VOL. 9, PP. 255-256 (1975)
J. BIOMED. MATER. RES.
C o m m e n t s o n “Corrosion Under Stress of Materials Composing Dental Amalgam” The paper of L. B. Johnson, Jr. and K. R. Lawless’ reports t h a t corrosion potential experiments on Cu, Ag, Zn, AgZHg3,Ag3Sn, and finished amalgam showed very small changes in corrosion potential as a result of stressing. The potentials of Sn and tin amalgam were reported to be significantly affected by stress. From these and other experimental results, Johnson and Lawless concluded that: “It appears doubtful therefore, that stress plays a significant role in the corrosion of dental amalgams under oral conditions.” Under conditions of static stress, i t can be shown that the change in corrosion t o lop6mV/lOOO psi.2 Under conpotential for metals and alloys is about ditions of monotonically incressing elastic stress (e.g. constant test frame crosshead velocity of 0.1 cm/min, as per Johnson and Lawless), the maximum effect is about 10-’ to 10-2 mV. Since the experimental sensitivity quoted by Johnson and Lawless is +2 mV, i t must be concluded t h a t their experiment was incapable of measuring the very small effect that stress has on corrosion potential. The effect reported for tin and tin amalgam is probably associated with the effect of mechanical twinning rather than the effect of stress on corrosion potential. While the effect of stress on corrosion potential is indeed very small, it cannot be concluded that the effect is unimportant. Numerous cases of stress-corrosion cracking are reported for alloys that are nominally inert to the environment associated with ~ r a c k i n g . ~ Several literature contributions containing clinical and laboratory evidence of the effect of corrosion on dental amalgams also contain suggestions that such corrosion is stress enhanced (e.g. Mateer and Reitz, 1972).4 Such enhancement can be accomplished by both static stress and cyclic stress (i.e. fatigue). I n as much as there appears to have been no definitive experimentation concerning the stress enhanced corrosion of dental amalgem, it is suggested that such experimentation should be undertaken. I n the event that this phenomena is found t o be an important contributing factor to the failure of dental amalgam, programs can be subsequently undertaken t o develop methods to minimize the effect. References 1. L. B. Johnson, Jr. and K. R. Lawless, J . Biomed. Muter. Res., 3, 569 (1969). 2. L. Yang, G. T. Horne, and G. M. Pound, in Physical Metallurgy of Stress Corrosion Fracture, Vol. 4,Interscience Publishers, N. Y., 1959.
255 @ 1975 by John Wiley & Sons, Inc.
256
J. BIOMED. MATER. RES. VOL. 9 (1975)
3. B. F. Brown, Stress-Corrosion Cracking in High Strength Steels and in Titanium and Aluminum Alloys, Naval Research Laboratory, 1972. 4. R. S. Mateer and C. D. Reitz, J. Dent. Res., 51, 1546 (1972).
DAVID A. HANSEN Departments of Mechanical & Aerospace Engineering and Bioengineering University of Missouri-Columbia Columbia, Missouri 66,901
Received June 20, 1974
J. BIOMED. MATER. RES.
C o m m e n t s o n “Corrosion Under Stress of Materials Composing Dental Amalgam” The paper of L. B. Johnson, Jr. and K. R. Lawless’ reports t h a t corrosion potential experiments on Cu, Ag, Zn, AgZHg3,Ag3Sn, and finished amalgam showed very small changes in corrosion potential as a result of stressing. The potentials of Sn and tin amalgam were reported to be significantly affected by stress. From these and other experimental results, Johnson and Lawless concluded that: “It appears doubtful therefore, that stress plays a significant role in the corrosion of dental amalgams under oral conditions.” Under conditions of static stress, i t can be shown that the change in corrosion t o lop6mV/lOOO psi.2 Under conpotential for metals and alloys is about ditions of monotonically incressing elastic stress (e.g. constant test frame crosshead velocity of 0.1 cm/min, as per Johnson and Lawless), the maximum effect is about 10-’ to 10-2 mV. Since the experimental sensitivity quoted by Johnson and Lawless is +2 mV, i t must be concluded t h a t their experiment was incapable of measuring the very small effect that stress has on corrosion potential. The effect reported for tin and tin amalgam is probably associated with the effect of mechanical twinning rather than the effect of stress on corrosion potential. While the effect of stress on corrosion potential is indeed very small, it cannot be concluded that the effect is unimportant. Numerous cases of stress-corrosion cracking are reported for alloys that are nominally inert to the environment associated with ~ r a c k i n g . ~ Several literature contributions containing clinical and laboratory evidence of the effect of corrosion on dental amalgams also contain suggestions that such corrosion is stress enhanced (e.g. Mateer and Reitz, 1972).4 Such enhancement can be accomplished by both static stress and cyclic stress (i.e. fatigue). I n as much as there appears to have been no definitive experimentation concerning the stress enhanced corrosion of dental amalgem, it is suggested that such experimentation should be undertaken. I n the event that this phenomena is found t o be an important contributing factor to the failure of dental amalgam, programs can be subsequently undertaken t o develop methods to minimize the effect. References 1. L. B. Johnson, Jr. and K. R. Lawless, J . Biomed. Muter. Res., 3, 569 (1969). 2. L. Yang, G. T. Horne, and G. M. Pound, in Physical Metallurgy of Stress Corrosion Fracture, Vol. 4,Interscience Publishers, N. Y., 1959.
255 @ 1975 by John Wiley & Sons, Inc.
256
J. BIOMED. MATER. RES. VOL. 9 (1975)
3. B. F. Brown, Stress-Corrosion Cracking in High Strength Steels and in Titanium and Aluminum Alloys, Naval Research Laboratory, 1972. 4. R. S. Mateer and C. D. Reitz, J. Dent. Res., 51, 1546 (1972).
DAVID A. HANSEN Departments of Mechanical & Aerospace Engineering and Bioengineering University of Missouri-Columbia Columbia, Missouri 66,901
Received June 20, 1974
