lecture 5

Question 1

desirable properties of impressions

Answer 1

Ease of manipulation

Reasonable cost

Adequate flow and wetting properties

Appropriate setting time and characteristics

Sufficient mechanical strength - elastic recovery and resistance to tearing during removal

Good dimensional accuracy – stable over time

Taste and odor acceptable to patient

Safe - not toxic or irritating

No significant degradation of properties as a result of disinfection

Compatibility with all die and cast materials

Good shelf life

Question 2

classificiation of impression materials

Answer 2

rigid–ZOE, for places will no undercuts

flexible–undercuts, loose teeth, removed over a bulge of a tooth without fracturing

• -aqueous (alginate hydrocolloid)
• -elastomeric –addition silicone

Question 3

advantages of flexible aq alginate hydrocolloid imp materials

Answer 3

Ease of mixing and minimum equipment necessary
Flexibility of set impression
Accuracy
Low Cost

disadv Low tear strength

Question 4

understand that some strain can be time-dependent (like with elastomeric impression materials)–>means the longer something is being deformed, the more plastic deformation it will retain even when the load is removed–>this is why we need to quickly snap impression materials out of the mouth

Answer 4

ye