1. Dr. Recep Uzgur Department of Prosthodontics
Impression Materials
Dr. Recep Uzgur
Department of Prosthodontics

2. Terminology
IMPRESSION : A negative likeliness or copy in reverse of the surface of an object; an imprint of the teeth and adjacent structures for use in dentistry.
IMPRESSION TRAY : A receptacle into which suitable impression material is placed to make a negative likeliness (or) a device that is used to carry, confine, and control impression material while making impression.
IMPRESSION MATERIAL: Any substance or combination of substances used for making an impression or negative reproduction.
IMPRESSION TECHNIQUE : A method and manner used in making a negative likeness.

4. Rigid
Elastic
Material
Use
Chemical Reaction
(Irreversible)
1.Plaster Of Paris
Edentuolus Ridge
1.Alginate
Teeth And
Soft Tissues
2.Zinc Oxide
2.Polysulfide
3.Polyether
4.Condensation Silicones
5.Addition Silicones
Thermally Induced
Physical Reaction
(Reversible)
3.Impression Compound
Preliminary Impression
Tracing
6.Agar

5. History
Philip Ptaff-1756 First described taking impression with softened wax
Christopher Francois Delabarre-1820 Introduced the metal impression tray
Chapin Haris-1853 First used Plaster of Paris for making impressions
Charles Stent-1857 Introduced the first impression compound
Sears First used agar hydrocolloids for recording crown impressions.
United States-1945 Introduced alginate during World War II.
SL Pearson-1955 Developed synthetic rubber base impression materials
Polysulfide- Late 1950’S First developed as an industrial sealant.
Condensation Silicone- Early 1960’s
Addition Silicone-1970’s
Polyether- Late 1970’s Polyether Urethane Dimethacrylate

6. Properties of An Ideal Impression
1) Complete plasticity before cure 2) Sufficient fluidity to record fine detail. 3) The ability to wet the oral tissues. 4) Dimensional accuracy. 5) Dimensional stability. 6) Complete elasticity after cure. 7) Optimal stiffness 8) Good taste and smell

7. 1. Plaster
Plaster of Paris is seldom used as an impression material now that elastomeric materials are available.
The main component of impression plaster is calcium sulfate hemihydrate, which reacts with water to form calcium sulfate dihydrate.
The water/powder (W/P) ratio recommended by the manufacturer should be measured out carefully.
Impression plaster is rigid and will break easily.
The plaster must be stored in an airtight container, because it will absorb water from the air.

9. 2. Impression Compound
It used to be used as an impression material, but no longer used.
Thermoplastic property allows it to be used warm (45°C) and then cooled to oral temperature (37°C), at which it is fairly rigid.
Impression compound is softened by heating over a flame or in a water bath.
Care must be taken to prevent volatilizing ingredients over a direct flame.
It is being used for tracing today.

11. 3. Zinc oxide–eugenol
The main use of zinc oxide–eugenol is for dentures on edentulous ridges with minor or no undercuts.
It can also be used as a wash impression over the compound in a tray or in a custom acrylic tray.
This material is commercially available in a form that two pastes. One paste, called the base or catalyst paste, contains zinc oxide (ZnO), oil, and hydrogenated rosin. The second paste, the accelerator, contains about 12% to 15% eugenol, oils, rosin, and a filler such as talc or Kaolin.

12. The setting time is shortened by increases in temperature and/or humidity.
The set material does not adhere to set dental plaster or stone.
These materials are usually mixed on a mixing pad with a spatula. Equal lengths of base and catalyst are extruded on the mixing pad.
Adequate mixing time is 45 to 60 seconds, pastes have an initial set time of 3 to 5 minutes.
Zinc oxide–eugenol gives high accuracy of soft tissue impressions.
The material is stable after setting, has good surface detail reproduction, and is inexpensive.
Zinc oxide–eugenol impressions can be disinfected by immersion in 2% glutaraldehyde or 1:213 iodophor solutions at room temperature.

14. 4. Agar Hydrocolloid
Agar hydrocolloids have been completely replaced by rubber impression materials, so its no longer used.
Agar hydrocolloids are available in both tray and syring consistencies. The material is supplied as a gel in plastic tubes.
The gel material can be converted to a sol (liquid) by heating; cooling the sol will return the material to the gel state.

15. 5. Alginate Hydrocolloid
Alginates are the most widely used impression materials in dentistry.
They are used for making impressions for removable partial dentures with clasps, preliminary impressions for complete dentures, and orthodontic and study casts. They are not accurate enough for fixed partial denture impressions
The powder is mixed with water to obtain a paste.
A lower W/P ratio increases strength, tear resistance, and consistency, and decreases working and setting times and flexibility.
One minute of thorough mixing for the regular-set material and 45 seconds for the fast-set material are generally recommended. Alginates have a relatively short working time of about 2.5 minutes and set about 3.5 minutes after mixing.

16. Alginate impression materials are inexpensive, easy to manipulate, pleasant tasting, able to displace blood and body fluids, hydrophilic, and easily poured in stone. They can be used with stock trays.
Alginates tear easily, must be poured immediately after removal from the mouth, have limited detail reproduction, are dimensionally unstable, and can only be used for single casts.

18. 6. Polysulfide
Due to their high accuracy and relatively low cost, polysulfide rubbers can be used for fixed partial denture application.
Polysulfides are supplied in tubes of base paste and catalyst paste, which are mixed together.
They are available in low, medium, and high viscosities.
Equal lengths of base and catalyst are extruded on a disposable mixing pad, and the components are mixed thoroughly with a stiff tapered spatula.

19. Adequate mixing time is 45 to 60 seconds, and the working time is about 5 to 7 minutes.
Both working and setting times are shortened by higher temperatures and humidity.
Cast or die should be poured within 1 hour of taking the impression.
These materials have a long working time, good tear strength, good flow before setting, good reproduction of surface detail, high flexibility for easier removal around undercuts, and lower cost compared with silicones and polyethers.
Polysulfides have an unpleasant odor and a tendency to run down the patient’s throat

21. 7a. Condensation Silicone
They are used mainly for fixed partial denture impressions.
These materials are supplied either as two-paste and are available in low, medium, high, and very high (putty) viscosities.
After condensation reaction a volatile alcohol is formed as a by-product.
The manipulation of condensation silicones is the same as for polysulfides and the setting time is less than that of the polysulfides, which saves some chair time.
Higher temperatures and humidity shorten the setting time.
They are highly elastic, and the setting time can be controlled with the amount of accelerator.

22. These materials tend to be inaccurate due to shrinkage on standing and should be poured within 1 hour.
They are very hydrophobic, require a very dry field, and are difficult to pour in stone.

23. 7b. Addition Silicones
The accuracy of addition silicones is due to a change in polymerization reactions to an addition type and the elimination of an alcohol by-product that evaporates, causing shrinkage.
These materials are available as two-paste systems in four viscosities—light, medium, heavy, and putty—and a range of colors, allowing monitoring of the degree of mixing.
They are expensive and hydrophilic.
The working and setting times of addition silicones are faster than polysulfides.

24. Addition silicones can be safely poured later or sent to a dental laboratory. The materials may be poured 1 week after taking the impression, and multiple pours are possible.
The material is expensive—twice the cost of polysulfides; it is more rigid than condensation silicones.

25. 8. Polyether
Polyethers are available in low-, medium-, and high viscosity materials.
Polyethers are similar to addition silicones that have a working time of 2.5 minutes and a setting time of 4.5 minutes.
The manipulation of polyethers is similar to that of polysulfides and silicones. Equal lengths of base and catalyst paste are mixed rapidly (30 to 45 seconds), because the working time is short.
A hand held gun-type mixer that provides quick, bubble-free mixes is available for Permadyne Garant (3M ESPE).
Also, an automatic mixing device (Pentamix, 3M ESPE) is available for use with a polyether packaged in polybags (Impregum Penta).

26. These materials are more accurate than polysulfide or condensation silicone impression materials.
The cost of these materials is high.
Polyether impressions can be disinfected by immersion in sodium hypochlorite.