Causes of Dentin Hypersensitivity: A Comprehensive Overview

Dentin hypersensitivity (DH) is a common dental condition characterized by a short, sharp pain arising from exposed dentin in response to stimuli such as thermal changes, tactile pressure, or chemical agents. The pain occurs in the absence of any other dental pathology. Though not considered a severe dental disease, DH can significantly affect the quality of life by interfering with normal eating, drinking, oral hygiene practices, and social comfort.

Understanding the underlying causes of dentin hypersensitivity is essential for effective diagnosis, prevention, and treatment. This article explores the etiological factors that contribute to the development of DH and the mechanisms behind them.

The Hydrodynamic Theory: The Basis of Sensitivity

The most widely accepted explanation for DH is the hydrodynamic theory, proposed by Brännström. According to this theory:

Dentin contains thousands of microscopic tubules (dentinal tubules) filled with fluid.
When exposed due to enamel loss or cementum removal, external stimuli cause rapid movement of fluid within the tubules.
This movement activates nerve endings located in the pulp-dentin border, triggering sharp pain.

Importantly, the exposure of dentin and open tubules are prerequisites for DH. Therefore, all causes of dentin hypersensitivity ultimately revolve around two conditions:

Loss of protective enamel or cementum, leading to dentin exposure.
Opening of dentinal tubules, allowing fluid movement.

Primary Causes of Dentin Exposure and Tubule Opening

1. Gingival Recession

Gingival recession is one of the most common causes of DH. When the gum tissue pulls away from the tooth surface, the cementoenamel junction (CEJ) and root dentin become exposed.

Contributing factors:

Periodontal disease: Chronic inflammation damages periodontal tissues, leading to gum recession and bone loss.
Overzealous tooth brushing: Aggressive or improper brushing techniques cause mechanical trauma.
Aging: Recession naturally increases with age.
Frenum pull, occlusal trauma, or orthodontic forces may also contribute.

Once the dentin on the root surface is exposed, even mild stimuli can cause significant discomfort.

2. Tooth Wear (Non-Carious Cervical Lesions)

Tooth wear results in the loss of enamel or cementum, exposing the underlying dentin. There are three primary mechanisms of tooth wear:

A. Attrition

Caused by tooth-to-tooth contact, usually from bruxism or habitual grinding.
Primarily affects incisal and occlusal surfaces but may extend to cervical regions over time.

B. Abrasion

Caused by external mechanical forces, typically from:
- Hard-bristled toothbrushes
- Abrasive toothpaste
- Improper brushing technique
Results in notched lesions at the cervical margins of teeth.

C. Erosion

Chemical dissolution of hard tissues by non-bacterial acids.
Sources:
- Dietary acids: Citrus fruits, sodas, vinegar, wine.
- Intrinsic acids: Gastric reflux, frequent vomiting (bulimia, GERD).
Erosion softens enamel and exposes dentin, especially when combined with mechanical forces like brushing.

3. Periodontal Therapy

Procedures such as scaling and root planing, although essential for treating periodontal disease, can result in temporary or permanent sensitivity due to:

Mechanical removal of cementum, exposing dentinal tubules.
Post-surgical gum recession, leading to root exposure.

Some patients experience DH as a side effect after undergoing periodontal treatments, especially if oral hygiene isn’t adequately maintained afterward.

4. Restorative Dental Treatments

Several dental procedures can lead to hypersensitivity:

Cavity preparation: Removal of enamel and dentin during drilling can stimulate the pulp or expose tubules.
Improper bonding or gaps in restorations allow fluid movement under restorations (microleakage).
Teeth whitening (bleaching): Hydrogen peroxide can penetrate enamel and irritate dentin, causing sensitivity.

5. Enamel Hypoplasia and Structural Defects

Teeth with developmental defects such as enamel hypoplasia or amelogenesis imperfecta have thinner enamel or areas where dentin is naturally exposed. These teeth are more vulnerable to stimuli.

6. Tooth Fractures or Cracks

Cracked tooth syndrome or fractured cusp can create a pathway for fluid movement or even bacteria to stimulate pulpal nerves. Patients often complain of sensitivity when chewing or exposed to temperature changes.

7. Orthodontic Treatment

Movement of teeth can lead to gingival recession, particularly in cases of rapid or excessive force application.
Brackets and wires can also make maintaining oral hygiene difficult, increasing the risk of plaque accumulation and gingivitis, indirectly leading to DH.

8. Dental Malocclusion and Bruxism

Occlusal trauma can cause tooth flexure, resulting in abfraction lesions—wedge-shaped notches at the cervical area.
These lesions can expose dentin and trigger hypersensitivity.

Secondary Factors That Contribute to Sensitivity

While the above causes directly expose dentin or open tubules, secondary factors can aggravate or perpetuate DH:

A. Poor Oral Hygiene

Plaque buildup leads to gingivitis and eventual recession.
Biofilm may also penetrate open tubules, intensifying pain.

B. Diet

Regular consumption of acidic or sugary foods exacerbates erosion and tubule exposure.
Frequent snacking reduces oral pH, increasing demineralization.

C. Smoking

Smoking impairs gum health and healing, increasing the risk of gingival recession.

D. Medical Conditions

GERD, bulimia, or chronic alcoholism increase the risk of enamel erosion due to frequent acid exposure.
Dry mouth (xerostomia) reduces saliva’s protective role, increasing sensitivity risk.

Combination of Factors

In many patients, DH does not result from a single cause but rather a combination of multiple risk factors. For example:

A patient may experience erosion from soda, brushing abrasion, and gingival recession from periodontitis, all contributing to widespread sensitivity.

Dentin hypersensitivity is a multifactorial condition primarily caused by the exposure of dentin and the opening of dentinal tubules, allowing fluid movement that stimulates pulpal nerves. Common causes include gingival recession, tooth wear, erosion, abrasion, periodontal treatment, and restorative procedures.

Understanding these causes enables dental professionals to create individualized treatment plans that not only address symptoms but also eliminate the underlying source of the problem. For patients, proper oral hygiene, dietary adjustments, and preventive care can go a long way in minimizing the risk of dentin hypersensitivity and maintaining long-term oral health.