W4 - Impression Problems - Abbott

Question 1

Is adhesive required for metal trays?

Answer 1

NO

Only for plastic and special trays

Question 2

Should you put vaseline on tooth in clinical setting prior to impression?

Answer 2

No - interferes with wettability

Use saliva instead

Question 3

ID problem + cause + solution

Answer 3

Inhibited / slow setting

cause: For PVS materials: Sulfur inhibition due to contact of latex gloves with impression material

Or

Residues from temp crown or cement present

Soln:

1. Wear gloves without sulfur
2. Fabricate temp crown after final impression has been made
3. Remove air-inhibited layer on exposed surface with alcohol wipe before final imp

Question 4

ID problem + cause + solution

Answer 4

Inadequate mix

cause: inadequate mixing, expired materials

Solution: bleed before applying mix tip, ensure tip is correctly attached, ensure correct ratio of catalyst and base paste

Question 5

ID problem + cause + solution

Answer 5

Lack of impression detail

Causes:

• Material stored too hot or too cold
• Blood/saliva around prep
• Exceeding working time
• inadequate retraction

Solution:

obvious

Question 6

ID

Answer 6

Poor retraction and syringing technique

Question 7

ID

Answer 7

Exceeding the working time

Question 8

ID + cause + solution

common

Answer 8

Voids on margins

cause: air trapped in syringe or whilst filling tray

Solution:

bleed syringe

keep tip immersed in material and do not stop when loading syringe

keep mix tip immersed in tray material while filling

must retake impression

Question 9

ID

Answer 9

Trapped air or moisture

Question 10

ID + cause + solution

Answer 10

ID - tearing at margin (insufficient tear resistance)

Cause: inadequate mix, insufficient retraction or expired material

Question 11

ID + cause

Answer 11

ID - tearing at margin (insufficient tear resistance)

Cause: inadequate mix, insufficient retraction or expired material

Question 12

ID + cause + solution

Answer 12

Lingual pull

Cause: exceeding working time, tray movement after seating, insuffiecient amount of impression material

Solution: follow manufacturers working time or use different material with longer working time, don’t move after seating, use more material

Question 13

ID + cause + solution

Answer 13

Tray tooth contact

Caused by: tray too small, insufficient material

Solution: test various sizes of tray, fill adequately

common with disposable trays

Question 14

ID + cause

Answer 14

Delamination

Caused by exceeding working time or material being stored in elevated temperature

Question 15

What can cause stone model discrepancies? (4)

Answer 15

Tooth contact with tray

Gauze of double bite tray causes water to leach out of tray, dehydrating stone

Problems casting the model

Hydrogen gas emission if using VPS

Question 16

How to avoid stone model discrepancies

Answer 16

Instruct pt to bite passively in centric occlusion when using dual arch trays

Fill tray with sufficient material

Provide lab with as much info as possible. (type of impression material, whether or not it has been disinfected)

Follow manufacturers instruction for casting time

Question 17

ID

Answer 17

Hydrogen Evolution voids

Caused if manufacturer does not use a platinum catalyst - creates hydrogen gas instead of silica

Question 18

ID

Answer 18

Moisture contamination

caused by alginate impressions that have been left for too long on stone model

• Stone model pulls the moisture out of the alginate