Impression Materials Flashcards
Why are physical impressions still important in modern days where digital impressions are possible?
Digital impressions are available but not always the best choice. Physical impressions can also be transformed into a digital impression quite easily
What are the types of crowns commonly used?
Ceramic, metal or PFM. In some applications it can be made of composite material (Indirect composite restorations not used at OHCWA but used elsewhere)
What are the key properties of impression materials?
Flow (ability to replicate intraoral surface details
Dimensional stability (Ability to retain its absolute dimensional size over time)
Tear resistance (Ability to resist tearing in thin sections (eg through feather edged material withing the gingival sulcus)
What are viscoelastic materials and how do they relate to impression materials?
Viscoelastic materials are materials that recovers following deformation (like a matress) Impression will open and recover following deformation (this is after it sets with the tooth structure on it)
Viscoelastic materials are very tear resistant to prevent this try to remove the impression material as quickly as possible when taking an impression.
What is the recovery of alginate and is this enough?
97% to 98% recovery however, this means that it is not a good material because it is too low.
What does low dimensional change tell us about the material?
Low dimensional change means that the material is storage friendly and will be effective for use.
What is the fold standard for impression materials?
No impression material fulfils all requirements so there is none.
What are non-elastic materials used for?
Non-elastic materials should only be used for complete dentures (even then not necessarily recommended) used for indirect coronal restorations.
What are the types of elastic impression materials to use for dentures?
Alginate
Agar/alginate
Agar
Can be used for replicating a small partial denture. DO NOT USE FOR INDIRECT CORONAL RESTORATIONS
What are the recommended impression materials for indirect coronal restorations?
Polysulfide (not recommended)
Silicone based impression material (If set by condensation or polymerisation it is slightly different)
Polyether is used in clinic at OHCWA and sets by addition reaction and is less elastic than addition silicone.
What is the difference between condensation and addition setting seen in silicone impressions?
Condensation silicone means that the monomers joine to form alcohol which evaporates and shrinks as a result
Addition polymerisation is better because it doesn’t lead to shrinkage because of no byproduct. This is used in the clinic
What are the differences between the low, medium, and high flow impression polyether materials?
Filler changes the viscosity between the low medium, and high flow polyether impression materials.
What is a colloidal system?
A colloidal system is between solution and suspension.
Have small size and suspended in the system. Mix alginate and water to form sol state
What is unset alginate called?
Sol
Why is alginate chosen over agar impression material?
Agar sets by reduction in temperature although it is more accurate.
Alginate is cheap and easy to use and is set by chemical reaction
