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Anatomy and physiology of the teeth

Transcript

Content Reviewers:

Rishi Desai, MD, MPH

Contributors:

Sam Gillespie, BSc

In the mouth, the bone holding the bottom row of teeth is the mandible, and the bone holding the top row of teeth is the maxilla.

The mandible and maxilla - like most bones in the human body - have a core of less dense cancellous bone, wrapped in an outer layer of more dense alveolar bone.

The part of the mandible and maxilla that are in the mouth are covered by the gums. And the teeth rest in bony sockets within the mandible and maxilla and are surrounded by the gums.

Usually, at around six months of age, infants will have their first pair of deciduous teeth, also called milk teeth or baby teeth, erupt through the gums and into the mouth.

New deciduous teeth continue to erupt every one to two months until the baby is around two years old and has a full set of deciduous teeth.

Since the mouth is symmetrically divided down the middle, let’s look at just one side of it.

The teeth that pair up vertically have the same names.

Starting at the front of the mouth, in the center, there are the central incisors and then the lateral incisors. These teeth are shaped like chisels and are good at biting off small bits of food.

Next, are the canines, which got their name from being the same teeth that are extra long and sharp in dogs. They’re also called the cuspids, which comes from the word cusp, meaning point. They’re good for puncturing holes, tearing things, and are an essential part of any vampire costume.

Both incisors and canines typically have one root each.

Then, there are the first molars and the second molars. Molars usually have four to five cusps, and are great for crushing and grinding food. That makes 20 deciduous teeth in total.

As the permanent teeth grow in the bone below the deciduous teeth throughout childhood, the roots of the deciduous teeth begin to get absorbed into the gums. This loosens them and allows them to fall out, making room for the permanent teeth to take their places.

These permanent teeth are also called the adult teeth or succedaneous teeth, which means to succeed or follow after.

Children usually begin to lose teeth starting around age six and the process finishes around age 12.

As the permanent teeth move in, a few more types of teeth begin to show up.

Starting from the center of the mouth again, the permanent teeth include the central and lateral incisors, and then the canines, just like before.

But then, the teeth that replace the deciduous molars are called the first and second premolars or bicuspids. As the name bicuspid suggests, they have two cusps each, and each has one root. Just like the molars, these teeth are great for crushing and grinding food.

As the jaw bones grow throughout adolescence, they make room for a few new teeth toward the back of the mouth.

The first permanent molars usually appear around age six and the second permanent molars around age 12.

The third permanent molars, or wisdom teeth, usually don’t erupt until around the ages of 17 to 25, but sometimes never erupt – remaining impacted in the jaw – or simply aren’t present at all. While the upper molars typically have three roots, the bottom molars only have two. All together, that makes 32 permanent teeth.

Now, let's build a model of a tooth and its surrounding structures.

Each bony socket, is lined on the inside by a periodontal ligament.

Protecting the alveolus on the outside is a layer of soft, supportive tissue called the gingiva, or gums, that sits on top of the bone and surrounds the teeth.

The gums meet the tooth at the cementoenamel junction - where the cementum and enamel come together.

The cemento-enamel junction is called the cervical area of the tooth.

Cervical means “neck”, so you can think of this area as the “neck” of the tooth. The gums surround it like a shirt collar.

The tooth itself can be roughly divided into a few parts. The first part is the root, and it sits within the bone.

Sources
  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Oral Histology" St. Louis ; Toronto : Mosby (1997)
  6. "Historical Perspectives of Oral Biology: A Series" Critical Reviews in Oral Biology & Medicine (1990)