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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

311.05-1 1-3 11056 1 June 30, 1970 10 278

Progress Report

on A METHOD FOR FINISHING COMPOSITE RESTORATIVE MATERIALS

by H. H. Chandler,* R. L. Bowen+ and G. C. Paffenbarger+

* 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 Grant DE02742-02

to the American Dental Association from the National Institute of Dental

Research and is part of the dental research program conducted by the

National Bureau of Standards in cooperation with the Council on Dental

Research of the American Dental 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; the National

Institute of Dental Research; and the Veterans Administration.

IMPORTANT NOTICE NATIONAL BUREAU OF ST

for use within the Government, and review. For this reason, thi whole or in part, is not author Bureau of Standards, Washingtc

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, either 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
-fT- •«
A METHOD FOR FINISHING COMPOSITE RESTORATIVE MATERIALS

I H. H. CHANDLER, DDS* Ro Lo BOWEN, DDS**

G. C. PAFFENBARGER, DDS***

This investigation was supported in part by Research Grant

DE02 742-02 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

F 3search 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 Administration.

* Research Associate American Dental Association Research

Program at the National Bureau of Standards, Washington,

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

State University College of Dentistry, Columbus, Ohio 43210

** Associate Director American Dental Association Research

Program at the National Bureau of Standards, Washington

D. C. 20234

** Senior Research Associate American Dental Association

Research Program at the National Bureau of Standards,

Washington, D. C. 20234
%

2i

't. ;
A METHOD FOR FINISHING COMPOSITE RESTORATIVE MATERIALS

SYNOPSIS

An instrument, designed for finishing composite restorative

materials, was made by bonding 1-5 pm (microng) diamond

particles to flexible paper discs. The surface finish left

by this instrument was superior to that obtained by fine

cuttlefish discs and inferior to surfaces that hardened in

contact with polished glass.

In the past few years several new composite materials have

been developed primarily as replacements and substitutes

for silicate cements in Class III and V restorations in

anterior teeth. They have also been used instead of direct

filling resins in Class IV restorations, and in Class I and

II restorations on an experimental basis.

These materials are composed basically of reinforcing

fillers that are chemically bonded to a resin matrix. The

fillers may be fused silica, quartz, various kinds of glass
2

or other materials. In commercial products,* the resin

matrix is composed of the hardened product of new monomers

that were specially developed for composite materials.^

One of the shortcomings of the composite materials is

that they cannot be finished to a smooth surface using instruments commonly available .

These instruments include

various grades of sand, emery, garnet, cuttlefish, and

other discs, mounted points containing silicon carbide,

alumina or diamond particles, and various shapes and sizes

of steel burs. The materials contained in these instruments

are either too coarse, too soft, or both, to produce a

smooth and glossy surface that is composed of hard particles

of reinforcing filler embedded in a relatively soft resin

matrix

.

The lack of a smooth surface results in restorations

that do not have optimum esthetic properties and do not

* Typical products are; Adaptic, Addent, Blendant, Dakor,

DFR, and Posite
3

feel smooth to the tongue. In addition^, there may be other

disadvantages associated with rough surfaces, such as a

tendency to collect debris and harbor microorganisms.

The only method presently available to the dentist

for achieving a relatively smooth surface on the composite

restoration is to leave, undisturbed, the surface that was

formed against the matrix strip. However, there is usually

a need for recontouring and dressing down at least part of

the restoration, thereby removing the matrix-strip finish.

This paper describes a method for improving the surfaces

of the composite restorations using very small diamond particles

bonded to paper discs. Results are presented in the form of

scanning electron photomicrographs.
4

Materials and methods*

The composite materials on which the finishing procedures were

evaluated were a commercially available product! (selected

because of the relative hardness of its quartz reinforcing

filler) and an experimental material containing fused silica

beads as the reinforcing filler. Specimens were made in the

form of discs that were allowed to harden between glass

plates under light pressure from "C" clamps.

The following instruments were used in the finishing

procedures: medium sandpaper discs,! fine sandpaper discs,!

fine cuttlefish discs,! and diamond paper discs.

The diamond paper discs were prepared by applying a

S thin coating of epoxy glue, thinned with acetone to a suitable

* Certain commercial materials and equipment are identified

in this paper to specify adequately the experimental procedure. In no instance does such identification imply recommendation or endorsement by the National Bureau of Standards

or that the material or equipment identified is necessarily

the best available for the purpose.

t Adaptic, Johnson & Johnson Co., New Brunswick, New Jersey

! E. C. Moore and Son Company, Detroit, Michigan

j Fix'n Patch, Specialty Plastics Co. Inc., Baltimore, Maryland
5

consistency, to a relatively stiff paper backing (the

back side of a medium garnet disc) . Diamond particles

1 to 5 pm (microns) in size* were applied to the wet

surface by dipping a small brush into the thinned

glue and then into the diamond particles and applying

the mixture to the disc surface until it was completely

covered with the particles. The discs were allowed to

remain undisturned for 24 hours before use.

composite

Three different surfaces for eacl/ material were

evaluated: (1) as cast against glass plates; (2) as

prepared by finishing with medium sandpaper discs to

remove the resin-rich outer surface and to simulate

removal of excess material clinically, then with fine

sandpaper discs, and finally with fine cuttlefish discs;

(3) as prepared exactly as in (2) except that the surface

was further finished with the diamond discs. All discs

were used dry in a low-speed dental handpiece

* The diamond particles were obtained at the National

Bureau of Standards, Washington, D. C. Commercial

sources include: The Amplex Corporation, Bloomfield,

Connecticut, Diamonds Unlimited Corporation, Rochester,

New York, and J. K. Smit and Sons, Incorporated,

Murray Hill, New Jersey
[

r Each of the three surfaces for each material was [ examined tactually with an explorer, visually and from r

pictures obtained by means of a scanning electron

microscope. i.

Results

The photographs of the commercially available material.

Adapt ic, are shown in Figure 1. The surface as cast

against the glass plates (Fig. I-A and B) appears to be

the smoothest. The texture of the surface is assumed to

be due to shrinkage of the resin between the filler particles

during hardening.

Figure I-C and D show the surface left by the

cuttlefish discs. This surface indicates that a great

many of the filler particles have been pulled from the

surface and those that remain show little evidence of

being significantly planed by the finishing procedure.
7

Figure I-E and F show the surface obtained by the

diamond disc. These photographs show that the filler

particles were planed smooth and were not pulled from

the surface. The resin matrix has also been finished

relatively smooth and is more nearly at the same height

as the filler particles compared to the surface shown

in Figure I-C and D.

Very small scratches can be seen on the exposed

surfaces of the filler particles in Figure I-F. Such

scratches would be expected to decrease the visual

shininess of the composite material by scattering light.

The scratches would have to be smaller than the wavelength

of visible light (about 0.5 (im) to yield a surface having

maximum shine.

Results similar to those shown in Figure 1 were

obtained in finishing the experimental composite material.

The visual and tactile examinations revealed that

those surfaces prepared by the diamond discs were smoother

than those prepared with cuttlefish discs as observed in
reflected light and by feel as the point of an explorer

was lightly traced over the surfaces. The smoothest

surfaces were those cast against the glass plates.

Although dental porcelains do not come under the

classification of composite materials, it was discovered

that the diamond paper discs would produce highly polished

and very smooth surfaces on porcelain that had previously

been ground. This procedure would be valuable in achieving

a highly polished surface on areas of porcelain that require

removal of the final glaze during adjustments.

Discussion

This preliminary study was carried out in part to determine

the validity of certain hypotheses concerning the requirements of finishing instruments for the composite materials.

These hypotheses were:

1. If a light-reflecting surface is to be obtained,

the cutting particles must be small enough so
9

that the scratches left by the instrument are

narrower than the wavelength of visible light.

When this occurs^ light is reflected instead of

scattered by the "hills and valleys" left by the

finishing instrument.

A visual examination of the specimens indicated that diamond particles in the size range

of 1 to 5 pm (microns) were partially successful

in bringing about a light-reflecting surface.

This was not the case when the cuttlefish discs

were used^ as they produced a dull non-reflecting

surface

2. The cutting particles must be relatively hard as

compared to the filler material. When materials

that are relatively soft are used, they are not

effective in planing the filler particles. The

ineffectiveness of the cuttlefish discs was

interpreted to be due to their relative softness.
10

Whether particles as hard as diamond are

necessary is not known. Some preliminary testing

with emery (aluminum oxide particles, about 15 (im

in size) paper discs revealed that the composite

surfaces obtained were smoother than those obtained

by the cuttlefish but not as smooth as those left

by the diamond discs. Other hard materials^’ ^ such

as boron carbide, silicon carbide and even aluminum

oxide particles should be investigated because they

are less expensive than diamond. However, the

hardness of diamond is very much greater than these

other materials, and thus might be more effective.

3. The cutting particles should be rigidly bound to

the finishing instrument to obtain the most-near ly

plane surface. When loose particles were used,

(one-micron diamond paste on a soft wool-felt wheel)

they polished only the tops of the filler particles

and left deep asperities between particles that projected out of the surfaces. The surfaces produced
1

however^ were visually shinier than those left by

!

{ the cuttlefish discs.

I

i 4. It follows from 3 (preceding) that all debris and

' loose particles should be immediately and continuously

J removed from the operating field. Coarse particles

; from initial finishing procedures would partly

nullify the effects of the ultrafine particles of

the polishing instruments if allowed to remain in

the operating field.

5. The surface of the instrument should be as flat

and smooth as the size of the cutting particles will

permit. If such is not the case^ there will be a

tendency for grooves or scratches to be formed that

are analagous to those caused by larger particles.

6. The cutting instrument should be somewhat flexible,

or at least be flexibly mounted on the mandrel.

A flexible instrument distributes lighter forces

over a larger area, which minimizes heat formation

and the removal of filler particles from the

resin matrix.
12

The foregoing are not presented as established facts,

but rather as working hypotheses that may guide further

research and development that is needed in this field.

The diamond disc instrument described in this report

is useful for only a short period of time due to the temporary

nature of the paper backing. Because of the relative

expense of using diamond particles, a more permanent backing

such as flexible plastic or metal is needed. Strips that

can be passed between the teeth are also needed, since a

disc is not appropriate for finishing proximal surfaces.

Instruments of other appropriate shapes and sizes are likewise needed for polishing lingual and other concave surfaces.

While relatively coarse cutting features are needed on

instruments for gross reduction of excess composite material,

the final polish requires abrading particles of extremely hard

material in sizes of about one [im (about 4 x 10”® inch) or

smaller. Freedom from coarser particles is imperative, since

even a few of these badly scratch and roughen a polished surface.

I /
13

Summary and conclusions

An instrument for finishing composite restorative materials was

constructed of 1 to 5 (im (micron#) diamond particles bonded to

flexible paper discs by means of an epoxy adhesive. The surface

finishes obtained with the diamond discs were superior to

those obtained by fine cuttlefish discs, but not as good as

the surfaces left by letting the material harden in contact

with glass plates. Evaluations of surfaces were made by means

of photographs taken with a scanning electron microscope,

by visual examination of reflected light and by subjective

tactile sense using a dental explorer.

Similar instruments need to be developed that utilize

sub-micron diamond or other very hard abrasive particles.

These polishing particles should be durably mounted. Not

only flexible discs, but other instruments of shapes and

sizes that can be used on proximal and lingual tooth surfaces

should be made available to dentists who restore teeth with

composite materials.
14 -

References

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

Polymer for Dental Restorations, JADA 66: 57-64,

Jan 1963.

2. Gilmore, H. W. Textbook of Operative Dentistry ,

St. Louis; The C. V. Mosby Co., 1967 pp 423-424.

3. Johnson, L. N. , Lynn, J. A., and Jordan, R. E.

Effects Various Finishing Procedures Have on

Composite Resin Surfaces, abstracted, lADR Program

and Abstracts of Papers, No. 408, 1970.

4. Weast, R. C. (ed.) Handbook of Chemistry and Physics ,

Cleveland; The Chemical Rubber Company, 1969-1970

(50th edition) p F-18.

5. Knoop, F., Peters, C. G., and Emerson, W. B. A

Sensitive Pyramidal-diamond Test for Indentation

Measurements, J Res Nat Bur Standards ^;39 July 1939.

USCOMM*NBS-DC
Legend

Figure 1: Photographs of Adapt ic taken with a scanning

electron microscope. A and B show the surface

obtained by allowing the material to harden

between polished glass plates. The lines seen

on the surface are artifacts. C and D show the

surface obtained by finishing with fine cuttlefish discs. E and F show the surface obtained

with the discs that were coated with 1 to 5 pm

(micron) diamond particles.



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