Dynamic mechanical properties of dental amalgams J.H. Chern Lin 1. E.H. Greener 1 T. Hanawa z T. Okabe z
1Northwestern University Dental School Department of Basic Science Division of Biological Materials 311 E. Chicago Avenue Chicago, Illinois 60611 2Baylor College of Dentistry Department of Dental Materials 3302 Gaston Avenue Dallas, Texas 74246 Received April 3, 1989 Accepted August 9, 1989 *Address reprint requests to: Dr. Jiin-Huey Chern Lin Department of Materials Engineering National Chung-Kung University 70101 -rainan, Taiwan Republic of China Dent Mater 6:41-44, January, 1990
Abstract-,rhe dynamic mechanical
properties of two high-copper amalgams (Tytin and Dispersalloy) and two traditional amalgams (Aristalloy and Aristalloy with Zn) were measured over a temperature range of 0-70°C and at frequencies of 0.1, 1, and 10 Hz by means of a DuPont DMA. Values of storage modulus (E') for the amalgams were equivalent to the Young's modulus (E) measured from static mechanical test methods, with Dispersalloy demonstrating the highest moduli. Values of E' decreased with increased temperature. E' of traditional amalgams decreased more rapidly than did those of the Cu-rich amalgams. Values of loss modulus (E") for Tytin were smaller than those of Dispersalloy and the two types of Aristalloy. High values of E" for the traditional amalgams correspond to a greater viscous behavior. Marked differences between the magnitude of tan5 and its temperature coefficients for traditional and high-copper amalgams were observed, which is indicative of differences in visco-elastic behavior between these two amalgam systems.
isco-elastic properties of dental amalgams have been demonstrated by the nonlinear relationship between the applied stresses and resulting strains in both tension and compression tests of the amalgams (Oglesby et al., 1968). The shape of the stress-strain curve is a function of temperature and frequency of the applied stress or strain (Oglesby et al., 1968; Diekson et al., 1968). Previously, the visco-elasticity of dental amalgams has been studied through the static or dynamic creep behavior of the amalgam in fixed-load and isothermal conditions (Greener et al., 1980, 1988; Her¢, 1983; Mahler and Adey, 1977; McCabe and Carrick, 1987; Okabe et al., 1980). Various models were established to describe the visco-elastic response of a material to an applied strain (Rosen, 1982). The viscoelasticity of a material can be separated into two components: One is a perfeet elastic solid, and the other is a viscous liquid. The resultant stress of the elastic solid from an applied
V
strain • is directly proportional to the strain with a proportional constant E which is known as the elastic modulus of that material: (r = E e
(1)
The resultant stress of a viscous liquid to an external strain is dictated by the rate of deformation and the viscosity of the liquid according to: cr = nde/dt
(2)
where n is the viscosity of the liquid, and d e/dt is the rate of deformation. Therefore, when a sinusoidal strain with angular frequency co is applied to an elastic solid, the resultant stress is in phase with the applied strain with a proportionality constant E'. According to Eq. (1), cr = E' A sin co t
(3)
E' is referred to as the storage roodulus of the material. When a sinusoidal strain is applied to a perfectly viscous liquid, the resultant stress is ~r/2 out of phase with the applied strain. According to Eq. (2),
Arm-Lockina Pins
.~,
, ,,~,
~.~IW..IL,,,~.I
,L , ~ , , V L . /
I II~IIIlUL;UU~.III~
l..el~llllp
Fig. 1. A schematic drawing of the configurations of a DuPont 983 DMA. Motion of sample arms is indicated by arrows.
Dental Materials~January 1990 41
d = displacement
Clamp
strain
10.0-
LOSS MODULI OF DENTAL AMALGAMS ( iHz )
9.6-
I
9.2
14.~.. Null Position (Zero Strain)
....
8.8
I I
....-
....
Flexure Pivots
....
. ..... ~.
°"
Aristalloy
8.4
).
--"
Aristalloy with Zn ---
Tytin
....
Dispersalloy
8,0
0
l
I
i0
20
Du Pont 983 DMA
I
l
30
l
40
50
!
I
60
70
8O
Temperature ( ° C )
Fig. 3. Storagemoduliof the amalgamsmeasuredat 1-Hz oscillationfrequency.
Electromagnetic Motor (Applied Stress)
10.8
F/g. 2. Sample deformationin DuPont983 DMA.
b.
TABLE ELASTIC MODULUS OF FOUR DENTAL AMALGAMS AT 25°0 AND 1 Hz (Gpa) Dynamic Mechanical Analysis 24-31"* Static Compression 21-34" *Powers, 1978. **Dispersalloy amalgam displayed highest E' in both types of tests. =
~ ~A coscot co = E"
~
~
~
~a~_
.~.-.
............
I0.0
Aristalloy
9.6
Aristalloy with Zn
(5)
Dynamic Mechanical Analysis
42
- -- ......
10.4
(4)
where E" is referred to as the loss modulus of the material. The terms "storage" and "loss" refer to the action of the material with respect to impacted energy. The r e s u l t a n t stress of a visco-elastic material will thus lag behind the applied strain by a phase angle ~. The storage modulus (E') represents the in-phase portion, and the loss modulus (E") r e p r e s e n t s the out-of-phase response. The tangent of that angle is proportional to the ratio of energy dissipated in each cycle of the sinusoidal strain to the maximum potential e n e r g y s t o r e d in each cycle (Rosen, 1982): tan5 = E"/E'
STORAGE MODULI OF DENTAL AMALGAMS ( 1 Hz )
•
Tytin Q ~ O t
Du Pont 983 DMA
Dispersalloy
9.2
0
I0
20
30
40
50
60
70
80
Temperature ( ° C )
Fig. 4. Loss moduliof the amalgamsmeasuredat 1-Hz oscillationfrequency.
(DMA) is one of the most sensitive single techniques for measuring the mechanical response of a material as it is subjected to a small oscillatory strain under various oscillation frequencies and t e m p e r a t u r e s . AIthough this technique has been used to measure the moduli and the glasstransition temperatures of dental polymers (Ferracane and Greener, 1986; Demarest and Greener, 1988; Wilson and Turner, 1987), the appli-
C H E R N L I N e t a U D Y N A M I C M E C H A N I C A L P R O P E R T I E S OF D E N T A L A M A L G A M S
cation of this technique to dental amalgams has not been developed. This study was undertaken to measure the visco-elastic nature of dental a m a l g a m s by DMA. The correlation between the moduli values generated by DMA and by traditional methods will be evaluated.
MATERIALS AND METHODS The dynamic mechanical properties of two copper-enriched amalgams
8 34
~DI
32
~
The movement of the arms occurred only in the horizontal plane. This is i l l u s t r a t e d in Fig. 2. Clamping torques of from 2 to 8 lb per inch were slowly applied to the samples so that they would not crack during placement or slip d m ~ g testing. The measurements were conducted at 5°C increments over a temperature range of 0-110°C, with a heating rate of 5°C/ min. Fixed-frequency modes with frequencies of 0.1, 1.0, and 10 Hz and a low-oscillation amplitude of 0.2 mm were selected for the test.
SPERSALLOY 106.3 °C .I-. 0.3
30
6
25
3o.81
"I
~9 =
~0.2
",,.I/ ,,,'/ \
~
t
24
4 !
I
i
I
//I/.~
.............
0.i
m
'2
-:.:.I.1
20 ,
-20
0
i
20
,
40
60
i
!
80
|
i00
'
0
140
120
Temperature ( °C )
Fig. 5. E', E" and tan values of Dispersalloy. 0.4 TAN DELTA OF DENTAL AMALGAMS .... Aris talloy
( IHz
)
Tytin 0.3
0.2
I
°
S" ~.s
0.i
"°
,.=....=.,. 6=-
Du Pont 983 DMA 0
I
!
!
i0
20
30
I
40
|
I
!
50
60
70
Temperature (°C)
Fig. 6. Tan ,~ values of dental amalgams.
(Dispersalloy, Johnson & Johnson, E. Windsor, N J; Tytin, S.S. White, Philadelphia, PA) and t w o traditional amalgams (Aristalloy and Aristalloy with Zn, E n g l e h a r d , Carteret, N J) were measured by a DuPont 983 DMA (DuPont Company Instrument Systems, Wilmington, DE). Samples with special configurations were required. Therefore, rectangular-shaped plates with dimensions of 30 mm x 3 mm x 1 mm were fabricated. The amal-
gam mass was hand-condensed into a rectangular-shaped acrylic die after trituration. The specimens were stored at 37°C in air for 24 h and polished in ice water through 600grit sandpaper prior to the test. A schematic drawing of the configurations of a DuPont 983 DMA is shown in Fig. 1. The samples were carefully mounted in the DuPont DMA by use of the vertical clamping arrangement. Samples were clamped between two parallel sample arms.
RESULTSAND DISCUSSION The representative storage moduli of the amalgams measured at l-Hz oscillation frequency are shown in Fig. 3. The range of E' values of the amalgams measured at 25°C is listed in the Table; these values were compared with those reported from traditional static testing (Powers et al., 1978). E' values of the amalgams were equivalent to those measured by the traditional method, with Dispersalloy demonstrating the highest modulus in both types of test formulation. E' values of the amalgams decreased linearly with increasing temperature. E' values of the traditional amalgam (Aristalloy) appeared to decrease more rapidly than those of the Cu-enriched amalgams (Tytin and Dispersalloy). This may be indicative of the delay in the phase transformation of Ag2Hg~ (71) to AgHg (61) phase in the Cu-enriched amalgam systems. Representative E" values of the amalgams at l-Hz oscillation frequency are shown in Fig. 4. E" values of Tytin were smaller than those of Dispersalloy and the Aristalloys. This is in agreement with the low creep value reported for Tytin (Osborne et al., 1978), in that high values for E" correspond to a greater visco-elasticity and hence higher creep values. E" of the amalgams increased with temperature. The 7~ to ~ phase-transition temperature of the amalgam is observed by the sudden decline of the E" or tan 3 values (Fig. 5). The phase-transition temperature in the Dispersalloy was observed at 106°C, which is equivalent to the phase-transition temperature (104.7 ± 14.2°C) measured from thermal expansion coefficient measurements (Mante et al., 1988). The complete viscoelastic behavior, as Dental Materials~January 1990 43
expressed by tan 5 for both Aristalloy and Tytin, is shown in Fig. 6. Marked differences between the magnitude of tan g and its temperature coefficients for traditional and high-copper amalgams w e r e observed. This indicates the potential for quite different mechanical behavior over the oral temperature range for the two amalgam types.
CONCLUSIONS Values of E' for the amalgams meas u r e d from D u P o n t DMA w e r e equivalent to those obtained by the traditional test method. Values of E' for the traditional amalgams decreased more with increasing temperature than did the Cu-enriched systems. With increasing temperature, values of E" for the traditional amalgams were higher than those for highCu amalgams. Values of E" for the amalgams increased with increased temperature. Differences in magnitude of tan and its temperature coefficient were seen between traditional and highCu amalgam, indicative of differences in visco-elastic behavior. Dynamic mechanical analysis may be an effective tool for future amalgam research.
ACKNOWLEDGMENT This research was conducted with the aid of NIDR Grant DE06994, whose support is gratefully acknowledged.
REFERENCES DEMAREST, V.A. and GREENER, E.H. (1988): Storage Moduli and Interaction Parameters of Experimental Dental Composites, J Dent Res 66: 221, AbEt. No. 868. DICKSON, G.J.; OGLESBY, P.L.; and DAVENPORT, R. (1968): The Steadystate Creep Behavior of Dental Amalgam, J Res Natl Bur Stds 72C: 215218. FERRACANE, J.L. and GREENER, E.H. (1986): The Effect of Resin Formulation on the Degree of Conversion and Mechanical Properties of Dental Restorative Resins, J Biomed Mater Res 20: 121-131. GREENER, E.H.; SZURGOT, K.; and LAUTENSCHLAGER,E.P. (1980): Time Temperature Behavior for Creep of Dental Amalgam, J Biomed Mater Res 14: 161-171. GREENER, E.H.; CHUNG, K.H.; AND CHERN LIN, J.H. (1988): Creep in a Palladium Enriched High Copper Amalgam, Biomaterials 9: 213-217. HER~, H. (1983): On Creep Mechanisms in Amalgams, J Dent Res 62: 44-50. MAHLER, D.B. and ADEY, J.D. (1977): Creep vs. Microstructure of Amalgam, J Dent Res 56: A78, AbEt. No. 144.
44 CHERN LIN et aUDYNAMIC MECHANICAL PROPERTIES OF DENTAL AMALGAMS
MANTE, F.; LIN, J.H.C.; M0SER, J.B.; and GREENER,E.H. (1988): Palladium Effects on Thermal Expansion and Phase Changes in Amalgam, J Dent Res 67: 308, AbEt. No. 1563. MCCABE, J.F. and CARRICK,T.E. (1987): Dynamic Creep of Dental Amalgam as a Function of Stress and Number of Applied Stress Cycles, J Dent Res 66: 1346-1349. OGLESBY, P.L.; DICKSON, G.J.; RODRIGUEZ, M.L.; and SWEENEY, W.T. (1968): Viscoelastic Behavior of Dental Amalgam, J Res Natl Bur Std 72C: 203-213. OKABE, T.; BUTTS, M.; MITCHELL, R.; and FAIRHURST, C. (1980): Grain" Boundary Sliding and Creep of Dental Amalgams, J Dent Res 59: 292, AbEt. No. 100. OSBORNE, J.W.; GALE, E.N.; CHEW, C.L.; RHODES, B.F.; and PHILLIPS, R.W. (1978): Clinical Performance and Physical Properties of Twelve Amalgam Alloys, J Dent Res 57: 983-988. POWERS, J.M. (1978): Tabulated Values of Physical and Mechanical Properties. In: An Outline of Dental Materials, W.J. O'Brien and G. Ryge, Eds., Philadelphia: W.B. Saunders Co., pp. 385-413. ROSEN, S. (1982): Fundamental Principles of Polymeric Materials, New York: John Wiley & Sons, pp. 236-277. WILSON, T.W. and TURNER, D.T. (1987): Characterization of Polydimethacrylates and their Composites by Dynamic Mechanical Analysis, J Dent Res 66: 1032-1035.
1Northwestern University Dental School Department of Basic Science Division of Biological Materials 311 E. Chicago Avenue Chicago, Illinois 60611 2Baylor College of Dentistry Department of Dental Materials 3302 Gaston Avenue Dallas, Texas 74246 Received April 3, 1989 Accepted August 9, 1989 *Address reprint requests to: Dr. Jiin-Huey Chern Lin Department of Materials Engineering National Chung-Kung University 70101 -rainan, Taiwan Republic of China Dent Mater 6:41-44, January, 1990
Abstract-,rhe dynamic mechanical
properties of two high-copper amalgams (Tytin and Dispersalloy) and two traditional amalgams (Aristalloy and Aristalloy with Zn) were measured over a temperature range of 0-70°C and at frequencies of 0.1, 1, and 10 Hz by means of a DuPont DMA. Values of storage modulus (E') for the amalgams were equivalent to the Young's modulus (E) measured from static mechanical test methods, with Dispersalloy demonstrating the highest moduli. Values of E' decreased with increased temperature. E' of traditional amalgams decreased more rapidly than did those of the Cu-rich amalgams. Values of loss modulus (E") for Tytin were smaller than those of Dispersalloy and the two types of Aristalloy. High values of E" for the traditional amalgams correspond to a greater viscous behavior. Marked differences between the magnitude of tan5 and its temperature coefficients for traditional and high-copper amalgams were observed, which is indicative of differences in visco-elastic behavior between these two amalgam systems.
isco-elastic properties of dental amalgams have been demonstrated by the nonlinear relationship between the applied stresses and resulting strains in both tension and compression tests of the amalgams (Oglesby et al., 1968). The shape of the stress-strain curve is a function of temperature and frequency of the applied stress or strain (Oglesby et al., 1968; Diekson et al., 1968). Previously, the visco-elasticity of dental amalgams has been studied through the static or dynamic creep behavior of the amalgam in fixed-load and isothermal conditions (Greener et al., 1980, 1988; Her¢, 1983; Mahler and Adey, 1977; McCabe and Carrick, 1987; Okabe et al., 1980). Various models were established to describe the visco-elastic response of a material to an applied strain (Rosen, 1982). The viscoelasticity of a material can be separated into two components: One is a perfeet elastic solid, and the other is a viscous liquid. The resultant stress of the elastic solid from an applied
V
strain • is directly proportional to the strain with a proportional constant E which is known as the elastic modulus of that material: (r = E e
(1)
The resultant stress of a viscous liquid to an external strain is dictated by the rate of deformation and the viscosity of the liquid according to: cr = nde/dt
(2)
where n is the viscosity of the liquid, and d e/dt is the rate of deformation. Therefore, when a sinusoidal strain with angular frequency co is applied to an elastic solid, the resultant stress is in phase with the applied strain with a proportionality constant E'. According to Eq. (1), cr = E' A sin co t
(3)
E' is referred to as the storage roodulus of the material. When a sinusoidal strain is applied to a perfectly viscous liquid, the resultant stress is ~r/2 out of phase with the applied strain. According to Eq. (2),
Arm-Lockina Pins
.~,
, ,,~,
~.~IW..IL,,,~.I
,L , ~ , , V L . /
I II~IIIlUL;UU~.III~
l..el~llllp
Fig. 1. A schematic drawing of the configurations of a DuPont 983 DMA. Motion of sample arms is indicated by arrows.
Dental Materials~January 1990 41
d = displacement
Clamp
strain
10.0-
LOSS MODULI OF DENTAL AMALGAMS ( iHz )
9.6-
I
9.2
14.~.. Null Position (Zero Strain)
....
8.8
I I
....-
....
Flexure Pivots
....
. ..... ~.
°"
Aristalloy
8.4
).
--"
Aristalloy with Zn ---
Tytin
....
Dispersalloy
8,0
0
l
I
i0
20
Du Pont 983 DMA
I
l
30
l
40
50
!
I
60
70
8O
Temperature ( ° C )
Fig. 3. Storagemoduliof the amalgamsmeasuredat 1-Hz oscillationfrequency.
Electromagnetic Motor (Applied Stress)
10.8
F/g. 2. Sample deformationin DuPont983 DMA.
b.
TABLE ELASTIC MODULUS OF FOUR DENTAL AMALGAMS AT 25°0 AND 1 Hz (Gpa) Dynamic Mechanical Analysis 24-31"* Static Compression 21-34" *Powers, 1978. **Dispersalloy amalgam displayed highest E' in both types of tests. =
~ ~A coscot co = E"
~
~
~
~a~_
.~.-.
............
I0.0
Aristalloy
9.6
Aristalloy with Zn
(5)
Dynamic Mechanical Analysis
42
- -- ......
10.4
(4)
where E" is referred to as the loss modulus of the material. The terms "storage" and "loss" refer to the action of the material with respect to impacted energy. The r e s u l t a n t stress of a visco-elastic material will thus lag behind the applied strain by a phase angle ~. The storage modulus (E') represents the in-phase portion, and the loss modulus (E") r e p r e s e n t s the out-of-phase response. The tangent of that angle is proportional to the ratio of energy dissipated in each cycle of the sinusoidal strain to the maximum potential e n e r g y s t o r e d in each cycle (Rosen, 1982): tan5 = E"/E'
STORAGE MODULI OF DENTAL AMALGAMS ( 1 Hz )
•
Tytin Q ~ O t
Du Pont 983 DMA
Dispersalloy
9.2
0
I0
20
30
40
50
60
70
80
Temperature ( ° C )
Fig. 4. Loss moduliof the amalgamsmeasuredat 1-Hz oscillationfrequency.
(DMA) is one of the most sensitive single techniques for measuring the mechanical response of a material as it is subjected to a small oscillatory strain under various oscillation frequencies and t e m p e r a t u r e s . AIthough this technique has been used to measure the moduli and the glasstransition temperatures of dental polymers (Ferracane and Greener, 1986; Demarest and Greener, 1988; Wilson and Turner, 1987), the appli-
C H E R N L I N e t a U D Y N A M I C M E C H A N I C A L P R O P E R T I E S OF D E N T A L A M A L G A M S
cation of this technique to dental amalgams has not been developed. This study was undertaken to measure the visco-elastic nature of dental a m a l g a m s by DMA. The correlation between the moduli values generated by DMA and by traditional methods will be evaluated.
MATERIALS AND METHODS The dynamic mechanical properties of two copper-enriched amalgams
8 34
~DI
32
~
The movement of the arms occurred only in the horizontal plane. This is i l l u s t r a t e d in Fig. 2. Clamping torques of from 2 to 8 lb per inch were slowly applied to the samples so that they would not crack during placement or slip d m ~ g testing. The measurements were conducted at 5°C increments over a temperature range of 0-110°C, with a heating rate of 5°C/ min. Fixed-frequency modes with frequencies of 0.1, 1.0, and 10 Hz and a low-oscillation amplitude of 0.2 mm were selected for the test.
SPERSALLOY 106.3 °C .I-. 0.3
30
6
25
3o.81
"I
~9 =
~0.2
",,.I/ ,,,'/ \
~
t
24
4 !
I
i
I
//I/.~
.............
0.i
m
'2
-:.:.I.1
20 ,
-20
0
i
20
,
40
60
i
!
80
|
i00
'
0
140
120
Temperature ( °C )
Fig. 5. E', E" and tan values of Dispersalloy. 0.4 TAN DELTA OF DENTAL AMALGAMS .... Aris talloy
( IHz
)
Tytin 0.3
0.2
I
°
S" ~.s
0.i
"°
,.=....=.,. 6=-
Du Pont 983 DMA 0
I
!
!
i0
20
30
I
40
|
I
!
50
60
70
Temperature (°C)
Fig. 6. Tan ,~ values of dental amalgams.
(Dispersalloy, Johnson & Johnson, E. Windsor, N J; Tytin, S.S. White, Philadelphia, PA) and t w o traditional amalgams (Aristalloy and Aristalloy with Zn, E n g l e h a r d , Carteret, N J) were measured by a DuPont 983 DMA (DuPont Company Instrument Systems, Wilmington, DE). Samples with special configurations were required. Therefore, rectangular-shaped plates with dimensions of 30 mm x 3 mm x 1 mm were fabricated. The amal-
gam mass was hand-condensed into a rectangular-shaped acrylic die after trituration. The specimens were stored at 37°C in air for 24 h and polished in ice water through 600grit sandpaper prior to the test. A schematic drawing of the configurations of a DuPont 983 DMA is shown in Fig. 1. The samples were carefully mounted in the DuPont DMA by use of the vertical clamping arrangement. Samples were clamped between two parallel sample arms.
RESULTSAND DISCUSSION The representative storage moduli of the amalgams measured at l-Hz oscillation frequency are shown in Fig. 3. The range of E' values of the amalgams measured at 25°C is listed in the Table; these values were compared with those reported from traditional static testing (Powers et al., 1978). E' values of the amalgams were equivalent to those measured by the traditional method, with Dispersalloy demonstrating the highest modulus in both types of test formulation. E' values of the amalgams decreased linearly with increasing temperature. E' values of the traditional amalgam (Aristalloy) appeared to decrease more rapidly than those of the Cu-enriched amalgams (Tytin and Dispersalloy). This may be indicative of the delay in the phase transformation of Ag2Hg~ (71) to AgHg (61) phase in the Cu-enriched amalgam systems. Representative E" values of the amalgams at l-Hz oscillation frequency are shown in Fig. 4. E" values of Tytin were smaller than those of Dispersalloy and the Aristalloys. This is in agreement with the low creep value reported for Tytin (Osborne et al., 1978), in that high values for E" correspond to a greater visco-elasticity and hence higher creep values. E" of the amalgams increased with temperature. The 7~ to ~ phase-transition temperature of the amalgam is observed by the sudden decline of the E" or tan 3 values (Fig. 5). The phase-transition temperature in the Dispersalloy was observed at 106°C, which is equivalent to the phase-transition temperature (104.7 ± 14.2°C) measured from thermal expansion coefficient measurements (Mante et al., 1988). The complete viscoelastic behavior, as Dental Materials~January 1990 43
expressed by tan 5 for both Aristalloy and Tytin, is shown in Fig. 6. Marked differences between the magnitude of tan g and its temperature coefficients for traditional and high-copper amalgams w e r e observed. This indicates the potential for quite different mechanical behavior over the oral temperature range for the two amalgam types.
CONCLUSIONS Values of E' for the amalgams meas u r e d from D u P o n t DMA w e r e equivalent to those obtained by the traditional test method. Values of E' for the traditional amalgams decreased more with increasing temperature than did the Cu-enriched systems. With increasing temperature, values of E" for the traditional amalgams were higher than those for highCu amalgams. Values of E" for the amalgams increased with increased temperature. Differences in magnitude of tan and its temperature coefficient were seen between traditional and highCu amalgam, indicative of differences in visco-elastic behavior. Dynamic mechanical analysis may be an effective tool for future amalgam research.
ACKNOWLEDGMENT This research was conducted with the aid of NIDR Grant DE06994, whose support is gratefully acknowledged.
REFERENCES DEMAREST, V.A. and GREENER, E.H. (1988): Storage Moduli and Interaction Parameters of Experimental Dental Composites, J Dent Res 66: 221, AbEt. No. 868. DICKSON, G.J.; OGLESBY, P.L.; and DAVENPORT, R. (1968): The Steadystate Creep Behavior of Dental Amalgam, J Res Natl Bur Stds 72C: 215218. FERRACANE, J.L. and GREENER, E.H. (1986): The Effect of Resin Formulation on the Degree of Conversion and Mechanical Properties of Dental Restorative Resins, J Biomed Mater Res 20: 121-131. GREENER, E.H.; SZURGOT, K.; and LAUTENSCHLAGER,E.P. (1980): Time Temperature Behavior for Creep of Dental Amalgam, J Biomed Mater Res 14: 161-171. GREENER, E.H.; CHUNG, K.H.; AND CHERN LIN, J.H. (1988): Creep in a Palladium Enriched High Copper Amalgam, Biomaterials 9: 213-217. HER~, H. (1983): On Creep Mechanisms in Amalgams, J Dent Res 62: 44-50. MAHLER, D.B. and ADEY, J.D. (1977): Creep vs. Microstructure of Amalgam, J Dent Res 56: A78, AbEt. No. 144.
44 CHERN LIN et aUDYNAMIC MECHANICAL PROPERTIES OF DENTAL AMALGAMS
MANTE, F.; LIN, J.H.C.; M0SER, J.B.; and GREENER,E.H. (1988): Palladium Effects on Thermal Expansion and Phase Changes in Amalgam, J Dent Res 67: 308, AbEt. No. 1563. MCCABE, J.F. and CARRICK,T.E. (1987): Dynamic Creep of Dental Amalgam as a Function of Stress and Number of Applied Stress Cycles, J Dent Res 66: 1346-1349. OGLESBY, P.L.; DICKSON, G.J.; RODRIGUEZ, M.L.; and SWEENEY, W.T. (1968): Viscoelastic Behavior of Dental Amalgam, J Res Natl Bur Std 72C: 203-213. OKABE, T.; BUTTS, M.; MITCHELL, R.; and FAIRHURST, C. (1980): Grain" Boundary Sliding and Creep of Dental Amalgams, J Dent Res 59: 292, AbEt. No. 100. OSBORNE, J.W.; GALE, E.N.; CHEW, C.L.; RHODES, B.F.; and PHILLIPS, R.W. (1978): Clinical Performance and Physical Properties of Twelve Amalgam Alloys, J Dent Res 57: 983-988. POWERS, J.M. (1978): Tabulated Values of Physical and Mechanical Properties. In: An Outline of Dental Materials, W.J. O'Brien and G. Ryge, Eds., Philadelphia: W.B. Saunders Co., pp. 385-413. ROSEN, S. (1982): Fundamental Principles of Polymeric Materials, New York: John Wiley & Sons, pp. 236-277. WILSON, T.W. and TURNER, D.T. (1987): Characterization of Polydimethacrylates and their Composites by Dynamic Mechanical Analysis, J Dent Res 66: 1032-1035.
