NATIONAL BUREAU OF STANDARDS REPORT

10 377

Progress Report

on

POOR MERCURY HYGIENE FROM

ULTRASONIC AMALGAM CONDENSATION

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

3 1 1.05-11-31 10561 November 12, 1970 10 377

Progress Report on POOR MERCURY HYGIENE FROM

ULTRASONIC AMALGAM CONDENSATION

H. H. Chandler*, N. W. Rupp** and G. C. Paffenbarger***

* Research Associate American Dental Association Research Program at the National Bureau of Standards, Washington, D. C. 20234

on a two-year leave of absence from Ohio State University College

of Dentistry, Columbus, Ohio 43210.

** Research Associate American Dental Association Research Program at the National Bureau of Standards, Washington, D. C. 20234. *** Senior Research Associate American Dental Association Research

Program at the National Bureau of Standards, Washington, D. C. 20234.

This investigation was supported in part by Research Grant

DE02742-02 to the American Dental Association from the National

Institute of Dental Research and is part of the dental research

program conducted by the National Bureau of Standards, in cooperation with the American Dental Association; the Dental Research

Division of the United States Army Medical Research and Development Command; the Dental Sciences Division of the School of Aerospace Medicine, USAF; the National Institute of Dental Research;

and the Veterans Administration.

NATIONAL BUREAU OF S

for use within the Government, and review. For this reason, t whole or in part, is not authr Bureau of Standards, Washing

the Report has been specificall

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

;ss accounting documents intended

; subjected to additional evaluation

? listing of this Report, either in

le Office of the Director, National

by the Government agency for which

copies for its own use. <NBS>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
i

i

j

A
POOR MERCURY HYGIENE FROM

ULTRASONIC AMALGAM CONDENSATION

ABSTRACT

There is a potential hazard of mercury poisoning in using

an ultrasonic device for amalgam condensation. A cloud of

mercury droplets and alloy particles was emitted from the

soft amalgam at the working tip of the instrument. Mercury

vapor levels as recorded by a vapor detector held 30 cm

from the working tip were 20% of the allowable threshold

limit value (0.1 mg Hg/m^ of air) and probably do not

represent unsafe levels.

The continued long-time use of the ultrasonic instrument would result in the deposition of a great many mercury

droplets throughout a dental operatory and could thereby

cause higher mercury vapor levels especially in poorly

ventilated spaces. In addition, the inhalation of the

emitted material by the patient and the dental health personnel cannot be considered good hygiene. Therefore, the

use of this instrument for amalgam condensation is contraindicated until such time as the safety of the instrument

for this purpose is firmly established.
2

Introduct ion

The potential hazard of mercury poisoning of dental

health personnel and dental patients has been studied by

many investigators. Souder and Swee^-'-^y found that the

amount of mercury vapor emitted from dental restorations

of silver amalgams was undetectable and that there was

little danger from the ingestion of mercury in solution

from these restorations. Nixon and Smith.^ found that the

amount of mercury in the fingernails and in the hair of

dental workers was often many times that of a control group.

Mercury vapor levels in dental offices are increased

during periods of manipulation of mercury and the mixed

amalgam. Airaksinen" analyzed the air in dental offices

and concluded there were safe levels of mercury vapor in

all cases. Highest levels were found during mixing but

he considered the danger of poisoning to be slight. Nossek'^

determined the mercury vapor content in the air following

ultrasonic amalgam condensation and observed no increase in

mercury vapor over that produced by hand condensation in spite

of macroscopically visible spraying of plastic amalgam.
-3-

Meyer^ determined that the threshold limit value of 0.1 mg

mercury per cubic meter of air® was exceeded by 2 to 4 times

during such procedures as amalgam carving and removal of old

amalgams but these concentrations existed for only short

durations

.

Most investigators, including Grossman"^ and Frykholm® ,

agree that if recommended precautions are followed the mercury

vapor concentration is maintained well below the threshold

limit® . But it is also agreed that the effects of long

periods of exposure to even minimal amounts of mercury vapor

is not well known and therefore, such exposure should be kept

at a minimum.

A preliminary investigation in this laboratory designed

to study the effects of ultrasonic condensation on the properties of dental amalgam, revealed that when the ultrasonic

instrument was being used, significant amounts of material

were emitted from the working area in the form of a cloud.

Figure 1. The nature of this cloud and the amount of mercury

vapor in the surrounding area while condensing dental amalgam

with the ultrasonic device were determined.
-4-

Materials and methods*

The ultrasonic device used in this study is reported to

develop 25,000 mechanical strokes per second at the working

tip with a stroke length of 0.001 inch.** An amalgam condensing insert was used with maximum water cooling and a power

setting of 2 (medium) . The temperature of the plashy amalgam

after removal from the mechanj.cal mixer and during compacting

with the ultrasonic plugger was about 35'^C as recorded with a

36 gauge (B and S) Type T thermocouple. During compaction

occasional transient peaks of 55 to 60® C v;ere recorded. Other

inserts and power settings and in one case an ultrasonic instrument of the same brand in a different operatory produced

essentially the same type of cloud.

* Certain commercial materials and equipment are identified

in this paper to specify adequately the experimental procedure. In no instance does such identification imply

recommendation or endorsement by the National Bureau of

Standards or that the material or equipment identified is

necessarily the best available for the purpose.

The frequency and amplitude were measured and found to be

24,850 ± 150 hz and 0.9 ± 0.1 thousandths of an inch,

respectively
-5-

Amalgam mixes were prepared with commercially available

alloys at 1:1 mercury-to-alloy ratio.

To collect a sample of material from the aerosol cloud, a

suction device containing an in-line filter (maximum opening

0,2 dra) was held 7 cm above the operating area. This distance

from the working tip was used for the collection of particles

whereas with the vapor detector the intake Lose openJ.ng as held

30 cm from the working tip. The material gathered on the filter

was examined nd photographed with a metallographic microscope.

Mercury vapor levels were determined wit'i an Instantaneous

Vapor Detector (General Electric Catalog #9790339Gl) . The instrument functions on a principle of ultraviolet light absorption as it passes through an atmosphere containing mercury

vapor. Vapor levels between 0.01 and 3.0 mg per cubic meter

of air are detectable.®

The intake hose of the detector was placed 30 cm from the

tip of the condenser to simulate operator-to-tooth working

distance. The position of the intake hose was adjusted so that

it was approximately in line with the air currents in the immediate working area. For comparison purposes, identical tests

were run using hand condensation and two mechanical condensers.*

* Hollenback condenser, Clev-Dent, Cleveland, Ohio

Vibrapak, Superba Dental Products, San Diego, California
- 6 -

The amaXgam mixes for vapor detection were condensed

for three minutes in a steel die containing a 4 x 8 rain

cylindrical mold. The amalgam cylinder without having any

excess removed from its top surface was undisturbed for

three minutes before removing to another room.

Results and discussion

Figure 1 shows the aerosol dispersed from the area of

the tip of the ultrasonic condenser. In some cases the

cloud could be seen to rise as high as 60 to 90 era. This

cloud is carried by air currents similar to cigarette smoke

%

and tlie particles settle in the 60 to 90 cm radius from the

working area. The operator, assistant and patient could inhale and or ingest the emitted material during amalgam

condensation. Higher power settings and mixes containing

more mercury resulted in the emission of more material than

when a low power setting and less mercury was used. However,

the ScUfne phenomena occurred even at the lowest power setting

and in mixes squeezed with pliers (as recommended by the

manufacturer of the condenser) containing as low as 45.5%
7

mercury. The greatest cloud formation occurred when

the tip of the instrument touched the wall of the

cavity prepared in an extracted or porcelain tooth or

the side of the steel die.

Figure 2 is a photograph of the material collected

on the filter as viewed through a metal] ographrc microscope. The material was composed of to 1.00 pm size

spheres of mercury and a great many alloy par doles

.

The percentage of particles penetrating the.- pulmonary

air spaces rises from essentially zero at 10 pm to a

maximum at and below 1 pm, where it eqiials the fraction

of tidal air which reaches the lungs. It is assumed

that the spheres of mercury contained some dissolved

alloy and that the alloy particles were partially reacted

with mercury. Souder^ analyzed the liquid squeezed from

an amalgam mix before crystallization had caused it to

harden. He reported 1.07% tin and 0.13% silver, therefore,

presumably these mercury droplets would be '98+% mercury.
8

Tests for mercury vapor revealed very little vapor

in the air drawn into the intake hose of the detector

when the opening was 30 cm away from the working

area. The highest reading obtained at 30 cm was

0,02 mg Hg/m^ of air during ultrasonic condensation.

This represents 20% of the threshold limit value of

0.1 mg Hg/m^ of air as established by the American Conference of Governmental Industrial Hygienists,^ The

vapor levels were about zero when using hand and mechanical methods of condensation, other than ultrasonic,

It was necessary to move the intake hose of the detector

to within 7 cm of the working area to obtain

vapor levels above the threshold limit value.

When condensation was stopped, the vapor levels

returned to near zero within approximately 3 to 4

minutes even when the condensed alloy and excess plashy

amalgam was allowed to remain in place.

Shepherd et al^ determined that the levels of

mercury vapor present in scientific laboratories was
9

primarily dependent on the amount of ventilation in the

rooms. Other important factors were the number and types

of sources and the degree to which these sources were

disturbed

.

The low levels of vapor found in the present study

may have been due to good air ventilation in the

operatory ( 10 cubic meters of air per minute in a room

containing approximately 50 cubic meters) Put reducing

the air circulation by blocking the intake and exhaust

vents did not produce significantly higher levels.

Figure 3 is a photograph of a porcelain tooth and

the surrounding operating field after condensation of

three amalgam mixes into the tooth. From viewing the

mercury droplets deposited in the field it is evident

that there is a considerable surface area for the

evaporation of relatively large amounts of mercury

vapor. Since these droplets contain dissolved tin and

a slight amount of silver the evaporation of mercury

may be reduced. Extended use of the ultrasonic device
10

would ultimately result in a great number of fine droplets

of mercury being deposited throughout a dental operatory

which in turn could cause a high level of vapor, especially

if the mercury droplets were disturbed. Whether toxic

levels could be achieved is not known but certainly awareness of the potential hazard is one of the primary factors

in prevention.

No quantitative value of the amount of mercury and alloy

particles that are dispersed are given because the amount dispersed for any one operation is subject to the following and

probably other variables; the mercury-alloy proportions, the

size and shape of the instrument tips, the size and shape of

the restoration, the power adjustments on the instrument, the

length of time the instrument tip is in contact with the

amalgam mix and the length of time the tip of the instrument

is in contact with the walls of the cavity.

In any event the dispersion of mercury droplets and

fine partially amalgamated alloy particles in the area
11

of operation when amalgam is condensed by ultrasonic

means is undesirable. Some of the debris will be swallowed

and some inhaled by the patient and the operating team.

Summary and conclusions

Amalgam condensation with an ultrasonic device resulted

in the emission of a cloud o’ mater i;:il from the area of the

working tip. This aerosol was compose'-’’ m u'cury droplets

and alloy particles. Mercury vapor levels of 0.02 mg Hg/m^

of air were found 30 cm from the condensing point. This

value represents 20% of the current (July 1970) threshold

limit value for mercury vapor and, in itself, probably does

not represent a poison hazard. However, the additive effect

of introducing this technic into an office having safe

levels of mercury vapor may be sufficient to develop

hazardous concentrations. The inhaling and swallowing

of alloy particles and mercury droplets cannot be considered

good practice in any case and may represent a health hazard

even though they apparently are not producing excessive

mercury vapors.
12

The continued use of an ultrasonic condensing

instrument for placement of amalgam restorations would

certainly result in the deposition of a great many small

mercury droplets throughout a dental operatory. It would

appear, therefore, that the use of ultrasonic amalgam

condensers would be contra-indicated until such time as

the safety of the instruments has been well established

especially after long periods of use in areas with poor

air ventilation.
-13-

References

1. Souder, W., and Sweeney, W. T. Is mercury poisonous

in dental amalgam restorations? Dental Cosmos 73;

1145 Dec 1931.

2. Nixon, G. S., and Smith, H. Mercury hazards in dental

surgeries. J Dent Res 43:968 Supplement Sept-Oct 1964.

3. Airaksinen, S. Risk of exposure of dental staff to

mercurial poisoning. D Abstracts 6:620 Oct 1961.

(Airaksinen, Sirkka. Ylioppilaiden Hamm.oshoitola

,

Lepasuonkatu 7A . Helsinki, Finland. Hamrnashoitohenkilokunnan Elomopeamyrk Tysvaarasta. Suomen

Hammaslaak, Toim, 57:27 March 1961.)

4. Nossek, V. H., Seidel, W., Der Quecksilberdampfgehalt

in der Luft zahnarztlichen PraxisrSume unter besonderer

Berlicksichtigung der Ultraschallkondonsation von

Amalgam, Dautsch. Stomat. 19 pp 787, 1969.

5. Meyer, A. Mercury poisoning: A potential hazard to

dental personnel. Dental Progress 2:190 April 1962.
-14-

6. Sax, N. I. Dangerous properties of industrial

materials. Ed 3, New York, Reinhold Book Corp.,

1968, p. 902.

7. Grossman, L. I., and Dannenberg, J. R. Amount of

mercury vapor in the air of dental offices and

laboratories. J Dent Re 28:435 Oct 1949.

8. Frykholm, K. O. Mercury from dental amalgam, its

toxic and allergic effects and some comments on

occupational hygiene. Acta Odont Scandinav 15:7

Supplement 22 1957.

9. Directions for use of Instantaneous Vapor Detector

(GEI - 37634) Catalog #9790339G1 and G2 Feb 1952.

General Electric Company, Schenectady, New York.

10. Hatch, T. F., and Gross, P. Pulmonary deposition and

retention of inhaled aerosols. New York, Academic

Press, 1964-

11. Shepherd, M. ; Schuhmann, S.; Flinn, R. H. ; Hough, J. W.

and Neal, P. A. Hazard of mercury vapor in scientific

laboratories. J Res Nat Bur Stands 26:357 Jan- June

1941 Research Paper RP1383

.
Fig. 1. A cloud of material, arrows, is being emitted from the

amalgam at the tip of an ultrasonic amalgam condensing instrument. The particles, also shown in Fig. 3, settle on the

instrument handle. A, and may be responsible for some of the

haze surrounding the handle.
F

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#

10

um ||

Fig. 2. Material collected by a suction and filter

device held 7 cm above the ultrasonic condensing

instrument during amalgam condensation. Mercury

droplets and alloy particles can be observed throughout.

^

•
Fig. 3. A porcelain tooth and the surrounding operating field

after condensation of 3 amalgam mixes into the tooth. The

background is plain black paper. Note the great number of

mercury and alloy particles that have been deposited around the

operating site. The dark area behind the tooth is a shadow

caused by the oblique lighting used in making the photograph.

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