Dental Cements: Properties and Applications

• Study notes on dental cements

Dental Cements

• Dental cements serve various purposes in dentistry, including cavity lining, luting applications, and sometimes as filling materials.
• They can protect the pulp from irritants (mechanical, chemical, thermal, or electrical) and act therapeutically as pulp-capping agents.
• Varnishes aren't cements but used with cements to protect the pulp.
• Cements are used in 40-60% of all restorations due to them being hard brittle materials formed by mixing a powder and liquid.

Applications of Dental Cements

• Permanent cementation of fixed restorations (inlays, crowns, bridges) involves using cements as luting agents for fixation.
• Temporary cementation, serving as a high or low strength as a liner.
• Cementation of orthodontic brackets and bands.
• Gingival tissue pack and surgical dressing
• Temporary and permanent filling materials, root canal filling

Requirements of Cements

Biological Properties

• Cements should be non-toxic and non-irritant to the pulp and other dental tissues.
• Desirable to have a bacteriostatic effect when used in cavities with residual caries.
• Provide protection to the pulp from restorative materials, acting as thermal and chemical insulation.
• Offers electrical insulation against galvanic effects under metallic restorations and an obtundent effect.

Mechanical Properties

• Cements must be strong enough for cavity lining and for filling material to be paced on (as insulating base).

Optical Properties

• Should match the tooth substance, especially for translucent porcelain and acrylic crowns.

Solubility

• They need to be insoluble in saliva to prevent marginal leakage, restoration loss, and recurrent caries.

Bonding

• Should adhere well to enamel, dentin, gold alloys, porcelain, and acrylic, but not dental instruments.

Rheological Properties

• Cement should have a low film thickness for luting.
• Reasonable working and setting time.
• Film thickness depends on powder particle size, powder/liquid ratio, and viscosity.

Classifications of Dental Cements

According to Chemical Ingredient

• Zinc Oxide-based cements (ZOE, ZPhC, ZPCC).
• Alumino-Silicate Glass-based cements (SC, GIC).
• Resin cements.
• Other cements (Varnishes, liners).

According to Setting Reaction

• Acid-Base reaction cements (ZOE, ZPhC, ZPCC, SC, GIC) use powder and liquid, where the liquid acts as the acid and the powder as the base.
• Polymerization reaction cements (resin cement) polymerize through light or chemical activation.
• Dual-cured cements (resin-modified glass ionomer) set via acid-base and polymerization.
• Tricure cements harden through all three mechanisms.

According to Application

• Type I is for luting crowns, bridges, inlays, onlays, and orthodontic appliances.
• Type II is for restorative applications, sealers, and temporary filling.
• Type III is for bases and liners.

Cements Based on Zinc Oxide

Zinc-Oxide Eugenol Cement

• Used extensively since 1890 with varied properties based on use.
• Generally have low strength, prompting the introduction of modified versions.
• Types include temporary cementation, permanent cementation, base/temporary restoration, and cavity liner.

Composition

• Presentation: powder and liquid or two-paste system.
• Powder components: Zinc oxide (primary), Magnesium oxide (small quantities), Zinc acetate (≤1% to accelerate setting).
• Liquid components: Eugenol (from clove oil), Olive oil, Acetic acid (accelerates setting).

Manipulation

• Requires a thick glass slab and stainless steel spatula.
• In a powder/liquid system, the powder is added to the liquid to achieve a thick consistency.
• Slow wetting of zinc oxide by eugenol requires prolonged and vigorous spatulation.
• A P/L ratio between 4:1 and 6:1 by weight is ideal.
• Two-paste systems use equal lengths mixed until uniform.

Setting Reaction

• Zinc oxide + eugenol (with water) → zinc eugenolate + unreacted zinc oxide.
• The set mass has residual ZnO particles bonded by a matrix of Zn eugenolate and free eugenol.
• If water is absent in the reaction, the reaction will not occur.

Factors Affecting Setting Time

• Finer powders have a greater surface area, speeding up the reaction.
• Thicker mixes (more powder) set faster.
• Increased temperature accelerates setting; cooling slows it.
• Accelerators include alcohol, glacial acetic acid, and water.
• Retarders include glycol and glycerin.

Applications

• As a temporary filling.
• Dressing for deep cavities.
• Pulp-capping material.
• Pulp protector under phosphate cements in deep cavities.
• Root canal filling material, temporary cementation of crowns and bridges with gingival tissue pack.

Properties of Zinc Oxide Eugenol Cements

• Sedative effect, making them suited for deep cavities.
• Bacteriostatic and obtundent.
• Protection of the pulp when used under metallic fillings.

Solubility and Disintegration

• High solubility, set cement dissolves in water and disintegrates rapidly when exposed.

Opacity

• The set cement is opaque because of the unreacted ZnO.

Film Thickness

• Influenced by powder particle size, P/L ratio, and mix viscosity.
• Film thickness is higher than other cements.

Strength

• Low compressive strength (0.7 to 7 MN/m²).
• Weakest dental cements besides calcium hydroxide.

Adhesion

• No chemical bonds with enamel and dentine.
• Should not be used as a lining under composite fillings to avoid inhibiting polymerization and staining.

Modified Zinc Oxide Eugenol Cements

• Aim to improve strength and reduce solubility through added ingredients.
• Available as resin-bonded (reinforced) and E.B.A. cements.
• Includes hydrogenated resin or polystyrene dissolved in eugenol.

Resin Bonded Cements

• Used as luting agents, bases, and temporary filling materials.
• Adequate strength for the final cementation of restoration.
• These cements have a long working time with a setting time of 6 to 10 minutes.
• Heat and moisture accelerate setting and cooling the glass slows it.
• Compressive strength around 38 MN/m², provide a bland effect on the pulp and good initial sealing.
• May cause softening/discoloration of polymeric composites.

E.B.A. Alumina Modified Cements

• E.B.A. is ortho-ethoxy-benzoic acid
• Used as a base under amalgam restorations, for cementation of inlays, crowns, and bridges.
• Can be used as a temporary filling material

Composition

• Powder: Zinc oxide (64%), Fused quartz or alumina (30%), and Hydrogenated resin (6%).
• Liquid: Ortho-ethoxybenzoic acid (62.5%) and Eugenol (37.5%).
• Compressive strength of E.B.A. cements is around 90MN/m².
• A P/L ratio of 7:1 or greater can be used.
• Film Thickness 25µm.
• Solubility and disintegration in water 0.05% wt.
• Mild effect on the pulp, can be comparable to those of zinc phosphate cements.

Other Modified Types

• Non-eugenol cements (suitable for patients sensitive to eugenol).
• Rapid-set Zinc Oxide-Eugenol cements.
• Zinc Oxide / Zinc Sulphate Cements

Zinc Phosphate Cements

• Introduced in 1878 and remains one of the oldest cements in dentistry.
• Used for cementation of inlays, crowns, bridges, and orthodontic bands.
• High strength base and to protect the pulp from mechanical, thermal and electrical stimuli along with temporary filling material.

Composition

• Powder: Zinc oxide (90%), Magnesium oxide (10%), and small amounts of pigments.
• Liquid: Concentrated Ortho-phosphoric acid (H3PO4) (38.5%), Water (40%), Alumina-phosphate (2.5%), and sometimes Zinc phosphate (5%).
• Specifications: -Type I, Fine grain for luting, (Film thickness should be 25 μm or less.) -Type II, medium grain for luting and filing with film thickness is not more than 40 μm
• Supplied as powder and liquid systems or capsules of pre-portioned powder and liquid.

Setting Reaction

• Zinc oxide + phosphoric acid → amorphous zinc phosphate (insoluble) + unreacted zinc oxide + heat.
• The resulting cement consists of residual zinc oxide in a phosphate matrix with heat given out during setting.
• Variations exist on manufactures
• The setting time is 4-9 minutes.
• Increased by using a cold mixing slab

Factors Accelerating the Setting Reaction

• A high powder to liquid ration results in a faster reaction.
• Fast addition of powder to liquid, presence of moisture.
• Higher temperatures will accelerate the reaction.

Manipulation

• Powder added to liquid in small portions to achieve the desired consistency.
• Proper mixing is done by stainless steel spatula using brisk circular motion.

Properties

• Thin mix is required to permit the cement to flow.
• pH rises (becomes neutral) within 1-2 days.
• Initial irritation and solubility is 0.3% by weight in distilled water and soluble in lactic solution.
• Opaque (UNREACTED Z O) with a film thickness of 15-20 microns.

Modified Zinc Phosphate Cements

• Used in cementation of splint and fixed orthodontic appliances.

Copper Cements

• Black copper cements contain cupric oxide.
• Red copper cements contain cuprous oxide.

Silver Cements

• Advantages over zinc phosphate cements have not been substantiated

Zinc Polycarboxylate Cements

• Created substituting phosphoric acid of zinc phosphate cement with polyacrylic acid.
• The first adhesive cement that bonds to tooth structure and metal, more biocompatibile
• Presentation; powder and liquid mix
• Can be used in cementation of inlays, crowns, bridges, porcelain.
• Molecular weight between 20.000-50.000 which accounts for viscous nature of the liquid.
• A glossy surface is required for adhesive group.
• Properties may vary, but strength and films are comparable.

Compisition

• 1-%5 Magnesium oxide
• Acid strength is weaker than phosphoric acid.

Setting reaction

• Setting material is a cored structure containing considerable unreacted Zinc oxide.

Strength

• Higher compressive strength is obtained with a high P/L ratio with alumina.

Glass-Ionomer Cements

• Combines silicate and polycarboxylate cements
• Adhesive color for good restoration.

Set time

• Takes 6-8 minutes from mixing.
• Improves handling characteristics, increases working time and shortens setting time.
• Slows release of aluminum in improved cross linking

Properties

• Anticariogenic properties with prolonged extended release.
• Solubility is high.
• Chemical adhesion for bonds.
• Transclusent cements for great esthetics.