As with most invasive medical or dental procedures, complications can occur. Here are some possibilities.
Sometimes when a root canal is opened for treatment, the oxygen in the air will trigger some bacteria to start growing, causing inflammation and pain.
Bacteria may get pushed out through the tips of the roots. Blood vessels enter the tooth through a small hole (the apex of the root) at the bottom of the root. Sometimes during a root canal procedure, bacteria are pushed out through this small hole into surrounding tissue. If this happens, the surrounding tissue will become inflamed and possibly infected. This can be treated with painkillers, and sometimes antibiotics, but the site could be painful until it clears up.
A root canal treatment can puncture the side of the tooth. This can happen if the canal is curved or if the canal cannot be located. The instruments are flexible so that they bend as the canal curves, but sometimes the instrument makes a small hole in the side of the tooth. If saliva can get into the hole, the tooth will have to be treated further or extracted. If the hole is far enough under the gum line that saliva can't reach it, it may heal.
A root canal may be missed or an entire canal may not be fully cleaned out. Locating canals within the tooth can be difficult. If a canal or an offshoot of a canal isn't located and cleaned out, the tooth can remain infected and the root canal procedure will have to be repeated. This also can happen if a canal isn't measured correctly and pieces of infected or inflamed pulp are left near the bottom. Occasionally, root canals have branches that are not accessible to traditional treatment. A file may break. The tip of a file may break off inside the tooth. Usually, it's possible to leave the piece in the tooth and finish the root canal. But if the cleaning of the canal has not been finished, the file piece may have to be removed. Sometimes this can be done from the top of the tooth. However, in some cases, the file can only be removed through a surgical procedure called an apicoectomy. A small incision is made in the gum to access the root of the tooth, and the portion of the root containing the file piece is removed.
Pain, or the Lack of It
In most cases, you will not experience any pain during the root canal procedure. Your dentist will completely numb your tooth and the surrounding area. If this doesn't seem to be working, alert your dentist right away. Some people fear the anesthetic injections more than the procedure itself, but numbing gels and modern injection systems have made injections virtually painless. Let your dentist know immediately and he or she can modify the technique to avoid repeating the pain.