impression compound Flashcards
classification of impression materials
1 on the basis of elasticity
1.1mode of setting
1.1 a irrevestible set by a chemical reaction
1.1b thermoplastic set by temp reversible
1.2 rigid
1.2a zinc oxide eugenol paste
1.3 b impression compund mad waxes
1.3 elastic
1.3 a alginate hydrocolloid
agar hydrocolloid
2 on the basis of tissue displacment during impression procedure
2.1 mucostatic dont allow diplacement eg impression plaster, low viscosity alginate
2.2 mucosompressive allow tiisue displacement eg impression compund high viscosity alginate
3 on the basis of use in dentistry
3,1 edentulous complete denture patient
not removed from undercuts without fracture eg zinc oxide eugenol impression compund impressio plaster
3.2 for dentulous mouth alginate
4 on the basis of tray used
cooled tray agar
perforated alginate
custom tray impression compund
alginate
irreversible hydrocolloid
sets by a chemical reactiom suppied as powder
setting reaction
sodium alignate + caso4 calcium sulphate = calcium alginate + na2 so4
crystalline structure of final gel basically will include a network of calcium alginate enclosing ureacted sodium alginate
manipuation
powser if fliffed by iverting the cane
prper water powder ratio isnmaintained
the measured powder is sprinkled on measured water in bowl
when all the pwder catches moisture rapid spatulation is initiated
a vigrous figure of 8 is maintained
advantages of alginate
easy to mix and manipulate
low cost
gives good details also in the presence of saliva
comfortable for patient
disadvantages
cannot be electroplated
cannot be corrected
cannont be stored for a long time due to synergesis and imbibition
zinc oxide eugenol - rigid impression material
components and uses
zinc main reactant for the catylyst
vegetable or mineral oil : acts as a plastisizer and reduce irritant activity of eugenol
clove il : 70- 85 percent eugenol reduce irritant effect of eugenol
polymerized rosin : speeds up the reaction
siica filler for proper comsistency
accelerators glacial acertic acid
setting reaction prper acid base rection resulting in chelation
zn(oh) 2 + 2he= znE2 +2h2
zinc oxide eugenol particles surrounding zinc hydroxide
manipulation
mixing tme 1 min
two lines of equal qidth and lenth are squeeezed from the tube to ensure proper proportioning
mixing os done with a flxible stainless steel spatula
uses
temporary filing material
root cant filling matrial
surgical packs during periodontal surgery
edentulous impression material according to ada flow of zno should be for type 1 : 30-50 mm
for type 2: 25-45mm
advatages
provides sufficient working time for bottom molding
can be repeatedly checked in mouth without deforming
minor defect can be corrected locally without discarding th whole impression
dimensionally stable
disadvantages
requires specific tray
sticks to oral tissue
classification of rubber base impression materials
on the basis of chemistry
polysulfide
condensation silicone
additon silicone
polyether
according to ada
type 1
type 2
type 3
based on viscosity
type 0 putty consutency
type 1 tray consistency
type 2 medium bodied
type 3 ligh bodies syringe consistency
wettablituly
hydrophillic
hydrophobic
polysulfide
mercaptan or thiocokol v
setting reaction base, and accelrator mixed reaction occurs between the polymer and the mercaptan
messy to work with odour,
sticky
very good surface details.
can be electroplated, high tear strength 4000g/cm
good shelf life
hig permananet deformation.
putty consistence.
