rigid impression materials dental material
DESCRIPTION
rigid impression materials dental materialTRANSCRIPT
Impression Materials
Making an imprint
Impression and Cast
Impression: -ve replica of the oral hard and soft tissues
Cast: +ve replica of the oral hard and soft tissuesDie: Metal cast or any cast for single tooth
Impression TraysContainer used to carry the impression material into or out from the patient’s mouth
Stock trays Special trays
Under cutAreas under the inclined planes
X
Ideal requirements of Impression materials
Biologically Non- toxic and non-irritant
InterfaciallyCompatible with different model and die materials
Chemically 1. Have long shelf life2. Dimensionally stable in storage Stable in storage
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
Practicability1. Inexpensive
2. Easy manipulated
3. Have reasonable working and setting times
Classification of Impression Materials
I. According to the mechanical behavior
A. Elastic materialsUsed 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) Polyether3. Gutta Percha
I. According to the mechanical behavior
B. Inelastic (Rigid) materials Used only with edentulous patients having no or shallow under cuts
1. Plaster of Paris2. Impression compound3. Zinc oxide Pastes4. Impression waxes
Classification of Impression Materials
II. According to the setting mechanism
A. Chemically-set materialsBecause of the irreversible reaction, they are used only for one time
1. Plaster of Paris2. Zinc oxide pastes3. Alginate hydrocolloid4. Elastomeric materials
Classification of Impression materials
II. According to the setting mechanism
B. Physically-set materialsBecause of the reversible reaction they are able to be reused
1. Impression compound2. Agar hydrocolloid3. Impression waxes4. Gutta percha
Classification of Impression materials
III. According to the usage
A. Materials for making 1ry impressionUsed 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
III. According to the usage
B. Materials for making 2ry impressionUsed 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
RIGID IMPRESSION RIGID IMPRESSION MATERIALSMATERIALS
1.Impression plaster
2. Impression compound
3. Zinc oxide pastes
Manipulation of these materials will be handled in the lab classes
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 - Ca2 So4. ½ H2O (-calcium
sulfate hemihydrate)
PresentationPresentation
The material is presented as powder to be mixed with water to form a slurry
(soft creamy mix)
Composition of the powderComposition of the powder
-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
-calcium sulfate hemihydrate
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.)
The calcium sulfate hemihydrate gets some water and changes into inter-meashed calcium
sulfate dihydrate crystals
PropertiesProperties1. 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).
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
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.
Types1. Low fusing (True impression material,
..…softening temp. 45-60oC)
1. High fusing (Tray compound,
….. softening temp. 70-130oC)
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
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
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
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
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
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 paste1. Impression material
2. Bite registration
3. Surgical pack
TypesTypes1. ZOE paste..contains eugenol in its
formulation
2. Eugenol-free paste.. contains carboxylic acid derivative instead of eugenol
The eugenol-free material overcomes The 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
Both types are Both types are presented as presented as
two-paste systems two-paste systems
(Base and Catalyst)(Base and Catalyst)
Base Catalyst
ZOE white paste red paste
E-free white paste blue paste
PresentationPresentation
CompositionComposition
Base pasteCatalyst paste
1.Zinc oxide2.Oils (olive oils)
3.Resins4.Accelerator (Zinc acetate )
Eugenol- containing materials1.Eugenol (Oil of clove)2.Fillers (Kaoline, talc)
3.Accelerator (Zinc acetate)4.Moisture
Eugenol-free materials1. Carboxylic acid drevative [e.g. EBA]2. Ethyl alcohol as vehicle
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
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
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