Impression

Question 1

Impression tray are

Answer 1

a device that is used to carry, confine
and control impression material while making an impression.

Question 2

Ideal requirements of impression materials

Answer 2

1. Non-toxic & non-irritant.
   • 2. Should have pleasant colour, odour and taste.
   • 3. Ease to manipulate with minimum equipments.
   • 4. Suitable working & setting time.
   • 5. Adequate shelf-life for storage.
   • 6. Should be elastic to allow the removal from the
   undercuts without permanent deformation.
   • 7. Adequate strength, so that will not break or tear
   on removal from the mouth.
   • 8. Should be dimensionally-stable

Question 3

Classification of Impression Materials

Question 4

stearic acid will function as

Answer 4

plasticizer
(plasticizer is a material that is added to increase the flow).

Question 5

Classification of impression compound

Answer 5

Type I: Low-fusing impression compound, may be
presented as sticks (green-stick compound) or as cake
form, their softening temperature is 55 - 60 ˚C

Type II: High-fusing compound (tray compound), this type
act as a tray by which an impression will be made using
another impression material like Zinc oxide & eugenol.

Question 6

Properties of impression compound:

Answer 6

poor conductor of heat
Type 1, flow is more than 85% at 45 ˚C

Softening temperature: Type 1 softens at 55 ˚C- 60 ˚C or 130 ˚F – 140 ˚F.

• Impression compound can not be used whenever undercut area

Question 7

Manipulation of impression compound:

Answer 7

Dry heat: for green-stick compound, which is used for border molding
of special trays

For manipulation of impression compound cakes:
• manipulated by heating in thermostatically-controlled water bath
(wet heat) at 55-60˚C, The impression
compound cake must be kneaded in the water bath

Question 8

impression compound application

Answer 8

ype I: Low-fusing compound:
– For making impression of completely-edentulous jaws (in case of
impression compound cakes).
– As border molding of special tray (in case of green-stick compound).
Type II: Tray compound:
– Type II used as tray

Question 9

erecommended disinfection solution for impression compound is

Answer 9

2% alkaline gluteraldehyde
solution (immersion for 10 minutes)

Question 10

Zinc oxide &eugenol impression pastes useful for

Answer 10

Edentulous patients

Question 11

For zinc oxide &eugenol impression pastes,
zinc oxide …
Vegetable oil …
Gum rosin …
Calcium chloride…..

Answer 11

Major constituent
Plasticiser
Facilities the speed of reaction
Accelerator

Question 12

Setting reaction of Zinc oxide &eugenol impression

Answer 12

Zinc oxide + water> zinc hydroxide

• Then the reaction occurs as a typical acid-base reaction (chelation)

Zinc hydroxide + Eugenol > Zinc eugenolate + water

Question 13

Control of setting time:

Answer 13

1. Proportioning: by a change in the proportion (length) of the zinc oxide paste
   to the eugenol paste (base & accelerator pastes).
2. Temperature and humidity: higher temperature and humidity shorten the
   setting time. So cooling the spatula and mixing slab will increase setting time.
3. Mixing: prolonged mixing reduce setting time.
4. Uses of modifiers:
   a. Accelerators:
   -Drop of water, -drop of alcohol, -zinc acetate
   b. Retarders:
   -Inert oil (olive or mineral oil) , -waxes, -vaseline

Question 14

Zoe Properties:

Answer 14

• Dimensional stability: Less than 0.1% shrinkage

• Excellent reproduction of tissue details.

Question 15

Zoe advantages

Answer 15

• 1. Adheres well to the dry surface of the impression tray.
• 2. Adequate working time.
• 3. Dimensionally-stable.
• 4. Hard enough to build up tray deficiencies.
• 5. Compatible with cast material, no separating medium is required
before pouring.
• 6. Registers accurate details of the tissue.
• 7. It can be disinfected by immersion in 2% acidic gluteraldehyde
solution (cidex) for 10 minutes

Question 16

Zoe disadvantages

Answer 16

• 1. May cause burning sensation to oral tissue due to
eugenol {alternatively non-eugenol (carboxylic acid
compounds) pastes are used}.
• 2. Can not be used in case of presence of undercut.
• 3. Difficult to clean
• 4. Temperature and humidity influence the setting time