Molar Teeth: First, Second and Third Molars, Roots, Eruption Age and Decay

Each quarter of the mouth has three molars, so an adult has twelve in total. The first molar is the earliest to arrive and the one most often missed by parents, because it comes up behind the last milk tooth without replacing anything. It is sometimes called the six-year molar. A child's milk molars are a separate set, and our guide to milk teeth explains them.

The second molar follows at around 11 to 13 years. The third molar, or wisdom tooth, comes through between the late teens and the mid twenties, if it comes through at all. The ages below are approximate: normal eruption varies by a year or more between people.

Chewing force is greatest at the back of the mouth, so molars have several roots spread apart to grip the bone, usually three in the upper jaw and two in the lower. The canals inside those roots can be narrow and curved, which is why a root canal on a molar takes longer than on a front tooth.

The chewing surface is covered in cusps, with grooves and pits between them. This shape is excellent for grinding but hard to clean, because a toothbrush bristle is wider than the bottom of many grooves. Food and plaque sit there, which is why the back teeth develop cavities earlier than the front ones. Our guide on the cavity in teeth explains how decay starts.

Brushing the chewing surfaces thoroughly, twice a day with fluoride toothpaste, is the main protection. Clean between the molars as well, because the contact points are where food packs in. Cutting down how often you snack on sweets, biscuits or sweetened tea helps as much as the brushing does.

A dentist can also seal the grooves of a newly erupted molar with a thin protective coating. This is most often done soon after the first and second molars come through, when the deep grooves are untouched. Our guide on pit and fissure sealants explains how sealing works and who it suits.

Wisdom teeth often lack the room to erupt properly. They may come in tilted, partly covered by gum or stuck under it, and the flap of gum can then trap food and become sore. See our guide on wisdom teeth for what is normal and when a dentist should look.

A molar that hurts on biting, throbs at night, or has a visible hole needs a dentist rather than waiting. Swelling of the face, fever, or difficulty swallowing or breathing means same-day care, and a hospital emergency if breathing or swallowing is affected. For how molars sit alongside the smaller teeth in front of them, see our guide to premolar teeth, or the main guide to the types of teeth.