L10 impression materials

Question 1

negative replica?

Answer 1

impression

Question 2

possitive replica /

Answer 2

cast

Question 3

factors needed for an accurate negative replica :

Answer 3

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

Question 4

elastic materials :

Answer 4

1.) hydrocolloids :

• irreversible alginate

-reversible agar

elastomeric material :

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

Question 5

what does colloid mean

Answer 5

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

Question 6

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

Answer 6

sol-gel

Question 7

what is sol and what is gel ?

Answer 7

sol: colloidal dispersion in continuous liquid medium

gel; suspension that behaves like elastic solid

Question 8

sucess of an impression material is dependant on ?

Answer 8

sol-gel transformation

Question 9

what is the most commonly used elastic impression material ?

Answer 9

alginate

Question 10

advantages of alginate :

Answer 10

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

Question 11

soluable salts of alginic acids are extracted from :

Answer 11

marine plant

Question 12

alginate is available as a ____ modified version comes in ___

Answer 12

powder

two paste

Question 13

describe the setting reaction of alginate

Answer 13

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

Question 14

reactor and retarder for alginate setting reaction :

Answer 14

reactor : sodium sulphate

retarder : sodium phosphate

Question 15

final mix should be :

Answer 15

smooth , creamy and homogenous

Question 16

strength:

accuracy :

dimentional stability :

dis-infection :

of alginate

Answer 16

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

Question 17

what is syneresis or imbibtion ?

Answer 17

syneresis : loss of water by evaportation

imbibtion : absorbtion of water by diffusion

Question 18

what tray is prefered for use of alginate ?

Answer 18

perforated metal tray— tray adhasive should be applied

Question 19

what is the minimum thickness of alginate impression ?

Answer 19

3mm

Question 20

what is the composition of agar impression :

Answer 20

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

Question 21

liquefaction temp and gelation temp of agar:

Answer 21

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

Question 22

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

Answer 22

agar

Question 23

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

Answer 23

agar

its easily removed from the mouth tho

Question 24

agar impression material is widely used in dental labs for ___

Answer 24

model duplication

Question 25

agar manipulation

Answer 25

* 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

Question 26

which stage is agar impression taken during ?

Answer 26

sol-gel stage

Question 27

gelation of agar is accelerated by :

Answer 27

circulating cool water in tray

Question 28

labratory agar is used to duplicate casts at ___

Answer 28

conditioning temperature

Question 29

which elastic material can retard setting of gypsum /

Answer 29

alginate

Question 30

which elastic material tears easily?

Answer 30

agar

Question 31

elastomers are polymers

Answer 31

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

Question 32

what are the 2 components of elastomeric impression materials ?

Answer 32

base-paste , catalyst paste

Question 33

describe the 4 types of elastomeric impression materials :

Answer 33

type 0: putty type 1: heavy bodies \ type 2: medium bodies type 3: light bodies

Question 34

composition of polysulfide :

Answer 34

base paste : liquid prepolymer + multi-functional mercaptan group + plasticizer and sulfur accelerator catalyst paste : lead dioxide filler plasticizer stearic acid retarder

Question 35

setting reaction of polysulfide yields ___ as a by product :

Answer 35

water

Question 36

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

Answer 36

polysulfide

Question 37

polyether composition :

Answer 37

base paste : copolyer of ethylene oxide and tetrahydrofuran polyether prepolymer fillers plasticizer catalyst paste : initiator aromatic sulfonate ester fillers and plasticizer

Question 38

describe the setting of polyether

Answer 38

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

Question 39

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

Answer 39

polyethyer

Question 40

setting reaction of condensation silicate :

Answer 40

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 )

Question 41

condensation silicon : condenastion polymerization addition silicon : addition polymerization

Question 42

addition silicone composition and by product

Answer 42

base paste : poly-dimethyl siloxane , inert fillers catalyst paste : siloxane pre-polymer , platinum as catalyst no by products

Question 43

setting reaction of addition silicone

Answer 43

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

Question 44

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

Answer 44

addition silicone

Question 45

what are the disadvantages of addition silicone ?

Answer 45

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