How can you tell if a tooth nerve is infected or just inflamed?

Go to the dentist! You can not run around with a infection in your tooth. If you think you have a infection in your tooth that is enough reson to go to the dentist. They know if a nerve is infected or inflamed.

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Even if it is inflamed that means that the dental nerve is infected with bacteria, and if left untreated it can lead to gangrene and root treatment.

See this video about infection of the dental nerve

http://www.checkdent.com/en/videos/tooth-inflammation-159.html