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Fixed Prosth 1 > Final Impression Materials and Technique > Flashcards

Final Impression Materials and Technique Flashcards

1
Q
  • An imprint or negative likeness

* Made from soft semi-fluid material allowed to set

A

Dental Impression

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2
Q

: ability of liquid to flow over a solid surface
•Related to surface energy of the solid and surface tension of the liquid
•Contact angle of wetting

A

Wettability

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3
Q

_______ materials:

contact angle > 90: surface not wetted

A

Hydrophobic

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4
Q

_____ impression materials:

contact angle < 90: surface wetted

A

Hydrophilic

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5
Q

: resistance of a liquid to flow or motion. Reverse of fluidity.•Shear stress/ Strain rate = MPa/sec•Related to the unset, liquid material•Liquids and viscosity:•Newtonian: viscosity constant•Pseudoplastic: ̄viscosity with ­shear rate

A

Viscosity

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6
Q

:shear thinningNot thixotropy/ thixotropic, incorrect term•Material does not flow until under pressure•Less viscous with increased shear rate•Why same material used in tray and syringe

A

Pseudoplasticity

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7
Q

:characteristic of solid that behaves as an elastic solid and a viscous liquid•Related to set impression•Mechanical properties dependent on loading rate•Associated with viscous nature•As ­load rate, properties improved•­tear strength & elastic limit•Quick removal, decreased distortion

A

Viscoelastic

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8
Q

= ability to replicate the intraoral surface details.

A

Accuracy

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9
Q

=ability to retain its absolute dimensional size over time.

A

Dimensional Stability

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10
Q

= ability to resist tearing in thin sections (such as through the feather-edged material within the gingival sulcus).

A

Tear Resistance

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11
Q

Were the first impression materials popular in the previous century rigid or elastic?

A

Rigid

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12
Q

______ impression materials

•Chemical reaction, cannot revert to preset state. Primary bonds.

A

Irreversible:

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13
Q

______ impression material
•Softens under heat and solidifies when cooled.
•Secondary bonds, no chemical change

A

Reversible:

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14
Q

______ impression material
•Rigid, cannot be removed from undercuts
•Edentulous impressions

A

•Inelastic:

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15
Q

______ impression material
•Can be removed from undercuts without distortion
•Dentate impressions

A

Elastic:

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16
Q

:gel relaxation, water extruded from gel (shrinkage)

A

Syneresis

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17
Q

:absorption of water causing expansion

A

Imbibition

18
Q

What are the 2 aqueous elastomeric impression materials?

A

Agar - reversible

Alginate - Irreversible

19
Q

What are the 3 Non-aqueous Elastomeric Materials“Elastic Polymers”?

A
  • Polysulfide (PS, sometimes called rubber base)
  • Vinyl Polysiloxane(VPS not PVS)
  • Polyether (PE)
20
Q

Which chemical setting reaction produces a by product of alcohol or water?

A

Condensation polymerization

21
Q

Which chemical setting reaction produces no by product?

A

Addition polymerization

22
Q

The impression tray Extends approximately __ to ____ mm beyond the third molar, retromolar, or tuberosity area of the arch.

A

2 to 3 mm

23
Q

The impression tray Is sufficiently deep to allow ___ to ___ mm of material between the tray and incisal or occlusal edges of the teeth.

A

2 to 3 mm

24
Q

a.Prevent impression distortion due to material pulling away from trayb.Mechanical perforations

A

Adhesives to tray

25
Q

Must be sufficiently rigid to:—
Carry the impression material into the oral cavity.—
Hold the material in close proximity to the teeth.—
Avoid breaking during removal.—
Prevent warping of the completed impression.

A

Impression trays

26
Q 
Goal:a fully or overextended impression of the arch, with all the anatomical landmarks. Good impressions are MADE not TAKEN!
•Evaluate Arch Form
•Anatomical Landmarks
•Musculature
•Soft tissue anomalies
•Fabrication of Custom Impression Tray
A

Preliminary impression

27
Q

Is alginate hydrophilic or hydrophobic?

A

Hydrophilic

28
Q

•Was developed as a substitute for the agar impression material when its supply became scarce during World War II. •Based on a natural substance extracted from certain brown seaweed•When the soluble alginates are mixed with water, they form a sol quite readily.•Alginate impression materials are hydrophilic, so moist tissue surfaces are not a problem.

A

Irreversible Hydrocolloid

29
Q

How long should the alginate impression be disinfected in bleach or iodophor in a wet paper towel in plastic bag?

A

10 mins

30
Q

How long should the cast material be allowed to set?

A

60 minutes

31
Q

What are the 2 factors that affect the shelf life of alginate?

A 
Storage temp
Moisture contamination (humidity)
32
Q

Is VPS hydrophilic or hydrophobic?

A

Hydrophobic

33
Q

Is polyether hydrophobic or hydrophilic?

A

Hydrophilic

34
Q

The thickness of the alginate impression between the tray and the tissues should be at least ___ mm.

A

3 mm

35
Q

•These are elastic impression materials called “non-aqueous” elastic impression materials. Distinguished from the Hydrocolloids which are aqueous materials.•They are synthetic rubber•They offer potential solutions to the two main problems associated with hydrocolloids:-Poor tear resistance-Poor dimensional stability

A

Elastomeric impression materials

36
Q

•Is an elastomer that is also known as “mercaptan” or simply “rubber base”
•The impression material is packaged in two tubes: A base and an accelerator.
Composition:
-The base contains a liquid polysulfide polymer mixed with an inert filler
-The accelerator which is usually lead peroxide mixed with small amounts of sulfur and acts as an oxidation initiator.

A

Polysulfide

37
Q

How long should you wait before pouring a polysulfide impression?

A

20-30 minutes

38
Q

How long should you wait before pouring a VPS impression?

A

20-30 mins

39
Q

a.BEST impression material for dimensional stability:
•Pouring should be delayed at least 4 hours for H2 out-gassing.
•Pouring can be delayed up to 7-to-10 days (or indefinitely).
b.Stiffness makes removal difficult.
c.Most material dispensed using auto-mixing gun and mixing tips

A

VPS

40
Q

Is VPS a condensation or addition reaction?

A

Addition rxn

41
Q

4.Difficult removal from mouth or cast
•Undercut blockout
•Initially thought due to higher PE stiffness
•Reformulated, less stiff than VPS
•Even though lower stiffness, still higher removal force
•Material stiffness and impression removal difficulty not correlated (Walker et al 2012, J Pros)
5.Hydrophilic: C-O-C
•Likely reason for impression removal difficulty
—higher interactions forces with impressed surface
6.High elastic recovery
7.Dimensional stability•Pour delay•Multiple pour

A

Polyether

42
Q

•a.Excellent impression accuracy and dimensional stability.
•b.Stiff and therefore difficult to remove without rocking.
•c.Break seal and rock slightly to prevent tearing: Low tear resistance.
•d.Negatively affected by H2O, saliva, and blood.
(1)Since it is hydrophobic, moisture increases marginal discrepancy
(2)Increased water absorption occurs if use thinning agents
•e.Can be dispensed from automated extruder and mixer (ESPE PentaMix)

A

Polyether

Fixed Prosth 1 (12 decks)

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