Tooth #18 in particular
About the lower left second molar
Tooth 18 is the lower left second molar, seventh from the midline on the bottom left and written as 37 in FDI notation or LL7 in Palmer. Tooth 19, the first molar, is in front of it, and tooth 17, the lower left wisdom tooth, is behind it when present. It chews against tooth 15, the upper left second molar. Second molars sit behind the first molars and share the grinding. This one generally erupts somewhere between 11 and 13 years. Its usual form is two roots with two to four canals, and in lower second molars a C-shaped canal, where the canals merge into a ribbon-like curve, is a recognized variation.
What tends to go wrong here
The problem most tied to tooth 18 is the tooth behind it. Lower wisdom teeth often lack room, and when tooth 17 is tilted forward it leans on the back of the second molar. Food and plaque collect in the wedge between them, below the gum line where neither brush nor floss gets in, and the result can be decay on the back root surface of tooth 18 or loss of the bone and gum behind it. Even without a wisdom tooth, being this far back makes the tooth harder to brush and floss, with the tongue on one side and the cheek on the other. Problems here tend to be found late because the area is hard to see.
If it needs treatment
Treatment of tooth 18 is shaped by two neighbors: the wisdom tooth behind and the nerve below. The roots can lie close to the main nerve of the lower jaw, so a dentist assesses that on x-rays before an extraction or an implant. Decay on the back surface caused by a wisdom tooth can be hard to restore, and the wisdom tooth usually has to be addressed as well. Ask your dentist whether tooth 17 should be removed and when, whether the damage on the back of tooth 18 can be reached for a filling, how close the roots are to the nerve on your imaging, and whether the canal shape affects who should do a root canal.
What it does
What the lower left second molar is for
Second molars sit behind the first molars and share the grinding. Often called the "twelve-year molars".
Anatomy
Roots and canals of tooth #18
Typically two roots with two to four canals. A C-shaped canal is a known variation in lower second molars. These are typical patterns. The only way to know the anatomy of your own tooth is an x-ray, which is why one is taken before a root canal or extraction.
Common problems
What tends to go wrong with second molars
Being far back, second molars are harder to brush and floss. They are also the tooth a wisdom tooth leans against, which can cause decay or gum problems on their back surface.
If it needs treatment
Root canal, crown, or extraction on tooth #18
The roots can lie close to the main nerve of the lower jaw, which a dentist assesses on x-rays before an extraction or implant.
| Root canal: what to expect |
| Tooth extraction: what to expect |
| Dental crown: what to expect |
| Extraction or root canal? |
General information · Not dental advice
This page describes a typical second molar. It cannot tell you anything about your own tooth #18. We always recommend seeing a dentist. Nothing on this site can examine your mouth or tell you what is wrong. If something hurts, looks wrong, or worries you, book an exam, and go sooner if it is getting worse.
Emergency? If you have trouble breathing or swallowing, swelling that is spreading toward your eye or neck, a fever with facial swelling, or bleeding that will not stop, call 911 or go to your nearest emergency room immediately. Full disclaimer