Patient-friendly definition from the DentistsDirectory.org dental glossary.
Molars are the large, broad teeth at the back of the mouth designed for the primary work of chewing — grinding and crushing food into pieces small enough to swallow safely. They have a flat, multi-cusped chewing surface and typically two to three roots that anchor them firmly in the jaw. Adults have twelve molars in total: three in each of the four quadrants (upper left, upper right, lower left, lower right).
The first molar is often called the "six-year molar" because it typically erupts around age 6 — before most baby teeth have been lost. This is the largest, most important molar in the mouth and the tooth most commonly treated with a dental sealant in childhood to prevent decay in its deep fissures. The second molar erupts around age 12. The third molar — the wisdom tooth — erupts between ages 17 and 25, and is frequently impacted or removed due to space limitations in the modern jaw.
Molars have deep grooves and pits on their chewing surfaces that trap food and plaque, making them the most cavity-prone teeth in the mouth despite being the most posterior and hardest to reach with a toothbrush. Their multiple roots and complex root canal anatomy make endodontic treatment significantly more challenging than on front teeth, which is why molar root canals are more expensive and more frequently referred to endodontists. Molar loss from decay or gum disease has outsized consequences for chewing function compared to the loss of any other tooth type.