NATIONAL BUREAU OF STANDARDS REPORT

3960

REPORT ON DENTAL RESEARCH

AT THE NATIONAL BUREAU OF STANDARDS

Progress Report

July 1 to December 31> 195^

Dental Research Laboratory

•<0>

U. s. DEPARTMENT OF COMMERCE

NATIONAL OUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards is suggested in the following listing of

the divisions and sections engaged in technical work. In general, each section is engaged 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.

Electricity. Resistance and Reactance Measurements. Electrical Instruments. Magnetic

Measurements. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Engineering Metrology.

Heat and Power. Temperature Measurements. Thermodynamics. Cryogenic Physics. Engines

and Lubrication. Engine Fuels. Cryogenic Engineering.

Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid

State Physics. Electron Physics. Atomic Physics. Neutron Measurements. Infrared Spectroscopy. Nuclear Physics. Radioactivity. X-Ray. Betatron. Nucleonic Instrumentation. Radiological Equipment. Atomic Energy Commission Radiation Instruments Branch.

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry.

Inorganic Chemistry. Electrodeposition. Gas Chemistry. Physical Chemistry. Thermochemistry.

Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics. Mass

and Scale. Capacity, Density, and Fluid Meters. Combustion Control.

Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Organic Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion.

Mineral Products. Porcelain and Pottery. Glass. Refractories. Enameled Metals. Concreting

Materials. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Heating and Air Conditioning. Floor, Roof, and Wall Coverings. Codes and Specifications.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering.

Electronics. Engineering Electronics. Electron Tubes. Electronic Computers. Electronic

Instrumentation. Process Technology.

Radio Propagation. Upper Atmosphere Research. Ionospheric Research. Regular Propagation

Services. Frequency Utilization Research. Tropospheric Propagation Research. High Frequency

Standards. Microwave Standards.

^Office of Basic Instrumentation ^Office of Weights and Measures.
I NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

0708~10-0707 January 31, 1955 3960

0708-20-3824

0708-20-3857

REPORT ON DENTAL RESEARCH

AT THE NATIONAL BUREAU OF STANDARDS

Progress Report

July 1 to December 31* 1954

Dental Research Laboratory

The dental research program at the National Bureau of Standards

is carried on in cooperation with the Council on Dental Research

of the American Dental Association, the Army Dental Corps, the

Air Force Dental Service, the Navy Dental Corps ^ and the Veterans

Administration

.

(Task 7756-41 BV No. 55-14)

NBS

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, rei ApProved f° r Public release by the

unless permission i; Director of the National Institute of

25, d.c. Suchper Standards and Technology (NIST)

cal ly prepared If t On October 9, 2015

In part, is prohibited

indards, Washington

port has been specifiiport for its own use,
’
REPORT ON DENTAL RESEARCH

AT THE NATIONAL BUREAU OF STANDARDS

1 . INTRODUCTION

Investigations of materials and equipment used in dentistry

and of natural tooth structures have been carried on in the Dental Research Section of the National Bureau of Standards during

the half year ending December 31* 195^-- Summaries of results

obtained on work now in progress are given below. Copies of

reports issued on phases of the work completed during this period

are also included.

2 . REPORTS ISSUED

NBS Report 3890 The Setting Reaction of Zinc Oxide and Eugenol.

NBS Report 3919 Revision of American Dental Association Specification No. 3 tor Dental Impression Compound.

NBS Report 3955

NBS Report

Some Factors Influencing the Cutting Characteristics of Rotating Dental Cutting Instruments.

Use of Ionization Chambers in Obtaining Data

on Radiation at Points Within the Head During

Dental X-ray Exposure

.

. , 3. WORK IN PROGRESS

3.1 Structure of Human Tooth Enamel and Dentin

The depolarization fluorometer constructed for use in obtaining data on the molecular weight of fluorescing materials has

been tested using' fluorescein solutions and has provided data

giving a value for the molecular weight of fluorescein within 10%

of the formula weight. Experiments on extracts of enamel and

dentin are now in progress but decay times must also be determined

before. weight values can be determined. In the meantime methods

of improving the precision of the fluorometer are being investigated.

By substitution of an ammonium dihydrogen phosphate crystal light

modulator for the rotating Polaroid discs now used, greatly Increased precision may be obtained.

The crystallographic studies of tooth-like materials have

been resumed. Synthetic calcium phosphates have been prepared

for X-ray diffraction studies. Methods of preparing large crystals

of non-stoichiometric apatites are being studied.

2

3.2 Determination of Contours of Dental

Impressions., Models and Dentures

The method of measuring the contours of impressions, models

and dentures using an instrument of the pantographic type has

been further developed. Recent improvements of the instrument

include the addition of an electronic device for determining the

point of contact with elastic impression materials and a 100$

humidity chamber to maintain the dimensional stability of agar

and alginate impression materials during measurement. A statistical analysis of results obtained indicates that the standard

deviation for the measurements is approximately 0.002 inch.

3-3 Low-Temperature Alloys

Attempts have been made to correlate the physical properties

of gallium-copper -tin alloys with the micro structure of the original copper-tin alloy. However, much difficulty has been encountered

in revealing the micro structure as the alloys are unusual and technics for use on them are not well defined.

Preliminary experiments indicate that an alloy made by combining gallium with a copper alloy containing 0.25$ beryllium may

have physical and chemical properties useful for dental applications .Arrangements were made with the School of Aviation Medicine,

Randolph Field, Texas, for determination of biologic response to

an alloy of gallium and speculum metal (68t Cu - 32$ Sn)

.

3 .4 Resins

(a) Polymerization of Resins.

Setting times and physical behavior of polymers cured from

monomer-polymer mixtures containing a series of tertiary amines

in varying amine -benzoyl peroxide concentrations were determined

by means of penetrometer tests and Rockwell superficial hardness

measurements. Polymers cured with dimethyl-p-toluidine which

is used in most commercial products gave satisfactory properties.

Only a few other accelerators gave desirable polymerization products .Another series of amine salts of p-toluene sulfinic acid

were prepared. Three solid salts of aliphatic amines not previously reported in the ^Literature were characterized by elementary analysis . Four solids gave sharp melting points but the

elementary analysis deviated considerably from the theoretical

values. Difficulties were encountered in purifying liquid salts

of aliphatic and heterocyclic amine salts. Most of these salts

are soluble in methyl methacrylate and act as polymerization accelerators . For aliphatic amine salts increased chain length

reduces the accelerating efficiency. Salts of heterocyclic amines

proved to be poor accelerators. Polymers cured with the N-methyl

aniline salt of p-toluene sulfinic acid gave somewhat lower

- 3

- indentation values as compared to salts prepared from p-toluene

sulfinic acid. N-ethyl-bis-[p-tolysulfon-methyl ]-amir£ which has

been reported to be an excellent polymerization accelerator was

prepared

.

(b) Water Sorption of Acrylic Resins.

The depolymerization of methyl methacrylate polymers in

boiling water was investigated. No degradation could be observed

for low molecular weight sample (M.W. = 45,000 to 100,000) . Speci

mens of 1,615*000 molecular weight showed a decrease in molecular

weight to 800,000 on prolonged storage in water.

(c) Dental Resins.

Addi tonal data were obtained on the physical and chemical

properties of dental resin cements and filling materials. Knoop

hardness values of these materials ranged from 7 to 23 or from

considerably below to slightly above the top value (approximately

20) usually reported for polymethyl methacrylate. Radio-opacity

measurements indicated that some of the materials are less opaque

than dentin and may therefore present a problem in dental X-ray

diagnosis. Observation of the adhesion of the cements to abraded

brass surfaces showed that none of the materials adhered after

immersion for two weeks in water. Volumetric shrinkage of these

materials on polymerization was found to vary from 5 to 12$.

Dimensional changes during storage in water were measured

on resin cement^ specimens 0.5 mm thick by 50 mm in diameter.

The specimens were kept at 80°C in air over night and then dried

at room temperature until constant weight was established _before

immersion in water. Peak linear expansions ranging from 012 to

0.7$ were obtained for most materials in approximately 3 days.

After this period shrinkage was observed.

A study of the color of heat-cured dental resins has been

started as part of a general study of methods for specifying

the colors of dental materials. Measurements are being made with

a Gardner automatic color difference meter. Methods are now being

developed for preparation of uniform and reproducible specimens.

Preliminary results show that some color differences of dental

resins can be correlated with small differences in the monomerpolymer ratio used in making the specimens

.

Work has been started on a study of the effects of pressure,

temperature and time of cure on the molecular weight of polymethyl

methacrylate made from a monomer-polymer mix. Preliminary invest!

gationS were made using a pressure of 200 lb per square inch and

a temperature of 100°C. Viscosity measurements made on specimens

cured for 2, 4 and 6 hours indicate that the molecular weights

decrease after the 2-hour period.

- 4 - 3.5

Chromium-Cobalt Alloys

A small vacuum and controlled atmosphere furnace has been

constructed for melting point determination of chromium-cobalt

alloys and is now under test. Chemical compositions of the alloys

are being determined. Data on these two properties will be used

with the previously reported data on tensile properties and hardness in the preparation of a specification for the dental chromiumcobalt alloys.

3.6

High-Speed Handpieces

Methods for evaluation of "high-speed” handpieces are being

developed. A testing bench has been constructed which will make

it possible to test simultaneously five or six handpieces running

at a constant speed under conditions approximating the normal use

of the instruments in the mouth. Data will be obtained on heat

rise, lateral play, run-out and backlash after various periods of

operation.

3.7

Panographic X-ray Investigation

The construction of a prototype X-ray machine for taking

panoramic dental X-ray exposures is almost completed. The machine

is in process of assembly, and should be ready for trials in about

30 days. It is anticipated that a series of 100 or more patients

will be radiographed with the device.

Measurement of the amount of ionizing radiation produced at

points in and about the human head during panoramic dental radiography has been completed. These results would indicate that the

panoramic device possesses a marked advantage over conventional

dental radiography in that the amount of ionizing radiation to the

patient during full-mouth examination is reduced by a factor of 50

in the areas receiving the heavier dosages.

3.8

X-ray Film Survey

The effect of aging on dental X-ray film is now being investigated. Density of film exposed and processed under standard

conditions after 1, 3* 6 and 9 months storage will be determined.

This work will bring to a close the X-ray film survey.

3.9

Motion Picture

Practically all of the photography for a motion picture on

the testing of dental materials has been completed.
.

.

" v •:£>,' 5

, 1 1

I

• •'

; I

:

.

.
- 5

3.10

Porcelain Restorative Materials

Mixtures of high and low fusing porcelain powders were made

in an attempt to reduce the large shrinkage which occurs in the

firing of porcelain restorations. Although the reduction in

shrinkage was very slight the method appeared to distribute the

shrinkage more uniformly throughout the specimen. * Investigations

of the solubility of various types of porcelains are now being

made

.

Work on the development of a simple test for the setting

time of dental amalgam is in progress. Most promising results

have been obtained from a system in which a thin disk of amalgam

is placed in a die through which a punch can pass and penetrate

the amalgam. The time at which the amalgam first supports the

punch is considered to be the setting time.

Materials evaluated for the Federal Dental Services and

the American Dental Association by specification or special test

methods included amalgam alloys, chromium- cobalt alloys, denture

base resins, gold casting alloys, handpieces, hydrocolloidal

impression materials, inlay waxes, investments, mercuries, wrought

gold wire and X-ray film.

3.11

Setting Time of Dental Amalgam

3.12

Evaluation of Materials

For the Director
.

% 1

1

.
NATIONAL BUREAU OF STANDARDS REPORT

THE SETTING REACTION OF ZINC OXIDE AND EUGENOL

Henry I. Copeland, ,, Jr . *, Gerhard M. Brauer**,

W. T. Sweeney^ and A. F. Forziati 0

. * Major, Dental Service, U. S. Air Force, stationed at the

National Bureau of Standards, Dental Research Section,

Division of Organic and Fibrous Materials.

** Chemist, Dental Research Section. ^ Chief, Dental Research Section.

° Research Associate, American Dental Association Research

Fellowship, Dental Research Section.

This work :Ls a part of the dental research program! conducted

at the National Bureau of Standards in cooperatic n with the

Council on Dental Research of the American Dental Association

the Army Dental Corps, the Air Force Dental Service, the Navy

Dental Corps and the Veterans Administration.

The data in this report was presented in a thesis by Henry I.

Copeland, Jr., in partial fulfillment of the requirements of

the Graduate School, Georgetown University, Washington, D. C.

for the degree of Master of Science.

NBS PROJECT

0708-10-3824 January 11, 1955

NBS REPORT

3890

Progress Report

(Task 7756-41 BV No. 55-14)

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprinting, or reproduction of this report in any form, either in whole or in part, is prohibited

unless permission Is obtained in wrttingfrom theOffice of the Director, National Bureau of Standards, Washington

25, D, C, Such permission is not needed, however, by a Government agency for which a report has been specifically prepared If that agency wishes to reproduce additional copies of that particular report for its own use,

±'n_Cj OJl'±'XJLlNUr rtHiiiO'rXUlM UI AJL1MO UA-LX 2f AND EUGENOL

Abstract

Zinc oxide-eugenol mixtures have been used

for a number of years in dentistry as temporary

filling materials* for surgical cements and as

impression pastes. In the present study the

mechanism of setting of these mixtures was ir>

vestigated. The setting rate is dependent on

the water of hydration and particle size of the

zinc oxide. X-ray diffraction data and electron

micrographs give evidence that a crystalline

compound is formed. Chemical analysis and molecular weight determinations show that this compound

corresponds to the empirical formula (C^qHiiC^) 2 Zrh

zinc eugenolate. Infrared data as well as the

non-reactivity of meta and para substituted phenols

as compared to the ortho isomers suggest that

the zinc eugenolate is a chelate. The hardened

mass resulting from mixes of zinc oxide and

eugenol consists of zinc- oxide embedded in a

matrix of long sheath-like crystals of zinc

eugenolate. The excess eugenol is sorbed by

both the zinc eugenolate and the zinc oxide

.

1 . INTRODUCTION

The zinc oxide-eugenol materials have been developed

for utilization in a number of dental applications. They

are most widely employed as palliative and anti -bacterial

agents in the treatment of carious lesions [1], With modi

fiers* these materials are used as impression pastes and

as surgical cements.

Generally 5 the use of zinc oxide and eugenol depends

on :;heir tendency to form a hardened coherent mass when

mixed. Unexplained variations in the behavior of the mixtures are important to the clinician who uses these materi

als to treat dental conditions. Of special concern are

variations in setting rate* hardness* and strength of the

set mass

.

The mechanism of the setting process of zinc oxide

and eugenol is unknown. Factors which have been reported

to produce variations in the physical behavior are the typ

of zinc oxide used* the amount of water present (both in

2

the zinc oxide and atmosphere) and the a' bient temperature.

The following theories have been advanced in regard to the

setting process: 1. The setting process is a purely physical one in which the constituents retain their individuality [2]. 2. A chemical reaction occurs and a compound

resembling zinc phenolate is formed [3]. 3

1

The setting

process is a combination of physical and chemical reactions [3].

The object of this investigation was to study the setting of zinc oxide and eugenol mixtures in order to more

nearly define physical and chemical processes involved.

2. MATERIALS AND METHODS

Materials

.

The zinc oxide (reagent grade) used had a particle size

of around 3.? 000 Angstroms and contained less than 2% water.

It was white. An experimental type- of zinc oxide (Merck

Hyperfine*) was also used. According to the manufacturer’s

specifications it had a particle size of 125-250 Angstroms

and contained approximately 5$ water. This zinc oxide was

reddish in color.

The eugenol was USP grade. All other chemicals used

were reagent grade

.

Experiments

.

Hardening

.

Mixes of zinc oxide (reagent grade) were made with

guaiacol, methyl guaiacol, eugenol. phenol, veratrole, safrol,

anethole, m-methoxy phenol and thymol. The mixtures were

made with a stellite spatula on a glass slab at room temperature. It was necessary to melt the phenol and thymol prior

to mixing. The maximum amount of ;:inc oxide that could be

wetted by the liquids was incorporated.

Samples of the zinc oxides were dehydrated by heating

at 110°C for 24 hours. The dehydrated zinc oxides were mixed

with eugenol in the same manner.

Heat of Reaction.

The change in temperature caused by the reaction

was determined by means of a calibrated iron-constantan

thermocouple connected to a Brown recording potentiometer.

Zinc oxide (Hyperfine) -eugenol mixtures were used in this

experiment

.

* The authors wish to thank J. B. Conn of Merck and Co .

,

Inc., for supplying the Hyperfine zinc oxide.

3

Analysis for Reaction Products.

Mixtures of 0.5 mole zinc oxide (reagent grade)

and 0.1 mole eugenol were prepared. The hardened mass was

pulverized by grinding in a mortar to a fine powder. The

particles were extracted with chloroform for 30 hours in

a Soxhlet extractor. The residue left in the filter thimble

was vacuum dried and weighed. The chloroform was distilled

off from the extract and the residue distilled over at 87 - 101 °C and 2 mm Hg pressure.

Equimolar mixtures of zinc oxide (Hyperfine) and eugenol

were prepared and extracted as above. The residue in the

filter thimble was dried to constant weight at 110 °C and

1-2 mm Hg pressure. The extract was filtered through a

weighed Gooch crucible and the residue washed with thr$e

10 ml portions each of chloroform* methanol and ether and

dried to constant weight. The low boiling solvents used

for extraction and washing were distilled off from the filtrate and the weight* refractive index and boiling point

of the remaining liquid were determined.

The experiments were repeated using methanol* benzene*

and chlorinated hydrocarbons other than chloroform as the

extraction solvent

.

Measurement of X-ray Diffraction.

The x-ray diffraction measurements were made by

the section on Constitution and Microstructure at the National Bureau of Standards . The instrument used was a

North American - Phillips Diffractometer utilizing a Geiger

counter and a recording potentiometer. All measurements

were made through 90 degrees . Patterns were obtained of

zinc oxide (reagent grade),, zinc oxide (Hyperfine)* eugenol*

mixtures of eugenol with each of the two zinc oxides and

a mixture of zinc oxide (Hyperfine) with guaiacol. Patterns

were also obtained of the purified reaction product and a

zinc oxide -water mixture.

Elementary Analysis.

The purified reaction product was analyzed for

carbon* hydrogen and zinc content using micro techniques.*

The dry combustion method was used for the carbon and hydrogen determinations while the zinc was determined as the sulfate by digestion in t^e presence of sulfuric acid.

Infrared studies.

Zinc 8-quinolinolate was prepared according to

Ztzsche [4], Zinc guaiacolate was obtained on mixing guaiaco

* Elementary analyses were performed by R. A. Paulson

of the National Bureau of Standards.

- 4 - with zinc oxide. The unreacted guaiacol was removed by

repeated washing with cold chloroform. The infrared absorption spectra of 8-quinolinol, zinc 8-quinolinolate,

eugenol, zinc eugenolate, guaiacol and zinc guaiacolate

were measured. The solid samples were incorporated in

potassium bromide pellets. All samples were examined with

a Perkins -Elmer, Model 21 Spectrophotometer.*

Electron Micrographs.

Electron micrographs of the Hyperfine zinc oxideeugenol mixture and the purified reaction product were

made at 10,000 and 4,000 diameter magnifications respectively.**

Water Sorption Study.

Dried zinc eugenolate samples were placed in a

desiccator over a saturated potassium nitrate solution

(93* 3^ relative humidity at 30°C)

.

3. RESULTS AND DISCUSSION

The mixtures of zinc oxide (reagent grade) with eugenol,

guaiacol or methyl guaiacol set into a hardened mass.

CHiL-cH=CH,

OH

r^Si

" 0

kJ

These aromatic oils have a methoxy group ortho to a phenolic

hydroxy group. Guaiacol has no substituent group in the

para position. Methyl guaiacol has a methyl group as a para

substituent. Eugenol has a para beta allyl group.

Mixtures of zinc oxide with phenol itself, veratrole,

safrol, anethole, thymol, and m-methoxy phenol, did not

harden

.

ocii 2 o © H

i 5

.. t

s I 3 | §

\ OH

I .9c'H

ocH

5 S

-t H “C H~

CM, * Infrared absorption spectra were made by J, E. Stewart

and G. Wyman of the National Bureau of Standards.

** Electron micrographs were made with F. A. Heckman of

the National Bureau of Standards

.

- 5

- These compounds do not have a methoxy group ortho to a hydroxy group

,

From the above considerations, it appears that the para

groups are not involved in the setting reaction, and the

ortho methoxy group is essential for the hardening to take

place

.

The dehydrated zinc oxides did not fcrm a hardened

mass when mixed with eugenol . The untreated reagent grade

zinc oxide (less than 2$ water) required more than 24 hours

to harden when mixed with eugenol. The Hyperfine zinc oxideeugenol mixture hardened in less than 15 minutes. This zinc

oxide had the greater water content ( 5$ according to manufacturer) and also had a much larger surface area. In all

experiments* the setting rate of either of the zinc oxides

mixed with eugenol* was more rapid in warn and humid weather

than when the relative humidity was low.

The hardening process was found to be exothermic in

nature. The temperature rise was directly related to the

rate of hardening and to the ultimate hardness of the product; e.g.* rapidly setting mixtures gave a harder product

and a greater temperature rise.

On extraction with chloroform the reagent grade zinc

oxide-eugenol mixture yielded approximately 80$ eugenol.

The residue in the filter thimble showed a 10$ increase in

weight over the original weight of the zinc oxide*- and analysis indicated that some eugenol was still present in the

residue. An insoluble film deposited in the extractor flask

suggested some chemical change had taken place.

Since the zinc oxide (Hyperfine) - eugenol mixture had

demonstrated faster setting and increased exothermic activity*

the extractions were repeated using this mixture. Table 1

gives the composition of a typical mixture of Hyperfine

zinc oxide and eugenol

.

Table 1. Composition of a Zinc Oxide-Eugenol Mixture.

A. Before Setting:

Zinc oxide (containing 1.3$ water) ... .9.60 g . .0.117 moles

Weight of dry zinc oxide . . . .9 .48 g.

Eugenol ..... 19.26 g 0.117 moles

Material in mixture 28.74 g.
.

.
6

B. After Setting:

Residue on extraction 15-5480 g.

Residue in extract (other than eugenol ) . . 1 . 1909 g.

Eugenol recovered 11 . 6676 g. . 65 . 2$

Material accounted for 28.4065 g. . 98.9$

After the chloroform was removed from the extract* the

residue soon formed an oily paste. This paste was composed

of a white crystalline material and eugenol.

X-ray diffraction measurements were made to determine

changes in crystal structure which might have occurred during

setting. Both reagent grade zinc oxide and the Hyperfine

zinc oxide gave the characteristic pattern indicating principal spacings of approximately 2 ,9 * 2.6* and 2.5 Angstroms.

The small particle size of the Hyperfine zinc oxide caused

broadening of the bases of the peaks in its pattern. Since

there were no other differences in the diffraction pattern*

the manufacturer's suggestion that the reddish color of the

Hyperfine was due to its small particle size appears > reasonable . Eugenol showed no peaks* being non-crystalline.

The mixture of reagent grade zinc oxide with eugenol

showed peaks indicating the presence of a new crystal form

with spacing of approximately 17.0* 8.8* and 7.0 Angstroms.

The zinc oxide (Hyperfine) mixed with eugenol demonstrated

the presence of the same crystal form with approximately

the same spacing. The peaks were much higher in the pattern

of ;he latter mixture which indicated the presence of a much

greater quantity of the new crystal form. Zinc oxide mixed

with guaiacol demonstrated the presence of a new crystal

form with spacings of 12.0* 9-3 j and 8.7 Angstroms. The

zinc oxide-water mixture gave only the characteristic zinc

oxide pattern.

The diffraction pattern of the purified reaction produce showed only the presence of the new crystal form although as little as 2$ of zinc oxide could have been detected

by the diffractometer used.

Representative x-ray diffraction patterns are shown in

Figures 1 and 2. The peaks between 30 and 82 degrees have

been identified as belonging to zinc oxide? [ 5 ]. The peaks

occurring between 6 and 26 degrees are the? result of chemical reaction. The reaction product is ide?ntified as zinc

eugenolate in pattern No. 1 of Figure 2.

- 7 - The anlaysis of the compound formed by the reaction

of Hyperfine zinc oxide and eugenol is given in Table 2 . As a compound resembling zinc phenolate had been suggested

[

3 ] as a possible reaction product, the composition of zinc

eugenolate was calculated from the empirical formula and

compared with the values obtained for the new crystalline

compound. The comparison indicated that the formula for

the compound would be that of zinc eugenolate, (C10H11O2) 2 ^n • Table 2 . Analysis of Reaction Product

CALC. FOUND

Carbon

Hydrogen

Zinc

Oxygen (by difference)

Molecular weight**

61 . 34$

5 . 6156

16.72$

16.33$

391

59.6$

5.7$

17.1$ — 17.6$

435

*The low carbon as well as the high zinc and oxygen

percentages would be explained by the presence of a small

amount of zinc oxide in the purified product.

The molecular weight was determined cryoscopically in

acetamide (molar freezing point depression Kf equals 36 . 3 °C).

Some physical properties of the zinc eugenolate are

given in Table 3.

Table 3 . Some Physical Properties of Zinc Eugenolate

M.P. (Dissociation Temperature) 245 °C.

Crystal Form (Electron micrograph*. Fig. 4 ) Monoclinic

Refractive Index P. ; ^ 5 ) 1.69

Density 1.6 g/ml

Solubility v.sl.s. hot

chloroform; sol . in

ammonium hydroxide,

pyridine, hot acetamide, and hot butyrolactone

.

Fluorescence** (excited by 3650 A° radiatr.on) . . . .White

*Figure 3 shows an electron micrograph of a zinc oxide

eugenol mixture

.

**The presence of zinc eugenolate may be readily detected

by means of the characteristic white fluorescence emitted

by :;his compound when excited by ultraviolet radiation.

When similiarly excited, zinc oxide and ei^genol fluoresce

bright yellow and dark brown, respectively. A mixture of

zinc, oxide and eugenol fluoresces deep red.
.

.

.

1

'

'
- 8

Zinc eugenolate was found to be insoluble in all

common organic solvents including anisole, mesityl oxide,,

a - chloronaphthalene, dioxanone, diethyl carbamate, ethylene carbonate, diethyl phosphite, dimethyl amido phosphate,

tributyl amine and dimethyl formamide

.

Infrared absorption spectra were studied in an attempt

to gain more information on the molecular structure of zinc

eugenolate. Zinc 8-quinolinolate was used for comparison

because an x-ray analysis of its structure had been reported [6], For further comparison, guaiacol and the zinc

oxide - guaiacol reaction product were used.

Interesting changes in infrared absorption occurred,

as shown in Figure 5- In the 7.1 to 7.^ micron area, the

absorption due to the hydroxy aromatic group of 8-quinolinol,

eugenol, and guaiacol was not evident in their zinc derivatives. The disappearance of this band is due to the replacement of the phenolic hydrogen by zinc. At 7-5 microns,

absorption was observed in all three zinc compounds whereas

none was present in the original hydroxy aromatics. This

absorption has been attributed to the appearance of bond

bending strain.

An absorption band at 6.08 microns due to the vinyl

group was present in both eugenol and its zinc derivative

spectra. This was evidence that the para substituent did

not take part in the reaction.

The apparent inability of the setting reaction to take

p'iace in the absence of the o-methoxy group, the insolubility

of the reaction product, and the infrared absorption changes

suggest that zinc eugenolate is related tc: the metallo-pyrocatechol complexes or chelates [7].

Zinc is a bivalent element with a common coordination

number of four. As such, zinc is a metal likely to form

a chelate. Eugenol, guaiacol and methyl guaiacol have a

replaceable hydrogen and a nearby donor in the oxygen of

the o-methoxy group. The chelate formed would have a proportion of two eugenol molecules to one zinc. It may be

represented as follows:

CHt-CH=CH1
-

.

•

.

.
- 9

- SUMMARY 1.

The setting of mixtures of zinc oxide and eugenol

involves both a physical and a chemical process.

2.

X-ray diffraction data and electron photomicrographs

give evidence that a crystalline compound is formed

by the chemical reaction.

3.

Chemical analysis and molecular weight determinations

show that this crystalline compound corresponds to the

empirical formula ( Cio^n^) z i- nc eugenolate.

4. Infrared absorption data suggest that zinc eugenolate

is a chelate compound with the following structure:

Igt -HC- ti ?C O- - cH

o- 4n - °

*O - r>' HA

ch*~CH -CHe

The hardened mass resulting from mixes of zinc oxide

and eugenol consists of zinc oxide embedded in a matrix

of long, sheath-like crystals of zinc eugenolate. The

excess eugenol is sorbed by both the zinc eugenolate

and the zinc oxide

.

The authors wish to specially acknowledge the generous

assistance given by H. Swanson and G. Ugrinic of the Microstructure Section, National Bureau of Standards, in performing x-ray diffraction measurements.

10

BIBLIOGRAPHY

1. Turkheim, H. J., Brit. Dent. J. 45 , 1 (1953).

2 . Forster, E., Stomatologia 27 , 217-221 ( 1921 )

.

3. Harvey, W. and Petch, N. J., Brit. Dent. J.

80, 1-8, 35-41 (1946).

4. Ztzsche, F., Silbermann, H., and Vieli, G.,

Helv . Chim. Acta 8, 592-602 (1925).

5. Swanson, H. E. and Fuyat, R., Nat. Bur. of Stands.

(U.S.) Circ. 539, Vol . II (1953).

6. Merrit, L., Jr., Anal. Chem. 25 , 718 (1953).

7. Martell, A. E. and Calvin, M., Chemistry of Metal

Chelates, Prentice -Hall Inc., New York " ( 1952) .

Figure 1. X-ray Diffraction Patterns. 1. ZnO (reag.).

2. ZnO (reag.)-Eug. mixture. 3 . ZnO (Hpf . )-

Eug. mixture.

I.

Figure 2. X-ray Diffraction Patterns. 1. Zinc eugenolate.

2. ZnO-Guaiacol mixture. 3« ZnO-V/ater mixture.
r : :

. . . .. , . ,
Figure 3. ELECTRON MICROGRAPH

An electron micrograph of a zinc oxide-eugenol mixture showing the small, rounded particles of zinc oxide

and the thin, elongated crystals of zinc eugenolate. The

sheaf-like aggregation is typical of the unextracted hardened mass.

Figure 4. ELECTRON MICROGRAPH

An electron micrograph of zinc eugenolate, palladium

shadowed 4:1, showing the crystal habit typical of the

extracted reaction product. The small, rounded particles

seen in the background and on the surfaces of the large,

crystalline formations are probably zinc oxide.
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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

0708-20-3821; December 31* 1954 3919

Progress Report

A Revision of

AMERICAN DENTAL ASSOCIATION

SPECIFICATION NO. 3 FOR DENTAL IMPRESSION COMPOUND

by

John W. Stanford’/ B.S.

George C. Paff enbarger-*, D.D.S.

W. T. Sweeney 0

, A. B.

-x- Research Associate, American Dental Association Research

Fellowship, Dental Research Section.

° Chief, Dental Research Section

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 Service, the Navy

Dental Corps and the Veterans Administration.

(Task 7756-41 BV No. 55-14)

<^BS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprinting, or reproduction of this report in any form, either in whole or In part, is prohibited

unless permission Is obtained in wrltingfrom theOffice of the Director, National Bureau of Standards, Washington

25, D. C, Such permission is not needed, however, by a Government agency for which a report has been specifically prepared If that agency wishes to reproduce additional copies of that particular report for its own use,
. •

•

'

.

-

:
A Revision of

AMERICAN DENTAL ASSOCIATION

SPECIFICATION NO. 3 FOR DENTAL IMPRESSION COMPOUND

Abstract

A revision of American Dental Association

Specification No 0 3 for Dental Impression Compound

is proposed in order to simplify testing procedures

and to obtain better reproducibility of flow test

results. The revision Is based on experience derived

from a recent survey of certified dental impression

compounds and a data exchange program with three of

the manufacturers of certified compounds. Two major

changes were made in the detail requirements. The

requirement for flow at the l+OoO°C (10i4-.0 o F) flow

testing temperature was deleted. Also, the requirement for flow at the 50.0°C (122.0°F) flow testing

temperature for tray compound was replaced with a

45oO°C (113oO*F) testing temperature. Precise

methods for preparation and testing the flow

specimen are incorporated In the revised specification.

Foreward

The American Dental Association revises Its specifications

for dental materials whenever new or Improved test methods and

materials become available. To promote these revisions, the

Council on Dental Research of the American Dental Association

seeks the help of the Dental Materials G-roup of the International Association for Dental Research. The aid given by the

Specifications Committee of this Croup is reflected In the

following current revision of American Dental Association
.

ill
2

Specification No c 3 for Dental Impression Compound and in the background work involved in the revision 0 The authors wish to express

their appreciation for the cooperation given them in this revision

by the following manufacturers: Mizzy, Inc., The Ransom and

Randolph Co., The S. S. White Dental Manufacturing Co.

1 e INTRODUCTION

Since 1931 when the A.D.A. specification for impression

compound'*' was first formulated, there have been no significant

p changes in the composition of the compounds. The first revision

of the specification and this, the second revision, were occasioned

primarily by refinements in the test procedure for determining

flow. In fact, with the exception of the requirement for flow,

the detail requirements of the specification remain unchanged.

The format of the specification has been changed to conform more

q nearly to the forirr for Federal specifications.

k

When products on the List of Certified Dental Materials

are surveyed for compliance with the respective specifications

and are found not to comply, an exchange of test data is made

between the Dental Research Section at the National Bureau of

Standards and the particular manufacturer. Such was the case

with one manufacturer when impression compounds were retested.

The exchange of data showed that differences existed between

results obtained at the National Bureau of Standards and those

obtained in the manufacturer’s laboratory. These differences were

thought to be due to one or more of the following factors: (1)

differences in lots or batches of compound; (2) differences in

methods of preparing specimens; and (3) differences in test

procedures

.
.

.
- 3 - An extensive data exchange program, enlarged to include

three manufacturers, was therefore set up to determine whether

or not the foregoing factors were responsible for the differences.

Also an independent investigation of the effect of variations in

the preparation of specimens and in test procedures was begun in

the Dental Research Section at the National Bureau of Standards.

2 o EXPERIMENTAL PROCEDURE AND RESULTS

2.1 Exchange program.

The data exchange program was set up as outlined in Table 1.

This scheme presents a method of sorting the variables with a

minimum number of tests. For Result A the impression compound

was supplied by the manufacturer and the specimens were prepared

and tested by him. Result A differed from Result B only In that

Result B was obtained from tests in the laboratories of the

National Bureau of Standards. Therefore, any difference between

Results A and B should seemingly be caused by the test procedure.

Likewise, Result A should differ from Result C and Result B

should differ from Result D only because of differences in

preparing the specimens. The entire test procedure was duplicated on impression compound obtained in the open market

(Results E, F, G- and H in Table 1) . The results obtained by following the outline in Table 1

with three manufacturers, X, Y and Z, are shown in Tables 2

through In the case of manufacturer Z, the upper half of the

outlined plan (Table 1) or Results A through D were obtained on

a different lot of material than that available at the National

Bureau of Standards. These results appear in Table 3o
•-

-

.

'

r
- 4 - Manufacturer Y also did not have the same lot available for

testing* The greatest difference in flow results between laboratories appeared in this part of the exchange program, the data of

which are in Table i|. An additional exchange of specimens and

data was made with manufacturer Y for Results A through D; however

in this case, revised methods for preparation and testing the flow

specimens were used* These data are given in Table £•

In Table 2 where the results of Interchange of data with

manufacturer X are given, there is fair agreement for results

obtained at 37«0°C (98 S 6°F). A flow of one percent amounts to

only 60 microns on a 6 mm high specimen. Thus the difference

between the highest values (Result F) , 3»8 percent, and the lowest

(Results A or H) , 1.9 percent, represents a difference in flow of

111], microns and the average deviation on Results A through H was

only ± 1.2 percent or ± 72 microns. The agreement at IpS • 0 °

C

(113.0°F) is almost as good, the average deviation being ± 1.7

percent (± 102 microns). At 1|0.0°C (10l]_.0°F) the critical flow

temperature, the poor agreement between Results E and 0 and

between F and H indicates that differences in preparing the

specimens was largely the cause.

Examination of Table 3 (Results E, G- and H) showing the

exchange of data with manufacturer Z, indicates that the agreement is good. Result F at i|0 e 0°C (10lj..0°F) Is most out of line.

When Result E Is compared with Result F and Result G- with

Result H, one sees that the test method used at the National

Bureau of Standards usually gave higher values than those from

the manufacturer. Also, the specimens made at the National
I

r 8

|

*.

\
- 5 - Bureau of Standards gave higher values for Result F than those

made by the manufacturer when tested by both groups (Result F

compared with Result H) . However, when Result E is compared with

Result G- the values of flow are reversed. It would seem that the

method of preparing the specimens was involved also.

By reference to Results E through H in Table 3, it will be

noted that the average flow of 9.8 percent for this compound at

l|.OoO®C (10l|. 8 0®F) prevented it from complying with the American

2 Dental Association specification which requires a minimum flow

of 20 percent. Moreover, the compound would not pass the

2 impression test In the current specification. Since the manufacturer had none of the batch that was available at the Bureau,

and as the sample at the Bureau was too small to permit complete

testing by both laboratories, the exchange was made using a

batch of compound furnished by the manufacturer (upper half of

Table 3 , Results A through D) . A comparison of these data with

those of Results E through H indicates a difference at 37.0°C and

l4- 0 . 0 °C between the two batches. These data show fair agreement

and much of the discussion of Results E through H applies. The

data also show that this batch complies with the A.D.A.

2 specification . The foregoing results indicate that the method of preparation of flow specimens should be described more specifically and

that test procedures should be revised to minimize differences

between laboratories. In section ij.. 3.1.1 of the proposed revision

of the specification (which follows) detailed directions for

heating the compound, forming the specimens and removal of the

specimens from the mold have been Included.
-
6

2*2 Investigation of test procedures.

The most important factors in the flow test procedure appear

to be: 1) the age of the specimen at the time of testing; 2)

slight temperature variations at the critical lj.0.0 o C (10]+.0®F)

flow temperature; and 3) the chilling of the top of the specimen

by the metal platen of the apparatus.

The effect of the age of a specimen upon its flow at 37.0°C

(98.6°F) under the conditions of test (1^.3. 1.2)^ is shown in

Figure 1. The specimens were stored in air at 20-25°C (68-77°F).

Tests conducted on specimens \ hour, 2 hours, 6 hours, 21\. hours,

and 1 week old showed that the flow of specimens 2i_j_ hours old or

older did not vary significantly. As the data in Figure 1 are

typical of the currently available compounds, there seems to be

no reason for extending the age of the specimens used in the test

2

for flow beyond the 2lp hour value in the present specification . It may be that the decrease In flow with time is caused by the

release of internal strain as the specimens age. This was suggested by data obtained several years ago when the flow of

specimens molded from a compound softened In the conventional

manner was compared with the flow of specimens made by pouring

the melted compound into the mold. It appeared that the incorporation of strain in the molded specimens resulted in greater flow.

Numbers refer to sections of the revised specification hereinafter printed.
-
7

As it was not possible to control how much strain was placed in

a specimen, the flow values on specimens made from softened

compound were not in reasonable agreement.

The effect of slight temperature variations upon the amount

of flow at the critical i|0 c 0°C (104.0°F) flow temperature is

shown by the steepness of the slope of the flow curves in

Figure 2, Here it will be noted that practically 70 percent

flow occurred between 38*0°C (100.4°^) an(i 42.0°C (107o6°F) and

at or near l\.0 o 0°C (10l|.0°F) a change of 0.1®C (0.l8°F) in the

temperature at which the compound was tested could make approximately a 2 percent difference in the flow values.

Therefore, it was decided to delete the requirement specifying a determination for the flow at 40.0°C (104*0®F).

Furthermore, there apparently is no reason why the requirement

of flow at 37cO®C (98.6®F) and at 45.0°C (113o0°F) will not be

sufficient to define a satisfactory compound.

The third major consideration was the chilling of the top

of the flow specimen by the metal platen of the test apparatus .

(C in Figure 3-3)

o

The truncated cone-shaped specimen resulting

from the flow test (A in Fig. 3 ) indicates that the temperature

of the top of the specimen was not as high as the temperature

of the bottom. A symmetr ical barrel-shaped flow specimen (B in

Fig. 3 ) shows the effect of testing a specimen which was

apparently nearly uniform in temperature throughout. To produce

this type of flow specimen it was necessary to reduce the

conduction of heat from the specimen through the platen and its

shaft. A hard rubber shaft (B in Fig. 3

- 3 ) having a low thermal

8

conduction was, therefore, substituted for a metallic shaft having

a high thermal conduction. Thus the temperature of the platen,

which is submerged in a constant temperature bath, is maintained

sufficiently close to the temperature of the bath to cause the

formation of symmetrically shaped specimens during the test for

flow.

In addition to the change in shaft, the diameter of the

platen (C in Fig. 3-3) was increased from -J- inch to 2 inches. This

was necessary since the compound at lf.5-0°C (113.0°F) flowed out

under the ^ inch platen and up its side.

2.3 Results obtained with revised procedures.

To determine the effectiveness of the new specimen preparation and test procedure, an additional series of tests were made

in cooperation with manufacturer Y using the methods outlined in

paragraphs I4

.. 3 .I.I and I4.. 3.1.2 of the proposed revision of the

specification. A comparison of the results shown in Tables I). and

5 indicates that with the revised procedure better uniformity

results both in specimen preparation and in test procedure in

every instance with the exception of the data showing differences

due to preparation of specimens for the 37°C (98.6°F) flow tests.

At this temperature the effect of specimen preparation was not

large under either the original or revised procedure. It is

possible that the better agreement shown in Table 5 as compared

to Table Ij. may be affected by the fact that material of different

batches was used for the two series of tests. The general agreement between the average values shown in Table I4

. and in Table 5> indicates, however, that the difference between the two batches

of material is small.
‘ I ;
- 9

- American Dental Association

SPECIFICATION NO. 3 FOR DENTAL IMPRESSION COMPOUND

Second Revision

(To be effective July 1, 1955)

1. SCOPE AND CLASSIFICATION

1.1 Scope. This specification is for dental impression

compound, sometimes called modeling compound. This compound is

thermally reversible, rigid when cold and plastic when heated a

few degrees above mouth temperature.

1.2 Classification.

1.2.1 Types. Dental impression compound covered by this

specification shall be of the following types as specified:

Type I. Impression Compound

Type II. Tray Compound

2. APPLICABLE SPECIFICATIONS

2.1 Specification. There are no other specifications applicable to this specification. (Copies of American Dental Association

specifications may be obtained free upon application to the

American Dental Association Research Fellowship, National Bureau of

Standards, Washington 25, D. C.)

3. REQUIREMENTS

3d Material.

3.1.1 Type I. The material shall be suitable for taking

impressions in the oral cavity.

3.1.2 Type II. The material shall be suitable for forming

trays to be used in the oral cavity.
. :

.
10

3.2

General. The compound shall have the following properties

3.2.1 Homogeneity throughout.

3.2.2 A smooth, glossy surface after flaming.

3.2.3 Firm, smooth margins after trimming with a knife at room

temperature

.

3.3 Detail

3.3.1 Flow. Type I Compound

3. 3.1.1 The flow at 37.0°C (98.6°F) shall not be more than

6.0 percent.

3. 3. 1.2 The flow at 45.0°C (113. 0°F) shall not be less than

85.0 percent.

3.3.2 Flow. Type II Compound

3. 3 .2.1 The flow at 37.0 °C (98,6°F) shall not be more than

2.0 percent.

3. 3. 2.

2

The flow at 45.0°C (113. 0°F) shall not be less than

70.0 percent, nor more than 85.0 percent.

3.3.3 Impression “Test

3. 3. 3.1 Type I compound shall record accurately the surface

detail of the test block (Fig. 1-3) referred to in 4. 3. 2. 2 at

45.o°c (113. 0 °F).

3.3.4 Manufacturer’s Instructions. Instructions, including

method of softening, working temperature, and a curve or data

showing the shrinkage of the compound from 2p0

0 C (104°F) to 20 ®C

(68®F) shall be supplied with each package.

11

4. SAMPLING, INSPECTION AND TESTING PROCEDURES

4.1 Sampling, Three packages or approximately one and onehalf pounds of compound shall be procured at retail by a member of

the American Dental Association. This sample shall be forwarded

in the original unopened package or packages to the American Dental

Association Research Fellowship at the National Bureau of Standards,

Washington 25, D. C.

[|_.2 Inspection. Visual inspection shall be used in determining compliance with the requirements outlined in 3*1, 3*2,

3.3.4* 5.1 and 5.2.

4.3 Physical Tests.

4.3.1 Flow

4. 3. 1.1 Preparation of specimens. A cake or cakes of compound shall be broken into pieces and placed in an iron crucible

of 50 ml capacity. The crucible shall be placed 130 mm (5.1 in.)

below a 250 watt infrared lamp bulb. The stirred compound shall

be heated to a temperature of 75 - 5°0 (16? - 9°F) (checked with a

thermometer) until melted throughout and then shall be poured into

a mold (Fig. 2-3). The mold shall be a flat, stainless steel

metal plate 6.0 mm (0.236 in.) thick, containing four holes 10.0 mm

(0.394 in.) in diameter. The mold shall be preheated to a

temperature of 55 ± 5®C (131 ± 9°F) and placed on a smooth glass

slab /T52 mm long, 76 mm wide, 19 mm thick (6 in., 3 in., and

0*75 in. Y/ preheated to the same temperature. After the mold has

been "Over-filled with material, a smooth flat tinfoil-covered

1 glass plate preheated to 55 ± 5°C ( 131 ± 9°F) shall be placed on
f-
12

top of the mold. A load of 9,000 g (20 lb) shall be applied to

the top of the tlnf oiled glass plate for ten minutes. Then the

mold shall be placed in water at a temperature of 10°C (50°F)

for ten minutes. The upper tinf oiled plate shall then be

removed and the excess material shall be trimmed away. This

can be accomplished by using a metal scraper with the top surface of the mold as a guide. The mold may then be removed from

the glass slab by gently tapping the side of the mold. The

specimens shall be removed from the mold by chilling in water

for ten minutes at 10®C (50°F) and shall be stored at room

temperature 20-25°C (68-77°F) for 2l\. hours before testing.

I|_.3.1.2 Method of test. The original length of the specimen shall be determined using a metric micrometer caliper.

Pour measurements shall be made around the circumference and

one measurement shall be made on the center of the specimen.

The measurements shall be recorded to the nearest 0.005 mm.

The specimen and flow testing instrument (Fig. 3-3) shall be

placed in a water bath and held at the testing temperature for

twenty minutes prior to testing. The flow testing instrument as

illustrated consists of the following: A- a weight, B- a nonconducting shaft, and C- a brass platen* The total weight in

air of these three components is 2,000 g {L\..L\_1 lb). The weight A

shall be separated a minimum of 76 mm (3 in.) from the brass

platen on the shaft. This shaft shall be of hard rubber or of

a similar poor thermal conductor to avoid loss in heat due to

conduction. The diameter of the brass platen which touches the

specimen shall not be less than 5l mm (2 in.). The thickness

of the brass platen shall not exceed 6.5 mm ( 0.25 in.).
:

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13

The temperature in the bath shall be controlled to within ± 0.1°C

(± 0.2°F) of the required temperature. (A calibrated thermometer

shall be used for determining the temperature.) A thin sheet of

waterproof cellophane shall be placed between the instrument and

each end of the specimen. The bottom of the specimen shall be

5l mm (2 in.) below the surface of the water in the bath. A constant axial load of 2,000 g ( i_j_ .ip lb) shall then be applied to the

specimen for ten minutes, after which the specimen shall be

removed and cooled in air to room temperature. The cellophane

shall be stripped off and the final length shall be determined

as is the original length. The flow, as evidenced by the change

in length, shall be reported as percentage of the original

length. The value for flow at any temperature shall be the

average value for two specimens and shall be reported to the

nearest 0.1 percent.

ij.,3.2 Impression test.

ip. 3. 2.1 Preparation of impression specimen. The impression

specimen shall be a disk IpO mm (1.57 in.) in diameter and between ij. mm (0.16 in.) and 7 mm (0.28 in.) in thickness. The

cake of compound shall be warmed in water and the disk cut. If

the cake is thinner than i| mm (0.16 in.), two cakes shall be

flamed and pressed together before cutting the disk.

lp.3o2.2 Method of test. A water bath shall be adjusted to

‘lp5„0 ± 0.1°C (113.0 ± 0.2°F). A flat plate (to support the

specimen while it is coming to the required temperature), a test

block (Fig. 1-3) and a brass weight, having a base $0 mm (1.97 in.)

in diameter and weighing 1,000 ± 5 g (2.2 ± .01 lb) in air,
'If-

:

.

,

'
- III. - shall be placed in the bath and allowed to come to the temperature of the bath. /The water level in the bath shall be

30 ± 5 nun (1.2 ± 0.2 in.) above the top surface of the test

block^y

The impression specimen shall then be placed in the water

bath on the flat plate. Twenty minutes later, the specimen

shall be centered on the test block, a sheet of waterproof

cellophane shall be placed over the specimen, and the weight

shall be placed on the specimen. Ten minutes later, the

weight shall be removed, the test block and specimen shall be

taken from the bath and chilled at a temperature of 10°C (50°F),

and the specimen shall be removed from the test block.

The impression shall be examined to determine if the

ridges corresponding to the large cross grooves (B, Fig. 1-3)

of the test block are sharp, and the ridges corresponding to

the fine grooves (C, Fig. 1-3) are complete and visible to the

unaided eye for at least 30 mm (1.2 in.) of their length.

5. PREPARATION FOR DELIVERY

5.1 Packaging. The material shall be packaged In accordance with accepted commercial practice.

5 • 2 Marking

.

5.2.1 Lot numbers. Each container shall be marked with a

serial number or a combination of letters and numbers which refer

to the manufacturer’s records for the particular lot or batch of

compound.
f

•

;
- 15 - 5.2.2 Date of manufacture. The date of manufacture (year

and month) shall be given on the container either as a separate

item or as a part of the lot number (5.2.1).

5 . 2.3 Net weight. The minimum net weight of the contents

shall be indicated on all containers.

SUMMARY AND CONCLUSIONS

The American Dental Association specification for dental

impression compound was revised with the assistance of the

Specifications Committee of the Dental Materials Group of the

International Association for Dental Research, with the aid of

three manufacturers, and with the information derived from a

recent survey of the certified brands of dental impression

compounds. Two major changes were made in the detail requirements. First, since the i|0.0°C (10lj..0 o F) flow testing temperature

appeared to present a critical point in testing, the requirement

for flow at this temperature was deleted. Second, the requirement for flow at 50.0°C (122.0°F) for tray compound was replaced

with a requirement for flow at iq.5 • 0 ° C (113.0°F). Therefore, in

the revised specification both impression compound and tray

compound will be tested at the same temperatures in determining

values of percent flow. After examination of possible variables

introduced in preparation and testing of flow specimens and after

examination of results of the data exchange program, more precise

methods for preparation and testing of specimens for flow were

incorporated in the revised specification.
-

.

.
16

1. Taylor, N. 0.; Sweeney, W. T.; and Paf f enbarger , G-eo. C.

A specification for dental impression compound. J.A.D.A.

18:53 (Jan.) 1931.

2. Sweeney, W. T. and Beall, John R. American Dental

Association specification no. 3 for dental impression

compounds. First revision 1939. J.A.D.A. 27:713 (May)

1940.

3. Outline of form and instructions for the preparation of

Federal specifications (21 October 1947). Superintendent

of Documents, U. S. Government Printing Office,

Washington 25, D. C.

4. List of certified dental materials revised to November 15,

1953. J.A.D.A. 47:693 (Dec.) 1953.
!
Table 1

Plan for exchanging data on impression compounds

Source of

Material made by

Spec imens

tested by Result

From the Mfr

.

Mfr. A

manufacturer NBS B

NBS Mfr. C

NBS D

Obtained on the open

market by the A.D.A. Mfr. Mfr. E

Research Fellowship at NBS F

the National Bureau of

Standards NBS Mfr

.

0

NBS H

-x- The value reported for each of the results is the

average of two specimens as required by the

specification.

Table 2

Data exchanged on. impr<3ssion compound with manuf ac tilrer X

Percent Flow at

Result 37“C (98. 6°F) 1+0°C ( 10i+°F) l+5'c (H3*F)

A 1.9 30.1+

B 2.2 21+.0 93.8

C 3.3 26.1+ 90.7

D 3.2 30 .

6

95.6

E 3.4 25.4 91.7

F 3.8 30.1+ 95.7

Gr 2.7 16.2 90.7

H 1.9 19.0 93.3

Average 2.8 ± 1.2 25.3 ± l+.l 93.1 ± 1.7
.

•

.

' r '
Table 3

Data exchanged on impression compound with manufacturer Z

Percent flow at

Result 37 °C ( 98 . 6 'F) 14. 0 ° C ( 104 °F) 45°c (h3

4 f)

A) 3.2 29.4 86.1

bJ* 3*6 33.0 95.8

c) 2.1 23.5 89.2

D) 3.2 30.0 . 94.7 .... n Average 3.0 ± 0.5 29.0 ± 2.7 91.4 ± 3.8

E) 0.6 7.8 86.4

F # 1.2 14.2 92.6

a) 0.8 8.2 88.2

H) 0.6 8.8 91.5

Average 0.8 ± 0.2 9.8 ± 2.2 89.7 + 2.4

Data exchanged with manufacturer Z on impression compound furnished by him and not the same lot or batch as

reported in Results E through H.

# Data exchanged with manufacturer Z on impression compound obtained in open market for survey.
''

; . ..

'

. -

;

:

.

. . -< • ' • ' J “

-

.

......i ....

... «•

. • ...
Table 1;

Data exchanged with manufacturer Y

on impression compound obtained in the open market

Percent flow at

Result 37’C (9b.T*Tj iiO°c (io4°f) 45*0 ( 113°F)

E 2.1 U4.o 87.2

P 3.2 34.7 90.4

G 1.0 21.0 87.0

H it.

6

55.2 96.0

Average 2.7 ± 1.2 38.7 ± 10.9 90.2 ± 3.0

Table 5

Data exchanged with manufacturer Y using revised

methods on impression compound furnished by him and not

the same lot or bat c h as reported in Table Ij. Percent flow at

Result 37°G (90.6°F) lj.0

0 C (10l; o P) i;5°C (113°F)

A 3.8 47.1 90.5

B 4.6 53.4 92.3

C 2.2 36.1; 90.4

D 3d . 45.1 92.6

Average 3.1; ± 0.B i;5 .5 ± i;.9 91.4 ± 1.0
1

•

‘
!N30d3d Nl 39NVH0 "IVN0ISN3WIQ

DECREASE

IN

FLOW

OF

IMPRESSION

COMPOUND

WITH

INCREASE

IN

AGE

OF

SPECIMEN

DIMENSIONAL

CHANGE

IN

PERCENT

10

20

i i i r

GO

70

80

90 —

100 -

LEGEND

SYMBOL MATERIAL

6REY (KERR)

SOFT GREEN *2

CERTIFIED

EXACT

J__l I L

35 36 37 38 39 40 41 42 43

DEGREES CENTIGRADE

FIGURE 2 FLOW OF IMPRESSION COMPOUNDS

44 45
.
FIGURE 3

Flow Specimens. A. Truncated-shaped specimen formed

using metal shaft,

B. Barrel-shaped specimen formed

using non-conducting shaft.

c

ALL DIMENSIONS IN MILLIMETER.

ALL GROOVES, 90°INCLUDED ANGLE, SIDES AT 45° TO

SURFACE OF BLOCK. ALL DIMENSIONS TO BE HELD TO *0.02. MM.

FIGURE 1-3

Test Block for Dental Impression Compounds

Mold

for

Forming

Flow

Specimens

FIGURE 3-3

Flow Testing Instrument • A. Weight

B. Non-conducting shaft

C. Platen

NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

0708-20-3824 December 31 , 1954 3955

Progress Report

SOME FACTORS INFLUENCING THE CUTTING CHARACTERISTICS

OF ROTATING DENTAL CUTTING INSTRUMENTS

by

Donald C. Hudson*, Jack L. Hartley 1 , Robert Moore'' and W. T. Sweeney**

* Colonel USAF (DC), Guest Worker, Dental Research Section

National Bureau of Standards

.

1 Major USAF (DC), Guest Worker, Dental Research Section,

National Bureau of Standards.

" Pfc., USA, Guest Worker, Dental Research Section,

National Bureau of Standards.

** Chief, 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 Service, the Navy

Dental Corps and the Veterans Administration.

(Task 7756-41 BV No. 55-14)

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprinting, or reproduction of this report in any form, either in whole or in part, is prohibited unlesspermissionts obtained in writingfrom theOffice of the Director, National Bureau of Standards, Washington

25, D, C. Such permission is not needed, however, by a Government agency for which a report has been specifically prepared if that agency wishes to reproduce additional copies of that particular report for its own use,

SOME FACTORS INFLUENCING THE CUTTING CHARACTERISTICS

OF ROTATING DENTAL CUTTING INSTRUMENTS

Abstract

The demand for more efficient rotating dental cutting

instruments has made it desirable to Investigate the factors

that influence cutting. This report includes the results

on steel burs, carbide burs, and diamond instruments. The

data obtained under controlled tests compare the cutting

rates of these tools on human enamel at speeds of 5,000

and 10,000 rpm under a load of 20 grams. The rates of

enamel cutting were slightly improved at high speed with

carbide burs. Diamond instruments have much higher cutting

rates and cutting efficiency than the metal burs in cutting

enamel

.

1 . INTRODUCTION

The Dental Research Laboratory of the National Bureau of Standards has been conducting research on methods of evaluating rotating dental cutting instruments for some time. Since 1950, when the

U. S. Air Force began active support of the program, the following

characteristics of conventional dental burs and abrasive instruments

have been examined: (l) temperatures developed in rotating dental

burs (2) vibration produced by dental burs and diamond abrasive instruments, and (3) dynamic studies, using high-speed motion picture

photography showing for the first time the behavior of these instru-
r-C '

.
2

ments as they cut tooth structures.

The purpose of these studies has been two-fold. Primary

interest has focussed on obtaining the most efficient operation

of rotary cutting instruments consistent with producing minimum

trauma from temperature rise and vibration on vital structures.

Secondly, it is hoped that information obtained from these studies

may be used in formulating specifications for burs and abrasive

instruments for the Armed Services.

Peyton, Vaughn, and Henry [1, 2 and 3] have conducted investigations at the University of Michigan on relationships between temperature rise and cutting rates of dental burs and their

rotational speeds. A study conducted at the National Bureau of

Standards also dealt with temperatures developed in rotating dental burs [4]. This study revealed that temperatures ranging from

l40°F to 600°F may be reached at the site of operation, depending

upon the speed of rotation, operating pressure, and the material

being cut. Such temperatures would contribute to the discomfort

of dental operative procedures and would damage vital tissues.

It is concluded from these laboratory studies that cooling

sprays or streams of water should be employed in clinical practice

even when instruments are operating at low rotational speeds.

Vibration caused by rotating instruments, while possibly

not as traumatic to vital structures as heat, annoys the patient

and contributes to his dislike of dental operations. Furthermore, a chattering instrument cannot be controlled by the operator

as he strives to carry out the finer details of cavity preparation

- 3 -

Walsh and Symmons [ 5 ] have made a study of vibration and its effect

on dental patients. They find that vibrational frequencies between

100 cps (cycles per second) and 200 cps produce the most unfavorable

response when applied to the teeth. Frequencies above 1000 cps are

generally beyond the upper range of average patient perception

(Figures 1 and 2) . Unfortunately the lower frequencies in the range

100 to 200 cps are dominant in eccentric burs rotated at speeds of

6000 to 10,000 rpm, speeds now in use by many practitioners.

2. EXPERIMENTAL PROCEDURE

Experimental apparatus used in our studies of vibration produced in rotating instruments consisted of the following: a hard

steel vane supported so that it rested against the periphery of

the bur or abrasive wheel being studied, and an electronic micrometer of the mutual inductance type energized by the 4.8 megacycle

output of a low-powered RF generator. The pickup was held close

to the steel vane and reacted to minute movements of this vane

as it was caused to shift in a plane normal to the long axis of

the pickup from irregularities in the rotating instrument (Figure 3 )

•

Instruments were rotated in a precision chuck of the drawcollet type, whose eccentricity was negligible; thus, any displacement of the steel vane was caused by instrument eccentricity or

surface irregularity. Output of the vibration pickup was applied

to the Y-axis deflection plates of an oscilloscope on whose screen

the wave forms were studied or photographed.

When observing the pattern of vibrations produced by dental

burs and abrasive wheels with no consideration of the effects of
I

.
- 4 -

handpiece looseness or irregularity, we found that the principal

cause of vibration was bur eccentricity. The amplitude of this

vibration was directly proportional to the degree of eccentricity

(Figures 4 and 5 )

.

A photograph of the oscilloscope trace produced by a truerunning 8-bladed bur, rotating at 10,000 rpm, shows eight lowamplitude peaks per revolution at a frequency of 1330 cps (Figure 6)

.

A similar bur, if eccentric and rotating at the same speed, produces

a fundamental frequency of 166 cps, with amplitude proportional to

the amount of eccentricity. The 1330 cps wave is still seen, modulating the lower frequency, but at an amplitude that is low in

comparison to that of the fundamental (Figure 7)

•

3. DISCUSSION

Thus, we see that a true-running bur at 10,000 rpm produces

vibration in a frequency range well above that which produces unpleasant reaction in the patient [5], while the eccentric bur produces vibration in the range of maximum unpleasantness . Application to clinical practice of the information obtained in this study

will, of necessity, await improvements in the manufacture of rotating instruments. Closer tolerances in fabrication and more symmetrical shaping of the cutting heads of burs and wheels, should,

to a great degree, remove the cause of annoying chatter and vibration

in the range of frequencies most distressing to the patient.

We cannot, however, ignore the effects of poor handpiece performance. A true-running instrument will not perform properly in

a handpiece that does not operate smoothly. To date, our studies
1

-
- 5 - at the National Bureau of Standards have not included dental handpieces. We plan to undertake such studies in the near future.

Data on relative cutting abilities of steel and carbide burs

in a synthetic dentin substitute were obtained in earlier experiments [ 4 ]. Preliminary results of our more recent work reveal

that they behave similarly in human dentin. There is little difference between cutting rates of steel and carbide burs and they

both cut faster as their speeds of rotation increased.

Further results of these more recent studies of steel and

carbide burs when cutting human tooth enamel are shown in Tables

1 and 2. Diamond abrasive instrument data are shown in Table 3 . These data reveal little difference in the amount of enamel

cut by steel burs of two different makes rotating at 5000 rpm and

cutting in specimens taken from a single molar tooth (Table l).

Carbide burs of two different makes, cutting specimens from the

same tooth under the same conditions, show little difference in

cutting rate (Table 2)

.

When speed of rotation was 10,000 rpm and specimens from

another molar tooth were cut, little difference- in rate of cut

was noted between two different makes of steel burs. Two different

makes of carbide burs also cut at about the same rate at this speed.

When cutting enamel at 5000 rpm, the rate of cut was substantially the same for carbide burs as for steel burs. At 10,000 rpm,

the rate of cut of carbide burs was twice that of steel burs in

the same tooth specimen.

No effort has been made to account for these differences

between carbide and steel bur cutting i^ates

.

- 6 - The enamel from one tooth was consumed during the evaluations

at 5000 rpm. Another was required for obtaining data at 10,000 rpm.

Since a possible variation in hardness of enamel between the two

teeth used must be considered, no valid comparison of the cutting

efficiencies of these burs at the two speeds can be made.

Diamond abrasive instruments, under the same experimental

conditions, removed 25 to 30 or more milligrams of enamel per

100 surface feet of operation (Table 3 ) . - Burs of steel and

carbide removed approximately 0.5 to 2.0 milligrams of enamel

per 100 SF (Table 2) . The cutting efficiency of the diamond instruments tested did not increase as the speed of rotation was

raised from 5000 rpm to 10,000 rpm. Cutting rates, however, were

approximately doubled at the higher speed.

This information is of clinical significance to us in pointing out the importance of choosing the most appropriate cutting

instrument for the operation being performed. The efficient accomplishment of operative procedures with a minimum of trauma to

vital structures, using conventional burs and stones, requires

careful selection and proper employment of these instruments.

Further improvements in design and closer control in production

should provide us with smoother running and more efficient rotating

cutting instruments

.

4. SUMMARY

Vibration in a frequency range most distressing to patients

is produced by eccentricity in rotating dental instruments. High

speed (10,000 rpm) rotation of dental Instruments is advantageous
:
- 7 - in that vibration produced by bur blades is raised in frequency

to a point above the range of maximum unpleasantness as defined

by Walsh and Symmons . Also at this higher speed diamond instruments cut more rapidly. Carbide burs cut at twice the rate of

steel burs at the rotational speed of 10,000 rpm. Cutting rates

of both steel and carbide burs are improved at the higher speed

when cutting dentin. Diamond abrasive instruments are many times

more efficient than steel or carbide burs when cutting tooth

enamel

.
r ' '
'A

- 8 -

BIBLIOGRAPHY

1. Vaughn, R. C. and Peyton, F. A. The Influence of Rotational

Speed on Temperature Rise During Cavity Preparation. J. Dent.

Res. 30:737 Oct. 1951.

2. Peyton, F. A. Temperature Rise and Cutting Efficiency of Rotating Instruments. New York Dent. Jnl . 18:439 Nov. 1952.

3. Henry, E. E. and Peyton, F. A. Vibration Characteristics

of the Rotating Dental Cutting Instrument. J. Dent. Res.

29:601 Oct. 1950.

4. Hudson, D. C. and Sweeney, W. T. Temperatures Developed in

Rotating Dental Cutting Instruments. J. Am. Dent. Assn.

48:127 Feb. 1954.

. Walsh, J. P. and Symmons, H. F. Vibration Perception and

Frequencies. New Zealand Dent. Jnl. 45:106 April 1949.

- 9 - Table 1

Cutting Rate in Human Enamel

With Steel Dental Burs (#559 ) at 200 g load

Sample Mfgr

.

No. Blades

Speed

Cutting

Rate

mg/nin

5 .,000 rpm*

Cutting

Efficiency

mg/100 SF

1 A 6 1 . of 1.33

2

11 ti 0 . 82 1.05

3

rt 11 0 . 66 0.85

4 C

n 1.25 1.60

5

n 11 i.&- 2.10

6

ti it

Speed

l . 5#

10,000 rpm**

1.98

7 A

11 0 . T

1-!- 0.48

8

n 11 0.96 0.61

9

11 TI 0.48 0.31

10 C

ft 1.04 0 . 66

11 ii II 0.76 0.49

12 11 II 0.62 0.40

* j8 surface ft. per min. All cuts in specimens from

tooth #1, cutting for 5 min.

** 156 surface ft. per min. All cuts in specimens from

tooth #3 j cutting for 5 min.
'
10

Table 2

Cutting Rate in Human Enamel

with Carbide Burs (#559) at

200 g load

Sample Mfgr . No. Blades Cutting Cutting

Rate Efficiency

mg/min mg/100 SF

Speed 5 , 000 rpm*

1 A 6 1,17 1.50

2

n n 0.82 1.05

3

M n 1.63 2.09

4 R 8 0.^2 0.92

5

it n 1 .04 1.33

Tt n 4.19 5.37

Speed 10*000 rpm**

7 A 6 1.10 0.70

8

M it 1.28 0.82

9

IT it 1.63 1.04

10 B 8 1 0 34 0.86

11 1! It 1.25 0.80

12 It 11 2.01 1.29

* jB surface feet per minute. All cuts in specimens

from tooth #1, cutting for 10 minutes,

** 156 surface feet per minute. All cuts in specimens

from tooth #3* cutting for 10 minutes,

*** A bur blade fractured; resulting eccentric instrument cut at higher rate but produced severe vibration ,

11

Table 3

Cutting Rates of Diamond Abrasive Wheels Approximately

1/4" in Diameter in Human Enamel at 200 g Load

Sample Mfgr . Cutting Cutting

Rate Efficiency

mg/min mg/100 SF

Speed 5*000 rpm*

1 A 125.7 27.94

2

n 125.7 27.93

3

n 130.9 29.09

4

n 155.1 34.46

5

tt 116.1 25.80

6 B 119.2 26.49

7

n 138.4 30.75

8

it 113.9 25.31

9

it 115.3 25.62

10 if 104.8 23.29

Speed 10,000 rpm*

11 A 214.9 23.87

12 IT 179.7 19.96

13 II 244.6 27.18

14 It 280.3 31.14

15 It 202.1 22.45

16 B 262.6 29.18

17 it 323.3 35.92

18 n 234.3 26.03

19 n 225.9 25.10

20 n 321.8 35.75

* Surface speed adjusted according to diameter of

instrument to 450 SFM and 900 SFM, respectively

corresponding to approximately 5000 and 10^000

rpirn Multiple tooth specimens were used in these

experiments . The enamel was removed from approximately 200 teeth while obtaining the data. Total

cutting time for each instrument was 10 minutes

.
s
CYCLES

PER

SECOND

IN

HUNDREDS

Figure

1.

Graph

showing

frequencies

found

to

produce

most

Unpleasant

reaction

when

applied

to

teeth.

(Walsh

and

Symmons)

.

UPPER

THRESHOLD

FREQUENCY

m

o o

* ro

o

cmo -

s r- n

co

lAl

c/> <

o

©

o

CYCLES

PER

SECONO

IN

HUNDREDS

Figure

2.

Graph

showing

upper

limits

of

vibration

perception

when

applied

to

teeth.

(Walsh

and

Symmons)

.

o

rotating

instrument.



Figure

6.

Trace

produced

by

8-bladed

true-running

dental

bur.

Frequency

of

vibration

1330

c.p.s.

at

10,000

rpm.

Figure

J.

Trace

produced

by

8~bladed

eccentric

dental

bur.

Frequency

of

high

amplitude

1

66

c.p.s.

and

modulating

component

1330

c.p.s.

of

low

amplitude.

Bur

rotated

at

10,000

rpm.

NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

0708-20-3857 December 31 , 1954 3956

Progress Report

USE OF IONIZATION CHAMBERS IN OBTAINING

DATA ON RADIATION AT POINTS WITHIN THE

HEAD DURING DENTAL X-RAY EXPOSURE

by

Donald C . Hudson*

and

John W. Kumpula**

* Guest Worker, Colonel U. S. Air Force Dental Service,

Dental Research Section, National Bureau of Standards.

** Laboratory Mechanic, 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 Service, the Navy

Dental Corps and the Veterans Administration.

(Task 7756-41 BV No. 55-14)

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprinting, or reproduction of this report in any form, either in whole or in part, is prohibited unless permission Is obtained in writingfrom theOffice of the Director, National Bureau of Standards, Washington

25, D, C. Such permission is not needed, however, by a Government agency for which a report has been specifically prepared If that agency wishes to reproduce additional copies of that particular report for its own use,
*
USE OF IONIZATION CHAMBERS IN OBTAINING

DATA ON RADIATION AT POINTS WITHIN THE

HEAD DURING DENTAL X-RAY EXPOSURE

Abstract

A study to determine levels of ionizing radiation at various points in and about the human head

during dental radiography was undertaken. A phantom

of tissue -equivalent wax was built around an adult

human skull, and measurements were made using small

Sievert ionization chambers placed at the skin and

within the skull at ten different locations.

Radiation absorbed during full-mouth intra-oral

dental radiography using conventional 8" skin -target

distance, 65 KV and. 10 ma with 1.5 mm of aluminum

filtration, and exposing 14 films, was measured.

Dosage at the skin of the cheek amounted to 20-25R

and various lower values were obtained at other points

within the head

.

A comparison of these radiation levels was made

with measurements taken at the same points in the head

when using a panoramic extra-oral radiographic technic.

Maximum dosage in this technic occurred in the lymphatic

region of the neck and a reading of .42R was recorded

there during full-mouth exposure. Levels within the

skull ranged downward from this value.
-

.

.

-
2

1 . INTRODUCTION

A project at the Dental Research Laboratory, National Bureau

of Standards, sponsored by the U. S. Air Force Dental Service, is

concerned with the development of a device for making extra-oral

full-mouth panoramic dental X-ray exposures. In connection with

this project, it was -desired to determine levels of radiation

produced at various points in and about the head using the panoramic device. For purposes of comparison, measurements were also

desired that would indicate radiation levels existing during fullmouth exposure using conventional dental X-ray technic.

2. APPARATUS EMPLOYED

Since the panoramic method employs a narrow beam of X-rays

in making exposure, an ionization chamber of small volume was required. Such a device was found in the Sievert ionization chamber

[1,2], which has an air volume slightly in excess of 30 mm, and a

physical size which was easily accommodated in the specimens to be

irradiated. The Sievert chamber (Fig. 1 and 2), is a condenser -type

R meter, having a wide range of sensitivity dependent upon the charge

applied, and can be relied upon to produce measurements accurate to

within ± 10% at the energies used in this experiment. All voltage

measurements after charging and after exposure to radiation were

made using the Kiethley Electrometer. Using calibration curves previously prepared for each chamber, and corrections for atmospheric

pressure and humidity, radiation levels to which the chambers had

been exposed were calculated.

The X-ray source was a standard radiographic unit, operated

at 6b KV and 10 ma, having \ mm A1 . equivalent Inherent filtration.
'

1

1

,
- 3

-

to which was added 1 mm A1 . The quality of the radiation was 18-20

KEV, calculated from its absorption coefficient.

A wax phantom head was constructed about an adult human skull.

The wax was of tissue -equivalent density to X-rays and consisted

of a mixture of 50$ paraffin and 50$ beeswax by weight to which was

added .5$ by weight of rosin [3]. The phantom was constructed to

permit access to points within the head for the placement of the

ionization chambers (Pig. 3 and 4).

3. EXPERIMENTAL METHOD

Ten points were chosen at which to measure radiation levels.

Several of these were chosen because they are located in areas rich

in lymphoid or glandular tissue. Points at which overlap or intersecting planes of radiation might be expected were also included.

These points were: (l) at the skin of the neck when using the panoramic exposure and at the skin of the cheek when using conventional

exposure; (2) in the region of the sella tursica; (3) in the region

of the parotid gland; (4) in the sublingual region; (5) in the center

of the base of the tongue; (6) in the cornea of the eye; (7) in the

region of the thyroid gland; (8) in the deep cervical lymphatic region;

(9) in a lower bicuspid tooth socket; and (10) at a point just posterior

and medial to the lower third molar tooth. The last-mentioned location was included since the axis about which the beam of X-rays was

rotated during panoramic exposure passed through this point. It was

desired to determine if any excessive concentration of radiation

occurred at this center of rotation.

Rate of delivery from the filtered X-ray source was approximately

558 mr/sec in air at 12” from the target when using the slit or narrow

beam in the panoramic technic* and about 647 mr/sec in the air at

the same distance when using a round cone of rays for the conventional intra-oral technic. Delivery rates were measured using the

Sievert chambers

.

Skin-target distance was 8

V when employing the standard intraoral 14 film radiographic method and varied from 8

r to 12.5” depending on the position of the X-ray source at any given time in its

cycle of motion about the head during radiography by the panoramic

method. Total exposure time was 25 sec. with the panoramic technic

and 40.5 sec. with the intra-oral method.

In each full -mouth exposure included in this experiment* the

conditions that would exist during actual clinical practice were

adhered to. Standard lead -backed dental films (Eastman Radiatized)

were positioned in the phantom for each single exposure by the conventional technic. One series of 14 exposures was found to be sufficient to produce radiation levels at all measuring points falling

within the range of the ionization chambers. It was necessary to

repeat the exposure ten times when using the panoramic method in

order to obtain levels of radiation that could be reliably measured*

using the same chambers

.

Total skin- surface area exposed to radiation at any point in

the exposure cycle using the panoramic method* amounted to less than

one square inch. During exposure by conventional methods* approximately 12 square inches of skin area were irradiated during each

individual film exposure and overlapping of irradiated areas is

unavoidable during a series of films required for full-mouth radiography .

- 5

-

4 . RESULTS

Levels of radiation measured at the points selected are graphically displayed in Figure 5* It will he noted that under the conditions of this experiment* the highest level of ionizing radiation

during full-mouth radiographic exposure using the panoramic technic

existed in the cervical lymphatic region of the neck and amounted

to .42R. The highest levels of radiation when using conventional

intra-oral radiographic technic* existed at the skin of the cheek

and in the region of the thyroid gland* where 23 and 27 R* respectively* were recorded.

5. SUMMARY

Levels of ionizing radiation produced at points in and about

a wax phantom of the human head* were measured during full -mouth

dental radiography by a panoramic method and by a conventional 14-

film intra-oral technic. The panoramic method was found to produce

radiation levels approximately l/50th as intense as those recorded

at comparable points when using conventional dental radiographic

technic

.

6

.

ACKNOWLEDGEMENT

The authors wish to express their appreciation to the personnel

of the Naval Medical Research Institute* Bethesda* Maryland* for

their cooperation in furnishing the ionization chambers and in charging and measuring voltages on the chambers during this experiment.

Lt. James W. Duckworth and Lt . (JG) Robert Sharp rendered most valuable service in performing the above mentioned technical procedures.
.

V j .

.

3>

8
- 6 -

BIBLIOGRAPHY

1. Wilson, C. R., Radium Therapy - Physical Aspects, Second

Edition. Chapman and Hall, Ltd., London, England, 97 (19^8).

2. Sievert, R. M., Acta Radiologica, Supplementum XVT, (1932).

3. Hasterlik, R. J., Argonne Cancer Research Hospital,

Chicago, Illinois, (Personal communication)

.

Figure 1. Sievert ionization chamber, showing small size

Figure

2.

Sievert

ionization

chamber.

(c)

Dielectric.

fa)

Outer

shell.

(dj

Thin-walled

cap.

(b)

Inner

condenser

element

(e)

Air

chamber,

with

antenna.

Figure 3- Wax phantom showing placement of ionization

chamber at skin of cheek and recessed location

for measurements in region of neck lymphatics.

Figure

4

.

Wax

phantom

disarticulated

for

placement

of

ionization

chambers

at

internal

points.

FULL

MOUTH

14

FILMS

6"

S.T.O.

FULL

MOUTH

PANORAMIC

65

KV

lOma.

1.5

mm

Al.

65

KV

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1.5

mm

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Figure

5.

Chart

showing

levels

of

radiation

measured

at

10

selected

points

in

and

about

the

human

head

phantom,

using a

conventional

and

panoramic

full-mouth

radiographic

technic.

THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards; the determination of physical constants

and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

development of standard practices, codes, and specifications. The work includes basic and applied

research, development, engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are issued to the sponsoring agency of a particular project

or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

summary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

which provides data for determining the best frequencies to use for radio communications throughout

the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications.

Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

the National Bureau of Standards ($1.25) and its Supplement ($0.75), available from the Superintendent of Documents, Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of

Standards, Washington 25, D. C.