Changes in Composition of Amalgam Alloys During Amalgamation and Condensation*

Changes in Composition of Amalgam Alloys During Amalgamation and Condensation*

1076 T he Journal of the American D ental Association In conclusion, I m ight suggest th e in­ advisability of operating fo r th e recovery of needl...

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1076

T he Journal of the American D ental Association

In conclusion, I m ight suggest th e in­ advisability of operating fo r th e recovery of needles in a septic field, w here the tissues have been trau m atized by previous attem pts a t recovery o r extraction, and

w here there is any suppurative process. T hese conditions should be treated and the tissues allow ed to re tu rn to th eir norm al tone before operation. 450 S utter Street.

C H A N G E S I N C O M P O S IT IO N O F A M A L G A M A L L O Y S D U R IN G A M A L G A M A T IO N A N D C O N D E N S A T IO N * By K. W. RA.Y, Ph.D ., and GEORGE S. EASTON, D.D.S., Iowa City, Iowa H E properties of am algam s seem to depend on several factors, some of th e m ore im p o rta n t of w hich are : ( 1 ) the m ethod of m aking, com m inuting and annealing the alloy; ( 2 ) the m ethod of m ixing, kneading and packing the am alg am ; (3 ) its composition, and (4 ) its age and integrity. T h e effects of each of these factors on the properties of am al­ gam s have been carefully studied and are now fairly w ell know n.1 In studying the effects of the composition, little atten tio n has been paid to any of the changes th a t m ig ht occur in the composition of the alloy d u rin g the process of am algam ation and condensation. I n preparing am algam for, and during the process of, insertion into the cavity, the dentist usually produces three distinct alloys, each of w hich has a different m er­ cury content. T h e first is produced w hen the excess m ercury is expressed from the mass of am algam , and consists largely of m ercury. T h e second is m ade up of the

T

*F rom the M e tallu rg y D ivision, D e p a rt­ m ent of Chem istry, a n d the College of D en­ tistry , State U n iv ersity of Io w a. 1. Black, G. V .: D ent. Cosmos, 38:982 (D ec.) 1896; G ray , A. W .: T r . Am . Inst. M in. and M et. Eng., 60:693, 1919. Souder, W ilm er, a n d P eters, C. G .: T ech . P a p e r of B u re au of S ta n d a rd s No. 157, 1920, and others. Jour. A . D. A., June, 1931

soft, semifluid m aterial th a t is b ro u g h t to the surface d u rin g condensation and then rem oved from th e cavity. T h e th ird con­ sists of the packed am algam , th a t is, the finished filling. T h is packed am algam is said to consist of a com pound of silver and m ercury (A g 3H g 4) and possibly a sim ilar com pound of copper and m ercury, together w ith a solid solution of tin .2 T h e m ore nearly com plete the elim ina­ tion of th e free tin, the stro n g er and m ore stable the filling is said to be.3 I t is w ell k now n th a t th e excess m er­ cury w hich is expressed d u rin g am alga­ m ation and condensation carries out some of the m etal co n ten t of the a llo y ; b u t it appears th a t little w o rk has been done to determ ine the am ounts of th e various constituents so removed. T w o general m ethods of am algam ation are in use. In the one, an excess of m er­ cury is used, th e alloy and m ercu ry are mixed and kneaded and th e excess is then removed before or d u rin g condensation. 2. H a rp e r, W . H . : Significance to D entists of Physicochem ical C hanges Incid en tal to A m algam ation and the H a rd e n in g of D ental A m algam s, J. A. D. A., 12:34 (Ja n .) 1925. 3. H a rp e r, W . H .: A m a lg a m : Its W o rk in g P ecu liarities a n d Its O p e ratin g D em ands, J.A .D .A ., 13:1122 (A u g .) 1926.

1077

Ray and Easton— Amalgam Alloys

Garrod-Thomas7 state that only 0.0024 per cent of copper is soluble in mercury, while Reenders8 gives the solubility of silver as 0.042 per cent at about room temperature. By applying these degrees of solubility to a practical example, their magnitude becomes clear. For example, if an amal­ gam is prepared using an alloy-mercury ratio of 6 :9, and if the excess mercury is expressed before or during condensation, leaving the packed amalgam to consist of 50 per cent alloy and 50 per cent mer­ cury, it is possible to calculate the com­ position of the packed amalgam and also to calculate the amount of the various

In the other, a minimum of mercury is used so that only a little can be expressed during condensation. It has been stated4 that by using an excess of mercury, a better mix is obtained, and that a harder and stronger amalgam can be secured, provided the excess mercury is removed before or during condensation. It is also held that this method gives a packed amalgam of a different composition from what would be estimated from the formula of the alloy, since the expressed mercury carries out the metals originally present in different amounts. The solubility of each of the constit­ uent metals separately in mercury is well T

able

1.— C o m p o s i t i o n

of

A

m a l g a m s as

C o m po n en t M

Com position of Original Alloy

Silver T in Copper Zinc M ercury

67.0 26.0 5.0 2.0 0.0

C

a lcu la ted fro m

e ta ls in

M

the

S o l u b il it y

of th e

ercury

Original M etals Rem oved P e r C ent

Original M etals in Packed Amalgam P er C ent

Com position of M aterial Rem oved

Composition of Packed Amalgam

0.03 0.13 0.07 7.15 33.33

99.97 99.87 99.93 92.85 66.66

0.08 0.32 0.17 17.54 81.87

33.58 13.00 2.50 0.92 50.00

known. Van Heteren5 has found that about a 1.24 atomic percentage (equal to 0.73 percentage by weight) of tin will dissolve in mercury at 35 C. Zinc is even more soluble. According to N. A. Puschin,6 2.84 per cent by weight is present in a saturated solution of zinc in mercury at 36 C. Copper and silver are much less soluble. T . W . Richards and R. N. 4. G ra y , A. W .: T r . Am . Inst. M in. Eng., Sup. Bull. No. 144, 1918. 5. V an H e tere n : Ztschr. A norg. Chem., 42: 129, 1904. 6. Puschin, N. A .: Z tschr. A norg. Chem., 36:214, 1903.

metals carried out. Table 1 shows the results of such a calculation. Thus, it is seen that only about 60 per cent of the amalgam is to be found in the packed portion (finished filling). This indicates that if the degrees of solubility of the metals of an amalgam alloy were the same as they are separately, the only appreciable change in composition during amalgamation and condensation would be a slight increase in the silver 7. R ichards, T . W ., a n d G a rro d -T h o m a s, R. N .: Z tschr. Phys. Chem., 72:165, 1910. 8. R een d ers: Z tschr. Phys. Chem., 54:609, 1904.

T he Journal of the American D ental Association

1078

co n ten t and a m edium decrease in the zin c content. J . W . M a lle t,9 w orking w ith p latinum -tin, platinum -silver and tin-copper alloys, found th a t the action of m ercury on alloys is not the sam e as on the com ponent m etals taken separately. T h erefo re, there m ay be several factors nearly as im p o rtan t as solubility in the change in composition occurring du rin g am algam ation and condensation. T h e rate of solution should be im p o rtan t. R . A . Jo y n e r10 found th a t, in some cases, th e m ercury had to rem ain in contact w ith the alloy fo r a w eek o r m ore before it became satu rated w ith the com ponent m etals. In ord in ary dental procedures, T

able

2 .— C o m p o s i t i o n

D

of

if f e r e n t

A

C o n d e n s a t io n

M etal

Alloy

it w ould if they w ere present in the u n ­ com bined state. A th ird factor m ig h t be the viscosity or fluidity of the constituents of the am algam . T h e m ercury expressed by the d en tist n early always carries some semisolid m aterial, an d is n o t a tru e solu­ tion. T h e m aterial thus carried out m echanically may or m ay n ot be different in composition fro m the am algam as a w hole. I t is thus seen th a t th e composi­ tion of the condensed am algam m ay or m ay not be different from th e composition as calculated from solubility alone. I t appears th a t little w o rk has been done to determ ine th e change in compo­ sition of am algam s d u rin g am algam ation

llo ys of

M

Silver T in C opper Zinc

67.30 26.95 4.60 1.08

Packed Am algam 68.03 26.32 4.64 0.87

T otal

99.93

99.86

M e rc u ry in p o rt ion (per cent)

54.0

O

b t a in e d

in im a x

D

u r in g

A

m a l g a m a t io n

and

178*

Expressed Excess M ercury 63.85 31.94 4.30 1.42

Fluid Portion Rem oved D uring Condensation 66.86 28.13 4.50 1.24

101.51

100.73

85.0

62.5

•R esults h a v e been calculated m erc u ry -free ; alloy-m ercury ratio, 6:9.

the m ercury is in contact w ith th e alloy fo r only a few m inutes before all the excess is rem oved. A second facto r may be th e state of com bination of the m etals in th e alloy. Since am algam alloys very seldom contain appreciable am ounts of free m etals, b u t usually consist of a m ix­ tu re or solid solution of interm etallic com pounds, such as A g 3Sn, S n4C u, etc., it should n o t be expected th a t the solu­ bility of the m etals w ould be the same as 9. M allet, J. W .: Proc. Roy. Soc., 80:83, 1908. 10. Joyner, R. A .: J. Chera. Soc., 99:195, 1911.

and condensation. J . H . J o n te 11 investi­ gated th e relation of th e com position of packed am algam s to the composition of the unpressed am algam s w hen varying am ounts of m ercu ry w ere used. F ro m these results, he calculated the change in com position of th e alloy d u rin g am alga­ m ation and packing. H e concluded th a t “ the excess m ercury, w hen pressed from an am algam , removes tin and copper in greater am ounts th a n it does silver.” Since he used only nonzinc alloys, since 11. Jonte, J. H .: T hesis, State U niversity of Iow a.

1079

R ay and Easton— Amalgam Alloys he packed the samples u nder very high pressure into steel m olds and since his re­ sults indicate experim ental errors, his w o rk is not of g reat value in answ ering this question from th e d en tist’s point of view.

E X PE R IM E N T A L M ETHODS

C ra n d a ll’s nonzinc, tw en tieth century, tru e dentalloy and m inim ax 178 w ere the alloys used in this w o rk . T h ese w ere chosen as being representative of am al­ gam alloys in general, all of them having passed the specifications of th e A m erican D e n ta l A ssociation.12 A n alloy-m ercury ratio is recom m ended by th e m anufac­ tu re r for all b u t one of th e alloys. M an y oth er alloys m ig h t have been chosen as equally representative as the ones used, b u t only fo u r w ere considered necessary. T h e alloys w ere am algam ated in accordance w ith the m a n u fa ctu re r’s pub-

I t w as the purpose of this investigation, therefore, to m ake a study, u n d er condi­ tions as nearly identical w ith those exist­ ing in dental practice as possible, of the changes in com position of am algam alloys th a t occur du rin g am algam ation and con­ densation of the am algam form ed. I t w as also desired to determ ine w heth er or not appreciable am ounts of any of the m etals T

able

3 .— C o m p o s i t i o n

of

D

if f e r e n t

A

llo ys

C o n d e n s a t io n

of

M

O

b t a in e d

in im a x

D

u r in g

A

m a l g a m a t io n a n d

178*

Alloy

Packed Am algam

Expressed Excess M ercury

Semifluid Portion Rem oved D uring Condensation

Silver Tin Copper Zinc

67.30 26.95 4.60 1.08

68.17 27.03 4.55 0.92

44.86 49.77 1.88 6.20

67.14 27.19 4.62 1.28

T otal

99.93

100.67

102.71

100.23

55.5

94.5

64.0

M etal

M ercury in portion (per cent)

*Results calculated m ercu ry -free ; alloy-m ercury ratio, 7:11.

are carried out by th e expressed m ercury, or removed w ith th e m ore fluid portions as they are taken from the cavity d u rin g th e process of condensation. T o do this, a chemical analysis w as m ade of ( 1 ) the alloy used, ( 2 ) the m ercury expressed a fte r am algam ation and before conden­ sation, (3 ) the semifluid portion removed d u rin g the packing process and ( 4 ) the packed am algam (finished fillin g ). T h e results w ere then calculated to the m er­ cury free basis and these results com pared and tabulated.

lished instructions w here any w ere f u r ­ nished. T h e correct am ounts of alloy and m ercury fo r th e ratios used w ere obtained by careful w eig h in g ; and tr itu ­ ration w as accom plished w ith a glass pestle in a glass m o rta r. T h e tritu ra tio n tim e w as th ree m inutes, an d all of the m ixing and condensing w as done at a tem peratu re of approxim ately 22 C. T h e am algam w as condensed into a specially prepared m old sim ilar to th a t 12. T a y lo r, N. O. : A Specification of D en­ ta l A m algam Alloys, J. A. D . A., 17:112 (Ja n .) 1930.

1080

T h e Journal of the American D ental Association

described by C. S. V an H o rn .13 I t con­ sists of a brass casing containing a steel plunger ground to a sliding fit. O n e end of the p lunger w as tooled to form the pulpal, axial and gingival w alls of a m esioclusodistal cavity, the su rrounding w alls of w hich w ere form ed by the brass casing. I t w as held in place by m eans of a tapered h ard steel pin extending through th e casing and plunger. W h e n the pin w as removed, the end of the p lunger con­ tain ing the packed am algam could be ex­ tru d ed from the casing and the am algam filling subsequently removed therefrom . T h e technic follow ed in condensing the T

able

4 .— C o m p o s i t i o n

of

D

if f e r e n t

A

C o n d e n s a t io n

M etal

Alloy

tion. T h e force of condensation was estim ated to be approxim ately from 800 to 1,100 pounds per square inch. M a lle t pressure w as n o t used. In this w ay, the samples w ere obtained fo r chemical analysis. O n e contained all of th e m ercu ry expressed before conden­ sation ; a second contained the soft, semi­ fluid m aterial removed d u rin g condensa­ tion, and the th ird consisted of the packed am algam . In those cases, w here the mix w as so dry th a t sufficient m ercury could not be expressed for a chemical analysis, any m ercury w hich w as expressed w as added to the soft m aterial removed dur-

llo ys

of

Packed Am algam

T

O

rue

b t a in e d

D

D

u r in g

A

m a l g a m a t io n

and

entalloy*

Expressed Excess M ercury

Semifluid Portion Rem oved D uring C ondensationf*

This portion was too dry to perm it of the expres­ sion of sufficient m ercury for an analysis (see text).

66.80 26.64 4.82 1.84

Silver Tin Copper Zinc

66.88 26.52 4.85 1.61

66.94 26.48 4.90 1.70

T otal

99.8

100.02

100.10

49.00

63.50

M ercury in portion (per cent)

*ResuIts calculated m erc u ry -free ; alloy-m ercury ratio, 9:11. t* T h is portion also contains the v ery sm all am ount of m ercury, expressed before con­ densation.

am algam w as sim ilar to th a t described by H a rp e r.14 N o m ercury w as removed from the first portion of the a m a lg a m ; some w as expressed from the second, and the th ird w as freed of as m uch as possible. G re a t care w as taken to prevent the loss of any of the expressed m ercury, or of the soft, semifluid m aterial th a t w as bro u g h t to the surface d uring condensa13. V an H orn, C. S.: D ent. Cosmos, 67:160 (F eb.) 1925. 14. H a rp e r, W . E .: J. D ent. Res., 1:446, 1919.

ing condensation, and the tw o portions w ere analyzed together. G rav im etric m ethods w ere used in m aking all of the chemical analyses. T h e original alloys w ere analyzed by the o rd i­ nary m ethods of dissolving in n itric acid, and determ ining th e tin as stannic oxid ( S n 0 2) , the silver as the chlorid in a Gooch crucible, the copper electrolytically, and the zinc precipitated as the sulphid and then ignited and w eighed as The oxid. T h e same procedure w as fol­ lowed for the am algam s except w here the

1081

Ray and Easton— Amalgam Alloys m ercury m ade changes necessary. A fte r the solution of th e sam ple in n itric acid, ab o ut 5 gm . of am m onium persulphate w as added to oxidize all m ercurous salts to the m ercuric state so th a t they w ould n ot in terfere w ith the silver determ ina­ tion. A fte r the silver determ ination, the m ercury w as separated from the copper and zinc by precipitation as the m etal by h y d raz in 15 from an am m oniacal solution. T h e copper and zinc w ere then deter­ m ined as before. RESULTS

T h e compositions of th e various por­ tions, calculated m ercury free, are given T

able

5.— C o m p o s i t i o n

of

D

if f e r e n t

C o n d e n s a t io n

M etal

Silver Tin Copper Zinc T otal

Alloy

A

of

T h e results obtained indicate th a t the change in com position d u rin g am algam a­ tion and condensation is n ot at all seri­ ous. T h e tin is carried o u t to a g rea ter extent th an any of the o th er m etals except zinc, b u t the packed am algam never be­ comes deficient in tin , since th e difference am ounts to only a few ten th s of 1 per cent. T h e silver content of the packed am algam seems to be increased slightly in m ost cases, w h ile the copper also seems to accum ulate in this portion. T h e g re a t­ est difference is in the case of zinc. T h is m etal is carried o u t in relatively large am ounts by the expressed m ercury in

lloys

T

Packed Am algam

O

b t a in e d

w e n t ie t h

D

u r in g

A

m a l g a m a t io n

and

C entury*

Expressed Excess M ercury

Semifluid Portion R em oved D uring Condensation

68.67 26.24 4.98 0.24

68.90 26.14 5.01 0.12

36.77 50.43 2.19 5.28

68.50 26.48 3.86 0.48

100.13

100.17

94.67

99.32

48.50

96.00

63.00

M ercury in portion (per cent)

*Results calculated m ercury-free ; alloy-m ercury ratio, 5 :9.

in T ab les 2 to 6. T h e am ount of m er­ cury in each is also shown. T h e am ount of expressed m ercury w as usually too sm all for accurate chem ical analysis, there being only about 0.5 gm. containing ap­ proxim ately 90 per cent m ercury, so th a t only about 0.05 gm. of alloy w as present. Since m icrodeterm ination w as not used, th e experim ental e rro r w as quite large in m aking the analysis of this portion. T h e general characteristics of this p a rt are w ell shown.

those cases in w hich th e m ercury-alloy ratio is high. Since th e zinc does n ot appear to be a v ery necessary constituent of am algam s, especially in large am ounts, the rem oval of a p a rt of this m etal by the expressed m ercu ry is probably not a seri­ ous defect. I t also the only semifluid densation

appears from the results th a t m a jo r difference betw een the m ateria l rem oved d u rin g con­ and the packed am algam is the

m ercury content. I f th is soft, semifluid

15. W illa rd , H . H., and Boldydreff, A . W .: m aterial w ere pressed free of the excess J. Am . Chem. Soc., 52:569, 1930.

1082

T h e Journal of the American D ental Association

m ercury, it could be used again, at least as fa r as com position is concerned.

3. T h e tin co n ten t is b u t slightly de­ creased.

C O N C L U S IO N S

4. T h e re is a slight increase in the silver and the copper content.

1. T h e m ercury expressed and the 5. T h e use of excess m ercury d u rin g semifluid portions rem oved du rin g the am algam ation and condensation of am al­ tritu ra tio n , and its subsequent rem oval gam alloys causes slight changes in the from the am algam , does n ot g reatly affect composition of the packed am algam as the com position of the packed am algam . T a b l e 6.— C o m p o s it io n o f D i f f e r e n t A l lo y s O b t a in e d D u r in g A m a l g a m a t io n a n d C o n d e n s a t io n o f C r a n d a l l ’s A l l o y *

M etal

Silver Tin Copper Zinc T otal

Alloy

Packed Amalgam

Expressed Excess M ercury

Semifluid Portion Rem oved D uring C ondensation!

70.04 26.20 3.85

70.21 26.24 3.80

0.00

0.00

100.09

100.25

99.81

49.50

62.00

M ercury in portion (per cent)

T his portion was too dry* to perm it of the expres­ sion o f sufficient m ercury ' for an analysis '{see 'text).

69.88 26.35 3.58

0.00

*Results calculated m e rc u ry -free ; alloy-m ercury ratio, 10:12. f T h is portion also contains the v e ry sm all am ount of m ercury expressed before condensation.

com pared w ith the com position of the 6. T h e excess m ercury so removed original alloy. does not carry o u t sufficient am ounts of 2. T h e zinc content is decreased to a any of the com ponent m etals to destroy com paratively large extent. the balance of th e am algam .