Dentin

What is dentin made of and how is it structured?

Dentin is an acellular tissue — odontoblast bodies are located in the pulp.

• Chemical composition: Composed of 72% inorganic substances: calcium phosphate, magnesium phosphate, and calcium fluoride. 28% is accounted for by organic substances: collagen fibers and proteoglycans.
• Ground substance (matrix): Inorganic substances are grouped into spherical structures — globules (calcospherites). Weakly calcified or uncalcified areas remain between them — interglobular spaces. In the root area at the border with cementum, their accumulation forms Tomes' granular layer.
• Dentinal tubules (canaliculi): Radially penetrate the ground substance of dentin. Inside the tubules are dentinal fluid, which provides trophic support to dentin and enamel, and peripheral odontoblast processes — Tomes' fibers.

Classification by fiber direction

The strength of dentin is due to the specific arrangement of collagen fibers in its layers:

• Circumpulpal (inner) dentin: Fibers are located tangentially, parallel to the tooth surface. They are called von Ebner's fibers.
• Mantle (outer) dentin: Located closer to the enamel. Collagen fibers here run radially, perpendicular to the surface, and are called Korf's fibers.
• Predentin: The least mineralized inner zone of circumpulpal dentin, directly adjacent to the pulp. It is the growth zone of dentin.

Types of dentin depending on the tooth's condition

Dentin undergoes changes throughout a person's life. Several types of dentin are distinguished:

• Primary: Formed during the period of physiological formation of the hard tissues of the tooth.
• Secondary (replacement): Continuously formed during the normal life activity of the tooth due to the activity of dentinoblasts; its formation persists in the presence of a living pulp.
• Tertiary (irregular): Formed in response to caries and non-carious dental lesions. With rapid formation, it is amorphous and devoid of dentinal tubules; with slow formation, it contains regularly arranged tubules.
• Sclerotic (transparent): A pathological type of dentin that occurs with caries. Calcium salts are deposited in the dentinal tubules up to their complete obturation, resulting in the formation of a protective barrier.
• Denticles: Rounded or oval formations consisting of dentin or dentin-like tissue and most often localized in the pulp. The source of their formation is odontoblasts.

Clinical significance and preparation features

Dentin is significantly softer than enamel, so it is easily prepared with steel or carbide burs. However, the procedure is very painful: peripheral odontoblast processes and nerve receptors transmitting pain sensitivity are located in the dentinal tubules.

• Topography of pain: The dentinoenamel junction and circumpulpal dentin are the most painful. In molars, the number of dentinal tubules is 1.5 times less than in incisors, so dentin preparation in incisors causes a more pronounced pain reaction.
• Spread of caries: The process in dentin proceeds faster than in enamel. This is facilitated by a lower content of inorganic substances, the presence of dentinal tubules with odontoblast processes, and weak mineralization of the dentin ground substance.
• Working with composites: When restoring carious cavities, dentin is etched with acid for an average of 15 seconds. When washing and drying, direct contact of water and air with dentin must be avoided. The surface must not be over-dried: it should remain slightly moist and retain its characteristic shine.

Class and exam questions

What else to study on this topic

• Dental enamel
• Dental pulp and odontoblasts
• Cementum
• Dentin caries and lesion zones

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.