Impression Materials Chapter 8 DAE/DHE 203

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

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 Impression materials have so many uses since so much of dentistry relies on an exact replication of the oral cavity to create a dental prosthetic or appliance. Some appliances may include ortho retainers or tooth movement appliances. Other appliances may include the fabrication of a space maintainer. Acrylic trays such as whitening trays or custom-fit mouthguards require an exact duplication of the oral tissues involved. Custom trays are also used to carry final impression materials into the mouth for the most accuracy – especially used in edentulous areas. These mentioned above, are cast in a stone or plaster model upon which the restoration or appliance can be fabricated. Here is a molar prepped for a crown. Before an impression is taken a “gingival retraction cord” is packed into the sulcus to retract the gingiva from the prep so that impression material can fit down into the sulcus and around the cervical area of the tooth. Sometimes these are impregnated with an astringent that allows for a decrease in bleeding also – so as not to harm the integrity of the impression in the area. This impression material is put into a Triple tray and inserted around the prep-site – the pt occludes into the tray and material and stays until it is set. You can see with this tray, the opposing teeth are also being “impressed” so that will give an accurate bite registration for the occlusal relationship to be accurately duplicated. If a triple tray is not used, the registration will need to be taken as a separate step. the impression removed from the prep – the dr. will check for accuracy – DA’s MAY pack cord and mix dental impression materials but may NOT take final impressions – these must be taken by the dentist!

Uses of Impression Materials: 4) The lab receives the impression and will pour-up the impression in gypsum stone (this is plaster in this picture –labs use a high strength stone for fabricating crowns) From this stone cast, dies are cut upon which the individual crown will be made. (This is NOT the cast from this series) 5) The crown is finished by the lab and sent back to the office for cementation. 6) Here is the crown seated into the patients mouth.

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 The materials we will talk about are available in varying VISCOSITIES – thicknesses. The material must have a LOW enough viscosity to FLOW into the detailed areas of a prep site – like a Class II inlay – to replicate the detail for the lab. Materials “Set” in a variety of ways – through a chemical or physical reaction – this process has to occur in a reasonable amount of time. If the replica is to be ACCURATE there must not be distortion of the impression material. It must be ELASTIC enough to be removed from the mouth and then RESUME the shape that it held in the mouth. Materials must be compatible with the body and not too unpleasant for the patient. Stability of the material is also critical for ACCURATE replication of detail – some materials have low stability and a cast must be created immediately, vs. others that are stable for hours and days.

Impression Trays: Used to carry the material to pt’s 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

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 INELASTIC materials do NOT have the elastic ability we just discussed – to resume the shape the material had in the mouth – therefore they cannot be used where there are “undercuts” For example: the cervical portion of a molar is more constricted than the height of contour of the buccal and lingual surfaces therefore what might happen when the tray is removed from a pt’s mouth if a RIGID material is used to take an impression? The impression material fractures. (Plaster used to be used for impressions – altho’ it was rigid and broke when it was removed from the mouth, the pieces would be glued back together to make a negative replication.)

Inelastic Impression Materials: Impression Compound ZOE Impression Paste Plaster

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 We will use other materials during the semester that are “thermoplastic” in nature. Think of how candle wax is – as it is heated it melts, when the heat is removed, the wax solidifies again – that is thermoplastic – the chemical make-up of the materials does not undergo change. Since the compound is slightly warmer than the human body temp, it will “harden” in the pt’s mouth is a few minutes and then can be removed. Obviously, this impression is now very heat-sensitive and would need to be handled accordingly. These compounds are rarely used in private practices today since materials have improved in this area – there are other materials that can be easily used to create a custom tray.

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 ZOE is rarely used in this application. As the other inelastic impression materials; they have been replaced with more convenient methods and more versatile impression materials. We will not be using the INELASTIC materials in our lab.

Elastic Impression Materials: Hydrocolloids: Reversible Hydrocolloids Irreversible Hydrocolloids Elastomers: Polysulfides Polyethers Condensation Silicones Addition Silicones - Polyvinylsiloxanes

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 The GEL form of the hydrocolloids is the material as it is “Set”. The SOL form is when it has flow and is in a liquid solution. This is important to remember as we discuss how hydrocolloid materials are used. Since hydrocolloids are mostly comprised of water, they are not dimensionally stable – they MUST be poured-up immediately in stone or plaster before the water has evaporated from the impression and changed the dimension.

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 The tubes of the material are used to dispense material into the impression tray. The syringe carpules are used to dispense the material in areas of the most detail – for example, the prep site. The syringe material will be extruded all around the prep; the tray will be filled from the tube; then the tray will be placed over the arch or quadrant. The syringe material will be imbedded into the tray material when it is set.

Hydrocolloids: Handling Reversible Hydrocolloid: Special water baths with 3 chambers are used 1) Material is immersed in boiling tank (212°F) for 10-20 minutes; turns from gel to sol 2) Place in storage bath (150°F); 10 minutes to few days; remains sol 3) Load tray; immerse in the tempering bath (110°F); 5-10 minutes; lowers temp for pt comfort The material boils for about 10 minutes if new. IF the tube has been previously boiled, it may require a longer boiling time to turn to sol (20 minutes).

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 pt’s mouth until cooled and transformed to gel state 8) Remove from pt’s mouth and pour immediately

Reversible Hydrocolloid: Advantages: Very accurate Excellent compatibility with gypsum Disadvantages: Labor-intensive Poor tear resistance Poor stability Need equipment space and very organized staff

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

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

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. Water temperature is a factor in setting time!! Cooler water will INCREASE the working time (Slows down the setting time) Warmer water will DECREASE the working time (Faster setting time) Can purchase regular or FAST set alginate.

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 Load the mandibular tray from a posterior and lingual direction. Press alginate into tray to make sure no air is trapped.

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 patient’s mouth until set (2 - 3 min) Loosen cheeks and lips with finger Remove occlusally with a firm snap You can check if material is set by feeling material left in bowl or probing into material on outside of impression – it should feel firm and not change shape when touched.

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. IF the impression is NOT okay, it must be re-taken.

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

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!

Elastomers: Two-paste systems: Set by chemical reaction 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 Tray adhesives vary per each elastomer – if a tray has good retention holes or perforations, then an adhesive may not be necessary. Latex gloves and rubber dams should not contact impression material – it will inhibit the set. Use of vinyl gloves are recommended when kneading putty or handling materials.

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.

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

Elastomers: Handling Polysulfides: Equal lengths of pastes on pad Pastes are “swirled” together, then stropped Material placed in custom tray Take impression – hold in place for up to 15 min. Remove from pt’s mouth slow & steady force Rinse & disinfect Pour-up impression within several hours

Polysulfides: Advantages: Economical Good tear resistance Good compatibility with gypsum Disadvantages: Malodor Stains clothing Long setting time Fair stability Less accurate

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 The better materials are hydrophilic – water loving and have better wettability for the gypsum. This material resulted in bubbles and voids in the stone, since it is hydrophobic – not attracted to water

Elastomers: POLYETHERS: Developed in 1960’s 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 The polymerization of the polyether does not yield a by-product as it sets.

Elastomers: Handling Polyether: Mix equal lengths of paste; or extrude through the automix cartridge tip Load syringe and apply to tooth thru tip Load tray and invert over area for impression Allow to set; 4 – 5 minutes Remove from mouth Rinse & disinfect

Polyether: Impregum

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

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

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

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 Can be poured up days after the Impression is taken.