NATIONAL BUREAU OF STANDARDS REPORT

9984

Progress Report

on THE PARTICLE SIZE AND SHAPE OF SILVER

ALLOYS FOR DENTAL AMALGAM

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U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

311.05-11-3 110560 December 31, 1968 9984

Progress Report

on THE PARTICLE SIZE AND SHAPE OF SILVER

ALLOYS FOR DENTAL AMALGAM

by H. J. Caul,* J. A. Barton, + and R. C. Manuszewski*

* Research Associates of the American Dental Association,

Dental Research Section, National Bureau of Standards,

Washington, D. C. Guest, Worker, National Bureau of Standards, Dental Research

Section, from the U. S. Air Force.

This investigation is part of the dental research program

conducted by the National Bureau of Standards, in cooperation with the Council on Dental Research of the American

Dental Association; the National Institute for Dental Research; the Dental Research Division of the U. S. Army

Medical Research and Development Command; the Dental

Sciences Division of the School of Aerospace Medicine, USAF;

and the Veterans Administration.

IMPORTANT NOTICE NATIONAL BUREAU OF ST/

for use within the Government,

and review. For this reason, the whole or in part, is not authori Bureau of Standards, Washingto

the Report has been specitically

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015

s accounting documents intended

subjected to additional evaluation

listing of this Report, either in Office of the Director, National

I the Government agency for which

pies for its own use.

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The dental profession, today, may purchase a large

number of excellent silver alloys for amalgam restorations

since there are now more than 90 alloys on the List of

Certified Materials of the American Dental Association.

The modern trend in these alloys has been toward the

finer particle size because the resulting surfaces after

carving are smoother. This is shown in Figure 20-8 of

Skinner and Phillips. In addition, the work of Demaree

( 2 ) and Taylor on spherical alloy particles showed definite

relationships between particle size or area and dimensional

change during hardening^ mercury content, and early strength.

It is the purpose of this paper to show the large

variation in particle size and shape that exists between many

of the present day alloys. The particle sizes of 54 dental

amalgam alloys were examined by means of photomicrographs

and by measurement of maximum particle thickness.

The maximum thickness was determined by the following

method

:

The combined thickness of two optical flats (2 x 2 x 0.4

cm) is measured with a micrometer caliper. The value as

- 2-

determined is the average of 10 measurements made in duplicate

at the center and at the four corners. A few particles of

alloy are dispersed at the center and near each corner of the

surface of one of the flats so that no particles touch each

other. The second flat is placed firmly on top of the

particles and the thickness is again measured. The difference in the average thickness of the flats, with and without

the particles, is recorded as the maximum thickness of the

alloy particles (Table 1, last column)

.

In order to obtain additional information on the size

and shape of the alloy particles a 4 x 5 inch photomicrograph

having a lOOX magnification was prepared for each alloy.

Figures 1, 2 and 3 show representative sections of these

i photomicrographs.

Because the method for determining particle thickness

measures the maximum thickness, length and width measurements

were made on the three largest and most distinct particles in

the original 4x5 inch photomicrograph using a millimeter

scale. The average values for length and width are reported

in Table 1.

-3-

Each of the alloys had wide variations in particle size

with some of the finer particles estimated to be 1 to 3

microns in dimension. Excluding spherical particles, the

length of the large particles range from 60 to 320, the width

from 10 to 70 and the thickness from 10 to 35 micrometers.*

The extremely wide variation in particle size and shape is

shown in Figures 1, 2 and 3.

The length-to-width ratio (Table 1) varied from 2 to 25,

which indicated that particle shape for some alloys is short and

wide while other alloys are composed of particles which are

needlelike in appearance.

Several of the alloys appear to be thicker than they are

wide (Table 1) . This may be due to differences in the two

methods of measurement or to the presence of a few large

particles in the samples placed between glass plates, but not

observed in the photomicrograph.

* The micrometer (urn) is an internation unit of length that

has replaced the micron (y) and is equal to it.

-4-

No correlation was found between particle size and the

dimensional change during setting, flow, tensile strength,

and mercury content of the resulting amalgams. This absence

of correlation may result from two factors. First, during

trituration the alloy particle may be reduced in size by

fragmentation which could result in a much larger surface

area being available for amalgamation. Second, other

characteristics of the alloy such as composition, mechanical

stresses, heat treatment, surface and the possible existence

of internal surfaces may compensate for differences which

would be observed if only particle size were varied.

Since these characteristics may vary widely in the

alloys, the absence of an observable correlation between

particle size and physical properties is not unexpected. In

the work of Demaree and Taylor [2]

,

on the other hand,

variations other than particle size were eliminated and

correlation between particle size and properties were

observed.

USCOMM-NBS-DC

Table 1

Average Dimensions of the Largest Particles

Alloy Length

** Width

**

L/W

Ratio Thickness t * No. Brand

[TmT urn Urn 1 Accurate Metalloy 140 20 7 25

2 Aristaloy 60 10 6 10

3 Baring (Improved fine cut) 100 10 10 20

4 Brewster 180 20 9 20

5 Certified Non-Zinc 100 20 5 15

6 Cresilver 200 .20 10 30

7 Dispersalloy 325 120 40 6 40

8 Dispersalloy 400 120 30 3 30

9 Ex-Cell 320 30 11 15

10 Fellowship 320 70 5 20

11 Filling Alloy - Abe Bass 130 10 13 15

12 Filling Alloy - Pure Lab 120 10 12 20

13 Garfield '

s

120 10 12 20

14 Gold Bond 140 40 3— 35

15 Line Alloy 100 10 10 10

16 Lustraloy Regular 220 30 7 15

17 Merrick - Fine Cut 120 30 4 10

18 Merrick - Non-Zinc 170 30 6 10

19 Midvalloy 150 20 15

20 Minimax #178 130 20 25

21 Minimax #178 Non-Zinc 200 20 10 25

22 Minimax #183 250 10 25 20

23 Modeloy 160 20 8 20

24 Mynol Improved 110 10 11 10

25 National Dental 120 20 6 20

*These numbers correspond to the numbered sections of the photomicrograph.

** Average of three largest particles.

t The data for thickness has been rounded to the nearest 5 micrcmeters.

+um = micrometer (formerly the micron)

.
t
Table 1

(continued)

Alloy

Length Width

L/W

Ratio Thickness

No. Brand

urn urn um

26 Peerless 100 10 10 10

27 Precision 90 20 4| 30

28 Royal 130 10 13 15

29 Safco 69 Fine Cut 120 20 6 20

30 Safco 69 Fine Cut Non-Zinc 110 20 20

31 Safco 69 Regular 120 20 6 25

32 Safco 72 Fine Cut Non-Zinc 110 10 11 . 15

33 Safco 72 Regular Non-Zinc 150 20 15

34 S-C Special Medium 130 20 15

35 S-C Special Quick 210 40 5 20 . 36 Shofu 50 30 — 30

37 Silver Crown Super Fine 100 30 3 15

38 . Silver Crown Super Fine 80 30 3 10

Non-Zinc

39 Silver Crown Medium 250 70 •^2 25

40 Silverloy 310 50 6 20

41 Spheraloy 40 40 — 35

42 Standard 300 70 4% 30

43 Theta Superb 230 30 8 15

44 True Dentalloy - New 130 70 2 20

45 . True Dentalloy Regular 240 20 12 30

46 True Dentalloy Zinc Free 140 30 5 25

47 Twentieth Century Fine Cut 160 30 5 20

48 Twentieth Century Micro 140 30 5 15

49 Twentieth Century Micro 100 30 3 15

Non-Zinc

50 Twentieth Century ReglilSf 310 70 4| 20

51 Ultra Brand 68% Regular 110 30 4 25

52 Ultra Brand 72% Fine Cut 190 30 6 25

53 Ultra Brand 72% Fine Cut 170 30 6 30

Non-Zinc

54 White Beauty 210 60 2 15

REFERENCES

Skinner, E. W. and Phillips, R. W. The

Science of Dental Materials, 6th edition,

W. B, Saunders Co., Philadelphia, 1967.

Demaree, N. C. and Taylor, D. F. Properties

of Dental Amalgam Made from Spherical Alloy

particles, J. D. Res. 41: 890 July-Aug, 1962

Certain commercial materials are identified. In

no case does such identification imply recommendation or

endorsement by the National Bureau of Standards, nor doe

it imply that the material is necessarily best for the

purpose

.

Legends for Figures 1, 2 and 3

Amalgam alloy particles. The photomicrograph for

each alloy is a representative 1-1/2 x 1-1/2 inch

section taken from an original 4x5 inch photomicrograph. The numbers correspond to those in

Table 1.





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