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Dental materials 2 > Impression materials( hydrocolloid alginate,elastomeric impression materials) > Flashcards

Impression materials( hydrocolloid alginate,elastomeric impression materials) Flashcards

1
Q

what is the function of an impression material

A

to accurately record the dimensions of oral tissues and their special relationships

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2
Q

is an impression a negative or positive reproduction

A

negative reproduction

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3
Q

give an eg of a + reproducion

A

model/cast-if large areas of the teeth are involved)

die-when a single or multiple tooth preps arerecorded-

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4
Q

what are the 2 classifications of impressions

A

flexible or rigid at the time of removal

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5
Q

when can a rigid material be used

A

it is limited to tooth prepared for a full crown or an edentulous arch

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6
Q

name one of the most widely used aqueous dental impression materials

A

alginate

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7
Q

name 5 advantages of alginates

A
  1. ease of mixing and manipulation
  2. low cost
  3. flexibilityof set impression
  4. high accuracy
  5. min needed equipment
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8
Q

what are the 2 disadvantages of alginates

A
  1. low tear strength

2. they do not transfer much detail to gypsum dies like agar or elastomeric impressions do.

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9
Q

what is the time of setting in the rxn controlled by

A

the amount of sodium phosphate present in the alginate powder.

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10
Q

what is the sodium phosphate called

A

a retarder because it delays the setting time

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11
Q

why are these materials referred to as irreversible

A

because once the paste sets into a gel, the process cannot be reversed.

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12
Q

which ingredient of the alginate powder serves as a retarder

A

sodium phosphate

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13
Q

which ingredient controls flexibility of impression

A

silicate powder

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14
Q

what is the relationship between the percentage of permanent deformation and consistency of mix

A

when thinner mixes are used permanent deformations increases

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15
Q

alginate impressions are less likely to tear during removal from the mouth when removed slowly or rapidly

A

rapidly

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16
Q

what are the best conditions to store alginate in

A

high humidity

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17
Q

What happens tot the set alginate impression if stored in air

A

water will evaporate and it will shrink

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18
Q

what happens to a set alginate impression is placed in water

A

it will absorb it and expand

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19
Q

what is the spatulation time of an alginate

A

45 sec

20
Q

how can we avoid the patient to gag while taking a max impression

A

the posterior of the tray must be seated first followed by the anterior which avoids a large portion of the alginate to flow into the palatal area

21
Q

define elastomeric impression materials

A

they are flexible crosslinked polymers when set

22
Q

what is the main reason for the domination of elastomeric impression materials in the market

A

1.their greater accuracy
2.dimensional stability with time
3.and ability to record detail
as compared with the hydrocolloid materials

23
Q

name 4 elastomeric impression materials

A
  1. polysulfides
  2. condensation silicones
  3. polyethers
  4. addition silicones
24
Q

what is also known as vinyl polysiloxanes (VPS)

A

addiition silicone impression materials

25
Q

addition silicone impression materials were developed as an alternative to which two materials

A
  1. polysulfides

2. condensation silicones

26
Q

what is the catalyst in addition silicone impressions

A

chloroplatinic acid

27
Q

the addition reaction occurs between which two groups

A

vinyl and hydrogen groups

28
Q

what is the final product in addition silicone impression reactions

A

rubber silicone

29
Q

why is addition silicone impressions not subjected to dimensional changes with time

A

because no volatile byproducts (water or ethanol) is formedin this reaction

30
Q

what product is added to the product to permit the immediate pouring of gypsum/epoxy dies

A

a hydrogen absorber, palladium, because when H is released gradually from the set impression it produces bubbles in gypsum dies.

31
Q

what are 2 noteworthy improvements of the additin silicones over condensation silicones

A
  1. less dimensional change

2. higher elastic recovery

32
Q

why should latex rubber gloves not be worn during the manipulation of addition silicone impressions

A

because components in the latex rubber will retard or prevent the setting by poisoning the platinum catalyst

33
Q

what are 2 disadvantages of polyether impression materials

A
  1. poor taste

2. limited dimensional stability over time.

34
Q

how are polyether impression materials supplied

A

base and catalyst system

base: polyether
catalyst: sulfonic ester

35
Q

which impression material is not commonly used in the dental office but rather as an accurate duplicating material in the dental labratory

A

condensation silicone impression material

36
Q

what byproduct is produced that contributes to the rather high shrinkage durng the first 24 hours after settin of condensation silicone impressions

A

ethyl alcahol

37
Q

what impression material is also known as rubber bas

A

polysulfide impression materials

38
Q

how are polysulfide impression materials supplied

A

as two pastes, 2 2 tubes each conatining a base and an accelerator respectively

39
Q

how many types are available for polysulfides and how are they classified

A

3, according to viscosity, low, medium and hiigh viscosity

40
Q

what type of polysulfide is used for denture impressions

A

low-viscosity polysulfides

41
Q

what are dentures

A

are prosthetic devices constructed to replace missing teeth, and are supported by the surrounding soft and hard tissues of the oral cavity.

42
Q

what doe the base-catalyst systems in polysulfides contain respectively

A

BASE: 80 % low-molecular weight organic molecule whith reactive mercaptan ( -SH ) groups
20% reinforcing agents such as silica
CATALYST : contains compounds which causes the mercaptan groups tp react to from polysulfide elastomer

43
Q

what is the catalyst of polysulfides carries in

A

an inert oil ( dibutyl )

44
Q

what is the most common catalyst used in polysulfides

A

lead dioxide which causes the paste to be dark brown or grey

45
Q

when copper hydoxide catalyst is mixed with the white base paste of polysulfides what is the resulting color

A

blue-green

Dental materials 2 (3 decks)

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