NATIONAL BUREAU OF STANDARDS REPORT

10 581

Progress Report

on INTERMEDIARY BASE

AND CEMENTATION

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

311.05-11-3110561 April 28, 1971 10 581

Progress Report

on INTERMEDIARY BASE

AND CEMENTATION

by

N. W. Rupp

Research Associate, American Dental

Association Research Unit at the

National Bureau of Standards

Washington, D. C. 20234

This investigation is part of the dental research

program conducted by the National Bureau of Standards

in cooperation with 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.

IMPORTANT NOTICE NATIONAL BUREAU OF ST,

for use within the Government, and review. For this reason, the 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.

s accounting documents intended

subjected to additional evaluation

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

y the Government agency for which

)pies for its own use. <NBS>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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Intermediary Base

An intermediary base is that portion of a restoration

placed; 1) directly between the dentin and the final restorative material, or 2) interposed between a therapeutic material

for pulp treatment and the restorative material. Ideally, the

intermediary base replaces some of the dentin lost by caries,

trauma or cavity preparation.

Selection of a material for use as an inteinnediary base

is dependent on the amount and condition of the remaining tissues

as well as the intended purpose of the base. Table 1 lists the brands* materials currently available. Some of the * in the

various classes are; Zinc phosphate cement (ZP) "Tenacin" ; zinc oxide-eugenol cement (ZOE) ; modified zinc oxide-eugenol

1

e.g. o-ethoxybenzoic acid (EBA) " EBAC" , aluminum oxide (AlgOg)

1 1

"Opotow EBA with alumina" and poly (methylmethacrylate) (PMMA)

4* ^ ^ "T & B" ; calcium hydroxide (Ca(OH)g) "Hydrex" and zinc poly-

^ ^ carboxylate or zinc polyacrylate (PC) "Durelon".

t

tt

ttt

Tenacin; L. D. Caulk Co., Milford, Del.

EBAC: The Lorvic Corp., St. Louis, Mo.

Opotow EBA with alumina: Opotow Dental Mfg. Corp.,

Brooklyn, N.Y.

T & B: L. D. Caulk Co., Milford, Del.

Hydrex; Kerr Manufacturing Co., Detroit, Mich.

Durelon; Premier Dental Products Co., Philadelphia, Pa.

* Certain commercial materials and equipment are identified

in this paper in order to specify adequately the experimental

procedure. In no case does such identification imply recommendation or endorsement by the National Bureau of Standards

nor does it imply that the material or equipment identified is

necessarily the best available for this purpose.
- 2 -

Condition of remaining tooth tissue

Dental caries and attrition gradually expose dentin

tubules, allowing the natural defensive mechanisms of the

tooth to form reparative and sclerotic dentin.^ This is

contrasted with operative procedures and trauma which immediately expose unaltered dentin tubular contents to destructive

forces such as heat, dehydration and chemicals. Generally,

2.0 mm of remaining unaltered dentin between the floor of the

cavity and the pulp provides an adequate insulating barrier

against irritating components of restorative materials.^

It is impossible to determine remaining dentin thickness

during a cavity preparation. Pulp tissue may be irritated

through open tubules of viable dentin. Damage may also occur

through an undetected exposure. Ischemia produced by the

epinephrine in the anesthetic often restricts bleeding so

that a small exposure is not noticed.

Functions of an intermediary base

The functions of an intermediary base are: (1) insulation

from chemical and thermal shock; (2) strength to resist the

forces transmitted toward the pulp by compaction of filling

materials or compression of cementing media; and (3) modification of the internal walls of cavity preparations. Some

authors'^ include insulation against electric shock as a

function but cements are seldom used to alleviate this problem.
-3-

Chemical and physical properties

Table 1 and Figure 1 present the various materials and

a comparison of essential properties.

Chemical irritation by the intermediary base or final

restorative material should be avoided, or kept to a minumimi,

since the pulp has recently been weakened by the carious process or operative procedure. The initial contact of the base

material with the dentin produces the greatest irritation and

injury to the pulp.

All of the materials given in Table 1 provide insulation

against temperature change. Voth^ observed that a layer 1.4

mm thick of Ca(OH)^, ZOE or ZP was an effective barrier against

both heat and cold but that a thin film was of no value. He

did not determine the optimum thickness; however, 0.5 ram is

accepted as a minimum to prevent discomfort caused by thermal

changes

In addition to chemical irritation of the pulp a chemical

reaction of the base with the final restorative material must

be avoided. Any material which hardens by free radical polymerization should not contact eugenol-containing bases because

the eugenol inhibits the polymerization. This is true for

acrylic resins, some composite filling materials and rubber

base impression materials. Two thin coats of varnish placed

over the cement are usually sufficient to control this polymerization inhibition.
-4-

The highest compressive stress is usually exerted during

compaction of the dental amalgam or gold restoration and is

within the first 3-8 minutes after mixing/' Early and

ultimate compressive strengths are included in Table 1. Thickness of the intermediary base to disseminate compressive forces

is also important. It has been shown that 1 mm thick bases

made of materials exceeding 14 kg/cm^ (200 psi) will not

crumble or be displaced by usual condensing forces. Since

there is sufficient space in deep cavities, it is better to

err on the side of using an excess of the material

Modifying internal cavity walls

Another function of a base material, modifying internal

walls of cavity preparations, is required for indirect restorations, i.e., those completed outside the mouth to be cemented

in place. Properly selecting and using material for this

function reduces the amount of tooth structure to be removed

and assists in the retention of the restoration. Selection

of a material for this base need not be limited to the usual

cements but can include dental amalgam and gold. Retention

of the final restoration will be improved when parallelism

can be achieved without removing excessive amounts of tooth

structure
-5-

Radiopacity

Since they are completely covered by the permanent

restorations, intermediary bases cannot be identified by

visual examination. To facilitate subsequent interpretation

of x-rays in diagnosis of recurrent caries the intermediary

base should be radiopaque. The relative radiopacity of

various materials is shown in Figure 1.

Mixing

Mixing base materials is in reality one of the final

steps in the manufacture of the cement. The ingredients

should be carefully formulated and packaged by the manufacturer after exhaustive experimentation and testing. Carefully

worded and illustrated instructions for each product are

generally included in the package to insure obtaining the

optimum physical properties. Consequently, detailed mixing

instructions have been omitted in this discussion of the

various classes of materials. The only way to assure success

is to follow the instructions provided with each package. As

one paint manufacturer so aptly stated on the label of his

product, "If you don't intend to follow our instructions,

don't use our paint".
-6 -

Several brands of intermediary base materials are being

packaged in preproportioned capsules for mixing in mechanical

devices. No results have been reported of tests made using

this technique. However, from experience with similar packaging

for silicate cements and dental amalgam, the resultant products

should be highly satisfactory.

Zinc phosphate cement

Zinc phosphate (ZP) cement continues to be the standard

used for the evaluation of all new dental cements. The powder

for this cement contains approximately 9 parts calcined zinc

oxide to 1 part magnesium oxide.® When this powder is mixed

with the liquid containing phosphoric acid buffered with salts

of aluminum or zinc, the compounds formed are phosphates of

zinc, magnesium and aluminum. The outer layers of the

particles react to form a phosphate matrix that surrounds the

unreacted cores of the larger particles. The proportion of

powder particles and matrix varies with the amount of powder

incorporated into a given amount of liquid. As the powder

particle content increases in proportion to the matrix, better

physical property values are obtained.

The liquid is a precisely balanced phosphoric acid and

water solution. The water content is sensitive to the room

atmosphere. In conditions of high humidity the phosphoric

acid takes on additional water and in dry conditions gives off
-7-

water. Either condition disturbs the setting reaction, consequently the liquid bottle should be open just long enough

to remove the needed amount. This should be done immediately

prior to mixing to protect the liquid on the mixing slab.

In the past few years a ZP cement has been introduced

using water as the liquid which replaces the unstable phosphoric acid. The resultant cements when compared to acid

liquid ZP have greater film thickness, less strength, higher

solubility and are equally irritating to the pulp tissue.®

Both of these cements, acid and water settable, are

irritating to the pulp tissue. However, placing an underlay

of two thin coats of varnish or a base of either Ca(OH)g or

ZOE will prevent this irritation. ZP cement has a high crushing strength, both early and late,^*^° Table 1, it is radiopaque.

Figure 1, and its thermal insulation is effective even in thin

layers

Zinc phosphate cement is mixed on a cool, clean and dry

glass slab. The powder is separated in small units so that

a little powder is incorporated at a time. The mixture is

spread with heavy pressure on a flexible steel spatula so the

heat of the reaction will dissipate into the glass. Most

manufacturers recommend l| minutes to complete the mix. As

stated earlier the amount of powder controls the physical

properties, more powder gives higher strength and lower solubility

than when less powder is used.
- 8-

Zinc oxide-eugenol cements

In the 1960 's considerable research and development

attention was focused on ZOE cements. The favorable response

by the pulp to this material stimulated interest in improving

physical properties such as crushing strength, solubility and

11,12

film thickness for cementation procedures. Table 2 presents representative products as they evolved from the addition

of zinc acetate to hasten the set to the most recent additive,

polycarbonate, which contributes strength and abrasive resistance

The products, with AI2 O 3 , Figure 2, and PMMA develop early crush

ing strengths much in excess of the minimum 200 psi required

to resist the forces used in compacting amalgam and direct

gold. Table 1.^*^° Virmani reports that two modified ZOE

cements, B & T and Temrex*, along with the ZP material Tenacin,

have sufficient early strength to resist forces necessary to

place gold foil, mat gold or powdered gold.

Pulpal tissue response to ZOE with additives (EBA, hydrogenated rosin, AlgOg or PMMA) is similar to the original

Zoe.i3*14

Zinc oxide-eugenol cements are mixed as prescribed by

each manufacturer by spatulating to wet the powder particles

and to develop the consistency desired by the operator. The

mixing procedure does not have as critical an effect on the

* Temrex: Interstate Dental Co., New York
-9-

physical properties as does the mixing of ZP, but again strength

and solubility are improved as the powder concentration increases.

Moisture accelerates the setting reaction consequently working

and setting times can be modified by carefully controlling the

moisture content. A few drops of glacial acetic acid in the

bottle of eugenol also accelerates the set.

These cements are radiopaque. Figure 1, and can be used

safely in deep cavities without danger to the pulp. The

development of secondary dentin, when actual exposures are

covered with ZOE with or without additives, has not been as

consistent as with Ca(OH)g. Therefore, when close to the

pulp tissue and there may be an undetected pulp exposure,

use of these cements is not the treatment of choice. In such

circumstances use of Ca(OH)g is indicated . ^

Calcium hydroxide cements

Calcium hydroxide, Ca(0H)2/ when mixed with distilled

water is an effective agent for the treatment of exposed pulp

tissue. Unfortunately the resulting product has no strength.

There are several commercial mixtures containing Ca(OH)g,

e.g., Dycal* and Hydrex, which, when hardened, have sufficient

early crushing strength to withstand compaction forces required

for amalgam but not direct gold. Table 1.^’^° These also permit

* Dycal: L. D. Caulk Co., Milford, Del.
-10 -

resolution of mild inflammation of the pulp and the formation

of reparative dentin . These materials are used mainly in

deep cavities for their therapeutic effect on the pulp and

remaining dentin. When they are placed on dry dentin they

flow freely filling the deepest portions, thus ensuring

complete adaptation. Moisture accelerates the set and interferes with coverage of the dentin wall. Ca(OH)g is not

radiopaque therefore the commercial products add varying

amounts of a radiopaque material. Figure 1.

Thanik^^ reported that with less than 0.1 mm of dentin

Ca(0H)g is the least irritating base material, with ZOE next

and ZP the most irritating. To avoid pulp displacement in

deep cavities, Ca(0H)g should be carefully placed over the

dentin in the pulpal or axial walls for there may be an

undetected pulp exposure. Sufficient bulk must be provided

so the combined dentin and intermediary base will withstand

compaction forces.

These Ca(0H)g bases are the material of choice under some

composite and resin restorations for there is no eugenol to

interfere with polymerization hardening. Berk^ ^ demonstrated

that these materials protect the pulp against irritation by

silicate and ZP cements. They are equally effective in protecting the pulp under composite restoratives.
Polycarboxyl ate cements

The relatively recently developed polycarboxylate

cement (PC) is a mixtiire of a modified zinc oxide powder and

polyacrylate acid liquid. Durelon, Poly-C,* Zopac,** and

PCA*** are representative products currently on the market.

The results of several studies^ show adhesion by Durelon

to enamel and to a lesser extent to dentin. This adhesive

action to tooth structure is of interest in its potential use

as an intermediary base to modify the contour of tooth preparations. It can be painted on undercut areas then, upon hardening,

the crown or inlay preparation can be completed. Its early

strength is not known; however, the 24 hour strength, Table 1,

should be adequate to help protect a thin dentin wall against

hydrostatic forces present during cementation of precision

castings. It is radiopaque. Figure 1, and is less irritating

to pulp tissue than zinc phosphate cement, ^ ^ ~

^ indicating a

potentially promising material. The extremely critical method

for handling to obtain maximum adhesion is discussed later in

the cementation section.

*

•k-k-k

Poly-C: Claudius Ash Inc., Niagara Falls, N.Y.

Zopac: The Lorvic Corp . , St. Louis, Mo.

PCA: S. S. White Mfg. Co., Philadelphia, Pa.
- 12 -

Siommary

As Manley^ stated, "The respect the operator shows for

the dentin is directly reflected in the health of tjie pulp."

To aid dentists in showing this respect for the dentin there

is a wide range of materials available to use as an intermediary base. Choice should be determined by the role the

operator wants the material to fill, e.g., strength (ZP)

non-irritating (ZOE, modified ZOE, or Ca(OH)g), adhesive

(PC) and radiopaque (all the zinc cements and others with

radiopaquing added) . Frequently a combination of materials

is desirable, such as Ca(OH)g to permit formation of a dentin

bridge followed by either ZOE with EBA and AlgOg or ZP. Some

commercial preparations of Ca(OH)g, such as Dycal and Hydrex,

have sufficient strength to be used alone under dental amalgam

compaction.

EBA, alumina and hydrogenated rosin in ZOE have improved

the early strength and solubility so these cements can be

placed on freshly-cut dentin with confidence that

there will be no pulp irritation and that the cement will

withstand compaction forces. They can be used as a temporary

restoration and the deeper portion retained as an intermediary

base when the final preparation is completed at a subsequent

appointment. Studies concerning the response of the pulp
- 13-

tissue to all the modified ZOE cements indicate that they

retain the "kind-to-the-pulp" characteristic of ZOE.

As newer materials and modifications of old ones are

brought on the market, they should first be evaluated for

pulp tissue response. This is true of any product even

though it may be only slightly varied in formulation from

an already cleared product.
-14-

Table 1

Intermediary Base

Material

Compressive

Strength

** Pulp

Response

Early

7 min

Ultimate

24 hr

Zinc

phosphate

1

Acid

kg6m^ ’ psi

1 (4f

77 1100

kgbms 1 psi

1 (4)

1190 16900

(21)

Water

settable

not

available

1 (9)

673 * 9550

(9)

H—1—1—(~

\

i

1

5 Zinc oxide- }i eugenol

1

Zinc

acetate

‘ (4)

40 600

1

1

^ (4) 88 1250 ^ ^

1

1

(15,20,21)

++

EBA &

400 1 (ten min)

- 1

(11)

900 113000

.(one week)

(13,1^

++

PMMA

' (4) 60 900

1 140 2000

1 -H- ( 13)

Cavetec

(4)

30 ' 400

, (4)

53 ' 750

(4)

++

i

i

t

i Calcium

i hydroxide

1

i

H2 O

1 0 J 0I 0 J 0

( 15,20,21)

Dycal

(4)

77 1 1100

(4) 77 1 1100 (4)

Hydrex

1 (4)

35 500

1

I (4)

100 1400

. - 1

(16)

; Poly1 carboxy1 late

not

aval lable

. ( 24)

350 5000

I

( 24)

+ -(-+

* Figures in parentheses represent reference

** Pulp response

a. Exposure

Dentin bridge -

b. Dentin unbroken

Mild inflammation ++

Moderate inflammation +++

Severe inflammation ++++
-15

Table 2

ZINC OXIDE-EUGENOL CEMENTS

Composition Commercial Products

Powder Liquid

Intermediary bases

Temporary restorations

Periodontal packs

Root canal sealers

ZnO

Hydrogenated rosin

Zn acetate

Eug.

ZnO

Hydrogenated rosin

EBA

Eug.

Opotow EBA

ProCem

Ultim EBA

EBAC

ZnO

Alg O 3

Hydrogenated rosin

Eug

EBA

Opotow EBA with alumina

ProCem with alumina

ZnO

PMMA

Eug

Acetic

acid

Fynal

IRM

T & B

Opotow temporary

ZnO

Polystyrene

Eug. -f ? Kalzinol

ZnO

Polycarbonate

Eug . -f ? Decigenol I

i ZnO

Polymerized resin

Carnaba wax

Zn acetate

Eug

Mineral

oil

Cavitec (ingredients 1 blended in two tubes)

1

4

1

1
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Cementation

The term cementation is used to describe the process

of using a soft substance which, when hardened, holds a

dental restorative appliance to oral structures or to

another dental appliance. Currently, retention of the

dental restorative appliance is dependent on mechanical,

not adhesive or bonding, factors. Some laboratory studies

appear promising in the quest for such a bonding agent as

active research studies continue.

Included in the physical properties responsible for

mechanical retention are: 1) crushing strength; 2) ability

to wet the surfaces of the tooth and restoration; 3) resistance to solubility and disintegration in the oral environment; and 4) film thickness. Among many additional factors

affecting retention are: 1) total area of the axial walls;

2) degree of parallelism of two opposing axial walls of the

preparation, e.g., mesial vs. distal or buccal vs. lingual;

3) accuracy of fit of the restoration; and 4) direction of

forces of occlusion in relation to the path of insertion of

the restoration or appliance.

The criteria for selecting a cementing medium are

based on these physical properties and the biological

response of the pulp tissue to the cement. The manner

of handling also has a bearing on selection since ease of

manipulation is extremely important in a clinical environment.
-2 -

The operator has some control over each of the above

factors by his design of the various tooth preparations

and by selecting the correct cement and manipulating it

properly. This discussion is limited to the selection

and handling of the materials. Crushing strengths of

cement, as Worner^® described so well, are a measure of

their cementing properties. He said, "The ability of

these materials to hold restorations in position appears

to be due to the fact that the finely divided particles

of cement fill small irregularities in the surfaces and

lock the metal in place. To remove requires a fracture

of these irregular extensions (exceeding the crushing or

shear strength of the material) ."

Jorgensen^*^ presented a comprehensive analysis of

various operator controlled factors which affect film

thickness. He states that the more viscous the cement,

the more difficult it is to seat the restoration completely.

Viscosity is dependent on the type of cement, the powderliquid ratio, duration of mixing time and the temperature.

Once the cement is mixed and placed on the materials to

be cemented the viscosity has been established. The amount

and method of applying the positioning force then becomes

the principal factor controlling the residual film thickness

at the tooth-restoration interface. The operator should
-3-

apply a steady 10 pound force^'^ until the cement has

hardened. A small dab of wet cement on an adjacent tooth

provides a good test sample. An additional element contributing to film thickness, which the operator controls,

is venting. In this way the hydrostatic pressure is released as the fluid cement escapes. An accurately fitting

casting placed in or on a tooth preparation with a minimum

of film thickness takes full advantage of both the frictional

resistance and the cement's compressive strength.

The American Dental Association Specification No. 8

for dental zinc phosphate cement® defines the limits of

certain physical properties. Table 3. Two types of cement,

based on powder particle size, are specified. The manufacturer should print on the package which Type, I or II, of

Specification No. 8 that the cement is guaranteed to meet.

Maximum film thickness permitted for Type I is 25 micrometers pm (0.001 in.) . Type II may have a film thickness

up to 40 pm (0.0016 in.) . Type I is designed to permit

seating of precision castings. Type II is suitable for

all other uses. These specified physical properties are

also used as a standard for comparison of the other classes

of cementing materials as listed on Table 3. Manufacturers

that claim comparable cementation film thickness for' their
-4-

materials should state in their directions the powder

to liquid ratio that will meet the Type I specification.

Zinc Phosphate Cement

Zinc phosphate cement, ZP, Type I, Tenacin, Fleck's*

etc., for cementation continues to be the standard for

comparison of other materials being developed for luting

precision castings. Although ZP is irritating to the pulp

tissue a liner of varnish (two thin layers) or a base of

either Ca(OH)s or ZOE, covering unaltered dentin effectively

protects the pulp. A thin but complete layer of varnish

does not reduce the retentive strength of ZP.^® Additives

to the phosphoric acid liquid, such as eugenol, are not

effective in reducing pulpal irritation. If in the event

of a weakened pulp the sedative effect of zinc oxideeugenol is desired, temporary cementation with one of the

ZOE cements is recommended. Permanent cementation with ZP

can be delayed until resolution of the hyperemia is complete.

Type I powder is used for cementing precision dental

castings. The liquid is handled and mtixing is completed

as described in the section on intermediary bases. To obtain

the cementation consistency the amount of powder incorporated

into the liquid is reduced.

* Fleck's: Mizzy, Inc., Clifton Forge, Va.
-5-

Should additional working time be required the

mixing slab is cooled to just above the dew point. If

too cold, water will condense on the slab and be incorporated

in the mix and interfere with the hardening reaction.

Another recommended method of prolonging the set is

to spatulate a "pinhead" of powder into the liquid and let

stand two to three minutes before mixing. This is not as

consistent or precise as controlling the mixing slab temperature, but in some situations may be the method of choice.

This technique cannot be employed in areas of high humidity

because the liquid is hygroscopic and must be dispensed

immediately before mixing to prevent upsetting the acidwater balance of the liquid component.

As stated earlier the greater the amount of powder

in a given quantity of liquid within the limits of the

system the better are the physical properties.^® Therefore,

careful mixing is important to: 1) increase the strength;

2) reduce solubility; and 3) provide a consistency which

permits seating a precision casting, Table 3. Careful

mixing means using a cooled slab, incorporation of small

increments, thoroughly wetting each particle of powder

before adding more, using heavy pressure on a flexible

spatula, spreading the mix over a large area of the slab

and using the full time prescribed by the manufacturer to

complete the mix. This is one and a half minutes for most

brands
-6 -

Water settable zinc phosphate cements are inferior

to the conventional ZP cements and should not be used.

Table

Polycarboxylate cement

The polycarboxylate cements, (PC) , Durelon, Poly-C,

Zopac and PCA have been introduced for the express purpose

of cementing stainless steel to enamel. This cement is

formed by mixing zinc oxide powder with polyacrylic acid

liquid. Smith claims that while the carboxyl bonds are

still available immediately after mixing, they form a bond

with the calcium ions in the tooth, thus effecting true

adhesion to the enamel and to a lesser extent to dentin.

Etching or other pretreatment of the enamel surface does not

change the bond strength. Thermal cycling apparently has

no effect on strengths evaluated by static fatigue, dynamic

fatigue and peal bond tests. Water uptake and solubility

are quite high in laboratory testing, indicating that considerable long term clinical testing is required before

routine use can be recommended.

Strict observance of the mixing instructions is necessary to obtain the maximum properties of the polycarboxylate

cements. The powder to liquid proportion for cementation

should be between l| to 2g parts of powder to one part liquid

by weight

.
-7-

The desired consistency should be developed through trial

and error. Once the proportions are determined mixing can

be completed by bringing all the powder into the liquid and

spatulating quickly. The cement should be completed in less

than 30 seconds and in contact with the restoration and tooth

immediately thereafter. Correct powder to liquid ratio and

prompt usage, well before the gloss disappears, develops the

strongest adhesive and physical properties. Operators who

have used this cement are enthusiastic over the lack of

discomfort experienced by the patient during the seating. of

the restorations.

Although polycarboxylate cements were specifically

formulated for cementation of stainless steel orthodontic

appliances to enamel, tests have been made on retention of

gold cast crowns on teeth prepared with a 10° taper.

Results have also been reported of laboratory testing of

retention of gold castings in Class I cavities prepared in

recently extracted teeth.

comparable force was required

in both experiments to remove crowns cemented with zinc phosphate and polycarboxylate. ZOE with polymer had about one

half the retentive strength of PC. These laboratory tests

do not indicate a superiority over ZP for cementing gold crowns.

Instability of this cement in water, high uptake and solubility , ^
- 8-

indicates potential risks in its routine use. Preliminary

reports, however, are very favorable from dentists who are

meticulous in following the recommended handling technique.

Modified zinc oxide-eugenol and EBA cements

The modified zinc oxide-eugenol and EBA cements,

discussed in the Intermediary Base section, are mixed to

cementing consistency and used as luting agents for precision

castings. Some have physical properties, as indicated on

Table comparable to ZP and viscosity and wetting

properties which are easier than ZP to use in seating precision

castings. These new EBA, AlgOg filled cements continue to have

the original ZOE pulp protective and sedative characteristics.^®'

In light of these favorable qualities these cements are

growing in popularity as luting agents. The EBA cements with

AlgOs have compressive strengths and retention values similar

to ZP, Table 3, but are somewhat higher in their solubility

values . ^ ® Solubility and disintegration data are based on the

specification test® that measures the residue after 24 hours.

Another aspect of disintegration related to solubility but

not determined by the 24 hour residue is the loss of eugenol

as shown by Wilson and Batchelor. These investigators

claim that aqueous leaching of eugenol from ZOE cement
-9-

( unmodified) is continuous as the cement matrix hydrolyzes

to eugenol and zinc hydroxide. Thus, the cement in 20 weeks

time loses mechanical strength and disintegrates. This longterm process is not evident in the 24 hour specification test.

As with ZP, mixing for intermediary base and cementation

differ only in the proportion of powder added to a given

amount of liquid.

Well controlled long-term clinical studies of cementation with modified ZOE or EBA have not been reported. Two

progress reports^^*^^ have indicated favorable results over

a short period of time. However, other operators are observing failures after one year, especially in those cases

involving bridge abutments or short crown teeth. Consequently,

until long-term (3 years or more) well controlled studies are

reported these modified ZOE cements are not recommended for

general use in cementation of fixed prostheses.

Silicophosphate cement

Silicophosphate cements such as Kryptex*, Lucent** and

the recently introduced Fluorthin* might be termed hybrid

cements for the powder is a mechanical mixture of about 9

parts silicate and 1 part zinc phosphate cement.^® Since the

* Kryptex, Fluorothin: S. S. White Mfg. Co

** Lucent: L. D. Caulk Co., Milford, Del.

• 9 Philadelphia, Pa
-10 -

liquid is similar to that for ZP the same handling precautions

are necessary.

The compressive strength of these products is superior

to ZP while the solubility is inferior, Table 3. The

fluoride which is a basic ingredient of the silicate portion,

is gradually leached out and may increase the resistance of

the adjacent enamel to solubility in mouth fluids.^® Along

with these qualities the ability to retain or hold crowns

and castings is almost as strong as ZP.^® The manipulative

characteristics, viscosity and film thickness, however, make

it difficult to seat accurately fitting castings. One brand,

Fluorothin, meets the film thickness specification of 25 pm

for Type I cement. A favorable feature is the silicate-like

translucency which blends well esthetically with porcelain and

acrylic restorations. Consequently, this class of cement is

used principally for their esthetic value in cementing crowns

and porcelain inlays.

Acrylic resin cements

The physical properties, esthetic qualities and manipulative

characteristics of acrylic cements such as Justi Resin Cement*

are similar to the direct filling acrylic resins. Solubility,

* Justi Resin Cement: H. D. Justi, Philadelphia, Pa.
- 11 -

which is near zero, and surface wettability are two

properties which are superior to ZP. Ihis surface wettability,

or adaptation, makes it seem as though a bonding reaction

has occurred. The apparent bonding is lost, however, as the

cement absorbs water and the cement-tooth interface becomes wet.

The acrylic resins are mixed by blending carefully

measured quantities of powder and liquid. Unless otherwise

specified, the desired portiou of powder is placed in a mound

on a paper mixing pad. A flexible stainless steel spatula is

used to make a crater in the powder and the corresponding proportion of the viscous liquid is dropped into the crater.

After letting the liquid soak into the powder for a few seconds

it is rapidly mixed, using approximately 1 square inch of the

mixing area, to a homogenous mass. The total elapsed time from

adding the liquid to the completion of mix should be less than

30 seconds. Immediately after cementation the excess material

must be removed from the tooth, restoration and spatula, for

any that is permitted to set is most difficult to remove.

The resin cements contribute to the desirable esthetic qualities

of porcelain inlays, thus they, like silicophosphate cements,

are used principally for their favorable appearance.
-12 -

Polyurethane

In recent years polyurethanes have attracted much attention as potential adhesive liners and tissue sealants. These

materials are still in the experimental stage but appear

promising

.

The isocyanates used in urethane formulations act as

water scavengers, reacting with residual water on the tooth

surface to form carbamate intermediates. The carbamate intermediate immediately decomposes to amines that in turn react

jWith excess isocyanate groups to yield a substituted urea,

polyurethane. Eventually, as the tooth surface is dried the

polyurethane is crosslinked. Urethanes can be formulated to

yield elastic films that appear suitable for use as adhesive

liners between dentin or enamel and conventional and composite

resins and amalgam restorations.

A modified polyurethane has been used to cement restorations to teeth without undercutting or removing an excessive

amount of tooth tissue. The bonding of acrylic restorations

was improved by adding a coupling agent to the urethane.

Etching the enamel with citric or formic acids before applying

the urethane further increased the retention of the acrylic

restorations

.
-13-

Temporary cementation of completed restorations

Two of the factors controlling the choice of a material for

temporary cementation are: 1) the need for a sedative material

and 2) the compressive strength required for retention of the

temporary coverage. Temporary cements vary from a sedative

ZOE that can be prepared with varying compressive strengths to

the high compressive strength of ZP that is irritating to the

pulp tissue.

Zinc oxide-eugenol cements can make a hypersensitive

tooth less sensitive and more receptive to subsequent permanent

cementation. Recently cut, non-sensitive dentin remains comfortable when sealed against oral fluids. Either ZOE or ZP will

maintain a marginal seal if formulated with the appropriate

compressive strength to maintain the retention of the restoration. Both Horn^"^ and Gilson^^ discuss selecting temporary • cements according to compressive strengths. An accurately

fitting restoration is almost self retaining; however, a

suitable material is needed to develop the marginal seal,

Horn^^ gives the following directions for preparing a

non-setting ZOE. Trial mixes should be made of a commercial

ZOE with varying amounts of silicone grease (Dow Corning 3

compound* or R. M. Silicone grease**) and about 1% methyl or

* Dow Corning, Midland, Michigan

** Rocky Mountain Products, Denver, Colorado
-14-

propyl parapen to establish the appropriate consistency to

permit seating a single or multiple casting. The parapen

additive contributes to the plasticity of the mix and is said

to increase the bacteriostatic or fungistatic capability of

the cement. This non-setting material maintains the marginal

seal and will not require undue force to remove the restoration when ready for further treatment.

As the accuracy of fit or the self-retaining capacity

of the temporary coverage is reduced, a more adhesive, stronger

temporary cementation material is needed. This can be made by

mixing varying amounts of petrolatum with ZOE. An ill-fitting

temporary crown may need the strength of a strong cement,

preferably ZP. In these cases varnish is used to protect the

pulp and the temporary crown can be cut off so that chance of

damage to the preparation during removal is reduced.
Physical

Properties

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- 16 -

References

1. Manley, E. B. , A review of pulp reactions to chemical

irritations. Int. Dent. J. 1:36, 1950.

2. Qrban's Oral Histology and Embryology , Sixth Edition,

Sicher, H., Editor, pp. 114.

3. Stanley, H. R. : Design for a Human Pulp Study. Oral

Surg., Oral Med., and Oral Path., 25:633-647, April

756-764 May 1968.

4. Phillips, R. W. , Swartz, M. L. , Norman, R. D. Materials

for the Practicing Dentist , C. V. Mosby, Saint Louis, Mo.

1969.

5. Voth, E.D., Phillips, R. W. , Swartz, M. L. Thermal diffusion through amalgam and various liners. J. Dent. Res.

45:1184-1190, 1966.

6. Lyall, J. S. Base forming materials for restorations of

silver amalgam. Aust. Dent. J. 5:132, 1962.

7. Chong, W. F. , Swartz, M. L. , Phillips, R. W. Displacement

of cement bases by amalgam condensation. J. Amer . Dent.

Assoc. 74:97-102, 1967.

8. Guide to Dental Materials and Devices , Fifth Edition,

American Dental Association, Chicago, 111. 1970-1971.

9. Simmons, F. F. , D'Anton, E. W. , Hudson, D. C. Property

studies of a hydrophosphate cement. J. Amer. Dent. Assoc.

76:337, 1968.

10. Virmani, R., Phillips, R. W. , Swartz, M. L. Displacement

of cement bases by condensation of direct gold. J. Am.

Acad, of Gold Foil Operators. Vol . XIII, No. 1, 39-43,

Apr 1970.

11. Civjan, S., Brauer, G. M. Physical properties of cements,

based on zinc oxide, hydrogenated rosin, o-ethoxybenzoic

acid and eugenol . J. Dent. Res., 42-281-299, Mar-Apr,

1964.

12. Brauer, G. M. , McLaughlin, R. P. , Huget, E. F. Aluminum

oxide as a reinforcing agent for zinc oxide-eugenol-EBA

cements. J. Dent. Res. 47:622 July-Aug. 1968.
-17-

13. Bhaskar, S. N. , Cutright, D. E., Beasley, J. D.,

Boyers, R. C. Pulpal response to four restorative

materials. Oral Surg., Oral Med., and Oral Path., 28:

126-133, July 1969.

14. Coleman, J. M. and Kirk, E. E. An assessment of a

modified zinc oxide-eugenol cement. Brit. Dent. J.

118:482 1965.

15. Glass, R. L. , Zander, H. A. Pulp healing. J. Dent. Res.

28:97-107, Apr. 1949.

16. Sayegh, F. S. , Reed, A. J. Correlated clinical and

histological evaluation of Hydrex in pulp therapy. J.

Dent, for Children, 34:471-477, 1967.

17. Hassan, E. H. , van Huysen, G., Gilmore, H. W. Deep cavity

preparation and the tooth pulp. J. Pros. Dent. 16:751-

755, July-Aug. 1966.

18. Accepted Dental Therapeutics , 33rd Edition 1969-1970.

American Dental Association, Chicago, Illinois.

19. Berk, H. Preservation of the dental pulp in deep seated

cavities. J. Am. Dent. Assoc. 54:226-233 Feb. 1957.

20. Massler, M. Indirect pulp capping and vital pulpotomy for

potential and actual pulp exposure. J. Tennessee Dent.

Assoc. 35:393-402, 1955.

21. Thanik, K. D. , Boyd, D. A., van Huysen, G. Cavity base

materials and the exposed pulp marginal blood vessels.

J. Pros. Dent. 12:165-172, 1962.

22. Smith, D. C. A new dental cement. Brit. Dent. J. 125:381

Nov 5, 1968.

23. Mortimer, K. V., Tranter, T. C. A preliminary laboratory

evaluation of polycarboxylate cements. Brit. Dent. J.

8:365 Oct. 21,1969.

24. Phillips, R. W. , Swartz, M. L. , Rhodes, B. An evaluation

of a carboxylate adhesive cement. J. Amer. Dent, Assoc.

81:1353-1359 Dec. 1970.
-18-

25. Stanley, H. R., Swerdlow, H., Stanwick, L., Suarez, C.

A comparison of biological effects of filling materials

with recommendations for pulp protection. J. Am. Acad,

of Gold Foil Operators, 12:56-62, Sept. 1969.

26. Worner, H. K. The properties of commercial zinc phosphate

cements. Aust. J. of Dent. 123-140, April 1940.

27. Jorgensen, K. D. Factors affecting the film thickness of

zinc phosphate cements. Acta Odont. Scand. 18:479, 1960.

28. Oldham, D. F., Swartz, M. L. , Phillips, R. W. Retention

properties of dental cements. J. Pros. Dent. 14:760, 1964.

29. Souder, W. , Paffenbarger , G. C. Physical properties of

dental materials. Circular of National Bureau of Standards

C433, Feb. 6, 1942.

30. Higashi, S., Morimoto, K. , Satomura, A. et al: Studies on

the water settable cement. Part 10. J. Nihon Univ. School

of Dent. Vol. 11, 105-8, Sept. 1969.

31. Mizrahi, E. and Smith, D. C. The bond strength of a zinc

polyacrylate cement: investigation in the behavior under

varying conditions. Brit. Dent. J. 127:410, Nov. 4, 1969.

32. Grieve, A. R. A study of dental cements. Brit. Dent. J.

127:405, No. 4, Nov. 4, 1969.

33. Brauer, G. M. , Huget, E. F. , Termini, D. J, Plastic

reinforced EBA cements as temporary restorative cement.

J. Dent. Res. 49:1487, Nov-Dec 1970.

34. Wilson, A, D., Batchelor, R. F. Zinc oxide-eugenol cements

II Study of erosion and disintegration. J. Dent. Res.

49:593-598 May-June 1970.

35. Gilson, T. D. , Myers, G. E. Clinical studies of dental

cements: IV A preliminary study of a zinc Oxide-eugenol

cement for final cementation. J. Dent. Res. 49:75-78

Jan-Feb 1970.

Horn, H. R. The cementation of crov/ns and fixed partial

dentures. Dental Clinics of North America . Mar 1965.

W. B. Saunders Co., Philadelphia, Pa. p. 76-79.

36 .
-19-

37. Griffith, J. R. , Ware, A, L. An evaluation of dental

cements. Aust. Dent. J. Vol . 5, No. 5:285-291 Oct. 1960.

38. Anderson, J. N. , Paffenbarger , G. C. Properties of silicophosphate cement. Dental Progress Vol. 2, No, 2, Jan. 1962

39. Norman, R. D., Phillips, R. W. and Swartz, M. L. Fluoride

uptake by enamel from certain dental materials. J. Dent.

Res. 39:11, 1960.

40. Schoube, P. J. , Paffenbarger , G. C., Sweeney, W. T. Resin

cements and posterior-type direct filling resins. J. Amer

Dent. Assoc. 52:584-600, May 1956.

41. Galligan, J. D. , Schwartz, A. M. , Minor, F. W. Adhesive

polyurethane liners for anterior restorations. J. Dent.

Res. 47:629-632, 1968.

42. Gilson, T. D., Myers, G. E. Clinical studies of dental

cements: III Seven zinc oxide-eugenol cements used for

temporary cementing completed restorations. J. Dent. Res.

49:14-20, Jan-Feb 1970.
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