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Impression Materials / orthodontic courses by Indian dental academy

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IMPRESSION MATERIALSFirst put your patient in a hot baking oven or a searing furnace, then turn them round and round in a centrifugal machine and pour hot metal on them. Or better still, heat them above 1000C in a ceramic furnace and fine till well done. Dont look shocked, - not a very pleasant idea right. Well, that what impression materials same us from.Lets confabulate on this topic under these myriad subheadings:



Definition and Classification

Ideal requisities

Impression materials and Respective techniques


Elastomeric materials.

Inelastic or rigid.

Latest Advances

Summary and conclusion



One of the cornerstones of modern dental practice is the accurate recording and reproduction of tooth tissue details. Material science plays a pivotal role in dentistry and impression materials form a vital core in that foundation. Mimicking the intricate details required in dental practice in the demanding and challenging oral conditions is an acid test for any material. Right from the advent of initial crude impression materials to the modern sophisticated elastomeric chemistries the quest for the perfect replicating material has spanned a diverse range of materials, techniques and devices. From dentures to implants, inlays to crowns, orthodontic to pedodontic to prosthodontist to restorative and endodontists, there is no branch of high quality dentistry untouched by the magic of these materials and no dentist who has not marveled at their ingenuity. Let in delve deeper into this fascinating and vitally important class of material science and understand them for their successful and ideal use.

An impression, in general terms is a mark produced on a surface by pressure. The word impression is divided from latin word impression.

From impression, it is possible to produce an exact replica of the dental structures of interest using a cast or die material such as dental stone or some type of plastic.

There are various categories of impression materials. Each type processes characteristics which influence the purpose to which it is best suited, i.e. different types of impression materials have been developed few different application. These materials have different physical properties and each has certain advantage or disadvantages.

Thus, an understanding of physical characteristics and limitation of each material is necessary for its successful use in clinical dentistry. It would be virtually impossible to perform high quality restorative dentistry without impression materials.


The history of dentistry has been influenced a great deal by development of impression materials. From the cumbersome and highly unpredictable materials of yore replicating materials now match highly exacting standards.

In fact the earliest dental impression materials was waxes that was used in 18th and 19th century. Beeswax was apparently the materials first used in making impression in the mouth.

In 1782 William Rae said that he get the measurement of jaws in a piece of wax pushed into the gums, afterward making a cast of it with plaster of paris.

In 1842, Montgemery discovered gutta-percha. In 1848 Colburn or Blake said that it should thoroughly soaked in boiling water, then kneaded and moulded in the same way as wax and immediately by placed in the mouth and firmly pressed to its place.

In 1930 according to Applegate, a series of true physiologic waxes was developed by cooperative effort of Drs. G.C. Bawles, S.G. Applegate.

The first real impetus in the use of the zinc oxide eugenol for impression materials came from two pioneer dentists, A.W. Ward and E.B. Kelly, during early 1930s.

Alginate type materials were experimented with over many years, however, the first patient was awarded in 1936. This in early 1940s the first irreversible hydrocolloidal (alginate) impression material was developed.

In middle 1950s the elastomeric impression materials were introduced. Polyethers were introduced to dental profession in Germany in late 1960s.

Recently, a new polyether urethane diamethacrylate photo-initiated elastomeric impression material has entered the market.

Definition and Classification:

Impression material is a dental materials whose function is to accurately record the dimensions of the oral tissues and their spatial relationship.

An impression essentially is a negative replica of some structure. In dentistry, this replica usually is made of teeth or gingival tissue of maxillary such as mandibular arch.


Impression Materials:





ZOEImpression compound

Agar Alginate




Lead peroxideClean

Condensation addition



Many criteria may be used to classify impression materials. They are listed as follows:

1) By their generic chemical same:

For example, one may refer to silicone materials or zinc oxide eugenol materials or even particular commercial brands of these materials.

2) According to the manner in which they harden:

A) Set by chemical reaction (Irreversible)

Plaster of paris

Zinc oxide eugenol.


Non-aqueous elastomers.

B) Set by temperature change (reversible)

These materials are again subclassified as:

1) Thermoplastic materials.

Impression compound.


2) Non-thermoplastic material and agar

3) According to the ability of set material to be withdrawn over undercuts.

A) Elastic impression materials:



Non-acqueous elastomers.

B) Non-elastic or rigid impression materials:

Impression compound.

Impression plaster.

Zinc oxide eugenol.


4) According to the use of material in dentistry:

A) Materials used for obtaining impression of dentulous mouth.



Non-acqueous elastomers.

These materials are used in crown and bridge, partial denture and inoperative dentistry.

B) Materials used for obtaining impression of edentulous mouth:

Impression compound.

Impression plaster.

Zinc-oxide eugenol.


5) According to the viscosity or the tissue displacement:

Materials which are initially vary fluid are often classified as mucostatic impression materials, because they are less likely to compress soft tissues, while materials which are initially more viscous are classified as mucocompressive.

A) Mucostatic materials:

Impression plaster.



B) Muco-compressive materials:

Impression compound.

Ideal Requirements of Dental impression materials:

To produce an accurate impression, the materials used to produce replicas of intraoral and some extraoral tissues should fulfill the following criteria.

1. Pleasant taste, odor and esthetic color.

2. Not contain any toxic or initiating ingredient.

3. Have adequate shelf life for storage and distribution.

4. Be economical.

5. Be easy to use with minimum equipment.

6. Have adequate setting characteristics that meet clinical requirements.

7. Possess satisfactory consistency and texture.

8. Adequate strength so that it will not break or tear while removing from the mouth.

9. Possess elastic properties with freedom from prominent deformation after strain.

10. Exhibit dimensional stability over temperature and humidity ranges.

11. Readily wets oral tissues.

12. Compatibility with cast and die materials

13. Accuracy and faithful reproduction of details.

14. Ability to be electroplated.

15. Readily disinfected.

16. No release of gas during setting of impression or cast and die materials.

They should be fluid enough to adapt to the oral tissue and viscous enough to remain content in the tray that delivers impression to the mouth.

While in the mouth they should transform (set) into a rubbery solid in a reasonable amount of time (should be less than 7 minutes).

The set impression should not distort or tear when removed from the mouth. Material should dimensionally stable so the cast can be poured.

In this seminar I will be discussing about the following impression material:




1) Hydrocolloids It is a suspension of time part less the 1m).

Colloids are often classified as a faster state of matter, the colloidal state, because of their difference in structure, constitution and reaction. If the particles are large and can be seen by the naked eye as through a microscope, the system is turned a suspension or emulsion. There suspended particles do not readily diffuse and tend to fall out of the suspending medium unless some type of bonding is employed to maintain the suspension or emulsion.

The molecules of the colloid remain dispersed nature of fact that they carry small electrical changes and repel one another within the dispersion medium.

Types of colloids:

With the exception of the gaseais state (two gases), colloidal sol may be composed of combination of any other states of matter.

For example:

Liquid / solid in air (aerosol).

Liquid / solid in liquid (Lysol).

Gas /liquid / solid in solid.

All solids are termed as sols, and not just more i

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