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Impression Materials Chapter 8 DAE/DHE 203. Impression Materials: Used to make replicas of oral structures “Negative” replica made by impression Cast

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Impression Materials Chapter 8 DAE/DHE 203 Slide 2 Impression Materials: Used to make replicas of oral structures Negative replica made by impression Cast material is placed into impression to yield a positive replica of the oral tissue Allows for the indirect restoration or dental appliance to be fabricated without the patient present Variety of materials for a variety of applications Slide 3 Uses of Impression Materials: Used in the fabrication of: Indirect restorations: Crowns & bridges Dental prosthetics Temporary crowns Orthodontic & Dental appliances Acrylic trays Bite registration Study models Slide 4 Uses of Impression Materials: Slide 5 Characteristics of Impression Materials: Fluid enough to flow around area of interest Must set in reasonable amount of time Can remove from mouth without distortion No harmful effects on tissues Relatively tasteless & odorless Dimensionally stable until a cast is created Give detailed reproduction Compatible with cast materials Slide 6 Impression Trays: Used to carry the material to pts mouth Must be sturdy enough to support the material Need to be disposed of or sterilized after use Metallic trays are autoclavable Stock trays available: full arch, quadrant Custom trays made of acrylic for most accuracy Triple trays takes impression of opposing teeth, occlusal registration, and prep site Perforated trays have holes for retention of material Slide 7 Categories of Impression Materials: INELASTIC Rigid Cannot be used with undercuts For edentulous or bite registration ELASTIC Flexible & rubbery Used with undercuts Generally used today Two subcategories: Hydrocolloids (Aqueous) Elastomers Slide 8 Inelastic Impression Materials: Impression Compound ZOE Impression Paste Plaster Slide 9 Inelastic Impression Materials: Impression Compound: Resins + wax Thermoplastic, solid material Heat to soften material Cool to set material Physical change only; NO chemical reaction Forms: plates and sticks Soften in water bath (10 warmer than body) Applied to tray and inserted in mouth to cool Used as a custom tray Slide 10 Inelastic Impression Materials: ZOE Impression Paste: Similar formulation as ZOE cements Pastes mixed together chemical reaction BASE + CATALYST Applied in thin layer in custom tray for edentulous arch; or to occlusal surfaces Sets in 4 5 minutes Slide 11 Elastic Impression Materials: Hydrocolloids: Reversible Hydrocolloids Irreversible Hydrocolloids Elastomers: Polysulfides Polyethers Condensation Silicones Addition Silicones - Polyvinylsiloxanes Slide 12 Elastic Impression Materials: HYDROCOLLOIDS water-based impression materials Colloid liquid suspension of particles Particles derived from seaweed & kelp Liquid = water GEL the rubber-like form of the material SOL the material in liquid solution Not dimensionally stable must be poured immediately Slide 13 Hydrocolloids: Reversible Hydrocolloid: Agar a gelatinous material + water Thermoplastic NO chemical reaction Reversible Goes from gel, to sol, and back to gel, by raising and lowering temperature Dispensed in tubes & syringes Very accurate final impression material Slide 14 Hydrocolloids: Handling Reversible Hydrocolloid: Special water baths with 3 chambers are used 1)Material is immersed in boiling tank (212F) for 10-20 minutes; turns from gel to sol 2)Place in storage bath (150F); 10 minutes to few days; remains sol 3)Load tray; immerse in the tempering bath (110F); 5-10 minutes; lowers temp for pt comfort Slide 15 Hydrocolloids: Handling Reversible Hydrocolloid: 4) Load syringe; extrude onto prep site 5) Seat tray in mouth 6) Attach cooling hoses to tray 7) Hold firmly in pts mouth until cooled and transformed to gel state 8) Remove from pts mouth and pour immediately Slide 16 Reversible Hydrocolloid: Advantages: Very accurate Excellent compatibility with gypsum Disadvantages: Labor-intensive Poor tear resistance Poor stability Need equipment space and very organized staff Slide 17 Hydrocolloids: Irreversible Hydrocolloid: ALGINATE impression material Formed by chemical reaction Powder + water; mixed NOT reversible; SOL to GEL only Protect from inhalation Dispensed in cans or bulk packages Used when less detail is required Slide 18 Hydrocolloids: What are indications for alginate impressions? Study models Opposing models of final casts Casts for mouthguards, whitening trays, custom trays, orthodontic appliances, provisional crowns, etc. To fabricate a direct provisional crown Slide 19 Hydrocolloids: Handling Alginate: Fluff powder and measure accurately Measure water temp! Mix in a flexible, rubber bowl Stir to wet powder Strop mixture against side of bowl to eliminate air bubbles Mix until creamy & homogeneous; 60 sec. Slide 20 Hydrocolloids: Handling Alginate: Load alginate into tray from posterior Press material into tray to eliminate voids Smooth & indent alginate with wet finger Use extra alginate to wipe onto occlusal surfaces of teeth Slide 21 Taking an Alginate Impression: Bead the tray as necessary Stand behind patient for maxillary (11:00) Center tray above teeth and seat posterior Press tray down & toward anterior and allow lip to cover tray; material should fill vestibule Hold tray in patients mouth until set (2 - 3 min) Loosen cheeks and lips with finger Remove occlusally with a firm snap Slide 22 Evaluating an Alginate Impression: Full coverage, including retromolar area Tray centered Clear & sharp impression No voids, air bubbles, or tears Has a peripheral roll (vestibular area) If all is OK, rinse & disinfect impression, pour-up in stone/plaster, or store in humid bag. Slide 23 Irreversible Hydrocolloid: Advantages: Easy & economical Many applications Patient comfort Excellent wetting by gypsum Disposable tray Disadvantages: Not enough detail for final impression Must be poured immediately Slide 24 Hydrocolloids: SYNERESIS shrinkage in impression due to loss of water from heat or exposure to air. IMBIBITION swelling of impression due to taking up moisture To avoid these conditions (dimensional distortion), pour-up immediately! Slide 25 Elastomers: Two-paste systems: Two tubes pastes mixed by hand Two putties mixed/kneaded by hand Cartridge & Extruder Gun automix tips used Cartridge & Motor-driven Mixer automix tips used Set by chemical reaction Warmth and moisture may slow setting Must use a tray adhesive (if tray not perforated) Latex may inhibit set of polyvinylsiloxanes Slide 26 Elastomers: Elastomers are used in a two-step process: Preliminary Impression - the material used to form the base or the tray material used in an impression; usually more viscous or heavy-body Secondary or Wash Impression the material applied through a syringe around the prep site for detail; usually less viscous; light or medium -body. Slide 27 Elastomers: POLYSULFIDE: Oldest elastomeric used in dentistry Two pastes mix base with catalyst Liquid polymer with sulfhydryl group contains sulfur rubber-base impression material Used best with custom trays Other materials have replaced this one Slide 28 Elastomers: Handling Polysulfides: 1. Equal lengths of pastes on pad 2. Pastes are swirled together, then stropped 3. Material placed in custom tray 4. Take impression hold in place for up to 15 min. 5. Remove from pts mouth slow & steady force 6. Rinse & disinfect 7. Pour-up impression within several hours Slide 29 Polysulfides: Advantages: Economical Good tear resistance Good compatibility with gypsum Disadvantages: Malodor Stains clothing Long setting time Fair stability Less accurate Slide 30 Elastomers: Condensation Silicones: Similar to silicone rubber products (but non-toxic) Setting by-product of alcohol Hydrophobic results in voids in stone Shrinkage occurs as it sets Must be poured immediately Accurate, but slow setting time Replaced by improved products Slide 31 Elastomers: POLYETHERS: Developed in 1960s No reaction by-product produced Shorter working and setting time Only come in a single viscosity Stiff material can use a triple tray Very popular Impregum No need to pour-up immediately Slide 32 Elastomers: Handling Polyether: 1. Mix equal lengths of paste; or extrude through the automix cartridge tip 2. Load syringe and apply to tooth thru tip 3. Load tray and invert over area for impression 4. Allow to set; 4 5 minutes 5. Remove from mouth 6. Rinse & disinfect Slide 33 Polyether: Impregum Slide 34 Polyether: Advantages: Short setting time Single viscosity Good stability Good tear strength Clean & easy to use Disadvantages: Bad taste Most difficult to remove from mouth Slide 35 Elastomers: ADDITION SILICONES: Polyvinylsiloxanes silicone polymer Two pastes or two putties Hydrophobic by nature manufacturers adding components to increase wettability Very accurate & fast setting Avoid contact with latex (gloves, rubber dams) Low setting shrinkage & very stable Slide 36 Elastomers: Handling Addition Silicone: Mix equal lengths of pastes, or automix Apply light-body material to tooth thru syringe Load tray with heavy-body Set tray over prep site Set in 4 5 minutes Rinse & disinfect Slide 37 Addition Silicone: Polyvinylsiloxane Advantages: Very stable Short setting time Good tear resistance Great accuracy No bad taste Disadvantages: May have poor wettability Two pastes to mix