A tooth is more than the simple white surface visible in the mouth; it is a complex organ with multiple internal layers. These structures are built to withstand immense forces while housing the delicate living tissue that maintains the tooth’s vitality. Understanding this internal architecture reveals how a tooth processes sensory information, defends against infection, and anchors itself firmly within the jawbone.
The Hardest Substance
The outermost layer covering the crown is the enamel, a highly mineralized tissue that serves as the body’s defense against the wear of chewing. Enamel consists of approximately 96% mineral content by weight, making it the hardest substance in the human body, tougher than bone. Its composition is primarily crystalline calcium phosphate, known as hydroxyapatite, arranged in a dense, rod-like structure.
The function of this hard shell is to protect the softer, underlying layers from physical damage and chemical erosion caused by acids. Enamel also provides insulation, shielding the sensitive interior from extreme temperature changes. Since enamel is non-living tissue, it cannot regenerate or heal itself once damaged by decay or fracture.
The Main Body and Sensitivity
Directly beneath the enamel lies dentin, which forms the main structure of the tooth, extending from the crown down into the roots. Dentin is a calcified tissue but is significantly softer and more porous than enamel, containing about 70% mineral content. This yellow layer largely determines the overall hue of the tooth, visible through the translucent enamel.
Dentin is characterized by millions of microscopic channels called dentinal tubules that radiate outward from the pulp cavity toward the outer surface. They contain fluid and cellular extensions from specialized cells in the pulp, creating a direct pathway to the tooth’s nerve center.
This network of tubules is why dentin is the source of tooth sensitivity when the protective enamel is breached. External stimuli like cold air or sweet foods cause rapid movement of the fluid within these tubules. This movement triggers the nerves in the pulp, resulting in the sharp sensation of sensitivity, a mechanism described by the hydrodynamic theory. Unlike enamel, dentin is a living tissue continually formed throughout life by cells called odontoblasts, allowing it to respond to irritation by depositing new dentin to protect the inner pulp.
The Living Center
The innermost chamber of the tooth is the pulp cavity, filled with soft tissue referred to as the dental pulp. The pulp houses the structures responsible for nutrient supply, defense, and sensation. This soft tissue mass is composed of connective tissue, blood vessels, and nerves.
The blood vessels deliver oxygen and nutrients to the tooth structure and remove waste products. The nerves provide sensory function, registering pain, temperature changes, and pressure. Specialized cells called odontoblasts line the periphery of the pulp chamber and are responsible for forming and maintaining the surrounding dentin.
The pulp chamber is continuous with the radicular canals, or root canals, which extend down the length of the tooth roots. These canals open near the tip of the root, allowing the nerves and blood vessels to connect with the body’s circulatory and nervous systems. When bacteria reach the pulp due to deep decay, the resulting inflammation and infection often requires a root canal procedure to remove the infected tissue and save the tooth.
Anchoring the Tooth
The tooth’s root system secures it within the jawbone. Covering the root dentin is the cementum, a bone-like, calcified tissue that is thickest at the root tip. Cementum is avascular, meaning it lacks its own blood supply, and receives nutrients from the adjacent soft tissues.
The cementum acts as the attachment point for the periodontal ligament (PDL), a dense network of fibrous connective tissue. This ligament functions as a sling, suspending the tooth in its socket and allowing for slight movement to absorb the shock of chewing forces. The fibers of the PDL, known as Sharpey’s fibers, are firmly embedded into both the cementum and the alveolar bone.
The final component is the alveolar bone, which forms the bony sockets that cradle the tooth roots. This bone, along with the cementum and the periodontal ligament, holds the tooth stable. The coordinated function of these structures ensures that the tooth remains securely fixed while tolerating the constant mechanical stress of mastication.