Increase water content = Expansion = Imbibition – absorption of water Twisting or torquing should be avoided.ĭepends on water content of the hydrocolloid,ĭecrease water content = Shrinkage = Syneresis – an exudation of fluid onto surface of set gel The impression is removed with a single stroke along the long axis of the tooth.The tray should be held with little pressure and should not be distributed until gelation is complete (convert sol to gel).Cool the tray with water at 13 ☌ for 3 minutes.The tray material is taken from the third chamber and the tray is seated in position.The syringe material is taken from the second chamber and injected into the prepared tooth.Tempering chamber: Tempering at 45 ☌ for 3 minutes after it has being placed in the tray.Storage chamber: Stored at about 65 ☌.For reused material, additional 3 minutes is required. Liquefying chamber: Boiling (100 ☌) for 10 minutes.Exactly at mouth temperature, surface stress may develop causing syneresis later.If too low: Temperature for gelation would be made difficult or impossible to attain.If too high: Injury to oral tissues due to increased temperature.The gelation temperature is critical when: This time is the manipulation time of the material. Hysteresis is the temperature lag (slow) between Liquefaction Temperature & Gelation Temperature. This helps in using agar as an impression material. WHAT DO YOU NEED TO KNOW ABOUT HYSTERESIS? It is called gelation temperature and it varies from 36 to 43☌. The sol can be converted to gel by decreasing the temperature below liquefaction. This increased temperature is called liquefaction temperature and is 71 to 100 ☌. They break at increasing temperature to the from sol. Sterilization of impression is difficult.Īgar gels have fibrils held together by weak forces. Multiple models cannot be poured like elastomeric impression materials.Ħ. Thin sections of impression tears easily.ģ. Distortion on removal is prevented due to elastic recovery.Ģ. Widely used at present for cast duplication (during fabrication of cast RPD).įor laboratory duplication material usage:ģ. Number of cylinders in a glass jar or cartridges (Syringe material)Ģ.Primary use of agar impression material: It is used to make secondary/final impression in dentolous patients requiring removable and fixed partial dentures.įor impression material usage, it comes in the form of: Alkyl-benzoates (0.1 %) – Preservative that increases shelf-life.ġ.Fillers – Hard waxes which improves strength.Potassium sulfate – Acts as a gypsum hardner.Borates – Improves strength but acts as a gypsum retarder.It is a mucilaginous substance that melts at high temperature (about 100 ☌) and solidifies into a gel at low temperature (about 36 ☌). ![]()
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