Pulp Protection Using Cavity Liners & Bases PDF

PULP PROTECTION USING CAVITY LINERS & BASES CONTENTS Introduction Remaining Dentin thickness Pulp irritation Pulp Protection Materials Introduction One of the main goal of operative dentistry is to preserve the health of dental pulp. Normal pulp is a coherent soft tiss...

PULP PROTECTION USING CAVITY LINERS & BASES CONTENTS Introduction Remaining Dentin thickness Pulp irritation Pulp Protection Materials Introduction One of the main goal of operative dentistry is to preserve the health of dental pulp. Normal pulp is a coherent soft tissue, dependent on its normal hard dentin shell for protection. Sound Dentin has excellent buffering capacity to neutralize the effects of cariogenic acids and has ability to insulate the pulp from temperature changes during cavity preparation. Introduction The number of tubules cut during cavity preparation and depth of the cavity will affect the area and magnitude of the pulpal response. Therefore, large and deeper cavities will have an intense pulpal response. Conservation of remaining tooth structure is more important to pulpal health than is replacement of lost tooth structure with a cavity liner or base. Remaining dentin Thickness The remaining dentinal thickness (RDT), from the depth of the cavity preparation to the pulp, is the single most important factor in protecting the pulp from insult. No material that can be placed in a tooth provides better protection for the pulp than dentin. Little pulpal reaction occurs when there is an RDT of 2 mm or more. Pulpal irritants Type of stimulus Examples of stimulus Physical ✓Thermal+ electrical Mechanical ✓Handpiece + ✓Traumatic occlusion Chemical ✓Acid from dental materials Biologic ✓Bacteria from saliva Are materials placed between dentin (and sometimes pulp) Materials used and the restoration to provide for pulp pulpal protection or pulpal response. protection Protective needs for a restoration vary depending on the extent and location of the preparation and the restorative material to be used.  9 materials used for pulp protection are classified as: Cavity Varnish  Functions and importance: Pulp protection: - Thermal & electrical Protection Conductivity of metallic restorations to thermal & electrical changes. - Chemical Protection  Acids and monomers in restorative materials. - Mechanical Protection  The force of condensation. - Biological Protection  Bacteria from saliva. Schematic view of needs for pulpal protection below metallic restoration. Varnishes, liners, and/or bases may be added to tooth preparation under amalgam for purposes of chemical, electrical, thermal, or mechanical protection, and/or pulpal medication. Ideal requirements of liners and bases: 2. Compatible with the restorative material → 1. Non-irritant to the i.e. not react with it or pulp. interfere with its setting reaction. 3. Strong enough to 4. Reduce the thermal withstand the force of conductivity of mastication and force metallic restorations. of condensation. Ideal requirements of liners and bases: 5. Improve 6. Prevent marginal seal of chemical 7. Reduce restorative exchange galvanic action of material and between the certain metallic adaptation to restoration and restorations. cavity walls and the tooth. margins. 8. Resist 9. Enhance the 10. Easy to be degradation in formation of manipulated and oral fluids. reparative dentin. applied. CAVITY SEALERS: Materials in this category provide a protective coating (2-5micron thick) to the walls of the prepared cavity and a barrier to leakage at the interface of the restorative material and the walls. The term sealer implies total prevention of leakage. They come in 2 categories:- a) VARNISH b) ADHESIVE SEALERS Cavity Varnish Also known as solution liners. Composed of natural gums such as copal, rosin, or synthetic resin dissolved in an organic solvent (acetone, chloroform or ether) Varnish coatings formed by the evaporation of the organic solvent leaving behind a protective film. Film is very thin [2-5 µm] and provides no thermal insulation. Two coats of varnish are necessary, otherwise small pinholes may occur. Cavity Varnish Reduces dentin permeability by 69% and marginal microleakage for 4-6 months. Applied on enamel & dentin. These are applied before application of acidic base (Zinc Phosphate) but after application of base if base bonds with dentin or a liner having therapeutic effect on pulp eg GIC and zinc polycarboxylate cements and Ca(OH)2 and Zinc oxide liner Advantages of Cavity Varnish Reduce marginal leakage Seal the dentinal tubules Reduces postoperative sensitivity Prevents discoloration of tooth by blocking the migration of ions into the dentin. Indications of Varnish: 1- Under amalgam restorations as it seals dentin surfaces. Reducing marginal leakage of oral fluids at tooth/ restoration interface. prevents migration of ions from metallic restoration to the tooth that results in : - Chemical irritation to the pulp. - Discoloration of the tooth (amalgam blues). 2- Under acid containing cements (zinc- phosphate) as it reduces acid penetration into dentin. N.B. Varnish layer at the restoration enamel interface also provides a means of electrically isolating metallic restorations from external electrical circuits with restorations in adjacent teeth. Otherwise, amalgam restorations may produce small electrical currents during the first few days that cause patient pain or discomfort. This sensitivity rapidly disappears as electrochemical corrosion and/or tarnish modify the surfaces of the amalgam. Contraindications of Cavity Varnish Use of varnish is contraindicated under glass ionomers as it interferes the bonding of tooth to these cements With restorative resins varnish is not used because the varnish liners dissolve in the monomer of the resin and it also interfere the polymerization of resins. Application: The cavity should be dried and cleaned. The varnish is applied with small cotton pellet which is placed in the solution only once to avoid contamination of the bottle of varnish. The varnish is then applied to the cavity in a continuous layer. As the solvent evaporates, it will leave small pits in the film of varnish → so, two or more layers of varnish should be applied.  Over thickness should be avoided to prevent spacing between the tooth and restoration. Excess varnish is removed from the external tooth surface by the solvent present in the varnish kit. N.B. - Varnish is applied to both enamel and dentin. - Varnish bottle should be stored in dark, cool place to prevent vaporization of the solvent. Varnish is applied on the walls of a prepared cavity to decrease the microleakage and prevent tooth discoloration of tooth N.B The bottle should be kept closed when not in use to reduce the amount of solvent that evaporates. If the liquid becomes too thick to be used clinically, a solvent thinner could be used. 2. ADHESIVE SEALERS Resin Bonding agents commonly used under composite restorations Uses: Acid etching and bonding agent ensures a durable bond to enamel by micromechanical retention. Sealing of dentinal tubules, reduction of dentin sensitivity Under amalgam restorations, the insoluble adhesive layer act as a barrier.  25 Cavity Liners  1. Calcium Hydroxide (Ca(OH)2 Types of cavity liners 2. Zinc oxide eugenol (type IV) 3. Glass Ionomer can be used a liner under composite (type III)  27 Calcium Hydroxide (Ca(OH)2  28 Advantages of Calcium Hydroxide (Ca(OH)2 Disadvantages: 1-Has no obtundant property. 2-It could not withstand the force of condensation and occlusal loading force. So, it is contra-indicated to be used under metallic restorations without strong base overlying it. 3-Weak compressive strength 4-High solubility A visible light-cured (VLC) calcium hydroxide liner consists of calcium hydroxide and barium sulfate dispersed in a urethane dimethacrylate resin containing initiators and accelerators activated by visible light. A visible light-cured (VLC) calcium hydroxide liner developed to overcome the limitations (poor physical properties) of the chemical cure calcium hydroxide. Advantages: 1. Set on command, 2. Improved Physical properties 3. Reduce solubility Indications: 1- As a liner (sub-base) to cover dentin forming the pulpal floor of deep cavities. 2- As capping agent either direct or indirect, to stimulate reparative dentin formation → so, it is the material of choice in deep cavities with suspected pulp exposure. (a) Calcium hydroxide set-up. (b) Step 1 – equal volumes of the base and catalyst are dispensed. (c) Step 2 – final mixed material with a homogenous color achieved. N.B Calcium hydroxide has largely been replaced by bioactive cements such as: Mineral trioxide aggregate (MTA) and biosilicate cement (Biodentine, Lancaster, PA) for the same function.  34 Zinc oxide eugenol Advantages: 1- perfect initial sealing which prevent the ingress of saliva, bacteria, and food debris to dentin. 2- Has effective thermal insulating capacity. 3-Capable of blocking the penetration of metallic ions of metallic restorations and acids of cements to dentin. Disadvantages: 1- Low crushing strength. 2- Slow setting. Indications: Usually used as temporary filling material to seal up cavities between visits. Contra-indications: 1-Contra-indicated to be used as base material due to its low crushing strength → i.e. could not withstand the force of condensation. 2-Contra-indicated to be used as sub-base material due to its slow setting which does not enable the immediate application of the overlying base. 3-In case of cavities prepared to be restored with resinous materials as composite → as the eugenol will retard or prevent its polymerization. 4-Contra-indicated to be used as direct pulp capping as it leads to pulp necrosis.  37 ✓ Glass ionomer liner: Flowable composites  CAVITY BASES Cavity bases are used as dentin replacement materials and for blocking out undercuts for indirect restorations. They are used to protect pulp against thermal injury, galvanic shock, chemical irritation. They should be able to provide support for the restoration that is subjected to occlusal loading. They are used in a thickness of greater than 0.75mm. (1-2mm) Generally used bases are: a. Zinc Phosphate Cement b. Reinforced ZOE (Type III) c. Polycarboxylate cement d. Fast setting GIC (Type III)  ZINC PHOSPHATE Material of choice as base under metallic restorations. It is an excellent thermal and electrical insulator. It has good compressive strength – over 119MPa. It has low solubility in water. Composed essentially of zinc oxide powder and aquas solution of phosphoric acid, it is acidic in nature when placed [ph of 3-4] and for a short time until the reaction is completed. After one hour it comes to 6. This acidity is very detrimental to the pulp dentin organ. It requires a cavity liner under the cement in deep cavities and varnish.  42 Advantages: 1- Low thermal conductivity → so, it is a good thermal insulator for the pulp. 2- High strength properties → So, it can withstand condensation and mastication forces. Disadvantages: 1- Increases dentin permeability due to etching by acids. 2- Irritation due to its acid content → so, cavity varnish or calcium hydroxide as sub-base are used to minimize or neutralize acidity of the cement. Indications: Replacement of the dentin lost by extensive dental caries to act as:→ Thermal insulating base under metallic restorations. Contra-indications: Due to its acidity → It is contra-indicated to be applied in deep cavities without calcium hydroxide sub-base. ZINC POLYCARBOXYLATE First dental cement to exhibit chemical bonding to teeth, Chemical adhesion to the calcium ions in enamel and dentin. Minimally irritating to the pulp. The acid has low diffusion mobility into underlying dentin due to high molecular weight and its immediate complexing with dentinal calcium and proteinaceous substances. Good thermal insulator. Varnish should not be applied under it as it inhibits the chemical adhesion ZINC POLYCARBOXYLATE Advantages: Disadvantages: 1- Adhesion to tooth 1- Twice soluble structure. than zinc phosphate cement. 2- Produces minimal 2- Lower pulp irritation as it is compressive less acidic than zinc strength than zinc phosphate cement. phosphate cement  Glass Ionomer Cement Type III GIC is used as base or liner. The powder is a mixture of ion leachable glasses, and the liquid is a copolymer of polyacrylic acid. Glass ionomer has been used as a cavity liner or base in an attempt to take advantage of 2 highly desirable properties: a) chemical bond to tooth structure and b) fluoride release which aids in anticariogenic action of GIC. Fluoride release decreases with passage of time. Pulpal response is more favorable than zinc phosphate. If the RDT is less than 0.5 mm, it may be necessary to protect the dentin from direct contact with the GIC by using calcium hydroxide liner. Glass ionomer cement: Composition: 1- Powder: → Fluoro-alumino-silicate glass). 2- Liquid: → Aqueous solution of copolymer of polyacrylic acid. Advantages of GIC: 1- Adhesive to tooth structure. 2- Anticariogenic: → Through fluoride release. 3- Biocompatibility to the pulp, due to: → a) Its high molecular weight. & b) weak polyacrylic acid. 4- Thermal and electrical insulator 5- Compatible with all restorative materials. 6- Semi-translucent color → when dealing with anterior restorative material it will not affect the color of the final restoration. 7- Higher modulus of elasticity, subsequently increased support for amalgam restorations. When mixed to a higher powder liquid ratio. Disadvantages of GIC: 1- Water sorption, leading to: → Leakage. → Discoloration. → Penetration of microorganisms. 2- Low wear or abrasion resistance: → So, when used as a restoration, it should not be placed in stress bearing areas.  51 Reinforced zinc oxide / eugenol cement: It is a modified zinc oxide/eugenol cement, where additives are added to both powder and liquid to overcome its disadvantages. The main disadvantages of Zn/E cement are: 1- Low strength. 2- Prolonged setting time. Composition: 1- Powder: → Zinc oxide and zinc acetate. → 10 – 20% resins → increase strength from (e.g. Polystyrene, Polycarbonate). → Alumina → For reinforcement. 2- Liquid: → 62.5% Ethoxy benzoic acid (EBA) (provides higher strength). → 37.5% Eugenol. Advantages: 1- Sedative and obtundant. 2- Thermal insulator → due to its low thermal conductivity. 3- Chemical insulating barrier. 4- The reinforced formulations with improved compressive strength can be used as base under amalgam restoration. 5- Radio-opaque in X-ray. Pulp Protection according to cavity depth: Type of Shallow Moderate Deep Restoration RDT>2mm RDT>0.5mm