Each tooth in your mouth sits in bone and is surrounded by gum tissue. Approximately two-thirds of each tooth (the root portion) is in jaw bone. Inside every tooth is a canal or canals (usually depending on the number of roots the tooth has). Each canal has a vein, artery and nerve in it. Collectively they are referred to as the pulp. Sometimes, because of trauma like decay or a large filling, the pulp becomes irritated and can get infected. In this case, root canal (a.k.a. endodontics) is necessary in order to save the tooth.