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Characterization of glass ionomer filling materials
Characterization of glass ionomer filling materials
G. Oilo NIOM - Scandinavian Institute of Dental Materials, Oslo, Norway
Oilo G. Characterization of glass ionomer filling materials. Dent Mater 1988: 4: 129-133. Abstract - Six glass ionomer cements, including a glass cermet cement, were compared to a silicate cement with regard to compressive and flexural strength, working and setting time as well as solubility. The structure of the cement powder particles was studied by scanning electron microscopy (SEM). The results showed great variations among the different glass ionomer cements in properties measured. The working time and solubility seem to be a problem for some materials. The silicate cement showed better compressive strength, working and setting times than the glass ionomers. The glass cermet cement showed high values for mechanical properties, and relatively low solubility. The SEM study of the cement powder showed that irregular silver particles partly covered by a layer of glass had been added to the glass cermet cement.
The use of glass ionomer cements as filling materials is increasing, both as a substitute for the old silicate cement and for an extended range of use. A number of products have been marketed since the first cement of this type, DeTrey A S P A (Amalgamated Dental) was introduced in 1972 (1). The newer products have other physical, chemical and esthetic characteristics than the first marketed cement, but there are great variations both in composition and properties among the different cements (2). A new type of glass ionomer cements, the so-called glass cermet cement, has been introduced recently (3). The powder contains glass-covered silver particles. Previous investigations have shown that the incorporation of metal fillers in the glass ionomer cements can improve several mechanical properties, especially the flexural strength (4). The aim of this investigation was to compare some of the physical/chemical properties of glass ionomer filling materials with those of traditional silicate cement. Material a n d m e t h o d s
The materials used in this study are shown in Table 1. Hand-spatulated cements were mixed according to the manufacturer's instructions, but on glass slabs (150•215 mm) at room temperature (23+1~ The powder/
liquid ratios are given in Table 1. The capsulated cements were mixed using a Silamat (Ivoclar, Liechtenstein) for 10 s according to the manufacturer's instructions. The powder particles of the cements were studied in a scanning electron microscope (JEOL JSM-840, Jeol, Tokyo, Japan) both by secondary electron image of gold-coated particles and, for two cements, by the use of a back-scattered electron image of embedded and polished particles. A n analysis of the particle composition was made by energy dispersive analysing equipment (LINK 860 serie 2, LINK Systems, High Wycombe, England). The compressive strength of each cement was measured by the use of cylindrical specimens, 6 mm in length and 4 mm in diameter in a universal testing machine (Instron 1121, Instron Ltd,
Key words: dental materials, silicate cement, glass cermet cement, compressive strength, flexural strength, solubility, working time, setting time. Dr. Gudbrand Oilo, NIOM - Scandinavian Institute of Dental Materials, Forskningsveien 1, 0371 Oslo 3, Norway. Received October 21, 1986; accepted June 13, 1987.
High Wycombe, England) with a crosshead speed of 0.75 mm/min. The number of specimens for each cement is given in Fig. 1. All cements were tested after 24 h storage in water at 37~ The flexural strength of the cements was measured by three-point bending of rectangular beams, 2 x 2 mm in cross section and 25 mm long, placed in a special jig with a distance of 20 mm between the lower supporting points. The jig was mounted in the universal tensile testing machine and loaded with a crosshead speed of 0.75 + 0.25 mm/ rain. The number of specimens tested for each cement is indicated in Fig. 2. All cements were tested after 24 h storage in water at 37~ The working time of the cements was measured with a plane, cylindrical indentor (mass 28 g, diameter 2 mm) as described in the newly published inter-
Table 1. Cements used in this study. Name
Code Producer
Batch no.
P/L ratio
DeTrey Chemfil II
CH
85/08
6.8:1
GC Fuji Ionomner Type II-F Kctac-Bond
FJ
280541
1.8:1
M310
3.4:1
Ketac-Fil
KF
Capsulated
Ketac-Silber
KS
NO23 NO65 M345
DeTrey Super Syntrex
SC
P:800909
3.7:1
KB
DeTrey/Dentsply Weybridge, Surrey, UK G-C Dental Ind. Corp. Tokyo, Japan ESPE GmbH Seefeld/Oberbay, FRG ESPE GmbH Seefeld/Oberbay, FRG ESPE GmbH Seefeld/Oberbay, FRG AD International Ltd Weybridge, Surrey, UK
Capsulated
130
Oilo TIME
MPa
CONDUCTANCE S. m-l,kg -1
min, 300
4 30
~-, 200
:Z
,-,
I
100
CH
FJ
KB
KF
KS
SC
MPa 40
30,
1 0 84
CH
20
,NR
Fig. 1. Compressive strength of various glass ionomer cements and a silicate cement (SC). Number of bottom of bars indicates number of specimens tested. Vertical line on the top of the bar indicates standard deviation. For coding below bars, see Table 1.
20
iiili
Iii FJ
KB
KF
KS
15
9
16 I
CH
FJ
KB
3 KF
KS
SC
Fig. 4. Setting time of various glass ionomer cements and a silicate cement. Coding as in Fig. 1. Vertical line indicates maximum value.
n a t i o n a l s t a n d a r d for glass polyalken o a t e (glass i o n o m e r ) c e m e n t s , I S O 7489-1986 ( E ) (5). T h e i n d e n t o r was placed o n the c e m e n t at 10 s intervals until the n e e d l e failed to m a k e a complete circular i n d e n t a t i o n . T h e n u m b e r of tests p e r f o r m e d for e a c h c e m e n t is indicated in Fig. 3. T h e setting time was r e c o r d e d in a similar m a n n e r with a p l a n e cylindrical i n d e n t o r (mass 400 g, d i a m e t e r 1 m m ) . T h e c e m e n t was p l a c e d in a m e t a l m o u l d c o n d i t i o n e d at 37 + 1~ as described in ISO 7489 (5), a n d t h e tests were p e r f o r m e d at the s a m e t e m p e r ature, m a k i n g i n d e n t a t i o n s at 30 s intervals. T h e solubility of t h e c e m e n t s was c o m p a r e d by i m m e r s i o n of two circular
O R ! CH
min. 4
KF
KS
SC
T h e results f r o m t h e c o m p r e s s i o n tests are s h o w n in Fig. 1. T h e s t r e n g t h of the silicate c e m e n t (SC) was significantly g r e a t e r t h a n t h a t of t h e glass i o n o m e r c e m e n t s . T h e difference b e t w e e n K B
TIME
KB
KS
Results
nomer cements and a silicate cement (SC). Coding as in Fig. 1. Vertical line: standard deviation.
FJ
KF
disks 20 m m in d i a m e t e r a n d 1 m m thick in distilled w a t e r 1 h after start of mixing. T h e rate of dissolution was quantified by m e a s u r i n g t h e i n c r e a s e in conductivity of t h e w a t e r b a t h a f t e r 23 h storage at 37~ (6,7). T h e differences in t h e various properties of t h e c e m e n t s w e r e t e s t e d for significance by a S t u d e n t ' s t test.
Fig. 2. Flexural strength of various glass io-
CH
KB
Fig. 5. Solubility of glass ionomer cements and a silicate cement (SC) measured by conductometric method. Coding as in Fig. 1. Vertical line indicates standard deviation.
SC
SC
Fig. 3. Working time of various glass ionomer cements and a silicate cement. Coding as in Fig. 1. Vertical line indicates maximum value.
FJ
Fig. 6. Powder particles of cement CH. White line = 10 ~tm.
Glass ionomer filling materials Fig. 7. Powder particles of cement KE White line = 10 ~tm.
Fig. 8. Powder particles of cement FJ. White line = 10 ~tm.
Fig. 9. Powder particles of cement KS. White line = 10 Ixm.
131
132
0i~ and polished powders from cements KF and KS are shown in Figs. 10 and 11. The rounded particles in cement KS (Fig. 11) were identified by E D A X analyses as having an irregular metal core of pure silver partly covered with calcium aluminosilicate glass. A small amount of Ti was also identified in cement KS. The bright particles in cement KF (Fig. 10) were identified as a cadmium-sulfide compound.
Discussion
Fig. 10. Back-scattered image of powder particles from cement KF (x 850). White line = 10 p,m.
and FJ was significant as well as the difference between cement FJ and the three other cements CH, K F and KS. The flexural strength of the various cements varied considerably (Fig. 2). Cement CH showed the highest mean flexural strength, but it was not statistically different from that of cement KS. The differences between these two cements and the cements SC, KF, FJ and KB were all statistically significant (p<0.0l). The results from the working time tests are shown in Fig. 3. Cement CH showed the shortest working time, and the silicate cement (SC) had the longest working time. The recorded setting times exhibited the same trend as for working time, i.e. cement CH had the shortest and cement SC the longest setting time (Fig. 4). It was observed that the time lapse from end of working time to the recorded setting time was short for some cements, especially cements KF and KS. The solubility of the various cements measured according to the conductometric method is shown in Fig. 5. Cement FJ showed a significantly higher solubility than all other cements (p<0.0f). The difference between the silicate cement SC and the glass ionomers CH, KF and KS, as well as the difference between K F and KS were significant (p<0.01). Micrographs from the microscopic inspection of the powders from cements CH, FJ, K F and KS are shown in Figs. 6-9. Both CH and K F showed a
glass flit with a varying particle size. The large sharp-edged particles and the small, more rounded ones (Figs. 6 and 7) were identified by E D A X as an aluminosilicate glass. The CH powder contained Na and Ca, whereas no Na was found in the K F particles. Cement FJ showed more rounded and porous type of particles. Even the smallest particles (Fig. 8) were all identified as an Na-Ca-aluminosilicate glass. Cement KS showed a mixture of a glass frit and some rounded particles (Fig. 9). The back-scattered images of embedded
The results of this study demonstrate a marked variation in properties among the different brands of glass ionomer fitlin~ materials. Cement KB is marketed as an etchable base material for composite fillings, and thus can not be directly compared to the other materials marketed as regular filling materials. However, according to the recommendations for use of this material, it may be exposed to the oral cavity (8). The compressive and flexural strength values reported in this study are higher than those reported in a previous study (2). The ranking of the materials is approximately the same, and the difference in measured properties may be explained by differences in method, and a major factor might be the time for the first exposure to water (2). A different ranking has also been reported (9), but can be explained by differences in powder/liquid ratio. This study also demonstrates that the in-
Fig. 11. Back-scattered image of powder particles from cement KS (• 850). White line = 10 ~tm.
Glass ionomer filling materials
crease in strength with time does not change the ranking of the materials. The working time r e c o r d e d for the water-hardening material C H is comparable to that r e p o r t e d by Atkinson & Pearson (10). T h e measured setting time, however, is considerably reduced in the present study. It may be speculated that s o m e of this difference is related to the problems of measuring the viscosity of such cements by methods that simultaneously add an oscillating motion to the material (11). The dissolving of silicate and glass i o n o m e r cements is a complex phenomenon, but the mechanisms seem to be similar for both cements (12). A correlation has b e e n shown b e t w e e n increased conductance and amount of dissolved substances from the silicate cement (6), but not for the glass ionomer cements. A direct comparison of the solubility b e t w e e n these two types of cements based on this m e t h o d may therefore be misleading. It is assumed, however, that the m e t h o d can give a reliable ranking of the glass i o n o m e r cements, except possibly for the cement KS. It is not known to what extent the added metals silver and tita-
nium can change the conductance in the described test. A p a r t from the reduced solubility, the addition of silver particles to the glass i o n o m e r has not changed the measured properties markedly. A n increased flexural strength is observed, but another c e m e n t (CH) without added metal has the same high flexural strength. The titanium identified in cement KS is probably titanium oxide added for color correction, and the cadmium sulfude identified in K F is added for fluorescence.
References 1. Wilson AD, Kent BE. A new translucent cement for dentistry. The glass ionomer cement. Br Dent J 1977: 132: 133-5. 2. Kullmann W. Werkstoffkundliche Eigenschaften yon Glasionomer-Zementen im Vergleich zu konventionellen Materialen. I. Untersuchungen zur Festigkeit. Dtsch Zahniirztl Z 1986: 41: 302-7. 3. McLean JW. Alternatives to amalgam alloys. Br Dent J 1984: 157: 432-5. 4. Wilson AD, Prosser HJ. A survey of
133
inorganic and polyelectrolyte cements. Br Dent J 1984: 157: 449-54. 5. International Organization for Standardization, ISO 7489-1986. Dental glass polyalkenoate cements. Geneva, Switzerland: ISO. 6. Prosser HJ, Groffman DM, Wilson AD. A sensitive conductimetric method for measuring the material initially waterleached from dental cements. 3. Dental silicate cements. ] Dent 1982: 10: 113-20. 7. International Organization for Standardization, ISO 4104-1984. Dental zinc polycarboxylate cements. Geneva, Switzerland: ISO. 8. McLean JW, Prosser HJ, Wilson AD. The use of glass-ionomer cements in bonding composite resins to dentine. Br Dent J 1985: 158: 410-14. 9. Wong Th CC, Bryant RW. Glass ionomer cements: dispensing and strength. Aust Dent J 1985: 30: 336--40. 10. Atkinson AS, Pearson GJ. The evaluation of glass-ionomer cements. Br Dent J 1985: 159: 335-7. 11. Smith D e . Dental cements. Current status and future prospects. Dent Clin North A m 1983: 6: 763-91. 12. Kuhn AT, Wilson AD. The dissolution mechanisms of silicate and glass-ionmer dental cements. Biomaterials 1985: 6: 378-82.
G. Oilo NIOM - Scandinavian Institute of Dental Materials, Oslo, Norway
Oilo G. Characterization of glass ionomer filling materials. Dent Mater 1988: 4: 129-133. Abstract - Six glass ionomer cements, including a glass cermet cement, were compared to a silicate cement with regard to compressive and flexural strength, working and setting time as well as solubility. The structure of the cement powder particles was studied by scanning electron microscopy (SEM). The results showed great variations among the different glass ionomer cements in properties measured. The working time and solubility seem to be a problem for some materials. The silicate cement showed better compressive strength, working and setting times than the glass ionomers. The glass cermet cement showed high values for mechanical properties, and relatively low solubility. The SEM study of the cement powder showed that irregular silver particles partly covered by a layer of glass had been added to the glass cermet cement.
The use of glass ionomer cements as filling materials is increasing, both as a substitute for the old silicate cement and for an extended range of use. A number of products have been marketed since the first cement of this type, DeTrey A S P A (Amalgamated Dental) was introduced in 1972 (1). The newer products have other physical, chemical and esthetic characteristics than the first marketed cement, but there are great variations both in composition and properties among the different cements (2). A new type of glass ionomer cements, the so-called glass cermet cement, has been introduced recently (3). The powder contains glass-covered silver particles. Previous investigations have shown that the incorporation of metal fillers in the glass ionomer cements can improve several mechanical properties, especially the flexural strength (4). The aim of this investigation was to compare some of the physical/chemical properties of glass ionomer filling materials with those of traditional silicate cement. Material a n d m e t h o d s
The materials used in this study are shown in Table 1. Hand-spatulated cements were mixed according to the manufacturer's instructions, but on glass slabs (150•215 mm) at room temperature (23+1~ The powder/
liquid ratios are given in Table 1. The capsulated cements were mixed using a Silamat (Ivoclar, Liechtenstein) for 10 s according to the manufacturer's instructions. The powder particles of the cements were studied in a scanning electron microscope (JEOL JSM-840, Jeol, Tokyo, Japan) both by secondary electron image of gold-coated particles and, for two cements, by the use of a back-scattered electron image of embedded and polished particles. A n analysis of the particle composition was made by energy dispersive analysing equipment (LINK 860 serie 2, LINK Systems, High Wycombe, England). The compressive strength of each cement was measured by the use of cylindrical specimens, 6 mm in length and 4 mm in diameter in a universal testing machine (Instron 1121, Instron Ltd,
Key words: dental materials, silicate cement, glass cermet cement, compressive strength, flexural strength, solubility, working time, setting time. Dr. Gudbrand Oilo, NIOM - Scandinavian Institute of Dental Materials, Forskningsveien 1, 0371 Oslo 3, Norway. Received October 21, 1986; accepted June 13, 1987.
High Wycombe, England) with a crosshead speed of 0.75 mm/min. The number of specimens for each cement is given in Fig. 1. All cements were tested after 24 h storage in water at 37~ The flexural strength of the cements was measured by three-point bending of rectangular beams, 2 x 2 mm in cross section and 25 mm long, placed in a special jig with a distance of 20 mm between the lower supporting points. The jig was mounted in the universal tensile testing machine and loaded with a crosshead speed of 0.75 + 0.25 mm/ rain. The number of specimens tested for each cement is indicated in Fig. 2. All cements were tested after 24 h storage in water at 37~ The working time of the cements was measured with a plane, cylindrical indentor (mass 28 g, diameter 2 mm) as described in the newly published inter-
Table 1. Cements used in this study. Name
Code Producer
Batch no.
P/L ratio
DeTrey Chemfil II
CH
85/08
6.8:1
GC Fuji Ionomner Type II-F Kctac-Bond
FJ
280541
1.8:1
M310
3.4:1
Ketac-Fil
KF
Capsulated
Ketac-Silber
KS
NO23 NO65 M345
DeTrey Super Syntrex
SC
P:800909
3.7:1
KB
DeTrey/Dentsply Weybridge, Surrey, UK G-C Dental Ind. Corp. Tokyo, Japan ESPE GmbH Seefeld/Oberbay, FRG ESPE GmbH Seefeld/Oberbay, FRG ESPE GmbH Seefeld/Oberbay, FRG AD International Ltd Weybridge, Surrey, UK
Capsulated
130
Oilo TIME
MPa
CONDUCTANCE S. m-l,kg -1
min, 300
4 30
~-, 200
:Z
,-,
I
100
CH
FJ
KB
KF
KS
SC
MPa 40
30,
1 0 84
CH
20
,NR
Fig. 1. Compressive strength of various glass ionomer cements and a silicate cement (SC). Number of bottom of bars indicates number of specimens tested. Vertical line on the top of the bar indicates standard deviation. For coding below bars, see Table 1.
20
iiili
Iii FJ
KB
KF
KS
15
9
16 I
CH
FJ
KB
3 KF
KS
SC
Fig. 4. Setting time of various glass ionomer cements and a silicate cement. Coding as in Fig. 1. Vertical line indicates maximum value.
n a t i o n a l s t a n d a r d for glass polyalken o a t e (glass i o n o m e r ) c e m e n t s , I S O 7489-1986 ( E ) (5). T h e i n d e n t o r was placed o n the c e m e n t at 10 s intervals until the n e e d l e failed to m a k e a complete circular i n d e n t a t i o n . T h e n u m b e r of tests p e r f o r m e d for e a c h c e m e n t is indicated in Fig. 3. T h e setting time was r e c o r d e d in a similar m a n n e r with a p l a n e cylindrical i n d e n t o r (mass 400 g, d i a m e t e r 1 m m ) . T h e c e m e n t was p l a c e d in a m e t a l m o u l d c o n d i t i o n e d at 37 + 1~ as described in ISO 7489 (5), a n d t h e tests were p e r f o r m e d at the s a m e t e m p e r ature, m a k i n g i n d e n t a t i o n s at 30 s intervals. T h e solubility of t h e c e m e n t s was c o m p a r e d by i m m e r s i o n of two circular
O R ! CH
min. 4
KF
KS
SC
T h e results f r o m t h e c o m p r e s s i o n tests are s h o w n in Fig. 1. T h e s t r e n g t h of the silicate c e m e n t (SC) was significantly g r e a t e r t h a n t h a t of t h e glass i o n o m e r c e m e n t s . T h e difference b e t w e e n K B
TIME
KB
KS
Results
nomer cements and a silicate cement (SC). Coding as in Fig. 1. Vertical line: standard deviation.
FJ
KF
disks 20 m m in d i a m e t e r a n d 1 m m thick in distilled w a t e r 1 h after start of mixing. T h e rate of dissolution was quantified by m e a s u r i n g t h e i n c r e a s e in conductivity of t h e w a t e r b a t h a f t e r 23 h storage at 37~ (6,7). T h e differences in t h e various properties of t h e c e m e n t s w e r e t e s t e d for significance by a S t u d e n t ' s t test.
Fig. 2. Flexural strength of various glass io-
CH
KB
Fig. 5. Solubility of glass ionomer cements and a silicate cement (SC) measured by conductometric method. Coding as in Fig. 1. Vertical line indicates standard deviation.
SC
SC
Fig. 3. Working time of various glass ionomer cements and a silicate cement. Coding as in Fig. 1. Vertical line indicates maximum value.
FJ
Fig. 6. Powder particles of cement CH. White line = 10 ~tm.
Glass ionomer filling materials Fig. 7. Powder particles of cement KE White line = 10 ~tm.
Fig. 8. Powder particles of cement FJ. White line = 10 ~tm.
Fig. 9. Powder particles of cement KS. White line = 10 Ixm.
131
132
0i~ and polished powders from cements KF and KS are shown in Figs. 10 and 11. The rounded particles in cement KS (Fig. 11) were identified by E D A X analyses as having an irregular metal core of pure silver partly covered with calcium aluminosilicate glass. A small amount of Ti was also identified in cement KS. The bright particles in cement KF (Fig. 10) were identified as a cadmium-sulfide compound.
Discussion
Fig. 10. Back-scattered image of powder particles from cement KF (x 850). White line = 10 p,m.
and FJ was significant as well as the difference between cement FJ and the three other cements CH, K F and KS. The flexural strength of the various cements varied considerably (Fig. 2). Cement CH showed the highest mean flexural strength, but it was not statistically different from that of cement KS. The differences between these two cements and the cements SC, KF, FJ and KB were all statistically significant (p<0.0l). The results from the working time tests are shown in Fig. 3. Cement CH showed the shortest working time, and the silicate cement (SC) had the longest working time. The recorded setting times exhibited the same trend as for working time, i.e. cement CH had the shortest and cement SC the longest setting time (Fig. 4). It was observed that the time lapse from end of working time to the recorded setting time was short for some cements, especially cements KF and KS. The solubility of the various cements measured according to the conductometric method is shown in Fig. 5. Cement FJ showed a significantly higher solubility than all other cements (p<0.0f). The difference between the silicate cement SC and the glass ionomers CH, KF and KS, as well as the difference between K F and KS were significant (p<0.01). Micrographs from the microscopic inspection of the powders from cements CH, FJ, K F and KS are shown in Figs. 6-9. Both CH and K F showed a
glass flit with a varying particle size. The large sharp-edged particles and the small, more rounded ones (Figs. 6 and 7) were identified by E D A X as an aluminosilicate glass. The CH powder contained Na and Ca, whereas no Na was found in the K F particles. Cement FJ showed more rounded and porous type of particles. Even the smallest particles (Fig. 8) were all identified as an Na-Ca-aluminosilicate glass. Cement KS showed a mixture of a glass frit and some rounded particles (Fig. 9). The back-scattered images of embedded
The results of this study demonstrate a marked variation in properties among the different brands of glass ionomer fitlin~ materials. Cement KB is marketed as an etchable base material for composite fillings, and thus can not be directly compared to the other materials marketed as regular filling materials. However, according to the recommendations for use of this material, it may be exposed to the oral cavity (8). The compressive and flexural strength values reported in this study are higher than those reported in a previous study (2). The ranking of the materials is approximately the same, and the difference in measured properties may be explained by differences in method, and a major factor might be the time for the first exposure to water (2). A different ranking has also been reported (9), but can be explained by differences in powder/liquid ratio. This study also demonstrates that the in-
Fig. 11. Back-scattered image of powder particles from cement KS (• 850). White line = 10 ~tm.
Glass ionomer filling materials
crease in strength with time does not change the ranking of the materials. The working time r e c o r d e d for the water-hardening material C H is comparable to that r e p o r t e d by Atkinson & Pearson (10). T h e measured setting time, however, is considerably reduced in the present study. It may be speculated that s o m e of this difference is related to the problems of measuring the viscosity of such cements by methods that simultaneously add an oscillating motion to the material (11). The dissolving of silicate and glass i o n o m e r cements is a complex phenomenon, but the mechanisms seem to be similar for both cements (12). A correlation has b e e n shown b e t w e e n increased conductance and amount of dissolved substances from the silicate cement (6), but not for the glass ionomer cements. A direct comparison of the solubility b e t w e e n these two types of cements based on this m e t h o d may therefore be misleading. It is assumed, however, that the m e t h o d can give a reliable ranking of the glass i o n o m e r cements, except possibly for the cement KS. It is not known to what extent the added metals silver and tita-
nium can change the conductance in the described test. A p a r t from the reduced solubility, the addition of silver particles to the glass i o n o m e r has not changed the measured properties markedly. A n increased flexural strength is observed, but another c e m e n t (CH) without added metal has the same high flexural strength. The titanium identified in cement KS is probably titanium oxide added for color correction, and the cadmium sulfude identified in K F is added for fluorescence.
References 1. Wilson AD, Kent BE. A new translucent cement for dentistry. The glass ionomer cement. Br Dent J 1977: 132: 133-5. 2. Kullmann W. Werkstoffkundliche Eigenschaften yon Glasionomer-Zementen im Vergleich zu konventionellen Materialen. I. Untersuchungen zur Festigkeit. Dtsch Zahniirztl Z 1986: 41: 302-7. 3. McLean JW. Alternatives to amalgam alloys. Br Dent J 1984: 157: 432-5. 4. Wilson AD, Prosser HJ. A survey of
133
inorganic and polyelectrolyte cements. Br Dent J 1984: 157: 449-54. 5. International Organization for Standardization, ISO 7489-1986. Dental glass polyalkenoate cements. Geneva, Switzerland: ISO. 6. Prosser HJ, Groffman DM, Wilson AD. A sensitive conductimetric method for measuring the material initially waterleached from dental cements. 3. Dental silicate cements. ] Dent 1982: 10: 113-20. 7. International Organization for Standardization, ISO 4104-1984. Dental zinc polycarboxylate cements. Geneva, Switzerland: ISO. 8. McLean JW, Prosser HJ, Wilson AD. The use of glass-ionomer cements in bonding composite resins to dentine. Br Dent J 1985: 158: 410-14. 9. Wong Th CC, Bryant RW. Glass ionomer cements: dispensing and strength. Aust Dent J 1985: 30: 336--40. 10. Atkinson AS, Pearson GJ. The evaluation of glass-ionomer cements. Br Dent J 1985: 159: 335-7. 11. Smith D e . Dental cements. Current status and future prospects. Dent Clin North A m 1983: 6: 763-91. 12. Kuhn AT, Wilson AD. The dissolution mechanisms of silicate and glass-ionmer dental cements. Biomaterials 1985: 6: 378-82.