THE HYDRODYNAMIC THEORY
The hydrodynamic theory of dentine hypersensitivity
There have been many theories of dentine hypersensitivity proposed over the years, but the hydrodynamic theory is by far the best supported.1
The theory states that dentine hypersensitivity is caused by movement of the dentinal tubule contents. Various stimuli alter the flow and pressure of the tubule fluid and thus by hydrodynamic action these changes are detected by the mechanoreceptors surrounding the odontoblast processes. The stimulation of these nerve fibres is believed to cause pain.1
Tubule diameter is an important determinant of pain. The rate of fluid flow in a tube is dependent on the radius. Hence, a doubling of the tubule diameter results in a sixteen-fold increase in potential fluid flow (mathematically, this is described as a fourth power relationship).
Sensitive teeth have up to eight times as many exposed tubules, and the tubules are twice as wide at the buccal cervical area. Hence exposed dentine with tubules that are available for fluid flow from pulp to tooth surface has the capacity for a huge increase in tubular fluid flow versus non-exposed dentine. This increase can be in excess of 100 times that of non-sensitive dentine. A study investigating dye penetration from the tooth surface to the pulp (in extracted teeth) showed complete dye penetration only in sensitive teeth. As tubule diameter normally increases toward the pulp, the effect of tooth wear will be to create wider tubule orifices at the worn tooth surface, allowing greater rates and amounts of fluid flow, which in turn will create greater stimulation of the receptors and increase the intensity of symptoms.1
- West NX. The dentine hypersensitivity patient – a total management package. Int Dent J 2007; 57: 411–419.