How painful is a deep scaling, i need to have it done on 3 small teeth?

Use local anesthetic: We always use local anesthetic (novocaine) and it is not painful at all.

Comfortable: Scaling and root planing is not uncomfortable with the use of anesthetic. You may hear horror stories about deep cleaning being painful. However, that is usually osseous surgery, done for more advanced perio disease that hasn't been treated. By having deep cleanings done sooner than later, it will be easier and then future, more frequent dental visits will keep disease from progressing.

Should be painless.: Most dentists use anesthietic to numb the area before deep cleaning, therefore the procedure should be painless. If done early and if appropriatley scheduled checkup appointments are kept, then more advanced procedures for repair of periodontal disease damage can be avoided, and hence avoidance of greater pain. Win win.