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Azhar Assuit - Asnan 25

Impression :- is a negative reproduction of the tissues

Cast :- is a positive reproduction of tissues.

Ideal Requirements

1- Sufficiently fluid (to reproduce all fine details).

2- Suitable setting time (to produce suitable working time).

3- Sufficient mechanical strength (not to tear or permanent deformation during insertion or removal).

4- Sufficient dimensional stability ( to pour the stone or other material).

5- Compatibility with die and cast materials (not need separation medium).

6- Safe (not toxic or irritant)

7- Acceptable to patient (acceptable taste-color-odour)

8- Good keeping qualities.

Chapter impression material

For first dental students

Done by asnan 25

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Azhar Assuit - Asnan 25

CLASSIFICATION OF IMPRESSION MATERIALS

ACCORDING BEHAVIOR AFTER SETTING

NON ELASTIC ELASTIC

Either fracture or permanent distortion during removal from under cut

Recovered after removal from undercut

1- Plastic impression. 2- Impression compound. 3- Zn-oxide\Eugenol.

Hydrocollid Elastomers

1- Agar Agar 2- Alginate

1- Polysulfide. 2- Silicone (condensation) 3- Silicone (Addition) 4- Poly ether

ACCORDING TO SETTING

Chemical reaction Physical changes

Soft Hard Hard heating-cooling soft

1- Plaster impression. 2- Zn-oxide\Eugenol

3- Alginate. 4- Elastomers

1- Impression compound. 2- Agar Agar.

ACCORDING TO THEIR USES

Complete denture Partial denture Crowns and bridge

1- Plaster impression. 2- Zn-oxide\Eugenol 3- Impression compound 4- Alginate

1- Alginate. 2- Elastomers.

Elastomers

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Azhar Assuit - Asnan 25

Comparison between NON ELASTIC impression materials

AZHAR ASSUIT 1. Plaster impression 2. Impression compound 3. Zincoxide Eugenol

Fluidity & Accuracy

- Very high fluidity. - Great accuracy. - Record fine details.

- Low fluidity. - Low accuracy. - Not record fine details.

- Sufficiently fluid. - To record all fine details.

Dimensional change

(Setting expansion)

- Minimum setting expansion - .06% - Due to K2SO4

- High setting expansion -0.4% - Due to highly coefficient Of thermal

expansion

- Little setting expansion. - 0,1%

Dimensional stability

(shrinkage degree)

- Very stable - Small degree of shrinkage

- Low stable due to high coefficient Thermal.

- So should be pour immediately

- Very stable - More high temp. lead to

distortion

Elasticity Rigid lead to fracture during removal form cast or mouth

Rigid material Lead to permanent distortion during removal from undercuts after its setting

Adhesion to tray Adhere Adhere Adhere

Cast compatibility Not compatible Need to separating medium

Compatible Not need a separating medium

Compatible Not need separating medium

Advantage - Easily assembled when

fractured - Thermoplasticity (Reversible) - Hard --heat/cold-- Soft

- Can use in undercut area - Thickness of Spacer is 0

Disadvantages - Dryness sensation to patient - Need separating medium

- Very difficult removal from undercut area which in mouth

- Eugenol can be irritant giving burning sensation to patient

Uses & Notebooks

- In complete denture construction in past

1. In complete denture construction 2. As impression trays for double tech. 3. As peripheral seal material 4. Single impression with copper band

1-On complete or partial denture without / with undercut 2- Stabilizing base plate in bite registration

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Azhar Assuit - Asnan 25

Comparison between RUBBER BASE impression materials

AZHAR ASSUIT Cond. Silicon Addition Silicon Poly ether Poly sulfide

Composition

80% Silicon (OH)group 20% Silica

Tin octate Ethel silicate

80%Silicon (vinyl)group 20% Silica

Ch

loro

pla

tin

ic a

cid

80% polyether (ethylene imine) 20% Silica Su

lfo

nic

ac

id e

ster

80% polysulfide (SH)group 20% Silica Le

ad

dio

xid

e

Fluidity Depend on consistency القوام by filler as silica:- types & route of application لجهاز المستخدم لتطبيع العجينة ا 1- Light body Syringe 2- Medium Tray 3- Heavy Tray + Syringe

Accuracy Increase with 2nd imp. Highest accuracy More accuracy Accurate

Tray & spacer thickness Should be acrylic tray -- Impression material thickness 2-4 mm

Dimensional change 0.6% .05 % 0.1 % .45% alcoholic evaporation

Shrinkage degree 0.2-1% in 24hrs Lowest shrinkage .3% in 24hrs .3-.4 %

Elastic recovery 99% 99.5% 98.5 % 96 %

Properties

1.

1. Handle mixing

2. Pouring ease

3. Pouring time

4. Tear strength

5. Cost / taste

6. Working time

7. Hydrophilic or

8. others

1. Easy mixing 2. Poor to adequate 3. Once تواor 1 hour 4. Adequate tear St. 5. Suitable حونين 6. Long 10 min 7. Very hydrophobic 8. Less distortion

1. Very easy mixing 2. Adequate in stone 3. 60min- 1 week 4. Adequate tear St. 5. High cost 6. Short 6-8 min 7. Hydrophilic 8. Doesn’t stain NB: should poured after

setting at least 30-60 min due to elastic recovery

1. Moderate mixing 2. Easily poured in stone 3. (1) week 4. Adequate tear St. 5. High cost -Bitter taste 6. Short 5-6 min 7. Distort if stored in

water (hydrophilic) 8. Allergic reaction

(sulfonic acid)

1. Moderate - difficult 2. Adequate pour 3. 1 hour 4. Highest tear St. 5. Bad odder 6. Long 12-14 min 7. Hydrophilic 8. Clothing stain - Condensation reaction

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Azhar Assuit - Asnan 25

Comparison between HYDROCOLLOIDS impression materials

AZHAR ASSUIT Alginate AGAR AGAR Fluidity Sufficiently fluid to record fine details Highly fluid – fine record

Accuracy Less than agar More accuracy

Tray & spacer thickness Perforated stock or special tray (shellac/acrylic) Special water tray with other equipment

Dimensional change Imbibition تشرب ماء in water (expansion)

Shrinkage degree Syneresis جفاف/تساحب الماء in air

Elastic recovery 97% 98.9%

Properties

1. Handle mixing 1- Easier 1- No mixing needed 2. Pouring ease 2- Good 2- Good

3. Pouring time 3- Immediately or at less in 15 min 3- Immediately or at less in 15 min

4. Tear strength 4- Very weak tear St. 4- Weak tear strength

5. Cost / taste 5- Cheep 5- High cost

6. Working time 6- Suitable working time 6- Long and difficult working 7. Hydrophilic or 7- Hydrophilic 8- Irreversible

7- Reversible

Not use now