Dental Cement

Dental Cements

Introduction
Dental cements are a classification of dental materials that are routinely used in the placement of indirect restorations.

Classification of Cements

Type I Luting agents, which include permanent and temporary cements Type II Restorative materials, such as glass ionomers Type III Liners or bases placed with the cavity preparation

Luting Agent

Type I dental cements act as adhesives to hold together the casting and the tooth structure. Luting agents are designed to be either permanent or temporary.

Fig. 45-1 Casting ready to be cemented.

Permanent Cement
Permanent cement is used in the long‑term cementation of gold and ceramic restorations such as inlays/onlays, crowns, bridges, veneers, and orthodontic fixed appliances.


Temporary Cement
Temporary cements are used if a restoration would have to be removed as a result of sensitivity or other symptoms, as well as for the temporary cementation of provisional coverage.

Variables Affecting Cements

Mixing time Before mixing, follow the manufacturer's directions.Measure the powder and liquid according to the intended use.Separate the powder and liquid to make space for mixing. Divide the powder into increments.When increment sizes vary, smaller increments are incorporated first.Incorporate each powder increment into the liquid and then mix thoroughly. (Cont’d)

Variables Affecting Cements

(Cont’d)Humidity Premature exposure to warm temperatures or humidity can result in a loss of water from the liquid or addition of moisture to the powder.Powder-to-Liquid RatioIncorporating too much or too little powder will alter the consistency. TemperatureSome cements undergo an exothermic reaction.

Types of Cements

Glass ionomerComposite resinZinc oxide–eugenol PolycarboxylateZinc phosphate

Glass Ionomer

Chemical makeup Liquid: itaconic acid, tartaric acid, maleic acid, and water Powder: zinc oxide, aluminum oxide, and calcium

Types of Glass Ionomer

Type IFor the cementation of metal restorations and direct‑bonded orthodontic bracketsType II Designed for restoring areas of erosion near the gingivaType III Used as liners and dentin-bonding agents

Benefits of Glass Ionomer

Powder is an acid‑soluble calcium. The slow release of fluoride from this powder helps inhibit recurrent decay. Glass ionomer causes less trauma or shock to the pulp than do many other types of cements. Glass ionomer has a low solubility in the mouth. It adheres to a slightly moist tooth surface. It has a very thin film thickness, which is excellent for seating ease.


Supply of Glass Ionomer
Type I (powder/liquid) Mixed manually on a paper pad or a cool, dry glass slab (slab increases the working time of the cement) Type I (premeasured capsules) Triturated and expressed through a dispenser.

Fig. 45-3 Premeasured capsules of glass ionomer permanent cement.

Composite Resin
Chemical makeup Physical properties comparable to those of composite resins Low film thickness (thinner in consistency than composite resins) Insoluble in the mouth

Uses of Composite Resin

Cementation of ceramic or resin inlays and onlays. Cementation of ceramic veneers. Cementation of orthodontic bands. Direct bonding of orthodontic brackets. Cementation of all metal castings.

Supply of Composite Resin

Powder and liquid mix Syringe-type applicator Base and catalyst Light-cure/dual-cure system Recommended portions of either application are dispensed onto a paper pad and mixed rapidly with the use of a spatula.

Fig. 45-4 Examples of composite resin cements supplied in variable systems.

ZOE
Chemical makeup Liquid: eugenol, H2O, acetic acid, zinc acetate, and calcium chloride Powder: zinc oxide, magnesium oxide, and silica

Types of ZOE

Type I Lacks strength and long‑term durability and is used for temporary cementation of provisional coverageType IIHas reinforcing agents added for the permanent cementation of cast restorations or appliances

Fig. 45-5 ZOE type I cement for temporary cementation.

Fig. 45-6 ZOE type II cement for permanent cementation.
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Supply of ZOE

Type I (paste) Supplied as a two‑paste system as temporary cementPastes dispensed in equal lengths on a paper pad and mixed Type II (liquid/powder)Mixed on an oil‑resistant paper padMixing time of 30 to 60 seconds Setting time in the mouth of 3 to 5 minutes

Polycarboxylate Cements

Chemical makeup Liquid: polyacrylic acid, itaconic acid, maleic acid, tartaric acid, and water Powder: zinc oxide
.

Use of Polycarboxylate

Permanent cement for cast restorations, stainless-steel crowns, and orthodontic bands As a nonirritating base under both composite and amalgam restorations As an intermediate restoration


Supply of Polycarboxylate
Powder/liquidLiquid may be measured with the use of either a plastic squeeze bottle or a calibrated syringe‑type liquid dispenser.The liquid has a limited shelf life because it thickens as its water evaporates.Mixing is carried out on a nonabsorbent paper pad.

Fig. 45-7 Powder and calibrated syringe of polycarboxylate cement.

Zinc Phosphate
Chemical makeup Liquid: phosphoric acid, aluminum phosphate, and water Powder: zinc oxide, magnesium oxide, and silica

Types of Zinc Phosphate

Type I (fine grain) This type is used for the permanent cementation of cast restorations such as crowns, inlays, onlays, and bridges. It provides the very thin film layer necessary for accurate seating of castings. Type II (medium grain) This type is recommended for use as an insulating base for deep cavity preparations.

Supply of Zinc Phosphate

Type I (powder/liquid) Powder is divided into increments of varying sizes. It is critical that the powder be added to the liquid in very small increments. The cement must be spatulated slowly over a wide area of a cool, dry, thick glass slab to dissipate the heat.

Fig. 45-8 Zinc phosphate type I cement for permanent cementation.

Cement Removal
Operator preparedness and knowledge The procedure requires certain instruments: Explorer, mouth mirror, excavator Use a fulcrum. Use dental floss in and around the embrasure areas.


Fig. 45-9 Excess cement must be removed after the setting process.