Dental Cements - Minia

Dental Cements

Selection of cement

A restoration holds on a prepared tooth by:

Mechanical luting.

Micromechanical bonding.

chemical bonding.

Often a combination of these mechanisms coexists.

Conventional castings mechanical luting

agents cements.

Adhesive-bonded restorations adhesive resins.

Properties of Ideal cements:

Adhesion: adhere to both tooth structures & restoration.

long working time.

low viscosity and easy flow.

low film thickness about 20-40 m.

good seal and insoluble in the oral cavity.

biocompatible.

adequate strength

anticariogenic property,

translucent.

easy excess removal .

Adhesion & Bonding 1- Mechanical or Non-adhesive luting cement:

Cement just fills the gap.

No adhesion.

The restoration is held in place by small

irregularities on the surfaces of both

tooth and restoration.

Most of the retention is provided by the

design of the preparation.

2-Micromechanical bonding:

The cement engages inside deep micro-irregularities both on the tooth surface

and the restoration.

Enamel: Irregularities by etching with

phosphoric acid.

Ceramics: Are etched with hydrofluoric

acid.

Metals: Etched with electrolytic or

chemical etching. Sandblasting or

incorporating salt crystals in the framework

may also be used to provide irregularities.

3- Chemical (Molecular Adhesion):

Chemical reaction between molecules of

different substances ex. Polycarboxylate

and glass ionomers

Working Time It is the time during which the viscosity of the mixed

cement allows flow under pressure to form a thin

film.

Factors affecting working time:

Powder: Liquid Ratio.

Rate of powder addition.

Slab temperature:

Cooling the slab prolongs the setting time

retards the chemical reaction

Film Thickness:

Low film thickness, 25 m, allows more flow, better wetting and seating

of the restorations

Flow and Viscosity:

Cements with low viscosity allow better restoration seating.

Translucency:

Translucent cements provide better esthetics than opaque

cements

Anticariogenic Property:

Continuous fluoride release decreases caries incidence..

Zinc Phosphate Cement Composition:

Powder: (90%) Zinc Oxide +magnesium

oxide.

Liquid: Phosphoric acid and water

Properties Adhesion: Bond is only mechanical

Biocompatibility: cause pulp irritation.

Working and setting time: (5 minutes)

Film Thickness : About 25µm.

Viscosity and Flow: viscosity rises during setting but

cement has good flow.

Solubility and disintegration: soluble

Mechanical Properties: Compressive strength 96-110

Mpa.

Excess cement Removal :easy

Anticariogenic : No

Translucency: Opaque cement.

Disadvantages:

No adhesive properties.

Not biocompatible, may cause pulp irritation.

Soluble in oral fluids.

No anticariogenic property.

Opaque.

Glass Slab Cooling:

Advantages of frozen slab:

Maximum powder is incorporated resulting in 50% increase

in P/L ratio. Maximum strength and minimum solubility.

Working time is increased.

Heat is dissipated.

Zinc Polycarboxylate

Powder : Zinc oxide & Magnesium oxide

Liquid : Polyacrylic acid

* Makes chemical molecular adhesion to

tooth structure

Properties 1. Tensile strength = PO4 , Compressive < PO4

2. Soluble

3. Low film thickness : 25 μm

4. Viscous; viscosity with rate of mixing

5. Less working time than PO4 = 2.5 min.

6. Biocompatible

7. Adhesion is chemically & mechanically

*It reacts with Calcium of the tooth.

1. Adhesion to clean tooth surfaces conditioned with 10%

polyacrlylic acid followed by rinsing with water

2. Does not bond to metal restorations unless clean & air

abraded

3. Bond strength to E. 9 MPa , Dentine 3.3 MPa

8. Not anticariogenic

9. Opaque

10. Difficult in excess removal as it is rubbery so removed

before rubbery stage ( semiset ) or after it has set

Glass Ionomer

A. Conventional

Powder : Ca-Fluor-alumino-silicate glass

Liquid : Polyacrylic acid + itaconic / maleic acid

Setting reaction : Acid base reaction

Properties 1. Adhesion : Chemically & Mechanically

Bond to E. & D. similar to polycarboxylate via carboxyl gp. to Ca.

Bonding to restorations by tin plating

2. Strength are developed slowly Compressive & tensile > PO4 & polycarboxylate

3. Highly initial soluble protected by varnish Moisture control is essential till hardening

soluble than PO4 on long term

4. Anticariogenic

5. Biocompatible

6. Translucent

7. Removal of excess after setting

8. Working time 3min.

Resin Modified Glass Ionomer

Hybrid Ionomer Cements

Acid base reaction modified by introducing

water soluble polymers.

Can be light cured via a methacrylate

group

Properties

1. Flouride release

2. Adhesion

3. strength

4. working time

5. solubility

6. microleakage

7. sensitivity to early moisture exposure

8. Reduced post cementation sensitivity

9. Disadv. : Water sorption & expansion

Resin Luting Cements

Conventional :

Resin matrix and an inorganic filler particles

Differ from restorative composite in their low filler content & low

viscosity

Bond is mechanical by etching E. with phosphoric acid

Adhesive

Bonds both mechanically & chemically

Adhesive properties capable of bonding to:

Tooth struc.,

Silanated porc.,

Sandblasted Base Metal Alloy ,

Tin plated Au alloys

Bonding to E. by acid-etch technique

Polymerization 1. Light cured

Ceramic restorations

2. Dual Cured

3. Chemically cured Metallic restorations

Properties

1. High retentive values used in case which lack adequate retention

2. Not soluble

3. Transluscent

4. High strength values

5. Removal of excess cement before polymerization or it becomes very difficult

6. Rapid increase in viscosity

7. Irritant to pulp

8. Polymerization shrinkage stresses marginal leakage

9. Conventional greater film thickness, recent adhesive cements 19 μm.

10. Not anticarriogenic , unless Fl is added.

11. Working time : Conventional -------- short

Adhesive -------------------controlled e.g. Panavia due to oxyguard

Temporary cements

Ideal properties

1. Low strength to easily removal of the restoration

2. Seal against leakage of oral fluids

3. Low solubility

4. Obtundent, palliative.

5. Chemically compatible with provisional materials.

6. Easy to use

7. Easy removal of excess

8. Adequate W.T. & short S.T.

Zinc Oxide & Eugenol 1. Palliative effect

2. Strength properties

Improved Zinc Oxide & Eugenol Type 1 : + Alumina / quartz & EBA

Type 2 : + polymer resin

Physical properties

Superior to conventional ZnO & E but inferior to other cements.

Biologic properties

Excellent, palliative

Excellent initial seal

Setting not affected by moisture.

Disadvantages

1. Durability is limited

2. No adhesion

3. Soluble

4. Opaque

5. Not anticariogenic

6. W.T.

7. Difficult in excess removal

8. ZnO causes reduction in tensile bond strength of resin

cements, so all traces of temporary cement must be

removed

9. Free Eugenol softens some methacrylate resins

USES

1. When biocompatibility & pulp protection are needed

2. Patients with excessive salivation

3. Temporary cement

Cement Selection

Conventional casting traditional

cements.

Adhesive-bonded restoration adhesive

resins

Zinc Phosphate: Successfull

In case of concern to pulpal response resort to another.

Zinc Polycarboxylate: In case of concern about pulp vitality it is a more biologically

acceptable cement.

Glass Ionomer: In case of high caries incidence;

Resin Cements: In case of adhesive restorations

used in cases where higher retention through micromechanical

bonding is desired .

Cementation of a long Span Bridge

Requirements:

Long working time.

High mechanical properties.

Adhesive cement is better.

Selection:

Glass Ionomer.

Zinc Phosphate.

Adhesive Cement.

N.B.

Zinc Polycarboxylate should not be used due to their

short working time

Patients with high caries index

Cement with anticariogenic properties

should be used.

Glass Ionomer or Resin cements with

Fluoride additions

Deep Reductions

Biocompatible

polycarboxylate or reinforced ZnO & E.

Cementation of Porcelain Jacket Crown

and Porcelain Laminates

Translucent.

Early mechanical Strength.

Adhesive to the etched ceramic

restoration.

Composite resin cement.

N.B.

Glass Ionomer should not be used as it would be result in

fracture due to slow development of strength properties

Cementation of a restoration to a core

Amalgam : any cement

High copper amalgam : enhances bonding with polycarboxylate cement.

Composite Resin : resin cement as it bonds to it chemically.

Glass Ionomer : glass ionomer cement due to chemical similarity.

Cast Core:

Precious

. Polycarboxylate cement exhibits higher bond to Au than

phosphate.

Resin cements bond better to Au.

Non Precious

glass ionomer , polycarboxylate.

Resin cements :bond well to non-precious alloys.

Cementation of Posts

High flow.

High Strength.

Glass Ionomer or ZnPo4.

Adhesive cements

Cementation of Resin Bonded Retainers

Bonds to treated metal and enamel surface.

High mechanical Properties

Insoluble

Resin cement

In oral cavities with difficult moisture

control

Modified Zn O & E cements

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