2. Non-elastic Impression Materials
Definition:
They are impression materials which fracture or distort upon removal
from the undercut area after setting.
They can’t record the undercut area.
Better to use them in completely edentulous patients.
Types:
1.
Impression wax.[Historical]
2.
Impression compound.
3.
Plaster.
4.
Zinc oxide & eugenol.
2
4. Impression Compound
Types:
Type I
Low fusing
compound
[soften at5060ºC]
-1ry impression
+Stock tray
-Single
impression +
Copper band
Type II
High fusing
compound
[soften
at70ºC]
Tray material to
hold 2ndry
impression
material.
Peripheral seal
4
5. Impression Compound
Composition:
1.Thermoplastic waxes & resins
Thermoplastic polymers
2.Fillers
body.
3.Gum
adhesive to the tray.
4. Plasticizers.
5. Pigments.
Setting reaction:
Being thermoplastic, it sets by physical setting reaction.[Reversible]
Impression compound[Hard] ~45ºC Impression compound [Soft]
5
6. Impression Compound
Manipulation:
1.As impression compound is of low thermal conductivity,
[Type of bonding] adequate time should be given for
uniform heating
Flow during impression
taking.
Soaking
in warm water-bath .[Sheets or cakes]
Over a flame.[Sticks]
Dry kneading with fingers.
6
7. Impression Materials
Manipulation:
Application as:
1ry impression material + stock tray.
Single impression + copper band.
Peripheral seal.
Tray material for 2ndry impression.
2. As impression compound is of low thermal conductivity,
adequate time should be given for uniform cooling.
Distortion on removal from the mouth.
7
9. Impression Compound
1.
2.
3.
Properties:
Viscous material
Low flow.[Mucocompressive technique]
.·.It can not record the fine details.
High coefficient of thermal expansion & contraction [Due to weak
intermolecular 2ry bonds]
Contraction during cooling from mouth-to room temperature 0.3-0.4%.
Rigid material:
.·.It is used only in minimum undercut.[Completely edentulous patient]
4.
Self adhesive to the tray (has gum).
9
10. Impression Compound
4.
5.
7.
Properties:
Non-elastic on removal from undercut
distortion.
Not dimensional stable during storage due to release of internal
stresses
Time + Temperature
distortion.
.·. Immediate pouring of the model is recommended.
Compatible with the model material:
a. The gypsum mix can adapt & fill the impression.
b. No separating medium is required.
c. Being thermoplastic ,the assembly [Tray + impression +
model] is immersed in warm water-bath to soften the impression
compound for easy separation from the model.
d. The single impression can be copper electroplated.
10
11. Zinc Oxide & Eugenol ZOE
Supplied form:
Two pastes of contrast colors in metallic collapsible
tubes.
11
13. Zinc Oxide & Eugenol
1.
2.
Types:
Eugenol free impression material for sensitive patients:
Other type of oil of cloves instead of eugenol.
Regarding setting time: [According to the amount of
accelerators & retarders]
Type I Hard
S.T. 10 minutes.
Type II Soft
S.T.15 minutes.
13
14. Zinc Oxide & Eugenol
Setting reaction:
It is acid base reaction.
Zinc oxide + water
Zinc hydroxide +2 Eugenol
[ZO+2Eugenol
Zinc hydroxide
Zinc eugenolate Chelate
[Salt]+H2O
Zinc Eugenolate]
14
15. Zinc Oxide & Eugenol
Setting reaction:
Chelation reaction:
It is the attachment of molecule or ion to metal ion at
more than one point.
The term Chelation is derived from the Greek word
meaning crab’s claw indicating2 projecting attachments.
A central zinc atom is held by 2 adjacent eugenol.
15
16. Zinc Oxide & Eugenol
1.
2.
3.
Manipulation:
Armamentarium:
- Oil resistant paper pad or glass slab & Stainless Steel spatula.
- Special tray.
Steps:
Two equal lengths of the two pastes.
Mix until homogeneous mix without streaks is obtained.
Factors affecting setting time:
High temperature & humidity: accelerate the setting reaction.
Cool glass slab & spatula: retard the setting reaction.
Application:
2ndry impression for completely edentulous patient + Special tray.
16
18. Zinc Oxide & Eugenol
1.
2.
3.
4.
5.
6.
7.
8.
Properties:
High flow
Record the fine details.
Slight contraction during setting.[0.1%]
Rigid
Use in minimum undercut. [completely edentulous patient]
Self adhesive to the tray.
Non-elastic
Can’t record the undercut. Distortion on removal.
Can be disinfected.
Dimensional stable during storage.
Compatibility with model materials:
a.
The gypsum mix can adapt & fill the impression.
b.
No separating medium is required.
c.
Immerse the assembly in warm water-bath for easy separation.
d.
Can not be electroplated.
18
20. Elastic Impression Materials
Definition:
Elastic impression materials are able to record the undercut area in
the dental arch on removal from the patient’s mouth.
They are able after setting to compress at the undercut area
facilitating their removal from the patient’s mouth.
This is known as flexibility.
Then they return back to the original recorded dimensions. This is
known as elasticity.
But these materials are not purely elastic, they are viscoelastic.
20
21. Elastic Impression Materials
What is viscoelasticity?
Viscoelasticity is a strain time relationship.
It is a combination of :
Elastic
• On stress application :Immediate strain , which
remains constant during stress application.
• On stress removal: Immediate recovery.
Anelastic
• On stress application: Gradual increasing strain
during stress application..
• On stress removal: Gradual recovery till reaching
zero.
Viscous
• On stress application: Gradual increasing strain
during stress application.
• On stress removal: No recovery
Permanent strain.
21
23. Elastic Impression Materials
1.
2.
What is the influence of viscoelasticity on the impression
material?
Don’t exert pressure on the tray after insertion.
Don’t move the tray.
Rapid snap removal of the impression in a direction as nearly // as
possible to the long axes of the teeth.
- Permanent deformation.
Tear strength.
Time is required to allow for the gradual recovery of the anelastic
recovery.
Types:
Hydrocolloids.[Aqueous elastic impression materials]
Rubbers [Elastomers][ Non aqueous elastic impression materials]
23
26. Hydrocolloids [Aqueous Elastic
Impression Materials]
States of hydrocolloids:
Sol [Viscous liquid]
Gelation
Gel [Jelly like material]
Types of hydrocolloids:
Reduction in temperature
reaction
Agar
[Reversible hydrocolloid]
Chemical
Alginate
[Irreversible hydrocolloid]
Both are introduced in the sol form intra-orally.
They are removed in the gel form from the patient’s mouth.
26
27. Hydrocolloids[Aqueous Elastic Impression
Materials]
Structure of hydrocolloid gel:
Gelation occurs by the agglomeration of the dispersed phase
[Solute] to form fibrils in a network pattern enclosing water
in-between.[Brush heap structure]
This is
accompanied by
slight
shrinkage.
Filler
Fibrils
H2O
27
28. Hydrocolloids [Aqueous Elastic Impression
Materials]
1.
2.
3.
Factors affecting gel strength:
Concentration of fibrils.
Concentration of fillers.
Temperature.
N.B. Hydrocolloids are of poor tear strength.
.·. - Use in thick section.[4-6mm]
- Rapid snap removal.
28
29. Hydrocolloids [Aqueous Elastic Impression
Materials]
Dimensional stability:
Being hydrocolloid
Dry condition
Wet condition
Loss of water
SYNERSIS
Gain of water
IMBIBITION
Shrinkage
Expansion
Poor dimensional stability
29
30. Agar[Reversible]
Supplied form:[Gel]
1. Sealed container.
2. Metallic collapsible tubes. [ High viscosity
Flow]
3. Syringe material.[ Low viscosity
Flow]
It is packaged -In plastic or glass cartridges that fit a
syringe.
- Preloaded syringe.
30
31. Agar[Reversible]
Composition:
The gel is composed of:
Agar
12%
Dispersed phase.[Natural polymer]
Water 8o%
Dispersion medium.
Viscosity.
Borax
Filler to control
Strength
but acts as retarder for the setting
of gypsum model.
Potassium sulfate Accelerator for the setting of
gypsum model.
31
32. Agar[Reversible]
Gelation reaction:
It is a physical reaction.[Reversible]
Sol
70 - 100ºC
Gel.
37 -45ºC
Hysteresis:
It is the temperature lag between the liquefaction & gelation
temperature, otherwise
- Gelation will be rapid.
- There will be thermal injury to the
patient’s tissues.
32
33. Agar[Reversible]
Manipulation:
Agar needs special armamentarium.
1.Heating & Conditioning Bath:
1st Compartment:[Boiling] Gel
Sol.
2nd Compartment:[Storage] Store in the sol state.
3rd Compartment:[Tempering] to avoid thermal
injury of the patient.
33
34. Agar[Reversible]
2.
Manipulation:
Use of water cooling system tray with means of retention. [Looped
wire]
Avoid –
3.
◦
◦
Exerting pressure on the tray after insertion.
◦
Iced water
Moving the tray during gelation.
Application as
Concentration of stresses.
-Full & quadrant impression for partially or
completely edentulous patients.
- Duplication material.
34
35. Alginate[Irreversible]
Supplied form:
Powder in
-Bulk container.
-Preweighed package for individual impression.
N.B. Preweighed package is preferable than large container,
because alginate is very sensitive to storage temperature &
moisture contamination.[Poor shelf life]
Precautions during storage:
1.
Stock only for 1 year.
2.
Store in cool dry place.
35
36. Alginate[Irreversible]
Composition
:
Action:
Sodium or Potassium alginate
12%
Calcium sulfate dihydrate 12%
Soluble salt.[Natural polymer]
Trisodium phosphate 2%
Filler
Fluoride
Glycol
Chemical indicators
To release Ca++ to react with
alginate. [Reactor]
Retarder .
Viscosity
To control
Strength
Accelerator for the setting
of gypsum model.
Decrease dust formation.
To indicate the pH changes during
manipulation.
36
37. Alginate[Irreversible]
Gelation reaction:
It occurs by chemical reaction.[Irreversible]
It occurs in 2 steps:
- Retardation reaction:[To prolong the working time]
Trisodium phosphate + Calcium sulphate dihydrate +H2O
Calcium phosphate + Sodium sulphate.
- Gelation reaction:
Potassium alginate + Calcium sulphate dihydrate
+H2O
Calcium alginate [gel]
+ Potassium sulphate
37
38. Alginate[Irreversible]
The gel structure:
The final structure sodium alginate
cross-linked with calcium ions.
Types:
According to the amount of
Trisodium phosphate [Retarder]
-Regular set
-Fast set
Cross-linking of Sodium alginate
39. Alginate[Irreversible]
1.
2.
3.
4.
Manipulation:
Armamentarium:
-Rubber bowl & stiff wide bladed Stainless Steel spatula.
- Perforated stock tray for retention.
Steps:
Proportioning for powder & water.
Vigorous mixing against the sides of the rubber bowl [Sol]
Mixing time: 1 minute [Regular set] 45 seconds [Fast set]
Gelation time: 1.5-5 minutes from the start of the mix till the
material looses tackiness.[Sol
Gel]
Avoid -Iced water for mixing.
-Exerting pressure on the tray after mixing.
-Moving the tray during gelation.
39
42. Agar & Alginate
Properties:
High flow, since the dispersion medium is water.
.·. Excellent in recording fine details.
Slight shrinkage during gelation due to agglomeration of the dispersed
phase.
Flexible.
Agar< Alginate[most flexible elastic impression material]
Not adhesive to the tray.
Need for mechanical retention.
e.g. Perforations.
Viscoelastic.
Record the undercut.
.·. No torque or twist during removal of the impression.
Rapid snap removal
Permanent deformation [Agar<Alginate]
Allow for gradual recovery before pouring the model.
42
43. Agar & Alginate
Properties:
Low tear strength.
.·. –Use thick section. [4-6mm]
- Rapid snap removal.
Can be disinfected only by spraying .
During storage they are subjected to synersis & imbibition.
.·.- Pour the model as soon as possible.
- Keep the impression in a humidor .[100%relative humidity]
- Wrap the impression in wet paper towel.
43
44. Agar & Alginate
1.
2.
3.
4.
Properties:
Compatibility with model materials:
Being hydrophilic , the gypsum model can be poured without air
pockets.
No need for separating medium.
.·. Easy separation if the impression is not left overnight.
Retarding effect on the model surface
Chalky soft
surface.
Therefore an accelerator for the setting of the gypsum model
is included in the material.
Can not be electroplated.
44
![Non-elastic Impression Materials
Definition:
They are impression materials which fracture or distort upon removal
from the undercut area after setting.
They can’t record the undercut area.
Better to use them in completely edentulous patients.
Types:
1.
Impression wax.[Historical]
2.
Impression compound.
3.
Plaster.
4.
Zinc oxide & eugenol.
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