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Dental materials > L10 impression materials > Flashcards

L10 impression materials Flashcards

1
Q

negative replica?

A

impression

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2
Q

possitive replica /

A

cast

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3
Q

factors needed for an accurate negative replica :

A

impression material should be fluid enough to adapt to oral tissue

it should also be viscous enough to be contained in a tray

able to transform to rubbery solid in mouth

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4
Q

elastic materials :

A

1.) hydrocolloids :

  • irreversible alginate

-reversible agar

elastomeric material :

-addition silicon
-condensation silicon
-poly ether
-poly sulfide

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5
Q

what does colloid mean

A

dispersed uniformly in another medium . hydrocolloid + that medium is water

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6
Q

reaction in which flowable state is transformed into solid elastomeric state :

A

sol-gel

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7
Q

what is sol and what is gel ?

A

sol: colloidal dispersion in continuous liquid medium

gel; suspension that behaves like elastic solid

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8
Q

sucess of an impression material is dependant on ?

A

sol-gel transformation

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9
Q

what is the most commonly used elastic impression material ?

A

alginate

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10
Q

advantages of alginate :

A

easy to manipulate
inexpensive
non-toxic
picks up fine detail
acceptable taste and odor

good working time and setting times

compatible with die and cast

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11
Q

soluable salts of alginic acids are extracted from :

A

marine plant

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12
Q

alginate is available as a ____ modified version comes in ___

A

powder

two paste

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13
Q

describe the setting reaction of alginate

A

when powder is mixed with water , sol-gel reaction takes place

in sol-gel: soluble potassium/ soddium alginate reacts with calcium ions from calcium sulfate resulting in the formation of insoluble calcium alginate —– calcium ions replace those of sodium and/ or potassium

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14
Q

reactor and retarder for alginate setting reaction :

A

reactor : sodium sulphate

retarder : sodium phosphate

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15
Q

final mix should be :

A

smooth , creamy and homogenous

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16
Q

strength:

accuracy :

dimentional stability :

dis-infection :

of alginate

A

good elastic recovery but less tear strength

acceptable accuracy but not for final impression

should be poured quickly to avoid syneresis or imbibtion. to prevent those processes alginate is also wrapped and sealed in a plastic bag

disinfection : idophores , glutaraldehyde , phenols

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17
Q

what is syneresis or imbibtion ?

A

syneresis : loss of water by evaportation

imbibtion : absorbtion of water by diffusion

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18
Q

what tray is prefered for use of alginate ?

A

perforated metal tray— tray adhasive should be applied

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19
Q

what is the minimum thickness of alginate impression ?

A

3mm

20
Q

what is the composition of agar impression :

A

agar , a polysaccharide is the main ingredient— reversible by heating and cooling

21
Q

liquefaction temp and gelation temp of agar:

A

L temp : 70-100
G temp: 37-50

22
Q

which elastic impression material is hydrophillic and can be used in conditions where moisture control is creating a problem ?

A

agar

23
Q

which elastic material is complicated in handling due to requirement of a special tray ?

A

agar

its easily removed from the mouth tho

24
Q

agar impression material is widely used in dental labs for ___

A

model duplication

25
Q

agar manipulation

A
  • 1stt step à liquefy the agar gel tube in boiling water at 100 °C
  • 2nd Step à Tube is kept in storage bath at 65 °C until it is needed
  • 3rd step à Impression tray filled with Agar is maintained at 45 °C
26
Q

which stage is agar impression taken during ?

A

sol-gel stage

27
Q

gelation of agar is accelerated by :

A

circulating cool water in tray

28
Q

labratory agar is used to duplicate casts at ___

A

conditioning temperature

29
Q

which elastic material can retard setting of gypsum /

A

alginate

30
Q

which elastic material tears easily?

A

agar

31
Q

elastomers are polymers

A

after setting (polymerization ) they can be rapidly stretched and yet rapidly revover to their original dimensions

32
Q

what are the 2 components of elastomeric impression materials ?

A

base-paste , catalyst paste

33
Q

describe the 4 types of elastomeric impression materials :

A

type 0: putty

type 1: heavy bodies \

type 2: medium bodies

type 3: light bodies

34
Q

composition of polysulfide :

A

base paste :
liquid prepolymer +
multi-functional mercaptan group + plasticizer and sulfur accelerator

catalyst paste :
lead dioxide
filler
plasticizer
stearic acid retarder

35
Q

setting reaction of polysulfide yields ___ as a by product :

A

water

36
Q

which elastomeric impression material has less accuracy due to its byproducts and could produce lead toxicity ?

A

polysulfide

37
Q

polyether composition :

A

base paste : copolyer of ethylene oxide and tetrahydrofuran

polyether prepolymer

fillers

plasticizer

catalyst paste :
initiator
aromatic sulfonate ester
fillers and plasticizer

38
Q

describe the setting of polyether

A

setting by cationic polymerization: via imine end group and catonic ring opening addition polymerization

39
Q

which elastomer impression material is used for inplant impression as it is rigid with no by products ?

A

polyethyer

40
Q

setting reaction of condensation silicate :

A

occurs via cross-linking of hydroxyl-groups of silicon and tetra ethyl silicate —> ethyl alcohol is by product formed ( considerable dimension change due to by producte )

41
Q

condensation silicon : condenastion polymerization

addition silicon : addition polymerization

A
42
Q

addition silicone composition and by product

A

base paste : poly-dimethyl siloxane , inert fillers

catalyst paste : siloxane pre-polymer , platinum as catalyst

no by products

43
Q

setting reaction of addition silicone

A

just like condensation silicone : – occurs via cross-linking of hydroxyl-groups
of silicon and tetra-ethyl silicate. but there is no ethyl alcohol by product

44
Q

which elastomeric impression material is hydrophallic ( surfactant is added to improve wetting
0

A

addition silicone

45
Q

what are the disadvantages of addition silicone ?

A

expensive
latex(sulfur) gloves inhibit the setting reaction—> vinyl gloves should be used instead

Dental materials (15 decks)

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