Previously
There's a root where your fang previously was. Your fang isn't there anymore, you ripped it out.
Look at the root where your fang previously was. Previously, when you were young, you had a lot of nice fangs but they're all rotting as you get older and you pull them out.
き
すで
None
To remember the beautiful fangs you previously had, you keep all of the ones you pull out in a box you lock with a key (き).
Previously you didn't have a key, but now you do to keep your old fangs safe.