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Impression Compound

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Dental Impression is a negative replica of the oral cavity, many impression materials are present which are capable of getting the perfect impression if the proper guidelines are followed. Impression Compound is used to take a negative replica or an Impression of the Edentulous Oral cavity in a process called Primary Impression. The material is a Reversible type material which means, it can be reused or softened using heat for a limited period of time to capture the perfect impression.

IMPRESSION COMPOUND

It is a rigid, reversible impression material which sets by physical change.

Classification:

According to ADA Specification Number 3:

Type I:

Type II:

  • High fusing compound – tray compound.

Supplied as:

  1. sticks, cakes, & cones.
  2. Colors – green, brown, red.

Applications:

Type I:

  • For making primary impressions.
  • For individual tooth impression
  • For peripheral tracing or border moulding.
  • To check undercuts in inlay preparation.

Type II:

  • To make a special tray.

Requirements of an ideal impression compound:

  1. It will harden after heat treatment when brought back to mouth temperature and be stable after hardening and removal from mouth.
  2. When softened it should have uniform consistency to help reproduce fine details of oral tissue.
  3. Should become hard uniformly throughout without discrepancies and distortion.
  4. It should not be harmful to Oral tissues when it is elastic in plastic state.
  5. Should not be harmful and not have toxic or Irritating materials to Oral tissue.
  6. Material should have cohesive property and not adhesive property.
  7. When exposed to flaming after removal from mouth should exhibit a smooth glossy surface.
  8. After hardening flaking and chipping should not be seen during trimming and reshaping using lacron carver.

Composition

  • Rosin 30
  • Copal resin 30
  • Carbuna wax 10
  • Stearic acid 5
  • Talc 25
  • Coloring agent.

Significance:

  •  softening of the material , the outside will soften first & inside last. So to ensure uniform softening the material should be kept immersed for a long time in water bath.
  • The layer adjacent to the mouth tissue swill remain soft. Therefore Its imp to cool the compound thoroughly before removing the impression.

Properties:

Thermal properties

i) Thermal conductivity:

  • has low thermal conductivity.

ii) Coefficient of linear expansion. (CTE)

  • high CTE , 0.3% acceptable.

iii) Flow

  • high fusing compounds – < 2% at 37 .C & < 70-85 % at 45.C
  • low fusing compounds – < 3% at 37 C& < 80-85% at 45 C

iv) Glass transition temp:

  • It is the temp. at which the material loses its hardness or brittleness on heating or forms a rigid mass.
  • App. 39.CMaterial removed from the mouth after glass transition temp. is reached.

v) Fusion Temp.

  • It’s the temp. at which the impression compound becomes plastic.
  • Its 43.5.C

vi) Dimensional stability.

  • Poor dimensional stability.
  • To prevent distortion pour the cast within 1 hr.

vii) surface detail reproduction is less because of high viscosity & low flow.

Manipulation

  • Sticks: Small amount softened over flame
  • Cakes: Softened in a thermostatically controlled water bath.

Precautions:

  • Prolonged immersion in a water bath is not indicated overheating
  • In water makes the compound sticky & difficult to handle.
  • Avoid incorporating water while kneading.

Advantages:

  • Cheap reusable
  • Does not produce irritation to the patient impression
  • Can be remodified & re-softned again till an accurate impression is obtained

Disadvantages

  • Difficult to record details accurately.
  • Soft tissues are compressed due to pressure applied while taking the impression.
  • Distortion.
  • Difficult to remove undercuts.
  • Does not have an pleasant taste.
  • Can be uncomfortable in patients because of the rigidity.

Comments

  7. thank u very much…now i can easily learn the topics which i feel difficult through this website….its really helpful

  11. Overheating causes leaching of stearic acid out of impression compound, and causes irregularities over the impression.

  14. Thank you ,very useful content. I have a query! how many times maximum can impression compound be reused?

  16. Plz chemical name of impression compound????
    Chemical name of inlay wax??
    Chemical name of sticky wax??

  18. impression compound compresses the soft tissue why is it still used?
    it wont record perfect replica of the individuals oral cavity

  19. That is the reason why it is used to take just the primary impression which is in turn used to make a primary cast. For secondary or final impression, the secondary tray along with ZOE Impression material is used which does not compress the soft tissue and it records precisely. Have seen many Dentists using Putty impression material as well to take secondary impressions.

  20. ecxuse me i have question,what is makette usage in dentistry,and some information about it in dentistry

  21. excuse me i want to know what is maquette, usage in dentistry ,and advantages and disadvantages!!!

  22. It is “Maquette” which means “a sculptor’s small preliminary model or sketch” which can be used to explain to the patient. In Dentistry we have a Maquette or model of a Jaw or Caries etc which helps in explaning to the patient what their problem is and also to show how brushing should be done etc.

  23. Hello,
    I was wondering how you do make the composition. I tried to make it but the resin does not melt. is there any order i should follow when pouring it together?

    Also i did found it difficult to find stearic acid, so i was wondering if it is really needed and if i could replace it with something else.

  25. Hi I was wondering if you could send the
    information to this email
    Thanks very much,

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