Elastomeric impression material-ALGINATE

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  1. 1. ELASTOMERIC IMPRESSION MATERIAL ALGINATE
  2. 2. I T I S A N E G A T I V E L I K E N E S S O R C O P Y I N R E V E R S E O F T H E S U B J E C T O R O B J E C T . E X A M P L E : A N I M P R I N T O F T H E T E E T H A N D A D J A S C E N T S T R U C T U R E S F O R U S E I N D E N T I S T R Y WHAT IS AN IMPRESSION
  3. 3. ALGINATE Alginate is classified as irreversible hydrocolloid. Hydrocolloid because it consists of particles of a gelatinous (colloidal) state in water (hydro) and irreversible because once it has jelled it cannot be returned to a liquid solution.
  4. 4. The Word Alginate comes from the term ALGIN. It is a peculiar mucous extract yielded by certain brown seaweed ( algae ) . The term ALGIN was coined by chemist from Scotland at the end of 19th century.
  5. 5. TYPES Type I Fast setting. Type II Normal setting.
  6. 6. MODES OF SUPPLY It is supplied as a powder that is packed: a) In bulk or in tins or in sachets (or) b) In pre-weighed individual containers. A plastic scoop is supplied for dispensing the bulk powder, & a plastic cylinder is supplied for measuring the water .
  7. 7. APPLICATIONS 1) Used for impression making : a) when there are undercuts b) In mouth with excessive flow of saliva c ) For partial dentures with clasps. 2) For making preliminary impressions for complete denture. 3) For orthodontic and study models. 4) For duplicating models.
  8. 8. COMPOSITION Potassium or sodium alginate(15%) Dissolves in water and reacts with ca+ ions Calcium sulfate(16%) Reacts with the potassium alginate to form the gel. Sodium phosphate(2%) Reacts preferentially with calcium sulphate/ retarder
  9. 9. Diatomaceous earth( 60 %) filler that adds bulk to the material. Zinc oxide (4%) Adds bulk to the material / filler Potassium titanium fluoride(3%) gypsum hardener Coloring and flavoring agent(traces) Peppermint, orange, etc
  10. 10. PHYSICAL PHASES OF ALGINATE The first phase is a sol (as in solution). In the sol phase, the material is in a liquid or semi liquid form. The second phase is a gel. In the gel phase, the material is semisolid, similar to a gelatin dessert.
  11. 11. SETTING REACTION Reaction occurs by a chemical reaction Soluble alginate reacts with calcium sulphate to produce insoluble calcium alginate as a gel The production of calcium alginate is delayed by the addition of a third soluble salt (tri sodium phosphate) to the solution, with which the calcium sulphate will react in preference to the soluble alginate to form an insoluble calcium salt.
  12. 12. In a nutshell , when powder is mixed with water to obtain a paste ,two main reaction occur during setting : a. 2Na3P04 + 3CaSo4---> Ca3(Po4)2+3 Na2SO4 b. sodium alginate(Powder ) + CaSO4 + H2O --> Ca alginate + Na2SO4(Gel)
  13. 13. First , sodium phosphate reacts with the calcium sulphate to provide adequate working time. Second ,after the sodium phosphate has reacted, the remaining calcium sulphate reacts with sodium alginate to form an insoluble calcium alginate which forms a gel with water.
  14. 14. WATER-TO-POWDER RATIO An adult mandibular impression generally requires two scoops of powder and two measures of water. An adult maxillary impression generally requires three scoops of powder and three measures of water.
  15. 15. MANIPULATION Fluff or shake the powder to distribute the powder particles evenly Use the specific measuring devices (water & powder) provided by the manufacturer for mixing Follow the manufacturer's direction regarding the ratio of water to powder. Use exact measurements
  16. 16. After the water and powder have been measured, place the water in a clean dry bowl. Shift the powder into the water. Adding the powder to the water ensures the powder particles are wet evenly. If mixed in reverse (the water is added to the powder) the chemical reaction will start early with some particles setting faster than others.
  17. 17. Mix the alginate for the specific amount of time and using a stiff spatula swipe the alginate mass against the sides of the bowl to avoid entrapment of air in the mix.
  18. 18. ALGINATE SETTINGS Working time The time allowed for mixing the alginate, loading the tray, and positioning the tray in the patient's mouth. Setting time The time required for the chemical action to be completed. Normal set alginate Working time of 2 minutes and a setting time of up to 41/2 minutes after mixing. Fast set alginate Working time of 11/4 minutes and a setting time of 1 to 2 minutes.
  19. 19. SETTING TIME OF ALGINATE Since alginate reacts or gels chemically, temperature is a major factor in the setting time. The colder the temperature of the water the longer it takes to set; conversely, the higher the water temperature the faster it sets. Ideal water temperature is 68 degrees or room temperature.
  20. 20. LOADING OF TRAY A perforated tray is used so that the material is forced out slightly through the holes in the tray during loading, thereby locking itself mechanically into the tray The surface of the alginate in the tray may be smoothened out by moistening the finger with water and running it over the surface of the alginate.
  21. 21. SEATING THE TRAY Before making the upper impression, saliva should be wiped off from the palatal region In order to prevent the material from flowing along the throat and causing nausea to the patient, the posterior portion may be seated first and then the anterior portion seated properly Since the material sets from tissues towards periphery, any movement during gelation may result in distortion. So once the tray is seated ,it must be held in place firmly without any movements.
  22. 22. REMOVAL OF THE IMPRESSION An alginate impression when set develops a very effective peripheral seal This seal should be freed by running the finger around the periphery. The impression must be removed suddenly ,with a jerk. After removal from the mouth, - washed with water to remove saliva. - cast should be poured as soon as possible.
  23. 23. MODIFIED ALGINATES Dust free alginates De-dusting agent (glycerin or glycol) Siliconized alginates silicon polymers are added to strengthen the material Alginates containing disinfectants eg :quaternary ammonium salts or chlorhexamine are added to alginate powder. Hard and soft set alginates by adjusting the amount of fillers Chromatic Alginates Alginates which change color on setting
  24. 24. PROPERTIES FLEXIBILITY It is about 14% at a stress of 1000g/cm2. Lower w/p ratio results in lower flexibility. ELASTICITY AND ELASTIC RECOVERY Alginate are highly elastic but less when compared to the agar. 97.3% elastic recovery occurs. Permanent deformation is less if the impression is removed from the mouth quickly.
  25. 25. STRENGTH The compressive strengths of alginate gels range from 0.5 TO 0.9 MPa The tear strengths vary from 0.4 to 0.7 MPa Both of these properties are time dependent with higher values being obtained if the time of removal is delayed.
  26. 26. DIMENSIONAL STABILITY : Alginate impression loses water by evaporation and shrinks on standing in air. If it is placed in water it absorbs water and swells. Therefore ,cast should be poured immediately after making the impression. BIOLOGICAL PROPERTIES No known chemical or allergic reaction have been identified. However , avoid breathing in Silica particles after fluffing alginate powder.
  27. 27. ADHESION Alginate does not adhere well to the tray, retention is obtained by mechanical locking features in the tray or by applying an adhesive. SHELF LIFE Alginate impression material have a short shelf life. They deteriorate rapidly when stored at elevated temperatures in a humid environment. Therefore ,it is better not to stock more than 1 year supply .
  28. 28. CAUSES FOR DISTORTION AND DIMENSIONAL CHANGE OF ALGINATE IMBIBITION If an alginate impression is stored in water or in a very wet paper towel, the alginate will absorb additional water and expand. This condition is called imbibition. SYNERESIS If an alginate impression remains in the open air, moisture will evaporate from the material, causing it to shrink and distort. This condition is called syneresis.
  29. 29. ADVANTAGES OF ALGINATE It is easy to mix and manipulate Minimum requirement of equipments Flexibility of the set impression Accuracy if properly handled Low cost Comfortable to the patient Gives a good surface detail even in the presence of saliva
  30. 30. DISADVANTAGES Cant be corrected. Cannot be electroplated so metal dies are not possible Poor dimensional stability Poor tear strength It is not recommended where higher degree of accuracy is required, example: for RPD, FPD, Crowns etc.
  31. 31. THANK YOU