The tooth root is the foundation of the tooth, embedded deep within the jawbone. While the visible crown handles the mechanical forces of chewing, the root’s primary function is to serve as the anchor that stabilizes the entire structure. It is significantly longer than the crown, making up roughly two-thirds of the total tooth length, ensuring the tooth remains firmly seated in its bony socket during biting and grinding. The root system also acts as the conduit for the tooth’s life source, allowing nerves and blood vessels to enter and nourish the internal tissues.
The External Structure of the Tooth Root
The visible crown transitions into the root at the cementoenamel junction (CEJ), also known as the cervical line or the neck of the tooth. This junction marks the meeting point between the crown’s hard enamel and the root’s covering layer, cementum, and is where the gums typically attach to the tooth. The overall form of the root is generally conical, tapering toward the tip, or apex, which provides a shape well-suited for anchoring within the jawbone.
The number of roots varies based on the tooth type. Single-rooted teeth, such as incisors and canines, typically have one relatively straight root designed for cutting and tearing. Teeth involved in heavy chewing, such as premolars and molars, often have multiple roots (bifurcated or trifurcated) to provide a broader base of support against occlusal forces. Mandibular molars commonly have two roots, while maxillary molars often have three; the area where these multiple roots separate is termed the furcation.
Unlike the crown, which is covered by highly mineralized enamel, the root is covered by cementum, which has a slightly dull and porous texture. This rough surface provides a secure attachment point for the thousands of tiny fibers that connect the tooth to the jawbone. This specialized covering is pale yellow in color and is softer than the dentin beneath it.
The Internal Anatomy of the Root
Forming the bulk of the root structure is dentin, a hard tissue that is softer than enamel but similar in structure to bone. Dentin is permeated by microscopic channels called dentinal tubules that extend outward from the central pulp cavity toward the cementum.
Covering the dentin is cementum. This layer is thickest at the root tip and thinnest near the neck of the tooth, and it contains no blood vessels or nerves. The cementum’s primary function is to anchor the tooth to the surrounding jawbone through connective tissue fibers.
Running down the center of the dentin is the root canal, which is the continuation of the pulp chamber found in the tooth’s crown. This central space houses the dental pulp, a soft tissue containing the tooth’s nerves, blood vessels, and connective cells. The pulp provides sensation and nutritional support to the dentin, keeping the tooth structure viable.
At the very tip of the root, the pulp tissue exits the tooth through a small opening known as the apical foramen. This opening is the gateway through which the nerves and blood vessels enter and exit the pulp cavity. The foramen typically measures between 0.3 to 0.4 millimeters in diameter. In some cases, the root tip may contain multiple accessory canals that form a complex, branching pattern called an apical delta.
The Root’s Supporting Structures
The root is held firmly in the jaw by a collective support system called the periodontium, which comprises the tissues immediately surrounding the tooth.
The alveolar bone is the dense bone of the jaw that forms the tooth socket, or alveolus, into which the root is securely seated. This bone is dynamic, constantly undergoing remodeling in response to the forces exerted on the tooth during chewing.
The periodontal ligament (PDL) is the specialized connective tissue that acts as a flexible attachment between the root and the alveolar bone. This ligament is a dense network of collagen fibers that attach to the cementum covering the root and to the bone. These embedded collagen bundles, called Sharpey’s fibers, suspend the tooth within the socket, allowing for slight movement while acting as a shock absorber during biting.
The third component is the gingiva, or gum tissue, which is the soft tissue that surrounds the neck of the tooth. The gingiva provides a protective seal around the tooth, covering the alveolar bone and the upper part of the root. The health of the gingiva is related to the stability of the root, as it prevents bacteria from reaching the deeper supporting structures.