Compressive strength of some polyalkenoates with or without dental amalgam alloy incorporation H.M.F. Beyls1 R.M.H. Verbeeck 2 L.C. Martens 1. L. Lemaitre3
'Department of Conservative Dentistry and Pedodontics University of Ghent De Pintelaan 185 B-9000 Gent, Belgium 2Research Associate, NFSR Laboratory for Analytical Chemistry 3Laboratory of Non-ferrous Metallurgy University of Ghent B-9000 Gent, Belgium Received January 25, 1990 Accepted May 10, 1991 *Author to whom correspondence should be directed Dent Mater 7:151-154, July, 1991
Abstract--The present study compares the
compressive strength after one week of some conventional glass-ionomer restorative materials with that of glass ionomers reinforced by the addition of ceramic-coated silver or dental amalgam alloy particles to the aluminosilicate glass powder. Apart from the commercially available Ketac Silver and Miracle Mix, experimental mixtures of Fuji II glass-ionomer powder, the old as well as the new version, with various amounts of either a spherical or lathe-cut amalgam alloy were investigated. For the conventional glass ionomers, the mean compressive strength based on all measurements amounts to 159.9 +4.5 MPa. Both formulations of Fuji II have a comparable strength after one-week maturation. The compressive strength of Ketac Silver does not differ significantly from that of Ketac Fill or from that of the conventional glass ionomers investigated. The effect of admixing amalgam alloy on the compressive strength is found to be determined by the shape and the amount of the alloy particles. Moreover, both parameters are interactive with the formulation of the Fuji glass ionomer used for preparation of the mixture. The results indicate that when dental amalgam alloy is added to the glass ionomer, lathe-cut particles are to be preferred but only in an amount up to 20% by weight.
he number of applications of glass ionomers (GI)in operative dentistry has increased steadily since their introduction by Kent and Wilson (1973) (see,e.g., Bitter, 1986; Croll and Phillips, 1986; Walls et al., 1988). GI exhibit remarkable advantages over more classical restorative materials, such as a longterm fluoride release and adhesion to both enamel and dentin (Aboush and Jenkins, 1986; Haller et al., 1988; Strubig, 1988). However, their general use as restorative materials is limited, especially by low wear resistance, brittleness, and relatively low strength (Gasser, 1987; Lloyd and Mitchell, 1984; McLean, 1985). Among the suggestions for improvement in these mechanical properties is the addition of ceramic-coated silver or dental amalgam alloy particles to the aluminosilicate glass powder (McLean and Gasser, 1985; Simmons, 1983;Walls et al., 1987). Although silver-reinforced GI apparently show improved abrasion resistance (Gasser, 1987; McKinney et al., 1988; McLean and Gasser, 1985; Moore et al., 1985; Sarkar et al., 1989; Walls et al., 1987), the general effects of metal inclusions on the strength properties of GI remain controversial. Whereas some investigators report improved strength properties (Miller et al., 1984; Walls et al., 1987), others found no or even a deteriorating effect when metal particles were included (Coury et al., 1986; E1 Mallakh et al., 1987; Kullmann, 1986; McKinney et al., 1988; Nakajima et al., 1989; Oilo, 1988). Such results may be partly due to differences in the formulation of the GI used, in the type of the metal inclusion, and/or in the shapes of the particles used. For this reason, the present study compares the compressive strengths of some conventional GI with those of metal-reinforced GI, in particular, those based on the addition of dental amalgam alloy.
T
M A T E R I A L S AND M E T H O D S
The materials used in this study are summarized in Table 1. In addition to KS, Miracle Mix (MM) was studied as a metal-reinforced glass-ionomer cement.
Whereas KS contains 40c~ sintered silver particles, the powder of MM is a mixture of Fuji II glass-ionomer powder with 53% of a spherical amalgam alloy (Lumi alloy, G-C Dental Industrial Corp., Tokyo, Japan). In addition to the classical Miracle Mix cement, based on FO (MM old), a Miracle Mix cement based on FN (MM new) was also prepared. The hand-spatulated GI, including the MM, were mixed according to the instructions of the manufacturer. The capsulated GI were mechanically mixed by use of a Silamat (Vivadent, Schaan, Liechtenstein) for 10 s according to the instructions of the manufacturer. For investigation of the effects of the amount and the shape of the admixed dental amalgam alloy on the compressive strength, mixtures of Fuji II glassionomer powder with either a spherical (Lumi alloy, G-C Dental Industrial Corp., Tokyo, Japan) or a lathe-cut (Dentoria fluor alloy, Laboratoires Dentaire, Cachan, France) amalgam alloy were prepared by thorough mixing of weighed amounts of GI powder and alloy. The resulting powders were mixed with the corresponding liquid according to the instructions for the Miracle Mix. Eight cylindrical samples (height, 12 mm; diameter, 6 ram) of each product were made according to ISO specification 7489-1986 (E), in split stainless steel molds which were coated with cacao butter. After being filled with the glassionomer material, the mold was closed and placed in an oven so that setting took place under pressure at 37°C and 100% RH. After one hour, the specimens were removed from the mold, covered with the corresponding varnish, and stored in the oven. The ultimate compressive strength was determined after one week by the loading of the flat ends of the specimens covered with a wetted blotting paper by use of a universal testing machine (Instron 1195, Instron Ltd., Buckinghamshire, England) at a crosshead speed of 0.5 ram/rain. RESULTS
The mean values of the compressive
Dental Materials~July 1991 151
strength for the conventional GI cements are represented in Fig. 1. The error bars give the standard deviation corresponding to the measurement. A Bartlett's test shows that the variances of the measurement depicted in Fig. 1 are not homogeneous (0.0050.20). The value for the global mean compressive strength based on all measurements for CF, KF, FO, and FN amounts to 159.9 _+ 4.5 MPa, with a standard deviation on the measurement of 25 MPa for this population. A t test then reveals that this global mean compressive strength differs not significantly (p>0.10) from the mean compressive
strength obtained for SF, i.e., 181 + 23 MPa. Fig. 2 represents the mean compressive strength for the reinforced GI cements together with the respective standard deviations on the measurement as given by the error bars. According to a Bartlett's test, the variance of the measurements is homogeneous (p>0.25) for the products considered, so that the pooled estimate for the standard deviation on the measurement is 18 MPa. However, an ANOVA analysis shows that there is a significant difference (p 30% (2) or 10% > 20% > 0% = 30% = M-Mix (3)
Products
Variance
Mean
KF vs. KS
p > 0.20
p > 0.50
FO vs. MM old
0.10 < p < 0.20
p < 0.001
FN vs. MM new
0.025 < p < 0.05
p > 0.10
TABLE 3 ANALYSIS OF VARIANCE FOR THE COMPRESSIVE STRENGTH OF THE ALLOY-CONTAININGGI CEMENTS REPRESENTED IN FIGS.3 AND 4 WHEN ATHREE-FACTOR FACTORIALDESIGNWAS USED Source of Variation
df
Sum of Squares
Mean Square
F
formulation (f)
1
1322.3
1322.3
1.61
0.205
shape (s)
1
8502.1
8502.1
10.32
0.002
degree (d)
3
98091.0
32697.0
39.71
'Department of Conservative Dentistry and Pedodontics University of Ghent De Pintelaan 185 B-9000 Gent, Belgium 2Research Associate, NFSR Laboratory for Analytical Chemistry 3Laboratory of Non-ferrous Metallurgy University of Ghent B-9000 Gent, Belgium Received January 25, 1990 Accepted May 10, 1991 *Author to whom correspondence should be directed Dent Mater 7:151-154, July, 1991
Abstract--The present study compares the
compressive strength after one week of some conventional glass-ionomer restorative materials with that of glass ionomers reinforced by the addition of ceramic-coated silver or dental amalgam alloy particles to the aluminosilicate glass powder. Apart from the commercially available Ketac Silver and Miracle Mix, experimental mixtures of Fuji II glass-ionomer powder, the old as well as the new version, with various amounts of either a spherical or lathe-cut amalgam alloy were investigated. For the conventional glass ionomers, the mean compressive strength based on all measurements amounts to 159.9 +4.5 MPa. Both formulations of Fuji II have a comparable strength after one-week maturation. The compressive strength of Ketac Silver does not differ significantly from that of Ketac Fill or from that of the conventional glass ionomers investigated. The effect of admixing amalgam alloy on the compressive strength is found to be determined by the shape and the amount of the alloy particles. Moreover, both parameters are interactive with the formulation of the Fuji glass ionomer used for preparation of the mixture. The results indicate that when dental amalgam alloy is added to the glass ionomer, lathe-cut particles are to be preferred but only in an amount up to 20% by weight.
he number of applications of glass ionomers (GI)in operative dentistry has increased steadily since their introduction by Kent and Wilson (1973) (see,e.g., Bitter, 1986; Croll and Phillips, 1986; Walls et al., 1988). GI exhibit remarkable advantages over more classical restorative materials, such as a longterm fluoride release and adhesion to both enamel and dentin (Aboush and Jenkins, 1986; Haller et al., 1988; Strubig, 1988). However, their general use as restorative materials is limited, especially by low wear resistance, brittleness, and relatively low strength (Gasser, 1987; Lloyd and Mitchell, 1984; McLean, 1985). Among the suggestions for improvement in these mechanical properties is the addition of ceramic-coated silver or dental amalgam alloy particles to the aluminosilicate glass powder (McLean and Gasser, 1985; Simmons, 1983;Walls et al., 1987). Although silver-reinforced GI apparently show improved abrasion resistance (Gasser, 1987; McKinney et al., 1988; McLean and Gasser, 1985; Moore et al., 1985; Sarkar et al., 1989; Walls et al., 1987), the general effects of metal inclusions on the strength properties of GI remain controversial. Whereas some investigators report improved strength properties (Miller et al., 1984; Walls et al., 1987), others found no or even a deteriorating effect when metal particles were included (Coury et al., 1986; E1 Mallakh et al., 1987; Kullmann, 1986; McKinney et al., 1988; Nakajima et al., 1989; Oilo, 1988). Such results may be partly due to differences in the formulation of the GI used, in the type of the metal inclusion, and/or in the shapes of the particles used. For this reason, the present study compares the compressive strengths of some conventional GI with those of metal-reinforced GI, in particular, those based on the addition of dental amalgam alloy.
T
M A T E R I A L S AND M E T H O D S
The materials used in this study are summarized in Table 1. In addition to KS, Miracle Mix (MM) was studied as a metal-reinforced glass-ionomer cement.
Whereas KS contains 40c~ sintered silver particles, the powder of MM is a mixture of Fuji II glass-ionomer powder with 53% of a spherical amalgam alloy (Lumi alloy, G-C Dental Industrial Corp., Tokyo, Japan). In addition to the classical Miracle Mix cement, based on FO (MM old), a Miracle Mix cement based on FN (MM new) was also prepared. The hand-spatulated GI, including the MM, were mixed according to the instructions of the manufacturer. The capsulated GI were mechanically mixed by use of a Silamat (Vivadent, Schaan, Liechtenstein) for 10 s according to the instructions of the manufacturer. For investigation of the effects of the amount and the shape of the admixed dental amalgam alloy on the compressive strength, mixtures of Fuji II glassionomer powder with either a spherical (Lumi alloy, G-C Dental Industrial Corp., Tokyo, Japan) or a lathe-cut (Dentoria fluor alloy, Laboratoires Dentaire, Cachan, France) amalgam alloy were prepared by thorough mixing of weighed amounts of GI powder and alloy. The resulting powders were mixed with the corresponding liquid according to the instructions for the Miracle Mix. Eight cylindrical samples (height, 12 mm; diameter, 6 ram) of each product were made according to ISO specification 7489-1986 (E), in split stainless steel molds which were coated with cacao butter. After being filled with the glassionomer material, the mold was closed and placed in an oven so that setting took place under pressure at 37°C and 100% RH. After one hour, the specimens were removed from the mold, covered with the corresponding varnish, and stored in the oven. The ultimate compressive strength was determined after one week by the loading of the flat ends of the specimens covered with a wetted blotting paper by use of a universal testing machine (Instron 1195, Instron Ltd., Buckinghamshire, England) at a crosshead speed of 0.5 ram/rain. RESULTS
The mean values of the compressive
Dental Materials~July 1991 151
strength for the conventional GI cements are represented in Fig. 1. The error bars give the standard deviation corresponding to the measurement. A Bartlett's test shows that the variances of the measurement depicted in Fig. 1 are not homogeneous (0.0050.20). The value for the global mean compressive strength based on all measurements for CF, KF, FO, and FN amounts to 159.9 _+ 4.5 MPa, with a standard deviation on the measurement of 25 MPa for this population. A t test then reveals that this global mean compressive strength differs not significantly (p>0.10) from the mean compressive
strength obtained for SF, i.e., 181 + 23 MPa. Fig. 2 represents the mean compressive strength for the reinforced GI cements together with the respective standard deviations on the measurement as given by the error bars. According to a Bartlett's test, the variance of the measurements is homogeneous (p>0.25) for the products considered, so that the pooled estimate for the standard deviation on the measurement is 18 MPa. However, an ANOVA analysis shows that there is a significant difference (p 30% (2) or 10% > 20% > 0% = 30% = M-Mix (3)
Products
Variance
Mean
KF vs. KS
p > 0.20
p > 0.50
FO vs. MM old
0.10 < p < 0.20
p < 0.001
FN vs. MM new
0.025 < p < 0.05
p > 0.10
TABLE 3 ANALYSIS OF VARIANCE FOR THE COMPRESSIVE STRENGTH OF THE ALLOY-CONTAININGGI CEMENTS REPRESENTED IN FIGS.3 AND 4 WHEN ATHREE-FACTOR FACTORIALDESIGNWAS USED Source of Variation
df
Sum of Squares
Mean Square
F
formulation (f)
1
1322.3
1322.3
1.61
0.205
shape (s)
1
8502.1
8502.1
10.32
0.002
degree (d)
3
98091.0
32697.0
39.71
