Lec 9: Impression Flashcards

1
Q

Negative impression or imprint made placing some soft, semifluid material in the mouth and allowing the material to set.

A

Impression

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2
Q

Ideal impression material:
1. Complete _____ before cure
2. Sufficient ______ to record define detail.
3. Ability to ____ oral cavity.
4. Dimensional ____
5. Dimensional ____
6. Complete _____ after cure
7. Optional ____-

A

Plasticity
Fluidity
Wet
Accuracy
Stability
Elasticity
Optional Utilities

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3
Q
  • Set to rigid consistency.
  • Cannot be removed from the mouth without fracture and reassembly.
A

Rigid impression materials

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4
Q

2 Rigid impression materials?

A

Plaster of Paris
Metallic oxide paste

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5
Q

Used in dentistry for over 200 years; was once the only material available.

A

Plaster of Paris / impression plaster

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6
Q
  • Usually made of some form of zinc oxide-eugenol combination.
  • Not used as primary material, never for impressions with remaining natural teeth.
  • Not used on stock impression trays.
A

Metallic oxide paste

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7
Q

2 thermoplastic impression materials?

A

Modelling plastic
Impression waxes & natural resins

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8
Q

Oldest impression material used in prosthodontic dentistry.

A

Modelling plastic / compound

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9
Q

Most often for border correction of custom trays for distal free-end classifications.

A

Modelling plastic / compound

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10
Q

Most commonly used modelling plastic for corrected impressions for extension base areas (softens at 132 F / 55.55 C).

A

Red-brown material

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11
Q

Obtainable in stick form for border molding.

A

Red, gray, green (modelling compound)

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12
Q
  • Used to record non-undercut edentulous portions and are usually used in combination with other impression materials.
  • To correct borders of impression = establish optimum contact at border.
  • To record border detail accurately and include correct width.
A

Impression waxes and natural resins

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13
Q

Used for:
> Corrective impression
> Bite registration

A

Impression waxes and natural resins

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14
Q

Iowa wax & Korecta wax are examples of this.

A

impression waxes

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15
Q
  • Those that remain in an elastic or flexible state after they have set and removed form the mouth.
  • Only ones that can be withdrawn without permanent deformation.
  • For making impressions and when tooth undercuts and surface detail must be recorded with accuracy.
A

Elastic impression materials

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16
Q

Example of reversible hydrocolloid

A

Agar-agar

17
Q
  • Fluid at higher temperatures, gel on reduction in temperature.
  • For fixed restorations
  • Acceptable accuracy
A

Reversible hydrocolloid

18
Q
  • Used for removable partial denture impressions and especially for secondary corrected or altered cast impressions.
  • Unpleasant odor, can stain clothes.
  • Moderately inepensive
  • High tear strength
  • Long working and setting times (8-10 mins)
  • Can be disinfected in liquid, cold-sterilizing solutions
A

Mercaptan Rubber-base / Polysulfide polymer (thiokol) impression material

19
Q
  • An elastic-type of material
  • Demonstrated good accuracy and thixotropic, which provides good surface detail and makes them useful for border molding material
  • Also hydrophilic, produces good wettability for easy cast forming.
  • Low to moderate tear strength and much shorter working and setting times.
A

Polyether impression materials

20
Q
  • More accurate and easier to use
  • Pleasant odor, moderately high tear strength, and excellent recovery from deformation
  • Hydrophobic, which can make cast formation a problem
  • Can be disinfected with no alteration in accuracy
  • Poured within 1 hour.
A

Silicone based materials

21
Q

Possible causes of an inacurate / weak cast (7)

A
  1. Distortion of hydrocolloid material
  2. Ratio of water to powder is too high = weak
  3. Improper mixing = weak / chalky
  4. Trapping of air (due to insufficient vibration)
  5. Soft or chalky surface from retarding action of the hydrocolloid or absorption of necessary water for crystallization by dehydrating hydrocolloid.
  6. Premature separation of the cast from the impression.
  7. Failure to separate the cast from the impression for an extended period.
22
Q

A stock tray should?
* Be sufficiently _______ to avoid distortion.
* Fit in the mouth about _______ clearance.
* Permits _____ and _____ to fit the mouth.

A
  • Rigid
  • 4-5mm clearance
  • Trimming & Shaping