Dental Materials LEC Elastomers and Hydrocolloids PDF

Dental Materials LEC Notes by Iryl hehe Shout out kay Kaesha at Wisia ELASTOMERS AND H...

Dental Materials LEC Notes by Iryl hehe Shout out kay Kaesha at Wisia ELASTOMERS AND HYDROCOLLOIDS DMD-3L ELASTOMERS POLYSULFIDE IMPRESSION COMMERCIAL MANNER OF STATE AND USE IN MATERIAL NAME HARDENING CONDITION DENTISTRY 1st Elastomeric Impression Material Introduced Elastomeric Rubber Chemical Flexible; For Partial Made of Polysulfide Polymer (Mercaptan) Impression Impression Reaction Paste and Complete ○ Cross-links under the influence of Material Material Edentulous oxidizing agents such as lead peroxide Essential Component of Polysulfide: Mercaptan Setting Time is called Polymerization Time/Curing Oxidizing Agent: Lead Peroxide Time It is the time it takes for the rubber to harden COMPOSITION There is no syneresis and Imbibition in Elastomers BASE CATALYST 1. Polysulfide Polymer 1. Lead Dioxide Elastomers are a group of synthetic polymer-based Contains Color Brown impression materials that have the elastic properties multifunctional Accelerator of natural rubber. Mercaptan ○ Decreases ST 2. Filler 2. Filler and Plasticizer 3 Types of Elastomers: Lithopone or Help in strength Titanium Dioxide Makes it not sticky 1. Polysulfide Increases strength 2. Polyether 3. Silicone 3. Plasticizer 3. Oleic or Stearic Acid a. Condensation Dibutyl Phthalate Retarder Confers appropriate ○ Increases ST b. Addition viscosity 4. Sulfur A group of flexible materials that are easily stretched 0.5% and can recover to go back to its original dimensions Enhances reaction when applied stresses are released Used in the construction of porcelain crown Setting Reaction of Polysulfide and other metallic substances Lead Dioxide + Polysulfide Polymer → Polysulfide + All elastomeric impression material: Water Good for fixed appliances because it takes all the necessary landmarks Yields water as by-product No dimensional change Setting time should be short to avoid distortion Working Time: 4-7 mins Setting Time: 7-10 mins Rubber impression materials are hydrophobic ○ Longer than other impression material Liquid hating material that will not cause change to the model CHARACTERISTICS OF POLYSULFIDE COMPARISON OF ELASTOMERS ADVANTAGES DISADVANTAGES Long Working Time Requires Custom Tray Initial ST: 7 Mins (Do not use metal) Final ST: 10 Mins Proven Accuracy Must be poured immediately High Tear Stretching leads to Resistance distortion | 1  Margins easily seen CONDENSATION SILICONE (A common advantage) Known as Conventional Silicone Less Hydrophobic Stains clothing Supplied as a base paste and a low-viscosity Moderate Cost Obnoxious Odor liquid catalyst (or paste catalyst) ○ A two-paste system or two-putty Long Shelf Life Pour within 1 hr system Compatible with Stone Putty is used as the tray material with low-viscosity silicone (Putty-wash technique) POLYETHER COMPOSITION Made of Ethylene Oxide and Tetra-hydro Fluoro BASE CATALYST Copolymers 1. Hydroxyl-terminated 1. Alkyl Silicate Polymerizes under the influence of an aromatic polydimethylsiloxane Tetraethyl silicate ester Aka Liquid Silicone ○ Accelerator for Prepolymer polymerization that causes COMPOSITION hardening of rubber BASE CATALYST 2. Filler 2. Tin Compound 1. Polyether Polymer 1. Alkyl-Aromatic Sulfonate Silica Dibutyl tin dilaurate Essential Component ○ Colloidal Will not harden without Silica it 2. Colloidal Silica 2. Filler Setting Reaction of Condensation Silicone Filler to increase Colloidal Silica strength Stannous Octate 3. Plasticizer 3. Plasticizer Glycol Ether or Phthalate Phthalate To avoid tearing of Dimethylsiloxane + Orthoethyl Silicate → Silicone rubber Rubber + Ethyl Alcohol Ethyl Alcohol is the by-product Setting Reaction of Polyether Working Time: 2.5-4 mins Polyether + Sulfonate Ester → Cross linked rubber Setting Time: 6-8 mins Working Time: 3 mins Setting Time: 6 mins CHARACTERISTICS OF CONDENSATION SILICONE ADVANTAGES DISADVANTAGES CHARACTERISTICS OF POLYETHER Putty for custom tray High polymerization ADVANTAGES DISADVANTAGES (Putty Wash Technique) shrinkage Fast-Setting Stiff, High Modulus Clean and Pleasant Volatile by-product Might not take all landmarks Good Working Time Low Tear Strength Automix Dispense Bitter taste Margins easily seen Hydrophobic Least Hydrophobic Need to Block Undercuts Pour immediately Margins easily seen Absorbs Water Putty Wash Technique Good Dimensional Leeches Components Construction of an individual or custom tray Stability High Cost ADDITION SILICONE Known as Polyvinyl Siloxane Note: Automix Dispense refers to tube catalyst and base coming out together in equal portions |2  Has terminal vinyl groups that cross-link with Contamination of latex that silanes on activation by a platinum or inhibit polymerization (Addition palladium salt crystal Silicone) COMPOSITION Rapid Polymerization from high humidity or temperature BASE CATALYST 1. Polymethylhydrosiloxane 1. Divinyl Polydimethylsiloxane High accelerator/base ratio As well as other (Condensation Silicone) siloxane prepolymers BUBBLES Air Incorporated during mixing 2. Divinylpolysiloxane 2. Platinum Salt Palladium Salt or Platinum Salt Too rapid polymerization, Base label contains preventing flow hybrid silicone IRREGULARLY Moisture or debris on surface of 3. Filler 3. Filler SHAPED VOIDS teeth Colloidal Silica Colloidal Silica ROUGH OR CHALKY Inadequate cleaning of Setting Reaction of Addition Silicone STONE CAST impression Excess wetting agent left on Platinum Salt impression Vinyl Siloxane + Hydrogen Siloxane → Silicone Rubber Premature removal of cast No by-products formed Improper WP Ratio of Stone Working Time: 2-4 mins Failure to delay pour that does Setting Time: 4-6.5 mins not contain palladium salt for at least 20 mins (Addition Silicone) CHARACTERISTICS OF ADDITION SILICONE DISTORTION Resin tray not aged sufficiently; still undergoing polymerization ADVANTAGES DISADVANTAGES shrinkage Putty for custom tray Hydrophobic Lack of adhesion of elastomer to the tray caused by not applying Automix Dispense No flow if sulcus is moist enough coats of adhesive, filling Clean and Pleasant Low Tear Strength tray with material too soon after applying adhesive, or using Margins easily seen Wash has low tear strength incorrect adhesive Ideally Elastic Putty too stiff Lack of mechanical retention to Pour Repeatedly Difficult to Pour Cast the impression tray Stable: Delay pour Excessive bulk of material Insufficient relief for the reline COMMON FAILURES THAT OCCUR WITH USE OF NON material AQUEOUS ELASTOMERIC IMPRESSION MATERIALS ROUGH OR UNEVEN Incomplete polymerization from Development of elastic properties SURFACE ON premature removal of mouth in the material before tray is fully IMPRESSION seated Improper Ratio of Mixing Components Continued pressure against impression material that has Presence of oil or other organic developed elastic properties material on teeth Movement of tray during polymerization |3  REVERSIBLE IRREVERSIBLE Premature removal of impression from mouth Agar Alginate Hardens by physical change Hardens by chemical react Improper removal of impression from mouth Subjected to Heat Not subjected to heat Needs special equipment Does not need special equip Delayed pouring of the polysulfide or condensation silicone impression DEFINITION OF TERMS HOW TO HANDLE RUBBER IMPRESSION MATERIAL COLLOIDS Solution in which the unit of the solute are 1. Equal amount of base and catalyst sufficiently large so it will 2. Mix uniformly for 1 minute not dialyze through a 3. Use an individual tray. NOT metal or ordinary tray suitable membrane 4. No separating medium needed DISPERSED PHASE/DISPERSED Particles in a solution PARTICLES To know if the rubber impression material is set: Press a blunt instrument like a spatula and try to DISPERSION solution containing a press the surface of the rubber. If it returns to its PHASE/DISPERSION MEDIUM suspension of particles original dimension, it is cured. It is hotter in the mouth so it sets faster in the SUSPENSION Dispersed phase and mouth dispersion medium are not of like phase Setting of cast is about 30 mins to 1 hr EMULSION Dispersed phase is of the same phase of the dispersion medium HYDROCOLLOIDS IMPRESSION COMMERCIAL MANNER OF STATE AND USE IN HYDROPHOBIC Strong aversion to water MATERIAL NAME HARDENING CONDITION DENTISTRY Water hating material Reversible Agar Physical Flexible; For Partial Hydrocolloid Change Gel and Complete HYDROPHILIC Strong affinity for water Edentulous Water loving Irreversible Alginate Chemical Flexible: For Partial material Hydrocolloid Reaction Powder and Complete Edentulous HYDROCOLLOID A colloid that contains water as the dispersion phase Made up of submicroscopic fibrils Spaces between fibrils: Micelles REVERSIBLE HYDROCOLLOID Agar impression material IRREVERSIBLE HYDROCOLLOID Alginate Impression Are the first flexible materials available to dentists material GELATION The transformation of Hardening of the material: Gelation hydrocolloid sol to gel Elastic enough to be drawn to undercuts without Gelation Temperature: 37C significant deformation LIQUEFACTION Transformation from gel to sol Two Forms: Sol Form Liquefaction Temperature: ○ Liquified Substance 60-70C ○ Low Viscosity, random arrangement of HYSTERESIS The difference between polysaccharide chains gelation and liquefaction Gel Form temperature ○ Solidified substance ○ More viscous, may develop elastic IMBIBITION Process of water sorption properties SYNERESIS Expression of fluid into the surface of gel structures |4  SETTING TIME The elapsed time of mixing Models/Dies until the impression Alkyl Benzoates 0.1% Preservative material becomes firm enough to resist Water 85% Dispersion Medium permanent deformation WORKING TIME Total time from the start of Other fillers: Diatomaceous earth, clay, silica, wax, mixing to the final time at rubber and similar inert powders are used to control which impression tray can strength, viscosity and rigidity. be fully seated without distortion Bactericidal Agent: Thymol AGAR (REVERSIBLE HYDROCOLLOID) Plasticizer: Glycerin Commercial Name: Agar impression material PROPERTIES Subjected to heat ADVANTAGES DISADVANTAGES Odorless Expensive Agar-agar Non-toxic; Non-irritant, Needs special equipment: Main active ingredient: Polysaccharide from red Non-staining Agar Conditioner and seaweed Non-perforated Tray Main constituent: Water Slow Setting Time Thermal Discomfort Adequate Shelf Life Poor Tear Resistance Chemical Composition: Beta-galactopyranose Easy to Pour into stone Pour Immediately Factors Affecting Strength of Agar Good surface detail Difficult to see margins 1. Brush heap density or concentration Accurate and pleasant Dimensional instability More fibrils, stronger 2. Temperature of Reversible Gel (Boiling) Reusable and easily sterilized by Needs to boil for 15-20 mins to liquify hypochlorite ○ High temperature: Weak Gel ○ Lower Temperature: Strong Gel HOW TO HANDLE REVERSIBLE HYDROCOLLOID 3. Addition of Modifiers Are caught between spaces of fibrils Presence of modifiers make strength 1. Boil for 15-20 mis stronger 2. Load it to the tray If patient is not yet around, put inside Two Dimensional Changes in Hydrocolloids agar conditioner 3. Take impression of the mouth Imbibition 4. Construct the cast once the impression is ○ Adsorption of water into surface gelled. No separating medium needed causing swelling 5. Setting in about 30 mins to 1 hr Syneresis 6. No need to put in warm water, pull it apart to ○ Evaporation of water from gel causing get cast shrinkage Exact Gelation of Agar Depends on: IRREVERSIBLE HYDROCOLLOID 1. Molecular weight of agar 2. Purity of agar Commercial Name: Alginate Impression Material 3. Ratio of agar to other constituents Not subjected to heat COMPOSITION The material is very common to dentists COMPOSITION AMOUNT ACTION Agar 12-15% Gelling Agent Made from Kelp Borax 0.2% Improves Strength Substance is Alginic Acid K2SO4 1-2% Provides Good Surface on Gypsum Types according to Setting |5  Type 1 There are more fillers added in Irreversible ○ Fast hydrocolloids than reversible hydrocolloids ○ 1-2 Mins ○ There are 60% added as a filler because Type 2 the alginate gel is very weak ○ Normal Contributions ○ 2-4.5 Mins ○ It is an accelerator ○ increase the strength and stiffness of METHODS TO CONTROL GELATION TIME the alginate gel ○ It assures a firm gel that is not tacky ○ It provides a smooth texture to the 1. W/P Ratio surface of the hydrocolloid gel High Ratio = Increase Gelation Time Low Ratio = Decrease Gelation Time 2. Mixing Time CAUSES OF FAILURE IN MANIPULATION OF ALGINATE Fast = Decrease Gelation Time GRAINY MATERIAL Improper Mixing Slow = Increase Gelation Time Prolonged Mixing 3. Addition of Retarders Undue Gelation Adding retarders delay gelation time W/P too low 4. Temperature TEARING Inadequate bulk Hotter = Decreased Gelation Time Premature Colder = Increased Gelation Time removal from Room Temp = 1-2 mins mouth Prolonged Mixing PROPERTIES EXTERNAL BUBBLES Undue gelation Air incorporation ADVANTAGES DISADVANTAGES during mixing Easy to Manipulate Not accurate/Rough IRREGULARLY SHAPED VOIDS Presence of Comfortable for the patient Tears easily moisture or debris on tissue Clean and Pleasant Pour Immediately ROUGH STONE MODEL Impression not Does not need special Can retard setting of gypsum cleaned equipment Because its composition is sodium phosphate Improper mixing Inexpensive CHALKY STONE MODEL Premature removal of the Long Shelf Life impression from the cast Model left in the COMPOSITION impression too long COMPOSITION WEIGHT % FUNCTION Excess water left Potassium Alginate 15 Soluble Alginate in the impression CaSO4 16 Reactor DISTORTION Impression not poured Zinc Oxide 4 Filler Particles immediately Potassium titanium 3 Gypsum Hardener Movement of tray fluoride during gelation Premature Diatomaceous 60 Filler Particles removal Earth Improper removal Sodium Phosphate 2 Retarder of the impression from the mouth Tray held in mouth Main component: Potassium Alginate too long Soluble Alginates (Potassium, Sodium or Triethanolamine ADVANTAGES OF IRREVERSIBLE FROM REVERSIBLE alginate) HYDROCOLLOID Diatomaceous Earth 1. Easier to handle and prepare 2. Comfortable to patients |6  Because it does not require hot water 3. Inexpensive 4. Less equipment needed HOW TO HANDLE IRREVERSIBLE HYDROCOLLOID 1. Mixing is done for 1 minute or less 2. Load into tray 3. Take impression It is ready if it does not adhere to fingers when touched 4. Wash it and construct model 5. Remove the cast from impression for 30 mins to 1 hr Pull it apart Note: Never delay construction of model to avoid syneresis and imbibition |7 |8