صناعة

Dental materialDENTAL CEMENTSz

Dental Cements (DC) are generally hard, brittle materials. They are widely used in dentistry for a variety of application, primarily for restorative purposes.

DC USES:

1. Luting agents: The major function of DC is the retention (cementation) of restorations (crowns, bridges, inlays, onlays, veneers).
2. some DC are used as temporary filling materials.
3. some DC are used to provide thermal insulation and mechanical support to teeth restored with other materials, such as amalgam, composite, or gold.
4. cavity liners: some DC are used as liners to provide protection to the pulp from irritants or serve as pulp capping materials.
5. some DC are used as for special purposes in endodontics, and orthodontics.


CLASSIFICATION
classified according to function
Cements
functions

Compomer, composite, glass ionomer,

hybrid ionomer, zinc oxide-eugenol, resin,
zinc phosphate, zinc polycarboxylate.
Cementation of restorations

Compomer, glass ionomer, hybrid ionomer,

zinc polycarboxylate.
high strength bases
Cavity bases
Calcium hydroxide, glass ionomer,
hybrid ionomer, zinc oxide-eugenol.
Low strength bases

Calcium hydroxide

Cavity liners


Resin in a solvent
Varnishes

Special applications:

Resin, glass ionomer, hybrid ionomer,
zinc phosphate, zinc polycarboxylate.
Cementation of orthodontic bands and brackets

zinc oxide-eugenol.

Endodontic sealer

REQUERMENTS OF LUTING MATERIALS

1. biocompatible.
2. It should be strong enough to retain the restoration and to resist fracture when loads are applied to the restoration.
3. it should have setting characteristics and low viscosity which allow mixing and applying the material and proper seating of the restoration.
4. low solubility.
5. adequate thermal and electrical insulation.

REQUERMENTS OF CAVITY LINER AND CAVITY BASE MATERIALS:

These materials are placed in the occlusal floor and on the pulpal wall of the cavity prior to placement of certain filling materials.
1. biocompatible to the pulp.
2. it should provide thermal, electrical, and chemical insulation.
3. adequate strength to support the filling above it.
4. it should be compatible with the filling material and it does not interfere with the setting characteristics or properties of the filling.
5. it should be radiopaque, thereby aiding the diagnosis of carries around the filling.

REQUERMENTS OF ENDODONTIC CEMENTS

Endodontic filling is a combination of an inert filler (most commonly gutta percha) and a cement as a sealer.
1. biocompatible.
2. resist dissolution.
3. it should form a good seal both along the walls and at the apex of the canal.
4. it should be radiopaque, thereby to ensure that the root canal filling is satisfactory.
5. setting characteristics enable them to be forced in the warm, moist root canal before setting.

REQUERMENTS OF ORTHODONTIC CEMENTS

1. biocompatible.
2. it should have good bonding strength to both the enamel and to the material of bands and brackets (alloy, ceramic or plastic) .
3. it should have a protective influence against plaque and decalcification of the enamel around the bands and brackets.
4. it should have setting characteristics and low viscosity which enable positioning and adjustment of the brackets before setting.
5. it should have a minimal residue attached to the teeth after removing the bands and brackets.

Zinc phosphate cement:

Composition: Powder: zinc oxide and magnesium oxide. And Liquid: phosphoric acid in water
Properties:
1. Adequate mechanical properties
2. mechanical retention with tooth and restoration
3. its initial acidity and exothermic setting reaction after mixing , irritate the pulp.


Zinc polycarboxylate cement:
Composition: Powder: zinc oxide and polyacrylic acid.
Liquid: polyacrylic acid in water
Properties: 1. Adequate mechanical properties
2. mechanical retention with tooth enamel
3. stimulate the formation of reparative dentin.

Glass ionemer cements (GICs)

Powder: aluminosilicate glass
Liquid: polycarboxylate copolymer in water
Properties: 1. Good mechanical properties
2. not irritant to the pulp
3. have anticariogenic effect because of its fluoride releasing
4. the retention is mainly micromechanical with some chemical bonding with the tooth structure.
GICs are modified by adding special types of fillers in order to improve their mechanical properties:
a. metal-modified GICs: are modified by inclusion of metal fillers.
b. resin-modified GICs: are composed of resin, glass filler, initiator.

Zinc Oxide-Eugenol Cements (ZOE)

Composition: Powder: zinc oxide and acrylic resin
Liquid: eugenol
Properties: 1. Moderate mechanical properties
2. not irritant (neutral PH)
3. micromechanical retention with the tooth and restoration
4. These cements are contraindicated with the composite restoration because their eugenol interferes with the polymerization process of composite.

Manipulation:

all the former types of cements (zinc phosphate, zinc polycarboxylate, GICs, ZOE) could be summarized as follow:
1. the powder is incorporated as increments into the liquid on a cooled glass slab and mixed ( in little bits) with metallic cement spatula to the recommended consistency. The use of cooled slab is to increase the working time. The use of glass is to avoid loss or absorption of some cement constituents.
2. The mixed material is handled by metallic instrument and applied into clean, dried prepared tooth surfaces And adapted well to the recommended thickness.

Calcium Hydroxide Cement:

Composition: self-cured: consists of: base paste: (calcium tungstate, zinc oxide, calcium phosphate).
and catalyst paste: (calcium hydroxide, zinc oxide, zinc stearate).
Properties: 1. The mechanical properties are stronger than those of ZOE
2. stimulate the formation of reparative dentin
3. not irritant (high PH values)
Resin Cements : Composition: resin, glass filler
Three systems: Light-cured, dual-cured, and self-cured products.
Properties: strong, radiopaque, good wear resistance.
Manipulation: 1. The involved tooth surface is etched, cleaned, and dried.
2. bonding agent is applied.
3. resin cement is applied.

Cavity Liners

They are suspensions of calcium hydroxide in water or in an organic liquid. These materials are applied in a thin film, with no mechanical strength and thermal insulation properties. They are used for following purposes:
1. they may neutralize acids. they act as a protective barrier between dentin and restoration.
2. they minimize the fluid leakage between the tooth and the restoration.
3. some contain fluoride, therefore, provide some therapeutic benefits to the tooth.
Varnishes
Varnishes are not cements but they are used with cements to provide pulpal protection from irritants.
Composition: they are natural or synthetic resin in a volatile solvent (chloroform or alcohol).
Manipulation: they are applied by small cotton pledget, then gentle stream of air. The solvent evaporates to leave a very thin porous resinous film (1-40 ϻm thick). Therefore, more than one layer is necessary. The resin helps to seal the ends of dentinal tubules.