These open dentine tubules allow access of hot and cold stimuli to the nerve receptors connected to the tooth pulp, which are directly linked to the central nervous system. De-sensitising toothpastes can be effective either by blocking the opening to the tubules or alternatively by deactivating the nerve receptors (typically using Potassium salts).
The outermost part of the tooth is enamel, a hard, wear-resistant protective coating composed of 98% mineral called Hydroxyapatite (Ca5(PO4)3OH) – which is a Calcium Phosphate mineral.
This Hydroxyapatite of the enamel is in dynamic equilibrium with Calcium Phosphate and Hydroxyl ions contained in saliva; saturated Calcium Phosphate solution. This is continually in a state of exchange and if the lost minerals from the enamel are not replaced, caries or tooth decay will develop. As salivary flow reduces with age, radiation therapy and smoking this risk of caries incidence increases.