The Reaction of Stannous Fluoride and Hydroxyapatite F. DAVID BABCOCK, JEANA C. KING, and TRUMAN H. JORDAN* Department of Chemistry, Cornell College, Mount Vernon, Iowa 52314
Systematic investigation of the chemical reaction of a slurry of SnF2, Calo(0H)2(PO4J6, and H20 shows that products other than CaF2 are determined by the relative concentrations of the reactants. In addition to Sn20HP04, and Sn3F3P04, a previously unreported compound, Ca(SnF3)2, has been observed as a product of the reaction.
J Dent Res 57(9-10):933-938, Sept.-Oct. 1978
Introduction. Application of stannous fluoride (SnF2) has been shown to be effective in the prevention of dental caries. The mechanism by which this effect is produced, however, is still unclear. It has been suggested that the stannous fluoride reacts with the enamel to form compounds which are more resistant to decay than normal enamel. In vivo studies of the reaction of stannous fluoride and dental enamel are hampered by the small quantity of material which actually reacts. Investigation of the in vitro reaction of stannous fluoride and the main chemical component of dental enamel, hydroxyapatite (Caj0(OH)2(P04)6), should suggest a possible path for the in vivo reaction. Previous studies of the reaction of stannous fluoride and hydroxyapatite have yielded conflicting results. Although CaF2 was found in most reactions, Sn2 OHPO4 (THP) was found to be the main product of some reactions,1'2 while Sn3F3PO4 (TFP) was found to be the main product of others.3'4'5 The purpose of this study was to undertake a systematic investigation of the reaction system in order to determine what the effects of the relative concentrations of the reactants are upon the products. Received for publication July 26, 1977. Accepted for publication March 18, 1978. This investigation was supported by the National Institute of Dental Research (NIH) Research Grant No. RO1 DE 4192, NSF-URP Grant SMI 76-02998, The Sloan Foundation, and The Research Corporation. *Person to whom all correspondence should be addressed.
Materials and methods. Each reaction was carried out in a plastic beaker instead of glass to avoid the possible side reaction of the free fluoride ion with the wall of the container. De-ionized water and commercial stannous fluoride* and hydroxyapatite+ were used in all reactions. The stannous fluoride and hydroxyapatite were both powders. Samples of each were analyzed by means of x-ray powder diffraction, and the resulting powder diagrams agreed with published values.6 A standard amount of 50 milliliters of water was used in the reaction, although there were exceptions. In reactions with a large amount of solid material (e.g., reactions which would require more than 20 grams of solids for the standard 50 milliliters of water), the amount of water was reduced to 25 milliliters. The initial conditions for each reaction were chosen, and the respective amounts of each of the reactants calculated. (For example, a reaction mixture of a 1 0% SnF2 solution at a molar Sn/P ratio of 6.00 would require 50.0 ml. of H20, 5.555g of SnF2 and 0.990g. of apatite.) The two powders were weighed out in the reaction vessel, and the water was then pipetted in. A tefloncoated magnetic stirring bar was put in each beaker, and the beaker was then put in a constant temperature bath maintained at 370 ± 10 C. Each of the mixtures was allowed to react for twelve hours, after which they were removed from the bath and filtered through a sintered glass crucible. The solid products were dried at approximately 2000C. for about two hours. Analysis was carried out by means of x-ray powder diffraction. Although the procedure for running the reactions presented no major difficulties, there are two items worthy of attention. Both of these are related to the agitation of the mixture during the reaction. *Ozark-Mahoning, Tulsa, Oklahoma 74119 +Stauffer Chemical Company, New York, New York 10017
933 Downloaded from jdr.sagepub.com at UCSF LIBRARY & CKM on March 11, 2015 For personal use only. No other uses without permission.
J Dent Res September-October 19 78
BABCOCK ET AL.
934
than 10 and Sn/P less than 1), the mixture was too thick to be agitated, and no reaction took place. While the reactions themselves were not particularly troublesome, analysis of the products proved to be somewhat more difficult because it was not possible to separate the reaction products. This fact precluded the use of usual analytic methods and left x-ray powder diffraction as the sole means of analysis. No attempt was made to quantify the x-ray analyses, and the data presented in Figure 1 are qualitative and serve only to identify the reaction products. Each of the three main products was prepared in a reaction independent of the stannous fluoride-apatite system. X-ray analysis of these products provided us with unambiguous powder diagrams which were then used in analysis of the stannous fluoride-apatite reactions.
The first involves the amount of agitation given each reaction. If the agitation was too gentle, the solids settled out of suspension and did not react. If the agitation was too strong, the reactants were spun against the walls of the beaker where they collected, and again no reaction took place. The second item concerns the feasibility of certain reactions. Although the amount of stannous fluoride compared to water is expressed as a %SnF2 solution, neither the stannous fluoride nor the apatite dissolved entirely; there were solids present throughout the reaction period. In reactions for which the concentration of stannous fluoride exceeded 25%, the powders formed a heavy slurry when the water was added. Agitation of these slurries was impossible, and no reaction took place. Similarly, at higher values for %SnF2 and small values for Sn/P (e.g., %SnF2 greater
SnF2 - CaiOH)2(PQ6-H20
370 C.
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Percent SnF2 Fig. 1. - Phase Diagram of the Reaction of Stannous Fluoride with Hydroxyapatite - Each point on the diagram represents a different reaction mixture. The relative amount of SnF2 and H20 in a mixture is determined by the %SnF2. The relative amount of SnF2 and apatite is determined by the molar Sn/P ratio. The reaction product for each particular mixture is indicated by a symbol. The meanings of the various symbols are explained above. Downloaded from jdr.sagepub.com at UCSF LIBRARY & CKM on March 11, 2015 For personal use only. No other uses without permission.
STANNOUS FLUORIDEAND HYDROXYAPA TITE
Vol. 57, No. 9-1 0
935
X-RAY POWDER PATTERN Sn2(OH) PO4 U
I
I K
a
a
14
16
18
20
22
24
26
28
30
Degrees 2E3 Fig. 2.
Sn2 OHPO4 was formed by the hydrolysis of Sn2ClPO47: Sn2 OHPO4 + HCl. Sn2C I PO4 + H20 1
also produced by this reaction, and it impossible to make a pure sample of Ca(SnF3)2 by this method.
Sn3F3PO4 was formed by the reaction of stannous fluoride and phosphoric acid4: 3SnF2 + H3PO4 -e Sn3F3PO4 + 3HF.
Results.
was
IOOOC.
H20
Ca(SnF3)2 was prepared by the reaction of stannous fluoride and calcium hydroxide in water. In this reaction the conditions of the original system were mimicked. To a 10% solution of SnF2, Ca(OH)2 was added such that the tin to calcium molar ratio was approximately 6. These conditions are similar to those of reactions of stannous fluoride and apatite, which yielded Sn3F3PO4 and Ca(SnF3 )2. The mixture was agitated by magnetic stirrer, and the products were analyzed by x-ray. Unfortunately, CaF2 is
X-ray analysis showed that the aqueous reaction of stannous fluoride and hydroxyapatite has four crystalline products: CaF2; Sn2OHPO4 (THP); Sn3F3PO4 (TFP); and a previously-unreported compound, Ca(SnF3 )2. The new compound was first observed as a series of unexplained peaks in the powder pattern of a reaction expected to yield TFP. Under polarized light, only one type of crystal was visible, and it did not resemble the needle-like crystals characteristic of TFP. One of these crystals was isolated and mounted for crystallographic study. Results of this study have shown this crystal to be Ca(SnF3)2.8 It
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936
BABCOCK ET AL.
JDent Res September-October 1978
X-RAY U
POWDER
F PO
Sn
3 3
U
U
PA TERN 4
a 0 4
I
0
I
U4
U
*
s
a
a
*
*
a
a
a
14
16
18
20
22
24
26
28
30
Degrees 2 9 Fig. 3. is the first reported compound containing both calcium and tin (II). While CaF2 was formed in almost every reaction, the other compounds were formed under specific conditions (see Figure 1). THP was found in reactions with values of Sn/P less than 5, although as the concentration of SnF2 increased, the threshold value for the formation of THP decreased. TFP was found in reactions with higher values for %SnF2 and Sn/P. There were also reactions with intermediate values in which both compounds were formed. At still higher values the new compound, Ca(SnF3)2, was also formed. While THP and TFP were found together in only a few reactions, Ca(SnF3)2 was found only in conjunction with TFP and never as the sole product of the reaction. The presence of trace amounts of unreacted apatite was detected in some product mixtures. Although the presence of unreacted apatite was irregular, it was generally
limited to reactions with Sn/P values less than or equal to 5. For reactions which yielded Ca(SnF3)2, it is difficult to detect the presence of CaF2. This is due to the fact that both of these compounds have a peak at 280 in their x-ray patterns. X-ray powder diagrams of the three types of product mixtures are shown in Figures 2, 3, and 4. The major powder lines for Ca(SnF3)2 are given in Table 1. All x-ray work was done with copper radiation, X= 1.5418 A.
Discussion. This study has shqwn that there are three possible tin compoiunds that might form when stannous fluoride reacts with dental enamel. In fact, only one of these compounds, Sn3 F3P04, has been identified as a product of the reaction of stannous fluoride with whole or powdered teeth.
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Vol. 57, No. 9-10
937
STANNOUS FL UORIDE AND HYDROXYAPA TITE
X-RAY
POWDER
0
S F
and
PATTERN Ca(SnF3)2
U
U4
.1*0 I
I
a 0
14
16
18
20
22
24
26
28
30
D eres 20 Fig. 4.
Electron microprobe studies9'10 have shown that teeth treated with stannous fluoride absorb both tin and fluorine. This has been observed for treatment periods of less than 30 seconds. An infrared studyll of enamel slabs has shown that Sn3F3PO4 was formed after a two-hour treatment with a 0% stannous fluoride solution. This long reaction time is consistent with a study12 of the effect of particle size on the reaction of human dental enamel and stannous fluoride. The study has shown that the amount of Sn3F3PO4 formed is inversely proportional to the particle size. Sn3F3PO4 has also been found in a scanning electron microscope (SEM) study13 of enamel surfaces treated with stannous fluoride. In addition to Sn3F3PO4, the study also found small plate-like crystals after the surfaces had
been exposed to stannous fluoride for prolonged periods. It is quite possible that these crystals are Ca(SnF3 )2, which crystallizes as small plates.
Conclusions. The systematic study of the in vitro reaction of stannous fluoride and hydroxyapatite shows that four main products are formed. Three of these products - Sn2OHPO4, Sn3F3PO4, and Ca(SnF3)2 are formed under specific conditions, and the fourth, CaF2, is formed in most reactions. The extent to which any of these compounds is formed in the in vivo reaction of stannous fluoride and dental enamel is still a matter of active research.
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-
938
JDent Res September-October 1978
BABCOCK ET AL
TABLE 1 MAJOR PEAKS OF THE POWDER PATTERN OF Ca(SnF3)2* 20
18.8 20.8 23.3 24.5 25.2 26.0 27.1 28.3 29.0 32.9 37.8 39.1 39.7
I/lo 60 20 10 60 75 20 30 100 50 30 5 3 8 10 6 7 10
41.1 42.3 43.8 44.5 47.6 30 50.3 15 51.6 20 *The values of I/Io represent an average over several different powder diagrams. The actual values of I/lo for any particular diagram will depend on the method of preparation and packing of the samples as well as the inherent intensity of the powder line. The 29 values are for Cu radiation (1.5418 A).
Acknowledgments. The authors wish to thank Mr. Scott Fritschel and Mr. Tim Hanusa for assistance provided during the course of experimentation.
REFERENCES 1. COLLINS, R.; NEBERGALL, W.; and LANGER, H.: A Study of the Reactions of Various Tin (II) Compounds with Hydroxylapatite, J. Am. Chem. Soc., 83:3724-3725, 1961.
2. COLLINS, R.: Reactions of Tin (II) Compounds with Hydroxylapatite, Ph.D. Thesis, Indiana University, Bloomington, Indiana, 1962. 3. WEI, S. H. Y.; and FORBES, W. C.: X-ray Diffraction Analysis of Carious Dentine Treated with Stannous Fluoride, Arch. Oral Biol., 13:407416, 1968. 4. JORDAN, T. H.; WEI, S. H. Y.; BROMBERGER, S. H.; and KING, J. C.: Sn3F3PO4: The Product of the Reaction of Stannous Fluoride and Hydroxyapatite, Arch. Oral Biol., 16:241-246, 1971. 5. BERNDT, A. F.: Reaction of Stannous Fluoride with Hydroxyapatite: The Crystal Structure of Sn3PO4F3, J. Dent. Res., 51:5357, 1972. 6. Powder Diffraction File Search Manual, Joint Committee on Powder Diffraction
Standards, Swarthmore, Pennsylvania, 1974. 7. BERNDT, A. F.; SYLVESTER, J. M.; JORDAN, T. H.; and SPENADER, T. F.: Crystal Data on Tin (II) Phosphate Chloride, Sn2C1PO4,J. Appl. Cryst., 5:248-249, 1972. 8. GERRITY, D.; and JORDAN, T. H.: Reaction of SnF2 with Hydroxyapatite: Sn2OHPO4, Sn3F3PO4, Ca(SnF3)2, J. Dent Res., 56 (Special Issue B): Bs3, Abst. #7, 1977. 9. WEI, S. H. Y.; and FORBES, W. C.: Electron Microprobe Investigations of Stannous Fluoride Reactions with Enamel Surfaces, J. Dent. Res., 53:51-56, 1974. 10. HOERMANN, K. C.; KLIMA, J. E.; BIRKS, L. S.; NAGEL, D. J.; LUDWICK, W. E.; and LYON, W. H.: Tin and Fluoride Uptake in Human Enamel in situ: Electron Probe and Chemical Microanalysis, J.A.D.A., 73:13011305, 1966. 11. KRUTCHKOFF, D. J.; JORDAN, T. H.; WEI, S. H. Y.; and NORDQUIST, W. D.: Surface Characterization of the Stannous Fluoride-Enamel Interaction, Arch. Oral Biol., 17:923-930, 1972. 12. WEI, S. H. Y.; and FORBES, W. C.: Effect of Particle Size on Reactions of Powdered Sound Human Enamel and Dentine with Stannous Fluoride Solution, Arch. Oral Biol., 17:14671472, 1972. 13. WEI, S. H. Y.: Scanning Electron Microscope Study of Stannous Fluoride-Treated Enamel Surfaces, J. Dent. Res., 53:57-63, 1974.
Downloaded from jdr.sagepub.com at UCSF LIBRARY & CKM on March 11, 2015 For personal use only. No other uses without permission.
Systematic investigation of the chemical reaction of a slurry of SnF2, Calo(0H)2(PO4J6, and H20 shows that products other than CaF2 are determined by the relative concentrations of the reactants. In addition to Sn20HP04, and Sn3F3P04, a previously unreported compound, Ca(SnF3)2, has been observed as a product of the reaction.
J Dent Res 57(9-10):933-938, Sept.-Oct. 1978
Introduction. Application of stannous fluoride (SnF2) has been shown to be effective in the prevention of dental caries. The mechanism by which this effect is produced, however, is still unclear. It has been suggested that the stannous fluoride reacts with the enamel to form compounds which are more resistant to decay than normal enamel. In vivo studies of the reaction of stannous fluoride and dental enamel are hampered by the small quantity of material which actually reacts. Investigation of the in vitro reaction of stannous fluoride and the main chemical component of dental enamel, hydroxyapatite (Caj0(OH)2(P04)6), should suggest a possible path for the in vivo reaction. Previous studies of the reaction of stannous fluoride and hydroxyapatite have yielded conflicting results. Although CaF2 was found in most reactions, Sn2 OHPO4 (THP) was found to be the main product of some reactions,1'2 while Sn3F3PO4 (TFP) was found to be the main product of others.3'4'5 The purpose of this study was to undertake a systematic investigation of the reaction system in order to determine what the effects of the relative concentrations of the reactants are upon the products. Received for publication July 26, 1977. Accepted for publication March 18, 1978. This investigation was supported by the National Institute of Dental Research (NIH) Research Grant No. RO1 DE 4192, NSF-URP Grant SMI 76-02998, The Sloan Foundation, and The Research Corporation. *Person to whom all correspondence should be addressed.
Materials and methods. Each reaction was carried out in a plastic beaker instead of glass to avoid the possible side reaction of the free fluoride ion with the wall of the container. De-ionized water and commercial stannous fluoride* and hydroxyapatite+ were used in all reactions. The stannous fluoride and hydroxyapatite were both powders. Samples of each were analyzed by means of x-ray powder diffraction, and the resulting powder diagrams agreed with published values.6 A standard amount of 50 milliliters of water was used in the reaction, although there were exceptions. In reactions with a large amount of solid material (e.g., reactions which would require more than 20 grams of solids for the standard 50 milliliters of water), the amount of water was reduced to 25 milliliters. The initial conditions for each reaction were chosen, and the respective amounts of each of the reactants calculated. (For example, a reaction mixture of a 1 0% SnF2 solution at a molar Sn/P ratio of 6.00 would require 50.0 ml. of H20, 5.555g of SnF2 and 0.990g. of apatite.) The two powders were weighed out in the reaction vessel, and the water was then pipetted in. A tefloncoated magnetic stirring bar was put in each beaker, and the beaker was then put in a constant temperature bath maintained at 370 ± 10 C. Each of the mixtures was allowed to react for twelve hours, after which they were removed from the bath and filtered through a sintered glass crucible. The solid products were dried at approximately 2000C. for about two hours. Analysis was carried out by means of x-ray powder diffraction. Although the procedure for running the reactions presented no major difficulties, there are two items worthy of attention. Both of these are related to the agitation of the mixture during the reaction. *Ozark-Mahoning, Tulsa, Oklahoma 74119 +Stauffer Chemical Company, New York, New York 10017
933 Downloaded from jdr.sagepub.com at UCSF LIBRARY & CKM on March 11, 2015 For personal use only. No other uses without permission.
J Dent Res September-October 19 78
BABCOCK ET AL.
934
than 10 and Sn/P less than 1), the mixture was too thick to be agitated, and no reaction took place. While the reactions themselves were not particularly troublesome, analysis of the products proved to be somewhat more difficult because it was not possible to separate the reaction products. This fact precluded the use of usual analytic methods and left x-ray powder diffraction as the sole means of analysis. No attempt was made to quantify the x-ray analyses, and the data presented in Figure 1 are qualitative and serve only to identify the reaction products. Each of the three main products was prepared in a reaction independent of the stannous fluoride-apatite system. X-ray analysis of these products provided us with unambiguous powder diagrams which were then used in analysis of the stannous fluoride-apatite reactions.
The first involves the amount of agitation given each reaction. If the agitation was too gentle, the solids settled out of suspension and did not react. If the agitation was too strong, the reactants were spun against the walls of the beaker where they collected, and again no reaction took place. The second item concerns the feasibility of certain reactions. Although the amount of stannous fluoride compared to water is expressed as a %SnF2 solution, neither the stannous fluoride nor the apatite dissolved entirely; there were solids present throughout the reaction period. In reactions for which the concentration of stannous fluoride exceeded 25%, the powders formed a heavy slurry when the water was added. Agitation of these slurries was impossible, and no reaction took place. Similarly, at higher values for %SnF2 and small values for Sn/P (e.g., %SnF2 greater
SnF2 - CaiOH)2(PQ6-H20
370 C.
0
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Percent SnF2 Fig. 1. - Phase Diagram of the Reaction of Stannous Fluoride with Hydroxyapatite - Each point on the diagram represents a different reaction mixture. The relative amount of SnF2 and H20 in a mixture is determined by the %SnF2. The relative amount of SnF2 and apatite is determined by the molar Sn/P ratio. The reaction product for each particular mixture is indicated by a symbol. The meanings of the various symbols are explained above. Downloaded from jdr.sagepub.com at UCSF LIBRARY & CKM on March 11, 2015 For personal use only. No other uses without permission.
STANNOUS FLUORIDEAND HYDROXYAPA TITE
Vol. 57, No. 9-1 0
935
X-RAY POWDER PATTERN Sn2(OH) PO4 U
I
I K
a
a
14
16
18
20
22
24
26
28
30
Degrees 2E3 Fig. 2.
Sn2 OHPO4 was formed by the hydrolysis of Sn2ClPO47: Sn2 OHPO4 + HCl. Sn2C I PO4 + H20 1
also produced by this reaction, and it impossible to make a pure sample of Ca(SnF3)2 by this method.
Sn3F3PO4 was formed by the reaction of stannous fluoride and phosphoric acid4: 3SnF2 + H3PO4 -e Sn3F3PO4 + 3HF.
Results.
was
IOOOC.
H20
Ca(SnF3)2 was prepared by the reaction of stannous fluoride and calcium hydroxide in water. In this reaction the conditions of the original system were mimicked. To a 10% solution of SnF2, Ca(OH)2 was added such that the tin to calcium molar ratio was approximately 6. These conditions are similar to those of reactions of stannous fluoride and apatite, which yielded Sn3F3PO4 and Ca(SnF3 )2. The mixture was agitated by magnetic stirrer, and the products were analyzed by x-ray. Unfortunately, CaF2 is
X-ray analysis showed that the aqueous reaction of stannous fluoride and hydroxyapatite has four crystalline products: CaF2; Sn2OHPO4 (THP); Sn3F3PO4 (TFP); and a previously-unreported compound, Ca(SnF3 )2. The new compound was first observed as a series of unexplained peaks in the powder pattern of a reaction expected to yield TFP. Under polarized light, only one type of crystal was visible, and it did not resemble the needle-like crystals characteristic of TFP. One of these crystals was isolated and mounted for crystallographic study. Results of this study have shown this crystal to be Ca(SnF3)2.8 It
Downloaded from jdr.sagepub.com at UCSF LIBRARY & CKM on March 11, 2015 For personal use only. No other uses without permission.
936
BABCOCK ET AL.
JDent Res September-October 1978
X-RAY U
POWDER
F PO
Sn
3 3
U
U
PA TERN 4
a 0 4
I
0
I
U4
U
*
s
a
a
*
*
a
a
a
14
16
18
20
22
24
26
28
30
Degrees 2 9 Fig. 3. is the first reported compound containing both calcium and tin (II). While CaF2 was formed in almost every reaction, the other compounds were formed under specific conditions (see Figure 1). THP was found in reactions with values of Sn/P less than 5, although as the concentration of SnF2 increased, the threshold value for the formation of THP decreased. TFP was found in reactions with higher values for %SnF2 and Sn/P. There were also reactions with intermediate values in which both compounds were formed. At still higher values the new compound, Ca(SnF3)2, was also formed. While THP and TFP were found together in only a few reactions, Ca(SnF3)2 was found only in conjunction with TFP and never as the sole product of the reaction. The presence of trace amounts of unreacted apatite was detected in some product mixtures. Although the presence of unreacted apatite was irregular, it was generally
limited to reactions with Sn/P values less than or equal to 5. For reactions which yielded Ca(SnF3)2, it is difficult to detect the presence of CaF2. This is due to the fact that both of these compounds have a peak at 280 in their x-ray patterns. X-ray powder diagrams of the three types of product mixtures are shown in Figures 2, 3, and 4. The major powder lines for Ca(SnF3)2 are given in Table 1. All x-ray work was done with copper radiation, X= 1.5418 A.
Discussion. This study has shqwn that there are three possible tin compoiunds that might form when stannous fluoride reacts with dental enamel. In fact, only one of these compounds, Sn3 F3P04, has been identified as a product of the reaction of stannous fluoride with whole or powdered teeth.
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Vol. 57, No. 9-10
937
STANNOUS FL UORIDE AND HYDROXYAPA TITE
X-RAY
POWDER
0
S F
and
PATTERN Ca(SnF3)2
U
U4
.1*0 I
I
a 0
14
16
18
20
22
24
26
28
30
D eres 20 Fig. 4.
Electron microprobe studies9'10 have shown that teeth treated with stannous fluoride absorb both tin and fluorine. This has been observed for treatment periods of less than 30 seconds. An infrared studyll of enamel slabs has shown that Sn3F3PO4 was formed after a two-hour treatment with a 0% stannous fluoride solution. This long reaction time is consistent with a study12 of the effect of particle size on the reaction of human dental enamel and stannous fluoride. The study has shown that the amount of Sn3F3PO4 formed is inversely proportional to the particle size. Sn3F3PO4 has also been found in a scanning electron microscope (SEM) study13 of enamel surfaces treated with stannous fluoride. In addition to Sn3F3PO4, the study also found small plate-like crystals after the surfaces had
been exposed to stannous fluoride for prolonged periods. It is quite possible that these crystals are Ca(SnF3 )2, which crystallizes as small plates.
Conclusions. The systematic study of the in vitro reaction of stannous fluoride and hydroxyapatite shows that four main products are formed. Three of these products - Sn2OHPO4, Sn3F3PO4, and Ca(SnF3)2 are formed under specific conditions, and the fourth, CaF2, is formed in most reactions. The extent to which any of these compounds is formed in the in vivo reaction of stannous fluoride and dental enamel is still a matter of active research.
Downloaded from jdr.sagepub.com at UCSF LIBRARY & CKM on March 11, 2015 For personal use only. No other uses without permission.
-
938
JDent Res September-October 1978
BABCOCK ET AL
TABLE 1 MAJOR PEAKS OF THE POWDER PATTERN OF Ca(SnF3)2* 20
18.8 20.8 23.3 24.5 25.2 26.0 27.1 28.3 29.0 32.9 37.8 39.1 39.7
I/lo 60 20 10 60 75 20 30 100 50 30 5 3 8 10 6 7 10
41.1 42.3 43.8 44.5 47.6 30 50.3 15 51.6 20 *The values of I/Io represent an average over several different powder diagrams. The actual values of I/lo for any particular diagram will depend on the method of preparation and packing of the samples as well as the inherent intensity of the powder line. The 29 values are for Cu radiation (1.5418 A).
Acknowledgments. The authors wish to thank Mr. Scott Fritschel and Mr. Tim Hanusa for assistance provided during the course of experimentation.
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