Dental Cements Libyan International Medical University
What are uses of dental cements • Pulpal protection a. liner b. base 2. Luting cementation 3. Restorations 4. Surgical dressing 5. Root canal sealer No cement is ideal for every clinical situation
Liners: materials that are placed as thin coatings, and their main function is to provide a barrier against chemical irritation. They do not function as thermal insulators. Selected primarily for pulpal medication. Base: cement base (1 to 2 mm) function as barriers against chemical irritation, provide thermal insulation, and resist forces applied during condensation of the restorative material.
Properties of dental cements Strength…….resin Vs ZOE Solubility……………microleakage Viscosity……….film thickness Biocompatibility Retention Esthetics
Requirements of dental cements • Non-toxic, non irritant to the pulp and other tissues • Insoluble in saliva and in liquids taken into the mouth • Adhesion between the cement and tooth tissue and between the cement and restoration • Antibacterial effect • Relief the pain of the pulp…..sedative
6. When used for cementation or luting, they should have: sufficient low viscosity to give a low film thickness, adequate working time, optical properties for cementation of translucent restoration. 7. When used for cavity bases and liners: protect the pulp from effects of other restorative materials, thermal insulation under large metallic restorations, chemical protection, electrical barrier to galvanism, rapid strength to permit packing of a filling materials and high modulus of elasticity to prevent fracture due to masticatory forces.
8. When used as filling materials: Ideally there should be bonding between filling and enamel and dentin and marginal leakage should not occur. Not dissolve in saliva or in fluids, low water absorption. Mechanical properties should be adequate to withstand force of mastication. Good esthetic and minimal dimensional changes. Coefficient of thermal expansion should be similar to that of tooth.
Zinc phosphate cement • Zinc phosphate is the oldest cement, it serves as standard for new types. • Powder: ZnO 90%, MgO, SiO2, pigments • Small particle size….fast setting. • Liquid: Phosphoric acid 40%, aluminum and zinc salts or metal ( why?) and water is 33% Buffering agents
Manipulation Zinc aluminophosphate + heat • Zinc oxide + phosphoric acid
Proper amount of powder should be incorporated into the liquid slowly on a cool slab….why? • Large amount of powder Temp. will increased and this speed-up the reaction. Particle size and P/L ratio
Retention.. Mechanical retention which based on the flow of cement into the microscopic irregularities on the tooth and surface of the restoration. • Biocompatibility…. Irritant to pulp? Depends on depth of cavity
Advantages: Good compressive strength (if correctly pro-portioned) Good film thickness Reasonable working time Resistance to water dissolution Disadvantages: Low tensile Strength no antibacterial action No chemical bonding brittle Not resistant to acid dissolution • Pulpal irritation? Low PH
Zinc phosphate cement Recommendations: Good cement for conventional crowns and posts with retentive preparations. Working time can be extended for cementation of multiple restorations by incremental mixing and cooled slab.
Zinc oxide eugenol cement • Characterized by their sedative effect on the pulp and neutral pH. • Powder: zinc oxide 69% + zinc stearate +zinc acetate + rosin • Liquid: Eugenol 85% + olive oil • Zinc oxide + eugenol zinc eugenolate • The reaction is reversible if there is moisture.
Applications • Temporary cementation of cast restorations. • Temporary filling material of teeth. • Cavity liner in deep cavity • Root canal sealer • Surgical dressing They are supplied in the form of powder and liquid or two paste-system or one ready made paste
Classical soft cement. • Attempts have been made to create a more permanent cement by adding O-ethoxy-benzoic acid (EBA) and by reinforcing it with aluminium oxide and polymethylmethacrylate. • But still it can not be recommended as a definitive lute for restorations.
Zinc polycarboxylate cements • Was the first cement system that developed an adhesive bond to tooth structure. • Powder: mainly zinc oxide with some tin or magnesium or aluminium oxide. Small quantity of fluoride can be added to provide leachable fluoride. • Liquid: 40% polyacrylic acid or an acrylic acid copolymer with other organic acids.
Setting reaction • Zinc oxide + polyacrylic acid zinc polyacrylate + unreactedZnO powder (amorphous gel matrix) • During mixing, powder is rapidly incorporated into the liquid in large quantities and mixed for 30 to 60 s over small area of glass slab to prevent destruction of the formed gel. • Working time approximately 2.5min as compared with 5 min. for zinc phosphate.
Applications • Cementation of cast or PFM restorations orthodontic bands. • Cavity liner or base. • Temporary filling material.
Retention • Chemically bond (ionicbond) to enamel and dentine. • It bonds to enamel more than dentine because of high content of calcium. • It does not bond to porcelain. • It bonds well to base of metal alloys and stainless steel (used in cementation of orthodontic band).
Advantages: 1. reasonable truck record 2. good compressive st. 3. adequate working time??? 4. bonds to enamel and dentine 5. adequate resistance to water dissolution (but less than zinc phosphate) 6. no adverse effect on pulp and less acidic than zinc phosphate cement.
Disadvantages: 1. low tensile st. 2. can deform under loading 3. can be difficult to obtain low film thickness. 4. not resistant to acid dissolution. 5. need for clean dry surfaces to utilize the adhesion potential.
Recommendations • Traditionally used for vital or sensitive teeth. • Occasionally useful to retain an unretentive provisional crown and bridge.
Resin cements • Basically its fluid composite, achieved by reduce amount of fillers. Advantages: Good compressive and tensile strengths. High tensile strength than conventional cements. Resistance to water dissolution. Relatively resistant to acid dissolution. Can enhance strength of ceramic restoration.
Disadvantages: • Film thickness varies between materials. • Excess material extruded at margin may be difficult to remove especially proximally. • Could be irritant to the pulp??
Recommendations • Must be used with or incorporation an effective dentine bonding agent. • Material of choice for porcelain veneers, ceramic onlays, inlays and crowns. • May be used to improve retention where preparation geometry sub-optimal, but clinical studies needed to determine long-term success.
Calcium hydroxide cements • Pulp-capping material that facilitate the formation of reparative dentine • Used as direct or indirect pulp capping. • Protective liner
Presented as: 1- calcium hydroxide suspensions:applied to the base of the cavity and dries out to give a layer of calcium hydroxide. Difficult to manipulate and form very weak lining. 2- chemical cured calcium hydroxide cement: Two paste system, most common Calcium hydroxide + salicylate calcium disalicylate Fillers such as barium sulphate provide radiopacity.
3- Light- cured calcium hydroxide cements: Its recently available and easy of application. Ca (OH)2 + Bis-GMA + barium sulphate + light sensitive material Properties: The pH (11-12). This degree of alkalinity stimulate odontoblast cells to produce reparative dentine. Easy manipulation Rapid hardening in thin layer Good sealing, high solubility, low compressive st. 5 MPa, they have antibacterial effect.
Varnishes • If amalgam or direct gold is to be used, the prepared cavity coated with a varnish. • Cavity varnish is natural or synthetic resin dissolve in a solvent such as ether. • The solvent evaporate leaving a thin film on the cavity preparation. • Main function to reduce microleakage that occur in conjunction with the amalgam restorations.
Cavity varnish inhibits microleakage during the first few weeks until corrosion products form. • A varnish is not used when the restoration is composite. Because it retard or prevent the polymerization.
Glass ionomer cements • GICs are widely (1970) used in the dental field because of their adhesion, bio-compatibility and anticariogenic properties. • Presented as: powder and liquid, capsules to be mixed with mixer, powder to be mixed with water.
Powder: mainly calcium aluminosilicate glass with fluoride salts. • Liquid: 50% aqueous solution of polyacrylic acid • GIC bond chemically to enamel and dentine during the setting process. • Ionic interaction with calcium and/or phosphate ions from the surface of the enamel or dentine.
Application 1. Cementation or luting for restorations 2. Cavity base or liners material 3. Orthodontic band cementation 4. Permanent restorations class III, V, especially for erosion/abrasion lesions and deciduous teeth 5. Pit and fissure sealant
Setting reaction • Acid base reaction between the ion leachable glass and polyacrylic acid, it involves three stages: • Dissolution • Gelation • Hydration
The structure of the set cement 1 2 3 (1) alumino-silicate glass, (2) silicate gel, (3) cross-linked polyacid
Un-reacted glass particles surrounded by silica gel held together by an amorphous matrix of hydrated calcium and aluminum polyacrylate salts. • Types: I. Cementation of restoration II. Restoration class III and V..low stress bearing areas. III. Lining or base material, pit and fissure sealing.
Working time about 2 min • GIC very sensitive to contact with water during setting • Initial set after 7 min • Cement margin should be coated with coating agent supplied with cement or Vaseline or varnish! • After 24 h, solubility in water is about 1%
Bonding • Ionic bond • Chelation of carboxyl groups of the polyacids with calcium in the apatite of enamel and dentine. • To achieve long lasting bond, the prepared surface must be clean and dry to remove a smear layer.
Advantages • Adhesion to tooth structure • Long term fluoride release • Biocompatibility • High compressive st • Low solubility in oral fluids
Disadvantages • Technique sensitive • Sensitive to water contamination and dehydration • Short working time and long setting time • Low abrasion resistance • Brittleness (low tensile st)
Metal reinforced GIC • Silver alloy admix, simple mix of silver alloy amalgam powder with GIC powder before mixing with acid. The addition of metals to regular GIC increase abrasion resistance, compressive st., and reduce the solubility in the oral fluids. However, it reduce fluride release and the bond st. Used as posterior filling material for decidous teeth.
Hybrid Ionomer (resin modified) • RMGIC, this material introduced to overcome the disadvantages of moisture sensitivity, short working time and long setting time of conventional GIC. • Addition of some polymerizable groups (resin) to the composition of GIC. • Could be light or chemical cure.
Dual cure GIC • THIS means that the cement sets by 2 reactions: conventional acid-base reaction and light curing reaction of resin.
Compomer • Combination of composite and conventional fluoride release GIC. • Has structure and physical properties and durability similar of composite and fluoride release of GIC, and it undergoes an acid-base reaction in the presence of saliva.
Applications • Restorations of deciduous teeth. • Class V (cervical caries, root erosion) • Class III • Intermediate class I and II • Cementation of cast alloys and all ceramic restorations