Applied Dental Material Second Year

1. Elastomers
comparison
Origin.
Supplied
form.
Shelf life.
Setting
reaction.
Thickness of
the
impression
Hydrocolloid
Agar
Alginate
Gel
Natural polymer.
Powder
Good.
Limited.
It is sensitive to
moisture&
temperature.
Chemical gelation
reaction.
Physical
gelation
reaction.
Thick section [4-6mm] to
avoid tearing
Flow.
Nature.
High flow
Since the dispersion medium is
water, they are hydrophilic.
Dimensional
accuracy
during
setting.
Slight contraction due to
agglomeration of the dispersed
phase.
Adhesion to
the tray.
Non-adhesive to the tray.
.·.They need mechanical
retention [perforation].
Highly
The most flexible
flexible.
among the elastic
impression
materials.
Flexibility.
Tear resist.
Polysulphide
Low tear resistance.
Good.
Elastomers
Condensation
Addition Silicone
Silicone
Synthetic polymer.
2pastes in different viscosities
Light, regular, heavy, putty.
Limited due to
Good.
oxidation of the
catalyst.
Condensation
Condensation
polymerization. polymerization.
Addition
polymeriztion
Polyether
Good.
Ring opening
polymerization.
Thin section [2-3mm] to reduce the polymerization &
thermal shrinkage.
Thick section to avoid tearing due to their
limited flexibility in hydrophylized addition
silicone & polyether.
High flow according to consistency
Hydrophobic.
Extremely
Hydrophilic due to
hydrophobic.
presence of ethylene oxide
.˙. Surfactant is
unit.
added.
Polymerization shrinkage due to decreased interatomic between monomer units.
Highest
Lowest
polymerization
polymerization
shrinkage.
shrinkage.
Non-adhesive to the tray.
.·. An adhesive is applied to the tray.
The most
flexible among
the elastomers
Flexible.
But the hydrophylized addition silicone &
polyether are of limited flexibility
High tear resistance

2. Elastic
recovery.
Disinfection
98.8%
97.3%
.·.The lowest
Since they are hydrophilic,
they can be disinfected by
spraying.
Dimensional
stability
during
storage.
Since the dispersion medium is
water, they suffer from
synersis & imbibition.
.˙. Immediate pouring is
required after the gradual
recovery.
Compatibilit
y to model
& die
Since they are hydrocolloids,
materials.
they retard the setting of
gypsum model.
They should contain an
accelerator for the setting of
gypsum to obtain a model with
adequate hard surface after
separation.
Since they are hydrophilic,
they can not be electroplated.
97.9%
99.5%
99.8%
98.5%
.·. The highest
Since they are hydrophobic, they can be disinfected by
immersion.
Since hydrophylized addition silicone &
polyether are hydrophilic, they can be
disinfected by spraying.
They suffer from polymerization shrinkage [continuous for 24 hours]
& thermal shrinkage from oral to room temperature.
.˙.Immediate pouring is required Lowest values
Since it is hydrophilic in
after the gradual recovery.
.˙.The most
nature, it suffers from
dimensional stable
imbibition.
in elastic
.˙. Better to pour it
impression
immediately after gradual
material.
recovery.
Compatible.
.˙. No need for separating medium.
Since they are hydrophobic,
There are 2
Since it is hydrophilic, it is
porous models are frequently
problems:
easily wetted by the
obtained.
* Extreme
gypsum.
Care should be given during
hydrophobic
pouring.
.˙. Surfactants are
added.
*Hydrogen gas
evolution.
.˙. Wait 1 hour
before pouring.
Or Gas absorber is
added.
Since they are hydrophobic, they can be electroplated
Since hydrophylized addition silicone &
polyether are hydrophilic, they can not be
electroplated.