DENTAL CEMENTS

DEFINATION:

Dental cements are hard, brittle materials formed by mixing powder and liquid together.

They are either resin cements or acid-base cements.

In the latter the powder is a basic metal oxide or silicate and the liquid is acidic

(A)Classification of dental cements according to bonding mechanism:

1.Phosphate: a) zinc phosphate;                                      b)zinc silicophosphate

                                     2.Phenolate:   a) calcium hydroxide silicylate; b)  ZnO eugenol: -polymer;                                                                -EBA;                                                                -alumina;

3.Polycarboxylate:a) zinc polycarboxylate;                                        b) glass ionomer;

4.Resin:       (a) Glass ionomer + polymetelmetacrylate = Hybrid ionomer

b) dimethylacrylate:   -filled;                                                                     -unfilled.

Type I: Luting agents that include permanent and temporary cements.

Type II: Restorative applications.

Type III: Liner or base applications

(B) Classification of cements according to the use:

Conventional cementZinc phosphate cementZinc oxide-eugenol cementPolycarboxylate cementGlass ionomer cement

Resin-base cementResin cementResin modified glass ionomer cement

IDEAL PROPERTIES OF A DENTAL CEMENT

• High compressive and tensile strengths• Adhesion to tooth structure and

restorative materials • Low viscosity and film thickness• Long working time with rapid set at oral

temperatures

•Low solubility

•High proportional limit •Anticariogenic properties •Biocompatibility •Translucency

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Properties of dental cementsStrength Depends on P:L. Brittle, C.S, T.S.

Resin cements > polycarboxylate cements

Solubility Influenced by powder ratio. Cements have solubility microleakage & pulpal irritation, except resin

Viscosity Affects luting agents.To get secondary consistency, powder

Biocompatibility pH of cement. Cements containing eugenol are sedative. Fluoride caries

Retention Chemical (GIC). Micromechanical with luting agents penetrating irregularities.

Esthetics Shades for luting agents for veneers & anterior crowns. Opaque cement to mask dentine discoloration. Try in paste available

Film thickness

The maximum allowable thickness is 25 µm (ADA specification No. 96)

Low film thickness value is preferred

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Uses of dental cements

Pulpal protection

(liners, bases, varnishes)

Luting cementation

(crowns, inlays, onlays veneers)

•Restorations (temporary and permanent)

•Surgical dressing (e.g. periodontal surgery)

• OthersRoot canal sealerCalciumhydroxide cementBite registration material

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Cement base

A thick layer of cement (>0.75mm) is applied under restoration to protect pulp against injuries.

The base should be strong enough to resist the condensation force during the placement of restoration.

Well insulation ability

Good sealing

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Luting cements

Desirable features:Good wettability Good flowThin film thickness: 25 µm or less to fill the space between

tooth structure and restoration.

If the luting agents layer is too thick:It will prevent proper seating of restorationExcess cement may wash out and cause irritation

and caries

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Restorations

Permanent:

cements are rarely used as restorations due to:Low strengthLow wear resistanceHigh solubility

The exception is GIC, used for class V

cavities and primary teeth.

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Temporary and intermediate restorations:Uses:

○ time is insufficient ○ In symptomatic teeth, a sedative provisional

restoration can be placed○ Between visits in cases of Endodontic treatment,

crowns, inlays

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21

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Surgical dressing

Purpose Protection and support of surgery siteHelp to control bleedingProvide comfort for patient

Material used: non eugenol dressing, mixed to soft putty like consistency.

CEMENT FORMING REACTION In general, cements are usually formed by an acid-

base reaction in which an acidic liquid and basic powder are mixed to produce a final set material which is composed of

: a core: of unreacted powder, surrounded by

:a matrix: formed by reaction products of powder and liquid.

or involve polymerization of a monomeric components.

ZINC OXIDE EUGENOL CEMENT (ZOE)

These cements have been used extensively in dentistry since 1890's.

Their pH is approximately 7 at the time of

placement, which potentially makes them the least irritating of all dental materials and are known to have an obtundant (sedative) effects.

Classification: 4 Types

Type I ZOE- Temporary luting cement

Type II ZOE- Long term luting cement

Type III ZOE- Temporary restorations

Type IV ZOE- lntermediate restorations

Composition

Powder Zinc oxide- 69% Principle Ingredient

White resin- 29.3% To reduce brittleness of set . Cement

Zinc stearate- 1.0% Accelerator, plasticizer

Zinc acetate- 0.7% Accelerator, improve strength

Liquid

Eugenol- 85% - Reacts with zinc oxideOlive oil- 15% - Plasticizer

Powder/liquid ratio - 3:1

Setting reaction

First

ZnO + Eugenol -- water Zn(OH)2

Second

Zn(OH)2+2HE ZnE2+H2O

Setting Time - 4-10 minutes

Water is essential for the reaction (dehydrated

zinc oxide will not dehydrated eugenol). The chelate formed is an amorphous gel that tends to crystallize importing strength to the set mass.

Thus the set cement consists of particles of zinc oxide embedded in a matrix of zinc eugenolate.

Water accelerates the reaction Zinc eugenolate is easily hydrolized by

moisture

Characteristics of ZOE Cements

The higher the powder/liquid ratio, the faster the material sets.

Cooling a glass-mixing stab slows the setting reaction unless the temperature is below the dew point.

Smaller particle sizes correspond to stronger set cement.

.

• The compressive strength ranges from 3-55mPa.

• Tensile strength ranges form 0.3-5.3mPa.

• Solubility and distingeration of 0.4% weight is highest among the cements. It can be reduced by increasing the powder/liquid ratio

• Adhesion: ZOE cements do not adhere well to enamel or dentin.

• Biologic Properties:

PuIpal response- classified as mild and least irritating of all cements.

Bacteriostatic and Obtundant Properties:

They inhibit the growth of bacteria and have a soothing effect on the pulp in deep cavities, reducing pain.

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Properties:

Sedative effect on pulp and antibacterialAlkaline pH (=7), biocompatible Can be irritant if in direct contact with pulpEugenol interferes with setting of resinModerate strengthRetention is mechanicalWater and temperature increase

accelerate setting

Specification requirements

Type Setting time [min]

Compressive strength[MPa]

Solubility[%]

Film thickness[µm]

Type I 4-10 35 maximum 2.5 25

Type II 4-10 35 maximum 1.5 25

Type III 4-10 35 maximum 1.5 -

Modified Zinc-Oxide Eugenol Cements

These were introduced to improve the mechanical properties of zinc-oxide eugenol cement. The modified ZOE cements are:

EBA- Alumina modified cements

Polymer reinforced

EBA- Alumina modified cements

Powder Liquid Zinc oxide- 70% EBA- 62.5% Alumina- 30% Eugenol-

37.5%

Polymer Reinforced ZOE cement Powder Liquid Zinc oxide- 80% Eugenol 85% Polymethyl methacrylate 20% Olive oil 15% Powder/liquid ratio - 4:1

Reinforced ZOE

Used as the intermediate restorative materials (IRMTM)

Add 10-40% resin polymer in the powder for strengthening the set cement

Compressive strength 35-55 MPa

EBA cement

PowderAdd 20-30% of aluminium oxide

Liquid Add 50-60% ethoxybenzoic acid in eugenol

Compressive strength 55-75 MPa

Uses:

•Low/high strength base•Temporary and Intermediate restoration•Temporary cementation•Root canal sealers•Periodontal dressings•New reinforced cements are used for permanent cementation (Type II)

Clinical applications

If cement contains eugenol, it is not to use with resin restorative material.

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Manipulation

Paste/pasteMix two equal pastes together until it obtains

the homogeneous color.

Powder/liquidUsually 4/1 for maximum strengthMix the large increment, firstlyNot require cool glass slap

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Zinc oxide eugenol

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Type II:

powder and liquid, powder in immediately incorporated into liquid ad mixed (30 seconds) yielding putty consistency, additional 30 sec. mixing provide fluid consistency.

Zinc Phosphate cement

•Composition Powder Liquid

• Zinc oxide- 90.2% Phosphoric acid 38.2%

• Magnesium oxide- 8.2% Water - 36.0%

• Other oxides (bismuth trioxide, Aluminium phosphate

1

16.2%

Calcium oxide etc)- 0.2% Aluminium – 2%

• Silica- 1.4% /Zinc- 7.1 %

ZnO

ZnO

ZnO

Zn+

Zn+Zinc aluminophosphate gel

Setting Reaction

When the powder is mixed with liquid, phosphoric acid attacks the surface of the particles, dissolving zinc oxide forming acid zinc phosphate.

The aluminium in the liquid is essential for cement

formation. The aluminium complexes with the phosphoric acid to form a zinc aluminophosphate gel.

The reaction is exothermic.

UnreactedZnO

UnreactedZnO

UnreactedZnO

UnreactedZnO

Zinc aluminophosphate matrix

The set cement has a cored structure consisting primarily of unreacted zinc oxide particles embedded in a cohesive matrix of zinc alumino phosphate.

Adding of water can accerlate the reaction.

Loss of water can lengthen the setting reaction.

Classification

Type I-

Fine grain for luting

Film thickness should be 25µm or less

Type II-

Medium grain for luting and filling

Film thickness should not be more than 40µm

Modified zinc phosphate cement

Fluoride cementAdd Stannous fluorideHigher solubility/ Lower strength

Zinc silicophosphateZinc phosphate + SilicateHigher strength/ lower solubilityFluoride releasedTranslucency

Working time and setting time

Working time commonly is 3-6 minute

Setting time is 2.5-8 minute(ADA specification No.96)

Depending on the manufacturer instruction

Mixing procedure

There are three steps: First : add the small amount of powder

into the liquid ○ To achieve the slow neutralization of the

liquid.○ To control the reaction.

Mixing procedure

Second : Larger amount of powder is added to liquid

○ For further saturation of liquid to newly form zinc phosphate.

○ This steps may not effect by heat released from the reaction.

{because of the less amount of unreacted acid}

Mixing procedure

Finally: the small amount of powder is added again

○ To control the optimum consistency

Effects of manipulation on some properties.

Manipulative variables

Properties

Copressive strength

Film thickness

Solubility

Initial acidity

Setting time

Decreased powder/liquid ratio

Increase rate of powder incorporation

Increase mixing temperature

Water contamination

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Properties Initial acidity with pH of 4.2, becomes neutral

after 48 hours. Retentive by mechanical retention

sandblasting of crowns or inlays Similar strength to GIC, high CS, low tensile

strength. Low solubility once set Fast setting Moisture adversely affects cement

Compressive strength- 103.5MPa

Tensile strength- 5.5.Mpa

Modulus of elasticity- 13.5Mpa

Biocompatibility

Acid can penetrate into the dentinal tubule irritate pulp

pH of cementLiquid = 2.03 minutes after mixing = 4.21 hour = 648 hours = 7

Characteristic properties

Setting time at 37O 5 – 9 minutes

Minimum compressive strength

75 MPa

Maximum film thickness

25 µm (for luting the prostheses)

Maximum Solubility 0.2% by weight

Clinical applications

Zinc phosphate cement Luting agentBase and temporary filling

Modified zinc phosphateLuting prosthesesLuting the orthodontics band

Zinc polycarboxylate cement

Or called Zinc polyacrylate cement

The first adhesive cementBond to tooth structure and metal

More biocompatibility than zinc phosphate cementPolyacrylic acid have more molecular weigth

Moderate strength/ moderate solubility

Composition Powder [the same as zinc phosphate cement ]

Zinc oxideMagnesium oxideStannous fluoride

LiquidAqueous solution of polyacrylic acidOther carboxylic acid

Setting reaction

Like zinc phosphate cement Retarded by cool environment

Manipulation

Mix first half of powder to liquid to obtain the maximum length of working time.

The reaction is thixotropic

The viscosity decreases when the shear rate increases

Bonding to tooth structure The polyacrylic acid is believed to react

with calcium ion via the carboxyl group.

The adhesion depends on the unreacted carboxyl group.

Specification requirements

Setting time at 37OC: 9 minutes Maximum film thickness: 25µm Minimum compressive strength: 50 MPa Maximum solubility: 0.2%

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Properties:

○ Lower compressive strength than other cements○ Mild acidity ○ Higher viscosity when mixed but reasonable flow○ Liquid should not be dispensed before needed, to

avoid water evaporation and viscosity ○ Retention is chemical and mechanical○ To increase working time use a cold slab

• Compressive Strength- 55MPa and is inferior to zinc phosphate

• Tensile Strength- 6.2MPa and is slightly higher than zinc phosphate

• Solubility and Disintegration- Its tends to absorb water and is slightly more soluble (0.6% weight) than Zn (Po4)z

•Biocompatibility:

•Pulpal response is mild and less irritant than ZnPo4 cement because The liquid is rapidly neutralized by the powder

•Penetration of polyacrylic acid into the dentinal tubules is less because of its higher molecular weight and larger size

Adhesion:

An outstanding characteristic of zinc polycarboxylate cement is that, the cement bonds chemically with the tooth.

The carboxyl group in the polymer molecules

chelates with calcium in the tooth structure.

Powder/liquid ratio- 1.5-1

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Zinc polycarboxylate Uses:

High strength baseFinal cementation of indirect restoration

•Cement inlays or crowns•Used as base•Temporary filling•Lute the stainless steel crown

CALCIUM HYDROXIDE CEMENT

. • Cavity Liners:

• When Ca(OH)2 used as cavity liner, is suspended in a solvent carries with a thickening agent. When it is placed on the pulpal floor, the solvent evaporates and leaves a thin film of calcium hydroxide.

•Bases:

•The cements are usually produced as a two-paste system with radio opaque fillies the setting reaction occurs between calcium hydroxide and salicylate, yielding calcium disalicylate. It can be used to line the cavity or it can be applied as a direct pulp capping material.

• Composition:• Base Paste

• Glycol Salicylate 40%-reacts with Ca(OH)2 and ZnO

• Calcium Sulphate

• Titanium dioxide- inert fillers, pigments

• Calcium tungstate or Barium sulphate- provides radio-opacity

Catalyst Paste:

•Calcium hydroxide- 50% Principal reactive ingredient

•Zinc oxide- 10%

•Zinc Stearate- 0.5% accelerator

•Sulfonamide- 39.5%- oily compound acts as carrier

Properties Lower compressive strength than others Resist to the condensation force of

amalgam filling High pH 9.2-11.7 [Alkaline] Bactericidal High solubility

Stimulate the secondary dentine formation in the area of thin dentine [<0.5mm]

Stimulate the dentine formation in the exposed-pulp lesion [Direct pulp capping]

SILICATE CEMENTS

• its ability to reduce development of secondary caries has made it a model for the development of caries- resisting dental materials.

• This beneficial characteristic is attributed to the presence of fluoride in silicate cement powder, which typically contains 15% fluoride.

• After the placement of the silicate restoration,

fluoride ion is released and reacts with the adjoining tooth structure. The enamel solubility is reduced, which builds up its resistance to acid attack and caries.

Properties

Compressive Strength: 180Mpa Silicate is the strongest of all the dental cements.

Tensile strength: (3.5Mpa). It is weak in tension

Hardness: (70KHN) and it is similar to dentin

RESIN CEMENT• Resin cement has become attractive as a luting agent

because of the development of direct- filling resins with improved properties, the benefit of the acid-etch technique for attaching resins to enamel and the potential to bond to dentin conditioned with organic or inorganic acid.

Applications:• Cementation of crown and bridges (etched cast

restorations) • Cementation of porcelein veneers• For bonding of orthodontic brackets to acid-etched enamel

• Composition• Powder• Resin matrix (diacrylate monomer) • Tertiary amine• Inorganic fillers• Coupling agent (organosilane)• Chemical or photointiators and activators• Liquid • Methyl methacrylate• Polymerization can be achieved by a conventional

chemical cure system or by light activation. Several systems use both mechanisms and are referred to as dual-cure systems.

Adhesive resin cement

Occur later from the direct filling resin

Become popular because of the improved properties, high bond strength.

Resin cement is flowable composite resin.

Composite resin cement Composite :

Resin matrix + inorganic filler

Silane coated

Composition

Filler Silica

MatrixBis-GMA (polymer)

The fillers binds with matrix by silane coupling agent

Setting reaction Polymerization

Chemical activationLight activationDual activation [chemical and light]

Preparations

Powder / liquid

Chemical, light, or dual cure

2 paste system [base / catalyst]

Chemical, light, or dual cure

Single paste

Light cure

Bonding system

Bond with the tooth surface by enamel an dentine bonding system.

Bond with metal by using metal primer.

Bond with ceramic restoration by treating the surface of porcelain with silane coupling agent

Properties

Very good bond strength High compressive strength Water sensitive Might irritate pulpal tissues

Applications

Tooth color filling materials Luting cements

GLASS IONOMER CEMENTS

developed by Wilson and Kent in England in the year 1972.

These glass ionomer are hybrids from the silicate cements and the polycarboxylate cements.

The greatest advantage of this cement was its

adhesion to enamel and dentin and

fluoride release for anti-cariogenic effect.

Classifications

According to Wilson and Mclean in 1988.• Type I- Luting cements• Type II- Restorative cements

a. Restorative Aesthetic

b. Restorative Reinforced

According to Application

•Type I- Luting cements

•Type II- Restorative cements– Aesthetic filling materials – Reinforced materials (Fuji IX, Fuji II LC)

•Type III- Lining cement

•Type IV- Fissure sealant

•Type V- Orthodontic cement

•Type VI- Core-build up cement

Newer Classification

Traditional Glass lonomer• a. Type I- Luting cement• b. Type II- Restorative cement• c. Type III- Liners and Bases

Metal Modified Glass lonomer • a. Miracle mix• b. Cermet cement

Light Cure Glass lonomer•a. HEMA added to liquid

Hybrid Glass- lonomer/Resin Modified Glass lonomer

•a. Composite resin in which fillers substituted with glass ionomer particles. •b. Pre-cured glasses blended into composites

According to Mclean in 1994.

•1. Glass ionomer cements (Traditional)•2. Resin modified glass ionomer cements•3. Poly acid modified composite resins

Composition Constituent's % by weight

• Silica (Sio2 ) 35-50

• Alumina (Al2o3) 20-30

• Aluminium Fluoride (AIF3) 1.5-2.5

• Calcium Fluoride (CaF2) 15-20

• Sodium Fluoride (NaF) 3.0-6.0

• Aluminium Phosphate (AIPo4) 4.0-12

 • Lanthanum, strontium, Barium in traces (for radio opacity)

•The powder of traditional GIC is a calcium-fluoro-alumino-silicate glass.

•This powder is referred to as an ion-leachable glass.

Liquid Polyacrylic acid- 45% Itaconic acid Maleic acid 5% (Decreases viscosity) Tricarboxylic acid Tartaric acid- Traces (increases working time and

decreases setting time) Water- 50% (Hydrates reaction product)

Modifications in Powder

The modifications were to improve upon the existing property in the manipulation and the area of clinical use. Some of the modifications of the powder are:

Dried poly acrylic acid (anhydrous GIC) Silver- Tin alloy (miracle Mix) Silver- Palladium/Titanium (cermet cement} BisGMA, TEGDMA and HEMA (light/Dual Cure

GIC).

Modifications in Liquid:

Only water and tartaric acid HEMA (Light Cure Components)

Setting reaction

There are three stages: Dissolution Gelation Hardening.

Water hardening or water setting

Silica gel

Glass core

Ca2+

Al3+

F-

Polyacid liquid

Hydrogen ions

Polyacid liquid

Ca2+

Al3+

F-

-COOH

Cross-linkedpolyacid

Gelation

Calcium ions have more reactivity than aluminium ions.

This is critical phase of contamination.

Polyacid liquid

Al3+ -COOH

Cross-linkedpolyacid

Hardening

Last as long as 7 days. The reaction of aluminium ions provides

the final strength of set cement.

Cross-linked polyacid

Glass core

Silica gel

Acid Base Reaction • The glass-ionomer cement is formed by the reaction

of three materials. A fluoro-alumino-silicate glass powder, an ionic polymer of polyacrylic acid and water.

• While mixing the powder and liquid the acid slowly degrades the outer layer of glass particles, calcium ions and aluminium ions.

• During the early stages of setting, divalent calcium ions are released more rapidly and are primarily responsible for reacting with the poly acid, cross linking with the adjacent carboxyl ions on polymer chain to form a reaction product, that is calcium polysalts.

At this stage, it has a critical relationship with water.

If the cement comes in contact with moisture then the aluminium ions that are slowly leached out may get washed out of the cement before it combines with the cement network. This will result in a weak cement as well as more soluble cement which will get more rapidly eroded by the oral fluids.

If the cement is dried then the water, which is essential for ion transfer to take place, will prevent further progression of the reaction. In this case, material is weak and also crumble easily. It also appears dull and white and exhibits poor esthetics.

• Aluminium ions are released more slowly and become involved in setting at a latter stage often referred to as secondary reaction stage. The aluminium ions are also replace divalent calcium ions and form tighter network of cross link between polymer chains. The set material consists of unreacted glass cores embedded in a matrix of cross-linked poly acid.

• Although it may appear to be hard arid set after the first 5 minutes it truly takes at least one full day (24 hours) before the material is set to a stable form, fluoride and phosphate ions form insoluble salts and complex sodium ions contribute to the formation of an orthosilicic acid on the surfaces of the particles and as the pH rises, this silica gel will assist in binding powder to the matrix.

Physical Properties of GIC

Compressive Strength: 150MPa. It is less than silicate. The finer the particle more will be the compressive strength.

Tensile Strength: Glass ionomer has higher tensile strength than silicates (6.6MPa).

Flexural Strength: GI cements are relatively brittle having flexural strength of only 15-20MPa.

Hardness: Less than silicates (48KHN)

Fracture toughness: Glass ionomer cements are much inferior to composites in this respect.

Other Properties are:

Sensitivity to Moisture:

GIC are very sensitive to moisture especially during initial setting phase. Both sorptions of water and over drying are deleterious to the properties of the set cement. Therefore protection of the cement during and after placement is mandatory.

Adhesion: It provides good adhesion to enamel and dentin.

Mechanism of Adhesion: Glass ionomer bonds chemically to tooth structure. The bonding is due to the reaction between the carboxyl groups of the polyacids and the calcium in the enamel and dentin.

The bond to enamel is always higher than that to dentine, probably due to the greater inorganic content of enamel and it's a greater homogeneity.

• Esthetics: Esthetically they are inferior to composites and ceramic. It is opaque, lacks translucency and may become dull and lifeless in course of time.

• Biocompatibility: The glass ionomer show a high degree of compatibility with living tissue. They elicit a greater pulp reaction than ZOE but generally less than that of ZnPo4. The polyacids are relatively weak acids and form long complex chain formation. They makes difficult for the acid to permeate through dentinal tubules.

Anticariogenic Properties:

Type II GIC releases fluoride in amounts comparable to silicate cements initially and continue to do so over an extended period of time. GIC have the potential for reducing infiltration of oral fluids at the cement tooth interface, thereby preventing secondary caries.

•Pulp Protection: In deep cavities, it is wise to place a thin layer of protective liner, that is Ca(OH)2 within 0.5mm of the pulp chamber.

Fluoride Release: Fluoride release from GIC and other compositions is diffusion limited and affected by the concentrations in both the matrix and the particles. For GI, the initially high burst of fluoride release is due to the high concentration of fluoride that exists in the matrix immediately after the setting reaction is completed.

Fluoride Recharging• Although in vitro date have shown that fluoride

release from glass ionomer remains detectable for years, the rate of release is reduced by as much as a factor of 10 within the first few months.

• It has also been shown that silicate cements are capable of absorbing fluoride from their environment.

• The level of re-release depends on the concentration of the storage medium and the duration of storage.

Modified Glass lonomer Cements

Anhydrous Cement: Anhydrous means that the acid has been freeze

dried and included in the powder. The polyacrylic acid can be vaccum dried and incorporated with the glass powder. The liquid then used being either water or dilute aqueous solution of tartaric acid.

Metal Modified Glass lonomers Miracle Mix or Silver Cermet Silver cermet was introduced by Simmons in

1983. Initially, it was prepared by the incorporation of silver-Tin alloy into the glass ionomer cement powder.

Glass is generally brittle and addition of silver was expected to improve the toughness of the cement as silver acts as stress absorber and also improves the abrasive resistance of cement.

Glass Cermets: This was introduced by Mclean and Gasser in

1985, Glass and metal powders were sintered at high temperature.

This was attempted to improve wear resistance, flexural strength and at the same time maintain the aesthetics.

Resin Modified Glass-lonomer Cement (Hybrid lonomer)

• Moisture sensitivity and low early strength of GICs are the result of slow acid-base setting reactions.

• Polymerizable functional groups can be added to impart more rapid curing when activated by light or chemicals to overcome these two inherent drawbacks and still allow the acid-base reaction to take its course long after polymerization.

These products are considered to be dual cure cements if only one polymerization mechanism is used;

if both mechanisms are used they are considered tri-cure cements

Clinical Applications

Hybrid ionomers can be used as liners, fissure sealants, bases, core buildups, restoratives, adhesions for orthodontic brackets, repair materials for damaged amalgam cores or

cusps and retrograde filling materials.

Composition and Setting Reaction

• The powder component consists of ion-leachable fluora-alumino-silicate glass particles and initiators the light curing and or chemical curing.

• The liquid component usually contains water and polyacrylic acid or modified with methacrylate and hydroxyethyl methacrylate (HEMA) monomers. The last two components are responsible for polymerization.

•The initial setting reaction of the material occurs by the polymerization of methacrylate groups.

•The slow acid base reaction will ultimately be responsible for the unique maturing process and the final strength.

Advantages

Stronger and nearly insoluble Fluoride release and good radio-opacity Easy manipulation Better aesthetics Early resistance to water attack Bond strength-excellent Minimal or no postoperative sensitivity bonding to

tooth-chemical and micro-mechanical,

Relative properties of a glass ionomer and a resin-modified GI cements

Property GIC RMGIC

Working time 2 min 3 min 45 sec

Setting time 4 min 20 sec

Compressive strength

202 MPa 242 Mpa

Tensile strength

16 Mpa 37 Mpa

Compomer (Polyacid modified composite Resins)

• This material has a structure and physical properties similar to those of composites. It also has the ability to release fluoride and it undergoes an acid-base reaction in the presence of saliva.

• It consists of silicate glass particles, sodium

fluoride and polyacid-modified monomer without any water.

•Because of absence of H2o in the formulation, the cement mixture is not self- adhesive like conventional GIC and hybrid GIC. Thus a separate dentin-bonding agent is needed for compomers used as restoratives.

Setting is initiated by photopolymerization of the acidic monomer that yields a rigid material. The set material begins to absorb water in the saliva that contributes the acid base reaction

Giomer

• They are based on pre-reacted glass-ionomer (PRG) technology.

• Chemically they consist of fluoroalumino silicate glass

reacted with polyalkenoic acid in water prior to inclusion into the silica-filled urethane resin.

•Giomers contain both of the essential components of glass-ionomer cements and resins but they cannot be classified as compomers in which a variable amount of dehydrated polyalkenoic acid is incorporated in the resin matrix and the acid does not react with the glass until water uptake occurs.

•These materials have so placed in a separate category of composites known as PRG composites

Indications

Restoration of root caries Non-carious cervicai lesions Class V cavities Deciduous tooth caries

.

Giomers have certain advantages such as fluoride release, fluoride recharging, biocompatibility, clinical stability, excellent aesthetic and smooth surface restorative materials.

Giomers are promising restorative materials and are considered to be most interesting development of near future

GIC modified by bioactive glass used for biomedical applications, mainly for bone

replacements

For orthopedic use,

bone cements lies in the lack of exotherm during setting, absence of monomer and potential for improved release of incorporated therapeutic agents

These GIC-BAG materials have been shown to be bioactive in simulated physiologic conditions, and they have been found to mineralize human dentin in vitro.

Depending on the amount of BAG, the materials may also possess antimicrobial properties

The compressive strength of the test specimens decreased with the increasing amount of BAG.

In the elemental composition, more Ca was detected in the BAG-containing materials than in the pure GICs.

•compromises the mechanical properties of the materials to some extent.

•Thus, their clinical use ought to be restricted to applications where their bioactivity can be beneficial, such as root surface fillings and liners in dentistry, and where high compressive strength is not necessarily needed

COMPARABLE PROPERTIES OF

CEMENTS

Compressive strength [MPa]

0

20

40

60

80

100

120

140

160

Zinc phosphate Polycarboxylate GIC RMGIC Resin cement

Bond strength

0

50

100

150

200

250

300

Zinc phosphate GIC RMGIC Resin

Separation forces [MPa]

Film thickness [µm]

0

10

20

30

40

50

Zinc phosphate Polycarboxylate GIC RMGIC Resin

Others

SolubilityZOE > Polycarboxylate > Zinc

phosphate~GIC > Resin cement

Irritation to pulp tissuesResin~Zinc phosphate > GIC >

Polycarboxylate > ZOE~Calcium hydroxide

CONCLUSION

• Manipulation of the cement is very important; variations in the powder and liquid ratio can influence the working and setting time, the consistency and flow, as well as the degree of solubility, erosion, strength and film thickness

factors to consider :

• solubility, • erosion, • tensile strength, • compressive strength, • toughness, • elastic modulus, • creep, • working and setting time,

•sensitivity to moisture during and after setting,

• thermal conductivity and diffusivity,

•pH during setting,

• biocompatibility, compatibility with other restorative materials, •potential for fluoride release,

•adhesion to enamel and dentin,

•rate of change of viscosity film thickness and dimensional change in the presence of moisture

References Textbooks

Kenneth J. Anusavice

Phillips’ science of dental materials

11th edition

• Robert G. CraigRestorative dental materials9th edition

TextbookRichard van Noort

Introduction to dental materials

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