silicon impression material

overview of the silicon impression material

1. SILICON RUBBER IMPRESSION MATERIAL BY PHILIP SHAIBILA BWALYA CHILESHE DENTAL TRAINING SCHOOOL, TECHNOLOGY STUDENTS

2. DEFINATION A dental impression is defined as the negative record of the tissues of the mouth . It is used to reproduce the form of the teeth and surrounding tissues. Impression material: Is any substance or combination of substances used for making an impression or negative reproduction.

3. Classification

4. SILICON RUBBER IMPRESSION MATERIAL…

5. There are two types of silicon rubber impression material, namely addition and Condensation

6. Condensation silicones • Condensation silicone was the first type of silicone impression material. • Also known as conventional silicones. • Setting occurs at room temperature , and so are also called RTV silicones.

7. PROPERTIES Sets time 8-9 min Mixing time 45 sec Excellent detail product Hydrophobic Shelf life 2 yrs

8. CONPOSITION 1.Base Paste Polydimethylsiloxane (Hydroxy-terminated) Colloidal silica or microsized metal oxide(filler) 35-75% Colour pigments 2. Accelerator Paste Orthoethyl silicate - (cross linking agent) Stannous octoate - catalyst

9. • ADVANTAGES It is clean and pleasant Good working time Easily seen margins

10. DISADVANTAGES High polymerization shrinkage Volatile alcohol byproduct Low tear strength Hydrophobic Pour immediately

11. ADDITION SILICONE • Also called as polyvinyl siloxanes • Has better properties than condensation silicones It has an excellent recovery of 99.93% Addition polysilicones are the most stable of all the existing materials It exhibits pseudoplastic properties.it can be used both as syringe and tray materials Extremely hydrophilic

12. PROPERTIES Setting time 5-9 min Mixing time 45 sec Excellent surface detail Low curing shrinkage Low flexibility Shelf life 1-2 years

13. Composition Base Poly(methyl hydrogen siloxane) Other siloxane prepolymers Fillers Accelerator : Divinyl polysiloxane Other siloxane prepolymers Platinum salt : Catalyst (chloroplatinic acid) Palladium (Hydrogen absorber) Retarders Fillers

14. ADVANTAGES Accurate impressions, very low shrinkage Very good surface detail Highly elastic Perfect elastic recovery. Dimensionally stable Non-toxic and non-irritant

15. DISADVANTAGES Hydrophobic – necessary to add a surfactant Setting inhibited by latex gloves or some adstringents (sulfur, heavy metals) Hydrogen release – surface bubbles – pouring time 1 h after removal from the mouth High price

16. FACTORS INFLUENCING WORKING AND SETTING TIME Decrease in temperature (Cooling of glass slab and storing materials at room temperature can help in prolonging the working and setting time) Decrease in viscosity Increase in temperature ( Rise in temperature accelerates the curing rate ) Increase in viscosity (Changing the proportions of base/catalyst can alter the setting reaction)

17. FACTORS AFFECTING DIMENSIONAL STABILITY

18. Manipulation Mixing: 1. Using paper pad (Glass slab) and Spatula; Light, medium and heavy consistencies 2. Hand Kneading; Heavy or putty consistency 3. Automixer and Dispenser; Cartridge form only (Light, medium, heavy) 4. Automatic mixing; All consistencies, special electric mixer + special material form

19. Manipulation

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