RESIN MODIFIED GLASS

IONOMERS

Resin modified glass ionomers were introduced in 1988

by Antonucci, Mc Kinney and Mitra with an objective

to combine some of the desirable properties of glass-

ionomer (fluoride release and chemical adhesion) with

high strength and low solubility of resins.

Antonucci et al. originally used the term resin-modified

glass-ionomer as the trivial name and resin-modified

glass polyalkenoate as the systematic name.

INTRODUCTION

NOTE: Although sometimes are referred to as

visible light curing GIC or hybrid GIC, such terms

should be discouraged as they are insufficiently

specific and can be confused with some of the

compomer materials.

Like the name implies, Resin-modified glass-

ionomer (RMGI) is a hybrid material derived from

adding water soluble polymers or polymerizable

resins to conventional glass-ionomer cement.

These materials can be

1. Chemically cured (chemical-cured, acid base

reaction)

2. Dual cured (light-cured and acid–base reaction)or

3. Tri-cured (chemical-cured ,light-cured and acid–

base reaction).

RMGI is available as

1. Powder/liquid

2. Pre proportioned

encapsulated form

3. Paste/Paste systems

NOTE: The powder liquid components are initially

hand mixed and loaded into the delivery system;

which facilitates the placement of the material

directly into the cavity.

This minimizes the inclusion of air bubbles and

voids. But, the delivery system has been criticized for

being fiddly and cumbersome as it can be difficult to

load the material into syringe.

COMPOSITION

Resin-modified glass-ionomers are of the glass-ionomer

family, and they contain basic ion-leachable glass

powder and a water-soluble polymeric acid such as

poly(acrylic acid).

In addition, they contain organic resin monomers,

typically 2-hydroxyethyl methacrylate (HEMA), and an

associated initiator system.NOTE: The choice of resin is limited by the fact that

glass ionomers are water-based materials and so the

resin needs to be water-soluble. HEMA is a very

effective hydrophilic monomer in this respect, as it

readily dissolves in water.

In addition to HEMA, some brands of resin-modified

glass ionomers are modified by the inclusion of

branches grafted onto the parent poly(acrylic acid).

These branches end in vinyl groups, and are capable of

copolymerizing with HEMA, once initiation has

occurred.

Which means, these particular RMGIs develop organic

cross links as they cure.

In powder liquid systems

Powder—Consists of an ion-leachable glass and

initiators for chemical/light-curing.

Enables polymerization reaction.

Reacts with the ion-leachable glass to allow acid–base

reaction

HEMA a hydrophilic methacrylate, enables both the resin

and acid components to coexist in an aqueous solution; It

also takes part in the polymerization reaction.

Water allows ionization of the acid component so that

acid–

base reaction can occur.Other components include polymerization activators and

stabilizers

Bis-GMA

1

POLYACRYLIC ACID

2

HEMA

3

WATER

4

LIQUID—CONTAINS FOUR MAIN INGREDIENTS

In chemically polymerized materials, an example of an

initiator/activator system would be hydrogen peroxide

as the initiator, ascorbic acid as the activator, and

cupric sulphate as coactivator.

In light activated materials, camphorquinone is used

as a visible-light photochemical initiator, sodium p-

toluene sulphinate as the activator, and ethyl 4-N N

dimethyl amino benzoate as the photoaccelerator.

NOTE: The role of HEMA is

1. To polymerize the materials and positively enhance the

bond strength to tooth and dentin.

2. To enhance penetration of dental adhesives to dentin.

3. Performs as a co solvent and comonomer, which will

enhance water solubility of vinyl containing polyacid.

Water is responsible for calcium and aluminum cation

transportation to the polyacid. If there is not enough water

due to desiccation, the above reaction will stop resulting in

crazing..

SETTING REACTION

The setting reaction comprises an acid–base

reaction of the glass ionomer components

occurring without light and chemical

polymerization by a redox catalyst, without the

necessity of light.

Therefore, chemically-activated polymerization of

the resin-modified glass-ionomer cement is

referred to as ‘‘Dark Cure’’, because the reaction

occurs in absence of light.

CHEMICALLY ACTIVATED SYSTEMS

The setting reaction comprises an acid–base

reaction of the glass ionomer and a light-

activated free radical polymerization initiated by

visible light.

DUAL CURE SYSTEMS

Firstly, an acid/base reaction identical to that of

conventional glass ionomer cements.

Secondly, a light-activated free radical polymerization of

methacrylate groups of the polymer and HEMA initiated

by visible light and occurs only where the light penetrates.

However, as depth of cure through irradiation will be

limited by the depth of penetration of the light there is a

third setting reaction included so that any remaining

monomer that has not set photo-chemically will undergo a

chemical polymerization.

TRI CURE SYSTEMS

In general, in the resin-modified glass ionomer,

the setting reaction is a dual mechanism.

1) The usual glass ionomer acid-base reaction

begins on mixing the material, followed by

2) Free radical polymerization reaction which

may be generated by either photoinitiators or

by chemical initiators or both. If chemical

initiators are included, then the polymerization

reaction will begin on mixing as well.

1. ACID-BASE REACTION

From the start of mixing there will be the conventional

acid/base reaction with the poly acrylic acid protons

liberating metal ions and fluoride from the glass,

forming a silica hydrogel around the glass surface.

The rising aqueous phase pH causes poly salt

precipitates to form from the migrating ions, which act

as cross-links to the poly acrylic acid chains.

Acid-base reaction: Fluoro alumino silicate glass

(base) + poly(acrylic acid) = calcium and

aluminum poly salt hydrogel.

NOTE: The final set structure is a complex composite

of the original glass particles , sheathed by a siliceous

hydrogel and bonded together by a matrix phase of

hydrated fluoridated calcium and aluminium

polyacrylates.

COOHCOOH

COOH

COOH

ACID BASE REACTION

Fluoro alumino-silicate glass

Poly acrylic acid

Calcium and aluminumpolysalt hydrogel

CO

OH

CO

O-

CO

O-

CO

O-

Ca++

Al+

++

F-

CO

O-

COO-

COOHCOOH

COO-

H+

H+

COO-

COOH

COO-

COO

-

COO-Ca++Al+++

F-

COO-

COO-

CO

OH

CO

OH

CO

O-

H+H

+

The RMGI differs from convention glass ionomer in that

the acid/base reaction is much slower, giving a

considerably longer working time.

This is because the HEMA has replaced some of the

normal water content and water is an essential

component of the acid/base reaction.

NOTE : Acid/ base component will be partly set within

7 to 10 minutes but the gelation is relatively slow and

the reaction will continue for weeks or even months.

2. POLYMERIZATION

REACTION

The second reaction is the polymerization of HEMA

to poly HEMA.

Because of the incorporation of traces of

camphorquinone and a tertiary amine in the

formula, irradiation of the surface layer will initiate

polymerization of the HEMA and this will be

complete in less than one minute, providing the

initial set.

NOTE: The polymerization reaction rate is much

faster than the acid base reaction.

Free-radical or photochemical polymerization

process is similar to that used in composite resins.

HEMA in presenceof photochemical initiators and activators

Poly HEMA Matrix

POLYMERIZATION REACTION:

COMBINATION OF REACTIONS

OH

OH

OH

OH

OH

CO

OH

CO

O-

CO

O-

CO

O-

Ca+

+

Al+

++

F-

CO

O-

COO-

COOHCOOH

COO-

H+

H+

COO-

COOH

COOH

COO-

COO-Ca+

+Al+++

F-

COO-

COO-

CO

OH

CO

OH

CO

O-

H+H

+

COO-

COO-

COOH

COO-

COO-

Ca++

Ca++

OH

OHO

H

OH

OH

O

H

OH

OH

OH

OH

OH

OH

CO

OH

CO

O-

CO

O-C

a++

Al+++

F-

COO-

COO-

COOH

COOH

COO-

H+

H+

COO-

COOH

COO-

COO

-

COO-

Ca

++

Al+++F-

COO-

COO-

CO

OC

OO

H

CO

O-

H+

H+

2 SEPARATE MATRICES

Poly HEMA

Poly acrylate salt

NOTE : It is certain that, the two matrices for

thermodynamic reasons, will not interpenetrate but will

form separate phases, which is not a desirable situation.

Therefore, in the simple water/HEMA system, two

matrices are formed;

1) The ionomer salt hydrogel and

2) Poly HEMA.

The initial set of the resin-modified glass ionomer

cement is the result of formation of polymer matrix

and the acid-base reaction serves to harden and

strengthen the formed matrix.

To prevent phase separation, another version of resin

glass-ionomer cement bas been formulated.

This is Vitrabond and is termed as a Class II material,

where poly(acrvlic acid) (PAA) is replaced by modified

PAAs.

These are based on graft copolymers of poly(acrylic acid)

in which a minor proportion of the carboxylic acid

functional groups was replaced with cross-linkable

branches that were terminated in vinyl groups and are

capable of copolymerizing with HEMA once initiation has

occurred.

These materials, too, required HEMA to retain

all of the components in a single phase.

MODIFIED POLY ACRYLIC ACID

COOHCOOH

COOH

CH=CH2

CH=CH2

CH=CH2

When a resin glass-ionomer cement containing a

modified PAA and HEMA is mixed with the glass

powder and activated by light, several types of

polymerization can take place.

The HEMA will polymerize to form poly HEMA.

The modified PAA, because it contains

unsaturated groups, will copolymerize with

HEMA; thus, poly HEMA will be chemically

linked to the polyacrylate matrix and phase

separation will not occur.

OH

OH

OH

OH

OH

CO

OH

CO

O-

CO

O-

CO

O-

Ca+

+

Al+

++

F-

CO

O-

COO-

COOHCOOH

COO-

H+

H+

COO-

COOH

COO-

COO-

COO-Ca+

+Al+++

F-

COO-

COO-

CO

OH

CO

OH

CO

O-

H+H

+

COO-

COO-

COOH

COO-

COO-

Ca++

Ca++

OH

OHO

H

OH

OH

O

H

OH

OH

OH

OH

OH

OH

CROSS LINKS BETWEEN THE MATRICES

Poly HEMA

Poly acrylate salt

CO

OH

CO

O-

CO

O-C

a++

Al+++

F-

COO-

COO-

COOH

COOH

COO-

H+

H+

COO-

COOH

COO-

COO

-

COO-

Ca

++

Al+++F-

COO-

COO-

CO

OH

CO

OH

CO

O-

H+

H+

Also, the modified PAA will further polymerize to

form a cross linked PAA, which should increase

the strength of the cement.

NOTE: The matrix of such a cement will contain both

ionic and covalent cross links.

CLINICAL PROPERTIES

Bonding of RMGIC to tooth is due to dual mechanism

of adhesion.

As for conventional glass ionomer the mechanism of

adhesion is thought to be based on a dynamic ion

exchange process, in which the poly alkenoic acid

softens and infiltrates the hydroxyapatite structure

and displaces calcium and phosphate ions out of the

substrate to form an intermediate adsorption layer of

calcium and aluminum phosphates and polyacrylates

at the glass ionomer - hydroxyapatite interface.

ADHESION ADHESION TO TOOTH:

As for resin based adhesives, micro mechanical

bonding mechanism occurs.

Laboratory shear bond strength of the resin-

modified cement to dentine is significantly

higher than that of conventional glass ionomer

cement.

NOTE: It may be because of the slowness of the acid-

base reaction in the modified cement that the polyacid

is available for a longer period, resulting in the

formation of a stronger adhesive bond.

To take advantage of resin content in RMGI, the

use of various adhesive systems has been tried to

improve bond strength to tooth, but these have

yielded mixed results.

Some products are supplied with primers. These

are visible light cured liquids which are composed

of HEMA, ethanol, photo-initiators and a modified

poly acrylic acid.

These primers are acidic in nature and act by

modifying the smear layer and wetting the tooth

surface to allow adhesion of the RMGIC.

Commercially available primers are:

1. Fuji dentin conditioner (GC)

2. Vitremer primer (3M ESPE)

3. Nano-ionomer primer (3 M ESPE)

NOTE: The disadvantage of these materials is that

they usually infiltrate the dentin and make alternative

adhesive restorations less successful.

Resin-modified glass ionomers have the advantage of

being able to directly bond to resin composite.

RMGIs produce a catalyst rich air-inhibited layer

which can polymerize with the composite, making

them useful in glass ionomer/composite laminate

restoration. NOTE: The bond strength between conventional GIC and

composite is limited by the low cohesive strength of glass

ionomers due to the lack of chemical bonding. This is

because of difference in setting reaction between composite

resin and GIC.

ADHESION TO COMPOSITE RESIN:

NOTE: The clinical technique described by Mount

suggests etching the initially set GIC for 15 seconds prior

to placing a layer of resin bond to develop a mechanical

bond between the two materials.

Bond strengths improve if the GIC is etched after 24

hours of maturation. However, this procedure requires an

additional clinical visit to complete a restoration.

Therefore, RMGIC shows an advantage over conventional

GIC in laminate technique.

ADHESION TO OTHER MATERIALS:

RMGIs are commonly used as sub-lining of

calcium hydroxide. There is no interaction or

bonding between these two materials.

It is therefore important that the RMGIC layer is

extended beyond the extent of calcium hydroxide to

gain adhesion to the surrounding dentin to form a

seal.

When used for luting, they will form chemical

bonds with tooth and not to the cast restoration

being cemented.

Hydrophilic nature of the added resin results in

a varied degree of long-term water sorption

leading to volumetric expansion.

This may help to reduce these marginal

discrepancies and also relieves polymerization

shrinkage stresses that develop along cavity

walls during the initial setting stage of these

materials.

WATER SORPTION

But, water that is absorbed into resin matrices

acts as a plasticizer which weakens the physical

properties of these materials

Furthermore, excessive expansion can in itself

create stresses that may possibly result in

undesirable cuspal flexures and fracture of

brittle, unsupported tooth structures.

NOTE: The increased water absorption in RMGIs

also provides channels for rapid leaching of potentially

cytotoxic residual monomers and photoinitiators.

NOTE : Relatively long periods are required for

hygroscopic expansion to be effective, during which

ingress of bacteria and by-products could have

already induced irreversible damage to the pulpo-

dentinal complex. Thus, the concept of rapid

compensation for polymerization contraction via

hygroscopic expansion should be viewed with caution.

The inclusion of resin phase brings with it the problem

of polymerization shrinkage, which is greater than that

in resin based composites.

The measured shrinkage is more akin to unfilled acrylic

resin, being in the region of 3-4%

This shrinkage can lead to loss of adhesion as stresses

at the interface between the tooth and the restorative

are generated with the onset of light activated

polymerization reaction.

POLYMERIZATION SHRINKAGE

They are less translucent because of significant

difference in the refractive index between resin

matrix and powder particles.

ESTHETICS

MECHANICAL STRENGTH

Inclusion of the resin component into the conventional

glass ionomers allows rapid development of strength

and more resistance to early moisture contamination.

The set cement has improved diametral tensile

strength, compressive strength and elastic modulus,

when compared with its conventional counterparts.

The resinous component renders it tougher and less

brittle.

Comparison of compressive and diametral tensile strength of RMGIC and conventional GIC

Zinc phosphate (ZP) Flecks

Glass ionomer (GI) Fuji I luting

cement

Resin-modified glass ionomer (RMGI)

RelyX Vitremer luting cement

Dual-polymerization resin (D-P R1),

photopolymerized (P) or

unphotopolymerized (U)

Dual-polymerization resin (D-P R2),

photopolymerized (P) or

unphotopolymerized (U)RelyX

Adhesive Resin Cement

Comparison of flexural strength among different luting agents

t 24 Hrs

Comparison of flexural strength among different RMGI

RMGIs are twice as flexible as water-based glass

ionomers and have a lower modulus of elasticity.

A cement with high modulus of elasticity is

important to provide better resistance to

deformation under occlusal force and marginal

gap formation.

Therefore a stiff material is required in regions of

high masticatory stress or in long span

prostheses and also to prevent micro leakage.

MODULUS OF ELASTICITY

Zinc phosphate (ZP) Flecks

Glass ionomer (GI) Fuji I luting

cement.

Resin-modified glass ionomer

(RMGI) RelyX Vitremer luting

cement.

Dual-polymerization resin (D-P R1),

photopolymerized (P) or

unphotopolymerized (U) Calibra.

Dual-polymerization resin (D-P R2),

photopolymerized (P) or

unphotopolymerized (U) RelyX

Adhesive Resin Cement.

Comparison of modulus of elasticity among different luting agents

NOTE: The low modulus of elasticity of RMGI can

have unfavorable consequences for long term success

if there is a thick layer of luting material remaining

between the restoration and the tooth.

The resin-modified glass ionomer cement had a

higher initial pH (3.6) than the conventional glass

ionomer and the zinc phosphate cement and has a low

reported incidence of pulpal sensitivity.

Resin-modified glass ionomer products for luting

therefore have a low reported incidence of pulpal

sensitivity. NOTE: The low initial pH values for the zinc phosphate

(2.2) and

conventional GIC (1.6) could contribute to the postoperative

sensitivity. Hence, the use of varnishes or resin-based dentin

desensitizing primers should be considered for pulp

protection when these low pH luting agents are used and

when the remaining dentin thickness is minimal.

pH

pH values of different luting cements

These materials provide a sustained release of

fluoride, which occurs in the same way as with

conventional GIC.

Majority of the release occurs in the early life of

the cement, usually during the first 10-15 days,

which is slightly higher than conventional GIC.

FLUORIDE RELEASE

NOTE: Though, the external fluoride concentration is

increased, this may be at the expense of the

restoration as it starts to degrade.

The long term release with RMGIC is slightly

greater, which may be due to the slower setting

of the glass ionomer phase of the cement. It may

also be because the poly HEMA matrix could

provide an easier pathway for the ionic species to

migrate through the cement.

Current ISO standards require a film thickness at

the time of seating of no greater than 25 μm for

water-based luting cements, and no greater than

50 μm for resin-based cements.

FILM THICKNESS

NOTE:The film thickness increases at the 3-minute

interval; depicting that the resin-modified glass ionomer

cement is likely to produce incomplete seating of the

restoration if placement is delayed, so clinicians using this

type of luting cement should probably consider subdividing

the cementation of a large number of restorations.

According to Andrew et al’s study, within 2 min

after mixing the film thickness of these luting

cements is 25μm or less, which meets the

relevant ISO standard.

If the restoration is luted within this time, it will

not interfere with seating.

NOTE: Setting time often extends several minutes

after working time for luting materials, so occlusal

loading by the patient should be prevented until it is

certain the cement has set.

NOTE: HEMA release occurs mainly in the first 24h

after polymerization.

The monomer HEMA, which is an essential

component of resin-modified glass-ionomers, and is

released from these materials under all cure

conditions, has a variety of adverse biological effects.

These include cytotoxicity, inducing of apoptosis,

persistent inflammation, respiratory problems,

allergy and contact dermatitis.

BIOCOMPATIBILITY

NOTE : Even in its polymerized form bound in

RMGIC, if HEMA is placed directly onto vital pulp

tissue it may cause the death of the pulpal tissue. For

this reason their use in direct contact with the pulp is

contraindicated.

NOTE: Nitrile gloves, have been found to provide good

protection against the passage of HEMA, and are

therefore recommended.

HEMA is volatile and may be inhaled, a hazard for

which face-masks do not provide protection.

The eyes may also be exposed to this monomer

vapor.

Latex gloves are inadequate as protection for the

skin, because they have been found to be

permeable to HEMA and other monomers.

In order to use resin-modified glass-ionomer cements

safely, the following precautions are recommended.

1) Ensure that the work space is well ventilated.

2) Avoid inhalation of HEMA vapor.

3) Touch unset material only with instruments, never with

hands, even when wearing gloves;

4) Avoid contact of resin-modified cement (set or unset)

with the oral mucosa of the patient; use with a liner to

prevent diffusion of HEMA to the pulp.

5) Build-up restorations in increments (optimum

thickness 1mm, maximum thickness 2mm) to

enable each increment to be properly cured,

thereby reducing the amount of HEMA

available for release.

6) Light-cure unused remnants of cement before

disposal, to reduce the possibility of exposure to

volatile HEMA vapor.

Compressive strength, diametral tensile strength,

and flexural strength are dramatically improved in

comparison to zinc phosphate, polycarboxylate,

and glass-ionomer cements but is less than resin

composites.

Abrasion resistance and fracture resistance are

greater than GIC.

Fluoride release pattern is similar to glass

ionomer cements.

ADVANTAGES

Less sensitive to early moisture contamination and

desiccation during setting and less soluble than

the glass-ionomer cement because of covalent

cross-linking of the poly acrylate salt from free-

radical polymerization.

Ease of mixing and use, because multiple bonding

steps are not required.

Minimal post-operative sensitivity as there is no

etching required.

Have adequately low film thickness.

They bond to resin composite.

High bond strength to moist dentin (14 MPa)

Retention of resin-modified glass ionomer

cements is not significantly affected by eugenol-

containing provisional materials, as long as the

provisional cement is completely removed with a

thorough prophylaxis.

DISADVANTAGES

A significant disadvantage of the resin ionomers is the

hydrophilic nature of poly HEMA, which results in

increased water sorption and subsequent plasticity and

hygroscopic expansion in the order of 3%

Because the matrix of the material is a mixture of

hydrogel salt and polymer light scattering will be greater

than in the conventional material; especially zinc-

containing glass of Class II-type materials is opaque,

making it difficult to formulate a translucent material.

After the snap set of the cement, the hard bulk of the

poses problems in excess removal.

If one waits for a longer time during cementation in the

posterior area of the mouth where embrasures are

small and tooth contacts large, proper removal of the

cement may be extremely difficult without damage to

tissues, which would expose the early cement margin

to blood, greatly reducing the bond strength and

accelerating erosion.NOTE : A dilemma results in that removal of excess

must occur right after the initial set, which may pull

unset material form under the restoration margin.

Most RMGI come encapsulated, which simplifies

mixing, but a unit dose price can be up to 35

times that of zinc phosphate cement.

Low flexural strength.

Resin ionomer cements present concerns

regarding biocompatibility due to the presence of

free monomer in the liquid.

Although rare, dimethacrylates may elicit an

allergic response in certain persons and careful

handling by dental personnel is recommended

during mixing.

Originally formulated as liner/base materials,

modern RMGIs can be used as restorative

materials, for core build-up and for luting.

INDICATIONS

PRODUCT GUIDE FOR LINERS/BASES

Vitrebond GC Fuji lining LC

Their use for luting purposes is becoming more popular

because of their relatively high bond strength to dentin,

and their ability to form a very thin film layer.

They are recommended to be used for luting metal or

porcelain fused- to-metal crowns and FPDs to tooth,

amalgam, resin composite, or glass ionomer core

buildups.

They are highly retentive when used with high strength

alumina or zirconium core all-ceramic crowns.

PRODUCT GUIDE FOR LUTING CEMENTS

Rely X Luting Rely X Luting Plus

Fuji Plus Ultracem

Clinical reports for specific uses, such as Class V

restorations, have shown them to be reliable

materials that give good results in terms of both

aesthetics and durability.

They have found particular use in pediatric

dentistry.

RMGICs have compressive strengths to

withstand occlusal load and provide adequate

wear properties for the posterior primary

dentition.

These are particularly useful in children less

than the age of 4, when cooperative behavior is

not anticipated.

OCCLUSAL CLASS II, III AND V RESTORATIONS:RESTORATIONS IN PEDIATRIC PATIENTS

NOTE: The advantages of not needing to acid etch tooth

structure before restoration placement and knowing that

the chemical setting reaction will occur, even in the

absence of light, makes the RMGIC favorable for the

pediatric patents, where speed is critical and isolation of

tooth is difficult.

NOTE :It may be due to thicker peritubular dentin in

primary teeth and relatively less intertubular dentin.

Since intertubular dentin is the major area where

resin bonding occurs, primary teeth dentin provides

lower bond strength with composite when compared

to permanent teeth.

In a study by Prabhakar et al, the composite

showed higher mean shear bond strength in

permanent teeth as compared to resin modified

glass ionomer cement, whereas in primary teeth it

showed significantly lesser shear bond strength

compared to resin modified glass ionomer cement.

PRODUCT GUIDE FOR RESTORATIVE

MATERIALS

(LIGHT CURABLE)

Photac- Fil

Vitremer

Fuji II LC

The use of resin composites for orthodontic bonding

requires some loss of enamel during etching and

debonding and the debonding procedure is relatively

laborious. But, as the bond strength of RMGIC is lower

than resin cement, the debonding is easy.

The bond strength of RMGIC is higher than GIC.

Therefore, it doesn’t show a cohesive failure as in GIC,

and the orthodontic bond is not expected to fail during

the treatment.

ORTHODONTIC BONDING

Commercial product to cement orthodontic bands.

CONTRA-INDICATIONS

Their use for cementing posts in non vital teeth is

questionable because of the potential for

expansion-induced root fracture.

Because of potential for substantial dimensional

change due to hygroscopic expansion, these

cements are not recommended for luting all-

ceramic restorations that are susceptible to

etching(silicate ceramics)

NOTE :In-vitro studies have shown that ceramic

crowns crack between 3 and 12months after

cementation with both RMGIs and compomers.

CLINICAL HANDLING

Prior to the placement of the material, the dentin

should not be dehydrated.

The recommended technique for using the

accompanying primer depends on the product so

always consult the specific manufacturer’s directions

for use.

Generally , primers are applied for 20-30 s using a

brush and lightly air dried. This is critical as the

ethanol must evaporate.

The primer is then light cured for 20seconds.

HANDLING OF RESTORATIVE MATERIALS

Resin-modified glass ionomers have greater curing

shrinkage than the conventional chemically-cured

cements.

Therefore, incremental placement techniques should

always be used to ensure complete curing at depth and

to minimize polymerization shrinkage.

The depth of cure is significantly higher than the

average composite resin, that has been shown to be 2.0-

2.5mm, and the presence of the auto cure component is

an added safety factor in development of adhesion in the

depths of a deep cavity.

However, the material that has not been irradiated is

not as strong as that which has been irradiated.

Hence, incremental buildup of the restoration is

recommended for any situation where the light

source is further than 3mm from the floor of the

cavity. Caution: Clinicians seem to assume that depth of cure is

not an important consideration with these materials,

because the acid-base reaction can take place at any

depth. In reality, any such glass-ionomer structure would

set more sluggishly and be weaker than a purely acid-base

cement, in addition to which there would be free HEMA

monomer in that part of the restoration closest to the pulp.

Consequently, and contrary to clinical advice, depth of

cure does matter in these materials.

Most manufacturers state that immediate

polishing can be carried out after light-curing.

However, the setting reaction will continue slowly

for at least 24 hours and the best result can be

obtained if finishing is delayed.

When immediate polishing is required, care must

be taken not to overheat the restoration as this

may cause excessive drying and cracking and may

prevent setting of the ionomeric component.

POLISHING

Finishing of the RMGI may be carried out by removing

excess material (flash) using a sharp instrument.

Alternatively, rotary instruments with water spray and

either diamond or tungsten carbide finishing burs may

be used.

Final polishing can be done using aluminum oxide

polishing discs or silicone polishers.

NOTE: Acid-base setting phase progresses for 24

hrs. So, excessive finishing and polishing at the initial

appointment should be avoided.

Finishing glosses are available with some products.

These are light-cured, resin based solutions that

contain bis-GMA and tri(ethylene glycol) TEGDMA.

Their use is optional, but they provide a smoother

surface by filling any surface irregularities.

NOTE : The use of finishing glosses is not

recommended when the product is being used as a

core build up material as the oxygen inhibited surface

may react with some of the currently available

impression materials.

Clinically, mixing and manipulation of RMGI is

very similar to conventional glass-ionomer cement,

cleaning of the tooth is the same (the smeared

layer should not be removed by heavy pumicing).

The cement should be mixed closely following the

manufacturer’s directions on a glass slab or

mixing pad (if not pre-encapsulated) and the

restoration quickly seated with firm finger

pressure while the material has a glossy

appearance.

HANDLING OF LUTING AGENTS:

As soon as the cement begins to harden (snap set),

removal of excess should begin (especially in inter

proximal areas).

Excess removal must be done quickly (or removal can

be extremely difficult) and carefully so as not to pull

material out from under the restoration margins.

As for glass-ionomer, the tooth should be well isolated

and the material kept dry for 7 to 10 minutes to

minimize loss of cement at the margins due to early

solubility.

REFERENCES

Introduction to Dental Materials By Richard Van Noot 4th edition

The biocompatibility of resin-modified glass-ionomer cements

for dentistry John W. Nicholsona, Beata Czarnecka dental

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Tooth-colored Restoratives: Principles and Techniques  By

Harry F. Albers.

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translucency GJ Mount, C Patel, OF Makinson Australian Dental

Journal 2002;47:(4):339-343

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M. Y. Hse, S. K. Leung, S. H. Y. Wei, Australian Dental Journal

1999;44:(1):1-11

Resin-Modified Glass-lonomer Cements Alan D. Wilson, Int J

Prosthodont 1990:3:425-429

The Influence of Hygroscopic Expansion of Resin-based

Restorative Materials on Artificial Gap Reduction Cui Huanga

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Hygroscopic expansion of resin based composites during 6

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Andrew R. Kious, Howard W. Roberts, and William W. Brackett (J

Prosthet Dent 2009;101:189-192)

A Clinical Guide to Applied Dental Materials:  By Stephen J.

Bonsor, Gavin J. Pearson

Early Childhood Oral Health By Joel H. Berg, Rebecca L. Slayto -Book

Orthodontic Materials: Scientific and Clinical Aspects  By Wiliam A.

Brantley, Theodore Eliades-Book

Esthetic Dentistry in Clinical Practice  By Marc Geissberger-Book

A Review of Luting Agents Cornelis H. Pameijer International Journal

of Dentistry, Volume 2012, Article ID 752861.

Resin modified glass-ionomers: Strength, cure depth and

Translucency GJ Mount, C Patel,OF Makinson Australian Dental Journal

2002;47:(4):339-343

Current status of luting agents for fixed prosthodontics Ana M.

Diaz-Arnold, Marcos A. Vargas, and Debra R. Haselton, J Prosthet Dent

1999;81:135-41.)

Comparison of shear bond strength of composite, compomer

and resin modified glass ionomer in primary and permanent

teeth : An in vitro study Prabhakar et al J Indian Soc Pedo Prev Dent

September (2003) 21 (3) 86 - 94

A clinically focused discussion of luting materials EE Hill, J Lott

Australian Dental Journal 2011; 56:(1 Suppl): 67–76

Mechanical and physical properties of contemporary dental

luting agents Nuray Attar, Laura E. Tam, and Dorothy McComb,

Prosthet Dent 2003;89:127-34.)

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Glass-ionomer Liner/Base S.B. MITRA J Dent Res 70(1):72-74,

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