Strontium chloride is a salt formed from the alkaline earth metal strontium and the element chlorine. This inorganic compound is typically encountered as a white, crystalline solid that is highly soluble in water. It is defined chemically by its simple composition, creating a neutral aqueous solution when dissolved.
Chemical Composition and Properties
Strontium chloride possesses the chemical formula SrCl2, indicating that one strontium ion is bonded with two chloride ions. As an ionic compound, it forms a crystalline structure with a high melting point, reaching 874°C in its anhydrous form. When the solid dissolves in water, it completely dissociates into charged ions, making it a strong electrolyte capable of conducting electricity.
The strontium ion (Sr2+) is chemically similar to calcium (Ca2+), which is why it readily substitutes for calcium in biological systems and mineral structures. The compound often crystallizes from water as a hexahydrate (SrCl2·6H2O), which is the most common form commercially available. The presence of strontium also gives off a characteristic bright red color when introduced into a flame, a property utilized in pyrotechnics.
Role in Dental Health
The most common interaction the public has with strontium chloride is through its use as an active ingredient in desensitizing toothpaste. This application targets the sharp, temporary pain known as dentin hypersensitivity, which occurs when the protective layers of the tooth are worn away. The pain results from external stimuli, like cold air or hot liquids, causing fluid movement within microscopic channels in the dentin called dentinal tubules.
Strontium chloride acts as a physical occluding agent, meaning it works by blocking these exposed dentinal tubules. When applied to the tooth surface, the strontium ions precipitate within the tubules, effectively forming a barrier or plug. This physical blockage prevents the fluid movement that stimulates the underlying nerve, providing relief from the sensitivity.
Concentrations of up to 10% strontium chloride have historically been used in over-the-counter desensitizing toothpaste formulations for this purpose. While modern formulations sometimes use strontium acetate, both strontium salts function on the same principle of physically sealing the vulnerable dentin surface. Consistent use of the toothpaste is required to maintain the occluding layer and sustain the reduction in tooth sensitivity.
Strontium Compounds in Medical Contexts
While strontium chloride is a topical agent for dental sensitivity, other strontium compounds are used systemically for bone health, which can be a source of confusion. About 99% of the strontium in the human body is concentrated in the bones.
The most notable systemic strontium medication is Strontium Ranelate, a drug that was formerly used to treat osteoporosis by stimulating bone formation and reducing bone resorption. Strontium Ranelate is chemically distinct from strontium chloride, as it is a salt of strontium and ranelic acid, not simple chloride. This systemic drug, which is not available in the United States, works very differently from the topical application of strontium chloride in toothpaste.
Beyond the ranelate compound, the radioactive isotope Strontium-89 chloride has a specialized medical application. This form is administered intravenously to provide pain relief for people suffering from bone pain caused by metastatic cancer. In this context, the radioactive strontium mimics calcium and is selectively absorbed by the bone, delivering localized radiation to the painful areas. Strontium chloride is also available as a common form in dietary supplements, though its efficacy and safety for oral supplementation are still subjects of ongoing research.