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The effect of glass heat treatment on the properties of a novel polyalkenoate cement
Clinical Materials
12 (1993) 113-l 15
The Elect of Glass Heat Treatment Properties of a Novel Polyalkenoate
on the Cement
A. D. Mew, V. Piddock & E. C. Combe Biomaterials Science Unit, Department Higher CaLmbridge Street, Manchester (Received
2 December
1991;
of Restorative Dentistry, Ml5 6FH, UK
sent for revision 31 January
University
1992; accepted
Dental
Hospital
10 March
of Manchester,
1992)
Abstract: The effect of heat treating the glass component
of a novel glass-ionomer (polyalkenoate) cement on cement properties has been determined, with specific reference to the reactivity of the glass, and the mechanical properties of the resultant cement. It has been shown that heat treatment is a suitable method of decreasing the glass reactivity and improving the handling characteristics of the mixed cement. Under some conditions, an increase in compressive strength was found, although the effect on tensile properties was not significant.
glass polyalkenoate cements after heating the glass powder to 100 “C prior to mixing, although significant annealing of the glass was unlikely at this temperature. The preparation and properties of cements based on novel aluminoborate glasses have been described in previous papers.6,7 This paper reports on the effect of heat treatment on a novel aluminoborate glass used to form a glass polyalkenoate cement.
INTRODUCTION The chemistry and structure of glass polyalkenoate cements based on fluoroaluminosilicate glasses is well-doc1~mented.l Such cements consist of crosslinked polyacrylate chains, reinforced by partially reacted glass filler particles. These filler particles comprise an outer layer of a siliceous hydrogel, which is formed from the ion-depleted reacted glass powder, and a core of unreacted glass. Whilst the manipulative characteristics of these materials are clinically acceptable, working and setting times being controlled by the addition of tartaric acid, the relatively poor mechanical properties compared with amalgam limit their usage.2 The development of mechanically improved glass ionomer cements must be achieved without adversely affecting their reactivity. It is likely that improvements in the strength of the filler particles could lead to an increase in the mechanical properties of the cement and reduction of thermal stresses in the glass particles induced by the shock cooling of the glass melts might offer a simple means of achieving this.3 The maximum reduction of thermal stresses occurs at the annealing point of the glass.4 Brune5 reported a 10 % increase in the compressive strength of aluminosilicate-based
METHODS Glass powder was prepared with the following initial formulation (mol %): Al,O, 12.6, B,O, 42.3, ZnO 35.1 and ZnF, 10X), as described in previous studies.6,7 Samples of glass powder, weighing 3-4 g were placed in silica crucibles, and were heated from room temperature to 30 “C in a chamber furnace (Carbolite, Sheffield, UK). The temperature was held at 300 “C for 2 h after wlhich the powder was allowed to cool slowly in the closed furnace. Cements were formed both from the heat-treated and untreated powders by combining them with freeze dried poly(acrylic acid) of viscosity average molecular weight 49000 and de-io:nised water. The working time, setting time, ldiametral tensile 113
Clinical Materials
0267-6605/93/$06.00
0 1993 Elsevier
Science Publishers
Ltd, England
iddock, E. 67. Gmbe
114
strength and the compressive strength of the cements were determined by the methods outlined in the British Standard Specification for Class with the following modiIonomer Cement? fications: the size of the compressive strength samples was reduced by a factor of three and the tensile strength samples by a factor of two. The cement samples were tested on a R.D.P. Howden BS 50 testing machine (R.D.P. Howden Ltd, Learnington Spa, Warwickshire, UK> at a cross head speed of 1 mm/mm The working time, setting time, compressive strength and tensile strength results of cements based on the heat-treated powder were compared with the values obtained from untreated glass. Table 1. Working heat-treated Heat treatment
and setting times of heat-treated glass-containing cements Powder/ liquid ratio
Yes Yes Yes No No British Standard British Standard
4:l 4:l 5:l 4:1 4:1 type 1 type 2
Table 2. Compressive Heat treatment
Yes Yes Yes Yes No No No No
Yes Yes No No
Setting time
(s)
($1
4:l 5:l 5:l 4:1 5:l
540 370 270 280 160 > 180 > 165
700 540 410 310 270 < 450 < 300
strength
Powder/ liquid ratio
Glass/ polyacid ratio
Storage conditions
Compressive strength @fPa)
5:l 5:1 6:1 6:1 5:l 5:l 6:l 6:l
5:1 5:l 5:l 5:l 5:l 5:l 5:l 5:1
wet
43.8 + 8.8 118~8+11.8 64.0 k 1.7 133.555.4 40.1& 6.8 89.1 i 23.0 60.7+2.3 126.2 f 5.0
Table 3. Diametral Heat treatment
Working time
dry Wet
dry wet dry
tensile strength
Powder/ liquid ratio
Glass/ polyacid ratio
5:1 6:1 5:l 6:l
5:1 s:1 5:B 5:1
Storage conditions
wet wet wet wet
show
of
the
cements
authe streng
rest&s of the chanical tests were statistica; analysis using a Student’s t-test.
and non-
Glass/ polyacid ratio
dry wet
es
Tensile strength VfPa) 7.9 * 1.1 8.950.7 7%_fO% 8.5 & 0.8
were not
When t~er~~al~y stress2 anneahng tem~eratnre, to relieve residual stresses.4 Provi relieved glass is coole residual stresses will b point occurs at a viscosity of 1@” poise4 w also the glass transition temperature, I&” ation of thermal stresses set up in a glass resulting from shock cooling of the ssibly lead to an increa
particles which act as a reinforcing filler in the cement matrix. A somewhat arbitrary choice of heat treat temperature for the ex erimental glass was e temperature of the sa 0 “C) for various greviously investigated ternary al~mi~obora~e gHasses,“’ an annealing te~~e~at~re of 300 “C beHng selected. Heat treatment cause of the glass powder (se cements based on this gla handling characteristics. powder treated in this proved the compressive strength of the ceme
Heat treatment
of polyalkenoate
liquid ratios except at the ratios 5: 1 and 5: 1 for powder/liquid and glass/polyacid under wet storage. Clearly if the deleterious effect of moisture on these novel cements is reduced then heat treatment could have a very important role in the preparation of the glass component. Increases in tensile strength were not significant, which might be expected as the tensile strength will depend ultimately on the strength elf the resin matrix determined by the bonds crosslinking the polymer chains.
115
cement
REFERENCES 1. Barry, T. I., Clinton, D. J. &Wilson, A. D., The structure of a glass ionomer cement and its relationship to the setting process. J. Dent. Res., 58 (1979) 1072-9. 2. Wilson, A. D. & McLean, J. W., Glass-lonomer Cement. Quintessence, Chicago, 1988, pp. 21-9. 3. Wood, D. & Hill, R., Glass-ceramic approach to controlling the properties of a glass ionomer bone cement.
Biomaterials, 12 (1991) 164-70. 4. Van Vlack, L. H., Elements L$ Materials Science and Engineering (5th edn). Addison-Wesley, Reading, Massachusetts,
1984.
5. Brune, D., Heat treatment
of glass ionomer, silicate, zinc and zinc polycarboxylate cements. Stand. J. Dent. Res., 90 (1982) 409-12. 6. Neve, A. D., Piddock, V. & Combe, E. C.: Development of novel dental cements I. Formulation of aluminoborate glasses. Cl&. Mater. 9 (1992) 13-20. 7. Neve, A. D., Piddock, V. & Combe, E. C., Development of novel dental cements. II. Cement properties. Clin. Mater. 9 phosphate
CONCLUSIONS
eat treatment of the glass component of glass polyalkenoate (ionomer) cements in the manner described would appear to be a suitable method of both controlling the reactivity of the resultant cements and also of enhancing the compressive strength. This could be an important factor in the manufacture of novel and existing cements.
(1992) 21-29. 8. British Standard
for Dental Glass Ionomer Cements, British Standards Institute, BS 6039 : 198 1. 9. Rawson, II., Inorganic Glass Forming Systems. Academic Press, London, 1967. C., Properties of aluminoborate glasses of 10. Hirayama, group 11 metal oxides: 1, glass formation and thermal expansion. J. Abstr. Am. Cerami. Sot., 44 (1961) 602-6.
ECM
12
12 (1993) 113-l 15
The Elect of Glass Heat Treatment Properties of a Novel Polyalkenoate
on the Cement
A. D. Mew, V. Piddock & E. C. Combe Biomaterials Science Unit, Department Higher CaLmbridge Street, Manchester (Received
2 December
1991;
of Restorative Dentistry, Ml5 6FH, UK
sent for revision 31 January
University
1992; accepted
Dental
Hospital
10 March
of Manchester,
1992)
Abstract: The effect of heat treating the glass component
of a novel glass-ionomer (polyalkenoate) cement on cement properties has been determined, with specific reference to the reactivity of the glass, and the mechanical properties of the resultant cement. It has been shown that heat treatment is a suitable method of decreasing the glass reactivity and improving the handling characteristics of the mixed cement. Under some conditions, an increase in compressive strength was found, although the effect on tensile properties was not significant.
glass polyalkenoate cements after heating the glass powder to 100 “C prior to mixing, although significant annealing of the glass was unlikely at this temperature. The preparation and properties of cements based on novel aluminoborate glasses have been described in previous papers.6,7 This paper reports on the effect of heat treatment on a novel aluminoborate glass used to form a glass polyalkenoate cement.
INTRODUCTION The chemistry and structure of glass polyalkenoate cements based on fluoroaluminosilicate glasses is well-doc1~mented.l Such cements consist of crosslinked polyacrylate chains, reinforced by partially reacted glass filler particles. These filler particles comprise an outer layer of a siliceous hydrogel, which is formed from the ion-depleted reacted glass powder, and a core of unreacted glass. Whilst the manipulative characteristics of these materials are clinically acceptable, working and setting times being controlled by the addition of tartaric acid, the relatively poor mechanical properties compared with amalgam limit their usage.2 The development of mechanically improved glass ionomer cements must be achieved without adversely affecting their reactivity. It is likely that improvements in the strength of the filler particles could lead to an increase in the mechanical properties of the cement and reduction of thermal stresses in the glass particles induced by the shock cooling of the glass melts might offer a simple means of achieving this.3 The maximum reduction of thermal stresses occurs at the annealing point of the glass.4 Brune5 reported a 10 % increase in the compressive strength of aluminosilicate-based
METHODS Glass powder was prepared with the following initial formulation (mol %): Al,O, 12.6, B,O, 42.3, ZnO 35.1 and ZnF, 10X), as described in previous studies.6,7 Samples of glass powder, weighing 3-4 g were placed in silica crucibles, and were heated from room temperature to 30 “C in a chamber furnace (Carbolite, Sheffield, UK). The temperature was held at 300 “C for 2 h after wlhich the powder was allowed to cool slowly in the closed furnace. Cements were formed both from the heat-treated and untreated powders by combining them with freeze dried poly(acrylic acid) of viscosity average molecular weight 49000 and de-io:nised water. The working time, setting time, ldiametral tensile 113
Clinical Materials
0267-6605/93/$06.00
0 1993 Elsevier
Science Publishers
Ltd, England
iddock, E. 67. Gmbe
114
strength and the compressive strength of the cements were determined by the methods outlined in the British Standard Specification for Class with the following modiIonomer Cement? fications: the size of the compressive strength samples was reduced by a factor of three and the tensile strength samples by a factor of two. The cement samples were tested on a R.D.P. Howden BS 50 testing machine (R.D.P. Howden Ltd, Learnington Spa, Warwickshire, UK> at a cross head speed of 1 mm/mm The working time, setting time, compressive strength and tensile strength results of cements based on the heat-treated powder were compared with the values obtained from untreated glass. Table 1. Working heat-treated Heat treatment
and setting times of heat-treated glass-containing cements Powder/ liquid ratio
Yes Yes Yes No No British Standard British Standard
4:l 4:l 5:l 4:1 4:1 type 1 type 2
Table 2. Compressive Heat treatment
Yes Yes Yes Yes No No No No
Yes Yes No No
Setting time
(s)
($1
4:l 5:l 5:l 4:1 5:l
540 370 270 280 160 > 180 > 165
700 540 410 310 270 < 450 < 300
strength
Powder/ liquid ratio
Glass/ polyacid ratio
Storage conditions
Compressive strength @fPa)
5:l 5:1 6:1 6:1 5:l 5:l 6:l 6:l
5:1 5:l 5:l 5:l 5:l 5:l 5:l 5:1
wet
43.8 + 8.8 118~8+11.8 64.0 k 1.7 133.555.4 40.1& 6.8 89.1 i 23.0 60.7+2.3 126.2 f 5.0
Table 3. Diametral Heat treatment
Working time
dry Wet
dry wet dry
tensile strength
Powder/ liquid ratio
Glass/ polyacid ratio
5:1 6:1 5:l 6:l
5:1 s:1 5:B 5:1
Storage conditions
wet wet wet wet
show
of
the
cements
authe streng
rest&s of the chanical tests were statistica; analysis using a Student’s t-test.
and non-
Glass/ polyacid ratio
dry wet
es
Tensile strength VfPa) 7.9 * 1.1 8.950.7 7%_fO% 8.5 & 0.8
were not
When t~er~~al~y stress2 anneahng tem~eratnre, to relieve residual stresses.4 Provi relieved glass is coole residual stresses will b point occurs at a viscosity of 1@” poise4 w also the glass transition temperature, I&” ation of thermal stresses set up in a glass resulting from shock cooling of the ssibly lead to an increa
particles which act as a reinforcing filler in the cement matrix. A somewhat arbitrary choice of heat treat temperature for the ex erimental glass was e temperature of the sa 0 “C) for various greviously investigated ternary al~mi~obora~e gHasses,“’ an annealing te~~e~at~re of 300 “C beHng selected. Heat treatment cause of the glass powder (se cements based on this gla handling characteristics. powder treated in this proved the compressive strength of the ceme
Heat treatment
of polyalkenoate
liquid ratios except at the ratios 5: 1 and 5: 1 for powder/liquid and glass/polyacid under wet storage. Clearly if the deleterious effect of moisture on these novel cements is reduced then heat treatment could have a very important role in the preparation of the glass component. Increases in tensile strength were not significant, which might be expected as the tensile strength will depend ultimately on the strength elf the resin matrix determined by the bonds crosslinking the polymer chains.
115
cement
REFERENCES 1. Barry, T. I., Clinton, D. J. &Wilson, A. D., The structure of a glass ionomer cement and its relationship to the setting process. J. Dent. Res., 58 (1979) 1072-9. 2. Wilson, A. D. & McLean, J. W., Glass-lonomer Cement. Quintessence, Chicago, 1988, pp. 21-9. 3. Wood, D. & Hill, R., Glass-ceramic approach to controlling the properties of a glass ionomer bone cement.
Biomaterials, 12 (1991) 164-70. 4. Van Vlack, L. H., Elements L$ Materials Science and Engineering (5th edn). Addison-Wesley, Reading, Massachusetts,
1984.
5. Brune, D., Heat treatment
of glass ionomer, silicate, zinc and zinc polycarboxylate cements. Stand. J. Dent. Res., 90 (1982) 409-12. 6. Neve, A. D., Piddock, V. & Combe, E. C.: Development of novel dental cements I. Formulation of aluminoborate glasses. Cl&. Mater. 9 (1992) 13-20. 7. Neve, A. D., Piddock, V. & Combe, E. C., Development of novel dental cements. II. Cement properties. Clin. Mater. 9 phosphate
CONCLUSIONS
eat treatment of the glass component of glass polyalkenoate (ionomer) cements in the manner described would appear to be a suitable method of both controlling the reactivity of the resultant cements and also of enhancing the compressive strength. This could be an important factor in the manufacture of novel and existing cements.
(1992) 21-29. 8. British Standard
for Dental Glass Ionomer Cements, British Standards Institute, BS 6039 : 198 1. 9. Rawson, II., Inorganic Glass Forming Systems. Academic Press, London, 1967. C., Properties of aluminoborate glasses of 10. Hirayama, group 11 metal oxides: 1, glass formation and thermal expansion. J. Abstr. Am. Cerami. Sot., 44 (1961) 602-6.
ECM
12