- Email: [email protected]
The release of fluoride and other chemical species from a glass-ionomer cement
The release of fluorideand other chemical species from a glass-ionomer cement AD.Wilson, D.M.Groffman Laboratory of the Government Chemist, Department London SE1 8x/. UK
of Trade and Industry, Cornwall House, Waterloo Road,
A.T.Kuhn Faculty of Science and Technology, Harrow College of Higher Education, Northwick Park Harrow, HA1 3TP, UK (Received 18 June 1984; revised 15 April 1985)
The elution of fluoride, sodium and silica from a glass-ionomer cement was studied for 598 days. It was found that these species were still being released when the experiments were concluded, however, the rate of release was much diminished. The release of fluoride, sodium and silica was incongruent. Only fluoride associated with sodium appeared to be available for release. Keywords: Dental materials, fluoride, cement, glass-ionomer
Glass-ionomer cement is used in dentistry both for filling cavities and cementing fixed prostheses. It is translucent, with optical properties similar to enamel, adheres both to enamel and dentine and releases fluoride’. This latter property is important for it confers caries resistance on adjacent tooth material. Early studies carried out over a period of a few weeks indicated that although the release rate decreased with time, fluoride would continue to be released indefinitely. However, more recently Causton* threw doubts on this assumption and reported that the release of fluoride ceased after a few months. If this were so, then the caries resistant properties of glass-ionomer cement would be of limited duration. A study of Kuhn, Winter and Davies3 gave a contrary indication to that of Causton*. The present study sought to clarify the situation by carrying out studies on fluoride release over a prolonged period of time i.e. some 20 mnth.
EXPERIMENTAL The glass-ionomer cement, Chembond, was used in this study. This material comes as a two-component pack, consisting of a powdered fluorine-containing alumino-silicate glass and a concentrated solution of an acidic polyelectrolyte. The composition of the glass by weight is: 12.5% Si, 15.6% Al, 17.7% Ca, 1.8% Na, 31 .O% 0, 18.9% F, 2.5% P; and of the liquid also by weight: 47.5% poly(acrylic/itaconic acid), 5.0% tartaric acid in water. The cement was prepared by mixing these two components together in the ratio 2.6 : 1 .O (by mass) at 23°C and 50% relative humidity. The freshly mixed paste was cast, using a suitable mould, either as a disc (20 mm diam. 0 1985
x 1.5 mm thick) or as a cylinder (12 mm high X 6 mm diam.). A platinum wire was inserted in each specimen before curing. After curing in a sealed mould for 60 min at 37”C, each specimen was removed from the mould, trimmed and weighed. Four samples of each type of test specimen were prepared. Each specimen, suspended by the platinum wire, was placed in 50 ml of distilled water at 37°C. The water was changed periodically during the course of the study. The water changes were made at 15,45, 105,225 min; 24,48 and 72 h timed from the initial immersion of the cement disc. Thereafter the water was changed at weekly intervals until the study was concluded. All the aqueous extracts were retained and analysed for sodium and silica using Induction Coupled Plasma Spectrometry. Fluoride was determined with a fluoride electrode using a TISAB (Total Ionic Strength Adjustment Buffer). (This reagent is: 0.1% trans-1,2diaminocyclohexane-N,N,N’ acid, 8.2% acetic acid, 5.8% sodium chloride, 0.5% sodium hydroxide adjusted to pH 5.8 with acetic acid). Mean values of four results (for both discs and cylinders) were recorded.
RESULTS AND DISCUSSION Experimental results can be conveniently expressed as cumulative log-log plots of fluoride, sodium and silica against time (Figures 7 and 2). These plots closely approximate to a straight line. Discs which have a greater surface area than cylinders, release proportionally greater amounts of fluoride, sodium and silica into solution. Contrary to the findings of Causton*, fluoride was still being released after 598 d (the period of the experiment) although at a diminished
Butterworth Et Co (Publishers) Ltd. 0142-9612/85/060431-03$03.00 Biomaterials
1985, Vol 6 November
431
Release of F: AD. Wilson et al.
rate. The release of fluoride, sodium and silica from the cement specimens is incongruent. Although there are only minor amounts of Na present in the cement (1.3%) compared with major amounts of F (13.65%) and Si02 (19.3%) the amount of sodium eluted is about twice that of both fluoride and silica Results show that a considerable proportion of the sodium present in the cement is released during the period of study. This point is illustrated in Tab/e 1. Since sodium is the only cation eluted in major amounts clearly in order to preserve elactroneutrality, equivalent amounts of fluoride must be released. Thus, the release of sodium controls that of fluoride. Fluoride associated with cations otherthan sodium appears to be unavailable for release. A reasonable inference to be drawn from these results is that between a third and a half of the available fluoride is released. thus even after 20 mnth there is still a
300(
2ooC E ou L 1ooc
a
200
400 Time
600
(d)
5ooc
;” P I 1.0
I
I
IO
100
10
)
Time (d) Figure 1 Log-log plot of the cumulative leach of F, Ne and SiO, from glassionomer cement discs against time at 37°C: 0. Na; X F; 0. SiO,.
I
i
I
I
I
200
b
400 Time
I
e 0
(d)
3ooc
c” 8 w 2ooc 0 ‘Z 1.0
10
100
1c
Time Cd) Figure 2 Log-log plot of the cumuletive leach of F, Ne and SiO, from glassionomar cylinders against time at 37°C: q. Na; X F; 0, SiO,
Table 1
432
Percentage element eked
from cement specimens (598 dj
Element
Discs
Cylinders
Na F Si02
47.0 2.3 2.2
32.0 1.1 1.1
Biomaterials
1985, Vol6 November
1000
i C Time
(d)
Figure 3 ~plication of Equation I to release of 3 separste specks, from a glass-ionomer cement monitored simu~affeoos~ over 598 d. (a) F; (b) Ne: (c) SiO,.
Release of E RD. Wilson et al.
reservoir of available fluoride. It would seem, ultimately, that when all the sodium in the cement is eluted, some 4.5% of the total fluoride present will be released. Clearly, if a greater fluoride release is demanded then ionomer cements will have to be formulated with glasses containing greater amounts of sodium. The leaching of soluble material from glass-ionomer and dental silicate cements has been reviewed in detail
Tab/e 2 Species
a
b
y = const + at” + bT
where y is the total cumulative amount of a species released in time t and a and bare constants. The goodness-of-fit for F, Na and SiOz: released from discs and cylinders is good (Table 2, Figure 3).
Goodness-of-fit (%)
1
From cement discs F Na SiO,
- 84.2 - 62.9 -220.9
From cement cylinders F - 24.8 Na - 21.2 SiO, - 64.6
+196.5 +552.5 i-273.6
- 2.317 -11.759 - 2.944
99.92 99.92 99.62
+ 64.3 +219.5 + 96.6
-
99.52 99.94 99.96
2
3 0.754 3.817 1.136
(1)
REFERENCES
Elution values for constants in Equation 1 Constant
elsewhere4, where it has been shown that the release with time can be described by the equation:
4
Wilson, A.D. and Presser. H.J., Aluminosllicate dental cements, in Biocompatibility of Dental Materials: Biocompatibility of Dental Restorative Materials (Eds DC. Smith and D.F. Williams), Vol. 3. CRC Press, Boca Raton, 1982, Ch. 3 Causton, B.E.. The physico-mechanical consequences of exposing glass-ionomer cements to water during setting, Biomateriak 198 1, 2, 112-115 Kuhn, A.T., Winter, G.B. and Davies, EM., Dissolution and fluoride release from silicate and glass-ionomer cement, J. Dent. Res. 1982, 6, 555 (IADA, Abs. no. 173). Kuhn. A.T. and Wilson, A.D.. The dissolution mechanisms of silicate and glass-ionomer cements, Biomaterials
Biomaterials
1985,
6, 378-382
1985. Vol6 November
433
of Trade and Industry, Cornwall House, Waterloo Road,
A.T.Kuhn Faculty of Science and Technology, Harrow College of Higher Education, Northwick Park Harrow, HA1 3TP, UK (Received 18 June 1984; revised 15 April 1985)
The elution of fluoride, sodium and silica from a glass-ionomer cement was studied for 598 days. It was found that these species were still being released when the experiments were concluded, however, the rate of release was much diminished. The release of fluoride, sodium and silica was incongruent. Only fluoride associated with sodium appeared to be available for release. Keywords: Dental materials, fluoride, cement, glass-ionomer
Glass-ionomer cement is used in dentistry both for filling cavities and cementing fixed prostheses. It is translucent, with optical properties similar to enamel, adheres both to enamel and dentine and releases fluoride’. This latter property is important for it confers caries resistance on adjacent tooth material. Early studies carried out over a period of a few weeks indicated that although the release rate decreased with time, fluoride would continue to be released indefinitely. However, more recently Causton* threw doubts on this assumption and reported that the release of fluoride ceased after a few months. If this were so, then the caries resistant properties of glass-ionomer cement would be of limited duration. A study of Kuhn, Winter and Davies3 gave a contrary indication to that of Causton*. The present study sought to clarify the situation by carrying out studies on fluoride release over a prolonged period of time i.e. some 20 mnth.
EXPERIMENTAL The glass-ionomer cement, Chembond, was used in this study. This material comes as a two-component pack, consisting of a powdered fluorine-containing alumino-silicate glass and a concentrated solution of an acidic polyelectrolyte. The composition of the glass by weight is: 12.5% Si, 15.6% Al, 17.7% Ca, 1.8% Na, 31 .O% 0, 18.9% F, 2.5% P; and of the liquid also by weight: 47.5% poly(acrylic/itaconic acid), 5.0% tartaric acid in water. The cement was prepared by mixing these two components together in the ratio 2.6 : 1 .O (by mass) at 23°C and 50% relative humidity. The freshly mixed paste was cast, using a suitable mould, either as a disc (20 mm diam. 0 1985
x 1.5 mm thick) or as a cylinder (12 mm high X 6 mm diam.). A platinum wire was inserted in each specimen before curing. After curing in a sealed mould for 60 min at 37”C, each specimen was removed from the mould, trimmed and weighed. Four samples of each type of test specimen were prepared. Each specimen, suspended by the platinum wire, was placed in 50 ml of distilled water at 37°C. The water was changed periodically during the course of the study. The water changes were made at 15,45, 105,225 min; 24,48 and 72 h timed from the initial immersion of the cement disc. Thereafter the water was changed at weekly intervals until the study was concluded. All the aqueous extracts were retained and analysed for sodium and silica using Induction Coupled Plasma Spectrometry. Fluoride was determined with a fluoride electrode using a TISAB (Total Ionic Strength Adjustment Buffer). (This reagent is: 0.1% trans-1,2diaminocyclohexane-N,N,N’ acid, 8.2% acetic acid, 5.8% sodium chloride, 0.5% sodium hydroxide adjusted to pH 5.8 with acetic acid). Mean values of four results (for both discs and cylinders) were recorded.
RESULTS AND DISCUSSION Experimental results can be conveniently expressed as cumulative log-log plots of fluoride, sodium and silica against time (Figures 7 and 2). These plots closely approximate to a straight line. Discs which have a greater surface area than cylinders, release proportionally greater amounts of fluoride, sodium and silica into solution. Contrary to the findings of Causton*, fluoride was still being released after 598 d (the period of the experiment) although at a diminished
Butterworth Et Co (Publishers) Ltd. 0142-9612/85/060431-03$03.00 Biomaterials
1985, Vol 6 November
431
Release of F: AD. Wilson et al.
rate. The release of fluoride, sodium and silica from the cement specimens is incongruent. Although there are only minor amounts of Na present in the cement (1.3%) compared with major amounts of F (13.65%) and Si02 (19.3%) the amount of sodium eluted is about twice that of both fluoride and silica Results show that a considerable proportion of the sodium present in the cement is released during the period of study. This point is illustrated in Tab/e 1. Since sodium is the only cation eluted in major amounts clearly in order to preserve elactroneutrality, equivalent amounts of fluoride must be released. Thus, the release of sodium controls that of fluoride. Fluoride associated with cations otherthan sodium appears to be unavailable for release. A reasonable inference to be drawn from these results is that between a third and a half of the available fluoride is released. thus even after 20 mnth there is still a
300(
2ooC E ou L 1ooc
a
200
400 Time
600
(d)
5ooc
;” P I 1.0
I
I
IO
100
10
)
Time (d) Figure 1 Log-log plot of the cumulative leach of F, Ne and SiO, from glassionomer cement discs against time at 37°C: 0. Na; X F; 0. SiO,.
I
i
I
I
I
200
b
400 Time
I
e 0
(d)
3ooc
c” 8 w 2ooc 0 ‘Z 1.0
10
100
1c
Time Cd) Figure 2 Log-log plot of the cumuletive leach of F, Ne and SiO, from glassionomar cylinders against time at 37°C: q. Na; X F; 0, SiO,
Table 1
432
Percentage element eked
from cement specimens (598 dj
Element
Discs
Cylinders
Na F Si02
47.0 2.3 2.2
32.0 1.1 1.1
Biomaterials
1985, Vol6 November
1000
i C Time
(d)
Figure 3 ~plication of Equation I to release of 3 separste specks, from a glass-ionomer cement monitored simu~affeoos~ over 598 d. (a) F; (b) Ne: (c) SiO,.
Release of E RD. Wilson et al.
reservoir of available fluoride. It would seem, ultimately, that when all the sodium in the cement is eluted, some 4.5% of the total fluoride present will be released. Clearly, if a greater fluoride release is demanded then ionomer cements will have to be formulated with glasses containing greater amounts of sodium. The leaching of soluble material from glass-ionomer and dental silicate cements has been reviewed in detail
Tab/e 2 Species
a
b
y = const + at” + bT
where y is the total cumulative amount of a species released in time t and a and bare constants. The goodness-of-fit for F, Na and SiOz: released from discs and cylinders is good (Table 2, Figure 3).
Goodness-of-fit (%)
1
From cement discs F Na SiO,
- 84.2 - 62.9 -220.9
From cement cylinders F - 24.8 Na - 21.2 SiO, - 64.6
+196.5 +552.5 i-273.6
- 2.317 -11.759 - 2.944
99.92 99.92 99.62
+ 64.3 +219.5 + 96.6
-
99.52 99.94 99.96
2
3 0.754 3.817 1.136
(1)
REFERENCES
Elution values for constants in Equation 1 Constant
elsewhere4, where it has been shown that the release with time can be described by the equation:
4
Wilson, A.D. and Presser. H.J., Aluminosllicate dental cements, in Biocompatibility of Dental Materials: Biocompatibility of Dental Restorative Materials (Eds DC. Smith and D.F. Williams), Vol. 3. CRC Press, Boca Raton, 1982, Ch. 3 Causton, B.E.. The physico-mechanical consequences of exposing glass-ionomer cements to water during setting, Biomateriak 198 1, 2, 112-115 Kuhn, A.T., Winter, G.B. and Davies, EM., Dissolution and fluoride release from silicate and glass-ionomer cement, J. Dent. Res. 1982, 6, 555 (IADA, Abs. no. 173). Kuhn. A.T. and Wilson, A.D.. The dissolution mechanisms of silicate and glass-ionomer cements, Biomaterials
Biomaterials
1985,
6, 378-382
1985. Vol6 November
433