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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