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Fixed Midterm Spring > 3. Impressions > Flashcards

3. Impressions Flashcards

1
Q

Is tissue management needed with CAD CAM technology

A

yes

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2
Q

What are the issues with taking impressions for a crown with stock trays

A
  • Often lack extension to support the impression material
  • Lack of stops stops makes positioning and stabilizing more challenging
  • Flexible (rebound on removal) –> distorted impression
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3
Q

Pros of custom trays

A
  • Less impression material wasted
  • Controlled uniform thickness of impression material more accurate impressions
  • Effective extension
  • Better positioning and stabilization
  • Rigid no distortion **
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4
Q

What are the 3 different materials that can be used to make a custom tray

A
  • Auto-polymerizing resin
  • Thermoplastic resin
  • Photo-polymerized resin
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5
Q

If making the custom tray out of autopolymerizing resin the tray should be fabricated how soon before the impression needs to be taken

A

9hrs

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6
Q

What is the material we use to make custom trays

A

photo-polymerizing resin

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7
Q

Which custom try material is the best to use

A

no difference

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8
Q

The custom tray should extend how far into the vestibule past the gingival margins

A

3-5 mm

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9
Q

How many layers of baseplate wax should be used to make a custom tray

A

2

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10
Q

Possible contaminants of a custom tray are _ and can be removed how

A
  • MRA (model releasing agent)
  • ABC (Air Barrier Coating)
  • Baseplate wax

Removed by washing with soap and water

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11
Q

Critical (important) features of a custom tray are

A
  • Rigidity **
  • Proper extension
  • Stops (optional)
  • Adequate thickness
  • No sharp edges
  • Uncontaminated
  • Effective handle
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12
Q

What impression materials are and aren’t used for custom trays

A

Not

  • Reversible hydrocolloid
  • Condensation silicone

Are

  • Polysulfide polymer
  • Polyether
  • Addition Silicone PVS
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13
Q

Recommended use for reversible hydrocolloid is

A

multiple preps

Problems with moisture control

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14
Q

Why is reversible hydrocolloid good to use in situations with poor moisture control

A

material is hydrophilic

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15
Q

Hallmark of polysulfide is

A

high tear strength

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16
Q

What impression material is the stiffest

A

polyether

17
Q

Condensation silicone is (hydrophilic/hydrophobic)

A

hydrophobic

18
Q

What impression material is the most dimensionally stable

A

addition silicone

19
Q

What are the three different impression techniques and which one is most commonly used

A
  • Monophase (one vistosity)
  • Single step (2 viscosities at the same time) **most common*
  • Double step (use material of different viscosity at each step)
20
Q

Advantages of polyvinyl siloxane (PVS) aka addition silicone

A
  • Easy to handle
  • Automix system
  • Favorable setting time (5 min regular set)
  • High dimensional stability
  • Excellent elastic recovery
21
Q

Disadvantages of addition silicone

A
  • hydrophobic
  • Some materials release gas (hydrogen) H2
  • Expensive
  • Set inhibited by sulfur compounds in latex glove
22
Q

How can the release of H2 from addition silicone be reduced

A

Pt or Pd as hydrogen scavengers

23
Q

Before taking an impression what should you look for in order to avoid locking the tray in the patient’s mouth

A
  • Bridges (always block out out under the pontic)
  • Black triangles
  • block out with periphery wax or oraseal
24
Q

What is important in selecting your adhesive for the impression tray

A

must be compatible with the impression material

25
Q

How can you avoid trapping air bubbles in the impression material when dispensing

A

-Keep tip at sulcus opening and in the impression material

26
Q

PVS takes how long to set

A

5 min

27
Q

Problems to look for when evaluating the impression

A
  • Major distortions
  • Voids or creases
  • Incomplete areas
  • Pulls and tears
  • Unset material
  • Syringe material not fused with tray material
  • Adhesive failure/separation from the tray
28
Q

Describe the protocol you should follow for impression analyzation

A
  • Rinse
  • Dry
  • Inspect
  • Make judgement
  • Show faculty
  • Disinfect
29
Q

Cavicide requires _ contact time

A

3 min

30
Q

T/F Cavicide slightly affects the accuracy of the PVS impression

A

F- no effect

31
Q

What should you make sure you make sure you do before the patient leaves

A

make sure all the cords are out

Fixed Midterm Spring (9 decks)

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