Хлорид стронция

Strontium chloride has been used in dentistry since 1956 — making it one of the original evidence-backed desensitizers. Seven decades on, the ingredient still appears in some commercial pastes. Here is what the science says.

What It Is

Strontium chloride (SrCl₂) is an inorganic salt of the alkaline-earth metal strontium. It is a white crystalline powder, highly soluble in water. Molecular weight: 158.5 g/mol. Most dental formulations use the hexahydrate form (SrCl₂·6H₂O, MW 266.6 g/mol).

Strontium sits directly below calcium in Group II of the periodic table. The ionic radius of Sr²⁺ (1.12 Å) is close enough to Ca²⁺ (1.00 Å) for strontium ions to substitute into the hydroxyapatite crystal lattice of enamel and dentin — though not identically, which matters for understanding both the desensitizing and potential remineralizing effects.

How It Works

Strontium chloride works through physical-chemical tubule occlusion — a fundamentally different mechanism from potassium nitrate, which suppresses the nerve signal.

The Brannstrom Hydrodynamic Theory

Dentin hypersensitivity is driven by fluid movement in dentinal tubules. When enamel is worn or the tooth root is exposed, temperature, osmotic, or pH changes create a flow of dentinal fluid. This flow activates mechanoreceptors at the tubule entrance and nerve endings in the pulp — triggering a pain signal.

The Role of Sr²⁺ Ions

When toothpaste containing strontium chloride contacts exposed dentin, Sr²⁺ ions diffuse into the open tubules. Two concurrent processes reduce pain:

1. Precipitation of insoluble salts. Sr²⁺ reacts with phosphates and carbonates in dentinal fluid to form sparingly soluble strontium-containing salts (strontium apatites). These precipitates physically narrow the tubule lumen, reducing fluid flow and the resulting pain signal.

2. Competitive substitution for Ca²⁺ in hydroxyapatite. Sr²⁺ incorporates into the surface layer of dentin mineral, partially replacing calcium. The resulting crystal is somewhat less acid-soluble, providing a degree of protection against demineralization.

Qu et al. (2016) demonstrated that a strontium-containing deposit layer penetrates up to 20 µm into tubules after 28 days of treatment. Critically, the same study found this layer to be water-soluble — undetectable after immersion in deionized water. This explains why continuous use is necessary: the effect is not durable after a single course.

Efficacy

Tarbet et al. (1980) — a controlled clinical trial of 10% SrCl₂ dentifrice in patients with post-surgical dentin sensitivity. At 7 weeks: 75.5% pain reduction in the test group vs. 34.2% in placebo. Statistically significant, though the study population (post-periodontal surgery patients) represents an especially vulnerable group.

He et al. (2012) — 148 adults using a 2% SrCl₂ + 5% potassium nitrate combination dentifrice. Significant reductions in tactile and air-blast sensitivity after 3 days. The contribution of each active agent cannot be separated in this design.

Sharif et al. (2013) systematic review — 7 RCTs met inclusion criteria out of 13 identified. Authors concluded: "there is insufficient evidence to state categorically about the efficacy of strontium toothpastes." Methodological quality of available trials was rated low to moderate.

Addy et al. (1992) — 2-month blinded study found no significant effect of SrCl₂ dentifrices on plaque accumulation or gingival inflammation. Strontium chloride has no meaningful antimicrobial action.

What Does Not Work

• Concentrations below 8% — insufficient for meaningful tubule precipitation.
• Single-use application — a cumulative effect over 2–4 weeks is needed.
• Acidic oral environment — frequent consumption of acidic beverages accelerates dissolution of strontium deposits.

Safety

Strontium is not an essential trace element, but it is physiologically inert at low doses. It occurs naturally in food (seafood, green vegetables), with typical daily dietary intake of 2–4 mg. Systemic absorption from toothpaste is minimal: most paste is expectorated, and gastrointestinal absorption of strontium is approximately 20–30%. Estimated daily strontium ion intake from toothpaste is below 0.1 mg — two orders of magnitude less than dietary levels.

Important note on radioactive strontium: ⁹⁰Sr is a radioactive fission product. Strontium in toothpastes is stable, naturally occurring ⁸⁶Sr/⁸⁸Sr — no radiation risk.

Regulatory status:

• EU: Strontium Chloride is listed in Annex III of Regulation (EC) No 1223/2009 (Cosmetics Regulation) as permitted in toothpastes at up to 3.5% calculated as strontium. A 10% SrCl₂ paste exceeds this cosmetic limit (~5.2% Sr by mass) and is therefore classified as a medicinal product in the EU.
• USA (FDA): 10% strontium chloride is included in the OTC Monograph (21 CFR Part 355) as an active ingredient in dental analgesics.
• CIR: The Cosmetic Ingredient Review (2005) found the ingredient safe at approved concentrations.

Comparison With Alternatives

| Ingredient | Mechanism | Onset | Durability | Evidence Level | |---|---|---|---|---| | Strontium chloride 10% | Sr²⁺ tubule occlusion | Weeks | Moderate (washes out) | Moderate | | Potassium nitrate 5% | Nerve depolarization | Days | Requires ongoing use | Moderate | | Nano-hydroxyapatite 10% | Tubule occlusion + remineralization | Days–weeks | High (biomatching mineral) | Growing | | Arginine 8% + CaCO₃ | Biomimetic tubule sealing | Hours | High (mechanically stable) | High | | Sodium fluoride 0.25% | Remineralization, partial occlusion | Slow | High with accumulation | High |

Strontium chloride is outperformed by nano-hydroxyapatite on two critical parameters: the chemical durability of the tubule deposit, and biological compatibility with tooth tissue. Nano-HAp is chemically identical to the mineral that makes up enamel and dentin; the strontium precipitate is a chemically foreign guest.

QDRO Position

QDRO does not include strontium chloride in its formulations. This is not a statement that it is ineffective — at 10%, it does reduce sensitivity. It is a statement that better-studied alternatives are available for every purpose strontium chloride serves.

In the v.pro "Second Enamel" line, the primary desensitizing and remineralizing agent is nano-hydroxyapatite (10–15%), which does not merely block tubules but actively rebuilds lost mineral. In combination with potassium nitrate (5%) for direct nerve pathway suppression, this represents a formulation with stronger evidence and better biological rationale.

Strontium chloride remains a historically significant, niche ingredient. Historical significance and optimal performance are not the same thing.

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Sources:

• Tarbet WJ et al. (1980). Controlled clinical evaluation of a 10% strontium chloride dentifrice in treatment of dentin hypersensitivity following periodontal surgery. J Periodontol. PMID: 7003091
• Poulsen S (1969). Strontium chloride toothpaste effectiveness as related to duration of use. Stomatologiia. PMID: 5293398
• Addy M et al. (1992). The effect of strontium chloride hexahydrate dentifrices on plaque accumulation and gingival inflammation. J Clin Periodontol. PMID: 1452797
• He T et al. (2012). Efficacy of a commercial dentifrice containing 2% strontium chloride and 5% potassium nitrate for dentin hypersensitivity: a 3-day clinical study. Clin Ther. PMID: 22385928
• Sharif MO et al. (2013). The Efficacy of Strontium and Potassium Toothpastes in Treating Dentine Hypersensitivity: A Systematic Review. J Dent. PMC3638644
• Qu X et al. (2016). Strontium effects on root dentin tubule occlusion and nanomechanical properties. Arch Oral Biol. PMID: 26764175