Dentin is a fundamental component of human teeth, forming the majority of the tooth structure. It is situated beneath the hard outer layer of enamel in the crown and beneath the cementum covering the root. This tissue provides the primary bulk and shape of the tooth. Dentin’s unique composition contributes significantly to the tooth’s overall strength and resilience.
The Mineral Framework
The hardness of dentin largely comes from its inorganic, mineral content, which constitutes approximately 70% of its weight. The primary mineral is hydroxyapatite, a crystalline form of calcium phosphate (Ca10(PO4)6(OH)2). This mineral provides rigidity and strength to the dentin.
Hydroxyapatite crystals in dentin are plate-like and about 30% smaller than those found in enamel. While dentin is notably harder than bone, it is less hard than enamel, which is almost entirely composed of minerals. This difference in mineral density allows dentin to absorb forces without fracturing, offering essential support to the more brittle enamel.
The Organic Matrix
Complementing the mineral framework, the organic matrix of dentin accounts for about 18% to 30% of its composition by weight. The most abundant organic material is collagen, specifically Type I collagen, which makes up about 90% of the organic matrix. This fibrous protein forms a complex network that provides dentin with flexibility, resilience, and structural integrity.
Beyond collagen, the organic matrix contains various non-collagenous proteins, proteoglycans, growth factors, and enzymes. These components regulate dentin formation and mineralization, contributing to its dynamic nature. Water also forms a significant part of dentin, typically ranging from 10% to 12% by weight, filling spaces within the matrix and microscopic tubules.
The Essential Role of Dentin
Dentin’s combined mineral and organic composition enables it to perform several functions. Its inherent hardness, derived from hydroxyapatite, provides structural support for the overlying enamel, helping to prevent the brittle enamel from fracturing under chewing forces. The flexibility provided by its organic collagen matrix allows dentin to absorb and distribute these stresses, acting as a buffer for the tooth.
Dentin also forms a protective barrier around the sensitive dental pulp, which contains nerves and blood vessels. Microscopic channels called dentinal tubules extend through the dentin from the pulp toward the outer surface. These tubules contain fluid and nerve endings, contributing to tooth sensitivity when dentin is exposed to external stimuli like temperature changes or acidic substances.