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
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Tooth-colored Restoratives: Principles and Techniques By
Harry F. Albers.
Resin modified glass-ionomers: Strength, cure depth and
translucency GJ Mount, C Patel, OF Makinson Australian Dental
Journal 2002;47:(4):339-343
Resin-ionomer restorative materials for children: A review K.
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
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The Influence of Hygroscopic Expansion of Resin-based
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Hygroscopic expansion of resin based composites during 6
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Film thicknesses of recently introduced luting cements
Andrew R. Kious, Howard W. Roberts, and William W. Brackett (J
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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
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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.)
Adhesion to Dentin and Physical Properties of a Light-cured
Glass-ionomer Liner/Base S.B. MITRA J Dent Res 70(1):72-74,
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Chemistry of glass-ionomer cements: a review John W. Nicholson
Biomaterials 19 (1998) 485-494