Many patients may ask, “I just have a cavity, just fill the material, why do I need to come back two or three times? In fact, if it’s just a small cavity that doesn’t hurt the pulp (commonly known as the dental nerve), it can be filled in one go, and the result is so good that it can last for years to decades. However, most people do not go to the hospital unless they have a toothache, so many people go back to the hospital when they have a toothache, and by this time they have already developed pulpitis. If the material is filled directly at this time, it will aggravate the pain. If you want to keep the painful tooth from becoming a problem in the future, the best treatment is root canal therapy, which is often referred to as “nerve extraction”. There are three major procedures involved in extracting the nerve: preparation of the root canal, disinfection of the root canal, and finally filling. The root canal is disinfected and finally the root canal is filled. Some doctors like to do these three procedures in three times, and some doctors do the first two at once, so in this way, it takes two to three times to fill a tooth, instead of filling it all at once.