The Remarkable Anatomy of a Living Tooth

 James Odell, OMD, ND, L.Ac.

Tooth Anatomy

The permanent dentition consists of 32 teeth. This is made up of four incisors, two canines (or cuspids), four premolars (or bicuspids), four molars, and two wisdom teeth (also called third molars) in each jaw. If wisdom teeth have been removed, there will be 28 teeth. The incisors are the middle four teeth on the upper and lower jaws. They are used for cutting, tearing and holding food. The biting section of an incisor is wide and thin, making a chisel-shaped cutting edge. The canines (or cuspids, meaning a tooth with a single point) are on either side of the incisors. They are used for holding and tearing food. Premolars (bicuspids) and molars have a series of elevations (points or ‘cusps’) that are used for breaking up particles of food. Each premolar generally has two cusps, hence the name bicuspid. They are used for holding and crushing food. Molars are flat teeth at the rear of the mouth. Each molar typically has four or five cusps. They are used exclusively for crushing and grinding. Wisdom teeth are also called third molars. They erupt from the age of 18 onwards and are often surgically removed for various reasons.

A tooth is an organ; it is alive with constant circulation via the dental canal from which nerves and blood vessels pass. Teeth are exactly like the heart, liver, or kidney in that they are organs with their own blood and nerve supply. They are connected to the autonomic nervous system and are the organs that are anatomically closest to the brain.

A tooth is made up of two anatomical parts, the crown and the root. The crown of a tooth is the top part that is exposed and visible above the gum (gingiva). It is covered with enamel, which protects the underlying dentine. The root of a tooth descends below the gum line, into the upper or lower jawbones, anchoring the tooth in the mouth. Different types of teeth have different numbers of roots and root formations. Typically, incisors, canines, and premolars will have one root, whereas molars will have two or three.

The neck is the dividing region of the tooth at the gum line, where the crown meets the root. The crown of each tooth is covered with enamel, which protects the underlying dentine. Enamel is the hardest substance in the human body, even harder than bone. This is because it is the most mineralized substance in the body, made up of crystalline calcium phosphate (hydroxyapatite). It is as hard as crystal.

Enamel is the only tissue that has no living cells. Because it is not alive, it can’t repair itself from decay or damage. The gingiva is the pink soft tissue that we call our gums. It protects the jaw (alveolar) bone and roots of the teeth and covers the neck of each tooth.

Dentine forms the major component of each tooth and extends almost the entire length of the tooth. It is a living tissue, softer than enamel, with a structure similar to bone. In contrast to the brittle nature of enamel, dentine is elastic and compressible. It is sensitive and is protected by enamel on the crown portion and cementum on the roots.  It is nourished by the pulp.

The pulp chamber is the innermost portion of the tooth, lying beneath the dentine and extending from the crown to the tip of the root. The pulp chamber holds the pulp, which is made up of soft tissue. It contains blood vessels to supply blood and nutrients to the tooth to keep it alive, and nerves to enable the tooth to sense temperature. It also contains small lymph vessels carrying white blood cells to the tooth to help fight bacteria.

The cementum is a layer of hard tissue that covers the root of the tooth. It is roughly as hard as bone but considerably softer than enamel. The connective tissues attach to the periodontal ligament and, through this, bind the roots of the tooth to the gums and jaw (alveolar) bone.

The root canal (also called the pulp canal) is the open space inside the root where the pulp extends from the pulp chamber. Blood vessels and nerves from the surrounding outside tissue enter the pulp through the root canal. The periodontal ligament is comprised of bundles of connective tissue fibers. One end of each bundle is attached to the cementum covering the root of the tooth. The fibers on the other end anchor the tooth root to the jaw (alveolar) bone and act as shock absorbers, allowing the tooth to withstand the forces of biting and chewing. There are also accessory canals. These are smaller channels that branch off from the main root canal through the dentine to the periodontal ligament. They are usually found near the root end of the tooth (apex). They supply blood vessels and nerves to the pulp. The apical foramen is the tiny opening at the tip of each root. This is what blood vessels and nerves from the surrounding outside tissue pass through to enter the tooth.

The alveolar bone is the jawbone that surrounds and supports the root of the tooth. It contains the tooth sockets within which the tooth roots are embedded.

References:

Cleghorn, Blaine M., Charles J. Goodacre, and William H. Christie. "Morphology of teeth and their root canal systems." Endodontics 6 (2008): 151-210.

Nelson, Stanley J. Wheeler's Dental Anatomy, Physiology and Occlusion-E-Book: Wheeler's Dental Anatomy, Physiology and Occlusion-E-Book. Elsevier Health Sciences, 2014.

Scheid, Rickne C. Woelfel's dental anatomy. Lippincott Williams & Wilkins, 2012.

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This article is for informational purposes only and is not intended to be a substitute for the direct care of a qualified health practitioner who oversees and provides unique and individualized care. The information provided here is to broaden our different perspectives and should not be construed as medical advice, diagnosis, or treatment.