To understand how a chemical desensitization agent works, one must first understand how a nerve cell transmits pain stimuli. Potassium (K+), sodium (Na+), and chloride (Cl–) ions are all involved in the electrical activity of nerve cells. When the nerve cell is at rest, the potassium ion concentration is higher on the inside of the cell than on the outside, while the sodium ion concentration is higher on the outside of the cell than on the inside (Figure 12). When the nerve cell is stimulated, these ions cross the nerve cell membrane through channels and move from an area of high concentration to an area of lower concentration (referred to as the concentration gradient). Thus, potassium ions flow from the inside to the outside of the cell and the sensation of pain is transmitted.
Potassium ion is a desensitization agent because it diffuses through dentin tubules and increases the extracellular potassium concentration at the nerve ending, eliminating the potassium ion concentration gradient across the nerve cell membrane. Without this concentration gradient, the nerve cell will not depolarize and will not respond to stimuli; thus the sensation of pain will not be transmitted. Potassium ion can be delivered in a variety of salt forms (e.g., potassium nitrate, potassium citrate). The most common potassium salt used in sensitivity dentifrices is potassium nitrate (KNO3).62
Video 5. How Nerve depolarization agents work.