Teeth that have pain, sometimes have infection in the nerve of the tooth. These canals need to be disinfected and filled. Most of the time, these teeth also need a crown afterwards.
Crown is a like a cap that goes over a tooth. American Dental Association (ADA) recommends that any teeth that have more than 50% of the tooth as filling should get a crown. So do teeth that are broken or have a large carious lesion. The crown protects teeth.