Impression Compound SIBAR INSTITUTE OF DENTAL

slide1. Impression Compound SIBAR INSTITUTE OF DENTAL SCIENCES Department of Prosthodontics Dr. Mounika, Sr.lecturer<br>
slide2. IMPRESSION : A negative likeness or copy in reverse of the structure of an object ;an imprint of the teeth and adjacent structures for use in dentistry
-GPT 9

First of many stages involved in the fabrication of dentures, crowns, inlays, bridges, orthodontic appliances, etc.
Inaccuracies are minimized at this stage, and otherwise they will be carried through and possibly compounded later on.<br>
slide3. IMPRESSION MATERIAL: Substance or combination of substances used for making an impression or negative reproduction -GPT 9

From this negative form of the teeth and surrounding structures, a positive reproduction, or cast is made.

The accuracy of fit and the functional efficiency of the appliance depends upon how well the cast replicates oral tissues

The accuracy of the cast depends on the accuracy of the impression in which it was cast<br>
slide4. IMPRESSION
COMPOUND
ADA NO -3
1857, a London dentist, Charles Stent, introduced the first impression compound
Oldest impression materials. Supplied in the form of sheets, sticks, cylinders and cones.
Impression compound are thermoplastic materials and are softened to their working consistency by immersion in hot water or by warming over a flame.<br>
slide7. PROPERTIES
It has a high coefficient of thermal expansion. On cooling during setting, there is considerable shrinkage.
The average linear contraction of compound on cooling varies between 0.3 to 0.4 %
Impression compound will distort on removal over undercut areas.
Thermal conductivity of the compound is low. Due to this the outside of a mass of compound will soft whereas the inner areas will remain hard during softening.
Adequate time has to be given for uniform softening<br>
slide8. It is dimensionally instable and this is due to relaxation of stresses.
Stresses are incorporated due to high coefficient of thermal expansion, poor thermal conductivity, relatively large temperature drop from mouth to room temperature

To minimise distortion the safest procedure- proper cooling of impression before removal and to construct the cast immediately after removal from the mouth at least within first hour<br>
slide9. GLASS TRANSITION TEMPERATURE
- Transition of amorphous materials from a hard and relatively brittle "glassy" state into a viscous or rubbery state -39 c
FUSION TEMPERATURE
- The temperature at which the crystalline fatty acids solidify (43.5 c)
- Above this temperature fatty acids liquify and lubricate the material to form a smooth mass
- Impressions are made above this temperature<br>
slide10. The very high viscosity characterizes muco compressive impression material.
MANIPULATION
The material can be softened by using a thermostatically controlled water bath at a temperature of 55 to 60 c<br>
slide11. PRECAUTIONS
- Prolonged immersion or overheating in water bath result in brittle and grainy because some of the low-molecular-weight ingredients may be leached out.
- Wet kneading is suggested as water incorporates and improves the flow of material
- Excessive Kneading should be avoided as it increases the flow of hardened compound and causes distortion on removal
- Cast should be constructed as soon as possible to prevent from war page due to relaxation of internal stresses<br>
slide12. APPLICATION
Used to record primary impression of edentulous patients
single tooth preparation using the copper ring technique
Used as a check on cavity preparations in the indirect inlay procedure.
Used for border extensions on impression trays.
Used to form a tray for construction of dentures.<br>
slide13. ADVANTAGES
Can be used for any technique requiring a closed peripherals
Can be added and readopted
DISADVANTAGES
They distort easily and should not be used when undercuts exist doesn't reproduced final details
As it can be re used and it can't be sterilized
Has high coefficient of thermal expansion of thermal expansion and low thermal conductivity
Dimensionally instable<br>
slide14. GREEN STICK COMPOUND
It is a low fusing using compound
Type 1 introduced by Green brothers It is similar to that of impression compound with more plasticizer it is softened by passing over flame and kneading(dry)<br>
slide15. Uses
It can be used in single tooth impression or tube impression technique
Can be used as a peripheral seal materialUsed for border extensions of special tray<br>
slide16. TRAY  COMPOUND
It is a high fusing compound it is similar to composition and working qualities of impression compound except that the temperature at which they soften i.e 70 cThey resemble the shape of tray
They are used to prepare custom-made preliminary impression that will later hold a secondary impression material
They lack strength and dimensional stability and hence they are replaced self cure acrylic resins<br>
slide17. THANK YOU…<br>