Effect of Surface Preparation on Phase Distribution of Amalgam Surfaces DANIEL B. BOYER, JOHN W. EDIE, and KAI CHIU CHAN
College of Dentistry, University of Iowa, Iowa City, Iowa 52242, USA Several types of amalgams were prepared with carved, burnished, or polished surfaces. Elemental analyses were made of these surfaces with the electron microprobe and the phase fractions were calculated from these data. The phase distributions were found to vary with the technique of
finzshing. J Dent Res 57(2): 271-276, February 1978.
In a preliminary study of spherical amalgam samples with surfaces finished by carving, burnishing, or polishing, the au-
polished surfaces were the smoothest. The grain size and number of the matrix phases, 'y1 and 'Y2, did not vary among the superficial, subsuperficial, and central layers of any of the specimens. Burnished surfaces were found covered with minute granular prominences after a period of 15 minutes. These were presumed to be -yl and '2 crystals that grew as a result of free mercury released on the surface by burnishing. Other investigators have shown that the contact of mercury with amalgam causes the growth of new crystals on the surface.4 5 The purpose of the present study was to quantify the surface phases of spherical and other types of amalgam and to investigate the effect of surface preparation on the composition of the surfaces. In particular, we were interested in determining whether burnishing produces increased Y2 on other types of amalgam as well as spherical amalgam. The fractions of the phases have been quantified using electron microprobe analysis. The microprobe is used in the x-ray mode to measure the elemental weight concentrations from which the amounts of the phases can be calculated knowing the compositions of the phases.
thors1 found the surfaces of the burnished samples covered with oblong granules and platelike crystals. X-ray analysis with an electron microprobe identified these particles as the tin-mercury phase ('Y2). These particles were not observed in similar large amounts on the carved and polished samples. Other investigators have found that 'y2 crystals tend to grow in larger amounts on external surfaces, in voids, and in high mercury areas. Wing and Ryge2 found a relatively large amount of Y2 on the undisturbed set surfaces of spherical and lathecut amalgams which could be reduced by polishing. Excess mercury and voids lead to Materials and Methods higher Y2 content of polished amalgams. Fusayama and Hayashi3 compared Carved, burnished, and polished samcarved, burnished, finished, and polished were prepared from five commercial specimens of lathe-cut and spherical amal- ples lathe-cut D,a M," V,c spherical amalgams: gams. Carved surfaces were roughest and S,d and dispersion Di.e The precondensation mercury was 50, 54, 50, 48, and 50 Received for publication April 14, 1977. Accepted for publication August 31, 1977. weight %, respectively. The amalgams Supported by USPHS Grant S-501 -RR-05313-14. were prepared according to the manufacturers' instructions and hand condensed in 'New True Dentalloy, S.S. White, Philadelphia, Pa. 'Micro, L.D. Caulk Co., Milford, De. molds with a force of about 1 kg lucite 'Velvalloy, S.S. White, Philadelphia, Pa. (against a 1 kg weight on a balance). All of dSpheraloy, Kerr Manufacturing Co., Romulus, Mi. the samples were carved immediately with 'Dispersalloy, Johnson and Johnson, East Windsor, NJ. 271 Downloaded from jdr.sagepub.com at MOUNT ALLISON UNIV on June 23, 2015 For personal use only. No other uses without permission.
272
BOYER, EDIE
& CHAN
j Dent
Res
February
1978
TABLE 1 ELEMENTAL COMPOSITION OF DENTAL AMALGAM (WT%)* Amalgam
Lathe-cut D Carved Burnished Polished Lathe-cut M Carved Burnished Polished Lathe-cut V Carved Burnished Polished Spherical Carved Burnished Polished Dispersion Carved Burnished Polished
Sn
Cu
Ag
Hg
14.44 + 1.04 23.23 + 2.42 11.83 ± 0.05
1.68 ± 0.66 0.80 ± 0.05 1.39 ± 0.20
25.45 + 0.55 21.24 ± 0.98 37.06 ± 2.14
58.35 + 1.23 54.70 ± 1.44 49.69 + 2.31
15.42 + 0.72 28.50 + 5.32 10.00 + 1.80
2.76 ± 0.20 1.67 + 0.13 1.85 + 0.16
28.84 ± 0.88 20.66 ± 2.36 29.38 ± 0.88
49.13 + 2.84
12.99 + 0.57 24.05 + 3.51 8.83 ± 0.54
2.04 ± 0.19 1.07 ± 0.14 1.53 ± 0.19
25.93 ± 0.35 21.24 + 0.95 31.09 ± 1.09
59.01 ± 0.85 53.61 + 2.43 58.53 ± 1.68
11.87 + 0.47 25.96 + 3.84 12.05 + 0.12
1.75 + 0.29 0.81 ± 0.04 1.63 ± 0.08
35.91 ± 1.07 21.89 ± 1.92 36.40 ± 0.95
50.43 + 0.73 51.32 ± 1.95 49.92 ± 1.10
7.49 + 0.30
3.28 + 0.22 2.29 + 0.37 5.73 ± 0.31
28.50 ± 0.37
60.70 + 0.24 63.37 + 1.69 53.05 + 1.18
8.77 + 1.93 13.06 + 0.21
25.53 ± 0.64 28.81 + 0.88
52.94 + 1.60
58.74 ± 2.38
*Normalized to 100%. Each value is the average of measurements on 3 samples + S.D. The samples were 14 at the time of analysis.
days old
a razor blade. Three samples of each amal- HgMo, AgLo, SnLO, and CUKOc characgam were left as carved, 3 were burnished, teristic lines. Although wavelength disperand 3 were polished. There was a total of sive analysis (WDX) is normally the more 45 samples. Amalgams D and V were bur- accurate method of quantitation, the ennished from 15 to 20 minutes after mixing ergy dispersive analysis (EDX) mode was with a No. 28 burnisherf mounted in a de- selected in this case because EDX is insensivice to maintain the force at 200 grams. tive to variations in specimen height, does The other amalgams were burnished at 10 not experience defocusing effects as a reto 12 minutes. Burnishing times were sult of electron beam scanning, and analychosen to avoid grooving the surfaces and zes all elements simultaneously. The deyet shine them. All of the samples to be creased peak resolution and possible diffipolished were polished at 24 hours with the culties in correcting for background radiasame technique which consisted of cuttle tion or overlapping peaks were not the madisks,9 a rubber disk,' pumice and Amal- jor contributors to experimental error. glossi on a felt wheel. The samples were The normal prerequisites for quantitamounted directly on a specimen stub for tive microanalysis with the microprobe are analysis at 14 days with the ARL EMX-SM that the specimen be homogeneous and the microprobe.j surface flat so that theoretical corrections The average weight concentrations to for electron scattering and x-ray absorpdepths of about one micrometer were esti- tion and fluorescence may be made. While mated from x-ray intensities for the these conditions are not fulfilled in this exfS.S. White, Philadelphia, Pa. periment, the argument is advanced that "E.C. Moore Co., Dearborn, Mi. when scanning over a large surface area, 5J.F. Jelenko and Co., New Rochelle, NY. the errors will be to an extent offsetting L.D. Caulk Co., Milford, De. jApplied Research Laboratory, Sunland, Ca. and that the resulting elemental determiDownloaded from jdr.sagepub.com at MOUNT ALLISON UNIV on June 23, 2015 For personal use only. No other uses without permission.
SURFACE PREPARATION & AMALGAM PHASES
V'ol. 5 7 No. 2
nation should be within 5 to 10% of actual values (compared to 1% for point analyses). Because of this, it is recognized that the method is an approximate one and that the accuracy decreases with increasing specimen roughness. Each specimen was examined under the operating conditions of 20 kV accelerating voltage, 2 nA (on Au) specimen current and 800 x 1000 jjm2 video raster. Net peak heights for each element and for standards (pure Sn, Cu, Ag, and Ag2Hg3) were obtained from the spectra accumulated over a 100-second interval. The data were input to the computer program MAGIC IV by Colby6 to give corrected weight concentrations. To aid in phase identification, photographs were taken in the secondary electron (SE), backscattered electron (BSE), and x-ray (Sn, Cu, Ag, and Hg) modes (Figure). The amounts of the phases were calculated using compositions determined by
273
Mahler et al.7 For lathe-cut and spherical amalgams these are: Ag3Sn (-y) Ag22SnHg27 ('y), Sn8Hg (-Y2), Cu3Sn (e), and Cu6Sn5 ( '). The eutectic spheres (d) of 71.9% Ag and 28.1 % Cu are also present in the case of the dispersion amalgam. Since the calculations were limited to four unknowns, the phases qualitatively identified on the backscattered and x-ray photographs to be present in the greatest amounts were selected. The presence of the copper phase e was readily apparent in the lathe-cut and spherical amalgams because it occurred as relatively large, discrete particles. Cu6Sn5 (-q'), however, was not readily identified from the photographs. For this reason, e was selected along with y, yp, and 72 as the phases to be calculated. The presumption of the copper occurring as e or -q ' or a combination of the two has little effect on the amounts of the other phases calculated. The 71 ' phase was chosen in the case of the dispersion amalgam based on the backscattered photographs.
TABLE 2 PHASE DISTRIBUTION OF DENTAL AMALGAM (%) Amalgam
Lathe-Cut D Carved Burnished Polished Lathe-cut M Carved Burnished Polished Lathe-cut V Carved Burnished Polished
-Y
-f
1.43 ± 1.53 -0.94 ± 0.17 21.42 ± 4.17
81.55 + 1.99 73.13 2.86 71.13 ± 3.01
14.26 + 1.21 26.49 + 3.04 5.02 + 1.44
2.73 + 0.28 1.30 ± 0.08 2.27 + 0.34
9.01 ± 2.09 2.09 ± 0.87 5.75 ± 2.53
74.16 ± 2.35 63.76 ± 5.92 83.89 + 3.83
12.32 + 0.51 31.42 ± 6.89 7.32 ± 1.54
4.48 ± 0.32 2.71 + 0.22 3.01 ± 0.26
1.39 ± 0.89 -0.23 + 0.59 8.01 + 2.44
83.04 ± 1.33 71.38 + 4.62 84.07 + 2.40
12.23 + 0.40 27.04 + 4.15 5.41 + 0.35
3.31 + 0.30 1.75 + 0.23 2.47 ± 0.31
19.45 ± 1.74 2.20 ± 1.01 20.43 + 1.90
72.25 + 1.00 67.58 ± 4.11 71.50 + 1.49
5.42 + 0.73 28.87 + 5.00 5.46 + 0.47
2.85 + 0.47 1.31 ± 0.07 2.59 + 0.07
Spherical Carved Burnished Polished
d
-Y
Dispersion Carved Burnished Polished
9.08 ± 1.08 9.68 ± 2.15 14.14± 1.19
82.47 ± 0.36 86.10 ± 2.46 72.08 ± 1.72
0.12 + 0.76 -5.96 + 2.12 -0.79 + 0.85
Calculated from the data of Table 1. Samples were 14 days old at the time of analysis. 3 samples ± S.D.
Each value is the
8.30 + 0.36 10.14 + 2.32 15.22 + 0.48 average of measure-
ments on
Downloaded from jdr.sagepub.com at MOUNT ALLISON UNIV on June 23, 2015 For personal use only. No other uses without permission.
274
BOYER, EDIE & CHAN
j
Dent Res
February
FIG -SEM photographs of several amalgam products with surfaces finished by carving (left column), burnishing (center columnl) or polishing (right column). The letters refer to the product codes given in the text. The arrows point out crystals of the gain ma-2 phase on the burnished specimens. Original m agnification was x 500. Downloaded from jdr.sagepub.com at MOUNT ALLISON UNIV on June 23, 2015 For personal use only. No other uses without permission.
1978
Vol. 57 No. 2
SURFACE PREPARATION e AMALGAM PHASES
Results and Discussion
The results of the elemental analyses of the amalgams are given in Table 1. Each value is the average + standard deviation of measurements of three samples. The weight totals of the four elements were slightly less than 100% for the carved and burnished samples, and slightly greater than 100% for the polished samples before normalization to 100%. Interestingly, the standard deviations of the measurements on the carved and burnished samples are of similar magnitude to those of the polished samples even though the former have much rougher surfaces. Elemental analyses of polished samples by the EDX and the wavelength dispersive analysis (WDX) methods have been found to yield similar values." Phase fractions calculated from the data on polished samples were similar to those predicted by the stoichiometric re-
action equations. It can be seen in Table 1 that burnishing leads to high amounts of tin on conventional amalgams. Also of note is the high mercury content, 58%, of the polished surfaces of amalgams M and V. Polished specimens might be expected to give the bulk concentration of mercury, 54 and 50% for these amalgams. Since the high concentrations were consistently observed on the three polished samples of these amalgams, it is concluded that the polishing procedure itself caused an increase in the mercury content of the surfaces. The calculated phase distributions are listed in Table 2. Means were statistically compared using oneway analysis of variance and the Duncan multiple range test (P < 0.05). The dependent variable was phase percent and the independent variable was, in turn, phase type, surface finish, or material. Data were limited to single groups of the variables other than the independent variable for a given test, so that N = 9 for each test. For example, differences in the magnitudes of the phase types were tested for each surface finish and each material. In the discussion that follows, stated similarities or differences are based on these tests at the 5 % level of significance. PHASE DISTRIBUTION WITH RESPECT TO FINISH AND MATERIAL. - On carved and
burnished surfaces of the conventional
275
amalgams the relative order of magnitude was 'y' > 'Y2 > y (E was either the lowest or similar to the lowest value). The exception was carved surfaces of amalgam S where -y' > Y > 'Y2. On polished surfaces -y > y > 72, except on alloys M and V where ey 'Y2There was no significant difference among materials (conventional amalgams) in levels of 'Y2 or 'yl on burnished surfaces and no differences among materials in levels of 72 and e on polished surfaces. Carved surfaces on amalgams D and V were similar in amounts of y and y,. Polished surfaces of amalgams D and S were similar in amounts of -y and 'y as were amalgams M and V. 'y Variation. - The percent of unreacted particles, -y, was lowest on burnished surfaces or of a similar low value on burnished and carved surfaces. The exception was lathe-cut M which had similar values of -y on burnished and polished surfaces. The percent of -y on polished samples was higher than on carved samples of amalgams D and V, but similar to the amounts on carved samples of amalgams M and S. One would expect the ey particles to be masked by the matrix formed after carving and especially after burnishing, and that polishing would remove the softer matrix and expose the unreacted particles. 'yj Variation. - No consistent pattern was evident among the finish types with respect to 'yl variation. The percent of 'y' was lower on burnished samples of amalgams M and V than on carved or polished surfaces of these amalgams. The amounts of 'y, on carved and polished samples of amalgam V were similar. Amalgam S samples had similar levels of -y' regardless of the finish type. Y2 Variation. - The percent of Y2 was higher on the burnished surfaces than on the carved or polished surfaces of all four conventional amalgams, and ranged from 26 to 31%. The percent of 'Y2 was lowest on the polished surfaces or of similar low value to that found on carved surfaces. Burnishing apparently releases mercury onto the surface which reacts with the surface phases to form new matrix crystals. Under these conditions, 72 grows more rapidly than yl.
Downloaded from jdr.sagepub.com at MOUNT ALLISON UNIV on June 23, 2015 For personal use only. No other uses without permission.
276
BOYER, EDIE & CHAN
e Variation. -The percent of e was lowest on the burnished samples. Carved samples of amalgam M and V had the highest amounts of c, and carved or polished surfaces of amalgams D and S had similar amounts of c. All of the copper was assumed to be in the form of Cu3Sn, although it is realized Cu6Sn5 may actually predominate in some cases. PHASE VARIATION ON DISPERSION AMALGAM. - The dispersion amalgam samples had different responses to the finishing procedures than the conventional amalgams. There was no increase in y2, and no decrease in y and -y on burnished samples. Polishing exposed the most ey and burnishing yielded the most -y, on the samples. Apparently, the detection of the eutectic (d) was blocked by reaction products or debris
(Fig). The photographs of the carved samples show that all samples are very rough with the contours of the particles visible and deep pores opening to the surface. The burnished samples have improved smoothness with the pores having been obliterated. However, scattered across the burnished surfaces are platelike crystals identified as -y2 in the lathe-cut and spherical amalgams. The smaller, equiaxed crystals are 'y,. The burnished surface of the dispersion amalgam exhibits only the y, particles. The polished surfaces are the smoothest. It is possible to distinguish cross sections of the unreacted particles in the matrix. There is some debris on the polished dispersion amalgam in the forrm of -y particles. Since the tin-mercury phase has been shown to be electrochemically the most active9 and to be severely attacked by in vivo corrosion, 10 burnished surfaces are likely to corrode more than polished surfaces in the case of lathe-cut and spherical amalgams. This would not be expected with burnished dispersion amalgam since 72 was not identified on its surface. Conclusions
The phase distribution on the surfaces of dental amalgams was found to vary with the technique of finishing. The conventional amalgams behaved similarly with respect to changes in phase distributions for
j Dent
Res
February
1978
different finishes with a few exceptions. More unreacted particles were exposed in polished specimens than in carved or burnished specimens. The most marked variation was the increase in the tin-mercury phase, Y2, on the surfaces of burnished conventional amalgams and the concomitant decrease in all other phases on these samples. No Y2 was detected on the burnished dispersion amalgam; rather, the amount of -y, was increased. The silver-copper eutectic was masked from detection by a reaction product or debris in samples with all types of surface finishes. References 1. CHAN, K. C.; EDIE, J. W.; and BOYER, D. B.: Microstructure Study of Amalgam Surfaces,JProsth Dent 36:644-648, 1976. 2. WING, G., and RYGE, G.: Setting Reactions of Spherical Particle Amalgams, J Dent Res 44:1325-1333, 1965. 3. FUSAYAMA, T., and HAYASHI, K.: Microstructure of Amalgam Structures, J Dent
Res49:733-741, 1970. 4. RYGE, G.; MOFFET, J. C.; and BARKOW, A. G.: Microstructural Observations and X-Ray Diffraction Studies on Silver-Tin Amalgams, J Dent Res 32:2, 152-167, 1953. 5. WING, G.: Phase Identification in Dental Amalgam, A ust DentJ 11:105-113, 1966.
6. COLBY, J. W.: Quantitative Microprobe Analysis of Thin Insulating Films, Advances in X-Ray Analysis, II, New York: Plenum Press, 1958, pp 287-305. 7. MAHLER D. B.; ADEY, J. D.; and VAN EYSDEN, J.: Quantitative Microprobe Analysis of Amalgam, J Dent Res 54:218-226, 1975. 8. MAHLER, D. B.; ADEY, J. D.; and VAN EYSDEN, J.: Microprobe Analysis of Amalgam: I. Effect of Surface Preparation, J Dent Res 52:74-78, 1973. 9. GUTHROW, C. E.; JOHNSON, L. B.; and LAWLESS, K. R.: Corrosion of Dental Amalgam and Its Component Phases, J Dent Res 46:1372-1381, 1967. 10. MATEER, R. S., and REITZ, C. D.: Corrosion of Amalgam Restorations, J Dent Res 49:399-407, 1970. 11. EDIE, J. W.; BOYER, D. B.; and CHAN, K. C.: Estimation of the Phase Distribution in Dental Amalgam with the Electron Microprobe,JDent Res 57:277-282, 1978.
Downloaded from jdr.sagepub.com at MOUNT ALLISON UNIV on June 23, 2015 For personal use only. No other uses without permission.
College of Dentistry, University of Iowa, Iowa City, Iowa 52242, USA Several types of amalgams were prepared with carved, burnished, or polished surfaces. Elemental analyses were made of these surfaces with the electron microprobe and the phase fractions were calculated from these data. The phase distributions were found to vary with the technique of
finzshing. J Dent Res 57(2): 271-276, February 1978.
In a preliminary study of spherical amalgam samples with surfaces finished by carving, burnishing, or polishing, the au-
polished surfaces were the smoothest. The grain size and number of the matrix phases, 'y1 and 'Y2, did not vary among the superficial, subsuperficial, and central layers of any of the specimens. Burnished surfaces were found covered with minute granular prominences after a period of 15 minutes. These were presumed to be -yl and '2 crystals that grew as a result of free mercury released on the surface by burnishing. Other investigators have shown that the contact of mercury with amalgam causes the growth of new crystals on the surface.4 5 The purpose of the present study was to quantify the surface phases of spherical and other types of amalgam and to investigate the effect of surface preparation on the composition of the surfaces. In particular, we were interested in determining whether burnishing produces increased Y2 on other types of amalgam as well as spherical amalgam. The fractions of the phases have been quantified using electron microprobe analysis. The microprobe is used in the x-ray mode to measure the elemental weight concentrations from which the amounts of the phases can be calculated knowing the compositions of the phases.
thors1 found the surfaces of the burnished samples covered with oblong granules and platelike crystals. X-ray analysis with an electron microprobe identified these particles as the tin-mercury phase ('Y2). These particles were not observed in similar large amounts on the carved and polished samples. Other investigators have found that 'y2 crystals tend to grow in larger amounts on external surfaces, in voids, and in high mercury areas. Wing and Ryge2 found a relatively large amount of Y2 on the undisturbed set surfaces of spherical and lathecut amalgams which could be reduced by polishing. Excess mercury and voids lead to Materials and Methods higher Y2 content of polished amalgams. Fusayama and Hayashi3 compared Carved, burnished, and polished samcarved, burnished, finished, and polished were prepared from five commercial specimens of lathe-cut and spherical amal- ples lathe-cut D,a M," V,c spherical amalgams: gams. Carved surfaces were roughest and S,d and dispersion Di.e The precondensation mercury was 50, 54, 50, 48, and 50 Received for publication April 14, 1977. Accepted for publication August 31, 1977. weight %, respectively. The amalgams Supported by USPHS Grant S-501 -RR-05313-14. were prepared according to the manufacturers' instructions and hand condensed in 'New True Dentalloy, S.S. White, Philadelphia, Pa. 'Micro, L.D. Caulk Co., Milford, De. molds with a force of about 1 kg lucite 'Velvalloy, S.S. White, Philadelphia, Pa. (against a 1 kg weight on a balance). All of dSpheraloy, Kerr Manufacturing Co., Romulus, Mi. the samples were carved immediately with 'Dispersalloy, Johnson and Johnson, East Windsor, NJ. 271 Downloaded from jdr.sagepub.com at MOUNT ALLISON UNIV on June 23, 2015 For personal use only. No other uses without permission.
272
BOYER, EDIE
& CHAN
j Dent
Res
February
1978
TABLE 1 ELEMENTAL COMPOSITION OF DENTAL AMALGAM (WT%)* Amalgam
Lathe-cut D Carved Burnished Polished Lathe-cut M Carved Burnished Polished Lathe-cut V Carved Burnished Polished Spherical Carved Burnished Polished Dispersion Carved Burnished Polished
Sn
Cu
Ag
Hg
14.44 + 1.04 23.23 + 2.42 11.83 ± 0.05
1.68 ± 0.66 0.80 ± 0.05 1.39 ± 0.20
25.45 + 0.55 21.24 ± 0.98 37.06 ± 2.14
58.35 + 1.23 54.70 ± 1.44 49.69 + 2.31
15.42 + 0.72 28.50 + 5.32 10.00 + 1.80
2.76 ± 0.20 1.67 + 0.13 1.85 + 0.16
28.84 ± 0.88 20.66 ± 2.36 29.38 ± 0.88
49.13 + 2.84
12.99 + 0.57 24.05 + 3.51 8.83 ± 0.54
2.04 ± 0.19 1.07 ± 0.14 1.53 ± 0.19
25.93 ± 0.35 21.24 + 0.95 31.09 ± 1.09
59.01 ± 0.85 53.61 + 2.43 58.53 ± 1.68
11.87 + 0.47 25.96 + 3.84 12.05 + 0.12
1.75 + 0.29 0.81 ± 0.04 1.63 ± 0.08
35.91 ± 1.07 21.89 ± 1.92 36.40 ± 0.95
50.43 + 0.73 51.32 ± 1.95 49.92 ± 1.10
7.49 + 0.30
3.28 + 0.22 2.29 + 0.37 5.73 ± 0.31
28.50 ± 0.37
60.70 + 0.24 63.37 + 1.69 53.05 + 1.18
8.77 + 1.93 13.06 + 0.21
25.53 ± 0.64 28.81 + 0.88
52.94 + 1.60
58.74 ± 2.38
*Normalized to 100%. Each value is the average of measurements on 3 samples + S.D. The samples were 14 at the time of analysis.
days old
a razor blade. Three samples of each amal- HgMo, AgLo, SnLO, and CUKOc characgam were left as carved, 3 were burnished, teristic lines. Although wavelength disperand 3 were polished. There was a total of sive analysis (WDX) is normally the more 45 samples. Amalgams D and V were bur- accurate method of quantitation, the ennished from 15 to 20 minutes after mixing ergy dispersive analysis (EDX) mode was with a No. 28 burnisherf mounted in a de- selected in this case because EDX is insensivice to maintain the force at 200 grams. tive to variations in specimen height, does The other amalgams were burnished at 10 not experience defocusing effects as a reto 12 minutes. Burnishing times were sult of electron beam scanning, and analychosen to avoid grooving the surfaces and zes all elements simultaneously. The deyet shine them. All of the samples to be creased peak resolution and possible diffipolished were polished at 24 hours with the culties in correcting for background radiasame technique which consisted of cuttle tion or overlapping peaks were not the madisks,9 a rubber disk,' pumice and Amal- jor contributors to experimental error. glossi on a felt wheel. The samples were The normal prerequisites for quantitamounted directly on a specimen stub for tive microanalysis with the microprobe are analysis at 14 days with the ARL EMX-SM that the specimen be homogeneous and the microprobe.j surface flat so that theoretical corrections The average weight concentrations to for electron scattering and x-ray absorpdepths of about one micrometer were esti- tion and fluorescence may be made. While mated from x-ray intensities for the these conditions are not fulfilled in this exfS.S. White, Philadelphia, Pa. periment, the argument is advanced that "E.C. Moore Co., Dearborn, Mi. when scanning over a large surface area, 5J.F. Jelenko and Co., New Rochelle, NY. the errors will be to an extent offsetting L.D. Caulk Co., Milford, De. jApplied Research Laboratory, Sunland, Ca. and that the resulting elemental determiDownloaded from jdr.sagepub.com at MOUNT ALLISON UNIV on June 23, 2015 For personal use only. No other uses without permission.
SURFACE PREPARATION & AMALGAM PHASES
V'ol. 5 7 No. 2
nation should be within 5 to 10% of actual values (compared to 1% for point analyses). Because of this, it is recognized that the method is an approximate one and that the accuracy decreases with increasing specimen roughness. Each specimen was examined under the operating conditions of 20 kV accelerating voltage, 2 nA (on Au) specimen current and 800 x 1000 jjm2 video raster. Net peak heights for each element and for standards (pure Sn, Cu, Ag, and Ag2Hg3) were obtained from the spectra accumulated over a 100-second interval. The data were input to the computer program MAGIC IV by Colby6 to give corrected weight concentrations. To aid in phase identification, photographs were taken in the secondary electron (SE), backscattered electron (BSE), and x-ray (Sn, Cu, Ag, and Hg) modes (Figure). The amounts of the phases were calculated using compositions determined by
273
Mahler et al.7 For lathe-cut and spherical amalgams these are: Ag3Sn (-y) Ag22SnHg27 ('y), Sn8Hg (-Y2), Cu3Sn (e), and Cu6Sn5 ( '). The eutectic spheres (d) of 71.9% Ag and 28.1 % Cu are also present in the case of the dispersion amalgam. Since the calculations were limited to four unknowns, the phases qualitatively identified on the backscattered and x-ray photographs to be present in the greatest amounts were selected. The presence of the copper phase e was readily apparent in the lathe-cut and spherical amalgams because it occurred as relatively large, discrete particles. Cu6Sn5 (-q'), however, was not readily identified from the photographs. For this reason, e was selected along with y, yp, and 72 as the phases to be calculated. The presumption of the copper occurring as e or -q ' or a combination of the two has little effect on the amounts of the other phases calculated. The 71 ' phase was chosen in the case of the dispersion amalgam based on the backscattered photographs.
TABLE 2 PHASE DISTRIBUTION OF DENTAL AMALGAM (%) Amalgam
Lathe-Cut D Carved Burnished Polished Lathe-cut M Carved Burnished Polished Lathe-cut V Carved Burnished Polished
-Y
-f
1.43 ± 1.53 -0.94 ± 0.17 21.42 ± 4.17
81.55 + 1.99 73.13 2.86 71.13 ± 3.01
14.26 + 1.21 26.49 + 3.04 5.02 + 1.44
2.73 + 0.28 1.30 ± 0.08 2.27 + 0.34
9.01 ± 2.09 2.09 ± 0.87 5.75 ± 2.53
74.16 ± 2.35 63.76 ± 5.92 83.89 + 3.83
12.32 + 0.51 31.42 ± 6.89 7.32 ± 1.54
4.48 ± 0.32 2.71 + 0.22 3.01 ± 0.26
1.39 ± 0.89 -0.23 + 0.59 8.01 + 2.44
83.04 ± 1.33 71.38 + 4.62 84.07 + 2.40
12.23 + 0.40 27.04 + 4.15 5.41 + 0.35
3.31 + 0.30 1.75 + 0.23 2.47 ± 0.31
19.45 ± 1.74 2.20 ± 1.01 20.43 + 1.90
72.25 + 1.00 67.58 ± 4.11 71.50 + 1.49
5.42 + 0.73 28.87 + 5.00 5.46 + 0.47
2.85 + 0.47 1.31 ± 0.07 2.59 + 0.07
Spherical Carved Burnished Polished
d
-Y
Dispersion Carved Burnished Polished
9.08 ± 1.08 9.68 ± 2.15 14.14± 1.19
82.47 ± 0.36 86.10 ± 2.46 72.08 ± 1.72
0.12 + 0.76 -5.96 + 2.12 -0.79 + 0.85
Calculated from the data of Table 1. Samples were 14 days old at the time of analysis. 3 samples ± S.D.
Each value is the
8.30 + 0.36 10.14 + 2.32 15.22 + 0.48 average of measure-
ments on
Downloaded from jdr.sagepub.com at MOUNT ALLISON UNIV on June 23, 2015 For personal use only. No other uses without permission.
274
BOYER, EDIE & CHAN
j
Dent Res
February
FIG -SEM photographs of several amalgam products with surfaces finished by carving (left column), burnishing (center columnl) or polishing (right column). The letters refer to the product codes given in the text. The arrows point out crystals of the gain ma-2 phase on the burnished specimens. Original m agnification was x 500. Downloaded from jdr.sagepub.com at MOUNT ALLISON UNIV on June 23, 2015 For personal use only. No other uses without permission.
1978
Vol. 57 No. 2
SURFACE PREPARATION e AMALGAM PHASES
Results and Discussion
The results of the elemental analyses of the amalgams are given in Table 1. Each value is the average + standard deviation of measurements of three samples. The weight totals of the four elements were slightly less than 100% for the carved and burnished samples, and slightly greater than 100% for the polished samples before normalization to 100%. Interestingly, the standard deviations of the measurements on the carved and burnished samples are of similar magnitude to those of the polished samples even though the former have much rougher surfaces. Elemental analyses of polished samples by the EDX and the wavelength dispersive analysis (WDX) methods have been found to yield similar values." Phase fractions calculated from the data on polished samples were similar to those predicted by the stoichiometric re-
action equations. It can be seen in Table 1 that burnishing leads to high amounts of tin on conventional amalgams. Also of note is the high mercury content, 58%, of the polished surfaces of amalgams M and V. Polished specimens might be expected to give the bulk concentration of mercury, 54 and 50% for these amalgams. Since the high concentrations were consistently observed on the three polished samples of these amalgams, it is concluded that the polishing procedure itself caused an increase in the mercury content of the surfaces. The calculated phase distributions are listed in Table 2. Means were statistically compared using oneway analysis of variance and the Duncan multiple range test (P < 0.05). The dependent variable was phase percent and the independent variable was, in turn, phase type, surface finish, or material. Data were limited to single groups of the variables other than the independent variable for a given test, so that N = 9 for each test. For example, differences in the magnitudes of the phase types were tested for each surface finish and each material. In the discussion that follows, stated similarities or differences are based on these tests at the 5 % level of significance. PHASE DISTRIBUTION WITH RESPECT TO FINISH AND MATERIAL. - On carved and
burnished surfaces of the conventional
275
amalgams the relative order of magnitude was 'y' > 'Y2 > y (E was either the lowest or similar to the lowest value). The exception was carved surfaces of amalgam S where -y' > Y > 'Y2. On polished surfaces -y > y > 72, except on alloys M and V where ey 'Y2There was no significant difference among materials (conventional amalgams) in levels of 'Y2 or 'yl on burnished surfaces and no differences among materials in levels of 72 and e on polished surfaces. Carved surfaces on amalgams D and V were similar in amounts of y and y,. Polished surfaces of amalgams D and S were similar in amounts of -y and 'y as were amalgams M and V. 'y Variation. - The percent of unreacted particles, -y, was lowest on burnished surfaces or of a similar low value on burnished and carved surfaces. The exception was lathe-cut M which had similar values of -y on burnished and polished surfaces. The percent of -y on polished samples was higher than on carved samples of amalgams D and V, but similar to the amounts on carved samples of amalgams M and S. One would expect the ey particles to be masked by the matrix formed after carving and especially after burnishing, and that polishing would remove the softer matrix and expose the unreacted particles. 'yj Variation. - No consistent pattern was evident among the finish types with respect to 'yl variation. The percent of 'y' was lower on burnished samples of amalgams M and V than on carved or polished surfaces of these amalgams. The amounts of 'y, on carved and polished samples of amalgam V were similar. Amalgam S samples had similar levels of -y' regardless of the finish type. Y2 Variation. - The percent of Y2 was higher on the burnished surfaces than on the carved or polished surfaces of all four conventional amalgams, and ranged from 26 to 31%. The percent of 'Y2 was lowest on the polished surfaces or of similar low value to that found on carved surfaces. Burnishing apparently releases mercury onto the surface which reacts with the surface phases to form new matrix crystals. Under these conditions, 72 grows more rapidly than yl.
Downloaded from jdr.sagepub.com at MOUNT ALLISON UNIV on June 23, 2015 For personal use only. No other uses without permission.
276
BOYER, EDIE & CHAN
e Variation. -The percent of e was lowest on the burnished samples. Carved samples of amalgam M and V had the highest amounts of c, and carved or polished surfaces of amalgams D and S had similar amounts of c. All of the copper was assumed to be in the form of Cu3Sn, although it is realized Cu6Sn5 may actually predominate in some cases. PHASE VARIATION ON DISPERSION AMALGAM. - The dispersion amalgam samples had different responses to the finishing procedures than the conventional amalgams. There was no increase in y2, and no decrease in y and -y on burnished samples. Polishing exposed the most ey and burnishing yielded the most -y, on the samples. Apparently, the detection of the eutectic (d) was blocked by reaction products or debris
(Fig). The photographs of the carved samples show that all samples are very rough with the contours of the particles visible and deep pores opening to the surface. The burnished samples have improved smoothness with the pores having been obliterated. However, scattered across the burnished surfaces are platelike crystals identified as -y2 in the lathe-cut and spherical amalgams. The smaller, equiaxed crystals are 'y,. The burnished surface of the dispersion amalgam exhibits only the y, particles. The polished surfaces are the smoothest. It is possible to distinguish cross sections of the unreacted particles in the matrix. There is some debris on the polished dispersion amalgam in the forrm of -y particles. Since the tin-mercury phase has been shown to be electrochemically the most active9 and to be severely attacked by in vivo corrosion, 10 burnished surfaces are likely to corrode more than polished surfaces in the case of lathe-cut and spherical amalgams. This would not be expected with burnished dispersion amalgam since 72 was not identified on its surface. Conclusions
The phase distribution on the surfaces of dental amalgams was found to vary with the technique of finishing. The conventional amalgams behaved similarly with respect to changes in phase distributions for
j Dent
Res
February
1978
different finishes with a few exceptions. More unreacted particles were exposed in polished specimens than in carved or burnished specimens. The most marked variation was the increase in the tin-mercury phase, Y2, on the surfaces of burnished conventional amalgams and the concomitant decrease in all other phases on these samples. No Y2 was detected on the burnished dispersion amalgam; rather, the amount of -y, was increased. The silver-copper eutectic was masked from detection by a reaction product or debris in samples with all types of surface finishes. References 1. CHAN, K. C.; EDIE, J. W.; and BOYER, D. B.: Microstructure Study of Amalgam Surfaces,JProsth Dent 36:644-648, 1976. 2. WING, G., and RYGE, G.: Setting Reactions of Spherical Particle Amalgams, J Dent Res 44:1325-1333, 1965. 3. FUSAYAMA, T., and HAYASHI, K.: Microstructure of Amalgam Structures, J Dent
Res49:733-741, 1970. 4. RYGE, G.; MOFFET, J. C.; and BARKOW, A. G.: Microstructural Observations and X-Ray Diffraction Studies on Silver-Tin Amalgams, J Dent Res 32:2, 152-167, 1953. 5. WING, G.: Phase Identification in Dental Amalgam, A ust DentJ 11:105-113, 1966.
6. COLBY, J. W.: Quantitative Microprobe Analysis of Thin Insulating Films, Advances in X-Ray Analysis, II, New York: Plenum Press, 1958, pp 287-305. 7. MAHLER D. B.; ADEY, J. D.; and VAN EYSDEN, J.: Quantitative Microprobe Analysis of Amalgam, J Dent Res 54:218-226, 1975. 8. MAHLER, D. B.; ADEY, J. D.; and VAN EYSDEN, J.: Microprobe Analysis of Amalgam: I. Effect of Surface Preparation, J Dent Res 52:74-78, 1973. 9. GUTHROW, C. E.; JOHNSON, L. B.; and LAWLESS, K. R.: Corrosion of Dental Amalgam and Its Component Phases, J Dent Res 46:1372-1381, 1967. 10. MATEER, R. S., and REITZ, C. D.: Corrosion of Amalgam Restorations, J Dent Res 49:399-407, 1970. 11. EDIE, J. W.; BOYER, D. B.; and CHAN, K. C.: Estimation of the Phase Distribution in Dental Amalgam with the Electron Microprobe,JDent Res 57:277-282, 1978.
Downloaded from jdr.sagepub.com at MOUNT ALLISON UNIV on June 23, 2015 For personal use only. No other uses without permission.
