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Questions and Answers
What is a requirement for the impression material after it has set?
What is a requirement for the impression material after it has set?
Which characteristic is NOT essential for setting impression materials?
Which characteristic is NOT essential for setting impression materials?
Which of the following describes thermoset impression materials?
Which of the following describes thermoset impression materials?
When are non-elastic impression materials typically used?
When are non-elastic impression materials typically used?
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What is the method of setting for thermoplastic impression materials?
What is the method of setting for thermoplastic impression materials?
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What is the elastic recovery percentage of the impression material mentioned as more elastic than polysulfides?
What is the elastic recovery percentage of the impression material mentioned as more elastic than polysulfides?
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Which characteristic of polyether impression material differentiates it from other rubbers in terms of flexibility?
Which characteristic of polyether impression material differentiates it from other rubbers in terms of flexibility?
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Which of the following is a disadvantage of the optical impression technique?
Which of the following is a disadvantage of the optical impression technique?
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What is the rate of polymerization shrinkage for polyether impression material within 24 hours?
What is the rate of polymerization shrinkage for polyether impression material within 24 hours?
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Which of the following is a key advantage of using polysulfide impression material?
Which of the following is a key advantage of using polysulfide impression material?
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What is a disadvantage of using alginate impression material?
What is a disadvantage of using alginate impression material?
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Which impression material is categorized as a non-elastic material?
Which impression material is categorized as a non-elastic material?
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Which process describes the absorption of water by impression materials?
Which process describes the absorption of water by impression materials?
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What is required to prevent syneresis and imbibition when storing alginate materials?
What is required to prevent syneresis and imbibition when storing alginate materials?
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Which of the following is an advantage of using alginate as an impression material?
Which of the following is an advantage of using alginate as an impression material?
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Which impression material is categorized under elastomers?
Which impression material is categorized under elastomers?
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Which of the following is NOT a property associated with hydrocolloid materials like alginate?
Which of the following is NOT a property associated with hydrocolloid materials like alginate?
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What type of impression material is Agar primarily classified as?
What type of impression material is Agar primarily classified as?
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What is the primary advantage of using elastomeric impression materials over Agar?
What is the primary advantage of using elastomeric impression materials over Agar?
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What is a characteristic of polysulfide rubber impression material?
What is a characteristic of polysulfide rubber impression material?
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Which of the following is NOT a type of mixing system used for elastomeric impression materials?
Which of the following is NOT a type of mixing system used for elastomeric impression materials?
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What is a disadvantage of condensation silicone?
What is a disadvantage of condensation silicone?
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Which technique combines multiple viscosities during the impression process?
Which technique combines multiple viscosities during the impression process?
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Which elastomeric impression material has the highest resistance to tear?
Which elastomeric impression material has the highest resistance to tear?
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What is the final setting time range for polysulfide rubber impression materials?
What is the final setting time range for polysulfide rubber impression materials?
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What is the primary chemical by-product causing dimensional instability in polysulfides?
What is the primary chemical by-product causing dimensional instability in polysulfides?
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Study Notes
Impression Materials
- Set impressions are negative reproductions of oral tissues. A positive reproduction is achieved by pouring a suitable model or die material into the set impression.
Desirable Properties for Impression Materials
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Adequate shelf life: Impression materials should last a sufficient time before use.
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Acceptable odour and taste: The material should not be overly pungent or unpleasant in taste.
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Biologically acceptable: The material shouldn't contain toxic or irritating constituents.
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Easily manipulated: The material should be easy to work with minimal equipment.
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Setting characteristics:
- Suitable working time: The time the material is workable.
- Suitable setting time: The time it takes for the material to set.
- Readily wets oral tissues: The material should have good contact with the tissues
- Not affected by oral fluids: The material should not react with saliva or other oral fluids.
- Does not release gas during setting: The material should not generate gases during setting.
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Properties of the set material:
- Sufficient mechanical strength: Should not break or tear on removal from the mouth.
- Elastic properties: Should not deform permanently after a strain.
- Good dimensional accuracy: Should create an accurate representation of the oral tissues.
- Dimensional stability: Stable over temperature and humidity ranges encountered in clinical and lab settings.
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No ideal impression material satisfies all requirements. Clinicians must select the best material for the clinical situation and techniques.
Classifications of Impression Materials
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Method of setting:
- Hardening by chemical reaction (thermoset): Plaster of Paris, alginates, and rubber impression materials (irreversible).
- Softening and hardening by heat (thermoplastic): These materials are reversible.
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Behavior after setting:
- Non-elastic: Used when there are no undercuts (e.g., Plaster of Paris, Zinc oxide eugenol).
- Elastic: Used when undercuts exist (e.g., hydrocolloids, rubber impression materials).
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Classification tree displays various impression materials, and their characteristics:
- Non-Elastic: Waxes, Plaster, Zinc-Eugenol compound
- Elastic: Alginate, Agar, Hydrocolloid, Rubber base (Elastomers): Poly-sulfides, Silicone (Addition, Condensation), Polyether
Non-Elastic Impression Materials
- Wax: A pliable material used in various dental procedures.
- Impression plaster (Plaster of Paris): A common material for creating models and casts.
- Impression compound: A material used for taking impressions.
- Zinc oxide-eugenol impression material: A compound used in dental practices.
Hydrocolloids
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Definitions: Solutions, suspensions, colloids
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Sol to Gel Transformation:
- Reduction in temperature
- Chemical reaction: Agar impression material, Alginate impression material
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Dimensional Effects by Syneresis and Imbibition:
- Syneresis: Loss of water, leading to shrinkage.
- Imbibition: Absorption of water, leading to expansion
Alginate Impression Material
- Advantages: Easy to mix and manipulate, minimal equipment, flexible, accurate, inexpensive
- Disadvantages: Limited material options for the models and die material, not accurate in fine details replication
- Uses: Preparing study casts, preparing gypsum models, removable partial denture, athletic mouth protectors
- Storage: Stored in 100% relative humidity to prevent syneresis/imbibition and shrinkage/expansion
- Manipulation Equipment: Powder-dispensing cup, water-dispensing cup, rubber mixing bowel, spatula
Agar Impression Materials
- Advantages: Excellent accuracy, highly accurate, elastic
- Disadvantages: Difficult manipulation, dimensional instability, patient discomfort from thermal shock
- 3-chamber conditioning unit: Boiling, storage, tempering
Rubber Base Impression Materials (Elastomers)
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Definition: Non-aqueous, elastomeric materials that are rubber-like, formed by long chain coiled molecules
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Advantages: High accuracy, more dimensional stability than Agar and alginate, easy manipulation, can be used with undercuts, can be electroplated
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Consistencies: Low (Syringe/wash), Medium (Regular), High (Tray), Putty (Extra high)
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Mixing systems: Hand mixing, Auto-mixing, and Dynamic mechanical mixing
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Types of Elastomeric Impression Materials: Polysulfides, Silicones (Addition, Condensation), and Polyether
Polysulfides
- Advantages: High dimensional stability, high strength and tear resistance, can be electroplated
- Disadvantages: Dimensional instability (water by-product), hydrophobic, bad odor (sulfide odor), staining of clothes. Relatively long setting time
Silicones
- Condensation silicones: Solve many problems of polysulfides. Advantages: moderate working time, better odor and taste, less permanent deformation. Disadvantages: hydrophobic, dimensional instability (alcohol by-product)
- Addition silicones: Advantages: accuracy, Dimension stability. Disadvantages: less flexible, lower flow
Polyethers
- Advantages: Better mechanical properties than polysulfides, less dimensional change than condensation silicone.
- Disadvantages: High working time, high stiffness, high cost
- Properties: High accuracy, dimensional stability with 0.25% shrinkage within 24 hours, least flexibility of all rubbers, viscoelastic with 98.9% elastic recovery, excellent compatibility, better tear strength than silicone, but less than polysulfides, Disinfectants compatible
Recent Advances in Impression Materials
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Optical Impression:
- Advantages: No need for materials or trays, impressions are transmitted and stored electronically, no mess, 3D/360° view of preparation is easily maneuvered, adjustments are made to virtual impressions (no need for second impression), no disinfection required.
- Disadvantages: High start-up cost, technique sensitivity, and requires more equipment.
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Description
Test your knowledge on various types of dental impression materials and their characteristics. This quiz covers essential aspects such as elasticity, setting methods, and advantages and disadvantages of each type. Perfect for dental students and professionals looking to refresh their understanding.
