L90: What two factors are there to consider when choosing an impression material?
- Material characteristics;
- Clinical performance (patient acceptance and ease of use).
L90: What properties contribute to patient acceptance?
- Time to set;
- Taste
L90: What material characteristics should be considered?
- Viscosity (ability to flow over tissues);
- Surface wetting;
- Level of accuracy;
- Level of elasticity (to capture undercuts);
- Elastic recovery;
- Tear strength;
- Dimensional stability.
L90: In an ideal elastomeric impression material, how viscoelastic do you want the material to be and why?
- Low viscoelasticity;
- Better elastic recovery;
- Small deformation (permanent strain).
L90: What is wettability?
Contact to tooth tissues
L90: What is tear strength?
A measure of how well a material can withstand tearing under an applied force
L90: What is rigidity?
Stress/ strain ratio, i.e. the amount of stress required to cause a material to change shape
L90: To meet current ISO standards, what level of detail must impression materials be able to distinguish between?
20 or 50 um, depending on material viscosity
L90: How can permanent strain be minimised when removing an impression from the oral cavity?
Sharp pull - reduced load time - less overall permanent strain
L90: How do working and setting times vary between polyethers and addition silicones?
Polyethers offer a slightly quicker setting time (1 minute quicker), but there is only a 2 minute working time as opposed to 4 with addition silicones
L90: What type of material are elastomeric impression materials?
Elastomers
L90: What are the two major types of elastomeric impression materials used?
- Polyethers;
- Addition silicones.
