DEPARTMENT OF COSERVATIVE DENTISTRY &

ENDODONTICS

LUTING CEMENTS

PRESENTED BY: V.P.VINCY BERNICE , IV YEAR BDS

INTRODUCTIONLuting : the use of moldable substance to seal a

space between two component. Luting Agent:In dentistry it is used to seal the space

between the tooth and the restoration

LUTING AGENTCommonly used are

Zinc phosphate cementZinc Polycarboxylate Cement Zinc Oxide Eugenol Cement Glass Ionomer Cement RMGIC Resin cements

Zinc phosphate cement

Introduction Zinc phosphate is the oldest among cementing

agent.

It serves as “Gold Standard” for all dental cements, adopted by A.D.A. in 1935, with specification no 8. & it designates them as two types on the basis of intended use.

Type I: Fine grained for luting. Film thickness 25 um or lessType II: Medium grain for luting and filling. Film thickness not more than 40um

CompositionPowder Zinc oxide – 90% - Principal constituent

Magnesium oxide – 8% - Helps in hydration process during setting reaction

Other oxides(Bismuth trioxide,Calcium Oxide etc)-0.2% - improves smoothness of the mix

Silica - 1.4% - Act as filler.

LiquidPhosphoric acid – 38.2% (pH < 2) - reacts

with zinc oxide. The acid content is 33 % wtWaters - 36% - controls acid-base reactionAluminium and zinc phosphate – 16.2 %

reduces rate of reaction.Aluminium and Zinc -10 %

SETTING REACTIONWhen the powder is mixed with liquid , the

phosphoric acid attacks the surface of the particles - releases zinc ions into the liquid – aluminium, which already forms a complex with the phosphoric acid , reacts with zinc - zinc alumino phosphate gel on the surface of the remaining portions of the particles.

Water is critical to the reaction.ZnO + H3PO4 Zn3(Po4)2 + H2O

Changes in composition and reaction rates might occur due to degradation of the liquid or water evaporation from the liquid

Liquid degradation effects are exhibited as clouding of the liquid

Loss of water from acid increases the setting time

Working and Setting TimesMixing time of 1.5 – 2 minsSetting time – 2.5 – 8 minsThe following procedures can extend the

setting timeReducing P/L ratioMixing in incrementsProlonging the spatulation of last increment.Cooling the glass slab

Physical PropertiesCompressive strength :104MPaTensile strength:5.5MPaThermal conductivity : 3.11

mcal.cm/cm2.sec.KLow water solubility 0.04wt%

More soluble in dilute organic acidsModulus of elasticity:13.7GPa

Quiet stiff & resistant to elastic deformationLoss/Gain water content compressive tensile

strength.

RetentionDoesn’t involve reaction with surrounding hard

tissue/restorative material

No chemical interactions

Mechanical bonding at interfaces

Biological PropertiesAcidity of cement is quite high during the time

of application - presence of phosphoric acid2 min after the start of mixing , Ph is 2

increases rapidly

reaches about 5.5 in 24 hrsPulpal damage can occur during first few

hours.High heat production during setting of the

cement can also cause pulpal injury.

ManipulationIncorporate powder - liquidRecommended p/l ratio – 1.4gm - 0.5mlA cool mixing slab prolongs the working and

setting time

Liquid dispensed onto the slab

evaporation

Powder -several incrementsspatulated : 15 – 20 secssmaller quantities - first few

increments – working - setting time.

middle of the mixing – larger amounts of powder– to further saturate the liquid with newly formed zinc phosphate.

Finally , smaller increments are added – so that the desired ultimate consistency of the cement is not exceeded

begins & ends with small increments

String test

Proper consistency for luting :

The mixture is strung up the mixture should produce about

a 1 inch “string” (without separation) when stretching the mixture up with a spatula.

Frozen Slab Method In this method, a glass slab is cooled in a

refrigerator at 6"C or a freezer at-10' C.No attempt is made to prevent moisture from

condensing on the slab when it is brought to room conditions. A mix of cement is made on the cold slab by adding the powder until the correct consistency is reached.

The amount of powder incorporated with the frozen slab method is50% to 75% more than with the normal procedures.

 The compressive and tensile strength of cement prepared by the frozen slab method are not significantly different from those prepared from normal mixes.

However, because incorporation of condensed moisture into the mix in the frozen slab method counteracts the higher powder/liquid ratio.

No difference exists in the solubility of frozen slab and normal mixes.

Advantages :The advantages of the frozen slab method are

:A substantial increase in the working time (4

to 11 minutes) of the mix on the slab A shorter setting time(20% to40% less) of the

mix after placement into the mouth. This method has also been advocated for

cementation of bridges with multiple pins.

FACTORS GOVERNING THE RATE OF SET OF ZINC PHOSPHATE CEMENT

Controlled by manufacturer

A) Powder composition B) Degree of powder calcinationC) Particle size of the powderD) Water content of liquidE) Neutralization of liquid

A)Powder/ liquid ratio B) Rate of powder

incorporation C) Mixing temperature D) Manner of spatulation E) Water contamination or loss from fluid.

CONTROLLED BY THE OPERATOR

ApplicationsLuting permanent restorationsBasesCementation of orthodontic bandsProvisional restoration

ADVANTAGESLong track record

Good compressive strength

DRAWBACKS• Zinc phosphate is brittle.

• It has a relatively high solubility in the mouth and it

does not adhere to tooth substance.

• Zinc phosphate relies on mechanical interlocking for

its retentive effect.

• It does not provide any chemical bonding to tooth or metal surfaces.

Modified zinc phosphate cementFluoride cement

Add Stannous fluorideHigher solubility/ Lower strength

Zinc silicophosphateZinc phosphate + SilicateHigher strength/ lower solubilityFluoride releasedTranslucency

Zinc Polycarboxylate Cement

IntroductionZinc polyacrylate cementFirst - adhesive bond to tooth structure.Supplied as

Powder and liquid

CompositionPowd

erZinc oxide – 72% Basic ingredient

Magnesium oxide – 7% Modifier , aids in sintering

Other oxides like bismuth and aluminium

Stannous fluorideIncrease strength, modifies setting time, imparts anticariogenic properties

LiquidAqueous solution of polycarboxylic acid (32-

48%)Or

Copolymer of acrylic acid with other unsaturated carboxylic acids (itaconic , maleic , tricarboxylic acids)

Chemical reactionWhen acid comes in contact with powder , acid

reacts and releases zinc, magnesium, and tin ions

They bond to the polymer chain , through the carboxyl groups

These ions also react with carboxylic groups of adjacent poly acid chains

Cross inked salts are formed

Bonding to tooth structurePoly acrylic acid reacts with calcium ions via

carboxyl groups on the surface of enamel or dentin.

Bond strength greater on enamel than dentin.

Enamel 3.4-13.1MPA Dentin 2.07MPA

Working and Setting timeWorking time : 2.5 minSetting time : 6-9 minLowering the temperature of chemical

reaction can increase the setting time.

Mechanical PropertiesCompressive strength : 55-67 MpaTensile strength : 2.4-4.4 GpaModules of elasticity is lower then zinc

phosphate cement 5.1GPaMore soluble than zinc phosphate cement

0.06%More soluble in organic acids.Not as brittle as zinc phosphate cementExcess removal is difficult.

Biological ConsiderationPulpal response termed as mildPh of liquid is 1- 1.7Freshly mixed cement – 3-4After 24 hrs – 5 -6

ManipulationA cooled glass slab / powder 1.5 parts of powder to 1 part of liquid by weightLiquid not dispensed , before the startLoss of water, increases viscosityPowder is rapidly incorporated into the liquid in

large quantitiesMixing time is with in 30 – 60 sec ,with half to all

of powder incorporated at once to provide the maximum length of working time

Surface - glossy , acid present to provide sufficient carboxylic groups to bond.

Glossy Appearance

Dull Appearance

ApplicationsPrimarily for luting permanent restorationsAs bases and linersCementation in orthodontic treatment

DRAWBACKS

High viscosity.

Short setting time.

High intraoral solubility

Zinc Oxide Eugenol Cement

IntroductionThese cements have been extensively used in

dentistry since 1890’ sThey are least irritant of all dental cementsHave an obtundant or sedative effectCompatible with the hard and soft tissues of

the mouth

ClassificationType 1 ZOE – for temporary cementationType 2 ZOE – permanent cementationType 3 ZOE – temporary filling material ,

thermal insulationType 4 ZOE – Cavity liners

CompositionPowder

Zinc oxide – 69% Principle ingredient

White rosin – 29.3% Reduce brittleness

Zinc stearate – 1% Accelerator , plasticizer

Zinc acetate – 0.7% Accelerator , improves strength

Magnesium oxide Added in some powders

Liquid

Setting reactionFirst , hydrolysis of zinc oxide to its hydroxideWater is essential for reaction to proceedreaction is a acid base one,Zinc hydroxide combines with eugenol to form a

chelate ZnO + H2O → Zn(OH)2

ZINC EUGENOLATEForms an amorphous gel, which later tends to

crystallize.Structure : particles of unreacted zinc oxide

embedded in a matrix of zinc eugenolate

Zn(OH)2 + 2HE → ZnE2 + 2H2O

Manipulationp/l ratio 4:1 to 6:1 by wtthe bulk - incorporated into the liquid -

spatulated thoroughly in a circular motion - a stiff bladed spatula

Small increments - until the mix is complete – consistency

Setting time - 4-10 minsComplete setting reaction between zinc oxide and

eugenol takes about 12 hrs

Factors affecting setting time:Particle size – smaller particle size, set fasterAccelerators – alcohol , glacial acetic acid , and

small amounts of waterRetarders – glycol, glycerineTemperature – high temperature , accelerate settingPowder/ liquid ratio – higher the ratio, faster the set

Physical propertiesRelatively week cementsCompressive strength : Ranges from 3-4mpa

to 50-55mpaTensile strength : 0.32 to 5.8mpaModules of elasticity : 0.22 – 5.4 mpa Excellent thermal conductivitySolubility of the set cement is high -

disintegrate in oral fluids - Solubility is reduced by increasing p/l ratio

Biological propertiesLeast irritating of all dental cementsPh is 6.6 – 8Pulp response is termed as mildThey inhibit the growth of bacteria , have an

anodyne or soothing effect on pulp , in deep cavities, hence reduces pain

FACTORS AFFECTING SETTING TIME Particle size: Smaller zinc oxide

particles set faster Powder to liquid ratio: Higher the ratio,

faster the set Addition of accelerators, e.g. alcohol,

glacial acetic acid and water makes the cement set faster.

Cooling the glass slab: Slows the reaction

The set can be retarded by addition of glycol and glycerine which act as retarders.

Modified MaterialsPolymer reinforced ZOEintroduced in an effort to increase

the mechanical properties of zoe.Contains Zinc Oxide and finely

divided natural or synthetic resin like poly methyl methacrylate resulting in good strength, improved abrasion resistance and increased toughness

Luting agent, Base, temporary filling material and as a cavity liner.

EBA and alumina modified ZOE cementPowder :

ZnO 70% Alumina 30%

Liquid:EBA 62.5%Eugenol 37.5%

Properties are better than unmodified zoe

Compressive strength increased 55 mpa

Tensile strength – 4.1mpa

Modulus of elasticity – 2.5 gpa

Solubility and disintegration – 0.05% wt

Non eugenol Zinc Oxide cementSuitabe for patients sensitive to eugenol.Eugenol acts as an inhibitor for free radical

polymerized materials

Glass Ionomer cement

INTRODUCTIONGlass ionomer cement is a tooth coloured

material, introduced by Wilson & Kent in 1972.Material was based on reaction between silicate glass powder & polyacrylic acid.They bond chemically to tooth structure & release fluoride for relatively long period.

CLASSIFICATIONI. For lutingII. For restorationIII. For liner & basesIV. Pits & fissure sealantV. As Orthodontic cementVI. For core build up

COMPOSITIONPowder :-Acid soluble calcium fluoroalumino silicate glass.Silica - 41.9%Alumina - 28.6%Aluminum fluoride - 1.6%Calcium fluoride - 15.7%Sodium fluoride - 9.3%Aluminum phosphate - 3.8% Fluoride portion act as ceramic flux.

Strontium,Barium or zinc oxide provide radio opacity.

Liquid :-1.Polyacrylic acid in the form co-polymer with

itaconic acid & maleic acid .2.Tartaric acid: improves handling

characteristic & increase working time.3.Water : Medium of reaction & hydrates the reaction products

SETTING REACTION When the powder & liquid are mixed, Surface of

glass particles are attacked by acid. then Ca, Al, sodium, & fluoride ions are leached into aqueous medium.

Contd..Calcium poly salts are formed first, then followed

by aluminum poly salts which cross link with poly anion chain.

Set cement consist of unreacted powder particle surrounded by silica gel in amorphous matrix of hydrated calcium & aluminum poly salts.

Calcium poly salts are responsible for initial set.

Aluminum poly salts form the dominant phase.

Water plays an important role in structure of cement. After hardening, fresh cement is extremely prone to the cracking & crazing, due to drying of loosely bound water .Hence these cements must be protected by application of varnish.

SETTING TIMEType I 4 - 5 minutes

Type II 7 minutes

PROPERTIESCompressive strength - 150 mpa

Tensile strength - 6.6 mpa.

Hardness - 49 KHN.

Solubility & Disintegration:-Initial solubility is high due to leaching of

intermediate products.

The complete setting reaction takes place in 24 hrs, cement should be protected from saliva during this period.

Contd..Adhesion :-☻Glass ionomer cement bonds chemically to the tooth

structure.☻Bonding is due to reaction occur between carboxyl

group of poly acid & calcium of hydroxyl apatite.☻Bonding with enamel is higher than that of dentin ,due

to greater inorganic content.Esthetics :-GIC is tooth coloured material & available in differentshades. Inferior to composites. They lack translucency & rough surface texture. Potential for discolouration & staining.

Biocompatibilty :-Pulpal response to glass ionomer cement is

favorable.Pulpal response is mild due to - High buffering capacity of hydroxy apatite. - Large molecular weight of the polyacrylic

acid ,which prevents entry into dentinal

tubules.

Anticariogenic properties :-• Fluoride is released from glass ionomer at the

time of mixing & lies with in matrix. Fluoride can be released out without affecting the physical properties of cement.

Initial release is high. But declines after 3 months.After this, fluoride release continuous for a long period.

Fluoride can also be taken up into the cement during topical fluoride treatment and released again ,thus GIC act as fluoride reservoir.

MANIPULATION1.Preparation of tooth surface :-The enamel & dentin are first cleaned with pumice

slurry followed by swabbing with polyacrylic acid for 5 sec. After conditioning & rinsing ,tooth surface should be isolated & dried.

2.Proportioning & mixing :- Powder & liquid ratio is 1.5:1 by wt. Powder &

liquid is dispensed just prior to mixing.First increment is incorporated rapidly to

produce a homogenous milky consistency.Mixing done in folding method to preserves gel

structure.Finished mix should have a glossy surface.

CONTD3. Protection of cement during setting :-Glass ionomer cement is extremely sensitive to

air & water during setting.Immediately after placement into cavity,

preshaped matrix is applied to it.4. Finishing :-Excess material should be trimmed from

margins.Hand instruments are preferred to rotary tools to

avoid ditching.Further finishing is done after 24hrs.

Contd.5.Protection of cement after setting :-

Before dismissing the patient ,restoration is again coated with the protective agent to protect trimmed area.

Failure to protect for first 24hrs results in weakened cement.

GLASS IONOMER MANIPULATION

Advantages♣Inherent adhesion to the tooth surface.♣Good marginal seal.♣Anticariogenic property.♣Biocompatibilty♣Minimal cavity preparation required.

Disadvantages:-♦Low fracture resistance.♦Low wear resistance.♦Water sensitive during setting phase .♦Less esthetic compared to composite.

Uses :- 1.Aesthetic restoration material for class III &

V restorations.2. For luting.3.For core build up.4.For eroded area .5.For atraumatic restorative treatment.6.As an orthodontic bracket adhesive.7.As restoration for deciduous teeth.8.Used in lamination/ Sandwich technique.

Resin-Modified Glass-Ionomer Cements

This cement was introduced in 1990s with an objective to combine some of the desirable properties of glass-ionomer cements (fluoride release and chemical adhesion) with high strength and low solubility of resins . Polymerizable functional groups were added to the conventional glass-ionomer cements to achieve rapid curing activated by light/chemical while still allowing acid–base reaction to take its course along with the polymerization. Wear resistance is also improved.

COMPOSITION It is available as powder/liquid, preproportioned encapsulated form or as a

two paste system

Powder—consists of an ion-leachable glass and initiators for chemical/light-curing

Liquid—contains four main ingredients A methacrylate resin (bis-GMA) which enables polymerization reaction. A polyacid which reacts with the ion-leachable glass to allow acid–base

reaction. Hydroxy-ethyl methacrylate (HEMA), a hydrophilic methacrylate which

enables both the resin and acid components to coexist in an aqueous solution; HEMA also takes part in the polymerization reaction.

Water, to allow ionization of the acid component so that acid–base reaction can occur.

Other components include polymerization activators and stabilizers

Setting reactionSetting reaction of this cement is a dual

mechanism. Acid–base reaction is induced after the powder and the liquid are mixed, forming a polyacrylate salt. Polymerization (the primary setting reaction) is initiated as soon as sufficient free radicals become available. Slow acid–base reaction is responsible for the final maturation and strength of the cement while polymerization reaction provides the initial set

Contd..Chemically-activated polymerization of the

resin-modified glass-ionomer cement is referred to as “Dark Cure” .

These cements can be chemical-cured, light-cured, dual-cured (chemical-cured/light-cured + acid–base reaction) or tri-cured (chemical-cured + light-cured + acid–base reaction).

Advantages: 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

Less sensitive to early moisture contamination and desiccation during setting and less soluble than the glass-ionomer cement because of covalent crosslinking of the polyacrylate salt from free-radical polymerization

Easy manipulation and use Adequately low film thickness

Fluoride release similar to conventional GIC Polymerization is not significantly affected by the eugenol-containing

provisional materials, as long as the provisional cement is completely removed with thorough prophylaxis

Minimal post-operative sensitivity. High bond strength to moist dentin (14 MPa)

Disadvantages:

Dehydration shrinkage due to the glass-ionomer component has been observed as late as 3 months after maturity together with the polymerization shrinkage

HEMA is responsible for increased water sorption, subsequent plasticity and hygroscopic expansion

Although rare, may elicit an allergic response due to free monomer. Careful handling is therefore recommended during mixing

Cement bulk is very hard and difficult to remove.

Resin CementsBased on Methyl Methacrylate:Methyl methacrylate based resin cements were

developed in 1950s but had poor physical properties, that is, high polymerization shrinkage and increased microleakage because of low filler content. They also had high residual amine levels which contributed to significant color shift after polymerization

Contd.Based on Aromatic DimethacrylatesAromatic Dimethacrylate-Based Resin CementIn 1963, Dr. Rafael Bowen developed the first

multifunctional methacrylate used in dentistry, called bis-GMA or Bowen’s resin. The bis-GMA {2,2-bis[4-(2 hydroxy-methacryloxypropoxy) phenyl]propane}resin can be described as an aromatic ester of dimethacrylate, synthesized from an epoxy resin and methyl methacrylate Bis-GMA is extremely viscous and a low viscosity dimethacrylate, such as triethylene glycol dimethacrylate (TEGDMA) is blended with it to reduce the viscosity.

Composition Resin cements used today are composed of

resin matrix of bis-GMA or urethane dimethacrylate

and filler of fine inorganic particles (20–80%) to ensure thin film thickness

They are available as powder/liquid, encapsulated, or paste/paste systems and are classified into three types based on the method of polymerization as chemical-cured, light-cured and dual-cured.

Advantages:

Superior compressive and tensile strengths (20–50 MPa) with low solubility

Micromechanical bonding to prepared enamel, dentin, alloys and ceramic surfaces

Available in wide range of shades and translucencies 

Disadvantages:Meticulous and critical manipulation techniqueHigh film thicknessMarginal leakage due to polymerization shrinkageSevere pulpal reactions when applied to cut vital

dentinOffers no fluoride release or uptakeLow modulus of elasticity, so cannot support long span

prosthesis.Difficulty in removing hardened excess resin cement

from inaccessible areas, precluding its use when subgingival margins are placed

Disadvantages:Use of eugenol-based provisional luting

agents inhibited the complete polymerization of the resin cement.

Due to low early bond strength and a maturation period of 24 h, patients must be advised to avoid loading restorations luted with chemically-cured resin cements in the first hour after cementation. Excess cement must be removed before it sets to avoid damaging the weak early bond

Loss of water from cement liquids when they are exposed to air.

Compressive strength [MPa]

020406080

100120140160

Bond strength

0

50

100

150

200

250

300

Zinc phosphate GIC RMGIC Resin

Film thickness [µm]

05

101520253035404550

ConclusionThough cements are used in small quantities

in oral cavity, it should be used with at most care, as it is very important. There are innumerable cements present with different properties, one should know all the properties to use it in order to give a successful restoration to the patient

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