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Prof Abbott > Week 4- Making Better Impression > Flashcards

Week 4- Making Better Impression Flashcards

1
Q

What are characteristics of a good impression?

A
  • Uniform, homogeneous mix of material
  • Tray is sufficiently filled with impression material
  • Thoroughly applied tray adhesive (Strong bond between impression and tray)
  • Rigid, sturdy impression tray
  • No voids, pulls or tears on margin detail
  • No tray show-through of the impression material and no tooth contact with tray.
  • Good blend between heavy body and light body materials
  • Complete information about the impression material used provided to the dental laboratory
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2
Q

What should you assess in pt clinically and on study models before placing crown or bridge?

A

What is occlusion like?

Any overerrupted teeth?

Space for tooth (large or small)?

Wear facets on teeth?

Excessive grinding?

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3
Q

How should you use light body material?

A
  1. Wait to inject material until DA is walking over to you with tray material.
  2. Need to rotate tip towards you until you hear click.
  3. Inject light body with purpose around tooth prepared (working time- 25 seconds).
  4. Ensure tip doesn’t come out of material or you’ll get air bubble. Wiggle and stir while syringing.
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4
Q

What is this impression material?

A

Polyether

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5
Q

What is light, medium and heavy body material?

A
  • Light body: syringe material dispensed around teeth
  • Medium-heavy body: tray material
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6
Q

Why is metal tray not ideal for silicone impression?

A

Metal tray and silicone impressions are not ideal as you don’t use adhesive. Material stays in tray due to rim lock and is difficult to get out of tray

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7
Q

How long should you wait for adhesive to set on tray before placing tray material?

A

5-10 minutes

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8
Q

What are causes of inhibited or slow setting?

A

PVS: latex gloves with traces of sulphur, residues from custom temporary cements present.

Polyether: substances with pH<4 (ferric sulphate, epinephrine)

Both: expired materials

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9
Q

What are causes of lack of impression details?

A
  • Material stored at elevated or low temp
  • Thick blood/saliva around prep
  • Inadequate retraction of sulcus around prep
  • Exceeding working time
  • Inadequate disinfection
  • Use of disposable tray rather than special tray
  • Substances pH<4
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10
Q

What are causes of voids on the margin?

A
  • Air trapped in syringe
  • Air trapped while filling tray
  • Improper syringe technique
  • Inadequate coverage of marginal area with light body impression material
  • Blood/saliva contamination
  • Tray not seated straight
  • Exceeding working time
  • Impression stored at elevated temp
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11
Q

What are causes of tearing at the margin?

A
  • Expired impression material
  • Inadequate mix
  • Insufficient retraction
  • Substances with pH<4 contacting polyether
  • Sulphur inhibition due to contact of latex gloves with PVS.
  • Residue from custom temporary cements present.
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12
Q

What are the causes of delamination?

A
  • Exceeding working time
  • Impression material stored at elevated temp
  • Sulphur or acrylic contamination of pre-set heavy body material in 2 step technique
  • Delay when placing tray material on light body material
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13
Q

What are causes of poor bond of impression material to tray?

A
  • Incompatible or no tray adhesive used
  • Inadequate drying time for tray adhesive
  • Thin, plastic tray allow deflection, which can cause rebound upon removal
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14
Q

What are causes of stone model discrepancies?

A
  • Hydrogen gas emission
  • Tooth contact with tray causes water to leach out of tray, dehydrating the stone.
  • Cast not made according to model preparation guidelines
  • Leaving alginate impression too long before pouring up models.
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15
Q

Why do stone model cusp tips sometimes become powdery?

A

Alginate impressions left too long before pouring up

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16
Q

What trays don’t use adhesive?

A

Never use adhesive for metal trays

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17
Q

How should you assess crown margin on impression?

A

Use loupes to identify crown and gingival margin. Need to ensure you can visualise crown margin all the way around.

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18
Q

What is the issue in this photo and how can it be avoided?

A

Inadequate mix

  • Bleed mix before application
  • Follow manufacturers instructions
  • Ensure mix tip is attached correctly.
  • When hand-mixing materials, ensure correct mixing ratio and thorough mix of catalyst and base paste.
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19
Q

What causes inhibition or slow setting of material?

A
  • PVS: latex gloves with traces of sulphur, residues from custom temporary cements present.
  • Polyether: substances with pH<4 (ferric sulphate, epinephrine)
  • Both: expired materials, inadequate mix
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20
Q

Why shouldn’t you lie pt plat while taking impression?

A

Material will go down their throat and drag marks will be created in impression. Always have pt seated upright.

21
Q

How should polyether impressions be sent to lab?

A
  • Rinse with water and blow dry
  • Don’t send in same bag as alginate impression
  • Avoid storing in sealed bags
  • Store impression at room temp away from sun
22
Q

How does inhibited or slow setting impression material appear and why is it an issue?

A

Visual: impression not completely set, shiny, no detail of site.

Result: inadequate surface detail on stone cast, poor fitting restorations

23
Q

What is the issue with this photo?

A

Surface inhibition

24
Q

What is the issue with this photo?

A

Inhibited setting

25
Q

What is the issue with this photo?

A

Lack of impression detail. Student used disposable tray with holes and thus there was no pressure generated.

26
Q

What is the issue with lack of impression detail?

A

Crowns may be too tight, loose or not fit correctly

27
Q

What has caused the issue in this photo?

A

Poor retraction and syringing

28
Q

What is the issue with this photo?

A

Exceeding the Working Time

29
Q

What is the solution if you’re doing polyether impression and you’re using retraciton cord with haemostatic agent

A

Use retraction materials having pH<4.

Select retraction materials and hemostatic agents not containing these chemicals (ferric sulphate and epinephrine)

Rinse hemostatic solution from the prep and dry before taking the impression

30
Q

What is the issue with voids on margins?

A
  • Fit and function of final resto may be compromised
  • Short crown margins and/or open margins.
31
Q

What is the issue with this picture?

A

Void caused by syringe technique

32
Q

What is the issue with this photo?

A

Trapped air or moisture

33
Q

What is the issue with tearing at margin?

A

Short crown margins and/or open margins

34
Q

What is the issue with this photo?

A

Poor retraction. Insufficient tear resistance.

35
Q

How can we solve the issue of insufficient retraction causing tearing at margins?

A
  • Displace tissue to allow the impression material to access prepared area.
  • Consider two-cord retraction. Leave pilot cord in the sulcus when taking the impression.
  • Use impression material with sufficient tear resistance.
    *
36
Q

How can you avoid residue contamination from custom temporary or provisional cements?

A

Do not use impressions already used to fabricate the temp restoration.

Fabricate the temp crown/bridge after final impression has been made.

Remove air-inhibited layer on the exposed tray surface with an alcohol wipe before making final impression.

37
Q

What is the issue with this photo?

A

Tearing at margin

38
Q

How can you overcome issue of sulphur inhibition due to contact of latex gloves with PVS?

A
  • Wear gloves proven not to contain traces of sulphur
  • If contamination suspected, scrub affected area with diluted hydrogen peroxide.
39
Q

What are causes of facial-lingual pulls?

A
  • Exceeding working time
  • Tray movement or repositioning after seating
  • Insufficient amount of impression material used
  • Impression tray does not support flow of impression material
40
Q

What is the issue with this photo?

A

Lingual pulls

41
Q

What is the issue with tray-tooth contact?

A

It will be visualised by tray show-through.

Resto may have slight distortion at marginal area, or rocks

42
Q

What is the issue with this photo?

A

Contact with impression tray

43
Q

What are causes of tray-tooth contact?

A
  • Prepped teeth contact sides or bottom of tray
  • Insufficient impression material used
44
Q

What is the issue with this photo?

A

Poor bond between heavy and light body material

45
Q

What should you do to prevent impression material separating from resin special trays (aside from tray adhesive)?

A

When you light cure a resin special tray it doesn’t set completely. Excess monomer in tray can leak out. This can interfere with adhesive and impression can stay in mouth and separate from tray. To overcome this, wipe tray with alcohol wipe or roughen with acrylic bur and then place adhesive.

46
Q

What is the issue with this photo?

A

Separation of material from tray

47
Q

What is the issue with this photo?

A

Stone model with hydrogen gas voids.

Some manufacturers don’t have platinum catalyst so you get by product of hydrogen gas (not just silicone). When you pour up stone, gas comes out and can crate small bubbles in stone.

48
Q

What is the issue with this photo?

A

Stone model with powdery cusp tips.

Caused by moisture contamination. If alginate impressions are left too long, the stone pools moisture out of alginate material.

Prof Abbott (8 decks)

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