NATIONAL BUREAU OF STANDARDS REPORT

10 063

Progress Report

on CLINICAL INVESTIGATION OF A RADIOPAQUE

COMPOSITE RESTORATIVE MATERIAL

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

31 1.05-1 1-31 1056 1 June 30, 1969 10 063

Progress Report

on CLINICAL INVESTIGATION OF A RADIOPAQUE

COMPOSITE RESTORATIVE MATERIAL

by H. H. Chandler*, R. L. Bowen"^, G. C. Paffenbarger"^,

and A. L. Mullineaux"^

* Research Associate from the American Dental Association

at the National Bureau of Standards, Washington, D. C. on

a two-year leave of absence from the Ohio State University

College of Dentistry, Columbus, Ohio 43210

•Research Associates from the American Dental Association at the National Bureau of Standards, Washington, D. C. 20234

This investigation was supported in part by Research Grants

DE-02742-02 to the American Dental Association from the

National Institute of Dental Research, and is part of the

dental research program conducted by the National Bureau of

Standards in cooperation with the Council on Dental Research

of the American Deotal Association; 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 S

for use within the Government

and review. For this reason, 1 whole or in part, is not auth Bureau of Standards, Washinf

the Report has been specitical

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

ress accounting documents intended

is subjected to additional evaluation

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

, by the Government agency for which

copies for its own use. <NB^

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

CLINICAL INVESTIGATION OF A RADIOPAQUE

COMPOSITE RESTORATIVE MATERIAL

H. H. CHANDLER, DDS* R. L. BOWEN, DDS**

G. C. PAFFENBARGER, DDS** A. L. MULLINEAUX**

This investigation was supported in part by Research Grants

DE02494-02 and DE02742-01 to the American Dental Association

from the National Institute of Dental Research and is part

of the dental research program conducted by the National

Bureau of Standards, in cooperation with the Council on

Dental Research of the American Dental Association; the

Dental Research Division of the United States Army Medical

Research and Development Command; the Dental Sciences

Division of the School of Aerospace Medicine, USAF; the

National Institute of Dental Research; and the Veterans

Admin istr at ion

* Research Associate from the American Dental Association

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

20234 on a two-year leave of absence from The Ohio

State University College of Dentistry, Columbus, Ohio 43210.

** Research Associates from the American Dental Association

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

20234.

CLINICAL INVESTIGATION OF A RADIOPAQUE

COMPOSITE RESTORATIVE MATERIAL

ABSTRACT

A radiopaque composite restorative material was developed

using a ternary eutectic dimethacrylate liquid formulation

as the binder and a BaFg-containing glass and fused silica

as the reinforcing fillers. One hundred and ten restorations were placed using this newly developed material.

The restorations will be observed over a prolonged period.

They had sufficient radiopacity and yet were esthetically

pleasing. Postoperative radiographs showed comparatively

radiolucent areas in and around many of the restorations.

These radiolucencies were usually caused by unfilled space

at the tooth restoration interface.
2

The purpose of this paper is to report on the development

of a radiopaque anterior restorative material, the initial

esthetic properties of this material, and an investigation

of the cause and prevention of one source of radiolucent areas observed in the postoperative radiographs of clinical restorations placed during this study.

One of the deficiencies of currently available esthetic

anterior restorative materials is their radiolucency . Therefore, the dentist often cannot determine, from the radiographs

alone, if a radiolucent area is an existing restoration or

primary caries nor can he easily differentiate the restoration and recurrent caries. Neither can he judge if there

is gingival overhang, sufficient contour, or complete

filling of the preparation. It is also desirable to have

all dental materials which are used in the mouth radiopaque

so that if aspirated, ingested or inadvertently embedded in

alveolar tissue they can be located radiographically.^
3

Materials and methods

Since an esthetic restorative material must match the optical

translucency of the natural teeth, ^ it is necessary that the

reinforcing fillers be transparent and that the finest particles

(especially those less than several micrometers (microns) in

size] have refractive indexes close to that of the polymeric

binder.^ It is also essential to have a filler that can be

chemically bonded to the resin by a suitable coupling agent.

A radiopaque glass was formulated previously^ that filled these

requirements. The glass used had the following batch formulation: SiOs, 44; BaFg, 28; B 2 O3 , 16 and AlaOa, 12, in mole

percent. The glass was ground to a very fine powder in a

porcelain jar mill using quartz pebbles. The powder that

passed through a U. S. Standard Sieve No. 400 .[37 pm (micrometers; microns) and finer] was further classified into

nearly equal parts of "coarser" and "finer" particles by

sedimentation. The finer powder was used.

One part by weight of the BaFg-containing glass was

combined with two parts by weight of vitreous silica having
4

particles in the 5 to 37 pm size range. Although more (or

less) BaFa -containing glass may be used, it is desirable to

use the least amount necessary for diagnostic purposes

because it has a higher coefficient of thermal expansion

[about 7.0 X 10"^ /°C (28-62®C)] than does the fused silica

[about 0.5 X lO^^/^C (25-50°C)] portion of the reinforcing

fillers. The coefficient of thermal expansion of the resin

binder is approximately 88 x 10"®/°C (26-48®C; dry).

The silica particles had been made spheroidal by a

plasma device.^ Although it was not done, it is believed

that it would be desirable to make spheres of the BaFscontaining glass particles if a suitable refractive index

could be maintained."^ The use of rounded reinforcing filler

particles with a suitable size distribution results in an

increased filler to resin ratio and thus a reduction in

the coefficient of thermal expansion, an increase in

stiffness, and in other desirable characteristics.^ The

glass and fused silica powders were made hydrophobic by

treatment with 0.5% 3-methacryloxypropyltr imethoxysilane;

this treatment significantly improves the bonding between
5

the resin and the fillers. Benzoyl peroxide (0.50%) and

lauroyl peroxide (0.82%) were dispersed into the mixed

powders with the aid of a volatile solvent (ether).

Seventy-nine parts by weight of this powder was mixed with

21 parts by weight of a ternary eutectic dimethacrylate

liquid formulation that will be described elsewhere.^

The materials were mixed for one minute on a glass surface

using an agate spatula.

One hundred and ten restorations (55 pairs) were placed

clinically. In one of each pair the cavity surfaces were

treated with an acetone solution of NPG-GMA^ [N-(2-hydroxy3-methacryloxypropyl)-N-phenylglycine ]

an adhesion-promoting

coupling agent. The other cavity preparation was treated

with acetone alone as a control. The liquids were applied

with a cotton pledget. Another cotton pledget was immediately

used to remove the excess and to dry the preparation.

Small amounts of the composite material (having a thick

putty-like consistency) were inserted into the preparation

with a hand instrument. The instrument has a plugger at one

end, 1.3 mm in diameter and a blade at the other end, about

2.0 mm long and 0.7 mm thick. With the plugger end an attempt
6

was made to pack the material into the retention forms that

had been prepared with a No. 1/2 round bur. The preparation

was then overfilled and grossly contoured with the blade end of

the instrument. A matrix strip was then drawn tight and held

motionless for two minutes beyond the time of the initial

hardening of the material. All of the Class III restorations

were placed using this technic which is a generally accepted

method for the placement of silicate cement having a similar

consistency . ® ^ °

The restorations were finished after a minimum of 24

hours using scalpels, stones, discs, and strips. The final

surface was attained with fine cuttlefish strips or discs

coated with a commercial lubricant often used for finishing

silicate cement restorations. Postoperative radiographs

were made at this time.

These paired restorations will be observed over a

prolonged period to determine the effects of the use of

the adhesion-promoting cavity primer (NPG-GMA) on changes

in color, marginal integrity, and tooth sensitivity. The

condition of adjacent soft tissues, changes in surface

texture and contour, fractures, and recurrent caries will

be noted. The foregoing will be followed by making gypsum
7

casts, color photographs, radiographs and by recorded

visual and tactile inspection. The long-term clinical

success of the formulation reported here remains to be

ascertained; the results of these observations are

planned for future publication.

Results and discussion

After the restorations were finished their esthetic values

were excellent and compared favorably with those of a

commercially available radiolucent composite (Fig. 1)

Figure 2 shows four different radiographs of the same

extracted tooth. The restoration has been replaced in each

instance by one having a different amount of the BaFgcontaining glass as explained in the legend. All formulations appeared to be esthetically similar. The formulation for clinical evaluation (Fig. 2-B), given previously,

was selected subjectively as having sufficient radiopacity

for diagnostic purposes.

Figure 3 shows a radiograph of one of the radiopaque

restorations. Radiolucent areas can be seen at the tooth-
8

restoration interface. Some form of radiolucency was

observed around most of the radiopaque restorations that

were evaluated radiographically.

To ascertain the causes of the radiolucent areas,

restorations were placed in extracted teeth, radiographed

and serially ground in about 10 increments per tooth.

After each grinding, the tooth restoration interface was

examined with the unaided eye and with an optical microscope

and a correlation was made with the radiographic

f indings

Figure 4-A pictures a radiograph of an extracted second

molar with a finished mesial (1) and a finished distal

restoration (2). Arrows point to radiolucent areas around

the restorations. Both restorations were made using a technic

similar to the one used clinically , ® ^ ° except that the mesial

restoration (1) was made by introducing a large excess of

material into the preparation in one increment without

packing or adapting it to the cavity walls with the hand

instrument. The tooth was ground from the buccal surface

in several increments and large unfilled spaces were uncovered. These spaces were filled with blue inlay wax for
9

contrast and photographs were taken (Fig. 4-B,C,D,E). Thus,

a correlation was established between the radiolucencies

in Figure 4-A and the voids shown in Figure 4-B,C,D,E.

The unfilled areas occurred most often in line angles,

in retentive areas and in small preparations where access

for the filling instrument was limited. These areas are

also ones in which air could be trapped easily and thus could

offer resistance to the flow of the material. It is evident

in Figure 4 that the technic used in placing the mesial

restoration (1) was inferior to that used in placing the

distal restoration (2).

During the initial stages of the placement of the

clinical restorations the operator became increasingly

aware of the presence of the radiolucencies on the post-

.operative radiographs. Consequently, an attempt was made

to avoid their occurrence by a more meticulous adaptation

of the first increments of the material to the walls of

the preparation. In subsequent radiographs there were

fewer radiolucencies using the improved technic.
10

The results suggested that similar conditions exist

in restorations made using other types of filling

materials. An unusually critical examination of clinical

radiographs of teeth containing silicate cement and resin

restorations placed by many dentistsves made, and similar

radiolucencies were observed even though there was little

contrast between the already translucent restorations

and the underfilled areas. Similar radiolucencies could

not be seen on radiographs of teeth containing amalgam

restorations because the radiopacity of the material

completely masked their presence. However, voids could

be seen on serial grinding.

One could not be certain that all of the radiolucencies

were caused by unfilled spaces or remaining decalcified

dentin. Radiolucent borders or halo-like areas were frequently seen in radiographs of radiopaque composite restorations placed in non-carious extracted teeth in which no

void spaces could be detected on serial grinding (Fig. 5).

Thus, in some cases it was not known what caused the
11

radiolucencies ; neither is it known if all the radiolucencies

are of clinical importance unless they are misdiagnosed as

car ies .

Certainly all voids at the tooth-restoration interface

are undesirable since they could serve as reservoirs where

debris and bacteria could collect by percolation.^^ The

detection of these voids radiographically is one of the

advantages of a radiopaque restorative material.

The experience gained in the development of this composite

material is being used in efforts to make denture base materials

radiopaque. Denture bases that can be located radiographically

are needed in the event of accidental aspiration or ingestion.

Summary

Radiopaque esthetic direct filling materials are needed to

facilitate dental radiographic diagnosis. A radiopaque

composite restorative material was developed that has adequate

esthetic properties. The resin binder is a ternary eutectic

dimethacrylate formulation. The powder consists of a BaFgcontaining glass and fused silica both treated with a silane

coupling agent and containing peroxide initiators.
12

One hundred and ten clinical restorations were placed

using the above formulation. Post-operative radiographs

showed radiolucent areas around many of the restorations.

Sectioning of extracted teeth containing similar restorations

revealed, in many instances, unfilled spaces which corresponded

with the radiolucent areas on the films. These spaces are

formed during the insertion of the plastic material into

the cavity preparation and can be minimized in size and

occurrence by careful adaptation of the initial increments

of the restorative material to the surfaces of the preparation .

Such unfilled areas are- not easily detected in

radiographs of restorations that are either radiolucent

or as radiopaque as amalgam.
13

References

1. Drinnan, Alan J. Dangers of radiolucent dental

materials. JADA 74:446 Feb 1967.

2. Paf f enbarger , G. C.; Schoonover^ I. C., and Souder, W.

Dental silicate cements; physical and chemical

properties and a specification. JADA 25:32 Jan 1938.

3. Bowen, R. L. Effect of particle shape and size distribu

tion in a reinforced polymer. JADA 69:481 Oct 1964.

4. Bowen, R. L., and Cleek, G. W. X-ray-opaque reinforcing

fillers for composite materials. J Dent Res 48:79

Jan-Feb 1969.

5. Bowen, R. L. Development of an adhesive restorative

material. National Institute of Dental Research -

Adhesive Restorative Dental Materials II (Austin,

R. H .

Wilsdorf, H.G.F., and Phillips, R. W. eds .

U. S. Public Health Service Publication No. 1494, 1966.

6. Bowen, R. L. Crystalline dimethacrylate monomers.

(To be submitted to The J Dent Res).
14

7. Bowen, R. L. Adhesion-promoting compounds. I ADR

Program and Abstracts of Papers March 1967 (p. 94)

abstract

8. Bowen, R. L. Adhesive bonding of various materials to

hard tooth tissues. II. Bonding to dentin promoted by

a surface-active comonomer. J Dent Res 44:895 Sept-Oct

1965.

9. Gilmore, H. W. Textbook of operative dentistry. St.

Louis, C. V. Mosby Co., 1967, p. 380.

10. Sturdevant, C. M. ; Barton, R. E., and Brauer, J. C.

The art and science of operative dentistry. New York,

McGraw Hill Book Co., 1968, p. 457.

11. Nelson, R. J.; Wolcott, R. B., and Paf fenbarger , G.C.

Fluid exchange at the margins of dental restorations.

JADA 44:288 Mar 1952.

The authors are grateful to Lt . Col. John A. Barton, Jr.

USAF,DC for the determinations of the coefficients of thermal

expansion
15

Legends

Figure 1: Photograph and radiograph of two Class III

restorations made of composite materials.

A is made from a commercial product and B

from the experimental material. Both have

good esthetic qualities but A is radiolucent

while B is radiopaque.

Figure 2; Four different radiographs of the same extracted

tooth. The restoration has been replaced in

each instance by one having a different amount

of the BaFa-containing glass. A: 40% BaFacontaining glass by weight; B; 26%; C: 20%,

and D; 16%. Especially in C and D it is apparent

that relative radiolucency occurs in areas

(indicated by the arrows) where enamel is replaced by the somewhat less radiopaque composite

material
16

Figure 3; Radiograph of a clinical radiopaque restoration

showing radiolucent areas designated by arrows.

Figure 4: A: Radiograph of an extracted tooth containing

radiopaque composite restorations in the mesial (1)

and distal (2) surfaces. Arrows designate radiolucent areas; B and C; Photographs of the tooth

shown in A after grinding away the facial surface

uncovering void areas in the mesial restoration.

The void areas have been filled with blue inlay

wax for contrast. The two sections (B and C) are

about 1 mm apart; D and E: Same as B and C except

distal restorations.

Figure 5; Radiograph of a non-carious extracted tooth containing mesial and distal radiopaque restorations.

Note the radiolucent line at the tooth-restoration

interfaces designated by arrows. No spaces could

be detected when the tooth was serially ground.















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