Impression materials polysulph poly ether

Impression materials polysulph poly ether

1. ELASTOMERIC IMPRESSION MATERIAL. Chemistry. They are liquid polymers converted to rubber at room temperature by mixing with a suitable catalyst. They consist of large molecules or polymers that are joined by cross linking. The first synthetic rubber like material was produced by a process known as ‘ vulcanization’ or curing.

2. Classification. Based on chemical composition : 1. Polyether. 2. Poly sulfides. 3. Silicones : Addition Condensation. Based On Viscosity : 1. light body or syringe consistency. 2. Medium or regular body. 3. Heavy body/ Putty

3. Uses of elastomers Final impression in fixed partial denture and removable partial denture construction. Impression of edentulous ridge with undercuts or highly resorbed ridges. For border moulding in CD. Bite registration material. Duplicating material. Record defects for oral and maxillofacial prosthesis(obturators).

4. Polysulfide elastomeric impression material Available as: Light bodied Medium bodied Heavy bodied

5. Composition Base paste: White coloured Sodium polysulfide polymer(co-polymer of ethylene chloride,Thiokol polysulfide, dimercapton polysulfide) 80-85% : Convert to solid rubber by oxidation. Lithophone and titanium dioxide 16-18% : Provide strength, viscosity and whiteness. znso 4 ,cuco 3 , zno , caso 4 or silica

6. Accelerator paste: Brown colored paste. Copper oxysulfate (alternate to lead dioxide) 60-68%: Oxidising agent act as catalyst Dibutyl or Dioctylphthalate 30-35%: plasticizer Sulfur 0.5-3%: to enhance reaction Castor oil 5-8%

7. Other substances such as magnesium stearate or oleic acid (retarder) 1-2%:to control setting time Deodorants (traces) pleasant smell. Tray adhesive: Butyl rubber or styrene acrylonitrile dissolved in a volatile solvant such as chloroform or ketone .

8. Setting reaction Mercaptan + lead dioxide =polysulfide +water Chain lengthening by oxidation of terminal –SH group Cross linking by oxidation of the pendant-SH group Exothermic reaction with rise of 3 – 4 degree C in temp. Heat and moisture accalerate the reaction.

9. Properties Setting time 5-8 min. Colder time increase setting time Drop of water accalerate reaction Excellent detail reproduction Dimensionallt stability Curing shrinkage 0.45% Shrinkage due to loss of byproduct

10. Permanent deformation 3-5 % (highest in elastomers) High tear strength 7000gm/cm 2 Good flexibility 7% Hydrophobic Can be electroplated with copper Toxic effects due to lead content

11. Advantages Long working time Proven accuracy High tear resistance Inexpensive to use Less hydrophobic Longer shelf life

12. Disadvantages Must be poured with dental stone immediately Potential for significant distortion Odor is offensive Messy and stains cloths Second pour is less accurate.

13. Single viscosity technique With putty With putty and lighter body material With flow-able material loaded in tray and syringe

14. Putty technique

15. Putty with lighter body wash

16. Addition silicone 2 Syringe cartridges with gun – base and accelerator supplied as Light, Medium or Heavy body

17. addition silicone

18. Polyvinyl siloxane

19. Direct and syringe mix