NATIONAL BUREAU OF STANDARDS REPORT

1446

Silicate Cement: Method of Mixing in a Closed Container

to Prevent Effects of Exposure to Atmosphere

by

A. H, Grunewald

I. C. Schoonover

George Dickson

NBS

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

A. V. As tin, Acting Director

U., S. DEPARTMENT OF COMMERCE

Charles Sawyer, Secretary

gaged in specialized research, development, and engineering in the field indicated by its

title. A brief description of the activities, and of the resultant reports and publications,

appears on the inside of the back cover of this report.

1. ELECTRICITY. Resistance Measurements. Inductance and Capacitance. Electrical Instruments. Magnetic Measurements. Electrochemistry.

2. OPTICS AND METROLOGY. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Gage.

3. HEAT AND POWER. Temperature Measurements. Thermodynamics. Cryogenics. Engines and

Lubrication. Engine Fuels.

1. atomic and raoiation physics. Spectroscopy. Radiometry. Mass Spectrometry. Physical Electronics. Electron Physics. Atomic Physics. Neutron Measurements. Nuclear Physics. Radioactivity. X-Rays. Betatron. Nucleonic Instrumentation. Radiological Equipment. Atomic Energy Commission Instruments Branch.

5. CHEMISTRY. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry. Inorganic Chemistry. Electrodeposition. Gas Chemistry. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

MECHANICS. Sound. Mechanical Instruments. Aerodynamics. Engineering Mechanics. Hydraulics. Mass. 'Capacity, Density, Mid Fluid Meters.

7. ORGANIC AND FIBROUS MATERIALS, fibber. Textiles. Paper. Leather. Testing and

Specifications. Organic Plastics. Dental Research.

8. METALLURGY. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy . Corrosion.

9* MINERAL PRODUCTS. Porcelain and Pottery. Glass. Refractories. Enameled Metals. Building Stone. Concreting Materials. Constitution and Microstructure. Chemistry 1 of Mineral

Products.

10. BUILDING TECHNOLOGY. Structural Engineering. Fire Protection. Heating and Air Conditioning. Exterior and Interior Coverings. Codes and Specifications.

11. APPLIED MATHEMATICS. Numerical Analysis. Confutation. Statistical Engineering. Ma- chine Development.

12- ELECTRONICS. Engineering Electronics. Electron Thbes. Electronic Computers. Electremie Instrumentation

13- ORDNANCE DEVELOPMENT- Mechanical Research and Development. Electromechanical

Fuzes. Technical Services. Missile Fuzing Research. Missile Fuzing Development. Projectile Fuses. Ordnance Components. Ordnance Tests. Ordnance Research.

IN. RADIO PROPAGATION. Upper Atmosphere Research. Ionospheric Research. Regular Propagation Services. Frequency Utilization Research. Tropospheric Propagation Research. High

Frequency Standards. Microwave Standards.

15- MISSILE DEVELOPMENT. Missile Engineering. Missile Dynamics. Missile Intelligence.

Missile Instrumentation. Technical Services. Combustion.
NBS PROJECT

0703- 22-3324

NBS REPORT

1446

Silicate Cement: Method of Mixing in a Closed Container

to Prevent Effects of Exposure to Atmosphere

by

A. H. Grunewald^

p I. C. Schoonover

George Dickson^

^Captain, DC, USN, stationed at the National Bureau of

Standards

.

2 Chief, Dental Research Section, National Bureau of

Standards

.

^Physicist, Dental Research Section, National Bureau of

Standards

.

This work is a part of the dental research program conducted at the National Bureau of Standards in cooperation

with the Council on Dental Research of the American Dental

Association, the Army Dental Corps, the Air Force Dental

Corps, the Navy Dental Corps and the Veterans Administration,

litis report is issued ft in any fora, either in wl fro* the Office of the D:

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015

», reprinting, or reproduction

aission in writing is obtained

ihington 25, D. C.
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Silicate Cement: Method of Mixing in a Closed Container

to Prevent Effects of Exposure to Atmosphere

Abstract

Since the properties of a silicate cement

restoration are radically affected by the temperature at which it is mixed and by the water

content of the cement liquid, it has been impossible to produce good restorations in a hot,

humid atmosphere. To overcome these difficulties

a method of mixing the cement in a closed, cooled

container was developed. Ey the use of this

method of mixing, satisfactory restorations

can be produced under all climatic conditions.

1 . INTRODUCTION

Silicate cement liquids, being essentially aqueous solutions of phosphoric acid., are hygroscopic. Consequently, when

exposed to air the liquids take on or give off water, depending

upon the amount of moisture present in the air. This gain or

loss of water, which greatly affects the setting time of the

cement, occurs principally when the cement liquid is exposed to

air during withdrawal of liquid from the bottle, while the

liquid rests on the glass slab prior to mixing, and during mixing of the powder and liquid. The cement liquid should therefore not be exposed to air if ideal conditions are to prevail

in mixing silicate cements. Also, the temperature of the glass

slab upon which the cement mix is prepared markedly affects the

amount of powder that can be incorporated into a given quantity

of liquid to produce a workable plastic mix. If the slab is

cold, a high powder-liquid ratio can be obtained and the cement

will be stronger and less soluble and will have less shrinkage

than if a warm slab is used. Unfortunately, however, water

will condense on the slab when it is chilled much below room

temperature during hot and humid weather. It was the purpose

of this investigation to devise a system which would eliminate

exposure of the silicate cement liquid to the air during storage or mixing and would permit cement to be chilled and kept

moisture free during mixing, independently of air temperature

and humidity. If such a procedure were practicable, then restorations of silicate cement with high compressive strenth, low

solubility and small shrinkage during setting could be made

repeatedly, regardless of weather conditions.

2. METHODS OF MIXING

Several methods of mixing silicate cement in a sealed container, at the same time maintaining a high powder-liquid ratio,

were investigated. The most satisfactory method developed consisted of mixing the cement in a sealed flexible container held

under cold water. Thin-walled, uncolored, paddle-shaped rubber

balloons were used as the mixing containers. A measured amount

of powder ample for the large majority of restorations was inserted with the aid of a glass funnel into a washed and dried

balloon. The balloon was cut off approximately one inch from

the bottom, and the bottom portion containing the silicate powder was sealed with rubber cement.

It was found that better mixes were obtained if most of the

air was extracted from the container after sealing in the powder. This was done routinely with a 24 gage needle and syringe.

In order to eliminate any possible seepage of air into the

balloon, a patch of balloon material was cemented over the

point of insertion of the needle.

The liquid was easily protected from air by storing it in

a small serum bottle with a self- sealing rubber stopper through

which a needle could be repeatedly inserted and the liquid

withdrawn as needed for injection into the powder container.

The liquid was injected into the balloon through the double-wall

thickness in the area of patch which provided a self seal.

Mixing was begun immediately after injection of the liquid.

The powder and liquid were kneaded rapidly between the fingers

and thumb of both hands for one minute, under water.

Some attempts were made to simplify the method by sealing

the liquid and powder in separate compartments of the mixing

container in such a way that the liquid could be forced into

the powder at the time of mixing, but it was found that the

rubber balloons and rubber cement used for sealing were attacked

by the silicate cement liquid at common storage temperatures.

It is probable that a method of packaging eliminating the separate bottle of liquid could be developed by further work.

3. PROPERTIES OF CEMENT MIXED IN SEALED CONTAINERS

3.1 Powder-Liquid Ratio

The standard testing consistency of the cement used in this

investigation, determined according to American Dental Association Specification No. 9, was 1.65 g of powder to 0.4 ml of

liquid. The manufacturers recommended consistency was 1.45 g

per 0.4 ml.

-3-

At a normal room temperature of 21° C (70° F) and a relative humidity of 65 ± 10 percent mixes at a consistency of

1.7 g per 0.4 ml were made in sealed containers in water at

21° C with no difficulty, and a consistency of 1.9 g per 0.4 ml

was possible. It was impossible to incorporate 1.9 g of powder

in 0.4 ml of liquid on a slab even though it was cooled.

At a room temperature of 32° C (90° F) and a relative

humidity of 90 percent it was impossible to incorporate 1.7 g

of powder in 0.4 ml of liquid on a slab cooled to just above

the dew point, 30.5° 0 (37° F) . 3y mixing in the rubber container a ratio of 1,7 g to 0.4 ml was obtained in water at

20° C with no difficulty, even though the room temperature

was 32° C (90° F)

3 .2 Setting Time

In Table 1 are shown the times of setting of a silicate

cement mixed in a sealed container in water at four different

temperatures Ll5° C (59° F), 20° C (63° F), 25° C (77° F) and

30° C ( S6° F)J and tested at 21° C (70° F) and 32° C (90° F)

Specimens used in these tests were mixed at a ratio of 1.7 g

to 0.4 ml. The tests were conducted as specified in American

Dental Association Specification No. 9, with the exceptions

that mixing was done in the sealed container and that a mix

one-half the size prescribed in the specification was used

(0.85 g of powder to 0.2 ml of liquid)

,

As can be seen from Table 1, specimens mixed under water

at temperatures ranging from 15° to 30° C (59° to 86° F) gave

setting times of 3~ to 22 minutes when the materials were

4 4

stored and the specimens were prepared at a room temperature

of 21° C (70° F) and a relative humidity of 65 ± 10 percent,

and setting times of 2i to 1-1 minutes when stored and prepared

at a temperature of 32° C (90° F) and a relative humidity of

90 t 10 percent. All mixes made under water at 20° C (68° F)

or less allowed ample time for proper insertion in the average

restoration even though the atmospheric temperature and humidity were high.

Mixes were also made under water at 10° C (50° F) and

35° 0 (95° F) . Water at 10° C (50° F) was found to be too

cold for the hands c Mixes made under water at 35° C (95° F)

set in the rubber bag during mixing.

-4-

Table 1

Setting Time of a Silicate Cement

Mixed Under Water in Sealed Containers

Temperature

of Water

Setting Time*

21° C (70° F)

Humidity 65±10%

32° C (90° F)

Humidity 90±10^

°C °F minutes minutes

15 59 2i

2

20 68 2I

2

25 77 a'2 2

i

30 86 21

4

^Setting time given is average of 3 mixes recorded

to nearest 15 seconds from start of mix. Mix

consisted of 0.85 g of powder to 0.2 ml of liquid.

4 CONCLUSIONS

The influence of atmospheric conditions upon the mixing

of silicate cements can be eliminated to a large extent by

mixing in a closed container. Thus a comparatively large

amount of powder can be incorporated into a given quantity

of liquid and satisfactory silicate cement restorations can

be made under all climatic conditions.

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