NATIONAL BUREAU OF STANDARDS REPORT

9804

Progress Report

on

ALUMINUM OXIDE AS A REINFORCING AGENT

FOR ZINC OXIDE-EUGENOL-EBA CEMENTS

<Jjbs£>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 provides measurement and technical information services

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. provides the central basis within the United

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includes Radio Standards Physics and Radio Standards Engineering—Office of Standard Refer- ence Data. THE INSTITUTE FOR MATERIALS RESEARCH . . . conducts materials research and provides

associated materials services including mainly reference materials and data on the properties of materials. Beyond its direct interest to the Nation’s scientists and engineers, this Institute yields services

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

311.05-11-3110560 December 29, 1967 9804

Progress Report

on ALUMINUM OXIDE AS A REINFORCING AGENT

FOR ZINC OXIDE-EUGENOL-EBA CEMENTS

By

G. M. Brauer, R. P. McLaughlin,* and E. F. Huget**

* Chemists, Dental Research Section, National Bureau of

Standards, Washington, D. C.

* * Guest Worker, National Bureau of Standards, Washington,

D. C., from U. S. Army Institute of Dental Research,

Walter Reed Army Medical Center, Washington, D. C.

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 Army Dental Corps; the Aerospace Medical Division, USAF School of Aerospace Medicine; and

Administration.

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015

NATIONAL BUREAU OF STA

for use within the Government. I and review. For this reason, the whole or in part, is not authori; Bureau of Standards, Washingtoi

the Report has been specifically |

the Veterans

i accounting documents intended

ubjected to additional evaluation

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

the Government agency for which

pies for its own use. <NBS>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

- 1 -

Aluminum Oxide as a Reinforcing Agent

for Zinc Oxide -Eugenol -EBA Cements

G. M. Brauer, R. P. McLaughlin and E. F. Huget

Aluminum oxide is a very effective reinforcing agent for o-ethoxybenzoic acid (EBA.)

cements. Addition of AlgO^ increases the amount

of powder that can be incorporated into the mix.

The compressive strength of the hardened cement

is increased up to 1055 kg/cm (15 ,000 p£i) and

the ADA film thickness decreased to 26u . The

materials adhere to tooth structure as well as

zinc phosphate cements and are suitable as crown

and bridge cements. With higher powder-liquid

ratios their high ten-minute compressive strength

and excellent tissue tolerance suggests their use

as bases under metallic restorations. These materials may also be employed as temporary restoratives, Mixes of AlgO-^ and eugenol or glycerine may

be of interest as a temporary non-hardening crown

and bridge cement.

Incorporation of AlgO^ whiskers did not improve the physical properties of these cements.

1. INTRODUCTION

The partial replacement of eugenol by _o-ethoxybenzoic

acid (EBA) in zinc oxide- eugenol (ZOE) cements has been shown
- 2- 1-3 to yield greatly Improved products . Results of these

Investigations have led to the development of a biologically acceptable crown and bridge cement consisting of a powder

composed of ZnO, hydrogenated rosin, fused quartz, and EBAeugenol liquid. A number of commercial products employing

these formulations having optimum physical properties have

recently become available. Alumina is often used as a reinforcing agent in ceramics. Since it is considerably more

4 *5 rigid than fuxed quartz ' , the present study was undertaken

to determine if alumina reinforcement would improve the

properties of EBA dental cements.

2. EXPERIMENTAL

2.1. Materials*

Zinc oxide, reagent grade, was passed through a No. 80

sieve. Crushed hydrogenated rosin was passed through a

No. 100 sieve. Unless otherwise specified, "tabular alumina"***

was used. The particle size range of this alumina varied

from <ln to >20n, with very few particles >20^. Smallest

particles were barely visible under the microscope (<0.5^).

Particles were irregular in shape and most grains were thinner

in one direction than in the other two. This material was

* Certain commercial materials and equipment are identified

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

recommendation or endorsement by the National Bureau of

Standards, ncr does it imply that the material or equipment

Is necesarily the best available for the purpose.

** Staybelite, Hercules, Inc., Wilmington, Delaware

*** T6l Tabular Alumina, Aluminum Co. of America, Bauxite, Ark.
-5-

heated to 700# C for two hours, passed through a No. 400

sieve and cooled. An irregular shaped "calcined alumina11

was also used in two formulations. It contained particles

ranging from 24n to those barely visible under the microscope (<0.5 mO. This alumina was also heaced to 700°C.

Whiskers consisting of loose sapphire (AloO^) fibers of **

**

varying particle size , sapphire submicron blades , silicon

carbide fiber crystals , aluminum nitride-oxide fiber crystals

*** and silicon carbide fibers were incorporated into the

powder. The dimensions of the whiskers are given in Table 6.

Poly (methyl methacrylate) powder, stearic acid (USP) and

talcum (USP) were passed through a No, ^0 sieve, aluminum

sulfate (reagent grade), zinc stearate (technical grade), a highly stabilized rosin and two highly stabilized ester

it rosins , were sieved through a No. 100 sieve.

EBA and eugenol were reagent grade, glycerine USP grace,

and the distilled tall oil technical grade.

The powders were mixed by tumbling weighed amounts of

the constituents in glass jars. Unless stated otherwise,

the liquid employed contained 62.5 percent EBA and 37.5 percent eugenol.

* A- 2 Calcined Alumina, Aluminum Co. of America, Bauxite, Ark. ** Thermokinetic Fibers, Inc., 136 Washington Ave., Nutley, N.J. *** The Carborundum Co., Niagara Falls, New York. **** Floral AX, Hercules, Inc., Wilmington, Delaware.

" Floral 85 and Floral 105, Hercules, Inc., Wilmington, Del.
-4-

2 . 2 Methods

The powder and liquid were mixed on a glass slab. A

mortar and pestle were used for those mixes that could be

mixed only with difficulty by spatulatlon. One formulation

was also mixed for J>0 seconds in a capsule containing a 9/32

inch steel ball in a mechanical amalgamator. Consistency,

setting time, film thickness, one- week compressive strength,

and solubility and disintegration were determined according

to American Dental Association Specification No. 8 . A Tinius

Olsen pendulum type testing machine was used to determine

compressive strength. Consistency and one-day solubility and

disintegration values were obtained employing American Dental

Association Specification No. 9 (dental silicate cements)^

for materials that were considered suitable for possible application as bases or restorative materials. The technique

o

of Oldham, Swartz and Phillips was employed in the study of

tensile adhesion of these cements. Two series of five teeth

each were prepared to receive one-surface inlays, and an average value for tensile adhesion was obtained from the five runs

In series 2, the order in which the adhesion values of the

various materials were measured was the reverse of that used

in series 1. This arrangement was employed to compensate for

any decrease in adhesion because of changes in the dentinal

surfaces on repetitive testing.

To evaluate the aluminum oxide- reinforced EBA cements
-5-

as a base, 1.7 Gm of powder containing 30 percent tabular

A1 20^, 6 percent hydrogenated rosin, and 64 percent zinc

oxide were mixed with 0.2 ml of liquid and placed as a base

under a series of amalgam restorations which were placed

with a packing pressure of l4o kg/cm (2,000 Ib/in ) using

a calibrated spring plugger. The teeth were sectioned after

43 hours to determine if the bases were capable of withstanding this packing pressure.

3 . RESULTS

For comparison, the physical properties of commercial

zinc oxide-eugenol (Z0E), EBA cements reinforced with 20 percent fused quartz, and zinc phosphate cements are given in

Table 1. The composition of the commercial EBA cement and

its physical properties were nearly the same as those reported earlier for an experimental cement.^ Increasing the

powder- liquid ratio of the EBA cement from 1.4 to 1.5 Gm/0.2

ml increased the compressive strength from 740 to 310 kg/cm . The solubility and disintegration values of the EBA cement ve re

considerably lower than those of the Z0E and zinc phosphate

cements. On substitution of A1 20^ for fused quartz (Table 2),

more powder could be incorporated into the mix, mixing properties and compressive strength were improved and film thickness was greatly reduced. Better mixing characteristics and

somewhat higher compressive strengths were obtained with the

tabular than with the calcined alumina. When the percentage

of A1 20^ was varied between 20 and 40 percent, the physical
- 6 - properties reached a maximum with a cement containing 50

percent tabular A^O-^, Using a powder-liquid ratio of 1.7

Gm/0.2 ml, an easily mixed slurry was obtained which on

hardening yielded a product with a one- week compressive

2 strength of 955 kg/cm (15,600 psi), a solubility and disintegration value of 0.05 percent, and a film thickness of

26m*. The EBA cements could also be mixed efficiently in a

mechanical amalgamator. The resulting mixes had a lower consistency, but otherwise physical properties very similar to

those obtained on hand spatulation using identical powderliquid ratios. As much as 2.1 Gm powder per 0.2 ml liquid

was easily incorporated by mechanical mixing. This product,

exhibited the best physical properties obtained for any EBA

2 cement, having a one- week compressive strength of 1055 kg/cm

(15,000 psi) and a solubility and disintegration of 0.05 percent. With a 1.7 Gm/0.2 ml powder- liquid ratio, a 10-minute

compressive strength of 470 kg/cm (6660 psi) was obtained.

A mix utilizing a USP zinc oxide that had been stored for

over ten years set very fast (4.5 minutes) and had a low consistency value. Analysis indicated that this particular ZnO

contained a considerable amount of zinc carbonate. Since

cements incorporating this zinc oxide showed promise as possible restorative materials, small amounts of sodium bicarbonate and water were added to freshly procured USP zinc oxides.

However, the resulting mixes had too low a consistency value

for clinical application.
The effect of addition of rosin derivates on tabular

AlgO^- reinforced EBA cements is shown in Table 5. Cements

containing stabilized rosin, rosin esters, or abietic acid

(the major constituent of rosin) had good mixing characteristics and low film thickness. However, the addition of

the rosin derivatives increased the solubility and decreased

the compressive strength of the resulting products. The addition of hydrogenated rosin up to eight percent enhanced

the mixing characteristics, reduced solubility and disintegration, but increased setting time from 5 to 10 minutes.

The compressive strength decreased when the hydrogenated

rosin content was greater than 2 percent.

Other additives modified the properties of the reinforced EBA cements (Table 4 and 5). Stearic acid, zinc

stearate, and talcum decreased the consistency values and

hence are useful in the formulation of base or restorative

materials where high .film thickness is of no importance.

Stearic acid and tall oil improved the mixing properties,

but lowered compressive strength. Addition of 0.5 to 1 percent zinc stearate slightly increased the solubility and

disintegration. The addition of 0.5 to 1 percent aluminum

sulfate slightly lowered the compressive strength and the

solubility and disintegration. Incorporation of 4 percent

methyl methacrylate polymer powder did not prove beneficial.

Partial replacement of the tabular A^O^ particles by
-3-

A 1 2

0

^ whiskers or silicon carbide whiskers did not result in

any improvement of the physical properties (Table 6 ). Mixing

characteristics were generally poor, but could be improved by

the addition of 0.5 percent stearic acid Cements with sapphire (A 1 20^) gave higher compressive strengths than those

containing silicon carbide whiskers. With sapphire (AlgO^) a

slight increase in compressive strength was obtained with decreasing particle diameter.

The tensile adhesion measurements gave larger standard

deviations than those experienced on measuring compressive

strength values (Table 7 ). The EBA cements adhered at lea3 t

as well as commercial zinc phosphate and much better than ZOE

cements. There was no significant difference between the tensile adhesion of tabular aluminum oxide and fused quartz reinforced EBA cements. Rupture of the specimens always occurred

at the cement-gold interface with the A 1 20^ -reinforced cements

rather than at the cement- dentin interface where all the other

materials failed in tension. A larger powder-liquid ratio of

EBA cement produced slightly improved adhesion. Mixes of zinc

oxide or aluminum oxide-reinforced powders with water did not

produce any significant adhesion between inlay and tooth surface. Thus, the liquid reactant in the respective cements

was necessary to produce adhesion.

When thin slurries of aluminum oxide were mixed with

either eugenol or glycerine and placed between glass plates.
-9-

these plate* could only be separated with difficulty even

after Immersion In vater for several months. Thus, such mixes

may prove useful as non-hardening temporary crown and bridge

cements

Figure 1 shows an MOD amalgam restoration placed over

an aluminum oxide-reinforced EBA cement. The base is still

intact whereas ZOE bases fractured at the pulpal- proximal line

angle.

4. DISCUSSION

Aluminum oxide-reinforced EBA cements have physical properties superior to those which are reinforced with fused quartz.

The preferred cement contained 30 percent tabular A^O^ ana 6

percent hydrogenated rosin. Using 1.7 Gm powder per 0.2 ml

liquid, a slurry can be mixed easily and hardens in less than

ten minutes. The resulting product has a compressive strength

p of 950 kg/cm and film thickness of 26m-. These properties

make the product very desirable for use as crovm and bridge

cements. On incorporation of more powder into the mix, excellent base materials can be obtained. The products have physical

properties much superior to those of conventional ZOE cements.

Especially desirable is their high 10-minute compressive

strength which can easily withstand the forces encountered in

condensing an amalgam.

Most additives investigated did not Improve the properties of the cements. When incorporated In EBA cements, aluminum
- 10- sulfate decreased the water solubility and disintegration of

the cements within the limits of the experimental error associated with this test. Addition of poly (methyl methacrylate)

did not improve the properties of the resulting cement.

Materials containing a polymer should be more resilient. This

would be advantageous in formulating a useful restorative material. Thus, further studies should be made to determine

possible beneficial effects of polymeric fillers.

Alumina whiskers have a tensile strength that is a whole

order of magnitude greater than aluminum oxide in bulk form,

but whisker reinforcement is dependent on a number of parameters including proper alignment and uniform distribution of

fibers and their complete wetting and bonding to the matrix.

If these conditions are met by the composite, the load or

stress can be transferred through the "weak" matrix to the

"strong" fibers which have a much higher elastic modulus. The

surface area of whiskers is very large. Using a fixed (minimum)

amount of EBA-eugenol liquid, the whisker concentration in the

powder must be kept low to retain good mixing characteristics

and tc obtain complete bonding between matrix and fiber. Since

whiskers were not found to improve the finished composites,

their concentration in the cement may have been Insufficient

or any of the prerequisites discussed above such as complete

wetting of the surface may not have been accomplished. Clustering of the fibers on dry mixing of whiskers with the remaining
- 11 - powder also caused difficulties. This clustering is the result of electrostatic surface interaction and might be overcome by proper pretreatment.

Mixes having a low consistency value may be useful as a

temporary restorative material. Clinical studies to determine the effective service life of these compositions are in

progress

Of interest would also be the application of a temporary

non-hardening crown and bridge cement consisting of a mixture

of AlgO

2

and eugenol or glycerine. The advantages of such a

cement would be to facilitate (l) periodic observation of

clinical crowns of abutment teeth, (2) periodic vitality testing of abutment teeth requiring full coverage, (3) post-insertion

root canal therapy without the involvement of the restoration,

(4) refabrication of pontics to obtain better ridge relationships for immediate insertion cases, (5) realignment of components to ” improve” esthetics or function, and (6) equilibration

and polishing.

3. CONCLUSIONS

Cements reinforced with tabular AlgO-^ yielded higher compressive strengths and lower film thicknesses than those containing fused quartz. Physical properties including tensile

adhesion of AlgO^ reinforced cements were in the same range

as those of zinc phosphate cements. Aluminum oxide reinforced

EBA cements should be very desirable for the cementation of
- 12 - crowns and bridges, and for bases under metallic fillings.

They may also find application as temporary restoratives.

Mixes of A1 20^ and eugenol or glycerine may be useful as

temporary non-hardening crown and bridge cements.

The addition of untreated commercial A1 20^ whiskers did

not improve the properties of the hardened cements.

USCOMM-NBS-DC
-13-

REFERENCES

1. Civjan, S. and Brauer, G. M. Physical Properties of

Cements, Based on Zinc Oxide, Hydrogenated Rosin, _o-Ethoxybenzoic

Acid and Eugenol. J Dent Res , 43:281-299, 1965,

2. Civjan S. and Brauer G. M. Clinical Behavior of oEthoxybenzoic Acid-Eugenol-Zinc Oxide Cements, J pent Res , 44:80-83, 1966.

3. Brauer, G. M. A Review of Zinc Oxide-Eugenol Type Filling

Materials and Cements, Rev Beige Med» Dent 20:323-364, 1965.

4. Soga, N. and Anderson, 0. L. High-Temperature Elastic

Properties of Polycrystalline MgO and A12 03 , S Am Ceram Soc

49:355-359, 1966.

5. Spinner, S. Temperature Dependence of Elastic Constants

of Vitreous Silica, J Am Ceram Soc 45:394-397, 1962.

6. Guide to Dental Materials , 3rd Ed. American Dental

Association, Chicago, Illinois 1966 p. 130.

7. Guide to Dental Materials, 3rd Ed. American .Dental

Association, Chicago, Illinois 1966, p. 133.

8. Oldham, D 0 F., Swartz, M. L. and Phillips, R. W.

Retentive Properties of Dental Cements, J Pros Dent 14:760-768,

1964
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