Dental Liners and Bases Guide

College of DentistryCollege of Dentistry
Operative Dentistry IIOperative Dentistry II
Intermediary Liners & Bases -2-Intermediary Liners & Bases -2-
Dr. Hazem El AjramiDr. Hazem El Ajrami

B.B. Suspension Liners:Suspension Liners:
These are aqueous liners that have theirThese are aqueous liners that have their
constituents suspended in water instead ofconstituents suspended in water instead of
dissolved. They produce the same effect asdissolved. They produce the same effect as
varnish but have greater film thickness (20-25varnish but have greater film thickness (20-25
µm). They are not quite as fast forming asµm). They are not quite as fast forming as
varnish because their water content should bevarnish because their water content should be
absorbed or evaporated to produce a solid film.absorbed or evaporated to produce a solid film.

 Cavity liner suspensions are combination ofCavity liner suspensions are combination of
alkaline calcium hydroxide and other basic metalalkaline calcium hydroxide and other basic metal
oxides (zinc oxide) in a resinous solution tooxides (zinc oxide) in a resinous solution to
provide a protective film having greater physicalprovide a protective film having greater physical
integrity, chemical neutralizing capacity forintegrity, chemical neutralizing capacity for
acids as well as pulpal protection. Unfortunately,acids as well as pulpal protection. Unfortunately,
the film thickness in which this material isthe film thickness in which this material is
applied is insufficient to provide any thermal orapplied is insufficient to provide any thermal or
electrical insulation. Examples for commerciallyelectrical insulation. Examples for commercially
available products include Hypocal andavailable products include Hypocal and
Pulpdent.Pulpdent.

C.C. Cement Liners:Cement Liners:
Types:Types:
1)1) Calcium hydroxide {Ca(OH)Calcium hydroxide {Ca(OH)22}.}.
2)2) Zinc oxide eugenol (ZOE).Zinc oxide eugenol (ZOE).
3)3) Glass ionomer cement (GIC).Glass ionomer cement (GIC).
4)4) Resin modified glass ionomer (RMGI).Resin modified glass ionomer (RMGI).

• Cement liners are materials placed in mediumCement liners are materials placed in medium
thickness (l00-500 µm) to provide pulpalthickness (l00-500 µm) to provide pulpal
medication and/or chemical protection. There aremedication and/or chemical protection. There are
two important aspects of pulpal medication; relieftwo important aspects of pulpal medication; relief
of pulpal inflammation and facilitating ofof pulpal inflammation and facilitating of
dentinal bridging for physiologic protection.dentinal bridging for physiologic protection.
Eugenol and calcium hydroxide are commonlyEugenol and calcium hydroxide are commonly
used to provide these functions.used to provide these functions.

• However, they are not mutuallyHowever, they are not mutually
compatible and cannot be used in the samecompatible and cannot be used in the same
formulation. Newer liners (GIC andformulation. Newer liners (GIC and
RMGI) place less emphasis on pulpalRMGI) place less emphasis on pulpal
medication and focus more on chemicalmedication and focus more on chemical
protection by sealing and on mechanicalprotection by sealing and on mechanical
protection.protection.

• Cement liners and cement bases are not fullyCement liners and cement bases are not fully
distinguishable in many cases.distinguishable in many cases.
• Modified formulations of Ca (OH)Modified formulations of Ca (OH)22 and ZOEand ZOE
can be used as cement base materials. GIC andcan be used as cement base materials. GIC and
RMGI are available as liner and as baseRMGI are available as liner and as base
formulations. Thus, the detailed use of theseformulations. Thus, the detailed use of these
cements as liners will be discussed together withcements as liners will be discussed together with
its use as base; with reference to difference inits use as base; with reference to difference in
formulations that makes a material suitable forformulations that makes a material suitable for
use as a liner or as a base.use as a liner or as a base.

• As a general rule, decreasing the Powder/LiquidAs a general rule, decreasing the Powder/Liquid
ratio of the cement will lead to a decrease inratio of the cement will lead to a decrease in
strength and an increase in flow and solubility.strength and an increase in flow and solubility.
The cement in this case is suitable for use as aThe cement in this case is suitable for use as a
liner or luting cement. While increasing theliner or luting cement. While increasing the
Powder/Liquid ratio will increase strength andPowder/Liquid ratio will increase strength and
decrease flow and solubility, then the cement isdecrease flow and solubility, then the cement is
used as base or temporary filling material.used as base or temporary filling material.
• N.B.: All cement liners and bases have someN.B.: All cement liners and bases have some
degree of solubility in oral fluids. Thus, theydegree of solubility in oral fluids. Thus, they
should be placed only on dentin and completelyshould be placed only on dentin and completely
removed from cavity walls and margins.removed from cavity walls and margins.

II.II. Cement Bases:Cement Bases:
Basically, these are materials with thickBasically, these are materials with thick
consistency applied in thick sections (500-2000consistency applied in thick sections (500-2000
µm) to substitute lost dentin and provide thermalµm) to substitute lost dentin and provide thermal
and mechanical pulpal protection.and mechanical pulpal protection.
Types of bases:Types of bases:
1)1) Resinous Hard-setting Calcium hydroxideResinous Hard-setting Calcium hydroxide
{Ca(OH){Ca(OH)22}.}.
2)2) Reinforced Zinc oxide and eugenol (RZOE).Reinforced Zinc oxide and eugenol (RZOE).
3)3) Zinc phosphate cement (ZPC).Zinc phosphate cement (ZPC).
4)4) Zinc polycarboxylate (PCC).Zinc polycarboxylate (PCC).
5)5) Glass ionomer (GIC).Glass ionomer (GIC).
6)6) Resin modified glass ionomer (RMGI).Resin modified glass ionomer (RMGI).

• Evolution of base cements:Evolution of base cements:
Zinc phosphate cement and reinforced ZincZinc phosphate cement and reinforced Zinc
oxide eugenol cements were widely used asoxide eugenol cements were widely used as
bases before the 1960s. Polycarboxylate cementbases before the 1960s. Polycarboxylate cement
gained popularity starting from 1970, as thegained popularity starting from 1970, as the
first adhesive dental cement. Glass ionomerfirst adhesive dental cement. Glass ionomer
cements became more popular afterwards,cements became more popular afterwards,
starting 1972. It was formulated by bringingstarting 1972. It was formulated by bringing
together the powder of silicate cement andtogether the powder of silicate cement and
liquid of PCC. The following figure shows theliquid of PCC. The following figure shows the
evolution as well as the basic composition ofevolution as well as the basic composition of
these cements.these cements.

Calcium hydroxide:Calcium hydroxide:
Form and Composition:Form and Composition:
It can be supplied as:It can be supplied as:
Two pastes (Chemical-cured), e.g.: Dycal andTwo pastes (Chemical-cured), e.g.: Dycal and
Life.Life.
One paste (Light-cured), e.g.: Dycal andOne paste (Light-cured), e.g.: Dycal and
Timeline.Timeline.

• Ca(OH)Ca(OH)22 can also be supplied as powder only orcan also be supplied as powder only or
made in suspension with water. However, directmade in suspension with water. However, direct
placement of these forms is as a liner isplacement of these forms is as a liner is
contraindicated since it is saturated andcontraindicated since it is saturated and
extremely caustic and can thus cause chemicalextremely caustic and can thus cause chemical
burns. The paste formulations, however, allowburns. The paste formulations, however, allow
low concentrations of calcium and hydroxyllow concentrations of calcium and hydroxyl
ions to be released to produce the desired effections to be released to produce the desired effect
of reparative dentin formation.of reparative dentin formation.

• As a liner, it is composed of calcium hydroxideAs a liner, it is composed of calcium hydroxide
dispersed in aqueous or resinous solutions. Thedispersed in aqueous or resinous solutions. The
development of ‘hard-setting’ Ca(OH)development of ‘hard-setting’ Ca(OH)22 has led tohas led to
decreased usage of Ca(OH)decreased usage of Ca(OH)22 suspensions. Thesuspensions. The
two-paste system comprises an acidic paste oftwo-paste system comprises an acidic paste of
alkyl salicylate and inert fillers for radiopacityalkyl salicylate and inert fillers for radiopacity
and a basic paste of calcium hydroxide. Theand a basic paste of calcium hydroxide. The
setting reaction is an acid-base to produce ansetting reaction is an acid-base to produce an
alkaline paste of PH = 11. The final set cement isalkaline paste of PH = 11. The final set cement is
hydrolytically instable; calcium, hydroxyl andhydrolytically instable; calcium, hydroxyl and
salicylate ions are continuously released from thesalicylate ions are continuously released from the
mass. With time, the entire mass will disappearmass. With time, the entire mass will disappear
from under the restoration.from under the restoration.

Properties and Indications:Properties and Indications:
Ca(OH)Ca(OH)22 is applied for pulpal medication whenis applied for pulpal medication when
the remaining dentin bridge is ≤ 0.5mm or inthe remaining dentin bridge is ≤ 0.5mm or in
direct contact with exposed pulpal tissue. It willdirect contact with exposed pulpal tissue. It will
stimulate odontoblasts to form reparative dentinstimulate odontoblasts to form reparative dentin
and form calcific bridging at the exposure site.and form calcific bridging at the exposure site.
It also relieves pulpal inflammation. This isIt also relieves pulpal inflammation. This is
owed to calcium ion concentration, alkalinityowed to calcium ion concentration, alkalinity
and antibacterial potential of this cement. It isand antibacterial potential of this cement. It is
thus used in direct or indirect pulp capping.thus used in direct or indirect pulp capping.

It is porous and soluble; therefore it is neitherIt is porous and soluble; therefore it is neither
an electric insulator nor a chemical insulator.an electric insulator nor a chemical insulator.
However, its alkalinity has a neutralizing effectHowever, its alkalinity has a neutralizing effect
on acids of subsequently placed base oron acids of subsequently placed base or
restorative material.restorative material.

Conventional formulations used as liners are tooConventional formulations used as liners are too
thin to provide thermal insulation. On the otherthin to provide thermal insulation. On the other
hand, resinous hard-setting formulations havehand, resinous hard-setting formulations have
excellent handling characteristics and can beexcellent handling characteristics and can be
built up to the thickness required for thermalbuilt up to the thickness required for thermal
insulation. These formulations are strong enoughinsulation. These formulations are strong enough
to withstand condensation forces, but since theyto withstand condensation forces, but since they
degrade over time, they can no longer providedegrade over time, they can no longer provide
mechanical support for the restoration.mechanical support for the restoration.

Hard-setting formulations rely on resin matricesHard-setting formulations rely on resin matrices
and this makes the release of Ca and OH ionsand this makes the release of Ca and OH ions
much more difficult.much more difficult.
It is compatible with pulp-dentin organ, baseIt is compatible with pulp-dentin organ, base
materials and all restorative materials. It has nomaterials and all restorative materials. It has no
effect on the setting reaction or properties ofeffect on the setting reaction or properties of
any base or restorative material.any base or restorative material.

Manipulation:Manipulation:
It is applied only onto the required area,It is applied only onto the required area,
when remaining dentin thickness ≤ 0.5mm.when remaining dentin thickness ≤ 0.5mm.
Water is an important component for theWater is an important component for the
chemical setting of Ca(OH)chemical setting of Ca(OH)22. To start the setting. To start the setting
reaction, some Ca(OH)reaction, some Ca(OH)22 must be dissociated bymust be dissociated by
moisture into Calcium ions. Thus, the sitemoisture into Calcium ions. Thus, the site
should not be dried excessively.should not be dried excessively.

Zinc oxide and eugenol (ZOE and RZOE):Zinc oxide and eugenol (ZOE and RZOE):
It is supplied in the form of a powder of zincIt is supplied in the form of a powder of zinc
oxide and a liquid of 85% eugenol or oil of clove.oxide and a liquid of 85% eugenol or oil of clove.
Many salts are added to accelerate the settingMany salts are added to accelerate the setting
reaction, such as zinc succinate. Polymers are alsoreaction, such as zinc succinate. Polymers are also
added to increase the strength and homogeneity ofadded to increase the strength and homogeneity of
the mix, and to decrease the flow and solubility.the mix, and to decrease the flow and solubility.

• Fillers such as silica or alumina may also beFillers such as silica or alumina may also be
added to increase the strength. In the modifiedadded to increase the strength. In the modified
formulations (RZOE), used as base material,formulations (RZOE), used as base material,
substitution of a portion of eugenol with ethoxysubstitution of a portion of eugenol with ethoxy
benzoic acid results in an appreciable increase inbenzoic acid results in an appreciable increase in
strength, yet the solubility is dramaticallystrength, yet the solubility is dramatically
increased. The setting reaction is a chelationincreased. The setting reaction is a chelation
reaction, where eugenol chelates zinc producingreaction, where eugenol chelates zinc producing
zinc eugonolate (or zinc benzoate in RZOE) andzinc eugonolate (or zinc benzoate in RZOE) and
water as a byproduct.water as a byproduct.

Functions:Functions:
It has multiple pharmacological actions.It has multiple pharmacological actions.
Eugenol produces palliative, sedative andEugenol produces palliative, sedative and
obtundant action on the pulp when used in veryobtundant action on the pulp when used in very
low concentrations. ZOE also has an antisepticlow concentrations. ZOE also has an antiseptic
and anti-inflammatory effect. It is thus used toand anti-inflammatory effect. It is thus used to
alleviate discomfort resulting from mild-to-alleviate discomfort resulting from mild-to-
moderate pulpal inflammation.moderate pulpal inflammation.
ZOE can be placed in moderately deep cavities,ZOE can be placed in moderately deep cavities,
when remaining dentin thickness is as low as lwhen remaining dentin thickness is as low as l
mm. However, RZOE can have irritating actionmm. However, RZOE can have irritating action
on pulp-dentin organ at this depth.on pulp-dentin organ at this depth.

It is an excellent thermal insulator in a filmIt is an excellent thermal insulator in a film
thickness as low as 0.25 mm.thickness as low as 0.25 mm.
It is an excellent electrical insulator and has a goodIt is an excellent electrical insulator and has a good
sealing ability.sealing ability.
ZOE has low strength properties, not rigid enoughZOE has low strength properties, not rigid enough
to be used as a base. Despite improved strengthto be used as a base. Despite improved strength
properties of RZOE, it is still inferior to that ofproperties of RZOE, it is still inferior to that of
other cements.other cements.

Indications:Indications:
ZOE can be used as a liner in moderately deepZOE can be used as a liner in moderately deep
cavities to enhance pulpal healing.cavities to enhance pulpal healing.
It can also be used as a temporary fillingIt can also be used as a temporary filling
material and for temporary cementation.material and for temporary cementation.
RZOE can be used as a base material, whenRZOE can be used as a base material, when
biological consideration is more important thanbiological consideration is more important than
mechanical one.mechanical one.

Contraindications:Contraindications:
Cannot be placed in very deep cavities (dentinCannot be placed in very deep cavities (dentin
bridge ≤ 0.5mm) or as a direct pulp cappingbridge ≤ 0.5mm) or as a direct pulp capping
material.material.
With resinous tooth colored restoratives, asWith resinous tooth colored restoratives, as
eugenol interferes with the setting reaction ofeugenol interferes with the setting reaction of
any polymer and can even depolymerize alreadyany polymer and can even depolymerize already
set polymeric materials.set polymeric materials.
With glass ionomer cements as well asWith glass ionomer cements as well as
polycarboxylate cement, where it would deprivepolycarboxylate cement, where it would deprive
the bonding capabilities of these materials.the bonding capabilities of these materials.

Manipulation:Manipulation:
After proper proportioning of Powder/LiquidAfter proper proportioning of Powder/Liquid
ratio, incorporation of all powder into liquid isratio, incorporation of all powder into liquid is
done. The zinc oxide is slowly wetted by thedone. The zinc oxide is slowly wetted by the
eugenol; therefore, prolonged and vigorouseugenol; therefore, prolonged and vigorous
spatulation is required to produce a homogenousspatulation is required to produce a homogenous
mix, especially for a base or temporary fillingmix, especially for a base or temporary filling
consistency. Water is an important component forconsistency. Water is an important component for
the setting reaction of ZOE; the setting reactionthe setting reaction of ZOE; the setting reaction
can be accelerated with moisture.can be accelerated with moisture.

Zinc phosphate cement (ZPC):Zinc phosphate cement (ZPC):
Form and Composition:Form and Composition:
ZPC is supplied in the form of a powder and aZPC is supplied in the form of a powder and a
liquid. The powder is mainly zinc oxide, with upliquid. The powder is mainly zinc oxide, with up
to 10% magnesium oxide. The liquid is ato 10% magnesium oxide. The liquid is a
buffered 45-55% aqueous solution ofbuffered 45-55% aqueous solution of
orthophosphoric acid. The setting reaction is anorthophosphoric acid. The setting reaction is an
acid-base reaction producing amorphous zincacid-base reaction producing amorphous zinc
phosphate.phosphate.

Properties:Properties:
It has high compressive strength. It is theIt has high compressive strength. It is the
most rigid, tough and durable intermediarymost rigid, tough and durable intermediary
base material and thus provides bestbase material and thus provides best
mechanical protection.mechanical protection.
It is an excellent thermal insulator inIt is an excellent thermal insulator in
thickness of 1 mm or more. It also providesthickness of 1 mm or more. It also provides
good electrical protection.good electrical protection.

It is the most irritating base material, owing toIt is the most irritating base material, owing to
its acidic PH. Two minutes after the start ofits acidic PH. Two minutes after the start of
mixing, the PH is approximately 2, and then itmixing, the PH is approximately 2, and then it
will increase to reach neutrality after 48 hours.will increase to reach neutrality after 48 hours.
It has an exothermic setting reaction and canIt has an exothermic setting reaction and can
thus cause thermal irritation if not properlythus cause thermal irritation if not properly
manipulated.manipulated.
It has no effect on the setting reaction orIt has no effect on the setting reaction or
properties of any permanent restorative materialproperties of any permanent restorative material
or base.or base.

Indications:Indications:
Used as a base under metallic restorations andUsed as a base under metallic restorations and
as a luting cement.as a luting cement.
Contraindications:Contraindications:
Cannot be used as liner as its acidity can beCannot be used as liner as its acidity can be
detrimental to pulp-dentin organ.detrimental to pulp-dentin organ.
It is not recommended to place ZPC whenIt is not recommended to place ZPC when
remaining dentin bridge is less than 1.5 mmremaining dentin bridge is less than 1.5 mm
without an underlying protective liner (sub-without an underlying protective liner (sub-
base).base).

Manipulation:Manipulation:
Two important points should be consideredTwo important points should be considered
during manipulation of ZPC. First, that theduring manipulation of ZPC. First, that the
reaction is exothermic; we need to neutralize orreaction is exothermic; we need to neutralize or
dissipate the heat of the reaction. Second, thedissipate the heat of the reaction. Second, the
reactivity of the powder with the liquid is veryreactivity of the powder with the liquid is very
violent and very fast. Thus, we need to extend theviolent and very fast. Thus, we need to extend the
working time during manipulation of the cementworking time during manipulation of the cement
into a base in order to incorporate the maximuminto a base in order to incorporate the maximum
amount of powder into the liquid.amount of powder into the liquid.

• To achieve this, a dry cool glass slab must beTo achieve this, a dry cool glass slab must be
used. In addition the powder should beused. In addition the powder should be
incorporated in small increments into the liquidincorporated in small increments into the liquid
and spatulated over a wide area. Properand spatulated over a wide area. Proper
proportioning of the powder/liquid and the timingproportioning of the powder/liquid and the timing
of mixing are also essential factors in successfulof mixing are also essential factors in successful
manipulation of the cement.manipulation of the cement.

Zinc polycarboxylate cement (PCC):Zinc polycarboxylate cement (PCC):
Form and Composition:Form and Composition:
PCC is supplied in the form of a powder and aPCC is supplied in the form of a powder and a
liquid. The powder is mainly zinc oxide withliquid. The powder is mainly zinc oxide with
small amounts of magnesium oxide and silica.small amounts of magnesium oxide and silica.
The liquid is an aqueous solution of 40-50%The liquid is an aqueous solution of 40-50%
polyacrylic acid. The setting reaction involves thepolyacrylic acid. The setting reaction involves the
release of zinc and magnesium ions which blendrelease of zinc and magnesium ions which blend
with the carboxylic groups forming a cross-linkedwith the carboxylic groups forming a cross-linked
polyacrylate matrix. The carboxylic groups thatpolyacrylate matrix. The carboxylic groups that
did not enter the reaction will chelate calcium ofdid not enter the reaction will chelate calcium of
the hydroxyapatite of the tooth structure andthe hydroxyapatite of the tooth structure and
chemically bond to the tooth.chemically bond to the tooth.

Properties and functions:Properties and functions:
It bonds chemically to tooth structure, whichIt bonds chemically to tooth structure, which
leads to proper chemical protection as well asleads to proper chemical protection as well as
decreased micro-leakage.decreased micro-leakage.
The PH of the cement liquid is (1.7). In spiteThe PH of the cement liquid is (1.7). In spite
of its initial acidic nature, it producesof its initial acidic nature, it produces
minimal irritation to pulp-dentin organ. Thisminimal irritation to pulp-dentin organ. This
is probably due to:is probably due to:

 The PH of the mixed setting cement rises rapidlyThe PH of the mixed setting cement rises rapidly
to 3.4 after two minutes from the start of mixing.to 3.4 after two minutes from the start of mixing.
 Polyacrylic acid is weaker than phosphoric acid.Polyacrylic acid is weaker than phosphoric acid.
 Polyacrylic acid has low diffusion mobility intoPolyacrylic acid has low diffusion mobility into
the underlying dentin due to its large molecularthe underlying dentin due to its large molecular
size and because of immediate complexing withsize and because of immediate complexing with
fluoride and calcium of tooth structure whichfluoride and calcium of tooth structure which
would hinder further penetration of the acid.would hinder further penetration of the acid.

PCC has somewhat lower compressive strengthPCC has somewhat lower compressive strength
than ZPC, but significantly higher tensilethan ZPC, but significantly higher tensile
strength. It provides proper mechanicalstrength. It provides proper mechanical
protection.protection.
It is a good thermal insulator in thickness notIt is a good thermal insulator in thickness not
less than 1.5 mm. It is also an electricalless than 1.5 mm. It is also an electrical
insulator.insulator.
It is compatible with all permanent restorativeIt is compatible with all permanent restorative
materials. It is compatible with othermaterials. It is compatible with other
intermediary materials with the exception ofintermediary materials with the exception of
ZOE and varnish.ZOE and varnish.

Indications:Indications:
It is used as a base under any restorativeIt is used as a base under any restorative
material and as luting cement.material and as luting cement.
Manipulation:Manipulation:
The setting reaction, like that of ZPC, isThe setting reaction, like that of ZPC, is
vigorous and fast. It has short working time (halfvigorous and fast. It has short working time (half
that of ZPC). The use of a cool dry glass slab isthat of ZPC). The use of a cool dry glass slab is
essential to extend the working time. The powderessential to extend the working time. The powder
also may be cooled but not the liquid since coolingalso may be cooled but not the liquid since cooling
increases its viscosity. Quick incorporation ofincreases its viscosity. Quick incorporation of
powder into liquid is performed. The mix shouldpowder into liquid is performed. The mix should
be glossy during insertion indicating thebe glossy during insertion indicating the
availability of unreacted carboxylic groups foravailability of unreacted carboxylic groups for
chemical adhesion.chemical adhesion.

Glass ionomer cements (GIC and RMGI):Glass ionomer cements (GIC and RMGI):
GIC is composed of an acid-soluble fluoro-GIC is composed of an acid-soluble fluoro-
alumino-silicate glass powder and a liquid ofalumino-silicate glass powder and a liquid of
polyacrylic acid (PAA), copolymers of PAApolyacrylic acid (PAA), copolymers of PAA
(iticortic, maleic and tricarballylic acids), in(iticortic, maleic and tricarballylic acids), in
addition to tartaric acid which increases reactivityaddition to tartaric acid which increases reactivity
and decreases the viscosity of liquid. The settingand decreases the viscosity of liquid. The setting
is through acid-base reaction.is through acid-base reaction.

• RMGI is a hybrid ionomer modified by resinRMGI is a hybrid ionomer modified by resin
monomers, usually Hydroxy Ethyl Methacrylatemonomers, usually Hydroxy Ethyl Methacrylate
(HEMA), added to the liquid, while photo-(HEMA), added to the liquid, while photo-
activated accelerator is added to the powder. Theactivated accelerator is added to the powder. The
setting of RMGI is basically by acid-basesetting of RMGI is basically by acid-base
reaction, in addition to immediate commandreaction, in addition to immediate command
setting light polymerization.setting light polymerization.

Properties and functions:Properties and functions:
It has an excellent sealing ability due toIt has an excellent sealing ability due to
chemical adhesion to tooth structure throughchemical adhesion to tooth structure through
carboxylate ions released from PAA liquid.carboxylate ions released from PAA liquid.
It has an anticariogenic property due to fluorideIt has an anticariogenic property due to fluoride
release from the powder glass component.release from the powder glass component.
It is biocompatible with P-D organ and allIt is biocompatible with P-D organ and all
permanent restorative materials. However, ifpermanent restorative materials. However, if
remaining dentin thickness is less than l mmremaining dentin thickness is less than l mm
protection of the pulp by a layer of Ca(OH)protection of the pulp by a layer of Ca(OH)22
liner is needed.liner is needed.

It provides adequate thermal, chemical andIt provides adequate thermal, chemical and
mechanical protection as well as proper sealing ofmechanical protection as well as proper sealing of
dentinal tubules. It is thus an excellent material todentinal tubules. It is thus an excellent material to
be used as dentin substitute.be used as dentin substitute.
Advantages of RMGI over GIC:Advantages of RMGI over GIC:
It has a flexible working time due to commandIt has a flexible working time due to command
setting by light curing. It also has improvedsetting by light curing. It also has improved
strength and wear properties in addition to ease ofstrength and wear properties in addition to ease of
handling. However, GIC has higher fluoridehandling. However, GIC has higher fluoride
release especially during the first 24 hours (initialrelease especially during the first 24 hours (initial
fluoride burst).fluoride burst).

Indications:Indications:
These are versatile materials; having manyThese are versatile materials; having many
uses in dentistry. They can be used as liners,uses in dentistry. They can be used as liners,
bases, luting cements as well as restorations. Bothbases, luting cements as well as restorations. Both
GIC and RMGI can be used as a liner/base underGIC and RMGI can be used as a liner/base under
any restoration. They are especially chosen underany restoration. They are especially chosen under
resin composite restoration in a technique knownresin composite restoration in a technique known
as the sandwich technique to combine the benefitas the sandwich technique to combine the benefit
of adhesion and fluoride release of GI with betterof adhesion and fluoride release of GI with better
esthetic and higher mechanical properties of resinesthetic and higher mechanical properties of resin
composite.composite.

• In addition, the use of GI base under resinIn addition, the use of GI base under resin
composite reduces the total volume of the cavitycomposite reduces the total volume of the cavity
preparation, thereby reducing the totalpreparation, thereby reducing the total
volumetric polymerization shrinkage of resinvolumetric polymerization shrinkage of resin
composite. Moreover, it does not interfere withcomposite. Moreover, it does not interfere with
the esthetics and optical properties of resinthe esthetics and optical properties of resin
composite. It is also more economical andcomposite. It is also more economical and
reduces the cost of the final restoration. RMGI isreduces the cost of the final restoration. RMGI is
more popular as a liner/base under resinmore popular as a liner/base under resin
composite owing to its ease of handling and itscomposite owing to its ease of handling and its
ability to bond to resin composite.ability to bond to resin composite.

Manipulation of GIC and RMGI:Manipulation of GIC and RMGI:
To promote adhesion, the cavity should beTo promote adhesion, the cavity should be
conditioned with polyacrylic acid before GIC andconditioned with polyacrylic acid before GIC and
RMGI application. Both materials are available asRMGI application. Both materials are available as
powder and liquid to be hand-mixed or in pre-dosedpowder and liquid to be hand-mixed or in pre-dosed
capsules that are mechanically mixed and thencapsules that are mechanically mixed and then
injected into the cavity. Manipulation of GIC isinjected into the cavity. Manipulation of GIC is
carried out in the same way as PCC. Packing of thecarried out in the same way as PCC. Packing of the
cement should be done before it loses its glossycement should be done before it loses its glossy
appearance, in order to gain its full adhesiveappearance, in order to gain its full adhesive
potential. GIC will undergo chemical acid basepotential. GIC will undergo chemical acid base
reaction during setting, while RMGI is dual-cured;reaction during setting, while RMGI is dual-cured;
first through light activated polymerization, then thefirst through light activated polymerization, then the
conventional acid-base reaction proceeds in theconventional acid-base reaction proceeds in the
usual manner.usual manner.

 Clinical considerations for use ofClinical considerations for use of
intermediary materials:intermediary materials:
Clinical judgment for the need of a specificClinical judgment for the need of a specific
liner or base material depends mainly on:liner or base material depends mainly on:
I.I. Remaining dentin thickness (RDT);Remaining dentin thickness (RDT); as theas the
depth of the cavity increases, the RDTdepth of the cavity increases, the RDT
decreases and there is more need fordecreases and there is more need for
intermediary materials before inserting theintermediary materials before inserting the
permanent restoration.permanent restoration.

II.II. Adhesive properties of liner or base;Adhesive properties of liner or base; to benefitto benefit
from its adhesive potential, an intermediaryfrom its adhesive potential, an intermediary
material should be placed directly on toothmaterial should be placed directly on tooth
structure except where pulpal medication isstructure except where pulpal medication is
essential.essential.
III.III. Type of restorative material;Type of restorative material; whether is awhether is a
metallic or adhesive esthetic restoration, a directmetallic or adhesive esthetic restoration, a direct
or indirect one.or indirect one.
A summary of clinical recommendations forA summary of clinical recommendations for
various restorative procedures at different cavityvarious restorative procedures at different cavity
depths are presented in the following table:depths are presented in the following table:

• After shallow tooth excavation (RDT ≥ 2mm),After shallow tooth excavation (RDT ≥ 2mm),
there is no need for pulpal protection other thanthere is no need for pulpal protection other than
chemical protection (i.e. sealing). In case of anchemical protection (i.e. sealing). In case of an
amalgam restoration, only a solution lineramalgam restoration, only a solution liner
(varnish, dentin sealer or bonding system in case(varnish, dentin sealer or bonding system in case
of bonded amalgam) is utilized. In case of resinof bonded amalgam) is utilized. In case of resin
composite, only its bonding system is needed.composite, only its bonding system is needed.
GIC restoration does not need any pulpalGIC restoration does not need any pulpal
protection in this case. While in case of indirectprotection in this case. While in case of indirect
restoration, a solution liner is needed for sealingrestoration, a solution liner is needed for sealing
in addition to the use of luting cement. In castin addition to the use of luting cement. In cast
gold restoration, a varnish or dentin sealer may begold restoration, a varnish or dentin sealer may be
used while with composite/ceramic inlays aused while with composite/ceramic inlays a
dentin bonding agent is used with luting cement.dentin bonding agent is used with luting cement.

• In moderately-deep caries excavation (RDT = 0.5-In moderately-deep caries excavation (RDT = 0.5-
2 mm), amalgam restoration would require the use2 mm), amalgam restoration would require the use
of a cement liner/base that is capable of pulpalof a cement liner/base that is capable of pulpal
sedation, e.g. ZOE or Ca(OH)sedation, e.g. ZOE or Ca(OH)22 in addition to ain addition to a
solution liner for sealing. With resin composite,solution liner for sealing. With resin composite,
dentin bonding agent will provide sufficientdentin bonding agent will provide sufficient
sealing, while a liner/base of GIC or RMGI mightsealing, while a liner/base of GIC or RMGI might
sometimes be needed to reduce the volume of thesometimes be needed to reduce the volume of the
cavity preparation not for pulpal protection. GICcavity preparation not for pulpal protection. GIC
restoration does not need placement of anyrestoration does not need placement of any
intermediary material. Indirect restorations willintermediary material. Indirect restorations will
also need sealing in addition to liner/base andalso need sealing in addition to liner/base and
luting cement.luting cement.

• If extensive dentin is lost (RDT ≤ 0.5mm), thereIf extensive dentin is lost (RDT ≤ 0.5mm), there
is strong need for pulpal protection. In this case,is strong need for pulpal protection. In this case,
pulpal medication with Ca(OH)pulpal medication with Ca(OH)22 is essential withis essential with
all restorative materials to induce secondaryall restorative materials to induce secondary
dentin formation and relief pulpal inflammation.dentin formation and relief pulpal inflammation.
Sealing is also essential in addition to a strongSealing is also essential in addition to a strong
base to substitute dentin loss. Thus, the samebase to substitute dentin loss. Thus, the same
recommended procedures for sealing andrecommended procedures for sealing and
placement of base cement previously mentionedplacement of base cement previously mentioned
for moderate depth (RDT = 0.5 - 2mm) becomesfor moderate depth (RDT = 0.5 - 2mm) becomes
mandatory at this depth (RDT ≤ 0.5mm).mandatory at this depth (RDT ≤ 0.5mm).

 Important considerations:Important considerations:
1.1. Sequence of placement of intermediarySequence of placement of intermediary
materials:materials:
The thickness of dentin bridge (RDT) and theThe thickness of dentin bridge (RDT) and the
dentist knowledge of the properties of thedentist knowledge of the properties of the
intermediary as well as the final restorativeintermediary as well as the final restorative
material, provides proper judgment for thematerial, provides proper judgment for the
sequence of placement of the chosen intermediarysequence of placement of the chosen intermediary
materials. It is clear that a material used for pulpalmaterials. It is clear that a material used for pulpal
medication, e.g. Ca(OH)medication, e.g. Ca(OH)22 should be directly placedshould be directly placed
on dentin. Requirements for sealing versuson dentin. Requirements for sealing versus
liner/base sequence depend mainly on the adhesiveliner/base sequence depend mainly on the adhesive
potential of these materials.potential of these materials.

• For instance, in a deep cavity preparation (RDTFor instance, in a deep cavity preparation (RDT
≤ 0.5mm), if an adhesive cement base (PCC,≤ 0.5mm), if an adhesive cement base (PCC,
GIC or RMGI) is chosen under amalgam or resinGIC or RMGI) is chosen under amalgam or resin
composite restoration, then the adhesive base iscomposite restoration, then the adhesive base is
applied directly over Ca(OH)applied directly over Ca(OH)22 medicament inmedicament in
direct contact with tooth structure to allowdirect contact with tooth structure to allow
chemical adhesion to occur. A sealer or bondingchemical adhesion to occur. A sealer or bonding
agent is then applied over the base. In contrast,agent is then applied over the base. In contrast,
an acidic cement base (ZPC) requires sealing ofan acidic cement base (ZPC) requires sealing of
dentin before its application.dentin before its application.

2.2. Dentin ledges:Dentin ledges:
With adhesive restorations, the tooth andWith adhesive restorations, the tooth and
restoration act as one unit. The tooth can thusrestoration act as one unit. The tooth can thus
benefit from mechanical support throughbenefit from mechanical support through
distribution of stresses from the restorationdistribution of stresses from the restoration
across the underlying dentin. However, whenacross the underlying dentin. However, when
placing metallic non-bonded restorationsplacing metallic non-bonded restorations
(amalgam and cast gold) in deep preparations,(amalgam and cast gold) in deep preparations,
the restoration should be seated or rested onthe restoration should be seated or rested on
sound dentin peripheral to the lined and/orsound dentin peripheral to the lined and/or
based regions that result from excavation ofbased regions that result from excavation of
carious dentin.carious dentin.

• These seats are called dentin ledges. TheseThese seats are called dentin ledges. These
seats maximize dentin contact areas and helpseats maximize dentin contact areas and help
distribute stresses laterally on sound dentindistribute stresses laterally on sound dentin
rather than rely on the cement base alone.rather than rely on the cement base alone.

3.3. With indirect restorations,With indirect restorations, any necessaryany necessary
base must be placed with its ownbase must be placed with its own
retentive features, either through mechanicalretentive features, either through mechanical
or chemical bonding. This guarantees that itor chemical bonding. This guarantees that it
will not be displaced during impressionwill not be displaced during impression
procedures or during removal of temporaryprocedures or during removal of temporary
restoration.restoration.

Dental Liners and Bases Guide

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