Getting the govt. college for you is not possible with the marks you obtained. As to get into the govt. college you must have scored 500 or above for medical or dental courses. You have to go for the private institutes only for the medical or dental courses. The list is given below for the dental colleges in tamilnadu you go through it so that you can have the better idea about the dental colleges.

https://medicine.careers360.com/colleges/list-of-bds-colleges-in-tamil-nadu