my left canine crown tooth fell off and I saw a little screw inside, can my crown be fixed?

From the sounds of things, I would expect that it can be cemented back, as long as your root hasn't suffered a fracture.  If your root is fractured, you will need the tooth pulled.  This is why it is important that you see your dentist very soon.  You do not want to damage your root,if not damaged already.  Good luck and I hope this helps. Follow me if you have more questions.Sarah Thompson, DMD

It sounds like that
little screw that is left inside is a post. This can detach from the
crown and sometimes the post itself can completely come out. So, in this case
provided that the tooth hasn’t fractured underneath and the crown fits
accordingly, you can often re-cement that. The dentist is the best person to
assess this because if the post needs some more sub structure to support the
crown then this can be built up. If the sub structure is beyond the boundaries
of the crown then most likely you will need a new crown.

That "screw" is called a post, which is oftentimes placed into the top portion of a root canal to strengthen the already weak tooth, and also aid in giving more substance (called a core) for the crown that will follow.If the post and core are both in good shape and have not broken, and the crown fits well, then the crown can usually be recemented onto your root.  If a substantial part of the post or core have been lost, then you might need a new post and core, followed with a new crown.