Tooth sensitivity is a common yet often misunderstood dental condition characterized by a sharp, transient pain when teeth are exposed to certain stimuli.

Though easy to experience, the underlying biological and structural causes of this discomfort are complex and involve intricate processes within the tooth.

Tooth Sensitivity: The Hydrodynamic Theory

The most widely accepted explanation for tooth sensitivity is known as the hydrodynamic theory. According to this theory, microscopic fluid-filled channels called dentinal tubules run through the dentin layer beneath the enamel.

When these tubules become exposed due to enamel loss or gum recession, stimuli such as extreme temperatures, tactile pressure, or certain tastes cause the fluid inside to move. This fluid movement stimulates nerve endings located deeper in the tooth, triggering the sensation of pain.

The exposure of dentinal tubules can occur through various mechanisms: mechanical wear (abrasion), chemical erosion, or biological factors such as gum tissue recession. Because the dentin layer itself houses these tubules directly linked to the nerves, once exposed, the tooth becomes highly sensitive to environmental triggers.

Causes of Tubule Exposure and Sensitivity

Several factors contribute to the exposure of dentinal tubules, which leads to tooth sensitivity:

Enamel Erosion: Acidic foods and beverages, as well as acid reflux, chemically wear down enamel, reducing its protective capacity and exposing underlying dentin.

Mechanical Abrasion: Vigorous or improper toothbrushing techniques can physically remove enamel at the gumline, exposing dentin and causing sensitivity.

Gingival Recession: The gum tissue recedes due to periodontal disease or aggressive hygiene, uncovering the root surface where enamel is absent and dentin is exposed.

Teeth Grinding (Bruxism): Excessive grinding wears down enamel and dentin, increasing sensitivity risk.

Cracked or Damaged Teeth: Cracks in the enamel allow stimuli to reach dentinal tubules more easily.

Recent Dental Procedures: Treatments such as cavity preparation can temporarily increase sensitivity by altering enamel or dentin surfaces.

Types of Stimuli Triggering Sensitivity

Once exposed, dentinal tubules react to various external stimuli that cause fluid shifts inside them:

Thermal: Cold stimuli are typically more provocative than heat, causing rapid fluid movement that activates nerve fibers.

Tactile: Physical contact from brushing or eating hard foods can lead to pain due to pressure changes in the tubules.

Chemical: Sugary or acidic foods induce osmotic fluid flow, stimulating sensory nerves.

This multi-factorial stimulation explains why sensitivity varies in intensity and duration among individuals and the circumstances provoking it.

Nerve Activation and Pain Response

The pain associated with tooth sensitivity originates from nerve endings in the pulp, a soft tissue inside the tooth. These nerves respond to signals generated by fluid movement within dentinal tubules. In some cases, inflammation caused by exposure can heighten nerve sensitivity, lowering the threshold for pain stimuli. This neural plasticity means that even normally harmless sensations may evoke discomfort in sensitive teeth.

Dr. Charles A. DiFranco, a respected figure in dental research, explains that tooth sensitivity primarily results from the loss of protective layers exposing dentinal tubules, which in turn transmit stimuli to pulpal nerves. Understanding this mechanism guides effective preventive and therapeutic approaches aimed at restoring the tooth's natural barrier and reducing nerve excitation.

Tooth sensitivity arises when protective enamel or gum coverage is compromised, exposing dentinal tubules that connect directly to nerve endings. The hydrodynamic movement of fluid within these tubules in response to environmental stimuli is the fundamental cause of the sharp pain experienced.

Various factors such as acid erosion, mechanical wear, gum recession, and dental treatments contribute to this condition. Recognizing these causes and the underlying biological mechanisms informs targeted prevention and treatment strategies to restore comfort and health.