Electron Microscopic Observations of the Differences in the Effects of Stannous Fluoride and Sodium Fluoride on Dental Enamel

Abstract

CLINICAL tests have shown that topical application of fluorides to erupted teeth will reduce dental caries.1 Stannous fluoride has been found to be more effective than sodium fluoride in reducing decay when applied topically.2, 3,4 In an attempt to elucidate the mechanisms by which the fluoride exerts its protective action, extensive studies5' 6, 7 have been made of the effects of inorganic salts on rate of solution of enamel in acid solutions. Since many salts, and particularly the fluorides, reduce the solution rate, studies of the nature of the chemical and physical changes which occur in the enamel have been made using electron microscopy and x-ray and electron diffraction.8-13 It has been shown that treatment of enamel with sodium fluoride results in the formation of calcium fluoride. The diffraction studies have shown no such changes after treatment with stannous fluoride, but have suggested the presence on the enamel surface of an amorphous layer of unknown composition. The prior work does not include a comparative study of the visible effects of the reagents on the structure and properties of intact enamel surfaces.The present work shows the effects on whole enamel surfaces of treatments with aqueous solutions of stannous fluoride, sodium fluoride, and nonfluoride stannous salts, over a range of pH values. In addition, the effects resulting from the exposure of these treated surfaces to acid buffer solutions are described. EXPERIMENTAL METHODThe teeth used in this investigation were human maxillary first incisors which were stored in a 0.5 per cent formaldehyde solution. No prior history of the teeth was available. Rectangular pieces of whole enamel from these teeth were cut from the labial surface. The area of the enamel surface varied between 4 and 16 sq. mm., and generally it was possible to cut 9 such specimens from a single tooth. The cutting was done with a circular jeweler's slotting high-speed steel saw operated at low speeds under water to prevent heating and drying of the tooth.

Kinetics of Crystal Growth and Dissolution of Calcium and Magnesium Fluorides

“…[3][4][5] The crystallization of calcium fluoride is of considerable importance in view of its use as a primary source of fluorine and also as single crystals in optical devices. Biologically, the topical application of fluoride solutions to tooth enamel results in a partial transformation of hydroxyapatite (HAP:Ca10 (P04) 6 (OH) 2) to fluorapatite (FAP:Ca10 (P04) 6F2) on the enamel surface, resulting in a much more caries-resistant phase. At higher concentrations of the fluoride ion, calcium fluoride forms at the tooth surface in addition to FAP.…”

“…The inhibition of dental caries that results from the topical application of fluoride salts has been related to a surface coating of calcium fluoride on enamel which protects the mineral phase, HAP, from dissolution. 6 Other theories stress the reduced solubility of FAP in contact with the salivary fluids.7,8 A recent model suggests that the calcium fluoride layer serves as a medium for transporting the reacting ion to the FAP-HAP interface. 9 One of the disadvantages of studying spontaneous precipitation processes is that the results are difficult to reproduce and the induction period that often precedes the precipitation reaction involves both nucleation and the growth of nuclei already formed.…”

Anti-bacterial Determinants of Stannous Fluoride

“…SnF2 solutions near neutrality showed no anti-microbial properties. Hydrolysis of SnF2 solutions at elevated pH's (Gray et al, 1958) probably results in reduced anti-bacterial properties.…”

Effect of Fluoride on the Growth of Hydroxyapatite and Human Dental Enamel

“…The inhibition of den tal caries resulting from the topical applica tion of relatively high concentration of fluo ride ion has also been related to a surface coating of calcium fluoride which protects the enamel phase [Gray et al, 1958]. Other theories stress the reduced solubility of FAP in contact with the salivary fluids [McCann, 1968;Mir and Higuchi, 1969;Brown et al, 1977].…”