Impression materials( hydrocolloid alginate,elastomeric impression materials)

Question 1

what is the function of an impression material

Answer 1

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

Question 2

is an impression a negative or positive reproduction

Answer 2

negative reproduction

Question 3

give an eg of a + reproducion

Answer 3

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

die-when a single or multiple tooth preps arerecorded-

Question 4

what are the 2 classifications of impressions

Answer 4

flexible or rigid at the time of removal

Question 5

when can a rigid material be used

Answer 5

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

Question 6

name one of the most widely used aqueous dental impression materials

Answer 6

alginate

Question 7

name 5 advantages of alginates

Answer 7

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

Question 8

what are the 2 disadvantages of alginates

Answer 8

1. low tear strength

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

Question 9

what is the time of setting in the rxn controlled by

Answer 9

the amount of sodium phosphate present in the alginate powder.

Question 10

what is the sodium phosphate called

Answer 10

a retarder because it delays the setting time

Question 11

why are these materials referred to as irreversible

Answer 11

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

Question 12

which ingredient of the alginate powder serves as a retarder

Answer 12

sodium phosphate

Question 13

which ingredient controls flexibility of impression

Answer 13

silicate powder

Question 14

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

Answer 14

when thinner mixes are used permanent deformations increases

Question 15

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

Answer 15

rapidly

Question 16

what are the best conditions to store alginate in

Answer 16

high humidity

Question 17

What happens tot the set alginate impression if stored in air

Answer 17

water will evaporate and it will shrink

Question 18

what happens to a set alginate impression is placed in water

Answer 18

it will absorb it and expand

Question 19

what is the spatulation time of an alginate

Answer 19

45 sec

Question 20

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

Answer 20

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

Question 21

define elastomeric impression materials

Answer 21

they are flexible crosslinked polymers when set

Question 22

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

Answer 22

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

Question 23

name 4 elastomeric impression materials

Answer 23

1. polysulfides
2. condensation silicones
3. polyethers
4. addition silicones

Question 24

what is also known as vinyl polysiloxanes (VPS)

Answer 24

addiition silicone impression materials

Question 25

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

Answer 25

1. polysulfides | 2. condensation silicones

Question 26

what is the catalyst in addition silicone impressions

Answer 26

chloroplatinic acid

Question 27

the addition reaction occurs between which two groups

Answer 27

vinyl and hydrogen groups

Question 28

what is the final product in addition silicone impression reactions

Answer 28

rubber silicone

Question 29

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

Answer 29

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

Question 30

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

Answer 30

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

Question 31

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

Answer 31

1. less dimensional change | 2. higher elastic recovery

Question 32

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

Answer 32

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

Question 33

what are 2 disadvantages of polyether impression materials

Answer 33

1. poor taste | 2. limited dimensional stability over time.

Question 34

how are polyether impression materials supplied

Answer 34

base and catalyst system base: polyether catalyst: sulfonic ester

Question 35

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

Answer 35

condensation silicone impression material

Question 36

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

Answer 36

ethyl alcahol

Question 37

what impression material is also known as rubber bas

Answer 37

polysulfide impression materials

Question 38

how are polysulfide impression materials supplied

Answer 38

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

Question 39

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

Answer 39

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

Question 40

what type of polysulfide is used for denture impressions

Answer 40

low-viscosity polysulfides

Question 41

what are dentures

Answer 41

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

Question 42

what doe the base-catalyst systems in polysulfides contain respectively

Answer 42

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

Question 43

what is the catalyst of polysulfides carries in

Answer 43

an inert oil ( dibutyl )

Question 44

what is the most common catalyst used in polysulfides

Answer 44

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

Question 45

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

Answer 45

blue-green