There are several methods of knowing that the nerve is dead, but only applying all them and doing a good analysis of the results will give us the real answer. There is: Reaction to cold Reaction to hot reaction to electricity horizontal hit vertical hit Normally when your tooth aches for hot is because the nerve is too swallowed and its irreversible, in these point is close to be necroses or dead. the electricity test will give a higher rate of electricity to make it react. Most of the times when you have an exposure and the put ZOE (eugenol with zinc oxide) which is a temporary filling you will not have any pain, these is because the Eugenol is a natural anesthetic but at the same time is a antibiotic. these will cease the pain for a while, the bad thing is that the tooth chamber is so enclosed that when it swallows in self defense cause of bacterias, It signs it's death penalty. the swallowing cause that defense cells not be able to get inside the tooth's nerve or out, even blood... so it dies. So sooner or later you will have to make a root canal. Some times the pain goes away and a small fistula forms (normally) in the vestibular part of the gums, so the pressure of the infection caused because of the necrosed nerve, goes out and it becomes a chronic infection, which by the way is more difficult to treat. I know that you don't want to make the root canal, I know that you may be will prefer OP, but I can tell you OP can be good for preventing but for taking out an infection .... I don't think so, what it would do is make it chronic.