Hello aspirate 

The cut off marks for bds changes every year. The government college has slightly high cut off than private medical college. The cutoff also depends on category you belong. The minimum marks required is 500+ .

Use the link below to know the cutoff for bds in Tamil nadu for government college 

https://www.google.com/amp/s/medicine.careers360.com/articles/neet-cutoff-tamil-nadu/amp

Hope it help you