Impression Materials Notes PDF

Impression Materials According to Dr. McCracken: - used to form replicas or copies of teeth and Rigid/Inelastic – harden at time of removal other oral structures from mou...

Impression Materials According to Dr. McCracken: - used to form replicas or copies of teeth and Rigid/Inelastic – harden at time of removal other oral structures from mouth - the impression is a negative reproduction - used on areas without undercuts, while the model or cast is the positive edentulous reproduction Example: Impression compound, - objective is to copy accurately the teeth and impression plaster, Zoe paste other structures in the oral cavity Elastic Setting Mechanism For dentate patients (with undercuts) Irreversible – reaction implies that Hydrocolloid chemical reaction has occurred, and o Reversible – agar that the material cannot revert to its o Irreversible – alginate present state. o Rubber impression material (elastomers) Example: Alginate, Zoe impression ▪ Polysulfides, polyether, paste, Impression plaster, and Elastomeric silicone: condensation impression materials. and addition Reversible – materials softened under heat and solidify when they are cooled, with no chemical change taking place Example: Reversible hydrocolloid, and Impression compound I. Primary Impression - alginate, impression compound, plaster II. Secondary/ Final/ Wash Impression - Corrective impression, the purpose of which is to construct a master cast or a working cast Types of Impression Tray for the fabrication of the prosthesis a. Stock tray b. Rim-locked tray c. Individual tray Classification of Impression Materials d. Perforated tray e. Water-cooled tray According to Manner of Hardening: Types of Impression Taking Thermoplastic – materials that set as a result Single Impression of change in temperature; soft when heated, Double Impression solidify when cooled; no chemical change o Preliminary Impression Example: Modelling compound or o Final Impression/Secondary impression compound “wash”  ▪ More accurate o Very brittle ▪ Corrects the defect of o Fractures easily preliminary impression o Reconstruct to form the completed impression Impression Plaster Other names: Type I Dental Gypsum; Soluble Impression Compound Plaster Other names: Modeling plastic, modeling Classification: Thermoset, Rigid, for Final or compound, dental impression compound Secondary Impression making Classification: Thermoplastic, rigid, Manner of Dispensing: Finely divided powder preliminary impression material added to water and sets as a result of hydration Manner of Dispensing: Cakes of different reaction; Color is light pink shapes and color; cones or stick forms Use: For final impression making of edentulous Colors: Pink, brown, maroon (cake forms) and arches green for the stick form Constituents/Composition Forms of Impression Compound 1. Calcium Sulfate Hemihydrate (Plaster) Cake form 2. Potato Starch = to render them soluble - Preliminary Impression 3. Potassium Sulfate (Accelerator); Sodium Stick Form Citrate (Retarder) - Border molding of individual tray 4. Alizarin Red (Coloring) - Copper tube impression technique 5. Peppermint (flavoring material) Cone Form Manipulation Impression Compound WP ratio:.50 -.75 Uses: Use plaster bowl and spatula a. For edentulous impression Type I/ Increase W/P ratio to reduce exothermic Impression Compound heat so as not to injure the soft tissue in b. In operative dentistry, to obtain impressions the mouth of single tooth Mix in a single rotary motion for 1 minute c. Tray compound used to form tray to be used Setting time is 3-5 minutes for other types of impression (IM) After mixing, pour on impression trays, tap a little to release air bubbles, then Types of Impression Compound seat the tray inside the patient’s mouth Type I Manner of withdrawal: Teasing True impression compound movement Low fusing compound, (55 - 65°C) Apply Cologuard- before pouring the Has high flow property gypsum Used to make a final impression of a tooth preparation Properties Type II Setting Expansion: 0.3% Tray compound Compressive Strength: 580+/-290 PSI High fusing compound (70°C) o Not popular in the market More rigid anymore For individual tray o Easy to break  Impression Compound: Components Disadvantage – if you fail to construct 1. Beeswax and Thermoplastic Resin the cast immediately after withdrawing Responsible for thermoplastic property the impression from the patient’s 2. Shellac, Gutta Percha, Stearic Acid mouth, the continuous flow property Act as plasticizer which can improve can be a source of error workability 3. French Chalk, Talc, Diatomaceous Earth Cast Construction and Separation Filler Wash in running water after withdrawal Hardening agents, Improve the strength No need for separating medium 4. Coloring pigments and Flavoring agent Mix Plaster of Paris to make a study cast Immerse in a hot water bath Manipulation: 2 Ways to Soften Impression o MC softens, if MC sticks to the Compound cast, soften a piece of MC and A. Dry Heat Method = heated over flame until allow it to come into contact with materials is softened; by direct flame (alcohol the melted MC lamp, Bunsen burner) or by oven B. Moist Heat Method = material is softened in Zoe Impression Paste hot water 50-70°C (Thermostatically controlled Is mixed to the consistency of a thin water bath) paste and is used in a custom-made compound or acrylic tray to record When a direct flame is used – do not allow impressions of completely or partially material to boil or ignite edentulous arches When large amount of compound is to be softened, moist heat method is best used Classification: Thermoset, Rigid (not used to record undercuts), Final/ Wash/ Disadvantages with the use of Moist Heat Corrective impression Method Manner of Dispensing: 2 – paste system in 1. Heated for an excessive period, it may collapsible tubes; base (white) & catalyst become brittle and grainy (brown, amber) 2. Chief Disadvantage – if water is incorporated plasticity is altered Types: Type I = Hard Set; 3-6 minutes IST / 10 min. FST Manner of Withdrawal: Teasing Method Type II = Soft Set; 3-6 minutes IST / 15 min. FST Properties of Impression Compound Zoe Impression Paste Poor thermal conductivity Uses: Dimensional change: Shrinks at 0.3- a. As final impression for an edentulous mouth 0.4% (soft set) With good flow property b. As a relining material for ill-fitting dentures Advantage – enables us to get a more c. For centric jaw registration detailed and accurate impression d. As a surgical dressing (periodontal surgery), The mixing of the two pastes is done on temporary filling material, cementing medium an oil-impervious paper or glass slab root canal filling material The proper proportion is 1:1 squeeze two ropes of paste of the same length Composition A flexible stainless-steel spatula is Base used for mixing a. Zinc Oxide = should be finely divided, The two ropes are combined with broad French processed and it should contain a very strokes in a sweeping motion, mixing is slight amount of water continued for 30-45 seconds to 1 b. Inert oil = mineral/vegetable oil; acts as a minute or until a uniform color is plasticizer, to make into a paste, and it also observed aids in masking the action of the eugenol as an irritant Setting time: 3-5 minutes c. Hydrogenated rosin = imparts Manner of Withdrawal: Teasing Method thermoplasticity to make zinc oxide more fluid Factors Controlling ST: Reactor/Catalyst = also called an accelerator 1. Presence of water, high humidity and a. Oil of cloves – contains 70-85% eugenol. Is increase in temperature (heat of the mouth) = easily identified by the characteristic odor of oil shortens or decreases the setting time cloves 2. Cool mixing slab or spatula = prolong setting b. Polymerized Rosin – facilitates speed of time reaction, and a smoother, more homogenous 3. Addition of chemical modifiers, zinc acetate product results; they prevent crystallization of or a small drop of water or alcohol to the base the paste or catalyst will decrease ST 4. Cool the spatula; addition of certain inert Composition (Catalyst) oils and waxes during mixing such as olive oil, c. Accelerators – of the setting time; calcium mineral oil to increase ST chloride, zinc acetate, primary alcohols, glacial 5. Altering the ratio of zinc oxide paste to the acetic acid. The accelerator can be eugenol paste; will result to poor consistency incorporated in one or both pastes and weak set material d. Olive oil, linseed oil, cotton seed oil – 6. Time of mixing – longer mixing time (within plasticizers, reduces burning sensation to limits) the shorter will be the ST tissues e. Canada Balsam, Peru Balsam = often used Construction of Casts to increase flow and mixing properties of the No separating medium needed paste After the stone has set, it can be f. Fillers = if the mixed paste is too thin or lacks separated from the impression by body before it sets; wax, or an inert powder immersion in hot water at 49C-60C for (kaolin, talc, diatomaceous earth, etc.) maybe 5-10 minutes added to one or both pastes The cast materials used with Zoe g. Coloring material impression materials are the gypsum h. Flavoring material type (Type II, III, IV)