Dental Cements 1 PDF

Dental Cements I By Dr. Dina Sami Associate Professor of Dental Biomaterials Contents 1. Uses of dental cements 2. Requirements of dental cements 3. Pulp protection 4. Classification and types of dental cements Zinc oxide eugenol cements Calcium hydroxi...

Dental Cements I By Dr. Dina Sami Associate Professor of Dental Biomaterials Contents 1. Uses of dental cements 2. Requirements of dental cements 3. Pulp protection 4. Classification and types of dental cements Zinc oxide eugenol cements Calcium hydroxide cements  Uses of dental cements 1. Luting or cementation of restorations: A cement behaves like a glue that fixes indirect restorations e.g. inlays crowns and bridges to the tooth structure. Cementation Permanent cementation: For the long-term cementation of indirect restorations such as inlays, crowns, bridges and laminate veneers Temporary cementation: cementation of a temporary restoration till the permanent restoration is fabricated. 2. Filling material Temporary restoration when final filling material can’t be finished at the same visit Permanent as in glass ionomer 3. Protection of the dental pulp as in varnishes, liners and bases 4. Cementation of orthodontic appliances 5. Gingival and periodontal packs 6. Endodontic sealers.  General requirements for dental cements 1. Biocompatible: non toxic and non irritant 2. Provide chemical or mechanical retention or both of restoration to tooth structure. 3. High tensile strength, fracture toughness and fatigue strength to resist fracture under forces transmitted to it from restoration. 4. Low solubility in neutral and acid environments to maintain marginal seal  General requirements for dental cements 5. Radiopaque: to distinguish between a luting agent and recurrent caries under a fixed prosthesis 6. Film thickness: luting agent needs to have low viscosity to fill the space between the crown or bridge and the tooth, and to ensure proper seating of the restoration with a film thickness of 25 µm or less  General requirements for dental cements 7. Aesthetics: Optical properties should be similar to tooth structure if used to cement translucent restorations e.g. all- ceramic restorations. 8. Has antibacterial effect Pulp protection From 1. Thermal injury 2. Chemical irritation 3. Galvanic shock 4. Mechanical forces during amalgam condensation and masticatory forces. Cavity liners: Thin layers of material (≤0.5 mm) used as chemical insulator between the restoration and the remaining dentine after cavity preparation. Base Cavity bases: Are used in thicker layers below permanent restorations (1-2 mm) to protect the pulp from injury from thermal, Liner electrical, mechanical (e.g. forces of amalgam condensation) factors Cavity varnish Varnish acts as a protective barrier between dentin and the restorative materials that MINIMIZES the penetration of oral fluids at the restoration-tooth interface. Varnishes are resins in a volatile solvent which when applied to a cavity surface, the solvent evaporates leaving behind a thin film. Pulp Capping Is placing a special material in contact with or close to the pulp to encourage formation of reparative dentin and promote the healing of the pulp. Types of Pulp Capping 1. Direct Pulp Capping When the pulp capping agent is placed directly over the pulp e.g. during; o Traumatic fractures of the tooth o Exposure during cavity or crown preparation 2. Indirect Pulp Capping When the material is placed indirectly over the pulp, it can still induce new dentin formation through the remaining thin dentinal wall. Indirect pulp capping During treatment of teeth with deep caries, most of the decay is removed, but some soft dentin remains over the pulp chamber If this layer is removed it would expose the pulp and cause irreversible pulpitis. The thin layer soft dentin is intentionally left in place then covered by a pulp capping material that promotes formation of reparative dentin Examples of pulp capping materials: calcium hydroxide, mineral trioxide aggregate (MTA) Types of dental cements 1. Cements based on Zinc Oxide. 2. Cements based on Alumino Silicate Glasses 3. Other cements Resin cements. Calcium –Hydroxide cements. Cavity liners and Varnishes. 1. Cements based on Zinc Oxide. Zinc Oxide powder Mix with Eugenol Phosphoric acid Polyacrylic acid Zinc oxide eugenol Zinc phosphate Zinc polycarboxylate cement cement cement 2. Cements based on alumino-silicate glass Alumino-silicate glass powder Mix with Polyacrylic acid Phosphoric acid Glass ionomer Silicate cement cement  1. Zinc oxide eugenol cement They have a sedative effect on the pulp due to presence of eugenol and their neutral pH. Types 1. Conventional zinc oxide eugenol 2. Modified zinc oxide eugenol Forms: powder and liquid 1. Conventional zinc oxide eugenol Composition Powder: 1. Zinc oxide (ZnO): main reactant. 2. Rosin: reduce the brittleness of the set cement 3. Zinc stearate: plasticizer 4. Zinc acetate: accelerator and improves strength of the cement Liquid: 1. Eugenol 85%: active ingredient of clove oil 2. Olive oil (15%): makes cement more plastic during mixing and decreases brittleness after setting. Setting reaction It is an acid – base reaction. First ZnO undergoes hydrolysis in presence of water to form Zn(OH) 2 ZnO+ H2O Zn(OH)2 Zn(OH)2 reacts with eugenol to form Zn eugenolate in a chelation reaction. Zn(OH)2 + Eugenol Zn eugenolate Water is important to begin the reaction, so the reaction is faster in a humid environment.  The microstructure of the cement are formed of unreacted powder particles of ZnO and eugenol embedded in a matrix of Zn eugenolate Zn eugenolate matrix  Manipulation Powder/ liquid is 3:1 Mixing is done using a glass slab and stainless steel spatula. Most of the powder is added to the liquid at once followed by smaller increments to adjust the viscosity.  Properties of Zn oxide eugenol cements 1. pH is about 7 so has little or no effect on pulp in deep cavities. 2. They have a palliative obtudent effect on the pulp due to the presence of eugenol 3. They have a bacteriostatic effect due to the presence of eugenol 4. Have high solubility in which leached eugenol is replaced by water.  Properties of Zn oxide eugenol cements 4. Have poor mechanical properties (compressive strength =15 MPa, tensile strength =5 MPa) 5. Opaque due to the presence of unreacted zinc oxide particles. 6. Bonding to enamel and dentine by mechanical interlocking. 7. Eugenol inhibits the setting of resins, so can not be used with resin composite restorative materials Uses of zinc oxide eugenol cements 1. Cavity liner in deep cavity 2. Temporary filling material 3. Temporary cementing agent 4. Surgical dressing 5. Root canal sealer 2. Modifications of ZnO eugenol 1. Polymer reinforced cements Resin polymer is added to increase strength of the set cement Composition 1. Powder Zinc oxide 80% Polymethyl methacrylate 20% 2. Liquid Polystyrene 10% dissolved in eugenol  Compressive strength 38 MPa. Uses Temporary filling material Final cementation Cement base 2. Ethoxy benzoic acid cement (E.B.A. cement) Composition 1. Powder: Zinc oxide 70% Alumina 30% 2. Liquid: EBA ethoxybenzoic acid 60% Eugenol 40% 2. Ethoxy benzoic acid cement (E.B.A. cement) Compressive strength 85 Mpa Uses Temporary filling material Final cementation Base under amalgam