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Zinc phosphate cement

Uses

•Cementation of fixed restorations

•Cavity base under metallic filing to protect the pulp

from thermal or electrical stimuli.

•Temporary filing.

Composition

Powder

ZnO (90%): main ingredient.

MgO (10%): aid in sintering by reduction of sintering temperature.

SiO2: filler.

Bi2O3: impart smoothness to the freshly mixed cement.

Liquid

H3PO4 (50%): main ingredient.

H2O (45%): it controls acid ionization

Al2(PO4) 3 and ZnPO4:-

They reduce the reaction rate ( retarder)

They stabilize the pH of the acid.

Setting reaction of Zinc phosphate cement

Manipulation

Powder/ liquid ratio.

Mix on thick walled and cool glass slab + stainless steel spatula.

To achieve slow neutralization of the liquid and allow heat

dissipation.

Mix over a large area.

Mix the cements in increments:

Add the small amount of powder into the liquid.

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.

Second Larger amount of powder is added to liquid

•For further saturation of liquid to newly form zinc

phosphate.

•This step may not effect by heat released from the reaction.

{because of the less amount of unreacted acid}

Finally the small amount of powder is added again

•To control the optimum consistency

Properties of Zinc phosphate cement

I) It is the standard against which to compare newer cements due to

•The long persistence of them in clinical performance.

•Their manipulation is easy.

•They have ideal rheological properties (set sharply to a relatively

strong mass from a fluid consistency) .

II) Working time and setting time

Working time commonly is 2-6 minute

Setting time is 2.5-8 minute

How to extend the setting time?

Reducing powder/ liquid ratio {not recommended}

Mixing on the cool glass slap {no moisture}

Mixing over a large area.

Mixing cements in increments.

Control of setting time at chair side (by operator)

1. Powder/liquid ratio

Reducing P/L ratio will increase working and setting times.

Drawbacks of this method:

•physico-mechanical properties.

•Lower initial pH (high acidity)

2 .Rate of powder incorporation

Add small quantity of powder into the liquid for the first few

increments to reduce the amount of heat generated and permits

more powder to be incorporated into mix. This method prolong

the working time without jeopardizing the physico-mechanical

properties, therefore it is a recommended method .

3. Spatulation time

Increasing spatulation time, prolong the working and setting times.

Prolonging spatulation time effectively destroys the matrix that was formed;

that is, extra time is needed to rebuild the bulk of the matrix.

4. Temperature of the mixing slab

It is the most effective method. Cooling the slab markedly retard the

chemical reaction between the powder and the liquid so matrix formation is

retarded. This permits incorporation of optimum amount of powder into the

liquid without the mix developing an unduly high viscosity.

III) Viscosity

It has low initial viscosity giving it these advantages:-

•Easy flow during restoration seating.

•Give low film thickness.

•Its viscosity increase rapidly with time, therefore the restoration

should be cemented rapidly after completing mixing to make use

of the lower initial viscosity.

IV) Mechanical properties

High compressive strength that allows amalgam condensation. In

10 minutes it attains 50% of its final strength which is attained

after 24 hours. It has low tensile strength (brittle). Its E is similar

to that of dentine. So it can support the overlying restoration and

occlusal stresses.

V) Solubility

•It is an important property especially when used for luting. Dissolution

contributes to the marginal leakage around restorations and result in looseness

of restorations or caries recurrence.

They have high solubility rate especially thin mixes. Once they set, their

solubility decreases, therefore they must be kept unexposed to oral fluid

during their setting.

VI) Biocompatibility

Irritant (pH is 2 and reach neutrality after 24 hours) so in deep

cavities, chemical insulator is needed.

Advantages

1. Speed and ease of usage.

2. Sufficient flow to form a thin layer for cementing of closely adapted crowns,

fixed partial dentures and inlays.

3. Low thermal conductivity beneath a metallic restoration.

4. High compressive strength that allows amalgam condensation.

Disadvantages

1. Solubility in mouth fluids.

2. Opaque material not suitable for visible surfaces.

Zinc polycarboxylate cement (ZPC)

The first cements that bond chemically to tooth structures.

They combine the strength properties of Zn PO4 +

biological acceptability of ZnOE.

These materials have gone through several stages of

development since their inception and progress is continuing.

Uses

1. Cementation of cast alloy, porcelain restorations and orthodontic

bands.

2. Cavity liners or base materials.

3. Temporary filling material.

Forms

• Conventional type: powder and liquid in two separate bottles.

•Water settable (anhydrous) type:

Its powder is the same like that of conventional type + freeze-dried

powder of the polyacid in one bottle. Its liquid is either distilled

water or weak solution of NaH2PO4.

Composition

Powder

Their composition and manufacturing are similar to those of zinc phosphate

cement.

Liquid

•30-40% aqueous solution of Polyacrylic acid or acrylic acid copolymer.

•Other organic acids such as:-

Itaconic acid to prevent gelation during storage.

Tartaric acid to control setting reaction.

•NaH2PO4 which viscosity of polyacid and S.T.

Setting reaction

The setting reaction is the same, whether the polyacid is freeze-dried and

subsequently mixed with water, or if the conventional aqueous solution of the

polyacid is used as liquid.

Properties

Working and setting times

It has shorter working time than zinc phosphate .

Lowering the temperature of glass slab increase the working time.

Cooling the powder only will retard the reaction without thickening the liquid.

Mechanical properties

Its compressive strength < zinc phosphate.

Tensile strength > phosphate cement

Solubility: It has low solubility in water.

Bonding to tooth structure

•Bonds chemically to E & D.

•The polycarboxylic acid reacts via COOH groups with calcium of

hydroxyapatite forming chemical bonding .

•Bonding to enamel is higher than to dentine, probably

because of the greater inorganic content and its greater

homogeneity from a morphologic standpoint.

•Smear layer removal by conditioning tooth surface with

10% polyacrylic acid for 10 seconds, will increase the bond

strength.

•It sticks to clean stainless steel.

Biocompatibility

•The effect of polycarboxylate cements on the pulp is comparable to or

less than that of zinc oxide-eugenol.

•pH of polycarboxylate cement (1.7) is higher than that of a zinc

phosphate cement (2) but polycarboxylate cement is more compatible

due to :-

•The rapid rise of the cement pH toward neutrality (few minutes for ZPC

but 24 hours for ZNPO4.

•Has bigger molecular size that block dentinal tubules.

Anticariogenicity

The fluoride containing cements release

fluoride, which is taken up by the neighboring

enamel, thus increasing its resistance against

caries.

Mechanism of action of fluoride in caries fitting

•Fluoride inhibits the enzymes responsible for carbohydrates fermentation.

•Fluoride shifts the equilibrium balance between demineralization and

remineralization toward remineralization.

•Fluorides act as a catalyst for uptake of calcium and phosphate ions.

Glass-ionomer cements (GICs)

Uses

•Restoration of erosion lesions

•Luting agent for crown and bridge

Types of GICs

•Conventional GICs.

•Metal reinforced GICs.

•Resin modified GICs.

Conventional GIC

Composition

Powder

Calcium aluminosilicate glass:-

•Silica (SiO2)

•Alumina (Al2O3)

•Calcium fluoride (CaF2) and NaF.

Function of the glass powder

•Releasing ions responsible for setting and properties of hard cement.

•Contributes to aesthetics.

Liquid is a Copolymer of

•Acrylic acid: main reactant.

•Itaconic acid: decrease viscosity of the liquid and inhibit gelation caused

by intermolecular hydrogen bonding.

•Tartaric acid: important hardener& controls pH during setting process.

Forms

•Powder/liquid form (conventional).

•Anhydrous cements (water settable).

•Capsules: pre-proportioned so achieve the correct p/l

ratio.

Setting reaction

It occurs in three steps:DissolutionGelation and hardeninghydration

Properties of GICS

Working and setting times

•It is less than that of ZnPO4.

•Water settable systems have longer working time and slower initial set than the

hydrous systems.

Mechanical properties

•Compressive strength: comparable to that of ZnPO4 cement.

•Tensile strength: slightly higher than that of ZnPO4 cement but still very low

(brittle behavior). Modulus of elasticity: less than that of ZnPO4

cement, i.e. less rigid and more prone to elastic deformation.

Film thickness

Similar to or less than that of ZoPO4 cement (25 μm or less).

Solubility

Good resistance to dissolution under oral conditions and improved by

varnish protection.

Bonding

The same as Zinc polycarboxylate cement.

Anticariogenic properties

GICs possess anticariogenic properties as a result of fluoride release

Biocompatibility

GICs are as compatible as zinc polycarboxylate cements for the same reasons

discussed before with polycarboxylate.

Aesthetics

1. GICs are considered inferior to many composite resins in aesthetic

appearance.

2. GICs appeared dull and lifeless, and this limited their application to the

restoration of erosion lesions and non-critical class III cavities.

3. In facts, the translucency of the GICs was more closely matched to that of

dentine than that of enamel.

Advantages of GICs

• Chemical bonding to tooth structures.

•Biocompatible.

•Long term fluoride release.

•Good compressive strength.

•Low solubility in oral fluids

Disadvantages of GICs

•Technique sensitive as they are very sensitive to

either water contamination or dehydration

•Low abrasion resistance.

•Short working time and long setting time.

•Brittleness (low tensile strength) and low fracture

toughness.

Resin modified glass ionomer cements (Hybrid GICs)

The aim: is to overcome some of the drawbacks of the

conventional GICs that result from the slow acid base

reaction such as:-

1. Short working time and long setting time.

2. Cracking on desiccation and moisture sensitivity.

3. Poor resistance to acid attack.

Composition

These products are hybrid of the two groups of materials, namely composite resin

and GIC.

Liquid

•Methacrylate resin which enables setting to occur by polymerization.

•Polyacid & ion-leachable glass to bring about setting by an acid-base mechanism.

•HEMA: a hydrophilic methacrylate which enables both resin and acid

components to co-exist in aqueous solution, the HEMA also takes part in the

polymerization.

•Water acid ionization enabling the acid-base reaction to occur.

Setting reaction of the Hybrid GICs

•The acid-base reaction

Free radical polymerization

Properties of resin modified GICs cement

•Release of fluoride.

•Ability to bind chemically to tooth structures.

•A prolonged working time and a rapid setting time.

•High strength.

•Higher resistance to desiccation and acid attack.

Metal reinforced glass ionomer cements

The aim of reinforcing the cement with metal is

•To overcome the drawbacks of conventional GICs which are:

Brittleness

Low abrasion resistance

Low fracture toughness

•To enable using them as posterior filling materials.

Methods of metal reinforcements

Silver alloy admix:

It is performed by simply mixing of silver amalgam alloy powder to the

conventional GIC (hand mix material).

Cermet cement

by sintering the silver only to the cement powder.

Uses of metal reinforced GICs

•Core build up material.

Posterior filling material for deciduous teeth

Disadvantages of metal reinforced GICs

•Reduction in fluoride release.

•Reduction in bond strength with tooth structures.

Advantages of metal reinforced GICs

•Increase in abrasion resistance.

•Little increase in compressive strength.

•Reduction in solubility.

Resin Cements

History

Introduced 1950’s as an unfilled resin

Current resin cements, introduced in late 1980’s

Problems of Resin

•High polymerization shrinkage.

•High thermal expansion.

•Lead to high microleakage.

Classification of Resin Cement (RC)

According to filler content

•Unfilled or filled (inorganic/glass filler particles)

•Resin cement vs Resin composite cement

According to polymerization reactions

•Light-activated (Light-cure);

•Chemical-activated (Chemical-, Self-cure);

•Dual-activated (Dual-cure)

According to use of dentin bond agent (DBA)

•Some resin cements do not require DBA, bonds directly to tooth (Adhesive RC).

•Resin cements require DBA applied prior to the RC; DBA bonds to tooth, resin

cement bonds to DBA (non-adhesive RC)

4-META/MMA-TBB resin cement product

4-META/MMA-TBB resin cement (unfilled)

Chemical-activation

Composition:

Base: 4-META/MMA (4-methyloxy ethyl trimellitic anhydride/

Methylmethacrylate)

Catalyst: TBB (tributyl boron oxide)

Powder: Polymethylmethacrylate powder (NO glass filler particles)

Manipulation

•Etch, rinse, and dry

•Mix Base + Catalyst , Apply 1st mix to tooth

•Add 2 scoops powder (PMMA) to 2nd mix of Base/Catalyst

•Apply 2nd mix to restoration

•Seat restoration

Application: metal-based restorations

Advantages

•Direct bond to tooth, No DBA

•Medium-high strength bond (~17 MPa)

Disadvantages

•Bond strength NOT long-term: ~10 MPa at 1 year.

•Higher solubility-- related to decreased bond strength.

Resin Composite Cements

Basic description

•Bis-GMA based resin (Bis-type methacrylate/TEGDMA resin )

•Filler: Silanated glass, silica particles

•Polymerization activation: Light, Chemical, Dual

•10 MDP: Phosphate ester, Adhesive monomer for tooth structure.

•Brand dependent use of DBA

Ex: Resin Composite Cement: Panavia 21 (Available at UMKC)

•Chemical-activation .

Manipulation

•Etch and prime tooth structure with self-etch ED primer

•Apply for 60 sec, then dry. Do not rinse.

•Acidic HEMA primer: pH ~2-3; Do not use conventional phosphoric acid

etch

•Mix catalyst & base pastes, 20 sec (Spread thin on pad, prevent premature

set)

•Apply to restoration, seat restoration

•Clean excess cement using;

microbrushes, gauze.

Floss between teeth to remove inter-proximal excess.