What does it mean when a dentist does an electrode test?

Tooth vitality test. There is a test called a pulp vitality test which tests if a tooth is "alive" or "dying" from a cavity, crack or trauma. The test involves passing a small electric current through the tooth and recording the value. Then the test is done again on a normal tooth for reference and to compare the values. If the tooth does not respond to the electric current, then the tooth may need a root canal.
Electric pulp test. Testing the vitality of the nerve of the tooth. In other words, if the nerve is alive or dead.