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Dental Material Science > Impression Materials > Flashcards

Flashcards in Impression Materials Deck (24)
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1
Q

what are impression materials used for

A

produce a replica of the patients hard and soft tissues, this is a negative impression, poured into with gypsum to produce a positive replica - used for designing dentures and orthodontic appliances

2
Q

what does the treatment using a cast hinge on

A

accuracy - of impression material, quality of impression - by operator

3
Q

how can impression materials be classified

A

clinically - mucostatic or mucocompressive

properties - elastic or not

4
Q

what are the ideal properties of an impression material

A

viscoelastic, low thermal expansion, storage

5
Q

why is viscoelasticity important

A

can flow around undercuts etc, into all areas, but must also be able to be removed and then once removed bounce back to the shape it was in the mouth once set

6
Q

describe the ideal viscoelasticity

A

when a load is applied, it is applied immediately, as the load remains, the strain is continuous, once the load is removed, the material goes back to the dimensions it was at the start with and the strain is removed

7
Q

what actually happens with the viscoelasticity

A

the load is applied over time, meaning the strain gradually increases, the longer the load is applied, the worse the strain, as the load is removed, the strain doesnt go back perfectly, some permanent deformity

8
Q

how can the permanent deformity be reduced when taking an impression

A

if the load is applied quickly, less strain is induced. also the less time the load is held for the less permanent deformity seen. have to do it quickly and take it off quickly

9
Q

what properties affect accuracy

A

elasticity, viscosity, thermal expansion, tear strength

10
Q

what is tear strength and what should it be

A

the strength it can withstand without distortion, want this to be high so it can be removed from undercuts without tearing the material

11
Q

what is alginate

A

a hydrocolloid

12
Q

what is the setting reaction of alginate

A

calcium sulphate with sodium alginate - forms calcium alginate as calcium induces cross linking in the alginate

13
Q

what particles are involved in the setting of alginate

A

calcium sulphate, sodium alginate, tri-sodium phosphate

14
Q

what is the role of tri sodium phosphate

A

calcium preferrentially bonds to this over sodium alginate, prevents calcium cross linking immediately so the operator can place the material before set

15
Q

what are the properties of alginate

A

good viscosity, elasticity is okay, poor tear strength - shouldnt be used in areas with large under cuts

16
Q

why should alginate be stored with damp gauze

A

prevents it taking on moisture or releasing moisture and drying out
taking on moisture - syneresis, releasing - imbibition

17
Q

give examples of elastomers

A

addition silicones, polyether

18
Q

what are some properties of elastomers

A

good flexability not rigid, low viscosity, surface reproduction and wetability, high tear strength, good elasticity

19
Q

what are ISO standards

A

the standards required to be met for a safe material, doesnt compare the best on the market just safe enough to be used

20
Q

give an example of an ISO standard

A

surface reproduction of an elastomer, has to be able to flow into small areas, gap size is dependant on the viscosity of the material - low viscosity - 20um, high viscosity - 50um

21
Q

what are the 3 different requirements for ideal properties of an elastomer

A

able to flow over the surface and into gap
obtain accurate detail
removal from undercuts

22
Q

what properties are important for the material to flow over hard and soft tissues

A

viscosity - cant be too thick that it doesnt flow into small gaps, wetability - have intimate contact with surface

23
Q

what properties are important for the material to obtain accurate detail

A

elasticity - want it to be a low number - high suggests large strain for a fixed load and thus permanent deformation, surface reproduction - dependant on viscosity

24
Q

what properties are important for the material to be removed from undercuts

A

flexability - want a low YM, not rigid

tear strength - want this to be high, not fractured with high stress on removal