Clinical Performance of a Gold-containing Amalgam DAVID B. MAHLER, RICHARD MARANTZ, and JEROME D. ADEY University of Oregon Health Sciences Center, School of Dentistry, 611 S. W. Campus Drive, Portland, Oregon 97201 In this study, the clinical performance (marginal fracture) of a gold-containing amalgam was compared to five traditional Y2-containing amalgams and one non-7Y2 amalgam. The results showed that the performance of this gold-containing amalgam was bettered by the non-Y2 amalgam and four of the five Y2-containing amalgams. A microprobe evaluation of a five-year-old clinical restoration made from this alloy revealed an unusual corrosion pattern. J Dent Res 58(11):2109-2115, November 1979
Introduction. In 1971, Johnsonl introduced a new spherical amalgam alloy having a nominal composition of 64% Ag, 26% Sn and 10% Au. The basic difference between this alloy and an alloy of traditional composition was the substitution of 1 0% Au for Ag. The purpose of this design was to eliminate the corrosionprone Sn-Hg phase (72) which is considered to be a causative factor in the marginal breakdown of clinical amalgam restorations. Using X-ray diffraction, no 'Y2 was detected in amalgam specimens made from this alloy which had been stored at 37 C for 2 weeks. In a later paper, Johnson et al.2 showed the corrosion behavior of this amalgam to be superior to that for traditional amalgams. However, three subsequent studies3,4,5 raised some doubts as to corrosion resistance and whether all of the 72 phase had been eliminated. Unlike the initial corrosion resulis reported,2 Svare and Chan,3 and Sarkar and Greener4 showed the potentiostatic anodic polarization behavior of this amalgam to be similar to that of traditional amalgams. Sarkar and Greener suggested that although the AuSn4 reaction product in Received for publication October 16, 1978. Accepted for publication December 4, 1978. This research was supported in whole by the National Institute of Dental Research, NIH, Research Grant Nos. RO1 DE 02320 and RO1 DE 02936.
the Au-containing amalgam behaved like Y2 in a saline solution, marginal integrity might be greatly different than for a y2containing amalgam, since AuSn4 is not a continuous phase. In the other study,5 both AuSn2 and AuSn4 were identified as reaction products in this amalgam. Theoretically, if any AuSn2 were to form, all of the Sn coming from the (Ag, Au, Sn)-Hg reaction would not be accounted for, and 72 should be present. Furthermore, the creep of this amalgam was measured to be 1.3%.6 This creep value is significantly higher than that for other non72 amalgams;* and, considering the relationship of creep to marginal fracture,9,10 the question was raised whether this amalgam would show an improvement in clinical performance when compared to traditional amalgams. Young, Fingar and Ross11 reported a clinical evaluation of this Au-containing amalgam and showed that its behavior was similar to that of a traditional amalgam. However, their results were based on a short time study with a limited sample size. In view of the several questions raised by previous studies, the purpose of this investigation was to evaluate the performance (marginal fracture) of this innovative Au-containing alloy and compare it to other previously-characterized alloys over a three-year period of clinical service.
Materials and methods. The alloy was supplied in the form of -400 mesh spherical particles.** Since the working time12 of amalgam made from this as-received alloy was too short for clinical
Most non-Y2 amalgams exhibit creep values within the range of 0.1 - 0.4%.7,8 **Courtesy of Dr. L. B. Johnson, Jr.; manufactured by- Western Gold and Platinum Co., Belmont, CA. 2109
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J Dent Res November 19 79
MAHLER ETAL.
2110
(0.5 min), the alloy was heat-treated at 1350C under vacuum for two hours to provide a working time of 4.5 min. No significant difference in creep resulted from this treatment.6 Microprobe examination of the amalgams made from both the asreceived and heat-treated alloys and stored at 370C showed a small amount Of Y2 after one week but no detectable 72 after three months.5 Two operators using standardized operative procedures placed the restorations, which were evaluated over a three-year period of clinical service. There were 42 restorations in 12 patients available for evaluation over the entire three-year period. The method of marginal fracture evaluation, which is described in detail in a recent publication,13 consisted of the following use
Results and discussion. Marginal fracture evaluation. -Preliminary evaluation of the data showed no difference in the results produced by the two operators who placed the restorations. Consequently, their data were pooled. In Table I and Figure 1 is shown the marginal fracture behavior of the Au-containing amalgam at one, two and three years, together with the marginal fracture behavior of six other alloys which have been previously reported.13 The higher the Marginal Fracture Index, the greater is the extent of fracture. The first point to be noted is the higher extent of marginal discrepancies at the
steps:
(1) A standard set of occlusal photographs of amalgam restorations depicting increasing extents of marginal fracture was selected, and each photo was assigned a linear numerical score. (2) Photographs of the test restorations taken at yearly recalls were compared to the standard set and scored accordingly. (3) For each yearly recall, the scores for all restorations within each patient were averaged to establish a within-patient mean.
(4) The within-patient means were then averaged to provide a marginal fracture index. (5) The variance of this index was calculated from a pooled within-patient estimate of the population variance. The above procedure provides a numerical index of the extent of clinical marginal fracture which can be used for inter-study comparisons. The methodology was developed to deal with patient effects, unequal numbers of restorations per patient, and situations with several alloys where all alloys are not present in all patients. In this present study the marginal fracture characteristic of the Au-containing alloy was compared to that for six alloys from a previous study.13 The same evaluators were used for both present and previous studies.
TABLE I MARGINAL FRACTURE INDICES OF A GOLD-CONTAINING AMALGAM AND SIX OTHER AMALGAMS
D N A P O V M
Year ]
Year 2
Year 3*
2.35 2.82 3.27 3.15 3.16 3.51 4.82
2.53 3.32 3.89 3.88 4.03 4.57 5.72
2.79 3.77 4.464.56-
4.885.21 6.66
*Statistical comparisons were made for the third year only, where Alloys A, P and 0 were pooled followed by multiple t testing with an overall error of a < .05. Values connected by lines are not different.
Alloys: D- Dispersalloy (1076), Western Metaflurgical, Ltd., Edmonton, Alberta, Canada N -New True Dentalloy (53164363), S. S. White Co., Philadelphia, Pa. A -Aristaloy (680315), Engelhard Ind., Baker Dental Div., Carteret, N. J. P- Spheraloy (01131014), Kerr Manufacturing Co., Romulus, Mich. 0 -Optaloy (4L67), The L. D. Caulk Co., Milford, Delaware V - Gold-Containing Alloy, Western Gold and Platinum Co., Belmont, Calif. M -Micro (13F66), The L. D. Caulk Co., Milford, Delaware
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Vol. 58 No.11I
x
GOLD-CONTAINING AMAL GAM
6_
z
:v
a
YEAR
Marginal fracture characteristics of Fig. 1 an Au-containing amalgam compared to six other amalgams.
polish stage for the Au-containing alloy.* The reason for this result is not known at this time, but could be related to such factors as particle size and mix plasticity. However, the most significant finding was the relatively large extent of marginal breakdown for this alloy with time in service. Its poor clinical performance was exceeded only by Alloy M, the worst performing Yy2-containing amalgam previously studied. 1 3 This behavior appears anomalous in view of the absence of detectable 72. In this regard, a question arises concerning Jorgensen's theory of marginal fracture (mercuroscopic expansion)14 which is based on the release of Hg from the electrochemical breakdown of 'Y2. Significant amounts of Hg would not be available from the small amount of 72 that might be present in this Au-containing amalgam. Mtcrostructural examination of a clinical restoration. - An attempt to explain this anomalous behavior was made by examining three clinical restorations which required replacement after three, five and seven years of service. After removal, these restorations were mounted, ground and polished to reveal an axial plane section. All three restorations showed similar results in the subsequent analysis. *No differences were found in the marginal fracture indices at the polish stage of the six alloys. These indices are shown as a pooled single value in Fig. 1. However, the index for Alloy V was found to be different using the t test.
2111
In the five-year-old restoration, the position of this plane section with respect to the entire restoration is indicated on the schematic diagram shown in Figure 2. A photograph of this section using the inverted sample current modet of a microprobe** revealed the presence of a layer at the occlusal surface which was uniquely different in appearance from the body of the restoration (Fig.3). A more highly magnified view of a section of this layer is shown in Figure 4. The nature of the amalgam in this apparently corroded layer can be compared to the nature of the amalgam just below this layer. The most apparent difference is exhibited by the reacted alloy particles. The dark color of the particles in the surface layer indicates the presence of a new phase(s) of lower average atomic number as compared to particles in the uncorroded layer. In Figure 5, a highly magnified invertedsample-current image of a reacted alloy particle in the uncorroded region of the restoration is shown on the left, and a reacted alloy particle in the corroded layer is shown on the right.§ The shape and
AXIAL PLANE
Fig. 2-Schematic drawing of the clinical restoration which was removed after five years of service. The dotted line indicates the axial plane section which was selected for microprobe examination.
t In an inverted sample current scan, phases of lower average atomic number show up darker than phases of higher average atomic number. **Model EMX-SM. Applied Research Laboratories, Sunland, CA § In order to clarify the nature of the uncorroded alloy particle, the contrast level was increased for this particle in this figure. In Figure 4, the true atomic number difference between uncorroded and corroded particles is represented.
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.1 Deii t Res iVoveiii her 1 9 79
MAILER ELT AL.
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Fig. 5-Higher magnification of two reacted alloy particles shown in Figure 4: left - particle in unattacked lower region of restoration; right particle in upper corroded layer of restoration.
character of the corroded alloy particle reveals what appears to be a uniaxial expansion of the particle where the matrix phase is present throughout the particle. The remainder of the particle shows the presence of a new phase(s) of lower average atomic number. From an analytical point of view, the normal reacted particle on the left consists of 'l, AuSn2, AuSn4 and original 7; the light rod-like regions are '1. The matrix These results have been proved to be VY documented in a previous publication.5 On the other hand, the reacted particle shown on the right, which is in the corroded layer, exhibits two separate regions, labeled A and B. These regions were examined in the microprobe, and the results are given in Fable It. Each analysis was taken in a different area of the specimen. The lighter area within the reacted particle, as well as the matrix, both labeled B, proved to be a form of 31 (Ag-Hg). Suprisingly, no 'Yl was found in the matrix of this corroded layer. The composition of 01 as measured in a laboratory specimen of this amalgam stored at 370C for two years is also presented in Table II. It is of interest to note that the 01 in the corroded layer of the clinical amnalgam has some Au but very little Sn, while the uncorroded laboratory specimen has some Sn but very little Au. In these same reacted particles, the dark areas labeled A proved to be high in Sn and contained oxygen but no chlorine. The presence of Ag, Hg and Au was considered to be
due to the excitation of a small amount of i1 and some original alloy in or around the analyzed volume. Because of uncertainties in the ZAF correction procedure for oxygen, this analysis is not considered to be precise. However, there is little doubt that tinoxide is present. The exact form can be speculated by viewing the Sn/O ratios shown in Table 11. This quantitative evidence suggests some mechanisms in regard to the corrosion dynamics of this Au-containing amalgam. First, corrosion in traditional amalgams is evidenced by the breakdown of the corrodible Y2 phase and the presence of Sn oxide in its place.15 Since AuSn4 and possibly AuSn2 are corrodible phases, as previously pointed out by Sarkarj and since they appear predominantly in reaction areas within the alloy particles, then one would expect Sn oxide in place of these phases in the reacted alloy particles; and this is exactly what has been found. Second, the complete conversion of '1l to 01 in this corroded layer is a characteristic not demonstrated by traditional ' -containing amalgams.16 Furthermore, the fact that this (1 has some Au but very little Sn, while the laboratory specimen has some Sn but very little Au, suggests that the Au is coming from the electrochemical breakdown of the Au-Sn reaction phase(s) rather than from the original alloy. Finally, previous theories of 'Y2 corrosion have assumed the continuity of the Y2 structure. Since the Au-Sn phases show
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2114
MAHLER ETAL.
Jete oebr17 J Den t R es Novem ber 1 9 79
TABLE II MICROPROBE ANALYSIS (WT.%) OF AREAS WITHIN THE OCCLUSAL CORRODED LAYER OF A FIVE-YEAR-OLD CLINICAL RESTORATION Areas Lahele,d B
x
Ag
Hg
Sn
Au
39.7 39.5 40.5 41.0 39.8
53.5 54.7 53.4 53.7 54.9
0.8 0.9 0.8 0.4 0.1
6.0 4.9 5.3 4.9 5.2
40.1 43.9
54.0 49.1
0.6 6.3
5.3 0.7
Ag
-Hg
Sn
Au
11.0 11.7 12.7 8.7
15.0 8.7 14.4 7.6
57.8 62.2 55.9 68.5
2.6 3.2 2.7 1.0
Areas Labeled A
11.0
11.4
61.1
2.4
The results showed that the clinical
performance of this amalgam was not better than that of traditional y2 -containing amalgams. In fact, in the range of performances exhibited by five traditional alloys, the performance of the gold-containing alloy was bettered by that of four of these alloys. A microprobe evaluation of a clinical restoration made from this alloy revealed an unusual corrosion pattern in a thin layer at the occlusal surface. Within this layer, the reacted alloy particles consisted of Sn oxide and a silver-mercury phase (01i) containing some Au but negligible Sn. The amalgam matrix in this layer also consisted of this f31 phase.
0
13.6 14.2 14.3 14.2
REFERENCES 1.
2.
SnO:
7.4 3.7
14.1
3.
JOHNSON,
Evaluation
no evidence of a continuous
6. 7.
8.
9.
Summary and conclusions. In this study, the clinical performance of gold-containing amalgam was investigated.
Evaluation was made after a three-y-ear period of clinical service on the basis of the extent of marginal fracture.
B.,
Jr.;
LAWLESS,
K.
R.;
of in
a Gold-containing Dental Ringer's Solution. IADR Progr
51:54, 1972. SARKAR, N. K. and GREENER, E. H.: Electrochemical Properties of Copper and Gold-containing Dental Amalgams, J Oral Rehab 2:157-164, 1975. MAHLER, D. B.; ADEY, J. D.; and VAN EYSDEN, J.: Microprobe Analysis of an Aucontaining Alloy and Its Amalgam, J Dent Res 55:1012-1022, 1976. and Abst
4.
may find some basis in the mechanism of grain boundary diffusion.
a
L.
Some Properties of Au-containing Dental Amalgam, Biomater Med Devices Artif Organs 1:223-238, 1973. SVARE, C. W.; and CHAN, K. C.: Corrosion
Amalgam
nature, ionic transport through the grain boundaries of 'Y1 could play a role in this corrosion process. This may be part of the mechanism in 'Y'2-containing amalgams as well, the continuous nature of the 'Y2 phase not being necessary for in-depth corrosion. There has been some question concerning the exact nature of the relationship between creep and marginal fracture. Since creep increases with decreasing grain size of 'Y (increasing amount of grain boundary surface per unit volume),17 the relationship of creep to corrosion and marginal fracture
Alloy,
STONER, G. E.; GARDNER, J.; YOUNG, R.; GEROSKY, T. R.; OPPENHEIMER, S.; BENDER, S. T.; and NEARY, M. J.:
4.3
Sn02:
A New Dental
IADR Progr and Abst 5 0:23, 19 71.
SnIO ratios: Areas Labeled A:
JOHNSON, L. B., Jr.:
10.
MAHLER, D. B.: Unpublished data. EAMES, W. B. and MACNAMARA, J. F.: Eight High-copper Amalgam Alloys and Six Conventional Alloys Compared, Oper Dent 1:98-107, 1976. JORGENSEN, D. D.: Recent Developments in Alloys for Dental Amalgams: Their Properties and Proper Use, Internat D J 26:369377, 1976. MAHLER, D. B.; VAN EYSDEN, J.; and TERKLA, L. G.: Relationship of Creep to Marginal Fracture of Amalgams, AADR Progr and Abst 5 4:5 53, 1 975. OSBORNE, J. W.; SWARTZ, M. L.; GALE, E. M.; and PHILLIPS, R. W.: Clinical Performance of Ten Amalgam Alloys. A OneYear Report, AADR Progr and Abst 56:No. 250, 1977.
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Vol. 58 No.10
GOLD-CONTAINING AMALGAM
11. YOUNG, F. A.; FINGAR, W. W.; and ROSS, S. A.: A Clinical Study of Dental Amalgam Containing Gold, IADR Progr and Abst 52: No. 205,1973. 12. EAMES, W. B. and SKINNER, E. W.: A Possible Test for Working Time of Dental Amalgams, IADR Progr and Abst 51: No. 53, 1972. 13. MAHLER, D. B. and MARANTZ, R. L.: The Effect of Time on the Marginal Fracture Behavior of Amalgam, J Oral Rehab 6:391398, 1979. 14. JORGENSEN, K. D.: The Mechanism of Marginal Fracture of Amalgam Fillings,
2115
Acta Odont Scand 23:347-389, 1965. 15. SARKAR, N. K.; MARSHALL, G. W.; MOSER, J. B.; and GRFENER, E. H.: In vivo and In vitro Corrosion Products of Dental Amalgam, J Dent Res 54:1031-1038, 1975. 16. MAHLER, D. B.; ADEY, J. D.; and VAN EYSDEN, J.: Transformation of 'Y1 in Clinical Amalgam Restorations, IADR Progr and Abst 52: No. 190, 1973. 17. MAHLER, D. B.; ADEY, J. D.; and MARANTZ, R. L.: Creep Versus Microstructure of Y2-Containing Amalgams, J Dent Res 56: 1493-1499, 1977.
ANNOUNCEMENT Postdoctoral Research Associateships, sponsored by the Naval Medical Research and Development Command in cooperation with the National Research Council, will be available at the Dental Sciences Department, Naval Medical Research Institute, Bethesda, Maryland 20014, U.S.A. Fields of interest include: (1) biologic responses of the oral tissue to restorative materials and treatment procedures, and (2) cellular mechanisms of bone deposition and resorption. Candidates within five years of their doctorate (M.D., D.D.S., Ph.D., D.V.M., or Sc.D.), either U.S. or Foreign Nationals, are eligible to apply. Selected candidates receive U.S. Civil Service Commission temporary appointment grade scale GS-1 1, currently $19,263/year, subject to both state and Federal taxes. One-way moving and travel expenses within the U.S. are additional. Complete application and research proposal must be submitted by 15 January 1980 for fellowship starting in the fall or winter of 1980. ADDRESS INQUIRY TO: Captain William R. Cotton, DC, USN, Chairman, Dental Sciences Department, Naval Medical Research Institute, Bethesda, Maryland 20014, U.S.A. REQUEST APPLICATION FROM: Associateship Office (JH 606), National Research Council, 2101 Constitution Avenue, N.W., Washington, D.C. 20418.
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Introduction. In 1971, Johnsonl introduced a new spherical amalgam alloy having a nominal composition of 64% Ag, 26% Sn and 10% Au. The basic difference between this alloy and an alloy of traditional composition was the substitution of 1 0% Au for Ag. The purpose of this design was to eliminate the corrosionprone Sn-Hg phase (72) which is considered to be a causative factor in the marginal breakdown of clinical amalgam restorations. Using X-ray diffraction, no 'Y2 was detected in amalgam specimens made from this alloy which had been stored at 37 C for 2 weeks. In a later paper, Johnson et al.2 showed the corrosion behavior of this amalgam to be superior to that for traditional amalgams. However, three subsequent studies3,4,5 raised some doubts as to corrosion resistance and whether all of the 72 phase had been eliminated. Unlike the initial corrosion resulis reported,2 Svare and Chan,3 and Sarkar and Greener4 showed the potentiostatic anodic polarization behavior of this amalgam to be similar to that of traditional amalgams. Sarkar and Greener suggested that although the AuSn4 reaction product in Received for publication October 16, 1978. Accepted for publication December 4, 1978. This research was supported in whole by the National Institute of Dental Research, NIH, Research Grant Nos. RO1 DE 02320 and RO1 DE 02936.
the Au-containing amalgam behaved like Y2 in a saline solution, marginal integrity might be greatly different than for a y2containing amalgam, since AuSn4 is not a continuous phase. In the other study,5 both AuSn2 and AuSn4 were identified as reaction products in this amalgam. Theoretically, if any AuSn2 were to form, all of the Sn coming from the (Ag, Au, Sn)-Hg reaction would not be accounted for, and 72 should be present. Furthermore, the creep of this amalgam was measured to be 1.3%.6 This creep value is significantly higher than that for other non72 amalgams;* and, considering the relationship of creep to marginal fracture,9,10 the question was raised whether this amalgam would show an improvement in clinical performance when compared to traditional amalgams. Young, Fingar and Ross11 reported a clinical evaluation of this Au-containing amalgam and showed that its behavior was similar to that of a traditional amalgam. However, their results were based on a short time study with a limited sample size. In view of the several questions raised by previous studies, the purpose of this investigation was to evaluate the performance (marginal fracture) of this innovative Au-containing alloy and compare it to other previously-characterized alloys over a three-year period of clinical service.
Materials and methods. The alloy was supplied in the form of -400 mesh spherical particles.** Since the working time12 of amalgam made from this as-received alloy was too short for clinical
Most non-Y2 amalgams exhibit creep values within the range of 0.1 - 0.4%.7,8 **Courtesy of Dr. L. B. Johnson, Jr.; manufactured by- Western Gold and Platinum Co., Belmont, CA. 2109
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J Dent Res November 19 79
MAHLER ETAL.
2110
(0.5 min), the alloy was heat-treated at 1350C under vacuum for two hours to provide a working time of 4.5 min. No significant difference in creep resulted from this treatment.6 Microprobe examination of the amalgams made from both the asreceived and heat-treated alloys and stored at 370C showed a small amount Of Y2 after one week but no detectable 72 after three months.5 Two operators using standardized operative procedures placed the restorations, which were evaluated over a three-year period of clinical service. There were 42 restorations in 12 patients available for evaluation over the entire three-year period. The method of marginal fracture evaluation, which is described in detail in a recent publication,13 consisted of the following use
Results and discussion. Marginal fracture evaluation. -Preliminary evaluation of the data showed no difference in the results produced by the two operators who placed the restorations. Consequently, their data were pooled. In Table I and Figure 1 is shown the marginal fracture behavior of the Au-containing amalgam at one, two and three years, together with the marginal fracture behavior of six other alloys which have been previously reported.13 The higher the Marginal Fracture Index, the greater is the extent of fracture. The first point to be noted is the higher extent of marginal discrepancies at the
steps:
(1) A standard set of occlusal photographs of amalgam restorations depicting increasing extents of marginal fracture was selected, and each photo was assigned a linear numerical score. (2) Photographs of the test restorations taken at yearly recalls were compared to the standard set and scored accordingly. (3) For each yearly recall, the scores for all restorations within each patient were averaged to establish a within-patient mean.
(4) The within-patient means were then averaged to provide a marginal fracture index. (5) The variance of this index was calculated from a pooled within-patient estimate of the population variance. The above procedure provides a numerical index of the extent of clinical marginal fracture which can be used for inter-study comparisons. The methodology was developed to deal with patient effects, unequal numbers of restorations per patient, and situations with several alloys where all alloys are not present in all patients. In this present study the marginal fracture characteristic of the Au-containing alloy was compared to that for six alloys from a previous study.13 The same evaluators were used for both present and previous studies.
TABLE I MARGINAL FRACTURE INDICES OF A GOLD-CONTAINING AMALGAM AND SIX OTHER AMALGAMS
D N A P O V M
Year ]
Year 2
Year 3*
2.35 2.82 3.27 3.15 3.16 3.51 4.82
2.53 3.32 3.89 3.88 4.03 4.57 5.72
2.79 3.77 4.464.56-
4.885.21 6.66
*Statistical comparisons were made for the third year only, where Alloys A, P and 0 were pooled followed by multiple t testing with an overall error of a < .05. Values connected by lines are not different.
Alloys: D- Dispersalloy (1076), Western Metaflurgical, Ltd., Edmonton, Alberta, Canada N -New True Dentalloy (53164363), S. S. White Co., Philadelphia, Pa. A -Aristaloy (680315), Engelhard Ind., Baker Dental Div., Carteret, N. J. P- Spheraloy (01131014), Kerr Manufacturing Co., Romulus, Mich. 0 -Optaloy (4L67), The L. D. Caulk Co., Milford, Delaware V - Gold-Containing Alloy, Western Gold and Platinum Co., Belmont, Calif. M -Micro (13F66), The L. D. Caulk Co., Milford, Delaware
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Vol. 58 No.11I
x
GOLD-CONTAINING AMAL GAM
6_
z
:v
a
YEAR
Marginal fracture characteristics of Fig. 1 an Au-containing amalgam compared to six other amalgams.
polish stage for the Au-containing alloy.* The reason for this result is not known at this time, but could be related to such factors as particle size and mix plasticity. However, the most significant finding was the relatively large extent of marginal breakdown for this alloy with time in service. Its poor clinical performance was exceeded only by Alloy M, the worst performing Yy2-containing amalgam previously studied. 1 3 This behavior appears anomalous in view of the absence of detectable 72. In this regard, a question arises concerning Jorgensen's theory of marginal fracture (mercuroscopic expansion)14 which is based on the release of Hg from the electrochemical breakdown of 'Y2. Significant amounts of Hg would not be available from the small amount of 72 that might be present in this Au-containing amalgam. Mtcrostructural examination of a clinical restoration. - An attempt to explain this anomalous behavior was made by examining three clinical restorations which required replacement after three, five and seven years of service. After removal, these restorations were mounted, ground and polished to reveal an axial plane section. All three restorations showed similar results in the subsequent analysis. *No differences were found in the marginal fracture indices at the polish stage of the six alloys. These indices are shown as a pooled single value in Fig. 1. However, the index for Alloy V was found to be different using the t test.
2111
In the five-year-old restoration, the position of this plane section with respect to the entire restoration is indicated on the schematic diagram shown in Figure 2. A photograph of this section using the inverted sample current modet of a microprobe** revealed the presence of a layer at the occlusal surface which was uniquely different in appearance from the body of the restoration (Fig.3). A more highly magnified view of a section of this layer is shown in Figure 4. The nature of the amalgam in this apparently corroded layer can be compared to the nature of the amalgam just below this layer. The most apparent difference is exhibited by the reacted alloy particles. The dark color of the particles in the surface layer indicates the presence of a new phase(s) of lower average atomic number as compared to particles in the uncorroded layer. In Figure 5, a highly magnified invertedsample-current image of a reacted alloy particle in the uncorroded region of the restoration is shown on the left, and a reacted alloy particle in the corroded layer is shown on the right.§ The shape and
AXIAL PLANE
Fig. 2-Schematic drawing of the clinical restoration which was removed after five years of service. The dotted line indicates the axial plane section which was selected for microprobe examination.
t In an inverted sample current scan, phases of lower average atomic number show up darker than phases of higher average atomic number. **Model EMX-SM. Applied Research Laboratories, Sunland, CA § In order to clarify the nature of the uncorroded alloy particle, the contrast level was increased for this particle in this figure. In Figure 4, the true atomic number difference between uncorroded and corroded particles is represented.
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.1 Deii t Res iVoveiii her 1 9 79
MAILER ELT AL.
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Fig. 4-Magnified
view
of Figure 3.
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Vo9l. -58 Nov. II
_M
~
~
GOLD-C1ONTAINING AiVALGAM
,L%-0
2113
OF
e
Fig. 5-Higher magnification of two reacted alloy particles shown in Figure 4: left - particle in unattacked lower region of restoration; right particle in upper corroded layer of restoration.
character of the corroded alloy particle reveals what appears to be a uniaxial expansion of the particle where the matrix phase is present throughout the particle. The remainder of the particle shows the presence of a new phase(s) of lower average atomic number. From an analytical point of view, the normal reacted particle on the left consists of 'l, AuSn2, AuSn4 and original 7; the light rod-like regions are '1. The matrix These results have been proved to be VY documented in a previous publication.5 On the other hand, the reacted particle shown on the right, which is in the corroded layer, exhibits two separate regions, labeled A and B. These regions were examined in the microprobe, and the results are given in Fable It. Each analysis was taken in a different area of the specimen. The lighter area within the reacted particle, as well as the matrix, both labeled B, proved to be a form of 31 (Ag-Hg). Suprisingly, no 'Yl was found in the matrix of this corroded layer. The composition of 01 as measured in a laboratory specimen of this amalgam stored at 370C for two years is also presented in Table II. It is of interest to note that the 01 in the corroded layer of the clinical amnalgam has some Au but very little Sn, while the uncorroded laboratory specimen has some Sn but very little Au. In these same reacted particles, the dark areas labeled A proved to be high in Sn and contained oxygen but no chlorine. The presence of Ag, Hg and Au was considered to be
due to the excitation of a small amount of i1 and some original alloy in or around the analyzed volume. Because of uncertainties in the ZAF correction procedure for oxygen, this analysis is not considered to be precise. However, there is little doubt that tinoxide is present. The exact form can be speculated by viewing the Sn/O ratios shown in Table 11. This quantitative evidence suggests some mechanisms in regard to the corrosion dynamics of this Au-containing amalgam. First, corrosion in traditional amalgams is evidenced by the breakdown of the corrodible Y2 phase and the presence of Sn oxide in its place.15 Since AuSn4 and possibly AuSn2 are corrodible phases, as previously pointed out by Sarkarj and since they appear predominantly in reaction areas within the alloy particles, then one would expect Sn oxide in place of these phases in the reacted alloy particles; and this is exactly what has been found. Second, the complete conversion of '1l to 01 in this corroded layer is a characteristic not demonstrated by traditional ' -containing amalgams.16 Furthermore, the fact that this (1 has some Au but very little Sn, while the laboratory specimen has some Sn but very little Au, suggests that the Au is coming from the electrochemical breakdown of the Au-Sn reaction phase(s) rather than from the original alloy. Finally, previous theories of 'Y2 corrosion have assumed the continuity of the Y2 structure. Since the Au-Sn phases show
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2114
MAHLER ETAL.
Jete oebr17 J Den t R es Novem ber 1 9 79
TABLE II MICROPROBE ANALYSIS (WT.%) OF AREAS WITHIN THE OCCLUSAL CORRODED LAYER OF A FIVE-YEAR-OLD CLINICAL RESTORATION Areas Lahele,d B
x
Ag
Hg
Sn
Au
39.7 39.5 40.5 41.0 39.8
53.5 54.7 53.4 53.7 54.9
0.8 0.9 0.8 0.4 0.1
6.0 4.9 5.3 4.9 5.2
40.1 43.9
54.0 49.1
0.6 6.3
5.3 0.7
Ag
-Hg
Sn
Au
11.0 11.7 12.7 8.7
15.0 8.7 14.4 7.6
57.8 62.2 55.9 68.5
2.6 3.2 2.7 1.0
Areas Labeled A
11.0
11.4
61.1
2.4
The results showed that the clinical
performance of this amalgam was not better than that of traditional y2 -containing amalgams. In fact, in the range of performances exhibited by five traditional alloys, the performance of the gold-containing alloy was bettered by that of four of these alloys. A microprobe evaluation of a clinical restoration made from this alloy revealed an unusual corrosion pattern in a thin layer at the occlusal surface. Within this layer, the reacted alloy particles consisted of Sn oxide and a silver-mercury phase (01i) containing some Au but negligible Sn. The amalgam matrix in this layer also consisted of this f31 phase.
0
13.6 14.2 14.3 14.2
REFERENCES 1.
2.
SnO:
7.4 3.7
14.1
3.
JOHNSON,
Evaluation
no evidence of a continuous
6. 7.
8.
9.
Summary and conclusions. In this study, the clinical performance of gold-containing amalgam was investigated.
Evaluation was made after a three-y-ear period of clinical service on the basis of the extent of marginal fracture.
B.,
Jr.;
LAWLESS,
K.
R.;
of in
a Gold-containing Dental Ringer's Solution. IADR Progr
51:54, 1972. SARKAR, N. K. and GREENER, E. H.: Electrochemical Properties of Copper and Gold-containing Dental Amalgams, J Oral Rehab 2:157-164, 1975. MAHLER, D. B.; ADEY, J. D.; and VAN EYSDEN, J.: Microprobe Analysis of an Aucontaining Alloy and Its Amalgam, J Dent Res 55:1012-1022, 1976. and Abst
4.
may find some basis in the mechanism of grain boundary diffusion.
a
L.
Some Properties of Au-containing Dental Amalgam, Biomater Med Devices Artif Organs 1:223-238, 1973. SVARE, C. W.; and CHAN, K. C.: Corrosion
Amalgam
nature, ionic transport through the grain boundaries of 'Y1 could play a role in this corrosion process. This may be part of the mechanism in 'Y'2-containing amalgams as well, the continuous nature of the 'Y2 phase not being necessary for in-depth corrosion. There has been some question concerning the exact nature of the relationship between creep and marginal fracture. Since creep increases with decreasing grain size of 'Y (increasing amount of grain boundary surface per unit volume),17 the relationship of creep to corrosion and marginal fracture
Alloy,
STONER, G. E.; GARDNER, J.; YOUNG, R.; GEROSKY, T. R.; OPPENHEIMER, S.; BENDER, S. T.; and NEARY, M. J.:
4.3
Sn02:
A New Dental
IADR Progr and Abst 5 0:23, 19 71.
SnIO ratios: Areas Labeled A:
JOHNSON, L. B., Jr.:
10.
MAHLER, D. B.: Unpublished data. EAMES, W. B. and MACNAMARA, J. F.: Eight High-copper Amalgam Alloys and Six Conventional Alloys Compared, Oper Dent 1:98-107, 1976. JORGENSEN, D. D.: Recent Developments in Alloys for Dental Amalgams: Their Properties and Proper Use, Internat D J 26:369377, 1976. MAHLER, D. B.; VAN EYSDEN, J.; and TERKLA, L. G.: Relationship of Creep to Marginal Fracture of Amalgams, AADR Progr and Abst 5 4:5 53, 1 975. OSBORNE, J. W.; SWARTZ, M. L.; GALE, E. M.; and PHILLIPS, R. W.: Clinical Performance of Ten Amalgam Alloys. A OneYear Report, AADR Progr and Abst 56:No. 250, 1977.
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Vol. 58 No.10
GOLD-CONTAINING AMALGAM
11. YOUNG, F. A.; FINGAR, W. W.; and ROSS, S. A.: A Clinical Study of Dental Amalgam Containing Gold, IADR Progr and Abst 52: No. 205,1973. 12. EAMES, W. B. and SKINNER, E. W.: A Possible Test for Working Time of Dental Amalgams, IADR Progr and Abst 51: No. 53, 1972. 13. MAHLER, D. B. and MARANTZ, R. L.: The Effect of Time on the Marginal Fracture Behavior of Amalgam, J Oral Rehab 6:391398, 1979. 14. JORGENSEN, K. D.: The Mechanism of Marginal Fracture of Amalgam Fillings,
2115
Acta Odont Scand 23:347-389, 1965. 15. SARKAR, N. K.; MARSHALL, G. W.; MOSER, J. B.; and GRFENER, E. H.: In vivo and In vitro Corrosion Products of Dental Amalgam, J Dent Res 54:1031-1038, 1975. 16. MAHLER, D. B.; ADEY, J. D.; and VAN EYSDEN, J.: Transformation of 'Y1 in Clinical Amalgam Restorations, IADR Progr and Abst 52: No. 190, 1973. 17. MAHLER, D. B.; ADEY, J. D.; and MARANTZ, R. L.: Creep Versus Microstructure of Y2-Containing Amalgams, J Dent Res 56: 1493-1499, 1977.
ANNOUNCEMENT Postdoctoral Research Associateships, sponsored by the Naval Medical Research and Development Command in cooperation with the National Research Council, will be available at the Dental Sciences Department, Naval Medical Research Institute, Bethesda, Maryland 20014, U.S.A. Fields of interest include: (1) biologic responses of the oral tissue to restorative materials and treatment procedures, and (2) cellular mechanisms of bone deposition and resorption. Candidates within five years of their doctorate (M.D., D.D.S., Ph.D., D.V.M., or Sc.D.), either U.S. or Foreign Nationals, are eligible to apply. Selected candidates receive U.S. Civil Service Commission temporary appointment grade scale GS-1 1, currently $19,263/year, subject to both state and Federal taxes. One-way moving and travel expenses within the U.S. are additional. Complete application and research proposal must be submitted by 15 January 1980 for fellowship starting in the fall or winter of 1980. ADDRESS INQUIRY TO: Captain William R. Cotton, DC, USN, Chairman, Dental Sciences Department, Naval Medical Research Institute, Bethesda, Maryland 20014, U.S.A. REQUEST APPLICATION FROM: Associateship Office (JH 606), National Research Council, 2101 Constitution Avenue, N.W., Washington, D.C. 20418.
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