Tooth Structure

Dentin

Evidence: High Tooth Structure Reading time: approx. 5 min. Reviewed: 10.08.2026 · KEERN Editorial Team

Dentin is the mineralized hard tissue beneath enamel that forms the bulk of the tooth crown and root and encloses the pulp. It is part of the biologically responsive dentin-pulp complex, threaded by microscopic tubules (dentinal tubules), and can form limited new tissue when the pulp remains vital. Exposed dentin with open tubules is a common basis for tooth sensitivity; the precise neurosensory mechanism is still being researched.

Related terms:Enamel Dental erosion Abrasion Attrition

Definition

Dentin is the mineralized hard tissue that makes up most of a tooth. In the crown, it lies beneath the enamel; in the root, beneath the cementum. On the inside, dentin encloses the pulp, the central tissue containing blood vessels, nerves, cells, and connective tissue.

Dentin itself is not directly supplied with blood vessels. Its biological responsiveness comes from the closely connected dentin-pulp complex: it contains microscopically fine channels, the dentinal tubules, which run from the pulp to near the enamel border and carry tissue fluid. This structure fundamentally distinguishes dentin from mature enamel, which is acellular and cannot biologically regenerate lost tissue.

In short

Dentin is less hard and less mineralized than enamel, but more elastic and tougher: it supports the more brittle enamel from within and helps distribute chewing forces. When dentin becomes exposed, for example through wear or exposed root surfaces, it often responds sensitively to cold, heat, and sweet stimuli.

Why exposed dentin hurts

The most widely accepted explanation is the hydrodynamic theory: external stimuli such as cold, heat, or a stream of air move the fluid within open dentinal tubules, which activates pain-signaling structures near the pulp. The exact molecular process is still being researched. Sensitive dentin tends to have more, or more widely open, tubules than insensitive dentin; individual pain perception cannot be reliably predicted from this alone.

Exposure alone does not necessarily produce hypersensitivity; symptoms depend in part on whether dentinal tubules are open and patent, as well as on individual sensory factors.

Other causes of sensitive teeth still need to be ruled out, including caries, cracks, or leaking fillings; for persistent symptoms, a dental evaluation is worthwhile.

A common misconception

It is often assumed that lost tooth hard tissue is fundamentally unrecoverable: what applies to enamel holds only to a limited extent for dentin. With a vital pulp, the dentin-pulp complex can form what is called tertiary dentin in response to sufficiently strong or persistent stimuli, including advancing caries or substantial wear, new tissue on the side facing the pulp. This can provide additional shielding for the pulp, though it does not restore tooth substance lost on the outside. It is no substitute for extensively lost substance, but it shows that dentin, unlike enamel, remains limitedly responsive.

What matters with exposed or sensitive dentin

Dental evaluation of the cause (such as dental erosion, abrasion, gum recession, or dental procedures), before treating symptoms alone
Gentle brushing technique and moderate pressure, to avoid further loss of substance
Specialized toothpastes for reducing sensitivity can help supportively, but do not replace an evaluation of the cause

Key takeaways

Dentin makes up most of the tooth crown and root; in the root, it lies beneath the cementum, not exposed on the outside
Dentin is part of the dentin-pulp complex and therefore has limited responsiveness, unlike acellular, non-regenerating enamel
Exposed dentin is a common, but not the only, cause of tooth sensitivity, and exposure alone does not guarantee symptoms
Tertiary dentin provides the pulp with additional protection, but does not restore substance lost on the outside
For persistent sensitivity, a dental evaluation of the cause is worthwhile

Frequently Asked Questions

Why does exposed dentin hurt?

According to the widely accepted hydrodynamic theory, fluid movement in the dentinal tubules triggers pain perception in response to cold, heat, or other stimuli. A newer study additionally discusses an ion transport mechanism, without so far displacing the established theory as consensus.

Can dentin form new tissue?

To a limited extent, yes: with a vital pulp, the dentin-pulp complex can form tertiary dentin in response to stimuli. This does not replace extensive external loss of substance, but it shows a genuine responsiveness that enamel does not have.

Why is dentin often described as less resistant?

Dentin is less mineralized than enamel and is therefore more susceptible to acid-mediated mineral loss. Mechanically, though, it is more elastic and tougher than the brittle enamel: the two tissues complement each other functionally, with dentin supporting enamel from within.

What exactly are dentinal tubules?

These are microscopically fine channels that run through dentin from the pulp to near the enamel border. They carry tissue fluid and, especially near the pulp, can contain odontoblast processes; they are central to how stimuli are transmitted.

When should tooth sensitivity be evaluated by a dentist?

For persistent or increasing sensitivity, since besides exposed dentin, this can also point to other causes that may need treatment, such as caries, cracks, or leaking fillings. Dentin hypersensitivity is a diagnosis of exclusion and should be evaluated accordingly.

KEERN Perspective

Dentin shows that not every tooth tissue responds the same way: treating enamel and dentin as equivalent overlooks important differences in sensitivity, responsiveness, and protective needs.

Persistent or newly exposed sensitive dentin warrants professional assessment of the underlying cause rather than symptom management alone.

Professional perspective

Clinical relevance

Differential diagnosis of the causes of exposed dentin and tooth sensitivity before symptomatic treatment
Framing tertiary dentin formation as a natural protective mechanism in a vital, adequately responsive pulp
Patient education on dentin's limited responsiveness in contrast to acellular enamel
Realistic framing of the benefit of desensitizing toothpastes relative to causal therapy

Structure and composition

By weight, mature dentin consists of roughly 70 percent inorganic substance, around 20 percent organic matrix (predominantly type I collagen), and about 10 percent water; the corresponding volume proportions are roughly 45/33/22 percent (Goldberg et al., 2011). The mineral phase is most often described in the literature as predominantly carbonate-substituted apatite, or a hydroxyapatite-like mineral phase, rather than stoichiometrically pure hydroxyapatite crystals. This lower mineralization compared with enamel (around 96 percent inorganic) explains both dentin's greater elasticity and its greater susceptibility to acid-mediated mineral loss.

Structurally, a distinction is made between physiological primary dentin (formed during tooth development) and secondary dentin (formed slowly and continuously after root completion), as well as tertiary dentin formed in response to external stimuli. Tertiary dentin formation is further differentiated: reactionary dentin is secreted by surviving, already differentiated odontoblasts, while reparative dentin forms after more severe damage, from newly differentiated odontoblast-like cells (Goldberg et al., 2011; Farges et al., 2015). This tertiary dentin formation requires a vital, adequately responsive pulp and deposits tissue on the side facing the pulp; it does not represent regeneration of externally lost tooth hard tissue and can additionally reduce the size of the pulp chamber.

Dentinal tubules extend from the pulp through the dentin toward the enamel-dentin or cementum-dentin junction. They carry tissue fluid and, particularly in areas near the pulp, can contain odontoblast processes; the extent of these processes is not uniform across regions.

Sensitivity mechanism: established theory and current research

The hydrodynamic theory (Brännström, developed from the 1960s onward) remains the widely accepted explanation for dentin hypersensitivity: thermal, osmotic, tactile, or evaporative stimuli set the fluid in open dentinal tubules in motion, and this movement stimulates mechanosensitive nerve endings near the pulp. Current reviews confirm that, despite unresolved details, this theory remains the clinical frame of reference (Liu et al., 2020). Sensitive dentin tends to have more, or more widely open, tubules; individual pain perception, however, cannot be reliably predicted from this alone.

A single, methodologically novel study (Chen et al., 2023) used electrochemical and electroneurophysiological methods to propose directional cation transport through the nanoscale, negatively charged dentinal tubules as an alternative or complementary trigger for nerve stimulation. This approach has not so far displaced the hydrodynamic theory as clinical consensus; it does show, however, that the exact molecular mechanism of dentin hypersensitivity continues to be actively researched.

Differential diagnosis

Dentin hypersensitivity is a diagnosis of exclusion. Caries, pulpitis, enamel cracks, leaking or fractured restorations, and postoperative discomfort can produce similar symptoms and must be ruled out before the diagnosis is made (Liu et al., 2020). Prevalence, differential diagnosis, and management options are covered in more depth in the dedicated article on dentin hypersensitivity.

Evidence summary

What current evidence supports

The structure and composition of dentin, and its role as part of the dentin-pulp complex, are well established
Primary, secondary, and tertiary dentin, along with reactionary and reparative dentin, are established biological concepts
The hydrodynamic theory remains the widely accepted clinical explanatory framework for dentin hypersensitivity
Newer mechanistic research is investigating complementary explanatory models, without so far displacing the established clinical consensus

Why this matters

Understanding dentin as part of a living dentin-pulp complex explains two clinically important facts at once: exposed dentin can become sensitive, but the tissue can also mount a limited internal protective response. Neither means that externally lost tooth structure regenerates.

What remains uncertain

No conclusive consensus on the exact molecular mechanism of dentin hypersensitivity (fluid movement versus ion transport versus other mechanisms)
No reliable prediction of the individual extent of dentin exposure at which sensitivity actually occurs
Limited evidence on the extent to which natural tertiary dentin formation alone provides clinically relevant protection against advancing damage

Goldberg, Kulkarni, Young, Boskey (2011): Dentin: structure, composition and mineralization. Frontiers in Bioscience (Elite Edition), 3(2), 711-735. Foundational review of dentin structure, composition, dentinogenesis, and the forms of dentin formation.

Farges, Alliot-Licht, Renard, Ducret, Gaudin, Smith, Cooper (2015): Dental Pulp Defence and Repair Mechanisms in Dental Caries. Mediators of Inflammation, 2015, 230251. Review of defense and repair mechanisms of the dentin-pulp complex, including reactionary and reparative dentin.

Brännström, Åström (1972): The hydrodynamics of the dentine; its possible relationship to dentinal pain. International Dental Journal, 22(2), 219-227. Foundational work; establishes the hydrodynamic theory of dentin hypersensitivity.

Liu, Tenenbaum, Wilder, Quock, Hewlett, Ren (2020): Pathogenesis, diagnosis and management of dentin hypersensitivity: an evidence-based overview for dental practitioners. BMC Oral Health, 20, 220. Current review; confirms the hydrodynamic theory as the still widely accepted framework and describes differential diagnosis and management.

Chen, Deng, Jiang, et al. (2023): The mechanism of dentine hypersensitivity: Stimuli-induced directional cation transport through dentinal tubules. Nano Research, 16(1), 991-998. Electrochemical and electroneurophysiological study; proposes directional cation transport as an alternative mechanism to classical fluid movement.

Sources

📚 Goldberg M, Kulkarni AB, Young M, Boskey A (2011): Dentin: structure, composition and mineralization. Frontiers in Bioscience (Elite Edition), 3(2), 711-735.
📚 Farges JC, Alliot-Licht B, Renard E, Ducret M, Gaudin A, Smith AJ, Cooper PR (2015): Dental Pulp Defence and Repair Mechanisms in Dental Caries. Mediators of Inflammation, 2015, 230251.
📚 Brännström M, Åström A (1972): The hydrodynamics of the dentine; its possible relationship to dentinal pain. International Dental Journal, 22(2), 219-227.
📚 Liu XX, Tenenbaum HC, Wilder RS, Quock R, Hewlett ER, Ren YF (2020): Pathogenesis, diagnosis and management of dentin hypersensitivity: an evidence-based overview for dental practitioners. BMC Oral Health, 20, 220.
📚 Chen N, Deng J, Jiang S, et al. (2023): The mechanism of dentine hypersensitivity: Stimuli-induced directional cation transport through dentinal tubules. Nano Research, 16(1), 991-998.

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The KEERN Lexicon provides evidence-based educational information about oral health. It is intended to support, not replace, individual advice from a dentist, physician, or pharmacist. Diagnosis and treatment decisions should always be based on a personal clinical assessment.

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