7.impression materials and techniques 2
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Dr. lama khaled El Banna Faculty of Oral and Dental Medicine Al – Azhar University Fixed prosthodontic
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7.impression materials and techniques 2
- 1. FIXED PROSTHODONTIC I Department of Fixed Prosthodontics
- 2. Impression materials Impression materialImpression material ElasticElastic NonelasticNonelastic HydrocolloidsHydrocolloids Zinc oxide eugenolZinc oxide eugenol Impression CompoundImpression Compound PlasterPlaster Non-aqueous elastomers Non-aqueous elastomers AgarAgar AlginateAlginate PolyethersPolyethers Addition silicone Addition silicone Condensation silicone Condensation silicone PolysulfidesPolysulfides Impression waxImpression wax
- 3. Hydrocolloid Impression Materials -Hydro means water. -Colloid means gelatin substance. -Material used to obtain preliminary impressions.
- 4. Irreversible Hydrocolloid “Alginate is the irreversible hydrocolloid most widely used for preliminary impressions”.
- 5. Makeup of Alginate Sodium alginate -As a thickening agent. Calcium sulfate -Reacts with the potassium alginate to form the gel. Trisodium phosphate -Added to slow down the reaction time for mixing.
- 6. Makeup of Alginate Diatomaceous earth -A filler that adds bulk to the material. Zinc oxide -Adds bulk to the material. Potassium titanium fluoride -Added so as not to interfere with the setting and surface strength.
- 7. 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.
- 8. Packaging and Storing of Alginate -Containers about the size of a coffee can are the most commonly used form of packaging. -Premeasured packages are more expensive, but save time by eliminating the need for measurement of the powder. -Shelf life of alginate is approximately 1 year.
- 9. Examples of packaging for alginate
- 10. Causes for Distortion and Dimensional Change of Alginate -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. -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.
- 11. Alginate Settings 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. 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.
- 12. Altering the Setting Times of Alginate -Cooler water can increase the setting time if additional time is needed for the procedure. -Warmer water can reduce or shorten the setting time of the procedure.
- 13. 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.
- 14. Scoop and water measure for alginate
- 15. Taking an Alginate Impression Explain the procedure to the patient: -The material will feel cold, there is no unpleasant taste, and the material will set quickly. -Breathe deeply through your nose to help you relax and be more comfortable. -Use hand signals to communicate any discomfort!
- 16. An Acceptable Alginate Impression -The impression tray is centered over the central and lateral incisors. -There is a complete "peripheral roll," which includes all of the vestibular areas. -The impression is free from tears or voids. -There is sharp anatomic detail of all teeth and soft tissues. -The retromolar area, lingual frenum, tongue space, and mylohyoid ridge are reproduced in the mandibular impression. -The hard palate and tuberosities are recorded in the maxillary impression.
- 18. Elastomeric Impression Materials “A material that is used when an extremely accurate impression is essential. The term elastomeric means having elastic or rubberlike qualities”.
- 19. Characteristics or Elastomeric Impression Materials Base Packaged as a paste in a tube, as a cartridge, or as putty in a jar. Catalyst Also known as the accelerator, is packaged as a paste in a tube, as a cartridge, or as a liquid in a bottle with a dropper top.
- 20. Forms of Elastomeric Materials Light-bodied Also referred to as syringe type, or wash type. This material is used because of its ability to flow in and about the details of the prepared tooth. A special syringe, or extruder, is used to place the light-bodied material on and immediately around the prepared teeth.
- 21. Forms of Elastomeric Materials Regular and heavy-bodied Often referred to as tray type materials,‑ they are much thicker. As the names imply, they are used to fill the tray. Their stiffness helps to force the light bodied‑ material into close contact with the prepared teeth and surrounding tissues to ensure a more accurate impression of the details of a preparation
- 22. Basic Impression Technique 1.The material selected depends upon the dentist’s preference and the type of impression required for the procedure. 2.The dentist prepares the tooth or teeth for the impression. 3.The light-bodied material is prepared and loaded into the syringe and transferred to the dentist. 4.The dentist places the light-bodied material over and around the prepared teeth and onto the surrounding tissues. 5.The heavy-bodied material is prepared and loaded into the tray and transferred to the dentist. 6.When the impression material has reached final set, the impression is removed and inspected for accuracy. 7.The impression is disinfected, placed in a biohazard bag, labeled, and readied for the laboratory technician.
- 23. Types of Elastomeric Materials Polyether Silicone Polyvinyl siloxane Polysulfide
- 24. Polyether Impression Material Chemical makeup Base: Polyether Cross-linking agent: Sulfate Catalysts: Glycol-based plasticizers Filler: Silica
- 25. Manipulation and Technique Considerations for Polyether Material -Material is very stiff, which makes it difficult to remove without rocking. -Water, saliva, and blood affect polyether material. -Added moisture will increase the impression’s marginal discrepancy. -Increased water absorption occurs if a thinning agent is used.
- 26. Steps: 1(Tray selection 2(Preparation of the square 3(Impression 4(Removal of the impression
- 27. many problems impression tray 1(Tray selection
- 28. Aesculap tray for lower with full dentition
- 29. Set of Aesculap
- 30. Deformation
- 31. preparation of the square Placement of the retraction cord
- 32. The instrument must be angled slightly toward the root to facilitate the subgingival placement of the cord
- 33. Finish
- 34. 3(Impression
- 37. Cutting Remove any undercuts Remove any interdental septum Do not cut to prepared surfaces
- 39. undercuts in lower 4(Removal of the impression
- 41. Undercuts in the upper
- 43. Which one of the impression materials we choose? •What’s the job you do? primary impression final impression •How accurate do you want? removable denture fixed prostheses •What technique do you use?