Teeth are sophisticated biological structures composed of four distinct layers. Each layer has a specialized role in protecting the tooth’s living core and anchoring it securely in the jawbone. These layers range from the hardest substance in the human body to soft, nourishing tissue, working together to allow us to chew, speak, and maintain the structure of the mouth.
The External Shield: Enamel
The outermost layer of the tooth, the enamel, acts as a durable shell covering the crown, the visible portion above the gum line. This substance is the hardest mineralized tissue in the human body, a property that allows it to withstand the immense forces of chewing and biting. Enamel’s strength is due to its composition, which is approximately 96% inorganic material, primarily a crystalline calcium phosphate known as hydroxyapatite.
The dense, organized structure of hydroxyapatite crystals forms rods that extend from the underlying layer outward toward the surface. Because the cells that form enamel, called ameloblasts, are lost when the tooth emerges, mature enamel is considered non-living and cannot regenerate or repair itself once fractured or worn away. However, this highly mineralized composition makes the enamel susceptible to demineralization, a process where acids produced by mouth bacteria dissolve the calcium and phosphate ions, leading to erosion and the formation of cavities.
The Main Body and Core: Dentin and Pulp
Dentin
Lying directly beneath the protective enamel is dentin, a yellowish tissue that constitutes the majority of the tooth’s mass. Dentin is softer than enamel but maintains significant hardness, comparable to bone tissue, and continues to form throughout life. Its unique structure contains millions of microscopic channels called dentinal tubules that run from the outer edge toward the center.
These tubules contain fluid and extensions of specialized cells, creating a connection between the sensitive interior and the outside environment. When enamel or cementum is lost, exposing the dentin, fluid movement within these tubules transmits stimuli like temperature or pressure to the central nerves, causing tooth sensitivity. Dentin provides structural support to the brittle enamel and acts as a secondary defense barrier for the tooth’s living core.
Pulp
The soft tissue core housed within the dentin is the dental pulp, which occupies the pulp chamber and the root canals. This non-mineralized, highly vascularized connective tissue contains blood vessels, nerves, and specialized cells. The pulp’s primary role is to provide nourishment to the surrounding dentin and to mediate sensation, with nerves transmitting signals of pain, pressure, and temperature.
Specialized cells within the pulp, called odontoblasts, are responsible for forming and maintaining the surrounding dentin. The pulp maintains the tooth’s vitality, and its immune cells provide a defense against invading bacteria when the outer layers are breached.
The Root’s Anchor: Cementum
Cementum is a thin, bone-like layer that covers the entire root surface, starting where the enamel ends at the gum line. This mineralized tissue is slightly softer than dentin, consisting of about 45% to 50% inorganic material, primarily hydroxyapatite. It is formed by cells called cementoblasts and is continuously deposited throughout life, which helps maintain the integrity of the tooth’s attachment.
The primary function of cementum is to provide physical attachment to the jawbone. It serves as the embedding point for the collagen fibers of the periodontal ligament. These fibers anchor the tooth securely within its bony socket, distributing the forces of chewing and keeping the tooth stable within the alveolar bone.