A tooth is a bit like a tree — only part of it is visible, and the roots lie beneath the surface. The roots of your teeth extend into your gums and beyond into the jaw bones. Your tooth has many layers. The outer layer (enamel) is made of hard crystal. The next layer (dentin) is softer. The pulp in the middle of the tooth contains nerves that conduct sensations of hot, cold and pain. The pulp also contains blood vessels.
- Crown — The crown of the tooth is the part that you can see above your gum line. The part of the tooth that is covered by enamel is called the "anatomical crown." The crown can appear to get longer as we age because gums recede and periodontal disease can destroy gum tissue. If this happens, your teeth may look longer even though they have not grown. Receding gums expose more of your tooth roots. This also can make the tooth become loose and unstable. The anatomical crown also can get smaller as we age because the enamel wears down over time. This process usually is very gradual. In some people, the process of wear speeds up because of an incorrect bite (malocclusion) or habits such as grinding the teeth.
- Neck — The neck of the tooth is where the crown meets the root.
- Root — The root of the tooth is the part that extends into the upper or lower jawbones. Different types of teeth have different root formations. Some, such as incisors and canine teeth, have a single root. Molars may have one, two or three roots depending on their type and location in the mouth. At the end of each root is a small opening called the apical foramen. Blood vessels and nerves pass through this opening to enter the tooth.
- Enamel — Enamel is the hard outer shell that covers the visible part (crown) of the tooth. It is able to withstand the stress of biting, chewing and grinding. But enamel is also very brittle. It is prone to cracking and chipping. The body cannot repair broken enamel the way it mends broken bones, so it is very important to protect your teeth. For example, people may need a mouth guard if they play sports or grind their teeth. Enamel is translucent. This means you can see light through it, but it is not clear. Although enamel is the outer layer of the tooth, the dentin underneath is mostly responsible for the color of the tooth. Coffee, tea, tobacco and poor hygiene can cause surface stains on the enamel. Your dentist can remove these stains with simple polishing. Other types of discoloration involve the dentin
- Cementum — Just as enamel covers the crown of the tooth, cementum covers the root or roots. It is not as hard or as white as enamel. Cementum attaches to tiny fibers that help anchor the tooth to the jawbone.
- Dentin — Dentin is the bone-like substance that makes up most of the tooth. It is found just under the enamel in the crown and under the cementum in the root. Dentin gives the tooth its color. To change the color of the tooth, the color of the dentin must be changed. Teeth are typically gray-white or yellow, not pure white. Stains and discoloration can be caused by certain diseases, overexposure to fluoride, or exposure to the antibiotic tetracycline while the teeth are developing. Teeth also can darken with age. This type of discoloration can often be improved with dental whitening.
- Pulp and pulp cavity — At the core of the tooth, beneath the dentin, is the pulp cavity. This space contains the blood vessels, nerves and connective tissue that make up the "pulp." The pulp's blood supply provides nutrients that help to keep the tooth alive. The part of the pulp cavity located in the root is called the pulp canal or the root canal. The parts of the pulp that point upward toward the cusps (points of the teeth) are called the pulp horns.
- Pulp canal(s) or root canal(s) — The pulp or root canal is the open space inside the root. Blood vessels and nerves enter the tooth through the root canal and become part of the pulp. Sometimes the pulp becomes inflamed, infected or is no longer able to feed nutrients to the tooth. In this case, root canal therapy may be able to save a tooth that otherwise would have to be pulled.
- Apical foramen — The apical foramen is the tiny opening at the tip of each root that allows nerves and blood vessels to enter the tooth.
What surrounds the teeth and keeps them in place is more than just the delicate pink flesh we call our gums. As a group, all these structures are called the periodontium. The treatment of gums and their diseases is called periodontics.
- Periodontal ligament — The periodontal ligament is composed of bundles of connective tissue fibers that anchor the teeth within the jaws. One end of each bundle is attached to the cementum covering the root of the tooth. The other end is embedded in the bony tooth socket (called the alveolar socket). These bundles of fibers allow the tooth to withstand the forces of biting and chewing.
- Alveolar process and socket — If you were to look at a skull that is missing teeth, you would see that the jaws are not just flat planes of bone. Within the bone are small craters that mark where the teeth had been. These craters are the alveolar sockets. The walls of the craters are called the alveolar processes. As teeth erupt through the gums, the alveolar processes develop around the teeth to help support them.
- Gingiva — The gingiva is the pink flesh we call our gums. It lies over the bones of the jaw and hugs the tooth tightly at its neck. The earliest stage of gum disease is called gingivitis. At this stage, gums can become red, inflamed and bleed easily. The later stages, when bone loss and possibly tooth loss can occur, are known as periodontitis.