Composition of clinically aged amalgam restorations D.B. Boyer J.W. Edie Department of Operative Dentistry College of Dentistry The University of Iowa Iowa City, Iowa 52242 Received June 5, 1989 Accepted April 18, 1990 This investigation was supported in part by USPHS Research Grant R01 DE06519. Dent Mater 6:146-150, July, 1990

Abstract-Twenty-five amalgam restorations ranging in age from two to 25 years were obtained from five subjects. An electron microprobe was used to analyze the specimens for bulk elemental composition and phase composition, and the volume fractions of phases were determined by pointcounting on back-scattered electron micrographs. Twenty-one of the specimens were conventional, low-copper amalgams, and the remaining four were high-copper amalgams. The bulk elemental compositions showed little variation from newly prepared amalgams except for the presence of a small amount of chloride and other contaminants. The compositions of the phases were essentially the same as is found in new amalgams, except that there was considerable internal amalgamation of gamma particles. The distribution of phases in the clinically aged amalgams was quite different from that of new amalgams. The low-copper amalgams had decreased amounts of gamma, gamma-l, and gamma-2 phases and increased beta-1 and tin-chloride. The high-copper admixed amalgams had decreased gamma, increased beta-l, and enlarged reaction rings (gamma-1 and eta').

ental a m a l g a m u n d e r g o e s changes in microstructure and composition due to phase transformations during aging and due to corrosion in oral fluids. These changes are potentially detrimental to the clinical durability of amalgam restorations. The major microstructural change is the transformation of the gamma1 phase into the beta-1 phase (Johnson, 1967a). Mercury is released during this transformation, and it reacts with gamma particles to form additional gamma-1 and gamma-2. The gamma-1 to beta-1 transition has been shown to occur in aged clinical amalgams as well as in laboratory specimens (Johnson, 1967b; Mahler et al., 1973; Vrijhoef and Driessens, 1974; Marshall et al., 1986). The transition is highly temperature-dependent, and laboratory specimens have frequently been heated to accelerate beta-1 formation. Jensen and J~rgensen (1978) found only a small amount of beta-1 after storage of amalgam at 37°C for two years, while Reynolds (1973) found that amalgam specimens were predominantly beta1 after being heated at 70°C for seven weeks. Beta-1 formation occurs in high-copper as well as conventional amalgams (Jensen and J~rgensen, 1981; Lin et al., 1983; Marshall et aL, 1986). Corrosion of amalgam increases the formation of beta-1 (Jensen, 1977; Lin et al., 1983). Beta-1 formation is potentially detrimental to amalgam, since internal stresses and porosity may result (Johnson, 1967a). Reduction in the amount of gamma, as a result of beta1 formation, would be expected to result in lower strength (Young et al., 1973). Okabe et al. (1985) have shown that the compressive strength of amalgam decreases as the beta-1 content increases. Several investigators have related the increase in resistance to creep of aged amalgam to beta-1 formation (Espevik, 1977; Jensen and J~rgensen, 1978; Okabe

D

146 BOYER & EDIE/COMPOSITION OF AGED A M A L G A M S

et aL, 1985). While resistance to creep is a desirable property, it may be accompanied by an undesirable increase in brittleness. Other microstructural changes that occur in aged amalgam include the decrease in gamma and increase in gamma-2 associated with beta-1 formation, as already mentioned. In addition, the gamma-2 that is initially formed in admixed, high-copper amalgams decreases with aging and eta' (Cu~Sns) increases (Marshall and Marshall, 1979; Jensen and J~rgensen, 1981). Additional changes occur due to corrosion in oral fluids. In conventional a m a l g a m s , the g a m m a - 2 phase dissolves (J~rgensen, 1965) and i s replaced with tin-hydroxychloride and SnO corrosion products (Sarkar et al., 1975; Marshall and Marshall, 1980). During corrosion of high-copper amalgams, the reaction zones around high-copper content particles are attacked, resulting in loss of eta' and the formation of Sn02. A recent study of the microstructure of clinically aged high-copper and conventional amalgam restorations showed that amalgams with similar clinical ratings had marked variability in corrosion, porosity, and phase contents (Marshall et al., 1987). There was no simple r e l a t i o n s h i p b e t w e e n clinical age and corrosion content. The purpose of the present study was to quantify the compositions and phase distributions of older clinical amalgam restorations. Most of the work just reviewed has been conducted with laboratory specimens that have been aged for a short period or heated to accelerate phase changes and clinical specimens no more than five years old. An exception is the recent work of Marshall et al. (1986, 1987), who examined clinical specimens from three to 10 years old. The main objective of this study was to quantify the amount of beta-1 formed in aged clinical amalgams.

MATERIALS AND METHODS

Twenty-five amalgam restorations were removed from five patients. The amalgams had originally been placed by the subjects' dentists, so that the alloys and procedures used were not under control of this study. The alloys, as stated by the dentists, are given in Table 1. Twentyone of the restorations were conventional, low-copper alloys, and 15 of these were 20th Century FineCut and Optaloy (L.D. Caulk Co.). The remaining conventional alloys were Spheraloy (Kerr) and Velvalloy (S.S. White). Only four restorations were of the high-copper type. Three of these were Dispersalloy (J & J), and one was Tytin (S.S. White). The ages of the restorations at removal were determined from the dental records (Table 1). The record was no longer available for subject B, so that the estimated age based on the subject's recall was used. The mean age of the low-copper amalgains was 15 years (range = 7 to 25). The mean age of the high-copper amalgams was four years (range = 2 to 6). The amalgams were embedded in epoxy, and the exposed cross-sectioned surface was metallurgically polished to a < 1 ~m finish. The surfaces were coated with a light carbon layer (< 20 nm). The composition of the amalgams was analyzed by an A R L E M X - S M microprobe with m e t h o d s previously described (Edie et aL, 1978). Three interior areas were arbitrarily selected and subjected to the f o l l o w i n g a n a l y s e s : (1) A calibrated, e n e r g y - d i s p e r s i v e x-ray analysis (EDX) spectrum was obrained while a 500 x area was being irradiated. The average x-ray intensity for Hg, Ag, Sn, Cu, and C1 was determined. The operating conditions were 15 kV, 10 hA, 200 s counting time, and an 800 x 1000 Fm video raster. (2) Point analyses of the phases appearing in one of the areas were conducted. (3) A 500 x b a c k - s c a t t e r e d electron (BSE) image was recorded. (4) The distribution of phases was determined by a point-count analysis, with a 13 × 17 point transparent grid used on the BSE micrographs.

shown by the analysis of 83 alloys on the list of Certified Dental Amalgams (Council on Dental Materials and Devices, 1968). The average composition was 69.4% Ag, 26.2% Sn, 3.6% Cu, and 0.8% Zn. The manufacturers' recommended mercury content of the mixes ranges from 48-54% for these alloys; however, the final mercury content of the amalgams will be lower if excess mercury is expressed with a squeeze cloth or during condensation. Because of the close agreement between the concentrations of Ag, Sn, and Cu in the clinical specimens and the calculated concentrations based on 45% Hg, this amount of mercury probably represents the residual

RESULTS

Bulk Elemental Composition-The bulk elemental composition (wt%) of the clinical amalgam specimens is given in Table 1. The mean composition of the clinical specimens is compared with the composition derived from the original composition of Optaloy and the alloy/mercury ratio of the clinical amalgams in Table 2. Optaloy contains 69.8% Ag, 25.7% Sn, 3.8% Cu, and 0.7% Zn. The composition of Fine-Cut is similar, with 0.9% less Cu (personal communication from L.D. Caulk Co.). The compositions of Spheraloy and Velvalloy are similar. The conventional alloys used in the 1960's and early 1970's had very similar compositions, as

TABLE 1 BULK ELEMENTAL COMPOSITION (wt%) OF CLINICAL AMALGAMS Sample Alloy* Age (yr) Hg Ag Sn Cu A3 F 17 45.6 38.6 12.4 2.9 A14 F 11 42.4 43.9 12.3 0.8 A19 F 11 41.8 43.1 13.8 0.8 A29 F 17 42.9 38.4 15.3 3.0 A30 F 7 46.6 35.4 15.6 2.3 A31 F 17 48.7 34.6 13.6 2.2 B2 F 23** 45.6 35.8 16.4 2.2 B4 F 23 51.7 32.1 13.5 2.5 B14 F 23 43.3 40.1 13.7 2.7 B15 F 23 43.5 39.8 13.5 3.0 B30 D 52.1 32.4 9.6 5.4 B31 F 23 42.6 39.8 14.6 2.8 C14 D 6 46.5 35.5 11.6 6.3 C15 14 44.3 32.9 18.4 2.5 C18 S 13 46.6 34.8 16.0 2.6 C19 S 13 46.3 34.4 16.4 2.7 C20 T 2 37.4 35.0 18.8 8.6 D2 0 44.0 38.4 14.1 3.0 D3 D 4 50.9 30.3 13.1 5.4 D14 0 16 46.0 38.2 12.9 2.8 D19 0 18 47.1 36.9 12.6 3.0 D31 0 14 50.1 34.5 12.3 2.5 E4 V 8 46.0 37.8 12.9 2.3 E5 V 8 44.5 41.0 11.2 2.6 E13 V 10 35.9 45.1 15.9 3.0 *F = Fine-Cut, D = Dispersalloy, S = Spheraloy, T = Tytin, 0 = Optaloy, V = Velvalloy. **Estimated mean age of alloy F was 23 years (range = 21-25 yr).

CI 0.6 0.6 0.5 0.5 0.0 0.9 0.1 0.2 0.3 0.3 0.5 0.2 0.1 1.9 0.2 0.2 0.1 0.5 0.5 0.2 0.5 0.5 1.0 0.7 0.2

TABLE 2 BULK COMPOSITION OF AMALGAM (wt%) N Hg Low-copper clinical 21 45.0 (3.3) Optaloy* 45.0 High-copper clinical 3 49.8 (2.9) Dispersalloy* 49.8 *Composition of amalgam calculated from ratio of the clinical specimens.

Ag

Sn

Cu

CI

37.9 (3.6) 38.4

14.2 (1.8) 14.1

2.5 (0.6) 2.1

0.5 (0.4)

32.7 (2.6) 11.4 (1.8) 5.7 (0.5) 0.4 (0.2) 35.1 8.5 6.0 the composition of the alloy and the mean alloy/mercury

Dental Materials~July 1990 147

TABLE 3 COMPOSITION OF AMALGAM PHASES (wt%) -y clinical Ag3Sn Mahler

N

Hg

Ag

Sn

Cu

CI

24

8.9(4.1)

64.8(4.4) 73.2 70.7

24.1(1.9) 26.8 24.9

2.1(1.0)

0.1(0.5)

1.8

0.9 (Zn)

67.6(1.3) 73.6 68.5

29.2(1.0) 26.4 30.0

2.6(0.8)

0.5(0.4)

0.1(0.1)

50.0(4.0) 60 50.0

42.4(2.0) 40 41.5

6.9(2.3)

0.6(0.6)

0.1(0.1)

1.7

'Y1 clinical Ag2Hg3 Ag22SnHg27 Pl clinical AgsHg4 Espevik .q, clinical Cu6Sn5

20

11

2.5(1.0)

0.9(0.9)

59.8(2.2) 60.9

36.8(2.2) 39.1

Sn-CI clinical Sn(OH)CI-H20

11

2.4(1.1)

1.1(1.6)

78.8(3.2) 62.7

0.2(0.2)

24

1.5

8.4

17.5(1.9) 18.7

TABLE 4 BULK PHASE CONTENT OF CLINICAL AMALGAMS (vol%) Sample ,,/ ~'1 61 ~'2/E1 A3 8.3 3.7 79.3 --A14 31.2 30.4 30.9 --A19 28.2 29.9 36.7 --A29 15.0 11.8 59.8 --A30 26.1 56.0 --12.3 A31 10.4 14.6 63.8 --B2 31.5 60.5 --3.9 B4 21.4 69.3 --2.1 B14 21.9 20.3 49.8 --B15 20.1 29.3 44.2 --B30 6.7 67.4 6.3 4.7E B31 20.5 33.3 41.9 --C14 20.3 57.6 --10.7E C15 16.1 32.1 39.4 --C18 25.0 65.8 --8.0 C19 32.1 63.0 . . . . . . C20 32.0 39.5 . . . . . . . . . D2 15.2 21.7 47.7 3.2 D3 11.5 58.8 6.2 8.4E D14 16.4 27.9 37.1 0.9 D19 13.6 38.9 34.4 4.1 D31 12.2 47.1 29.3 --E4 16.1 21.3 48.6 --E5 20.4 18.5 54.9 --E13 30.2 24.2 39.5 --1E= eutectic, R = reaction ring for high-copper amalgams. 2p = porosity. Includes CuSn and SnCl. 3Calculated from EDX scan data.

mercury in the amalgams after they were placed. This agreement does not support the view that approximately 5% mercury has been lost from the restorations due to corrosion, vaporization, or leaching. It should be era-

p2 8.7 7.4 5.2 13.4 5.0 11.2 3.9 7.2 8.0 6.4 1.3 4.2 1.8 12.3 1.2 4.8 10.6 4.4 15.0 9.0 8.1 14.0 6.2 5.4

CuSn3/R1 3.8 ---

--3.9 2.9 2.9 2.7 3.6 3.3 3.8 11.2R 3.5 9.5R 3.4 3.5 3.6 25.3R 3.9 10.4R 3.6 4.0 3.4 2.8 3.1 3.4

SnCi3 3.2 3.2 2.7 2.7 --4.8 0.5 1.1 1.6 1.6 2.7 1.1 0.7 10.2 0.9 0.9 0.5 2.7 4.4 1.1 2.7 2.7 5.3 3.7 1.1

phasized that the interior areas of these amalgam specimens were analyzed, not the surfaces, which were highly corroded. There was also close agreement between the composition of the clin-

148 BOYER & EDIE/COMPOSITION OF AGED AMALGAMS

ical Dispersalloy specimens and the calculated composition based on the alloy composition of 70% Ag, 17% Sn, 12% Cu, and 1% Zn. The amount of mercury in Dispersalloy mixes is 50%, and essentially all of this was found in the clinical specimens. Composition of Amalgam Phases. - The compositions of the phases determined by point analysis with the microprobe are given in Table 3. Nominal compositions of the phases and literature values are given for comparison (Mahler et al., 1975; Espevik, 1977). In general, there was good agreement between the compositions of the phases in the aged clinical specimens and the literature values, indicating no changes in the phases with aging. The exception is the remaining gamma particles, which contain a substantial amount of mercury (8.9% on average). Considerable internal amalgamation of the original particles has occurred, so that they are a mixture of gamma and gamma-1. The tin-chloride corrosion products were rich in tin and thus were mixtures of tin-oxides and tin-hydroxy-chloride complexes, as shown by Sarkar et al. (1975) and Marshall and Marshall (1980). Phase D i s t r i b u t i o n s . - The phase contents of the interiors of the clinical amalgam specimens are given in Table 4. The phase distributions were determined from the point-count analysis of BSE photographs. The values for porosity, P, include all black f e ~ r e s , such as SnC1 and CuSn. The concentrations of these two phases were estimated from the elemental composition scans. The mean values of the phase concentrations of the low-copper and high-copper clinical specimens are shown in Table 5. The low-copper amalgams showed marked decreases in gamma, gamma-l, and gamma-2 and increased beta-1 and SnC1 compared with laboratory specimens (Marshall et al., 1987; Edie et al., 1978). Betai was determined to be the light areas of the matrix, as shown in Fig. 1. The high-copper, admixed clinical s p e c i m e n s exhibited d e c r e a s e d gamma, increased beta-l, and increased reaction rings surrounding the eutectic particles. The reaction ring consists of a mixture of gamma1 and eta'.

70

6O

5o

i

4o

20

y

64x

40

10 0 8

10 AGE

12

14

16

(YEARS)

Fig. 2. Beta-1 content vs. age for conventional

amalgams from subject A.

0.145 after two years for laboratory specimens stored at 37°C. Fig. 1. Back-scattered electron micrograph (500X) of an 11-year-old conventional amalgam (specimen A14).

DISCUSSION

There has been limited work quantifying the amount of beta-1 in clinical or laboratory amalgam specimens that have been aged at 37°C. Marshall et al. (1986) found that the beta1/gamma-1 ratio was 0.37 for clinical low-copper amalgams from three to nine years old. Jensen and Jcrgensen (1978) found that the .beta-l/ gamma-1 ratio calculated from x-ray diffraction peaks ranged from 0.1 to 0.37 after two years' storage at 37°C. They determined from stoichiometric calculations t h a t the b e t a - l / gamma-1 ratio would be 10:1 at equilibrium. The main finding of this study was the high amounts of beta-1 present in conventional amalgam restorations with a mean age of 15 years. The mean a m o u n t of beta-1 was 35.1%, as determined from the backscattered electron micrographs. The mean beta-i/gamma-1 ratio was 1.02 (from Table 5). The increased amount compared with the aforementioned studies is probably due to the increased age of the specimens in this study, but may also be related to differences in measurement techniques or other factors, such as materials and the thermal and corrosion histories of the amalgams. The gamma-1 to beta-1 transition is age-dependent, as shown by Jensen and J0rgensen (1978, 1981) with laboratory samples, but this is dif-

ficult to demonstrate with clinical samples. The a m o u n t of beta-1 formed depends on the thermal history and the degree of corrosion of the amalgams, and these are not related simply to age. Marshall et al. (1986) found no relationship between the amount of beta-1 and age from three to nine years. Similarly, in this study, no relationship was found between the amount of beta-1 and age when the specimens from all subjects were included. One subject had conventional amalgams of widely differing ages, and the dependence of beta-1 on age was clear (Fig. 2). There were too few high-copper amalgams obtained from the subjects of this study for fwm conclusions to be drawn with regard to amounts of beta-1 found. The beta1/gamma-1 ratio was 0.056 (Table 5) for the four specimens with an average age of four years. Marshall et al. (1986) found this ratio to be 0.67 for 3-9-year clinical specimens, and Jensen and J0rgensen (1981) found

REFERENCES COUNCIL ON DENTAL MATERIALS AND DEVICES (1968): Guide to Dental Materials and Devices, 4th ed., Chicago: American Dental Association, p. 17. EDIE, J.W.; BOYER, D.B; and CHAN, K.C. (1978): Estimation of the Phase Distribution in Dental Amalgam with the Electron Microprobe, J Dent Res 57: 277-282. ESPEVIK, S. (1977): Creep and Phase Transformation in Dental Amalgam, J Dent Res 56: 36-39. JENSEN, S.J. (1977): Formation of ~, by Corrosion of Dental Silver Amalgam, J Dent Res 56: AS0, Abst. No. 151. JENSEN, S.J. and JORGENSEN, K.D. (1978): Creep and ~ Formation in Dental Amalgam, Scand J Dent Res 86: 408-411. JENSEN, S.J. and JORGENSEN, K.D. (1981): Stoichiometric and X-ray Diffraction Analysis on the ~2--'~' Transformation in a Dispersant Phase Silver Amalgam, Scand J Dent Res 89: 108112. JOHNSON, L.B., JR. (1967a): X-ray Diffraction Evidence for the Presence of (Ag-Hg) in Dental Amalgam, J Biomed Mater Res 1: 285-297. JOHNSON, L.B., JR. (1967b): Confirmation of the Presence of Beta (Ag-Hg)

TABLE5 BULK PHASE CONTENT OF AMALGAMS (vol%) N ~ ~1 ~1 x2 P* Low-copper clinical 21 20.6 (7.3) 34.3 (19.0) 35.1 (23.2) 1.6 (3.2) 8.0 (3.7) High-copper clinical 4 17.6 (11.1) 55.8 (10.2) 3.1 (3.6) eutectic 1.9 (1.8) 6.0 (4.7)

CuSn

SnCI

3.1 (1.1) 2.6 (2.2) reaction 2.1 (1.6) ring 14.1 (7.5)

*P = porosity. Includes CuSn and SnCI.

Dental Materials~July 1990 149

in Dental Amalgam, J Biomed Mater

Changes in Cu-rich Amalgams, J

Res 1: 415-425.

Biomed Mater Res 13: 395--406.

J¢RGENSEN, K.D. (1965): The Mechanics of Marginal Fracture of Amalgam Fillings, Acta Odontol Scand 23: 347-389. LIN, J.-H.C.; MARSHALL, G.W.; and MARSHALL, S.J. (1983): Microstructures of Cu-rich Amalgams after Corrosion, J Dent Res 62: 112-115. MAHLER, D.B.; ADEY, J.D.; and VAN EYSDEN, J. (1973): Transformation of Gamma 1 in Clinical Amalgam Restorations, IADR Prog & Abst 52: No. 190. MAHLER, D.B; ADEY, J.D.; and VAN EYSDEN, J. (1975): Quantitative Microprobe Analysis of Amalgam, J Dent Res 54: 218-226. MARSHALL, S.J. and MARSHALL, G.W., JR. (1979): Time-dependent Phase

MARSHALL, S.J. and MARSHALL, G.W., JR. (1980): Sn4(OH)6C12 and SnO Corrosion Products of Amalgams, J Dent Res 59: 820-823. MARSHALL, S.J.: MARSHALL, G.W., JR.; LETZEL, H.; and VRIJHOEF, M.M.A. (1986): Beta-1 Phase Content in Amalgam Restorations, IADR Prog & Abst 65: No. 36. MARSHALL, G.W., JR.; MARSHALL, S.J.; LETZEL, H.; and VRIJHOEF, M.M.A. (1987): Microstructures of Cu-rich Amalgam Restorations with Moderate Clinical Deterioration, Dent Mater 3: 135-143. OKABE, T.; MITCHELL, R.J.; BUTTS, M.B.: GALLOWAY, S.S.; and TwmGs, W.S. (1985): Change in Creep Rate and Microstructure in an Aged, Low-cop-

15{} BOYER & EDIE/COMPOSITION OF AGED AMALGAMS

per Amalgam, J Biomed Mater Res 19: 727-746. REYNOLDS, C.L., JR. (1973): The Redistribution of Mercury as Observed in the Phase Transformations in Amalgams, J Biomed Mater Res 7: 335-352. SARKAR, N.K.; MARSHALL, g.w., JR.; MOSER, J.B.: and GREENER, E.H. (1975): In vivo and in vitro Corrosion Products of Dental Amalgam, J Dent Res 54: 1031-1038. VRIJHOEF, M.M.A. and DRIESSENS, F.C.M. (1974): L o n g - t e r m Phase Changes in Dental Amalgam after Setting, J Biomed Mater Res 8: 435442. YOUNG, F.A.; WILSDORF, H.G.F.; and PAFFENBARGER, G.C. (1973): Some Relationships between Microstructure and Strength of Ag3Sn and Dental Amalgam, J Dent Res 52: 281-290.

Composition of clinically aged amalgam restorations.

Twenty-five amalgam restorations ranging in age from two to 25 years were obtained from five subjects. An electron microprobe was used to analyze the ...
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