Bell's palsy: Will local anesthetic worsen it?

The short answer is no. Bell's palsy affects the facial nerve (cranial nerve VII or CN-VII), which controls facial movement. During dental procedures, a dentist may inject a local anesthetic into a branch of the trigeminal nerve (CN-V) — which is a different nerve. The trigeminal nerve controls sensation and pain in the face, mouth, teeth and gums. For this reason, local anesthetic doesn't involve the nerves affected by previous Bell's palsy.