L10 impression materials Flashcards
negative replica?
impression
possitive replica /
cast
factors needed for an accurate negative replica :
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
elastic materials :
1.) hydrocolloids :
- irreversible alginate
-reversible agar
elastomeric material :
-addition silicon
-condensation silicon
-poly ether
-poly sulfide
what does colloid mean
dispersed uniformly in another medium . hydrocolloid + that medium is water
reaction in which flowable state is transformed into solid elastomeric state :
sol-gel
what is sol and what is gel ?
sol: colloidal dispersion in continuous liquid medium
gel; suspension that behaves like elastic solid
sucess of an impression material is dependant on ?
sol-gel transformation
what is the most commonly used elastic impression material ?
alginate
advantages of alginate :
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
soluable salts of alginic acids are extracted from :
marine plant
alginate is available as a ____ modified version comes in ___
powder
two paste
describe the setting reaction of alginate
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
reactor and retarder for alginate setting reaction :
reactor : sodium sulphate
retarder : sodium phosphate
final mix should be :
smooth , creamy and homogenous
strength:
accuracy :
dimentional stability :
dis-infection :
of alginate
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
what is syneresis or imbibtion ?
syneresis : loss of water by evaportation
imbibtion : absorbtion of water by diffusion
what tray is prefered for use of alginate ?
perforated metal tray— tray adhasive should be applied
what is the minimum thickness of alginate impression ?
3mm
what is the composition of agar impression :
agar , a polysaccharide is the main ingredient— reversible by heating and cooling
liquefaction temp and gelation temp of agar:
L temp : 70-100
G temp: 37-50
which elastic impression material is hydrophillic and can be used in conditions where moisture control is creating a problem ?
agar
which elastic material is complicated in handling due to requirement of a special tray ?
agar
its easily removed from the mouth tho
agar impression material is widely used in dental labs for ___
model duplication
agar manipulation
- 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
which stage is agar impression taken during ?
sol-gel stage
gelation of agar is accelerated by :
circulating cool water in tray
labratory agar is used to duplicate casts at ___
conditioning temperature
which elastic material can retard setting of gypsum /
alginate
which elastic material tears easily?
agar
elastomers are polymers
after setting (polymerization ) they can be rapidly stretched and yet rapidly revover to their original dimensions
what are the 2 components of elastomeric impression materials ?
base-paste , catalyst paste
describe the 4 types of elastomeric impression materials :
type 0: putty
type 1: heavy bodies \
type 2: medium bodies
type 3: light bodies
composition of polysulfide :
base paste :
liquid prepolymer +
multi-functional mercaptan group + plasticizer and sulfur accelerator
catalyst paste :
lead dioxide
filler
plasticizer
stearic acid retarder
setting reaction of polysulfide yields ___ as a by product :
water
which elastomeric impression material has less accuracy due to its byproducts and could produce lead toxicity ?
polysulfide
polyether composition :
base paste : copolyer of ethylene oxide and tetrahydrofuran
polyether prepolymer
fillers
plasticizer
catalyst paste :
initiator
aromatic sulfonate ester
fillers and plasticizer
describe the setting of polyether
setting by cationic polymerization: via imine end group and catonic ring opening addition polymerization
which elastomer impression material is used for inplant impression as it is rigid with no by products ?
polyethyer
setting reaction of condensation silicate :
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 )
condensation silicon : condenastion polymerization
addition silicon : addition polymerization
addition silicone composition and by product
base paste : poly-dimethyl siloxane , inert fillers
catalyst paste : siloxane pre-polymer , platinum as catalyst
no by products
setting reaction of addition silicone
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
which elastomeric impression material is hydrophallic ( surfactant is added to improve wetting
0
addition silicone
what are the disadvantages of addition silicone ?
expensive
latex(sulfur) gloves inhibit the setting reaction—> vinyl gloves should be used instead
