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2 Dental Materials > Hydrocolloid impression materials and impression disinfection > Flashcards

Hydrocolloid impression materials and impression disinfection Flashcards

1
Q

what are the 2 types of impression tray?

A

stock trays
special trays

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2
Q

what are stock trays?

A

made to fit the average patients mouth

perforated

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3
Q

what are special trays

A

unique in dimension to the patient

not perforated

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4
Q

what are the 2 classifications of impression material?

A

non elastic

elastic

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5
Q

what are the 2 types of elastic impression materials?

A

hydrocolloids
synthetic elastomers

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6
Q

what are the 2 types of hydrocolloids with examples?

A

reversible - agar
irreversible - alginate

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7
Q

3 examples of synthetic elastomers

A

polysulphides
silicone rubbers
polyethers

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8
Q

how are silicone rubbers set? 2

A

condensation curing
addition curing

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9
Q

what are hydrocolloids?

A

colloidal suspensions of polysaccharides in water

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10
Q

what is agar derived from?

A

seaweed

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11
Q

steps to use agar 3

A

supplied in gel
water bath conditioning
placed in water cooled trays

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12
Q

advantages of agar 2

A

takes up moisture - accurate impressions
can be re-used in a lab setting

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13
Q

disadvantages agar 4

A

special equipment
cost
low tear strength
dimensionally unstable due to water content

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14
Q

what is syneresis in agar?

A

loss of water from squeezed chains

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15
Q

what is imbibition in agar?

A

uptake of water - swelling due to chain separation

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16
Q

clinical use of agar 3

A

partial dentures, crowns and bridges

17
Q

lab use of agar

A

duplicating material for pre-existing models

18
Q

how are alginates supplied and used?

A

supplied as powder
mixed with water

19
Q

composition of alginate 4

A

Na or K salt of alginic acid
calcium sulphate dihydrate
sodium phosphate
inert filler

20
Q

what is the function of Na or K salt of alginic acid in alginate?

A

forms a sol with water and in set becomes a cross-linked gel

21
Q

what is the function of calcium sulphate dihydrate in alginate?

A

source of calcium to cross link the chains of alginic acid

22
Q

what is the function of sodium phosphate in alginate?

A

retardant
controls the working time by limiting the availability of calcium ions

23
Q

what is the function of inert filler in alginate?

A

provide body for manipulation

24
Q

what is in some alginates to signify set?

A

reaction indicator

25
Q

what are modified alginates

A

alginates incorporated with silicone polymers

26
Q

advantages of modified alginates 2

A

better detail reproduction and tear resistance

27
Q

disadvantage of modified alginates

A

poor dimensional stability

28
Q

how does DDH disinfect impressions?

A

ACTICHLOR

29
Q

name an alternative to impressions

A

CAD CAM - intra-oral scanners

2 Dental Materials (4 decks)

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