The creep behavior of glass-ionomer restorative materials Y. Papadogiannis* M. Helvatjoglou-Antoniadi R. C. Lakes1" M. Sapountjis Department of Operative Dentistry School of Dentistry Aristotle University of Thessaloniki PO Box 519 Thessaloniki, 54006, Greece tDepartment of.Biomedical Engineering University of Iowa Iowa City, Iowa 52242 Received January 23, 1990 Accepted July 20, 1990 *Corresponding author Dent Mater 7:40-43, January, 1991
Abstract-The creep of microspecimens of five glass-ionomer filling materials and one glass-ionomer-cermet cement was studied by means of a torsional creep apparatus. The glass-ionomer specimens were aged one week and conditioned in 37°0 water. Shear stress of 2.47 X 10 -4 N.m was maintained for three h, and recovery was followed for 50 h. Creep curves were obtained at 21, 37, and 50°C. The effect of temperature increase was studied. All the glass ionomers exhibited linear visco-elastic behavior at low deformations. Their shear moduli and resistance to creep were similar to those of some composites measured by the same method. The increase of temperature influenced the creep behavior and moduli of the materials (Le., increased creep and residual strains and decreased shear modulus). Although the applied torque was very small, there was permanent deformation, the result of viscous flow in all experiments which was more pronounced at 50°C.
he use of glass-ionomer cements as restorative materials is increasing, and many brands of glass-ionomer cements are now commercially available. They have been used successfully for the esthetic filling of cavities subjected to low s t r e s s e s - f o r example, the restoration of class V erosion lesions and class III cavities-and for the filling or sealing of pits and fissures. However, the weakness of those materials lies in t h e i r m e c h a n i c a l properties, which reflect the brittle n a t u r e of cements. The flexural strength of the glass ionomers is low, and they lack toughness (McLean, 1984). Resistance to wear on occlusal contacts is also inadequate, and clinical studies show that a gradual loss of contour can be expected due to chemical degradation and surface wear. This weakness in physical and mechanical properties makes glassionomer cements unsuitable for use in high-stress-bearing areas such as class II and MOD r e s t o r a t i o n s (McLean, 1980; Prosser et al., 1986).
T
In order to improve the physical and mechanical properties of these materials, very fine metal particles were incorporated into the cementforming glass, the so-called "cermet cements" (McLean and Gasser, 1985). Considerable research work has been done on the physical and mechanical properties of these materials but only a few concerning their creep behavior. The purpose of this study was to determine the shear moduli and creep behavior of five glass-ionomer restorative products and one cermet with a static creep method in torsion. The effect of temperature was also investigated. MATERIALS AND METHODS
Five commercial glass-ionomer cements and one cermet cement were selected for study and are listed in Table 1. Specimen preparation was the same as described in other earlier articles (Papadogiannis et aL, 1984,
TABLE 1 GLASS-IONOMER RESTORATIVE MATERIALS INVESTIGATED Glass Ionomers Ketacfil
Ketacsilver
Chemfil II
Fuji Ionomer Type II Aqua set III Ionofil U
40 PAPADOGIANNIS et aL/CREEP OF GLASS IONOMERS
Composition Glass Ionomer Poly-maleic acid Glass Ionomer Poly-maleic acid reinforced with Ag 40% Glass Ionomer Polyacrylic acid Glass Ionomer Polyacrylic acid Glass Ionomer Polyacrylic acid Glass Ionomer Polyacrylic acid
Type
Manufacturer
conventional
ESPE GmbH Germany
cermet capsulated
ESPE GmbH Germany
water hardening
DeTrey Dentsply U.K.
conventional
G.C. Dental Industrial Corp.
water hardening
S.S. White Siproda, France
conventional
Voco Chemie Cuxhaven, Germany
CREEP CURVE5OF KETACF~L
3
3.
CREEP
&Temper.21C 2.5
?
CURVE5
OF KETACSILVER
3
A T e m p e r ,21C • ~r e roper .37C
• Temper .37C 0 T e m p e r ,50C
232 oTemper.50C /
2.5
CREEP
CURVES
OF CFEMFIL
I1
6 Ternper 2qC • Temper.3 ?C lITemper-5QC
2
z_.
Abstract-The creep of microspecimens of five glass-ionomer filling materials and one glass-ionomer-cermet cement was studied by means of a torsional creep apparatus. The glass-ionomer specimens were aged one week and conditioned in 37°0 water. Shear stress of 2.47 X 10 -4 N.m was maintained for three h, and recovery was followed for 50 h. Creep curves were obtained at 21, 37, and 50°C. The effect of temperature increase was studied. All the glass ionomers exhibited linear visco-elastic behavior at low deformations. Their shear moduli and resistance to creep were similar to those of some composites measured by the same method. The increase of temperature influenced the creep behavior and moduli of the materials (Le., increased creep and residual strains and decreased shear modulus). Although the applied torque was very small, there was permanent deformation, the result of viscous flow in all experiments which was more pronounced at 50°C.
he use of glass-ionomer cements as restorative materials is increasing, and many brands of glass-ionomer cements are now commercially available. They have been used successfully for the esthetic filling of cavities subjected to low s t r e s s e s - f o r example, the restoration of class V erosion lesions and class III cavities-and for the filling or sealing of pits and fissures. However, the weakness of those materials lies in t h e i r m e c h a n i c a l properties, which reflect the brittle n a t u r e of cements. The flexural strength of the glass ionomers is low, and they lack toughness (McLean, 1984). Resistance to wear on occlusal contacts is also inadequate, and clinical studies show that a gradual loss of contour can be expected due to chemical degradation and surface wear. This weakness in physical and mechanical properties makes glassionomer cements unsuitable for use in high-stress-bearing areas such as class II and MOD r e s t o r a t i o n s (McLean, 1980; Prosser et al., 1986).
T
In order to improve the physical and mechanical properties of these materials, very fine metal particles were incorporated into the cementforming glass, the so-called "cermet cements" (McLean and Gasser, 1985). Considerable research work has been done on the physical and mechanical properties of these materials but only a few concerning their creep behavior. The purpose of this study was to determine the shear moduli and creep behavior of five glass-ionomer restorative products and one cermet with a static creep method in torsion. The effect of temperature was also investigated. MATERIALS AND METHODS
Five commercial glass-ionomer cements and one cermet cement were selected for study and are listed in Table 1. Specimen preparation was the same as described in other earlier articles (Papadogiannis et aL, 1984,
TABLE 1 GLASS-IONOMER RESTORATIVE MATERIALS INVESTIGATED Glass Ionomers Ketacfil
Ketacsilver
Chemfil II
Fuji Ionomer Type II Aqua set III Ionofil U
40 PAPADOGIANNIS et aL/CREEP OF GLASS IONOMERS
Composition Glass Ionomer Poly-maleic acid Glass Ionomer Poly-maleic acid reinforced with Ag 40% Glass Ionomer Polyacrylic acid Glass Ionomer Polyacrylic acid Glass Ionomer Polyacrylic acid Glass Ionomer Polyacrylic acid
Type
Manufacturer
conventional
ESPE GmbH Germany
cermet capsulated
ESPE GmbH Germany
water hardening
DeTrey Dentsply U.K.
conventional
G.C. Dental Industrial Corp.
water hardening
S.S. White Siproda, France
conventional
Voco Chemie Cuxhaven, Germany
CREEP CURVE5OF KETACF~L
3
3.
CREEP
&Temper.21C 2.5
?
CURVE5
OF KETACSILVER
3
A T e m p e r ,21C • ~r e roper .37C
• Temper .37C 0 T e m p e r ,50C
232 oTemper.50C /
2.5
CREEP
CURVES
OF CFEMFIL
I1
6 Ternper 2qC • Temper.3 ?C lITemper-5QC
2
z_.
