Tin(II) fluoride, commonly referred to commercially asstannous fluoride[1][2] (fromLatinstannum, 'tin'), is achemical compound with the formula SnF2. It is a colourless solid used as an ingredient intoothpastes.
Stannous fluoride is an alternative tosodium fluoride for the prevention of cavities (tooth decay). It was first released commercially in 1956, inCrest toothpaste. It was discovered and developed byJoseph Muhler and William Nebergall. In recognition of their innovation, they were inducted into theInventor's Hall of Fame.[1]
The fluoride in stannous fluoride helps to convert the calcium mineralhydroxyapatite in teeth intofluorapatite, which makestooth enamel more resistant to bacteria-generatedacid attacks.[3] The calcium present in plaque and saliva reacts with fluoride to formcalcium fluoride on the tooth surface; over time, this calcium fluoride dissolves to allow calcium and fluoride ions to interact with the tooth and form fluoride-containing apatite within the tooth structure.[4] This chemical reaction inhibits demineralisation and can promote remineralisation of tooth decay. The resulting fluoride-containing apatite is more insoluble, and more resistant to acid and tooth decay.[4]
In addition to fluoride, the stannous ion has benefits for oral health when incorporated in a toothpaste. At similar fluoride concentrations, toothpastes containing stannous fluoride have been shown to be more effective than toothpastes containing sodium fluoride for reducing the incidence of dental caries anddental erosion,[5][6][7][8][9] as well as reducinggingivitis.[10][11][12][13][14] Some stannous fluoride-containing toothpastes also contain ingredients that allow for better stain removal.[15][16] Stabilised stannous fluoride formulations allow for greater bioavailability of the stannous and fluoride ion, increasing their oral health benefits.[17][18] A systematic review revealed stabilised stannous fluoride-containing toothpastes had a positive effect on the reduction ofplaque, gingivitis and staining, with a significant reduction incalculus andhalitosis (bad breath) compared to other toothpastes.[16] A specific formulation of stabilised stannous fluoride toothpastes has shown superior protection against dental erosion anddentine hypersensitivity compared to other fluoride-containing and fluoride-free toothpastes.[19]
Stannous fluoride was once used under thetrade name Fluoristan in the original formulation of the toothpaste brandCrest, though it was later replaced withsodium monofluorophosphate under the trade name Fluoristat. Stabilised stannous fluoride is now the active ingredient in Crest/Oral B Pro-Health brand toothpaste. Although concerns have been previously raised that stannous fluoride may cause tooth staining, this can be avoided by proper brushing and by using a stabilised stannous fluoride toothpaste.[15][16] Any stannous fluoride staining that occurs due to improper brushing is not permanent, and Crest/Oral B Pro-Health states that its particular formulation is resistant to staining.
Readily soluble in water, SnF2 is hydrolysed. At low concentration, it forms species such as SnOH+, Sn(OH)2 and Sn(OH)3−. At higher concentrations, predominantly polynuclear species are formed, including Sn2(OH)22+ and Sn3(OH)42+.[21] Aqueous solutions readily oxidise to form insoluble precipitates of SnIV, which are ineffective as a dental prophylactic.[22] Studies of the oxidation usingMössbauer spectroscopy on frozen samples suggests that O2 is the oxidizing species.[23]
SnF2 acts as aLewis acid. For example, it forms a 1:1 complex (CH3)3NSnF2 and 2:1 complex [(CH3)3N]2SnF2 withtrimethylamine,[24] and a 1:1 complex withdimethylsulfoxide, (CH3)2SO·SnF2.[25] In solutions containing the fluoride ion, F−, it forms the fluoride complexes SnF3−, Sn2F5−, and SnF2(OH2).[26] Crystallization from an aqueous solution containingNaF produces compounds containing polynuclear anions, e.g. NaSn2F5 or Na4Sn3F10 depending on the reaction conditions, rather than NaSnF3.[20] The compound NaSnF3, containing the pyramidal SnF3− anion, can be produced from a pyridine–water solution.[27] Other compounds containing the pyramidal SnF3− anion are known, such asCa(SnF3)2.[28]
SnF2 is areducing agent, with a standard reduction potential of Eo (SnIV/ SnII) = +0.15 V.[29] Solutions in HF are readily oxidised by a range of oxidizing agents (O2, SO2 or F2) to form the mixed-valence compound Sn3F8 (containing SnII and SnIV and no Sn–Sn bonds).[20]
Themonoclinic form contains tetramers, Sn4F8, where there are two distinct coordination environments for the Sn atoms. In each case, there are three nearest neighbours, with Sn at the apex of a trigonal pyramid, and the lone pair of electrons sterically active.[30] Other forms reported have theGeF2 andparatellurite structures.[30]
In the vapour phase, SnF2 forms monomers, dimers, and trimers.[26] Monomeric SnF2 is a non-linear with an Sn−F bond length of 206 pm.[26] Complexes of SnF2, sometimes called difluorostannylene, with analkyne and aromatic compounds deposited in an argon matrix at 12 K have been reported.[31][32]
Stannous fluoride can cause redness and irritation if it is inhaled or comes into contact with the eyes. If ingested, it can cause abdominal pains and shock.[33] Rare but serious allergic reactions are possible; symptoms include itching, swelling, and difficulty breathing. Certain formulations of stannous fluoride in dental products may cause mildtooth discoloration; this is not permanent and can be removed by brushing, or can be prevented by using a stabilised stannous fluoride toothpaste.[15][16][34]
^Groeneveld, A.; Purdell-Lewis, D. J.; Arends, J. (1976). "Remineralization of artificial caries lesions by stannous fluoride".Caries Research.10 (3):189–200.doi:10.1159/000260201.ISSN0008-6568.PMID1063601.
^Zhao, X.; He, T.; He, Y.; Chen, H. (2020-02-12). "Efficacy of a Stannous-containing Dentifrice for Protecting Against Combined Erosive and Abrasive Tooth Wear In Situ".Oral Health and Preventive Dentistry.18 (1):619–624.doi:10.3290/j.ohpd.a44926.PMID32700515.
^Hu, Deyu; Li, Xue; Liu, Hongchun; Mateo, Luis R.; Sabharwal, Amarpreet; Xu, Guofeng; Szewczyk, Gregory; Ryan, Maria; Zhang, Yun-Po (April 2019). "Evaluation of a stabilized stannous fluoride dentifrice on dental plaque and gingivitis in a randomized controlled trial with 6-month follow-up".The Journal of the American Dental Association.150 (4):S32 –S37.doi:10.1016/j.adaj.2019.01.005.ISSN0002-8177.PMID30797257.S2CID73488958.
^Archila, Luis; Bartizek, Robert D.; Winston, J. Leslie; Biesbrock, Aaron R.; McClanahan, Stephen F.; He, Tao (2004). "The Comparative Efficacy of Stabilized Stannous Fluoride/Sodium Hexametaphosphate Dentifrice and Sodium Fluoride/Triclosan/Copolymer Dentifrice for the Control of Gingivitis: A 6-Month Randomized Clinical Study".Journal of Periodontology.75 (12):1592–1599.doi:10.1902/jop.2004.75.12.1592.ISSN1943-3670.PMID15732859.
^Séby, F.; Potin-Gautier, M.; Giffaut, E.; Donard, O.F.X. (2001). "A critical review of thermodynamic data for inorganic tin species".Geochimica et Cosmochimica Acta.65 (18):3041–3053.Bibcode:2001GeCoA..65.3041S.doi:10.1016/S0016-7037(01)00645-7.
^Hsu, C. C. & Geanangel, R. A. (1977). "Synthesis and studies of trimethylamine adducts with tin(II) halides".Inorg. Chem.16 (1):2529–2534.doi:10.1021/ic50176a022.
^Hsu, Chung Chun & Geanangel, R. A. (1980). "Donor and acceptor behavior of divalent tin compounds".Inorg. Chem.19 (1):110–119.doi:10.1021/ic50203a024.
^abcEgon Wiberg, Arnold Frederick Holleman (2001)Inorganic Chemistry, ElsevierISBN0-12-352651-5.
^Salami, Tolulope O.; Zavalij, Peter Y.; Oliver, Scott R.J (2004). "Synthesis and crystal structure of two tin fluoride materials: NaSnF3 (BING-12) and Sn3F3PO4".Journal of Solid State Chemistry.177 (3):800–805.Bibcode:2004JSSCh.177..800S.doi:10.1016/j.jssc.2003.09.013.
^Kokunov Y. V.; Detkov D. G.; Gorbunova Yu. E.; Ershova M. M.; Mikhailov Yu. N. (2001). "Synthesis and Crystal Structure of Calcium Trifluorostannate(II)".Doklady Chemistry.376 (4–6):52–54.doi:10.1023/A:1018855109716.S2CID91430538.
^Housecroft, C. E.; Sharpe, A. G. (2004).Inorganic Chemistry (2nd ed.). Prentice Hall.ISBN978-0-13-039913-7.
^Bogdanov, SE; Faustov, VI; Egorov, MP; Nefedov, OM (1994). "Matrix IR spectra and quantum chemical studies of the reaction between difluorostannylene and hept-1-yne. The first direct observation of a carbene analog π-complex with alkyne".Russian Chemical Bulletin.43 (1):47–49.doi:10.1007/BF00699133.S2CID97064510.
^S. E. Boganov, M. P. Egorov and O. M. Nefedov (1999). "Study of complexation between difluorostannylene and aromatics by matrix IR spectroscopy".Russian Chemical Bulletin.48 (1):98–103.doi:10.1007/BF02494408.S2CID94004320.
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