How our teeth and jaws work together

Our teeth are made of a hard, bone-like substance. They are held in small hollow spaces in our upper and lower jawbones, called tooth sockets or dental alveoli. These are a part of the periodontium. Strong fibers anchor the teeth in place there.

Your teeth are arranged in two arches. When you close your mouth and bite, these two arches typically fit together with a slight overlap.

A full set of adult teeth includes 16 upper teeth and 16 lower teeth at the most. Each row has:

• 4 incisors in the middle
• 2 canine teeth next to the incisors; 1 to the left and 1 to the right
• 5 back teeth on each side, including the premolars, molars and wisdom teeth

So, the upper and lower jaws contain a total of 32 teeth.

Teeth have different shapes because they have different jobs to do. The incisors have narrow edges, and the canine teeth are sharp at the tip. When we close our mouth to bite, the lower incisors are pushed up just behind the upper incisors. This helps the front teeth to tear off bite-sized pieces of food – for instance, from a carrot or a sandwich.

The molars look different: They have wide chewing surfaces with raised mounds (cusps) and small grooves. When we bite down, the cusps of the upper molars fit into the grooves of the lower teeth. That way, they can grind food when we chew. The back teeth just behind the canine teeth are called premolars.

When children are born, their jawbones already contain a "bud" for every tooth. The teeth later develop from these buds. When a tooth pushes through a baby's gums and can be seen, we say that it has come in, or that it has “erupted.”

Known as teething, this process starts around the age of six months. It can be painful and may sometimes cause a fever. The child’s first set of 20 baby teeth is usually complete by the age of two years.

At that point, toddler’s skulls have not yet reached their full size. Because the baby teeth don’t get any bigger, they are gradually replaced by 32 larger teeth, starting when the child is about six years old. The baby teeth fall out first to make room for these permanent teeth. That way, adults have teeth that are the right size for their mouths.

Most people have all of their permanent teeth by the time they reach their early teens. One exception is the molars right at the back of the mouth, known as wisdom teeth: They often start appearing around the age of 18 or later. But not everyone has wisdom teeth in their jaw. And if they do, only some of these teeth may erupt or none at all.

Bones and muscles play an important role when it comes to chewing, as well as opening and closing your mouth.

The skull is made up of several plate-like bones. These include the upper jawbone (maxilla) and the lower jawbone (mandible). Our teeth are embedded in these bones.

The upper jawbone is rigidly fixed to other bones of the skull, but the lower jawbone is not: A bit like a swing, it is attached to the temporal bones at the two joints of the jaw, allowing it to move.

Several muscles run between the lower jawbone and the skull. When these muscles are tensed (tightened), the lower jaw can be pulled up tightly against the upper jaw. This helps us to take a powerful bite. When the muscles are relaxed, our mouth opens. Some of the muscle fibers can actively help to open the mouth as well. Through the interactions of the various muscle groups, the lower jaw can also be moved slightly sideways and forward or backward. That makes it easier to grind food between our back teeth.