Elastic Impression Materials Notes PDF

ELASTIC IMPRESSION REVERSIBLE HYDROCOLLOID – AGAR MATERIALS CLASSIFICATION: Thermoplastic, Final/Wash Impression HYDROCOLLOID IMPRESSION MATERIALS MANNER DISPENSING:...

ELASTIC IMPRESSION REVERSIBLE HYDROCOLLOID – AGAR MATERIALS CLASSIFICATION: Thermoplastic, Final/Wash Impression HYDROCOLLOID IMPRESSION MATERIALS MANNER DISPENSING: A. Reversible Hydrocolloid – AGAR GEL in a Collapsible Tube = Water B. Irreversible Hydrocolloid – ALGINATE Cooled Tray GEL in a Glass Jar = Syringe Type RUBBER IMPRESSION MATERIALS 1. Polysulfide Rim USES: 2. Silicone Rim a) To make impressions of dentulous & 3. Polyether Rim edentulous mouths b) As a duplicating material for casts duplication HYDROCOLLOID IMPRESSION MATERIAL HYDRO – water ADVANTAGES: COLLOID – mixture of 2 or more - Good surface detail substances in which one substance is - Reusable & easily sterilized suspended or dispersed within another surface DISADVANTAGES: A substance deforms when removed - Need special equipment (water bath) & from the mouth and springs back to its special technique original form – FLEXIBLE GEL. - Dimensional instability All colloids are termed as SOLS, (LIQUID LIKE) COMPOSITION: 1) AGAR – basic constituent SOL to GEL formation – Temperature - extracted from seaweed change - Tray material: 12-15% - Syring material: 6-8% HYDROPHILIC (Liquid Loving) sols is term for 2) WATER = principal ingredient by weight 80- hydrocolloid impression materials are solids 85% suspended in liquids. 3) BORAX = 0.2% - strength improver, increases viscosity The sol may be changed to a gel or jelly, of the sol, acts as retarder when the temperature is DECREASED. 4) POTASSIUM SULFATE = 1-2% ensures The temperature at which this change proper setting if the gypsum model and die occurs is known as the GELATION materials against the agar TEMPERATURE. 5) FILLERS = for the control of strength, viscosity and rigidity; diatomaceous earth, clay, TYPES: silica, wax, rubber and similar inert powders I. Reversible Hydrocolloids (SOL-GEL-SOL) 6) Coloring and flavoring materials II. Irreversible Hydrocolloids (SOL-GEL) 7) Plasticizer = Glycerin 8) ANTI-MICROBIAL AGENTS = Thymol (Bactericide) 9) Preservatives = 0.1% Benzoates E. DIMENSIONAL CHANGES - cast must be constructed within 15 minutes APPARATUS NEEDED Hydrocolloid conditioner Dehydrate = stiff and difficult to remove → Agar hydrocolloid fracture of cast Water cooled trays with tubing - Prolonged contact of agar with gypsum will MANIPULATION result in a rougher that normal surface on the Hydrocolloid conditioner (100°C for 10 model minutes) F. HYSTERESIS = - Gelation a solidification process, from so to MANNER OF WITHDRAWAL gel Impression is removed rapidly from the - The hydrocolloid gel does not return to the sol mouth with a SINGLE STROKE, at the same temperature it is solidified. SUDDEN JERK, SUDDEN PULL, NO - Liquefaction temperature: must be heated SIDE MOVEMENTS. at a high temperature Although the agar impression is flexible, - Hysteresis. The temperature lag between the it does not completely recover from gelation temperature and the liquefaction being deformed during removal from temperature of the gel undercut areas A slow removal is a common cause of Agar exhibits hysteresis, melting at 85°C inaccuracy (358K, 185°F) and solidifying from 32-40°C. (305-313K, 90-104°F) PROPERTIES: A. STRENGTH (TRAY) - Tear strength: 4 LB/IN2 (715 GM/CM2) IRREVERSIBLE HYDROCOLLOID - ALGINATE - Compressive strength: 116 LBS/IN2 (8000 GM/CM2) DESCRIPTION: ** The syringe material has POORER - From the “ALGIN” dental compound; derived mechanical properties from a brown seaweed (algae) that yields a B. CONSISTENCY AND RIGIDITY peculiar mucous extraction - Homogenous and free of lumps when used for - One of the most widely used dental impression impression material - Fluid enough to be easily transferred - Upon setting it becomes a little stiff ADVANTAGES: C. POOR MECHANICAL PROPERTIES 1. Easy of missing and manipulating - Increases stiffness, material becomes brittle 2. Minimum equipment necessary and fractures 3. Flexibility of the set impression D. SHELF LIFE = poor shelf life; storage of agar 4. Accuracy of handled properly impressions is to be avoided. After impression 5. Low cost making, if storage is unavoidable, it should be 6. Comfortable to the patient limited to 1 hour in 100% relative humidity. SYNERESIS: Dehydration CLASSIFICATION: Thermoset; Elastic, IMBITION: Storage in water causes swelling of Preliminary/Final Impression Material the impression MANNER OF DISPENSING: STAGES DURING GELATION: CHEMICAL Powder + Water = SOL → GEL EQUATION: Powder is placed in a pre-weighed 1. When alginate is mixed with water individual containers (pouch) 2NA3PO4 + 3CASO4= CA3(PO4)2 + 3NA2SO4 TYPES BASED ON SETTING TIME: Main ingredient must first react with 1. TYPE I – Fast set (Must gel in not less than 60 NA3PO4, a retarder, until the latter is seconds nor more than 120 seconds used up. 2. TYPE II – Normal set (Must gel between 2-4.5 2. When alginate is already in the patient’s minutes) mouth KNALG + NCASO4 = NK2SO4 + CANALG USES: SOLUBLE SOL INSOLUBLE SOL 1. For full mouth impressions – dentulous & Before it reacts with soluble sol to edentulous produce insoluble gel 2. For quadrant impressions 3. As a duplicating material MANIPULATION: W/P ratio = 15-18 gram: 40-50 CC water COMPOSITION: Water first before powder 1) NA or K Alginate – main ingredient, soluble Use horizontal figure 8 while swiping or salts of alginic acid; FUNCTION: to dissolve in stropping the mixture against the sides water to form sol of the bowl 2) CA SO4 – Reactor, Mixing time: 45 sec to 1 minute Dihydrate: Commonly used Result: Smooth, Creamy mixture Hemihydrate: Increases shelf life of the Tray material: The proper size of tray powder and increases dimensional should be selected before mixing, stability of the gel loading of the tray should be done 3) NA PO4 – Trisodium Phosphate quickly Retarder Material is added to the posterior 4) Diatomaceous Earth or Silicate Powder portion of the tray then pushed toward (Fillers) the anterior part Increases strength and stiffness Wait for 2-3 minutes after gelation Produces a smooth texture before withdrawing the Ensures a firm gel surface that is not IMPRESSION: Single firm motion, tacky sudden pull or sudden jerk Disperses the alginate powder particles in water FACTOR TO CONTROL GELATION TIME: 5) K TI Fluoride – accelerates setting of the W/P ratio stone; Plaster hardener effect the surface o More water: increased gelation finish time 6) Organic Glycol – makes alginate “dust-free” o More powder: decreased 7) Quaternary Ammonium Compounds – gelation time provide self-disinfection Mixing time 8) Flavoring and coloring materials o Shorter: increased gelation time o Longer: decreased gelation time  Temperature o Low: increased gelation time o High: decreased gelation time SHELF LIFE 2 Major Factors to consider: o Storage temperature o Moisture contamination from the air Store in cool, dry environment in containers with tight lids PROPERTIES: A. Dimensional Stability = is loss of accuracy with increased time of storage 1. SYNERESIS – water evaporates = SHRINKS 2. IMBIBITION – placed in water = SWELL/EXPANDS B. STRENGTH = alginate may be greater than that of agar materials. Tear strength: 2-4 LBS/IN (358-716 GM/CM) Compressive strength of 5000-7000 GM/CM2 C. FLOW = good flow property → Accuracy and detail D> ADHESIVE PROPERTY = or the property for alginate to be TACKY before setting