Hydrocolloid Impression Materials and Impression Disinfection

Question 1

What are the Requirements of Impression Material:

• Surface detail reproduction

Answer 1

• Surface detail reproduction
  
  • Viscosity
    
    • High – less detail but can displace soft tissues
      
      • Useful for denture extension but not for flabby ridges
    • Low – more detail but tray won’t contain
    • Changes with time
  • Hydrophobicity
    
    • Moist surfaces repel

Question 2

What are the Requirements of Impression Material:

• Dimensional accuracy and stability

Answer 2

• Dimensional accuracy and stability
  
  • Type of tray
    
    • Flexible tray distorts
    • Must have effective bonding adhesive
  • Flexibility and recovery
    
    • Removal from undercuts
  • Storage prior to casting
    
    • No dimensional changes

Question 3

What are all other Requirements of Impression Materials?

Answer 3

• No changes when exposed to disinfectants
• No interaction with model/die materials
• Non-toxic
• Easily manipulated
• Palatable taste
• Realistic working/setting time

Question 4

What are the 2 Impression Materials Classifications?

Answer 4

• Non elastics: impression plaster, impression compound, zinc oxide and eugenol pastes
• Elastic: hydrocolloids and synthetic elastomers

Question 5

What are the advantages and disadvantages of Agar?

Answer 5

Agar

Advantages

• Take up moisture
• Re-usable

Disadvantages

• Special equipment
• Cost
• Cross infection concerns of reuse
• Low tear strength
• Dimensionally unstable due to water content
  
  • Syneresis – loss of water from squeezed chains
  • Imbibition – uptake of water – swelling due to chain separation

Question 6

What is an alginate?

Answer 6

• Supplied as powder that mixed with water
• used as a thickner, binder or lubricant

Question 7

What is the clinical and lab use of Agar

Answer 7

Clinical use of agar

• Partial dentures, crowns and bridges

Lab use

• Duplicating material

Question 8

What is Agar?

Answer 8

Agar

An aqueous impression material used for recording maximum details; for example, as in the production of dies for fixed restorations.

Reversible hydrocolloidal impression material.

It gives good detail reproduction than any other material

Question 9

What limits availability of calcium ions?

Answer 9

Sodium phosphate

Question 10

What are Alginate Properties?

Answer 10

• Low viscosity – mucostatic
• Adequate working time – operator may control with water temperature
• Rapid set
• Elastic
• Must use no less than 3-5mm thick to prevent distortion on removal
• Susceptible to syneresis or imbibition – pour soon

Question 11

What are Alternatives to impressions ?

Answer 11

CAD CAM, intraoral scanner