3. Impression and Cast
Impression: -ve replica of the oral hard and soft
tissues
Cast: +ve replica of the oral hard and soft tissues
Die: Metal cast or any cast for single tooth
4. Impression Trays
Container used to carry the impression
material into or out from the patient’s mouth
Stock trays Special trays
6. Ideal requirements of
Impression materials
Biologically
Non- toxic and non-irritant
Interfacially
Compatible with different model and die materials
Chemically
1. Have long shelf life
2. Dimensionally stable in storage Stable in storage
7. Ideal requirements of
Impression materials
Mechanically
1. When set they should behave elastically
2. Have sufficient mechanical properties ie. tear
strength to resist tearing during impression removal
from the undercuts
3. Have sufficient flow under pressure that helps in
recording the fine details of the oral structure
Practicability
1. Inexpensive
2. Easy manipulated
3. Have reasonable working and setting times
8. Classification of Impression
Materials
I. According to the mechanical
behavior
A. Elastic materials
Used for both edentulous and dentate patients having
undercuts
1. Hydrocolloids
Reversible hydrocolloid (Agar)
Irreversible hydrocolloid (Alginate)
2. Elastomeric Materials
Polysulfide
Silicones (Condensation-polymerizing & addition-
polymerizing)
Polyether
3. Gutta Percha
9. I. According to the mechanical
behavior
B. Inelastic (Rigid) materials
Used only with edentulous patients having no or
shallow under cuts
1. Plaster of Paris
2. Impression compound
3. Zinc oxide Pastes
4. Impression waxes
Classification of Impression
Materials
10. II. According to the setting
mechanism
A. Chemically-set materials
Because of the irreversible reaction, they are used
only for one time
1. Plaster of Paris
2. Zinc oxide pastes
3. Alginate hydrocolloid
4. Elastomeric materials
Classification of Impression
materials
11. II. According to the setting
mechanism
B. Physically-set materials
Because of the reversible reaction they are able to
be reused
1. Impression compound
2. Agar hydrocolloid
3. Impression waxes
4. Gutta percha
Classification of Impression
materials
12. III. According to the usage
A. Materials for making 1ry
impression
Used in stock trays, thick consistency, record
poor details
1. Impression compound
(Complete denture)
2. Alginate hydrocolloid
(Removable and fixed prosthesis)
3. Putty and heavy consistencies
of rubber impression materials
(Removable and fixed prosthesis)
Classification of Impression
materials
13. III. According to the usage
B. Materials for making 2ry impression
Used in special trays, thin consistency, record fine
details
1. Plaster of Paris (Complete denture)
2. Zinc oxide pastes (Complete denture)
3. Impression waxes (Complete denture)
4. Agar hydrocolloid
(Removable and fixed prosthesis)
5. Medium and light consistencies of
rubber impression materials
(Removable and fixed prosthesis)
Classification of Impression
materials
16. 1. IMPRESSION PLASTER1. IMPRESSION PLASTER
It is a rigid impression material, used
in shellac special trays to make 2ry
impressions for edentulous patient has
no or shallow undercuts.
It is one of the gypsum products that
based on β- Ca2 So4. ½ H2O (β-calcium
sulfate hemihydrate)
18. Composition of the powderComposition of the powder
β-calcium sulfate
hemihydrate….basic constitute
Potassium sulfate….anti expansion and
accelerator
Borax……retarder
Coloring agent…… Alizarine red
Flavoring agent….Ment
Starch….Facilitate the removal of stone cast
β-calcium sulfate hemihydrate
19. Setting reactionSetting reaction
The material sets via chemical reaction
named crystallization
The reaction is characterized by heat
generation and setting expansion
The reaction could be influenced by;
P/L ratio, Mixing rate (time and speed),
Particle size, Temperature, Additives (Acc. &
Ret.)
20. The calcium sulfate hemihydrate gets some
water and changes into inter-meashed calcium
sulfate dihydrate crystals
21. PropertiesProperties
1. Biological properties
Non toxic and non-irritant
Cause dehydration to oral soft tissues
2. Interfacial properties
Requires separating medium before pouring of
gypsum cast and die materials
3. Mechanical properties
Rigid after setting and should not be used in
patients with sever undercuts
Brittle after setting and could be fractured in clean
cut lines during impression removal from shallow
undercuts (i.e. fractured parts could be assembled).
22. PropertiesProperties
4. Chemical properties
Little degree of dimensional changes due to the
presence of anti-expansion additives.
Material’s powder should be stored in dry, tightly
closed containers to elongate the shelf life
5. Practicability
Easy manipulation
Resenable setting time
Somewhate short working time
23.
24. 2. IMPRESSION COMPOUND2. IMPRESSION COMPOUND
It is a rigid thermoplastic impression
material, used in stock trays to make 1ry
impressions for edentulous patient has
no or shallow undercuts.
Types
1. Low fusing (True impression material,
..…softening temp. 45-60o
C)
1. High fusing (Tray compound,
….. softening temp. 70-130o
C)
25. PresentationPresentation
L.F. Cakes for full impression
H.F. Cakes for making special trays
L.F. Green sticks for border tracing
L.F. Cones for copper ring impressions
26. CompositionComposition
Thermoplastic resins…
gives thermoplastic behavior
Waxes…
↑Flow, ↑stickiness, and give thermoplastic
behavior
Filler (Talc, chalk)…
↑consistency, ↓ stickiness
Plasticizer (Stearic acid) …
↑ moldability (plasticity) and facilitate the flow
Coloring agent
27. Setting ReactionSetting Reaction
Thermoplastic material changes its Physical
state by temperature change
On Heating ……Hard Soft
On Cooling ……Soft Hard
The material is bad thermal conductor, so
sufficient heating is required for
homogenous softening. Sufficient cooling is
also required for proper hardening
28. PropertiesProperties
1. Biological properties
Non toxic and non-irritant
Overheated material could burn the soft
tissue
2. Interfacial properties
Does not require separating medium before
pouring the gypsum cast
3. Mechanical properties
Rigid after cooling and should not be used in
patients with sever undercuts
29. PropertiesProperties
4. Chemical properties
Thermoplastic material
Little degree of dimensional changes due to
thermal change and release of stresses
Overheating evaporates the plasticizer ↓
Moldability
5. Practicability
Easy manipulation, Reasonable W.&S. Times
The material could be reused
Impression should be disinfected before
pouring in gypsum and sterilized before reusing
30.
31. 2. ZINC OXIDE PASTES2. ZINC OXIDE PASTES
It is a rigid impression material, used in
acrylic special trays with border tracing
to make 2ry impressions for edentulous
patient has no or shallow undercuts.
Uses of Zinc oxide pasteUses of Zinc oxide paste
1. Impression material
2. Bite registration
3. Surgical pack
32. TypesTypes
1. ZOE paste..contains eugenol in its formulation
2. Eugenol-free paste.. contains carboxylic acid
derivative instead of eugenol
The eugenol-free material overcomesThe eugenol-free material overcomes
the drawbacks of the eugenol;the drawbacks of the eugenol;
1. Eugenol taste could be unaccepted by some patients
2. Eugenol could irritate the soft tissue
3. Leaching of the eugenol out of the material could
cause gastric troubles
33. Both types areBoth types are
presented aspresented as
two-paste systemstwo-paste systems
(Base and Catalyst)(Base and Catalyst)
Base Catalyst
ZOE white paste red paste
E-free white paste blue paste
PresentationPresentation
35. Setting ReactionSetting Reaction
ZOE sets through chemical reaction named
chelation
(1)….ZnO + H2O → Zn(OH)2
(2)…. Zn(OH)2 + Eugenol (2HE) → ZnE2 + H2O
The reaction could also be accelerated in presence of
higher temperatures, little amount of moisture, 1ry
alcohol
Eugenol-free material sets through chemical
reaction named saponification
ZnO + 2RCOOH → (RCOO)2 Zn + H2O
36. PropertiesProperties
1. Biological properties
Non toxic and non-irritant
Eugenol could irritate the soft tissue
2. Interfacial properties
Does not require separating medium
because of its oil content
3. Mechanical properties
Rigid after setting and should not be used in
patients with sever undercuts
37. PropertiesProperties
4. Chemical properties
Impression inaccuracy could result from the
warpage of acrylic trays
Dimensionally stable on storage
5. Practicability
Easy manipulation, Reasonable W.&S. Times
Impression should be disinfected before
pouring in gypsum, however long term
immersion could cause erosion of impression
surface