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GDAN yr 2 - AGEING > impression materials 2 > Flashcards

impression materials 2 Flashcards

1
Q

what are flexible materials

A

hydrocolloids

elastomers

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2
Q

hydrocolloids

A

heterogeneous mixture of 2 phases where the 2 phases are not readily differentiated

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3
Q

solution

A

homogenous mixture of single phase

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4
Q

suspension

A

mixture of two phases

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5
Q

hydrocolloids can be ..

A

irreversible or reversivke

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6
Q

example of reversible hydrocolloid

A

agar

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7
Q

agar composition and hydrocolloid properties

A 
natural state gel
heating becomes sol
1)	Agar (colloid)
2)	Borax (strengthen gel)
3)	Potassium sulphate
4)	Water (dispersion medium)
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8
Q

properties of agar

A

1) Good surface detail
2) can be used on undercuts but liable to tear on deep undercuts
3) non toxic and non irritant
4) slow setting time
5) poor tear resistance
6) adequate shelf life
7) ca be sterilised by an aqueous solution of hypochlorite

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9
Q

advantages/dis of agar

A

1) good surface edtail
2) reusable
3) easily sterilised
Disadvantages
1) Need special equipment
2) Dimensional instability

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10
Q

alginate type of hydrocolloid an compostion

A 
irreversible
- sodium alginate (hydrogel former)
calcium sulphate dihydrate (provide calcium ions)
sodium phosphate (control working time)
potassium sulphate (enhance setting)
fillers (consistency )
sodium silicofluoride (control ph)
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11
Q

how is solid alginate formed

A

polymer chains forma and link

- interchange of calcium and sodium

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12
Q

properties of alginate

A

1) dust free powder
2) cheap
3) limited shelf life
4) well controlled working and setting time
5) mucostatic
6) hydrophilic
7) poor surface reproduction
8) poor storage stability
- imbibition (water sorption)
- syneresis (water loss)
9) low tear strength
10) excessive permanent deformation

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13
Q

imbibition

A

shape change as water is absorbeed by solid hydrocolloids causing an increase in volume

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14
Q

syneresis

A

shape changes as loss of a liquid from a gel causing a reduction in volume

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15
Q

elastomer impression materials

A

1) Polysulphides
2) Poly ethers
3) Silicones
- condensation cured
- addition curred

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16
Q

polysulphide composition

A 
Base paste
-	polysulphide
-	filler (TiO2)
Activator pate
-	sulphur
-	lead dioxide
-	plasticiser (dibutyl phthalate)
17
Q

how do polysulpides change state

A

liquid to solid
sulphur groups join the tw chains
condensation polumerisation

18
Q

applications of polysulphides

A

1) Crown
2) Bridge work
3) partial denture
4) over dentures
5) implants

19
Q

polyether impression material

A 
Base paste
-	polyether
-	filler (colloidal silica)
Activator paste
-	filler
-	plasticiser (dibutyl phthalate)
-	aromatic sulphonate ester
20
Q

how is polyether set

A

cross linking with amine group ends

addition polymerisation

21
Q

addition polymerisation sets

A

activation
initiaiton
propagation
termination

22
Q

applications for polyether

A

1) crowns
2) bridge work
3) partial dentures
4) implants
5) over dentures

23
Q

silicon impression composition for condensation cured

A 
Base paste 
-	silicone polymer
-	filler (colloidal silica)
-	organo tin compound
activator paste
-	silicone polymer
-	filler (colodial silica)
-	tetra-ethyl silicate)
Hydroxyl groups 
tin is the catalyst
-	condensation reaction with release of a a molecule eg ethanol (depends on what is joining)
24
Q

silicon impression composition for addition cured

A 
Base paste 
-	silicone polymer
-	filler (colloidal silica)
-	silanol
activator paste
-	silicone polymer
-	filler (colodial silica)
-	Pt catalyst

Reaction is driven by a radical by addition polymerisation
no by products

25
Q

applicaitonsfor silicone

A

1) crown
2) bridge work
3) partial dentures
4) implants
5) over dentures

26
Q

Elastomertic impression materials merits

A

handling
- polysulhpides and condensation cured silicone difficult to mix
Working/setting times
- polysulphides long tie
condensation cured erratic setting due to moisture contamination
polyethers good setting times
addition cured silicones can be inhibited by latex gloves

27
Q

mechanical properties and order

A

stiffness
- PSPE>CCS>ACS
tear strength
PS»PE>CS=AS

28
Q

surface detail of elastomers

A

polyethers best

all have good reproduction of surface detail

29
Q

failures of impressions

A

rough or uneven surface
air bubbles
irregualr shaped voids

30
Q

what can cause air bbbles

A

rapid set
improper miing
surface contamination e.g. moisture

31
Q

poor fit of impressions

A

distortion

casting too big/too small

32
Q

intraoral scanners ad and dis

A 
Ad:
-	patient comfort
-	dentist auto evaluation
-	reduced model time
-	favours clinical lab communication
Dis
-	cost investment 
-	training
-	just surface registration
-	coating (as that laser might not get insuffiencent detail)

GDAN yr 2 - AGEING (6 decks)

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