rigid impression materials dental material

1. Impression
Materials

2. Making an imprint

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

5. Under cut
Areas under the inclined planes

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

15. RIGIDRIGID
IMPRESSIONIMPRESSION
MATERIALSMATERIALS
1.Impression plaster
2. Impression compound
3. Zinc oxide pastes
Manipulation of these materials will be
handled in the lab classes

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)

17. PresentationPresentation
The material is presented as powder to
be mixed with water to form a slurry
(soft creamy mix)

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

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

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

34. CompositionComposition
Base paste Catalyst paste
1.Zinc oxide
2.Oils (olive oils)
3.Resins
4.Accelerator (Zinc acetate )
Eugenol- containing materials
1.Eugenol (Oil of clove)
2.Fillers (Kaoline, talc)
3.Accelerator (Zinc acetate)
4.Moisture
Eugenol-free materials
1. Carboxylic acid drevative
[e.g. EBA]
2. Ethyl alcohol as vehicle

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