CURRENT STATUS OF DENTAL LUTING CEMENTS

Ideal Properties of a Dental Cement

1.They should be non-toxic, and non-irritant to the pulp and other

tissues.

2.Insoluble in saliva and liquids taken into the mouth.

3.Mechanical properties: These must meet the requirements for their

particular applications for example, for a cavity lining, a cement

should develop sufficient strength rapidly to enable a filling material

to be packed on it.

4.Protection of the pulp from effects of other restorative materials.

a.Thermal insulation – A cement used under a large metallic

restorations should protect the pulp from temperature changes.

b.Chemical protection – A cement should be able to prevent

penetration into the pulp of harmful chemicals from the restorative

material.
 c.Electrical insulation under a metallic restoration to minimize

galvanic effects.

5.Optical properties- For cementation of translucent restoration (for

example, a porcelain crown) the optical properties of the cement

should parallel to those of tooth substance.

6.Cement should ideally be adhesive to enamel and dentin, and to gold

alloys, porcelain and acrylics, but not to dental instruments.

7.A cement should be bacteriostatic if inserted in a cavity with residual

caries.

8.Cements should have an obtundent effect on the pulp.

9.Rheological properties are important. A luting cement should have

sufficient low viscosity to give a low film thickness and should have

adequate working time at mouth temperature to permit placement of

the restoration.
Classification of Dental Cements:

Dental cements have a variety of uses and can be classified

according to them some of the classifications put forward have been

by:
- Craig.
- Skinner.
- Combe.
- William O’Brien
CRAIG:

FUNCTIONS CEMENTS
Final cementation of completed Zinc phosphate, zinc
restorations. silicophosphate, reinforced zinc
oxide eugenol, zinc
polycarboxylate, glass ionomer.
Temporary cementation of Zinc oxide eugenol, noneugenol
completed restorations or zinc oxide.
cementation of temporary
restorations.
High-strength bases Zinc phosphate, reinforced zinc
oxide eugenol, zinc
polycarboxylate, glass ionomer.
Temporary fillings Zinc oxide-eugenol, reinforced
zinc-oxide-eugenol, zinc
polycarboxylate.
Low-strength bases Zinc oxide-eugenol, calcium
Liners hydroxide.
Calcium hydroxide in a suspension.
Varnishes Resin in a solvent
Special applications:
Root canal sealer. Zinc oxide-eugenol, zinc
polycarboxylate.
Gingival tissue pack Zinc oxide eugenol
Surgical dressing Zinc oxide eugenol, zinc oxide
preparation
Cementation of orthodontic bands Zinc phosphate, zinc
polycarboxylate
Orthodontic direct bonding. Acrylic resin, composite resin.

SKINNER

Cement Principal use Secondary uses

Zinc phosphate Luting agent for Intermediate
restorations and restorations.
orthodontic appliances Thermal insulating
bases. Root canal
restorations.
Zinc phosphate with Intermediate restorations
silver or copper salts
Copper phosphate (red or Intermediate restorations
black)
Zinc oxide eugenol Temporary and Root canal restorations.
intermediate Periodonic bandage.
Temporary and
permanent luting agent
for restorations.
Thermal insulating bases
pulp capping agent.
Polycarboxylate Luting agent for Luting agent for
restorations. orthodontic appliances
Thermal insulating intermediate restorations.
bases.
Silicate Anterior restorations.
Silicophosphate Luting agent for Intermediate
restorations. restorations. Luting
agent for orthodontic
appliances.
Glass ionomer Coating for eroded areas Pit and fissure sealant.
luting agent for Anterior restorations.
restorations. Thermal insulating
bases.
Resin Luting agent for Temporary restorations.
restorations.
Calcium hydroxide Pulp capping agent.
Thermal insulating
bases.

E.C. COMBE:

The materials may be classified as follows:

a. Acid-base reaction cements.

b. Polymerizing materials:
i. Cyanoacrylates.
ii. Dimethacrylate polymers.
iii. Polymer-ceramic composites.

c. Other materials.
i. Calcium hydroxide.
ii. Guttapercha.
iii. Varnishes.

Zinc phosphate

Zinc polycarboxylate

Zinc oxide-eugenol
 Resin

Glass ionomer

William J. O’Brien:

Type (matrix bond) Class of cement Formulations

Phosphate Zinc Phosphate Zinc phosohate

Zinc phosohate fluoride
Zinc phosohate copperoxide/salts
Zinc phosohate silver salts

Zinc silicophosphate Zinc silicophosphate

Zinc silicophosphate mercury salts

Phenolate Zinc oxide-eugenol Zinc oxide-eugenol

Zinc oxide-eugenol polymer
Zinc oxide-eugenol EBA/alumina

Calcium hydroxide salicylate Calcium hydroxide salicylate

Polycarboxlate Zinc polycarboxylate Zinc polycarboxylate

Zinc polycarboxylate fluoride

Glass ionomer Calcium aluminium polyalkenoate

Calcium aluminium polyalkenoate-
Polymethacrylate

Resin Acrylic Poly(methyl methacrylate)

Dimethacrylate Dimethacrylate unfilled
Dimethacrylate filled

Adhesive 4-META

Resin-modified Hybrid ionomers Self cure

Glass ionomer Light cured
General Cement-Forming Reaction

Cements are usually formed by an acid/base reaction in which an acidic

liquid and a basic powder are combined to produce a matrix of reaction

products in which are embedded unreacted powder particles. In most cases,

the powders are either zinc oxide or aluminosilicate glasses while the

liquids are phosphoric acid, polyacrylic acid, or eugenol.

Many of the common cements used in dentistry just represent different

combinations of these powders and liquids as shown in the table below:

LIQUID
Phosphoric
acid
POWDER Polyacrylic acid Eugenol

Zinc oxide Zinc Zinc Zinc-oxide

phosphate polycarboxylate eugenol

cement cement cement

aluminosilicate
Glass-ionomer
glass
cement
Zinc Phosphate Cement

One of the oldest and most widely used cements, zinc phosphate cement is

the standard against which new cements are measured. Commercially

available products include Fleck's Zinc (Mizzy), Hy-Bond (Shofu), and

Modern Tenacin (LD Caulk).

The set cement consists of a zinc phosphate matrix in which unreacted 2- to

8-micron-diameter zinc oxide powder particles are embedded. Crystals of

hopeite, or tertiary zinc phosphate, are found on the surface of the cement.

Composition

Powder

ZnO 90.2%

MgO 8.2%

Si02 1.4%

Bi2O3 0.1%

Misc (BaO,Ba2SO4,CaO) 0.1%

Zinc oxide is the principle constituent. Magnesium oxide is

used to aid in sintering that is to reduce the temperatures of the

 calcinations process. The silica also aids in the calcinations process

and the other ingredients of the powder are sintered at temperature

between 1000°C and 1400°C into a cake that is subsequently ground

into the fine powder. The smaller the particle size, the faster the set

of the cement.

Liquid

H3PO4 38.2%

H2O 36.0%

Aluminium phosphate or Zinc phosphate 16.2%

Zn 7.1%

Al 2.5%

The water content of most liquids is 33%±5% and controls the ionization

of the acid, which in turn influences the rate of the liquid-powder reaction. The

phosphoric acid reacts with zinc oxide which the aluminium or zinc phosphate

act as buffer to reduce the rate of reaction.

Two types of zinc phosphate cement exist:

Type I: used for cementation of precision castings;

ADA Specification No.8 calls for a film thickness of less than 25 microns.
Type II: used as a base and for luting orthodontic bands;

ADA specification calls for a film thickness between 25 and 40 microns.

Working time is approximately 4 to 5 minutes

CHEMISTRY OF THE SETTING REACTION

ZnO + ZH 3 PO 4  Zn (H 2 PO 4 ) 2 + H 2 O
ZnO + Zn(H 2 PO 4 ) 2 + 2H 2 O  Zn 3 (PO 4 )z 4H 2 O (hopeite)

When the powder is mixed with the liquid, the phosphoric acid

attacks the surface of the particles dissolves the zinc oxide forming

acid zinc phosphate. The aluminium reacts with the phosphoric acid

to form zinc aluminophosphate gel on the surface of the remaining

portion of the particles. Although no crystalline phosphate is

involved in the setting process of the cement, there can be

subsequent growth of the crystalline hopeite Zn3(PO4)2 4H2O in the

process of excess moisture during setting. The set cement is a cored

structure consisting primarily of unreacted zinc oxide particles

embedded in a cohesive amorphous matrix of zinc aluminophosphate.

Advantages
 Long record of clinical acceptability.

High compressive strength.

Acceptably thin film thickness.

Disadvantages

Low initial pH which may lead to post-cementation sensitivity.

Lack of an ability to bond chemically to tooth structure.

Lack of an anticariogenic effect.

PROPERTIES

Physical and biological properties of the cement are relevant to the

retention of fixed prosthesis. Two of the physical properties are the

mechanical properties and the solubilities.

1. Compressive strength:

i. Zinc phosphate cements are stronger than zinc oxide

eugenol cements but not as strong as silicophosphate

cements. The set cement gains 75% of its maximum

strength in the first hour maximum strength is attained

in the first day.

 ii. When properly manipulated ZnPO4 cements exhibit a

compressive strength of 104Mpa (15000psi). The

strength of ZnPO4 cement is sufficient when used as a

base or luting agent. However, when exposed to the oral

environment, e.g. temporary restoration, its brittleness

and low strength causes it to fracture and disintegrate.

Also, the prolonged contact with the oral fluids or water

gradually reduces its strength. This may be due to the

slow dissolution of the cement.

iii. The compressive strength varies (and perhaps tensile

strength) varies with:

1. P:L ratio – The recommended P:L ratio for this

ZnPO4 cement is about 1.4g to 0.5ml.

2. Water content – A change in the water content of

the liquid, either loss or gain, reduces the

strength.

2. Tensile strength :
 ZnPO 4 cement when properly manipulated exhibit a diametral

tensile strength of 5.5Mpa (300psi).

3. Modulus of elasticity:

It is comparatively high. This makes it stiff and resistant to elastic

deformation even when it is employed as a luting agent for

restoration that are subjected to high masticatory stresses. ZnPO4

cement has a modulus of elasticity approximately 13Gpa (1.96 x

10 6 psi).

4. Solubility and disintegration: ZnPO 4 cement according to ADA

specification shows a relatively low solubility of 0.06% wt.

However, in the mouth they show greater disintegration over a period

of time. This shows that the other factors (like wear, abrasion,

attacks by – products from decaying food). The solubility is greater

in dilute organic acids like lactic, acetic, and especially citric acids.

I. Effect of P:L ratio : A thicker mix shows less

solubility and disintegration than thinner mixes.

II. Effect of H 2 O content of liquid: Any change

in H 2 O content is accompanied by increased solubility.

 III. Effect of moisture contamination: Premature

contact of the incompletely set cement with H2O results in the

dissolution and leaching of the surface. Varnish application over

the exposed cement margin is beneficial.

5. Film thickness:

According to ADA specification No. 8 for Type I – film thickness

not more than 25µm for Type II – film thickness not more than

40µm.

Advantages of a thinner film:

It has a better cementing action.

It helps in more complete seating of the casting.

It minimizes the air spaces and structural defects present in

the bulk of the cement.

Film thickness depends on the particle size – smaller the particle

size, less is the film thickness. The thickness is lesser than the

size of the particle because, during mixing the particles are

crushed and dissolved. The thickness can also be reduced by

applying pressure on the casting during seating.

6. Thermal properties:

Zinc phosphate cements are good thermal insulators and may be

effective in reducing galvanic effects.

7. Adhesion property:

These cements do not form a chemical bond with enamel or

dentin. The retention of cemental restoration depends on the

mechanical interlocking of the set cement with the surface

roughness of the cavity and restoration. The thickness of the film

between the casting and the tooth also is the factor, in the

retention. The thinner the film, better is the cementing action.

8. Biological properties:

The acidity of the cement is quite high when a prosthesis is

placed on a prepared tooth because of the presence of the

phosphoric acid. Two minutes after the start of mixing the pH of

ZnPO4 cement is approximately 2 and increases rapidly but still

is only 5.5 at 24 hours. When thin mixes are employed the pH is

lower and remains lower for a longer period of time. Any damage

to the pulp, from acid attack by ZnPO4 cement, occurs during the
 first few hours after insertion. A thickness of dentin as great as

1.5mm can be penetrated by the acid of the cement of dentin is

not protected against infiltration of this acid, pulpal injury may

occur.

9. Pulp protection: Pulpal reaction can be minimized by protecting the

pulp with:

Zinc oxide eugenol.

Calcium hydroxide.
Cavity varnish.

10.Optical properties:

The set zinc phosphate cement is opaque.

Manipulation

The following points should be observed in the manipulation of

ZnPO4 cements:

1) Proportioning of the P:L ratio is not necessary as the

desired consistency may vary according tot eh chemical

situation. However, the maximal amount of powder

 possible for the operation at hand should be used to ensure

minimum solubility and maximum strength recommended

P/L ratio is 1.4gm/0.5ml.

2) The use of a cool mixing slab prolongs the working and

setting time and permits the operator to incorporate the

maximum amount of powder before the matrix formation

proceeds to the point at which the mixture stiffness.

3) The liquid should not be dispensed onto the slab until

mixing is to be initiated because H2O will be lost to the air

by evaporation, these changes can cause a decrease in pH and

an Increase in viscosity of the mixed cement.1

3) The powder is added in small increments initially with bulk

spatulation. Completion of the mix usually takes 1 minute

and 30 seconds. A large area is covered during mixing in

order to dissipate the exothermic reaction. Each increment

is mixed for 15-20 seconds before the next is added.

4) Before matrix formation occurs the casting should be

seated with a vibratory action if possible. After the casting

 is seated, it should be held under pressure until the cement

sets to minimize the air spaces. The operation field should

be kept dry.

5) A layer of varnish or other impermeable coating should be

applied to the margin so as to allow the cement more time

to nature and develop an increased resistance to dissolution

in oral fluid.

6) The cement liquid should be stored in stopper bottles with

minimum exposure to the air of it becomes cloudy, it

should be discarded.

7) Orthodontists often mix the cement using the "frozen slab"

technique which greatly extends the working time (by as much as

300%) and allows incorporation of from 65% to 95% more

powder into the liquid than normally occurs. This offsets the

possible deleterious effects of incorporating water into the mix.

Film thickness increases (3 to 5 microns), pH increases, and

setting time is shortened.

 Water contamination of the cement should be avoided while it is

setting. If moisture contaminated, phosphoric acid leaches out of

the cement and solubility greatly increases.

Uses:
1) Prefabricated and cast posts.
2) Metal inlays and onlays.
3) Crowns and FPDS.
4) All ceramic creams.

Recent Products
Product Working Setting
Composition Shelf life
name time time

Powder – Zinc oxide

1. Mizzy 2 years 3-5 min. 7-11 min.
Liquid – Phosphoric acid

Powder ZnO, MgO, Zinc

fluoride
Strontium fluoride, tannic
2. Shofu 4 years 2-5min. 8 min.
acid.
Liquid – Phosphoric acid,
aluminium phosphate.

Powder – Zinc oxide,

magnesium oxide.
3. Dentsply 5 yrs 1.5 min 8 min
Liquid – Phosphoric acid,
aluminium trihydrate

A 1970 study2 of nearly 800 crown and bridge units cemented with zinc

phosphate cement found the following reasons for failure:

-caries: 36.8%

-loss of retention (i.e., they had become loose): 12.1%

-defective margins: 11.3%

-periodontal disease: 6.8%

-periapical involvement: 2.9%

The average lifespan of the restorations was 10.3 years.

Zinc Polycarboxylate Cement

Zinc polycarboxylate cement, also known as zinc polyacrylate cement, was one of

the first chemically adhesive dental materials. Introduced by Smith in 1968. The

adhesive bond is primarily to enamel although a weaker bond to dentin also forms.

This is due to the fact that bonding appears to be the result of a chelation reaction

between the carboxyl groups of the cement and calcium in the tooth structure;

hence, the more highly mineralized the tooth structure, the stronger the bond.
 When zinc oxide and polyacrylic acid are mixed, hydrated protons formed

from ionization of the acid attack the zinc and magnesium powder particles.

This causes the release of zinc and magnesium cations which form

polycarboxylates that crosslink the polymer chains. The result is a zinc

polycarboxylate crosslinked polymer matrix in which unreacted zinc oxide

particles are embedded.

Commercially available products include Durelon (3M ESPE),

Fleck's PCA (Mizzy), Liv Carbo (GC America), Hy-Bond Polycarboxylate

(Shofu), and Tylok-Plus (LD Caulk).

Composition:

Zinc polycarboxylate cement is available as powder and liquid which

is either supplied in bottle as precapsulated powder / liquid system. It may

also be supplied as a powder which is mixed with water (water settable

cements). The liquid is a water solution of polyacrylic acid, the formula

being:

– CH 2 – CH – CH 2 – CH –
| |
C=O C=O
| |
 O O
| |
H H

Powder
- Zinc oxide
- Magnesium oxide.
- Other oxides like bismuth and aluminium.
- Stannous fluoride.
- Basic ingredients.
- Principle modifier.

The cement powder is essentially zinc oxide and magnesium oxide

that have been sintered and ground to reduce the reactivity of zinc oxide.

Stannous fluoride increases strength, modifies setting time and imparts

anticariogenic properties.

Liquid:

- Aqueous solution of polyacrylic acid or.

- Co-polymer of acrylic acid with other unsaturated carboxylic

acids such as itaconic acid.

Most commercial liquids are supplied as a 32% to 42%

solution of polacrylic acid having a molecular weight of 25,000 to

50,000. The manufacturer controls the viscosity of the cement liquid

by varying the molecular weight of the polymer or by adjusting the

 pH by adding sodium hydroxide. Itaconic and tartaric acid may be

present to stabilize the liquid, which can get on extended storage

Water settable cements:

In these cements, the polyacid is freeze dried and the powder is then

mixed with the cement powder. Water is used as the liquid. When the

powder is mixed with water, the polyacrylic acid goes into the solution and

the reaction proceeds as described for the conventional cements.

CHEMISTRY OF THE SETTING REACTION

The setting reaction of this cement involves particle surface

dissolution. By the acid that releases zinc, magnesium, and tin ions, which

bind to the polymer chain via the carboxyl groups. These ions react with

carboxyl groups of adjacent polyacid chains so that a cross linked salt is

formed as the cement sets. The hardened cement consists of an amorphous

gel matrix in which unreacted particles are dispersed. The microstructure

resembles that of zinc phosphate cement in appearance.

– CH 2 – CH 2 – CH 2 -
| |
C C
O OH HO O
 Zn

O OH HOO
C C
| |
– CH 2 – CH 2 – CH 2 –

The role of carboxylate functional groups in polycarboxylate cements

– yielding matrix through cross-linking by zinc ions.

PROPERTIES

1) ANSI/ADA specification No. 96

This specification establishes maximum values of setting time, film

thickness, acid erosion, arsenic and lead content, and a minimum value

of compressive strength for zinc polyacrylate cement.

2) Viscosity

The initial viscosity is essentially unaffected by the

temperature increased from 18° to 25°C. The initial viscosity of zinc

polyacrylate cement is higher than zinc phosphate cements, and a

delay of 2 minutes in cementation reverses the situation. They

achieve an acceptable film thickness because they are pseudoplastic and

exhibit a decrease in viscosity when sheared. The liquid of this cement

tends to be viscous because it is a partially polymerized polyacrylic acid.

3) Mechanical properties:

a) Compressive strength: The compressive strength of

polycarboxylate cement is approximately 55Mpa (3000psi)

hence the cement is inferior to zinc phosphate in this respect.

b) Tensile strength: Its tensile strength is slightly higher than

zinc phosphate cement being 6.2Mpa (900psi).

c) Modulus of elasticity: Its modulus of elasticity is less than

half that of zinc phosphate cement. In addition it is more

brittle than ZnPO4 cement and this hard to remove the excess

after cementation.

4) Working and setting time:

The working time for polycarboxylate cement is much shorter than

that for ZnPO4 cement, that is approximately 2.5 minutes as compared

to the 5 minutes for zinc phosphate.

 The setting test measures the time at which the cement is sufficiently

hard to resist indentation by a standard intender. The net setting time

should occur with 2.5minutes to 8 minutes so that the final procedures

associated with the restoration can occur. Setting of zinc

polycarboxylate cements usually occurs within 7-9 minutes from the

start of mixing.

The temperature of the cool slab can cause polyacrylic acid and to

thicken and thus make the mixing procedure more difficult. Therefore it

has been suggested that only the powder should be refrigerated before

mixing as the reaction occurs on the surface and the cool temperature

retards the reaction without thickening the liquid.

5) Film thickness

At the recommended P:L ratio the carboxylate cements appear to be

more viscous than a comparable mix of ZnPO4 cement. However they

undergo thinning at an increased shear ratio. Clinically this means that

the action of spatulation and seating with a vibratory action reduce the

viscosity of the material, and yield a film thickness of 25µm or less.

6) Solubility and disintegration

 Slightly more soluble than zinc phosphate and tends to absorb water.

Solubility in distilled water does not always correlate with solubility in

vivo. Solubility in water at 1 day varies from 0.12% to 0.25% for typical

zinc polyacrylate cements. ANSI/ADA specification No. 96 specifies the

maximum rate of acid. Though the solubility in water is low, but when it

is exposed to organic acids with a pH of 4.5 or less, the solubility

markedly increases. Also, a reduction in the P:L ratio results in

significantly higher solubility and disintegration rate in the oral cavity.

7) Biologic considerations:

The presence of zinc polycarboxylate in contact with either the hard

or soft tissues has been found to result only in a very mild response. The

pH of the cement liquid is approximately 1.7. However the liquid is

rapidly neutralized by the powder and the pH of the freshly mixed

cement is 3.0-4.0 after 24 hours, pH of the cement is 5.0-6.0.

They are less irritant to the pulp than ZnPO4 cement. This is

because,

a) The pH of polycarboxylate cement rises more rapidly than

that of ZnPO4.
 b) Penetration of polyacrylic acid into the dentinal tubules is

less because of its higher molecular weight and larger size.

The excellent biocompatibility with the pulp is a major factor in the

popularity of the cement system. The histological reactions are similar to

ZnOE cements, but more reparative dentin is formed with polycarboxylate.

Post operative sensitivity effects are negligible for both cements.

8) Adhesion

The fact that zinc polycarboxylate cement bonds chemically with

tooth structure is one of its outstanding characteristics. This is due to

the ability of the carboxyl group in the polymer molecules to chelate

with calcium in the tooth structure.

The bond strength enamel ranges from 3.4 to 13.1 Mpa and that to

dentin is 2.07Mpa.

a) Under ideal conditions of manipulation, the adhesion of a

polycarboxylate to clean dry surface of enamel is much

greater than that of other cements.

b) If the cavity surface of the restoration is not clean, the

cement cannot bond with the metal. So to improve the

 mechanical bond, the surface should be carefully abraded

with a small stone or with alveolar adhesives.

c) The presence of saliva reduces the bond strength.

d) Unlike ZnPO4 cements, adhesion is better to smooth surface

than rough surface.

e) Does not adhere to gold or porcelain.

f) Adhesion to stainless steel is excellent.

9) Optical properties:

They are very opaque due to large quantities of unreacted zinc.

10) Thermal properties

Polycarboxylate cements are good thermal insulators.

MANIPULATION:

To obtain satisfactory results, the operator must follow instructions

carefully and take every precaution to avoid undesirable complications.

Areas of major concern are the mixing of the cements, the surface

preparation of the prosthesis, the nature of the tooth surfaces receiving the

prosthesis, and the time at which the excess cement is removed.

a) The tooth surface should be meticulous by clean in order to

provide intimate contact and interaction between the cements

and the tooth.

This can be achieved by use of 10% polyacrylic acid solution

followed by rinsing with water, or 1 to 3% hydrogen peroxide

may be used. The tooth can then be dried and isolated.

b) The P:L ratios required to produce a cement of suitable

cementing consistency may vary from product to product.

Generally, they are in the range of 1.5 parts of powder to 1

part of liquid by weight.

c) Mixing should be carried out on a surface that does not

absorb liquid like a glass slab also because once cooled it

retains the temperature longer.

d) The powder may be cooled, but the liquid should not be

cooled since the viscosity of the liquid increases.

e) The liquid should not be dispensed before the time when the

mix is to be made. It loses water to the atmosphere rapidly

which results in marked increase in its viscosity.

f) The powder is incorporated into the liquid in large quantities

(90%) with a stiff cement spatula and remaining powder is

added to adjust consistency. The mixing should be completed

within 30 to 40 seconds in order to provide sufficient

working time. The mix appears quite thick, but this cement

will flow readily into a thin film when placed under pressure.

g) The cement should be used while the surface is still glossy.

Loss of luster and dull, stringy, rubbery consistency indicates

that the setting reaction has progressed to an extent that

proper wetting of tooth surface by the mix is no longer

possible. If the surface is not creamy and shiny, and is matted

and tends to form cobwebs, the mix should be discarded. The

glossy appearance indicates a sufficient number of free

carboxyl acid groups on the surface of the mixture that are

vital for bonding to tooth structure.

h) The excess cement that has extruded beyond the margins

should not be removed while the cement is in the rubbery

stage as some of the cement may be pulled out from beneath

 the margins, leaving a void. Excess should be removed only

when the cement has hardened.

Uses:

Cementation of a single metal unit in low stress areas on sensitive

teeth.

Advantages

Kind to the pulp,

Chemically bonds to tooth structure.

Disadvantages

Short working time.

Requires separate tooth conditioning step prior to cementation.

 Zinc Oxide-Eugenol Cement

Certain types of zinc oxide, when mixed with eugenol sets to a hard

cement that is compatible with the hard and soft tissues of the mouth.

These cements have been used extensively in dentistry since 1890’s.

E.g.: Lining cavities, cementing restorations, as bases, root canal

sealants, periodontal dressings, and temporary and intermediate

restorations. Depending on their use they vary widely in their properties. In

general, they are cements of low strength. Also they are the least irritating

of all dental cement, and are known to have an obtundant (sedative) effect

on exposed dentin.
 To improve the strength many modified zinc-oxide eugenol cements

have been introduced. E.g.: EBA to eugenol. Experimental vanillate and

syringate cements without eugenol are presently under investigation.

Classification:

ADA specification No. 30 has listed 4 types of zinc-oxide eugenol

restorative materials.

Type I ZOE – For temporary cementation.

Type II ZOE – Permanent cementation.

Type III ZOE – Temporary filling material and thermal insulation.

Type IV ZOE – Cavity liners.

Mode of supply:

It is dispensed in two forms: a) Powder and liquid.

b) Two paste system.

Commercial names:

1. Unmodified
- Tempac – Type III.
- Cavitic – Type IV
- Tempbond – Type I.

2. EBA alumina modified Opoton

- Alumina – Type II
- EBA.
3. Polymer modified
- Fynal – Type II
- IRM – Type III

4. Noneugenol
- Neogenol – Type I
- Freegenol – Type I

Composition
Powder

Zinc oxide – 69% - Principal ingredient

White rosin – 29.3% - To reduce brittleness of set cement

Zinc stearate – 1.0% - Accelerator, Plasticizer

Zinc acetate – 0.7% - Accelerator, improves strength.

Magnesium oxide – Is added in some powders. It acts with eugenol in a

similar manners as zinc oxide.

Liquid

Eugenol – 85.0 – Reacts with zinc oxide.

Olive oil – 15.0 Plasticizer.

Setting Reaction

As the basic components of the cement are zinc oxide and eugenol,

the setting reaction and microstructure are the same as that of the

impression pastes.
 In the first reaction hydrolysis of zinc oxide to its hydroxide takes

place. Water is essential for the reaction to proceed (Dehydrated zinc oxide

will not react with dehydrated eugenol).

ZnO + H 2 O ---------------- Zn (OH) 2

The reaction proceeds as a typical acid-base reaction to form a

chelate.

Zn (OH) 2 + 2HE -------------- ZnE 2 + 2H 2 O

Base Acid Salt

(Zinc hydroxide) (Eugenol) (Zinc Eugenolate)

The chelate forms an amorphous get that tends to crystallize

imparting strength to the set mass.

Structure of set cement

Thus the set cement consists of particles of zinc-oxide embedded in a

matrix of particles of zinc eugenolate.

Setting time: 4-10 minutes.

Factors affecting setting time: The complete reaction between zinc oxide

and eugenol takes place in about 12 hours. This is too slow for clinical

convenience.

1. Manufacture: The most active zinc oxide powders are those formed

by decomposing zinc salts like zinc hydroxide and zinc carbonate by

heating at 300°C.
 2. Particle size: Cements from powders containing smaller zinc oxide

particles set faster.

3. Accelerators: Alcohol, glacial acetic acid, and small amounts of

water accelerates the reaction.

4. Heat : Higher temperatures accelerate setting.

Lower temperature, e.g., cooling the glass slab, slows the reaction.

5. Retarders : The set can be retarded with glycol and glycerine.

6. Powder to liquid ratio: The higher the ratio, the faster the set.

Properties:

1. Mechanical properties:

a. Compressive strength:

They are relatively weak cements. The strength depends on the

intended use of the materials. For example, cements intended for

temporary purposes like temporary restorations and cementation

(Type I), and cavity lining (Type IV), will have a lower strength.

Cements intended for permanent cementation (Type II) and

intermediate restorations will be more stronger. The compressive

strength ranges from a low of 3 to 4 Mpa upto 50-55 Mpa.

Particle size affects the strength. In general, the smaller the

particle size, the stronger the cement. The strength can also be

increased by reinforcing with alumina-EBA or polymers.

 b. Tensile strength:

It varies according to its intended use.

Ranges from 0.32 to 5.8 Mpa.

c. Modulus of elasticity:

This is an important property for those cements intended for

use as bases.

Ranges from 0.22 to 5.4 Gpa

0.03 to 0.79 psi.

2. Thermal Properties:

a. Thermal conductivity.

Their thermal insulating properties are excellent and are

approximately the same as for human dentin.

The thermal conductivity of zinc oxide-eugenol is the range of

insulators like cork and asbestos.

3.98 (Cal.Sec -1 cm -2 (°C/cm -1 ) x 10 -4 .

b. Coefficient of thermal expansion: 35 x 110 -6 /°C.

3. Solubility and disintegration:

This property is important for cements used for permanent

cementation.
0.04%wt.

The solubility of the set cement is high, the highest among the dental

cements. They disintegrate in oral fluids. This beak down is due to

hydrolysis of the zinc eugenolate matrix to form zinc hydroxides and

eugenol. Solubility is reduced by increasing the powder / liquid ratio.

4. Film thickness:

This property is important for those cements used for cementation of

restorations. The film thickness of zinc-oxide-eugenol cements is higher

than other cements. 25µm.

5. Adhesion:

These cements do not adhere to enamel or dentin. This is one of the

reasons why they are not often used for final cementation of dental

restoration.

6. Biological properties:

a) pH and effect on pulp: They are the least irritating of

all dental cements. In terms of pulpal response they are classified

as mild.

pH is 6.6 to 8.0

b) Bacteriostatic and obtundant properties: They inhibit

the growth of bacteria and have an anodyne or soothing effect on

the pulp in deep cavities, reducing pain when it is present.

 7. Optical properties:

The set cement is opaque

Manipulation

Powder-Liquid system : Powder/Liquid ratio : 4:1 to 6:1 by wt.

The bottles are shaken gently. Measured quantity of powder and

liquid is dispensed onto a cool glass slab or paper pad. The bulk of the

powder is incorporated into the liquid and spatulated thoroughly in a

circular motion with a stiff bladed stainless steel spatula. Smaller

increments are then added until the mix is complete.

Oil of orange can be used to clean eugenol cements from

instruments.

Two paste system:

Equal lengths of each paste are dispensed and mixed until a uniform

color is observed.

Setting time: 4-10 minutes.

Zinc oxide-eugenol cements set quickly in the mouth due to moisture

and heat.
MODIFIED ZINC OXIDE EUGENOL CEMENTS
EBA-ALUMINA MODIFIED CEMENTS

These were introduced in an effort to improve the mechanical

properties of zinc oxide-eugenol cement.

Composition:

Powder Liquid
Zinc oxide - 70% EBA - 62.5%
Alumina - 30% Eugenol – 37.5%

Properties:

In general, their properties are better than that of unmodified ZOE.

1. Compressive strength is increased – 55Mpa (8000psi).

2. Tensile strength – 4.1 Mpa (600psi).

3. Modulus of elasticity – 2.5Gpa (0.36 psix10 6 ).

4. Film thickness – 25µm.

5. Solubility and disintegration in water – 0.05% wt.

Manipulation:

Glass slabs are recommend for EBA-alumina modified cements.

After dispensing the powder is incorporated into the liquid in bulk and
kneaded for 30 seconds, and then stopped for an additional 60 seconds with

broad strokes of the spatula to obtain a creamy consistency.

They have long working times.

Setting time : 9.5 minutes.

Polymer reinforced zinc oxide eugenol cement:

The polymer reinforced cement was introduced in an effort to

improve the mechanical properties of conventional zinc oxide eugenol

cement. These have been used as:

1. Luting agent.

2. As base.

3. As temporary filling material and

4. As cavity liner.

Composition:

Powder Liquid
Zinc oxide Eugenol
Finely divided natural or Acetic acid – accelerator
Synthetic resins Thymol – antimicrobial agent.

The zinc oxide powder is surface treated. The combination of surface

treatment and polymer reinforcement results in good strength, improved

abrasion resistance and toughness.

Setting reaction:

The setting reaction is similar to zinc oxide eugenol cements. Acidic

resins, if present, may react with zinc oxide, strengthening the matrix.

Setting time: 6 to 10 minutes.

Factors affecting setting time:

1. Powder-liquid ratio: Lower powder liquid ratio, increases setting

time.

2. Moisture: Accelerates setting time.

Properties:

1. Compressive strength : 48Mpa (7000psi).

2. Tensile strength : 4.1Mpa (600 psi).

3. Modulus of elasticity : 2.5Gpa (0.36 psix10 6 ).

4. Film thickness : 32µm.

5. Solubility and disintegration : 0.03% wt.

6. Pulp response : Similar to unmodified ZOE-moderate.

Improved abrasion resistance and toughness.

Manipulation:

The proper powder / liquid ratio is dispensed on a dry glass slab. The

powder is mixed into the liquid in small portions with vigorous spatulation.
Working time: These cements have a long working time.

Cements containing vanillate esters:

Recently, cements have been developed contaiing Hexyl Vanillate

and Orthoethoxy Benzoic acid (HV-EBA), as a substitute for eugenol. This

liquid is mixed with zinc oxide powder. It has been claimed that these

cements have high strength and low solubility.

Special zinc oxide eugenol products:

Some zinc oxide-eugenol materials contain-antibiotics such as

tetracyclines, and steroids as anti inflammatory agents. Their principal use

in pulp capping and root canal therapy. Another product also contains

barium sulphate, which is radioopaque.

Advantages

Obtundent effect on the pulp.

Good short-term sealing

Disadvantages

Weak.

Soluble in oral fluids.

Examples of commercially available zinc oxide-eugenol cements include

Opotow Alumina EBA (Teledyne Getz), Super EBA (Bosworth), and Fynal

(LD Caulk).

Caulk's Fynal is a polymer-reinforced zinc oxide-eugenol cement.

Resin Cement

As a general rule, resin cements are the best choice for luting ceramic

restorations.3 This conclusion is based on three types of research:

laboratory studies measuring the fracture resistance of restorations luted

with resin versus other types of cements; clinical studies; and laboratory

studies evaluating thesealing/strengthening effect of resin cements. The

resin cements were first developed in the early 1950s for use as crown and

bridge luting agents but had poor physical properties (high polymerization

shrinkage and excessive leakage) because of their low percentage filler

content. Modern products are more highly filled and have better physical

properties. Resin cements are either visible light-activated, chemically-

activated, or dualactivated (both visible light- and chemically- activated).

Visible light-activated cements are generally reserved for the luting of cast

ceramic, porcelain, and resin composite veneers or for other light-

transmitting restorations that are thin enough(i.e., "d1.5-mm thick) to

transmit light. The chemicallyactivated forms are used for the cementation

of: resin-bonded fixed partial dentures; thick (i.e., "e2.5-mm-thick) cast

ceramic, porcelain, and resin composite restorations; and metal restorations.

Dual-activated resin cements are used for luting thin to moderately-thick

(i.e., from 1.5-mm- to 2.5-mm-thick) cast ceramic, porcelain, and resin

composite restorations where light penetration may be limited.

Commercially available products include: Biomer (Dentsply/Caulk),

Comspan (Dentsply/Caulk), Variolink II (Ivoclar Vivadent), Enforce

(Dentsply/Caulk), Calibra (Dentsply/Caulk), Ultra-Bond (Den-Mat),

Mirage FLC (Chameleon), Insure (Cosmedent),RelyX Veneer Cement (3M

ESPE), C&B-Metabond (Parkell), Nexus 2(SDS/Kerr), RelyX ARC (3M

ESPE), RelyX Unicem (3M ESPE), Panavia21 (Morita), and Illusion

(Bisco).

Composition

BIS-GMA or urethane dimethacrylate resins filled from 30% to 80% with

generally submicron filler particles.

Advantages

High compressive strength.

Low solubility

Disadvantages

Irritating effect on the pulp.

High film thickness.

Dual affinity resins, the so called "Japanese acrylics", are resin cements

whose manufacturers claim they have the ability to chemically bond to both

tooth structure and metals. These cements contain adhesive monomers such

as MDP, HEMA, and 4-META and include such products as Panavia 21 (J.

Morita) which contains MDP and C&B-Metabond (Parkell) which contains

4-META.

These cements may be of clinical benefit in providing increased retention

for restorations when minimal retention form exists because several studies

have found these cements to be more retentive than zinc phosphate, glass-

ionomer, and conventional resin cements.4-6

Panavia, first marketed in 1983, has been described as a phosphonated

methacrylate or a modified phosphate ester of BIS-GMA. The first form of

the product was marketed from 1983 to 1994 and consisted of a powder and

a liquid. The powder was a BIS-GMA based resin filled to 76% by weight

with quartz particles. Also present in the powder was a benzoyl peroxide

initiator. The liquid consisted of aliphatic and aromatic methacrylates,

phosphate monomers, tertiary amine and sulfinate activators, and

stabilizers. Also in the liquid was the bifunctional adhesive monomer 10-

methacryloyloxydecyl dihydrogen phosphate (also known as MDP or

M10P). Adhesion to tooth structure appeared to result from both

mechanical and secondary bonding (hydrogen bonding and/or Van der

Waals forces).

Panavia's bond strength depended on the substrate. Bond strength to metal

varied from 20 to 40 MPa while bond strength to tooth structure ranged

from 8 MPa (dentin) to 28 MPa (enamel).

The new product, Panavia 21, differs from its predecessor because it has an

enamel/dentin primer and is provided as two pastes rather than as a powder

and a liquid. The pastes are supplied in a unique, automated, syringe-type

dispenser that facilitates consistent paste-to-paste dispensing. A cartridge

refill for the dispenser provides enough cement for approximately 55

applications. The primer comes in two separate bottles and is mixed just

before use. It contains hydroxyethyl methacrylate (HEMA), N-

methacryloyl 5-aminosalicylic acid (5-NMSA) and MDP.

Morita claims that the primer enhances bond strength to dentin which had

been relatively low with the old product. When using Panavia 21 to bond

resin-bonded fixed partial dentures to tooth structure, the metal should not

be etched. Etching results in a lower bond strength, possibly because

mechanical irregularities in the metal trap air and water which inhibit
Panavia 21's polymerization. If the casting is a base metal, simply air

abrade it with 50-micron aluminum oxide at from 60 to 100 psi and then

ultrasonically clean it. If the casting is a noble metal, it should be air

abraded, tin plated, and ultrasonically cleaned. Tin plating enhances

mechanical as well as chemical bonding because it increases roughness of

the surface.

When bonding to uncut enamel, etching of the tooth structure is

recommended. A 40% phosphoric acid etchant in a syringe is provided with

the product. If the enamel has been prepared, only primer is applied; no

etching is necessary.

Dentin is treated by applying the primer for 60 seconds and then drying it.

Panavia 21's polymerization is strongly inhibited byoxygen, so a

polyethylene glycol gel, Oxyguard II, must be usedto cover the exposed

cement to ensure completeness of polymerization. The gel contains a

sulfinate activator that is said to hasten setting of the covered cement.

Panavia 21 is available in three shades: TC (tooth color) which is very

translucent; EX (standard white) which is partially translucent; and OP

(opaque) which is opaque. All three shades are said to be radiopaque. Film

thickness is reported by the manufacturer to be 19 microns however an

average value of 46 microns has been measured in the DIS laboratory. Shelf

life is approximately 18 months when the product is refrigerated.

C&B-Metabond is based on the 4-META/MMA-TBB system developed in

Japan in which bonding occurs as monomers flow into demineralized

intertubular and peritubular dentin. The product contains a dentin activator

solution (citric acid/ferric chloride), enamel etchant (phosphoric acid), base

(4-META, MMA), catalyst (tributyl borane), and tooth colored and clear

powders (PMMA). When using this cement for the luting of resin-bonded

fixed partial dentures, prepare the casting surface as described for Panavia;

the tooth surface should be treated with the enamel etchant or dentin

activator as appropriate. Film thickness may intentionally be varied from 15

to 50 microns by altering powder to-liquid ratio.

Dual-cure resin cements achieve only a portion of their polymerization

from chemical curing.7 It is, therefore, very important to ensure that they

are adequately light activated.

Generally, film thickness has been reduced for the resin cements due to the

8
use of smaller filler particles and incorporation of diluent monomers,

however some products still cause excessive film thicknesses, especially if

used improperly.
 It is recommended that patients be advised against loading restorations

newly luted with chemically-activated resin cements because early bond

strengths are weak and need a period of 24 hours to fully mature. Generally,

the patient should be told to be careful to avoid loading for the first hour. It

is alsosuggested that excess marginal cement be removed before it sets to

avoid damaging the weak early bond.9

Cementing provisional restorations with eugenol-containing temporary

cements remains controversial. Although it is clear that free eugenol

inhibits resin polymerization, several studies have found no effect on

resulting resin-to-dentin bond strengths.10,11

GLASS-IONOMER CEMENTS

Glass ionomer cements were invented by Wilson and Kent in 1969

and developed by McLean and Wilson during the 1970’s. This class of

material has achieved widespread use as translucent materials for

restoration of Class V erosion lesions and Class III cavities, fast setting

liners and bases for attaching composite resins to tooth preparations, fine

grained luting agents, fissure sealants, and metal reinforced core build up

materials.
 These cements have combined properties of silicate cements and

polycarboxylate cements. The name of the cement is glass ionomer

because, the powder is glass and the setting reaction and adhesive bonding

to tooth structure is due to ionic bond. This cement is also referred to as:
- Poly (alkenoate) cement.
- GIC.
- ASPA (alumino silicate polyacrylic acid).

The word “ionomer” was coined by the Depont Company to describe

its range of polymers containing a small proportion of ionized or ionizable

groups, generally by the order of 5% to 10%. This does not clearly apply to

the components of the glass ionomer cement and therefore the term glass

polyalkenoate cement was devised. However, unlike the term glass ionomer

cement, it does not apply to the recently developed experimental poly

(vinyl phosphoric acid) cements. The term glass ionomer is therefore a

generic one for all glass-polyacid cements, e.g., polycarboxylate,

polyphosphonate etc.

McLean, Nicholson and Wilson (1994) offered the following

definition of a glass ionomer cement.

 A cement that consists of a basic glass and an acidic polymer which

sets by an acid-base reaction between these components.

Classification:

Type I – For luting.

Type II – For restoration.

Type III - Liners and bases.

Type I glass ionomer cements are used for the cementation of cast

alloy and porcelain restoration and orthodontic bonds.

Composition:

Powder

The powder is an acid soluble calcium fluoro-alumino silicate glass.

It is similar to that of silicates, but has a higher alumina-silica ratio. This

increases the reactivity with the liquid. The composition of a commercial

glass ionomer powder is given:

Weight %
Silica (SiO 2 ) - 41.9
Alumina (Al 2 O 3 ) - 28.6
Aluminium fluoride (AlF 3 ) - 1.6
Calcium fluoride (CaF 2 ) - 15.7
Sodium fluoride (NaF) - 9.3
Aluminium phosphate (AlPO 4 )- 3.8

The raw materials are fused to a uniform glass by heating them to a

temperature of 1100°C to 1500°C. The fluoride component acts as a

‘Ceramic flux’. Lanthanium, strontium, barium or zinc oxide additions

provide radiopacity. The glass is ground into a powder having particles in

the range of 20 to 50µm.

Liquid:

Earlier the liquid was a 50% concentration aqueous solution of

polyacrylic acid. It was very vexous and had a tendency to gel.

In most current cements, the liquid contains,

- Polyacrylic acid in the form of copolymer with itionic acid,
maleic acid and tricarballylic acid.

- Tartaric acid.
- Water.

Copolymerizing with iticonic, maleic or tricarballyic acid tends to

increase reactively of the liquid, decreases viscosity and reduce tendency

for gelation.

Tartaric acid – improves the handling characteristics, increases working

time and shortens setting time.

Water – is the most important constituent of the cement liquid, it is the

reaction medium and it hydrates the reaction products. The amount of water

in the liquid is critical. Too much water results in a weak cement while too

little impairs the reaction and subsequent hydration.

Water Settable Cements

One glass coromix formulation consists of freeze dried acid powder

and glass powder in one bottle and water or water with tartaric acid in

another bottle as the liquid component. This extends the working time.

When the powder is mixed with water, the polyacrylic acid powder goes

into solution to reconstitute the liquid acid. Then the chemical reaction

proceeds as for powder and liquid. These cements have a longer working

time with a shorter setting time and are occasionally referred to as water

settable GIC’s and erroneously as anhydrous GIC’s.

CHEMISTRY OF THE SETTING REACTION

When the powder and liquid are mixed together, the acid liquid

attacks the surface of the glass particles. Thus, calcium, aluminium, sodium

and fluoride ions are leached into the aqueous medium, probably in the

form of complexes. The polyacrylic acid chains are cross-linked by the

calcium ions and form a solid mass.

As the cement natures over the first 24 hours and beyond,

progressive cross linking occurs and the set cement becomes stronger and

less moisture sensitive. The salts hydrate to form a gel matrix and the
unreacted glass particles are sheathed by silica gel which arises from

removal of cations from the surface of the particles.

The set cement consists of agglomerates of unreacted powder

particles surrounded by silica gel and embedded in an amorphous matrix of

hydrated Ca and Al polysalts.

Role of water in the setting process:

The water content of the cement is an important part of its structure.

It serves as the reaction medium initially, and it then slowly hydrates the

cross linked matrix, thereby increasing the strength of the material. The

water is sometimes referred to as being loosely band or tightly bond.

The loosely bound water is that which is easily removed by

dessication and it decreases with time.

Tightly bound cannot be removed by dessication. If freshly mixed

cements are kept isolated from the ambient air, the loosely held water will

slowly become tightly bound over time. Of the same mixes are exposed to

ambient air without any covering, the surface will crack and craze as a

result of the dessication. Any contamination by water that occurs at this

stage can cause dissolution of the matrix forming cations and anions to the
surrounding areas. So, the cement must be protected from water changes in

structure during placement and for a few weeks after placement if possible.

Working and setting times:

Type I glass ionomer cement has a working time ranging from 3-5

minutes. The water settable cements have somewhat longer working times.

The setting time for the different brands of cement is usually between 5 and

9 minutes. The water added cements have a more rapid initial set than those

that use the polyacid liquid.

Properties:

1) Film thickness – 25µm or less.

2) Compressive strength after 24 hours is 90-140Mpa.

3) Diametral tensile strength after 24 hours is 6-8Mpa.

4) Modulus of elasticity (Gpa) – 7.3.

5) Solubility and disintegration in water (wt%) – 1.25%. Solubility in

water during the first 24 hours is high. It is important that the cement

should be protected from any moisture contamination during this

period. After the cement has been allowed to nature fully, it becomes
 one of the most resistant of the non resin cements to solubility and

disintegrates in the oral cavity.

6) Good adhesion to enamel and dentin – 225MN/m2 after 7 days – The

bonding is due to the reaction between the carboxyl groups of the

polyacids and the calcium in the opacity of the enamel and dentine.

The bond of enamel is always higher than that to dentin probably due

to greater inorganic content of enamel and its greater homogeneity.

7) Biologic properties: The water settable cements show higher acidity

as compared to powder / polyacrylic acid. Type I GIC are more

hazardous, because of the high acidity and slower set, which is due

to the lower powder/ liquid ratio.

Precautions should be taken to protect the pulp when cementing

restoration with glass ionomer. The biologic considerations take

precedence over other matters, such as the potential for adhesion that

ensures a strong bond to the tooth structure. The smear layer on the cut

surface of the cavity preparation should not be removed but should be

left intact to act as barrier to the penetration of the tubules by the acid
 component of the cement. All the deep areas of the preparation should

be protected by a thin layer of a hard setting Ca(OH) 2 cement.

8) Anticariogenic properties: Type I glass ionomer cements release

fluoride over an extended period time. The adjacent enamel and more

remove areas take up fluoride so, the anticariogenic effect is ensured

at the margins. In addition, due to its adhesion effect they have the

potential for reducing infiltration of oral fluids at the cement tooth

interface thereby there by preventing secondary caries.

MANIPULATION

As described for polycarboxylate cement surface preparation, cement

mixing and excess cement removal are areas of concern.

As glass ionomer has a potential adhesion to tooth surface, the

prepared tooth surface should be cleaned with a slurry of pumice, rinsed

and then dried but not dehydrated. Under dessication opens up the tubules,

again enhancing penetration of the acidic liquid.

The mixing procedure is similar to that described for zinc

polycarboxylate cement. The powder is introduced into the liquid in large

increments and spatulated rapidly for 30 to 45 seconds. The recommended

P:L ratio varies with different brands, but it is in the range of 1.25 to 1.5gm

of powder per 1ml of liquid.

As the cement does not bond properly to the metal in the chemically

contaminated as cast or picked condition, the inside surface should be

cleaned cementation should be carried out before the cement loses its

glossy surface. Glass ionomer like ZnPO4 becomes brittle once it has set,

and excess should be removed by flicking or breaking at the margin when

the cement hardens. This cement is susceptible to water during setting,

therefore the margins of the restoration should be coated to protect the

cement from premature exposure to water.

PRECAUTIONS:

1) The mix should have a glossy surface as this indicates that the during

the reaction the pressure of residual polyacid has not been used up in

the setting reaction. This ensures adhesive bonding to the tooth. The

mix with the dull surface should be discarded as it indicates

prolonged mixing and reduces the adhesion.

2) Liquid should not be placed in the refrigerator if it contains

polyacids as it becomes very viscous.

 3) Glass slab should not be cooled below dew point, as moisture may

condense on the slab and change the acid-water balance.

METAL-MODIFIED GLASS IONOMER CEMENT (CERMET)

These cements were developed in an attempt to improve the strength,

fracture toughness and resistance to wear and get maintain the potential for

adhesion and anticariogenic property. Two methods were employed:

1) Silver alloy admixed : The spherical amalgam alloy powder is mixed

with Type II GIC powder – Simons (1983) : MIRACLE MIX.

2) Cermet : Silver particles are bonded to glass powder particles by

fusion. This is achieved by sintering of a mixture of the powders at a

high temperature developed by McLean and Gasser (1985).

Properties:

1) Mechanical properties:

- The strength properties of either type of metal modified

cements (150Mpa) are not greatly improved over that of

conventional cement.
 - Fracture toughness is the same as conventional GIC.

- Ceramic material for more resistant to wear than GIC.

- Compressive strength (24 hour) : 15Mpa (22,000 psi).

- Diametral tensile strength (24 hour): 6.7Mpa (970 psi).

- Hardness (kHN) – 39.

2) Anticariogenic properties:

Due to bleaching of fluoride both metal modified ionomers have

anticariogenic capability.

However less fluoride is released from cermet cement than from

Type II GIC, since a portion of the original glass particle is metal

coated. The admixed cement release more fluoride than Type II GIC,

since the metal filler particles are not bonded to the cement matrix and

this, pathways for fluid exchange are created, which greatly increase the

surface area for leaching of fluoride.

 3) Esthetics:

Unsuitable as anterior restoration due to the presence of metallic

which impart a grey colour.

Clinical considerations:

1. Due to there brittle nature then use is restricted for

restoration of conservative Class I cavities as an alternative to

amalgam or composite resins. They are particularly suited for use in

young patients who are prone to caries.

2. They can be used for core-build up for teeth to be

restored with cast crowns but not in cases where the cement

constitutes more than 40% of the total core build up.

RESIN-MODIFIED GLASS IONOMER CEMENT

Bracket and Robinson (1990); Guin (1993); Hammisfahr (1994);

Mclean (1994) developed light cured resin-modified glass ionomers. These

have a variety of different chemistries and setting behavior.

 Guin (1993), Croll (1993) and Mclean (1994) found that the

mechanical properties, compared to conventional glass ionomer cements

were improved light cure glass ionomer cements have been used as lining

materials beneath composite restorations. (Davidson and Abdalla, 1993)

and for Class I restoration in permanent teeth (Croll 1993).

Lin et al (1992) and Smith (1992) gave evidence that light cured

resin-modified glass ionomers penetrated through the smear layer and

established mechanical interlocking in the dentinal tubules.

Tasaki and Hirota (1994) suggested the feasibility of using light-

cured resin modified glass ionomers as luting agents for composite and

ceramic inlays based on their properties.

Slow acid base reactions resulting in moisture sensitivity and low

early strength are seen in conventional glass ionomer cements. Therefore

these groups of materials were introduced to impart additional curing

processes that can overcome these two inherent drawbacks and allow the

bulk of the material to mature through the acid-base reaction. These

materials have been given several names such as:

1) Light cured GIC’s.

 2) Dual cure GICs (for light cured and acid base reaction).

3) Tri-cure GICs (dual cure + chemical cure).

4) Resin-ionomers.

5) Compomers.

6) Hybrid ionomers (not used anymore).

Composition:

Powder: Non-bleachable glass.

Initiators for light or chemical curing or both.

Liquid: Water

Polyacrylic acid or polyacrylic acid with some carboxyl group

with some carboxylic groups modified with methacrylate and hydroxyethyl

methacrylate monomers.

Setting reaction:

Polymerization of methacrylate groups taken place initially and the

final maturity and strength are achieved by the slow acid base reaction. The

overall water content is less for this type of material to accommodate the

polymerizable ingredients. A slower setting reaction of cements with an

acid base reaction is expected compared with that for resin-modified GIC

and base reaction.

Properties:

1. Physical properties:

Variations of properties from glass ionomer cements can be

attributed to the presence of polymerizable resins and lesser amount of

water and carboxylic acids in the liquid. There is a reduction in

translucency because of a difference in the refractive index between the

powder and set resin matrix.

2. Strength of resin modified glass ionomers are higher than

conventional GICs due to the greater plastic deformation that can be

sustained before fracture occurs.

- Compressive strength (24 hour): 105 Mpa (15,000 psi).

- Diametral tensile strength (24 hour): 20Mpa (2,900 psi).

- Hardness (kHN) : 40.

3. Adhesion to tooth structure is similar to conventional GICs.

4. Microleakage is greater than conventional GICs when these

cements are used as liners with a higher P:L ratio. This is due to the

lower water and carboxylic acid content which reduces the ability of the

cement to wet tooth substrate.

5. Water sensitivity: This cement group is still susceptible to

dehydration and can absorb water which produce significant

dimensional changes.

6. Clinical considerations:

- Use of calcium hydroxide for deep preparation.

- Transient temperature increase associated with polymerization

process.

7. Solubility is low.

8. Anticariogenic property is high.

9. Biologic effect : Initial pH is higher (pH-4) than conventional

GIC (pH-2).

10. Film thickness > 25µm.

11. Working time: 2-4 minutes.

12. Setting time: 2 minutes.

Applications:
1) Metal or porcelain fused to metal crowns and freed partial dentures.

2) Liner.

3) Fissure sealant.
 4) Base.

5) Core-build up.

6) Restoration.

7) Adhesive for orthodontic brackets.

8) Repair material for damaged amalgam cores or cusps.

9) Retrograde root filling.

Luting agents harden by setting reactions that lead to the fabrication

of metal polyacrylate salts and a polymer.

These cements hardens by an acid base reaction between fluoro-

alumino silicate glass powder and an aqueous solution of polyalkenoic

acids modified with findout methacrylate groups, and by photo-initiated on

chemical inverted free radical polymerization of methacrylate.

They are of two types:

1) Resin ionomer.
2) Compomers.

Properties:
Property Resin ionomer Compomer
1) Film thickness. > 25µm > 25µm
2) Working time. 2-4 min. 3-10 min.
3) Setting time. 2 min. 3-7 min.
4) Compressive strength. 40-141 Mpa 174-200Mpa
5) Modulus of elasticity. n/a 17 Gpa
6) Pulp irritation. High High
7) Solubility. Very low Very low
8) Microleakage. Very low High to very high
9) Removal of ions. Medium Medium
10) Retention. N/a Moderate
11) Anticariogenic High High

Advantages

Chemical bond to enamel and dentin.

Anticariogenic effect.

Coefficient of thermal expansion similar to that of tooth structure.

High compressive strength.

Low solubility

Disadvantages

Low initial pH which may lead to post cementation sensitivity.

Sensitivity to both moisture contamination and desiccation.

The latest development involving the use of glass ionomers as luting agents

has been the introduction of self-cured hybrid resin/glass-ionomer products

such as Fuji Plus (formerly Fuji Duet, GC America), FujiCem (GC

America), and RelyX (formerly Vitremer Luting Cement, 3M ESPE).

Hybrid resin/glass ionomers were initially introduced as light-activated

liners/bases and later as dual-activated restorative materials. These new

cements have several advantages compared to traditional glass-ionomer

luting agents such as Ketac-Cem, Ketac-Cem Aplicaps, and Fuji Cap I.

They have greater tensile strength and are less brittle. In addition, they

12
release at least as much fluoride as traditional glass ionomers, are less

soluble, and are less sensitive to moisture contamination and desiccation. 13

Although the three brands are similar in that they are all self setting (i.e.,

self curing), differences exist between them in many ways (e.g., how the

prepared tooth is treated prior to luting and the number of clinical uses for

the cement). For example, no additional treatment is performed prior to

using RelyX. With Fuji Plus, however, the prepared tooth surface must be

treated immediately before luting with an acidic conditioner. While RelyX

is used only for luting, Fuji Plus is used for luting as well as a liner/base.

FujiCem is the only one of the three that is a twopaste system; the other two

are powder and liquid. It is important to know that these cements should not

be used to lute all-ceramic crowns such as IPS Empress (Ivoclar) or In-

Ceram (Vident) because of clinical fractures. Most researchers believe this

is due to post-placement hydrolytic expansion of the cement caused by

water sorption.
Additional Cement Facts

Cement Rankings

1. Compressive Strength (highest to lowest):

Resin; glass ionomer; zinc phosphate; polycarboxylate; ZOE

2. Solubility (lowest to highest):

Resin; glass ionomer; zinc phosphate; polycarboxylate; ZOE

3. Cement film thickness is dependent upon powder-to-liquid ratio, powder

particle size, and pressure generated during seating of the casting.

The most important clinical property of a cement is solubility. Generally a

cement dissolves when the solvent attacks the cement's matrix, however

with zinc polycarboxylate cements, both the matrix and powder particles

are attacked.

Increasing a cement's powder-to-liquid ratio generally has the following

effects:

compressive strength: increases

 solubility: decreases

pH: increases

viscosity: increases

film thickness: increases

setting time: shortens it because more powder surface area is

available for acid interaction

When using zinc phosphate, resin, and glass-ionomer cements, researchers

have found that increasing the roughness of the internal surfaces of castings

using coarse-grit aluminum oxide in an air abrader significantly increases

the retention of the castings compared to using fine-grit aluminum oxide.14

The roughness of the preparation also affects retention. In another study

using zinc phosphate cement, retention was significantly greater for

castings cemented to preparations made with a diamond bur than to those

prepared with a carbide bur.15

One way to reduce the potential for post-cementation sensitivity with zinc

phosphate and glass-ionomer cements is to use a resinbased desensitizer on

the prepared tooth prior to luting. Recent research has found that this type

of desensitizer does not adversely affect crown retention.16

Cement Summary and Indications for Use

Zinc Phosphate Cement: a good choice for routine prosthodontic use; has a

long, positive clinical history but must be used properly to avoid

postcementation sensitivity.

Zinc Polycarboxylate Cement: acceptable for single units or

short span fixed partial dentures; chemically bonds to tooth

structure and is extremely kind to the pulp; recommended for

cases involving hypersensitive teeth.

Zinc Oxide-Eugenol Cement: acceptable for single units and

short span fixed partial dentures; has an obtundent effect on the

pulp but low strength and moderately high solubility.

Resin Cement: excellent choice for luting porcelain, cast

ceramic, and composite resin restorations; possesses high

strength and low solubility but can cause pulpal sensitivity.

12
 Glass-Ionomer Cement: excellent for general prosthodontic

use especially when the patient would benefit from fluoride

release; exhibits low solubility with the ability to chemically

bond to tooth structure and leach fluoride; avoid using when

teeth are hypersensitive.

Recommended Cements for Clinical Use

Encapsulated Glass-Ionomer Cement: for routine use.

Examples are Fuji Cap I, Ketac-Cem Aplicap, and Ketac-

Cem Maxicap.

Zinc Polycarboxylate Cement: for cases involving

hypersensitive teeth or where preparations encroach on

the pulp. Examples are Durelon and Tylok Plus.

Adhesive Resin Cement: for cases where inadequate

retention/resistance form exists after preparation

(i.e., preparation is overtapered and/or short).

Examples are Panavia 21 and C&B-Metabond.

Product name Filler Particle Curing Shelf Resin Working Setting time
content size life fully time
1) C to B 46% 5µm Self 2 yrs BISGMA 3-4 min. 6-7 min.
 luting
composite.
2) C to B Unfilled 1µm Self 2 yrs BISGMA 1 min. 10 min.
methanol
3) Cavit. 68% 1µm Self 2 yrs BISGMA 3 min. 4 min.
4) CPVS 80% 6µm Dual 2.5yrs BISGMA 5 min. 7 min.
5) Dicon 74% 2-9µm Dual 1 yr. BISGMA 3-4 min. 11 min.
MGC
6) Dual 61% Microfil Dual 2 yr. BISGMA 4-6 min. 14-20min.
cement
7) Duo 71% 0.5µm Dual 6m BISGMA 4 min. 8 min.
cement
8) Duo 67% 1µm Dual 3 yrs BISGMA 3.5 min. 8 min.
link 66% 1µm Light/dual 1 yr BISGMA 3 min. 6 min.
9) Km 71% 4µm Light/dual 1 yr BISGMA 2 min. 8 min.
force 65% 8µm Self 2 yrs BISGMA 2 min. 5 min.
10) FLC 77% 3µm Dual 2 yrs BISGMA 3.5 min. 7-5 in.
vision 75% 1.5µm Light/dual 3 yrs BISGMA 0.5 min. 8-8.5 min.
11) Flexi 65% 0.8µm Light/dual x BISGMA 5 min. 4-5 min.
flow 68% 0.6µm Light/dual 1.5yrs BISGMA 3.5 min. 10 min.
12) IDRC 82% 1.4µm Light/dual 3 yrs BISGMA 4 min. 6 min.
13) Insure
14) Lute it 75% n/a Self - BISGMA 3 min. 1 min.
15) Nexus 77% n/a Self - BISGMA * 1 min.
16) Opal 70% 1.5µm Dual 2 yrs BISGMA * 6-8 min.
luting 78% 1.4µm Dual 3 yrs BISGMA 5 min. 6 min.
composite
17) Panavi 73% 0.7µm Dual 13 m BISGMA 3 min. 4-5 min.
a n/a n/a Light/dual 14 m BISGMA n/a n/a
18) Panavi 73% 1µm Light/dual 1.5yrs BISGMA 4 min. 15 min.
a 21
19) Permul
ate
20) Scotch
bond
resilient
21) Twin
lock
22) Ultrab
ond
23) Varolli
um

References

1. Hondrum SO. Effects of evaporation on the properties of

water-based dental luting agents. Gen Dent 2000;48:286-290.

2. Schwartz NL, Whitsett LC, Berry TG, Stewart JL.

Unserviceable crowns and fixed partial dentures: life-span and

causes for loss of serviceability. J Am Dent Assoc 1970;81:1395-

1401.

3. Burke FJT, Fleming GJP, Nathanson D, Marquis PM. Are

adhesive technologies needed to support ceramics? An assessment

of the current evidence. J Adhes Dent 2002;4:7-22.

4. Tjan AH, Li T. Seating and retention of complete crowns with

a new adhesive resin cement. J Prosthet Dent 1992;67:478-483.

5. Caughman WF, O _Connor RP, Williams HA, Rueggeberg FA.

Retentive strengths of three cements using full crown

preparations restored with amalgam. Am J Dent 1992;5:61-63.

6. Eakle WS, Giblin JM. Retention strength of tin plated gold

inlays bonded with two resin cements. Gen Dent 2000;48:406-410.

7. El-Mowafy OM, Rubo MH, El-Badrawy WA. Hardening of new resin

cements cured through a ceramic inlay. Oper Dent 1999;24:38-44.

8. McComb D. Adhesive luting cements - classes, criteria, and

usage. Compend Contin Ed Dent 1996;17:759-773.

9. Burrow MF, Nikaido T, Satoh M, Tagami J. Early bonding of

resin cements to dentin - effect of bonding environment. Oper

Dent 1996;21:196-202.

10. Mayhew JT, Windchy A, Sleet HW, Gettleman L. Effect of

sealant cement and irrigation agents on dentatus post retention

luted with Panavia 21 [Abstract]. J Dent Res 1996;75:55.

11. Ganss C, Jung M. Effect of eugenol-containing temporary

cements on bond strength of composite to dentin [Abstract]. J

Dent Res 1996;75:127.

11&12.

12. Robertello FJ, Coffey JP, Lynde TA, King P. Fluoride

release of glass ionomer-based luting cements in vitro. J

13

Prosthet Dent 1999;82:172-176.

13. McComb D. Adhesive luting cements - classes, criteria, and

usage. Compend Contin Ed Dent 1996;17:759-773.

14. Juntavee N, Millstein PL. Effect of surface roughness and

cement space on crown retention. J Prosthet Dent 1992;68:482-

486.

15. Felton DA, Kanoy BE, White JT. The effect of surface

roughness of crown preparations on retention of cemented

castings. J Prosthet Dent 1987;58:292-296.

16. Swift EJ, Lloyd AH, Felton DA. The effect of resin

desensitizing agents on crown retention. J Am Dent Assoc

1997;128:195-200.