many factors like Competition, No. Of students, No. Of seats, No. Of colleges. So it may vary from 450 - 300.
If you are talking about any Deemed or Private University/College then passing/ Eligibility marks is cutoff. I.e. 50%ile.
Moreover if you are under reserve category then also above stats will decrease as per your Category.
I hope this helps