Composition and Histological Structure of Dentin
Dentin is an acellular tissue—the cell bodies of odontoblasts are located in the dental pulp.
- Chemical composition: Composed of 72% inorganic substances: calcium phosphate, magnesium phosphate, and calcium fluoride. Organic substances account for 28%: collagen fibers and proteoglycans.
- Ground substance (matrix): Inorganic substances are grouped into spherical structures called globules (calcospherites). Slightly mineralized or unmineralized areas, known as interglobular spaces, remain between them. In the root region near the cementum, their accumulation forms the Tomes' granular layer.
- Dentinal tubules: Radially penetrate the dentin matrix. Inside the tubules are dentinal fluid (which provides nutrition to dentin and enamel) and the peripheral processes of odontoblasts, known as Tomes' fibers.
Classification by Fiber Orientation
The mechanical strength of dentin is due to the specific arrangement of collagen fibers within its layers:
- Circumpulpar (inner) dentin: Fibers are arranged tangentially, parallel to the tooth surface. They are called Ebner's fibers.
- Mantle (outer) dentin: Located closer to the enamel. Collagen fibers here run radially, perpendicular to the surface, and are termed Korf's fibers.
- Predentin: The least mineralized inner zone of circumpulpar dentin, directly adjacent to the pulp. It serves as the growth zone of dentin.
Types of Dentin Based on Tooth State
Dentin undergoes changes throughout a person's life. Several types of dentin are distinguished:
- Primary dentin: Formed during the physiological development of the hard tissues of the tooth.
- Secondary (replacement) dentin: Continuously formed throughout the normal functional life of the tooth due to odontoblast activity; its production persists as long as the pulp remains vital.
- Tertiary (irregular/reparative) dentin: Formed in response to caries and non-carious tooth lesions. When formed rapidly, it is amorphous and devoid of dentinal tubules; when formed slowly, it contains regularly arranged tubules.
- Sclerotic (transparent) dentin: A pathological type of dentin occurring during caries. Calcium salts are deposited within the dentinal tubules up to their complete obliteration, forming a protective barrier.
- Denticles: Round or oval calcified bodies composed of dentin or dentin-like tissue, most commonly localized within the pulp chamber. Their source of formation is odontoblasts.
Clinical Significance and Preparation Features
Dentin is significantly softer than enamel and is therefore easily cut with steel or carbide burs. However, the procedure is very painful: peripheral odontoblastic processes and nerve receptors located in the dentinal tubules transmit nociceptive signals.
- Topography of pain: Pain is most acute at the dentinoenamel junction and in the circumpulpar dentin. In molars, the number of dentinal tubules is about 1.5 times lower than in incisors, making dentin preparation in incisors elicit a more pronounced pain response.
- Caries progression: The carious process spreads faster in dentin than in enamel. This is facilitated by the lower inorganic content, the presence of dentinal tubules with odontoblastic processes, and the weaker mineralization of the dentin matrix.
- Working with composites: During cavity restorations, dentin is etched with acid for an average of 15 seconds. When rinsing and drying, direct blasts of water and air on the dentin must be avoided. The surface should not be over-dried: it must remain slightly moist and retain a characteristic glossy appearance.