Impression Materials

Properties
1. Viscosity
  1. High = less detail & mucocompressive
    1. Putty
    2. Heavy bodied addition silicone
    3. Compound
  2. Low = more detail & mucostatic
    1. Alginate
    2. ZOE
    3. Light bodied silicone
2. Elasticity
  1. Elastic = can be removed past undercuts
    1. Light bodied silicone
    2. Alginate
  2. Non-elastic = cannot be removed past undercuts or is permanently deformed when it does
    1. Compound
    2. ZOE
3. Dimensional stability
  1. Unstable
    1. Alginate
    2. Compound
  2. Stable
    1. Addition silicone
    2. ZOE
Compound
1. Types
  1. Sheet form
    1. C/C & P/P Primary imps
  2. Greenstick
    1. C/C Major imps
    2. Tray modifications
2. Thermoplastic setting
  1. Hard at mouth temp.
  2. Soft at 55-60°C
3. Advantages
  1. Muco-compressive
  2. Easily modified/added to
  3. Short ST
4. Disadvantages
  1. Can't record undercuts
  2. Low detail
  3. Dimensionally unstable
    1. Pour cast within 1hr
ZOE
1. C/C Major Imps
2. Chelation acid base reaction (ionic)
3. Pseudoplastic = less viscous when pressure applied
4. Advantages
  1. Fine detail
  2. Hydrophilic
  3. Dimensionally stable
  4. Easily modified/added to
5. Disadvantages
  1. Can't record undercuts
  2. Mucostatic - must be supported by tray
  3. Can cause burning sensation
    1. Xerostomia
Alginate
1. Irreversible hydrocolloid
2. Use
  1. P/P Primary & Major imps
  2. Study models
  3. C/C Primary imp w/ flabby ridge/bony undercuts
3. Setting reaction = Sol to Gel
4. Advantages
  1. Fine detail
  2. Easiest to remove from undercuts
  3. Hydrophilic
  4. Cheap
5. Disadvantages
  1. Dimensionally unstable on storage
    1. Imbibition
    2. Syneresis
  2. Low tear strength
  3. Requires adhesive & perforated tray
Silicones
1. Use
  1. C/C Major imp
    1. Light bodied
  2. Crowns & Bridges
    1. Light & Heavy bodied/Putty
  3. Denture adjustments
    1. Light bodied
2. Addition silicone = Polyvinylsiloxane
  1. Addition (cross-linking) reaction
    1. Platinum catalyst
  2. Heavy bodied
    1. More stable
    2. Less detail
  3. Light bodied
    1. Fine detail
  4. Putty
    1. Most stable
    2. Least detail
3. Advantages
  1. High tear strength
  2. Records undercuts
  3. Fine detail
    1. Light bodied
  4. Dimensionally stable
4. Disadvantages
  1. Hydrophobic
  2. Expensive

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Impression Materials

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