After the tooth has lost its nerve, it cannot feel cold or heat, and there is no pain. If the tooth has decayed again at this point, there is no discomfort. Pain or sensitivity to cold or heat is a kind of tip of the tooth, so it is necessary to protect the nerve of the tooth, to avoid caries too large injury to the nerve, once the nerve is damaged after the symptoms of inflammation, need to carry out root canal treatment. Without the nerve, the tooth also lacks the nutrient supply of blood vessels, the tooth will become very gray and very fragile, when biting hard objects, it is easy to splinter. A tooth that has undergone root canal treatment will need to be further restored with a crown or inlay.