What is a 'hot' nerve in a tooth that needs root canal?

Inflammed or infecte. Also may mean sensitivity to heat or cold, which is indicative of a possible root canal problem.
Inflamed. We as dentist describe a nerve as "hot" when it is inflamed, typically irreversibly. What this means is that the inflamed nerve will not heal itself and will need to be removed...This is done with a root canal. "hot" teeth are typically hard to numb.
Painful tooth. A hot nerve describes the nerve in a tooth that is highly responsive to stimulation. The patient is typically in severe pain and the the risk of pain increases during and after treatment in these cases.