IMPRESSION MATERIALS

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1 IMPRESSION MATERIALS DR ZURYATI AB GHANI BDS (WALES), Grad Dip Clin Dent (Adelaide), Doctor in Clinical Dentistry (prosthodontics( prosthodontics), Adelaide, FRACDS (Australia)

2 Impression materials Non Elastomeric Elastomers Plaster Compound ZOE paste Wax Aqueous Reversible hydrocolloid (Agar) Irreversible hydrocolloid (Alginate) Non Aqueous Polysulphide Condensation Silicone Additional Silicone Polyether

3 DESIRABLE PROPERTIES Easy to mix and dispense Dimensionally stable Good wetting Accuracy in detail Accuracy after cold sterilisation Odor and taste neutral Good elastic recovery Good tear strength Compatibility with die materials Long shelf life Adequate working time No irritation to tissues

4 KEY LEARNING ISSUES Classification of materials Understanding setting reaction Properties Delivery systems Problems and their solutions

5 Non elastomeric impression materials Compound

6 Compound Composition: 40%resin, 7% waxes, 3% organic acids, 50% fillers, colouring agents Capable of moulding impression at 45 C Primary impression in the edentulous ridge

7 Zinc oxide Eugenol Composition Tube 1 Zinc oxide Oils Additives Tube 2 Eugenol Oil Resin Additives

8 Zinc oxide eugenol Used in custom made tray to record usually edentulous arches, sometimes referred as wash impression Mixing time 30 to 45 secs Setting time 3 to 5 mins Brittle, messy, sometimes irritates patient due to eugenol content

9 Zinc oxide eugenol

10 Impression waxes Useful for correction of small imperfection in ZnOE impression, or for recording partial lower free end saddles

11 Aqueous elastomeric impression materials 1) Agar- Reversible hydrocolloid 2) Alginate irreversible hydrocolloid

12 Alginate One of the most widely used impression materials ADVANTAGES: Easy to mix and manipulate, cheap, flexibility of set impression, minimum equipment, accuracy if handled properly.

13 ALGINATE Composition Sodium or potassium alginate Sodium phosphate Silicate powder Potassium sulphate or potassium zinc fluoride Organic glycol Chlorhexidine Function To dissolve in water To react with alginate Control setting time To aid setting of die material Min dust during dispensing Self disinfection

14 Mixing time: 1 min Setting time: mins Fast set: 1-21 mins Temp setting time. Do not alter powder liquid ratio to change setting time

15 Dimensional changes. Can be stored at 100 % humidity for 1 hr without dimensional changes Not very accurate Low tear resistance

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17 Non-Aqueous Elastomers Polysulfides Condensation Silicones Addition Curing Silicones Polyethers

18 Also known as thiokol rubbers or mercaptans Provided as two pastes: Base and Catalyst Composition Base: Polysulfide polymer Titanium oxide or Zinc Oxide Calcium Sulfate Catalyst: Lead dioxide Sulfur Dibutyl phthalate Products: Permlastic (Kerr); Omniflex (GC-America)

19 SETTING REACTION Condensation reaction between SH (sulfydryl groups) with lead dioxide and sulfur to produce disulfide links and water. Chain lengthening and cross-linking occurs Increase in viscosity Elastic properties arise Water accelerates the setting reaction Heat accelerates the setting reaction

20 O from Pb 2 O Sulfydryl group

21 ADVANTAGES Good tear strength and flexibility Low cost Increased working time DISADVANTAGES Poor dimensional stability due to water loss Offensive odor Long setting time More permanent deformation on removal and less elastic recovery due to reduced degree of polymerisation compared to silicones and polyethers

22 DIMENSIONAL CHANGE FROM: Temperature transition upon removal from mouth Water loss which is a setting reaction by-product Shrinkage from continued polymerisation

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24 Initial mix on pad Final mix ready for dispensing

25 COMPOSITION Base: Dimethyl polysiloxane Alkyl silicate Catalyst: Stannous octoate Setting reaction: Cross-linking of a hydroxy terminated dimethyl polysiloxane by an alkyl silicate catalysed by stannous octoate

26 Dimethyl polysiloxane Tetra ethyl orthosilicate

27 ADVANTAGES More stable than polysulfides Good tear strength Good working and setting times DISADVANTAGES Odor from alcohol byproduct Dimensional instability Most accurate impressions with condensation silicones are generated via a putty-wash technique. Products: Formasil, Accoe (GC America)

28 Poly-Vinyl Siloxanes Setting reaction can be inhibited via a sulfur compound in some latex gloves by the name of zinc diethyl dithiocarbamate This chemical interacts with the chloroplatinic acid catalyst in the PVS formulation Not all latex gloves cause problems for PVS materials

29 PolyVinyl Siloxanes SETTING REACTION Crosslinking reaction of a vinyl terminated dimethyl polysiloxane Catalysed by chloroplatinic acid. Hydroen gas can be released as as by-product. The more contemporary products have hydrogen gas scavengers. VISCOSITIES Putty Monophase Heavy Intermediate Light

30 PVS Setting Reaction Mandikos 1992

31 PolyVinyl Siloxanes ADVANTAGES Very stable dimensionally Impression re-pours possible Odor and taste neutral Good elastic recovery Good tear strength Good wetting of prep surface Good working and setting times Excellent delivery systems

32 Poly-Vinyl Siloxanes DELIVERY SYSTEMS Automix System Pentamix System

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34 Poly-Vinyl Siloxanes PROBLEMS Setting retardation via sulfur in latex gloves Setting retardation from sulfur in Astringident solution Tearing of wash material away from tray material Hydrogen gas release Locking into undercuts and open embrasures Porosities

35 COMPOSITION Base: Polyether polymer Colloidal silica filler Glycol ether or phthalate plasticizer Catalyst: Alkyl aromatic sulfonate Plasticizers and fillers as above Permadyne

36 PENTAMIX delivery system can be used for dispensing Polyether impresssion material

37 Polyether based polymer cured by reaction between aziridine rings which branch off a copolymer of ethylene oxide and tetrahydrofuran Aromatic ester (Initiator) Cross-linking occurs via cationic Polymerisation of imine end groups

38 ADVANTAGES Excellent accuracy and wetting Good dimensional stability Very good shelf life (~ 5years, less in warm conditions) PROBLEMS Very stiff when set / problem in undercuts, embrasures Cold disinfection Poor tear strength Odor Paste-paste mixing (messy, porosities) Shorter working time than PVS silicones Sensitivity to aromatic sulfonate Water condensation on chilled mixes

39 A θ 1 θ 2 B B = Material has superior wetting, a desirable property PVS silicones have good wetting properties and are advertised as having high hydrophilicity when in fact they are HYDROPHOBIC

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41 CLINICAL TIPS TO AVOID PROBLEMS Use correct adhesive on tray Block out locking embrasures and undercuts prior to impression Tooth surface must be clean Preparation margins must be well defined and clear Margins free of fluids and blood Mix impression material correctly Do not overload stock trays Have a high velocity suction handy Apply material efficiently without delays Leave in place without tray movement for correct time Remove tray carefully Wash away any blood on impression surface Disinfect Inspect marginal detail Retake impression if major flaws arise

42 Mandikos MN. Polyvinyl siloxane impression materials: An update on clinical use. Aust Dent J 1998;43: Wassel RW, Barker D, Wall AWG. Crowns and other extra oral restorations. Impression materials and technique. British Dental Journal 2002;192:

43 References 1. Mandikos MN. Polyvinyl siloxane impression materials: An update on clinical use. Aust Dent J 1998;43: Wassel RW, Barker D, Wall AWG. Crowns and other extra oral restorations. Impression materials and technique. British Dental Journal 2002;192: Mc Cabe JF, Wall AWG. (1998) Applied dental materials, 8th edition. Blackwell Science 4. Shillingburg HT, Sumiya H, Whittsett 3rd edition. Fundamentals of fixwd prosthodontics.. Quintessence books 5. Rosenstiel,, Land, Fujimoto. Contemporary fixed prosthodontics 3rd edition 6. Lectures from Dr tom Berekally.. Consultant prosthodontist/lecturer University of Adelaide, South Australia

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