Impression Materials

Impression Materials

1. Properties

   • Viscosity
     • High = less detail & mucocompressive
       • Putty
       • Heavy bodied addition silicone
       • Compound
     • Low = more detail & mucostatic
       • Alginate
       • ZOE
       • Light bodied silicone
   • Elasticity
     • Elastic = can be removed past undercuts
       • Light bodied silicone
       • Alginate
     • Non-elastic = cannot be removed past undercuts or is permanently deformed when it does
       • Compound
       • ZOE
   • Dimensional stability
     • Unstable
       • Alginate
       • Compound
     • Stable
       • Addition silicone
       • ZOE

2. Compound

   • Types
     • Sheet form
       • C/C & P/P Primary imps
     • Greenstick
       • C/C Major imps
       • Tray modifications
   • Thermoplastic setting
     • Hard at mouth temp.
     • Soft at 55-60°C
   • Advantages
     • Muco-compressive
     • Easily modified/added to
     • Short ST
   • Disadvantages
     • Can't record undercuts
     • Low detail
     • Dimensionally unstable
       • Pour cast within 1hr

3. ZOE

   • C/C Major Imps
   • Chelation acid base reaction (ionic)
   • Pseudoplastic = less viscous when pressure applied
   • Advantages
     • Fine detail
     • Hydrophilic
     • Dimensionally stable
     • Easily modified/added to
   • Disadvantages
     • Can't record undercuts
     • Mucostatic - must be supported by tray
     • Can cause burning sensation
       • Xerostomia

4. Alginate

   • Irreversible hydrocolloid
   • Use
     • P/P Primary & Major imps
     • Study models
     • C/C Primary imp w/ flabby ridge/bony undercuts
   • Setting reaction = Sol to Gel
   • Advantages
     • Fine detail
     • Easiest to remove from undercuts
     • Hydrophilic
     • Cheap
   • Disadvantages
     • Dimensionally unstable on storage
       • Imbibition
       • Syneresis
     • Low tear strength
     • Requires adhesive & perforated tray

5. Silicones

   • Use
     • C/C Major imp
       • Light bodied
     • Crowns & Bridges
       • Light & Heavy bodied/Putty
     • Denture adjustments
       • Light bodied
   • Addition silicone = Polyvinylsiloxane
     • Addition (cross-linking) reaction
       • Platinum catalyst
     • Heavy bodied
       • More stable
       • Less detail
     • Light bodied
       • Fine detail
     • Putty
       • Most stable
       • Least detail
   • Advantages
     • High tear strength
     • Records undercuts
     • Fine detail
       • Light bodied
     • Dimensionally stable
   • Disadvantages
     • Hydrophobic
     • Expensive