Dental cement

Topic

General requirements for dental cements

Classification of dental cements Component and properties Setting reaction Mixing process The uses of dental cements

Definition

Dental cements : materials made from two components, powder and liquid, mixed together.

Powder + Liquid

Pastelike or flowable material

Hardens to a rigid solid

Uses of dental cements

Luting agent• Temporary cement• Permanent cement

Pulp protection or cavity sealer Cavity varnish Liner Base

Uses of dental cement

Filling Temporary filling Permanent filling

Others Root canal sealer Calciumhydroxide cement Bite registration material

Luting agent

Luting : the use of moldable substance to seal a space between two component.

Most dental treatment necessitate attachment of prostheses to the teeth by means of luting agent.

General requirements for luting agents

Biocompatibility Retention High tensile strength, fracture

toughness, fatique strength Good marginal seal

General requirements for luting agents

Low film thickness Ease of use Radiopacity Aesthetics

Film thickness

The thickness of film between two flat surface

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

Low film thickness value is preferred

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

Classification of dental cements

Conventional cement Zinc phosphate cement Zinc oxide-eugenol cement Polycarboxylate cement Glass ionomer cement

Resin-base cement Resin cement Resin modified glass ionomer cement

Conventional cement

Typically powder/liquid system Liquid is an acid Powder is a base ; insoluble in oral

fluid

When mixed together Acid-base reaction

Zinc Phosphate cement

Zinc phosphate cement

Powder Liquid

Zinc oxide Phosphoric acid

Magnesium oxide

Water

Alumenium phosphate

ZnO

ZnO

ZnO

Zn+

Zn+Zinc aluminophosphate gel

UnreactedZnO

UnreactedZnO

UnreactedZnO

UnreactedZnO

Zinc aluminophosphate matrix

Setting reaction

Exothermic reaction Adding of water can accerlate the

reaction. Loss of water can lengthen the

setting reaction.

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

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.

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

1

23

4 5

67

8

1

23

4 5

67

8

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

ADA specification NO.8 for Zinc phosphate cement

Effects of manipulation on some properties.

Manipulative variables

PropertiesCopressive strength

Film thickness

Solubility

Initial acidity

Setting time

Decreased powder/liquid ratio

Increase rate of powder incorporation

Increase mixing temperature

Water contamination

Biocompatibility

Acid can penetrate into the dentinal tubule irritate pulp

pH of cement Liquid = 2.0 3 minutes after mixing = 4.2 1 hour = 6 48 hours = 7

Modified zinc phosphate cement Fluoride cement

Add Stannous fluoride Higher solubility/ Lower strength

Zinc silicophosphate Zinc phosphate + Silicate Higher strength/ lower solubility Fluoride released Translucency

Clinical applications

Zinc phosphate cement Luting agent Base and temporary filling

Modified zinc phosphate Luting prostheses Luting the orthodontics band

Zinc oxide-eugenol cements

Lower strength than Zinc phosphate cement.

Sedative effect Usually used as temporary filling

Zinc oxide-eugenol cement

Simple ZOE Reinforced ZOE EBA cement

Compositions of simple ZOE Powder

Zinc oxide Rosin : reduce the brittleness of the

set cement Zinc stearate : plastcizer Zinc acetate : improve strength

Liquid Eugenol and olive oil

Setting reaction

First

ZnO + Eugenol -- water Zn(OH)2

SecondZn(OH)2+2HE ZnE2+H2O

Setting reaction

Water accelerates the reaction Zinc eugenolate is easily

hydrolized by moisture

Manipulation

Paste/paste Mix two equal pastes together until it

obtains the homogeneous color. Powder/liquid

Usually 4/1 for maximum strength Mix the large increment, firstly Not require cool glass slap

Classification Type I

Temporary luting cement Type II

Permanent cementation Type III

Temporary restoration [for a few days] Type IV

Cavity liner

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 -

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

Powder Add 20-30% of aluminium oxide

Liquid Add 50-60% ethoxybenzoic acid in

eugenol Compressive strength 55-75 MPa

Clinical applications

Base Temporary cementation Permanent cementation

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

Zinc polycarboxylate cement

Or called Zinc polyacrylate cement The first adhesive cement

Bond to tooth structure and metal

More biocompatibility than zinc phosphate cement Polyacrylic acid have more molecular weigth

Moderate strength/ moderate solubility

Composition Powder [the same as zinc

phosphate cement ] Zinc oxide Magnesium oxide Stannous fluoride

Liquid Aqueous solution of polyacrylic acid Other carboxylic acid

Manipulation

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

The reaction is thixotropicThe viscosity decreases when the shear

rate increases

Setting reaction

Like zinc phosphate cement Retarded by cool environment

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%

Applications

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

Glass ionomer cement

Or called Polyalkynoate cements Conventional glass ionomercement Resin-modified glass ionomer

cement [RMGICs] Powder + Liquid/ Powder + water/

Encapsulated

Composition

Powder Calcium aluminum fluorosilicate glass

Liquid Polyacid

Copolymer of polyacrylic / itaconic acid Copolymer of polyacrylic / maleic acid Add tartaric: accelerator

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

Properties

Film thickness is similar or less than zinc phosphate cement.

Setting time 6 to 8 minutes from start of mixing.

Less pulpal irritation. Bacteriocidal or bacteriostatic. Prevent caries.

Strength

The 24-hour compressive strength is greater than zinc phosphate cement.

The compressive strength increase to 280MPa between 24 hours to 1 year after initial setting.

Bonding

It can be chemically bonded to the tooth structure.

The mechanism of bonding is the same as polyacrylate cement.

The dentine bond strength may be lower than polyacrylate because of technique sensitivity.

Modified GI

Cermet Combination of glass and metal No significantly improve the strength More wear resistance and short

setting time Resin-modified GI

Resin-modified glass ionomer cement

Add polymerizable function groups Both chemical & light curing Overcome moisture sensitive & low

early strength Names: Ligth cured GICs, Dual-cured

GICs, Tri-cured GICs, Hybrid ionomer, Compomers, Resin-ionomers

Setting reaction Polymerization

initial setting - Acid base reaction

maturing process & final strength Heat released from the

polymerization reaction.

Properties

Higher strength than conventional GI

Higher adhesion to resin material Less water sensitivity

Can be polished after curing

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

Applications

Type I : Luting agent Type II : Filling material Type III : Base and liner

Conventional GI for cementation

GI filling material

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

Matrix Bis-GMA (polymer)

The fillers binds with matrix by

silane coupling agent

Setting reaction

Polymerization Chemical activation Light activation Dual 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

Calcium hydroxide cement Used as base and

liner High pH value Good

biocompatibility

Composition

2 Pastes system Base

Salicylate reaction Calcium tungstate and barium sulfate radiopacity

Catalyst Calcium hydroxide

Properties

Lower compressive strength than others

Resist to the condensation force of amalgam filling

High pH 9.2-11.7 [Alkaline] Bactericidal High solubility

Properties

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]

Comparable properties of cements

Compressive strength [MPa]

0

20

40

60

80

100

120

140

160

Zinc phosphate Polycarboxylate GIC RMGIC Resin cement

Zhen Chun Li and Shane N. White, 1999

Bond strength

0

50

100

150

200

250

300

Zinc phosphate GIC RMGIC Resin

Separation forces [MPa]

Sule Ergin and Deniz Gemalmaz, 2002

Film thickness [µm]

0

10

20

30

40

50

Zinc phosphate Polycarboxylate GIC RMGIC Resin

Shane N. White, Zhaokun Yu, 1992

Others

Solubility ZOE > Polycarboxylate > Zinc

phosphate~GIC > Resin cement

Irritation to pulp tissues Resin~Zinc phosphate > GIC >

Polycarboxylate > ZOE~Calcium hydroxide

References

Textbooks Kenneth J. Anusavice

Phillips’ science of dental materials 11th edition W.B. Saunders company 2003

References

Textbook Robert G. Craig

Restorative dental materials9th editionMosby company 1993

References

Textbook Richard van Noort

Introduction to dental materials2nd editionMosby company 2002

References Journals

Li ZC, White SN. Mechanical properties of dental luting cements. J Prosthet Dent 1999;81(5):597-609

White SN, Yu Z. Film thickness of new adhesive luting agents. J Prosthet Dent 1992;67(6):782-90

Ergin S, Gemalmaz D. Retentive properties of five luting cements on base and noble metal copings. J Prosthet Dent 2002;885:491-97