Tubule Blocking or Occluding Agents
Another strategy to treat/prevent dentinal hypersensitivity is to reduce the permeability of the dentin by occluding or blocking the exposed dentin tubules. This prevents stimuli from causing fluid flow in the tubules, thereby preventing the nerve endings inside the tooth from being stimulated.58,59,63
General mechanism of action. Several dentifrice ingredients can be used to occlude or block the dentinal tubules. All of these agents have similar mechanisms of action, forming salt precipitates on the surface of the exposed dentin and inside the dentinal tubules. These precipitates effectively reduce or block the fluid flow in the tubules and exert a desensitization effect. Strontium chloride was the desensitizing ingredient used in the original Sensodyne® dentifrice, and it acted via this mechanism by forming strontium salt precipitates; however, it is rarely used anymore because of its strong metallic taste and incompatibility with fluoride.
Newer tubule-occluding agents. Other tubule-occluding agents new to the market include arginine with calcium carbonate (Pro-Argin™), strontium acetate, and calcium sodium phosphosilicate (Novamin®).
Arginine and 8% calcium carbonate (Pro-Argin™). Pro-Argin™ blocks tubules upon its application by depositing calcium- and phosphate-containing minerals within the dentinal tubules. Both arginine and calcium carbonate (CaCO3) are required for this action (Figure 11). Arginine, found naturally in saliva, may help usher calcium to open tubules for incorporation of calcium phosphate into dentin. Calcium carbonate creates a basic environment, and calcium phosphate salts are less soluble at higher pH (more basic). The combination of high local calcium concentration at the dentin tubule at basic pH is designed to promote precipitation of calcium phosphate salts.64
Strontium acetate. Unlike the original strontium chloride, strontium acetate (Figure 12) can be formulated into fluoride-containing dentifrices. Upon toothbrushing, strontium-based precipitates form to occlude dentinal tubules and build a resistant barrier over time.
Calcium sodium phosphosilicate (Novamin®). In saliva, Novamin® releases calcium and phosphate ions and raises the pH (Figure 13). Under these conditions, calcium phosphate salts precipitate from solution to not only block dentin tubules but also to form an insoluble calcium phosphate layer on the surface of enamel.58,65,66
Figure 11. Pro-Argin.
Arginine is a naturally occurring amino acid, and calcium carbonate creates basic (high pH) environment.
Figure 12. Strontium acetate.
Figure 13. Novamin.
Calcium and Phosphate ions are released via Hydrolysis reaction.
Stannous fluoride. Stannous fluoride is also a tubule-occluding agent that can treat dentinal hypersensitivity. Stannous fluoride, through hydrolysis and oxidation reactions, forms many insoluble metal salts that can precipitate in dentinal tubules and on the dentin surface (Video 6) to provide effective relief against hypersensitivity.24,56,67 Stannous fluoride is the only fluoride delivering protection from caries68 and plaque/gingivitis47,69 as well as hypersensitivity56,70 and dental erosion.35,45
Video 6. Tubule occlusion.