Dentine hypersensitivity: the two mechanisms call for different products

Dentine hypersensitivity is one of the commonest reasons for consultation and one of the most trivialised. The patient often receives a desensitising toothpaste without the cause being investigated.

The pain mechanism is explained by the hydrodynamic theory: exposed dentinal tubules contain fluid, and a thermal or mechanical stimulus causes it to move, which stimulates the nerve endings of the pulp.

Pain therefore requires two simultaneous conditions: exposed dentine and open tubules. The distinction between the two families of products rests on this.

Occluding products physically block the tubules. Strontium salts, arginine with calcium carbonate, and calcium sodium phosphosilicate form a deposit that reduces fluid movement.

Products acting on nerve transmission contain potassium nitrate. Potassium ions depolarise the nerve endings and reduce their excitability, without occluding anything.

The practical difference lies in timing. Occluding agents can give relief within a few days; potassium nitrate requires repeated application over weeks before reaching full effect.

This must be explained to the patient, who would otherwise abandon the product after a few days concluding that it does not work. A correct expectation is part of the treatment.

Patient behaviour affects the result more than the product does. Rinsing immediately afterwards removes the deposit just formed; the correct advice is to apply the paste with a finger to the sensitive area and not rinse.

Dietary acids reopen occluded tubules within hours. A patient consuming citrus, carbonated drinks or vinegar undoes every evening what the morning achieved, and without addressing this the treatment does not hold.

In-office products with immediate effect exist: fluoride varnishes, adhesive resins, dentine sealers. They give rapid but temporary relief, and serve to bridge the interval while the home product takes effect.

Sensitivity that responds to nothing after weeks warrants reassessment, because it may not be dentine hypersensitivity. An incomplete fracture, caries beneath a restoration, or early pulpitis give similar symptoms.

The distinguishing feature is duration: hypersensitivity pain ceases when the stimulus ceases, whereas pain persisting after the stimulus is removed indicates pulpal involvement.

In summary: occluding agents act within days and potassium nitrate over weeks, do not rinse after application, dietary acids cancel the effect, and pain persisting after the stimulus needs different investigation.