NATIONAL BUREAU OF STANDARDS REPORT

99i6

Progress Report

on

X-RAY-OPAQUE REINFORCING. FILLERS

FOR COMPOSITE MATERIALS

U. S. DEPARTMENT QF COMMERCE

NATIONAL BUREAU OF STANDARDS
MATIQNAL BUREAU OF STAMDARPS

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following areas of science and engineering

:

Applied Mathematics—E iectricity—Metrology—Mechanics—Heat—Atomic Physics—Cryogenics-—Radio Physics2 —Radio Engineering2—Astrophysics2—Time

and Frequency.2 THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to methods, standards of measurement, and data needed by industry, commerce,

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research services to other government agencies. The Institute consists of an Office of

Standard Reference Materials and a group of divisions organized by the following

areas of materials research

:

Analytical Chemistry—Polymers—Metallurgy — Inorganic Materials — Physical

Chemistry.

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of the Institute may be broadly classified as programs relating to technological meas- urements and standards and techniques for the transfer of technology. The Institute

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:

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

311.05-11-3110560 June 30, 1963 9916

Progress Report

on

X-RAY- OPAQUE REINFORCING FILLERS

FOR COMPOSITE MATERIALS

By

R. L. Bowen and G. W. Cleek

* Research Associate, American Dental Association Research

Div. at the National Bureau of Standards, Washington, D. C. ** Chemist, Inorganic Glass Section, National Bureau of

Standards, Washington, D. C. 2023^.

This investigation is part of the dental research program

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

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

Medical Research and Development Command; the Dental Sciences

Division of the School of Aerospace Medicine, USAF; and the

Veterans Administration.

IMPORTANT NOTICE NATIONAL BUREAU OF SI

for use within the Government, and review. For this reason, th whole or in part, is not autho Bureau of Standards, Washingti

the Report has been specifically

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, pither in

e Office of the Director, National

>y the Government agency for which

opies for its own use.

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

X-ray-Opaque Reinforcing Fillers

f n* Composite Materials

R. L. Bowen and G. W. Cleek

Clear, colorless glasses that absorb roentgen rays

were prepared by melting together compounds yielding

silica, boric oxide, alumina, barium oxide and barium

fluoride. Barium made the glasses radiopaque, fluoride

lowered the ref ^active indexes, and alumina tended to

stabilize the glasses. These glasses are part of the

reinforcing fillers for composite dental restorative

materials

.

Roentgenograms have been practically useless in

the detection of the secondary caries or underlying

decalcified dentin that might be a sequellae to the

placement of unreinforced direct filling resins or

the first composite materials to become available.

This is due to the fact that these materials are

relatively radiolucent; consequently, there has been

a continued interest in means of making such restorative materials radiopaque

.
- 2 -

The introduction of inorganic reinforcing fillers

into resin restorative materials, ~ commonly called com2 posite materials, suggested the possibility of making

such materials opaque to X-rays. This can be done by

the incorporation of an element of relatively high atomic

number or weight into the glass that constitutes part

or all of the reinforcing filler. Many of such elements

are not suitable because of the color they impart to the

glass, or, in the case of lead, because of the possibility

of discoloration through the formation of sulfides.

The purpose of this paper is to report investigations of various barium-containing glasses, especially

formulated for use in dental composite materials.

Normally, the introduction of barium oxide into a

glass formulation raises its refractive index. The

commercially available glasses containing the required

amount of barium have refractive indexes that are above

optimum for the purposes of this application. Furthermore,
3

most commercial barium glasses contain alkali elements,

such as sodium, potassium or lithium and these elements

3

can catalyze the hydrolysis of silica. The presence of

these monovalent alkali elements in a glass formulation,

in the opinion of the authors, might be detrimental to

the durability of the bond between the glass and the

silane coupling agent. The quality of the bonding between

the polymer and the filler particles determines whether or

not the filler is a reinforcing filler, and is of utmost

importance in determining the strength of the composite

mater ial .

Since the introduction of the fluoride ion into

5 6 glass formulations lowers the refractive index, °

it was important to determine if clear glasses having

the proper value of refractive index could be formulated

utilizing barium fluoride in the place of barium oxide.

3 Other possible effects of the fluoride ion concentration

remain to be determined.
- 4

MATERIALS AND METHODS

The formulations of the glasses that were prepared

in this project are given in the Table. The glasses

were melted in an electric furnace in a platinum crucible

6.35 cm in diameter by 7.62 cm deep. After the batch was

melted, the melt was stirred with a motor-driven platinum

10%-rhodium double-bladed propeller-type stirrer to obtain

homogeneity. The time of melting and fining depended on

the characteristics of the melts as did the maximum

temperature used. Usually, about 1.5 hours was required

to fill the crucible and about the same length of time

for stirring the melt. The maximum temperature used was

about 1550°C but this was decreased to about 1150°C for

the melts containing a relatively large amount of fluoride.

A small amount of the molten glass was poured into a metal

mold, and the rest was poured into clean water to quench

the glass and break it up into small pieces so that it

could be conveniently ground in a jar mill.
5

The retractive indexes were determined with a

microscope by the oil-immersion method.

RESULTS

From the data given in the Table, it appears that

clear glasses containing large proportions of barium

fluoride can be prepared. Some of these compositions

have refractive indexes close to those of the polymeric

binders of current and experimental composite materials

(n^5 about 1 . 55 ; the refractive index of the polymeric

binder varies somewhat depending on its chemical compos ition, extent of polymerization, water content and

other factors).

Glasses containing 24 to 28 mole percent of barium

fluoride or oxide, if used as the sole reinforcing

filler for a dental composite material, yield materials

that are more radiopaque than necessary. As a first

estimate, about one part by weight of such a bariumcontaining glass (as a silane-treated powder) combined

with two parts of silane-treated fused silica yields

a composite restoration with a radiopacity intermediate

between that of enamel and dentin.
- 6

The powder of one of these glasses (F1515) was passed

through an oxygen-acetylene flame, converting the irregularshaped particles into spheres. This was done because the

use of rounded particle shapes and an intermittant size7 distribution (gap grading) has been shown to give an

increase in the powder-to- liquid ratio. However, as a

result of this high temperature processing,, the refractive

index of the glass beads formed was higher than that of the

starting material. Presumably s the molten glass particles

had lost some of their fluoride,, possible as volatile BF^

or SiF^. Subsequent ly s a lower-temperature flame and a

shorter residence time will be used to prepare spheres of

the F1519-1 composition, which has been selected for further

investigation.

DISCUSSION

An ideal glass for use as a reinforcing filler would

have, among other desirable properties, a refractive index

(to visible light) very close to that of the polymer matrix

of the composite restoration. It should be colorless or

have a color suitable for use in matching the color of the
7

composite material with that of the tooth. It should

be transparent and have a low coefficient of thermal

expansion. Since barium-containing glasses have higher

thermal expansions that does fused silica, the total

barium content of the composite should be no more than

necessary to yield a composite with optimum radiopacity;

one would expect this to fall in the range between that

of enamel and dentin. Glass compositions that meet these

particular requirements could not be found in the

available literature.

A moderate alumina content has been shown to stabilize

fluoride glasses against phase separation or devitrification

5,6 that would be objectionable in this application. Formulations that yield two immiscible liquids in the molten

8

stage must be avoided.

It would be desirable to make use of the "boric

9-14

oxide anomaly" and the less-well-known "alumina

.10 , 12-14

anomaly to obtain a glass with the lowest possible
8

coefficient of thermal expansion. Whether or not a matching

of the molar proportions of BaO and BaF^ with the Al^O^ plus

13 14

B2 O

3

in the glass s gives a minimal thermal expansion has

yet to be determined.

CONCLUSIONS

X-ray-opaque glasses can be prepared that are clear

and colorless and that have refractive indexes suitable

for use in composite restorative materials. The batch

composition for one such glass } for example, is: Si 02 * 44;

BaF2

* 28; 820^ 16; and A^O^* 12 8 in mole percent. The

refractive index is influenced by the thermal history of

the glass.
9

REFERENCES

1. Bowent R. L. : Development of an Adhesive Restorative

Material, in Adhesive Restorative Dental Materials II ,

University of Virginia Workshop, Public Health Service

Publication No. 1494, 1966, pp 225-231.

2. Broutman, L. J. , and Krock, R. H. : Modern Composite

Materials, Reading , Mass; Addison-Wes ley Pub. Co.,

1967

3. Alexander, G. B.; Polymerization of Monosilicic Acid,

J Am Chem Soc 76:2094-6, 1954.

4. Bowen, R. L. Properties of a Silica-Reinforced

Polymer for Dental Restorations, J Am Dent Assoc

66:57-64, 1963.

5. Cleek, G. W ., and Scuderi, T. G. : Effect of Fluorides

on Infrared Transmittance of Certain Silicate Glasses,

J Am Ceramic Soc 42:599-603, 1959.

6. Tooley, F. V.: Handbook of Glass Manufacture. Vol. II ,

New York: Ogden Pub., 1960.
10

7. Bowen, R. L. : El feet of Particle Shape and Size Distribution in a Reinforced Polymer , J Am Dent Assoc

64:481, 1964

8. Charan, R. : Handbook of Glass Technology, 3rd Edition,

Banaras (India): Banaras Hindu University Press, 1956.

9. Weyl, W. A., and Marboe, E. C.: The Constitution of

Glasses, Vol. I , New York: Interscience Publishers,

1962 .

10. Morey, Go W. : Properties of Glass a New York: Re inhold

Publishing Corporation, 1954.

11. Hamilton, E. H. ; Cleek, G. W.; and Grauer, 0. H.

Some Properties of Glasses in the System Barium-Oxide

Boric Oxide-Silica, J AM Ceramic Soc 4JL:209-215, 1958.

12. Galant, E. I.: Refractive Index and Coordination

Transformation in Aluminoborosilicate Glasses,

The Structure of Glass. Vol. 2 , New York: Consultants

Bureau, 1960, pp 451-453.
11

13. Appen, A. A. , and Fu-si } Kan: Borate and Aluminobor ate

Anomalies of the Properties of Silicate Glasses, The

Structure of Glass. Vol. 2 , New York: Consultants

Bureau, 1960, pp 445-450.

14. Demkina, L 0 I 0 : Additivity of the Properties of Silicate

Glasses in Relation to Their Structure, The Structure

of Glass. Vol. 2 , New York: Consultants Bureau, 1960,

pp 40-45, 472.

15. Levin, E. M. , and Cleek, G. W. : Shape of Liquid

Immiscibility Volume in the System Barium Oxide-Boric

Oxide-Silica, J Am Ceramic Soc 41:175-179, 1958.
TABLE

Compositions

and

Properties

of

Glasses

Arranged

CDa

•H

wa

o

T3 a) c c

rtf d)tn

Oh CD CD 0 CD 0 G G >-i G

5-1 5-1 Sh 1 -H U 0 5-1 u 5-1 0 •H CD 5-i 5-1 •H 5-1

rtf rtf rtf •H i—l rtf rtf rtf rtf rtf rtf rH 4J rtf rtf H rtf CD 0 CD 6 rtf CD CD <D a) (D CD rtf (D CD CD rtf CD

l—1 rH rH CD Q-i i—t rH rH rH rH 1—1 0, rt f—1 1—1 a, rH O O o CO 0 0 u u o o O 0 0 a 0 0

00 in H cO CM c£) o 00 ct CM CM o o UO

1—1 o o O0 oo oo CO 00 CO co CO CO CO CD co uo

cD cO cO m uo UO UO UO uo uo UO uo UO UO uo UO

1—1

1

1

1 1 rH i—1 rH 1

1 I—I 1—1 H rH 1—1 1—1 rH rH i—1

04 O O O

£ •H On N Eh S

cO OO

00 CD CO ^ CO ^co oo m

^

oo ^ cO CO CO

CO CO

CO ^ uo

co no co ^ vd m co

^ 'sf ^}* 'sf CM CM CM (N CN 04

CO OCO 00 "sf CM CM CM

CM O O

CM CM CM m o o

CM i-H CM 00 CD O

cO ^

rH CM

co cm

O 00 CO CM CM 'tf' cO O

CM

00 00 00 o

CM r—

no o^o o cm

I—1 I—t

1—I I—

cm O no

*

CM O O

CM O rH

r> m

H OO CM CM no OO O UO no OO rH CM

i—i—

rH UO i—l •sf UO 1 1 CM 1 1 H i—i UO

LD UO UO CM uo 1 1 1 1 LO uo ln LO uo t—

rH 1—

r—

1 1 1

I rH rH rH 1—

i—i i—

1

l

i—

W it Cl, Cl, Cl, Cl, Cl, Cl, Cl, Cl, Cl, Cl, PL, Ih Cl, Cl,
Composition

of

Batch

(mole

percent)

CDUG

CD H- U +v p CO p

<d CD rd

CD 1 1 CD rH id t—

H-p

rd

(D

CD o Pi

Uu 0 0 CD CD CD c >1 >i c c C Po

id 5-1 r—

5-i CD r-H 5-1

p •pH •rH •pH pH P id 5-4 (d U P id rd r-H r—

rH 5m

id CD rd CD id rd CD CD rd id rd id

CD rH CD 1 1 5-1 CD

H 1 1 a Pi Pi CD

ao C o P C

uu 0 0 0 C &X

0) £G

CD of o CO rH o <TC in CD CO CO o > cn in G* G* G ro 00 00 CN rH o

•H in if) LTl lD £ in in inm in in P Q U G pH rH rH rH rH H rH H H i—1 H

rdp

4-1CD DC P

CD £po o

S'

G'

nn oo

fe fc Pm < < <

CO CO P

CN

04 o

•H

CO

G" £ d1 co Is g*

G< £ G<G1 LD G<

00 CN ro ro

in cd g*

00

O

CN

DO

CD ro cfl CD CD CD ro i—1 i—

CO (N

r—

O

rd CQ

LD r-- r- r- i—I r—

os

Pm CO

Id (N

00

CO

00

O cn

CN CN

COCN

ro

O

CN CN

G (N CN <N 04 00 1 1 1 1 r—

H 1 1 1 1 <

H—

H— +- pH • ac H G 0 CO i G 2 H G cn CD CN H cD

O

H

G* CN

H

H CN | 04 04 04 04

CO | m

mm in

G in

m in

m

CO roH pH i—1 H

H

HHHH

id 2 Pm Pm Pm Pm

a Pm Pm Pm Pm

CD id > G P

-P •H • •H 0

rd -p tn CO TO rd G CO CO c i—1 •H I—

CD CD 0 p

p CD

pG

U

G •H 0

CD P rH i G •H

p £ CD ro CD p rd co -P CTi 2 2 P 0 N G 0 H CD G •H 0

lO rH P P rH rH •H

CD iH rd i—4M

p •H

p £ Cli P CD •H p rd -p G B 13 £ rd G • CD CD rH •H 0 B P CD G 0 B • CO 53 •H co £ P > id

CD

p CD P rd

p

p

p CO CD P P COG P g co Pi (D CO 0 CO -p rd X P C P CD O 0

rd rH PD •H 0 rH

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CD CD £ p •H

G

G P

-P cp £ P •H •H •H !> •H 0 P W CO rH

rH

C 0 CD Co

H 4-J

GG rd Pi 0 C rd <—

CD 0 •H £ B

G •H P CD £ •H P 0 CD p CO £

-p -p £ o P rH CP

rd CD P CD

G P £ B P P CD £ P co CD Co 0 rd id Co CD P CD •H P Pi Pi P P •H P < 1 4-1 CD CD rd rd £ I 1 P P rH £ CD rd 0 c Pi Pi 0 P B P

CD co CD P G co £ CD rH rd B P CD rd • £ G £ id CD rd £ G P >. P G co G P G £

rH rH CO £ CD rd

CD co

G i £ CD Pi

pg •HG P £ B • CO

CD o rH 0 P rH CD CO CD £ -p £ 2 £ £ p Pm £ C > CD £ rd •H CD 0 t 04 CD CO P CO rd B p CO CD P £

04 P G t—

CO £ G CD CO CO CD t" Pi (D rd CO £ —- -—

N

rH CD 2 rH co CD 0 C •H

PD £ P 0 CD P H rd CO P p

CD CD CO Pi CD rd ID * £ £ • Co CO £ ro rH *H > 0 CO rH C rd CD C Cm £ P rH 2 P CO i •H H P rd CQ £ CD G

rH CD CO

G Co rd

G P Pi

co £ P rH P co CO £ rd

co

G

G in 0 P X P rd

B • P

rd Pi P rH 0 G CD i—

rH CD CD l—

rd Pm 0 £ CD £ H rC i—1 •ro 0 C P 4m P C B U rd O Pi

CD CD • 0 •H

G e p £ £ G CD Pi 0 CD P CO CO rd id C 0 £1 B S3 P CO CD CD £ co rd

CD

G CD > CO CO £

rd -P

p CO CD £ •H P £ CD £ £ £ P 0 CO B P p rd C C CD CD CD rd G p rd P o i—

G •H P rH £ £ CD i—

P CD id 0 rd P rd U

CD £ 0 rd

O

p £ Pi P CD CD

C

CD > Co Pi c p P B

C £ C CD £ id •H 0 CD •H CD •H 0 0 C G G

E-i £ as P Q CO P u 0 G <!

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