Liners & Bases PDF

Liners & Bases Salma Abuelgasim Mohamed 2022 update 2023 Objectives By the end of this session the participants should be able to Define the liners Demonstrate the pulp irritation Indications Illustrate the different types of liners Liners and bases m...

Liners & Bases Salma Abuelgasim Mohamed 2022 update 2023 Objectives By the end of this session the participants should be able to Define the liners Demonstrate the pulp irritation Indications Illustrate the different types of liners Liners and bases material act as pulp protection agents require consideration of: Chemical Protection, Mechanical Electrical Protection Protection, Pulpal Thermal Medicatio Protection, n, (1) Thermal irritants: a. Sudden changes in temperature in the oral cavity i.e. when the pt. drinks or eats hold or cold substances. b. Heat generated by certain filling materials during setting (exothermic reaction) (2) Chemical irritants: Some filling materials i.e Phosphoric acid in silicate materials, and acrylic monomers in some resin-based materials. (3) Electrical irritants: Irritation is caused when two dissimilar metals are placed adjacent to or opposing each other (e.g. amalgam/gold) it is possible to set up a galvanic cell which accelerates corrosion & can cause pain.  Reasons for use of base and lining materials: 1. Insulation against temperature changes and electrical stimuli under metallic restorations such as amalgam. 2. Mechanical protection provides by distributing local stresses from restoration across the underlying dentin surface. Diffusion of the bacteria, oral fluids, ions 3. To reduce the risk of microleakage. and molecules into the tooth and the filling material interface  Reasons for use of base and lining materials:cont 4. Cementation of cast or ceramic restorations. 5. As a pulp capping. 6. Some have bactericidal or bacteriostatic properties. 7. Prevention of the risk of along-term damage to the pulp-dentin organ from operative treatment. 8. Cementation of orthodontic bands.  The ideal properties of the lining material : Be compatible with the restorative materials. It should not irritant to the pulp. Prevent injuries of the pulp-dentin from restorative materials. Be insoluble in the oral fluids.  Prevent heat/cold conduction from metallic restorations. It should have a bacteriostatic effect e.g.: zinc oxide eugenol. It should improve the marginal seal and have sealing ability e.g.: zinc oxide eugenol, so we use it as a temporary restorative material. It should be easy to manipulation and apply. It should be radiopaque in the X-ray  Definitions Liners Thin layers of material used to provide a barrier to protect the dentine from thermal, chemical or electrical irritations. Some types of liners may provide pulpal treatment. Indications for using a liner Liners are indicated with metallic non- insulating restorations, that extend close to the pulp & that are not well bonded to tooth structure i. e amalgam and cast gold. Classification of Liners Thin film liners (1 to 50 µm) can be subdivided into solution liners (varnishes, 2 to 5 0um) And suspension liners (typically 20 to 25 Um). Thicker liners(200 to 1000 um = 0.2 to 1 mm), selected primarily for: pulpal medication and thermal protection, are some-times identified as cement liners.  Routinely, no liner is used for direct composite restorations, indirect composite or ceramic restorations, and resin-modified glass- ionomer due to their sealing effect and insulating nature. However, a liner maybe used with these restorations if the cavity is extremely close to the pulp and pulpal medication is needed. Thin liners Thick liners (cement liners) Solution liners (200 to 1000 um = 0.2 to 1 Cavity varnish mm (2 to 5 0,m) selected primarily for pulpal Suspension medication & thermal liners(20-25Um) protection Fig 1. Materials which can be used as liners and bases, with approximate date of introduction.  Liners: are materials that are placed as thin coating or layer. Function:- 1. To provide a barrier against chemical irritation. (They do not function as thermal isolators). 2. Reduce marginal leakage around most filling materials (amalgam) so reduce the inflammatory reaction and post-operative sensitivity caused by marginal leakage. 3. Electrical insulation (treatment of galvanic shock). The need for liners is greatest with metallic restorations that are not well bonded to tooth structure. eg: Varnish, Ca (OH)2,and resin bond. Cavity varnish (solution liners): Consists of a solution of a natural or synthetic resin in a volatile solvent. It is painted into the cavity and the solvent evaporates to leave a very thin layer of resin which helps to seal the ends of the dentinal tubules.  Varnishes do not provide adequate thermal protection in deep cavities since they form only a thin layer. Varnishes must be painted in two layers to provide adequate coverage. Suspension liners: These liners are based on water & have many of the constituents suspended instead of dissolved. Suspension liners can produce the same effect as varnishes , but dry more slowly and produce thicker films.  The typical film thickness is 20 to 25 um in contrast to the 2 to 5 um film produced by solution liners (varnishes). Both types of liner should be extended over the cavosurface margins of the preparation.  Cement liners (thick liners): Cement liners have 2 main functions thermal insulation & pulpal protection To provide thermal insulation to the pulp a minimum of 2 mm of dentine should exist over the pulp after cavity preparation remaining dentine thickness Cement liners: As the tooth preparation extends closer to the pulp, a thick liner or a base is used to augment dentin to the proper thickness. These liners cannot harden by evaporation of solvent or water because it would not dry effectively. They harden by chemical reaction. liners Cavity varnish Calcium hydroxide Zinc oxide eugenol GIC Resin  Classification of Liners The three most commonly used cavity lining materials are: 1. Cavity varnish (solution liner) seals dentinal tubules without adding bulk Reduces marginal leakage + improves the marginal seal for the short term Helps prevent penetration of acid, protects pulpal tissue from the phosphoric acid in zinc phosphate cements Prevents mercury penetration into the dentinal tubules from amalgam restorations Prevents discoloration of dentin Note: Cavity varnish does not act as a thermal barrier. It should not be used with composite restorations since it will inhibit polymerization. Functions of Varnish and Sealer It prevents microleakage. It prevents post-operative sensitivity by not allowing the ingress of fluids from the cavity margin It also prevents the penetration of the toxic material into the dentin from the restorative material and also prevents discoloration. Suspension liners: It contains calcium hydroxide, zinc oxide eugenol (Type 4) 2. Calcium hydroxide (suspension liner or cement liner) Ca(OH)2 (Calcium hydroxide) is the material introduced in clinical dentistry in 1921 by Hermann Prevents thermal shock Prevents passage of acid from restorative materials Has enough strength to resist forces used in placing restorations. Important: The mechanism action of calcium hydroxide for the formation of mineralized barrier, is the product of irritation of pulp tissue by the cement, possibly mediated by activation of transforming growth factor beta and cellular growth factor. NB! Also, when viewed radiographically, calcium hydroxide can be easily confused with caries - both are radiolucent  Calcium hydroxide Form 2 paste system {dycal} Powder & liquid Chemical composition (paste):- Base Salicylate Catalyst Calcium hydroxide, zinc oxide & ethylene toluene sulphonamide Setting reaction Involves the formation of calcium disilicate Base catalyst ratio 1:1 Setting time 1 min outside the oral cavity & decreases in the oral cavity due to increased heat & humidity Physical characteristics Poor physical characteristics, so unsuitable to be used as a cement, however, the strength is physically high to withstand forces of condensation of amalgam. Properties 1. Bacteriostatic or bactericidal due to Alkaline PH=11 Antiseptic effect from ethylene toluene sulphonamide 2. Highly soluble 3. Immediately reduces dentine permeability due to deposition of CaoH in dentine 4. Long term dentine permeability reduction due to intratubular depostion of mineral salts in dentine 5. Stimulates secondary dentine formation Forms:- Hard setting cement Paste Powder/liquid mixture The three most commonly used cavity lining materials are 2. Zinc oxide eugenol (suspension liner or cement liner) Prevents penetration of acids Prevents thermal shock Has adequate strength so that it can be used under permanent restorations Note: ZOE is a particularly good liner due to the fact that it is palliative (soothing) to the pulp. Commonly used for temporary fillings.  Zinc oxide eugenol (ZOE) (example: Intermediate Re-storative Material, DENTS-PLY Caulk) materials provide an excellent seal of the cavity preparation. The ability of ZOE to reduce postoperative sensitivity The clinician should allow approximately 24 hours to pass prior to placing amalgam above a ZOE base. Chemical composition: Powder Zinc oxide 70% Rosin 30% Zinc acetate (traces) Liquid Eugenol 100% Properties: a. Powder: liquid ratio, 3:1 b. Good insulator & sealer for the pulp c. Has antiseptic properties for bacteria remaining in dentine d. Has a sedative effect and anti- inflammatory effect on the pulp e. When inserted into the cavity it has neutral PH of 7. f. Has low strength so can not resist masticatory forces g. Lacks resistance to wear h. Has high solubility in the oral cavity Types: 2 types are available Type 1 : Used as a base or temporary restoration Type 2 : Used as cavity liner and cementation for appliances Setting reaction: Factors increasing the setting reaction time: Humidity (presence of water) Additives i.e resins, zinc stearate, zinc acetate Greater zinc oxide to eugenol Setting Reaction: Factors slowing the setting reaction time: Excessive water Smaller powder particle size High temperature Form: Powder & liquid paste-paste Manipulation: Stainless steel spatula & clean Glass slap or paper pads Modifications to ZOE EBA (ethexo-benzyonic acid) modified ZOE cements: Addition of ortho ethexo- benzyoic acid (EBA) to the eugenol ( 62.5% EBA, 37.5% eugenol) Resin reinforced ZOE cements: Addition of fused Quartz or aluminum oxide or resin polymer to the powder component These help improve the setting, handling and working characteristics Uses: 1. Cavity liner 2. Cavity base 3. Temporary restorative material 4. Temporary luting cement 5. Root canal sealer Contraindications : 1. On dentin or enamel prior to bonding ~ compromises bonding. 2. As a base or liner for composite resins ~ eugenol interferes with polymerization. 3. Patients who are allergic to eugenol 4. Direct pulp capping ~ eugenol is a pulpal irritant when in direct pulpal contact  Resins These materials can be grouped into one of 3 classes, based on the method of curing. Self-cured and are available in powder/liquid or paste/paste delivery systems light-cured versions with a single component. dual-cured products.  Classification of Liners Resin Since there are different types of resins Unfilled resin Filled resin These will be discussed separately.  Primer/Unfilled Resin The newest generation of resin materials includes the use of a dentin primer. A primer is essentially a hydrophilic, low-viscosity liquid that promotes the bonding of a resin to the tooth. It contains either ether, alcohol , or water.  When these materials are placed on the prepared tooth, they form a hybrid layer. The hybrid layer or zone, with occluded tubules, results in a reduction in dentin permeability. therefore, these materials are essentially a liner. Example of resin-liners: primer/unfilled resins is ADHESE(Ivoclar Vivadent), Optibond product (Kerr)  Filled resin Flowable resins Flowable resins are essentially composites with a reduced filler content, which provides a consistency that allows the material to flow readily and spread uniformly, reducing polymerization shrinkage and improving adaptation to the cavity preparation. Flowable resins These materials reduce micro-leakage due to their ability to flex with the tooth to maintain the seal These materials are promoted as a liner, but the primer/bonding agent needs to be placed first. Advantages 1. A decrease in gap formation. 2. A reduction in microleakage, secondary caries, and pulpal inflammation. 3. Some flowable resins contain fluoride but the amount that is released is very low and decreases during the first 3 weeks. An example of resin-liner: flowable is Tetric Flow (ivoclar vivadent), Virtuoso Flowable (Denmat) Summary Pulpal Protection (Medicament/ Liner / Sealer)