I had a tooth filled, then a few days later face became paralyzed on that side. dr. said bells palsy. what is that?

Unknown: Bell's palsy is a condition where one side of the face is paralyzed for an unknown reason. To make that diagnosis, all other causes must be excluded. Movement sometimes returns, but is occasionally permanent. It sounds like it was not caused by the dental procedure.

Injury to a nerve: Bell's palsy is due to an injury to the facial nerve which innervates the muscles of the face. In bell's palsy, the facial muscles lose their motor innervation and become paralyzed. This was probably due to an injury to the facial nerve when you received a novocaine injection. This paralysis will pass as the facial nerve heals.