Dental Impressions Quiz
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Questions and Answers

Which property is essential for impression materials to capture fine details?

  • Suitable setting time
  • Dimensional stability
  • Good taste and odour
  • Sufficient fluidity (correct)

    • What type of impression material is classified as reversible?

  • Impression compound
  • Agar (correct)
  • Zinc oxide eugenol
  • Alginate

    • Which material is considered non-elastic for making dental impressions?

  • Putty
  • Impression wax (correct)
  • Polyether
  • Alginate

    • What is a key characteristic of impression plaster?

    <p>It does not flex over undercuts.</p> Signup and view all the answers

    Which of the following is NOT an ideal requirement for impression materials?

    <p>Rigid after setting</p> Signup and view all the answers

    What classification system is used for dental impressions based on the underlying tissues?

    <p>Mucocompressive and mucostatic</p> Signup and view all the answers

    Which type of dental impression material is primarily used for making removable prostheses?

    <p>Light body elastomers</p> Signup and view all the answers

    What is the disadvantage of using impression plaster?

    <p>It breaks easily when used over undercuts.</p> Signup and view all the answers

    What characteristic should impression plaster possess to fracture cleanly?

    <p>It should be weak and brittle.</p> Signup and view all the answers

    Which component is added to some impression plasters to help in the removal from casts?

    <p>Cornstarch</p> Signup and view all the answers

    What is the primary use of impression compound in clinical settings?

    <p>Creating custom impression trays</p> Signup and view all the answers

    What temperature range does high-fusing impression compound typically flow at?

    <p>135 to 140 °F</p> Signup and view all the answers

    Why is impression compound rarely used in partial denture work?

    <p>It does not accurately return to its former shape.</p> Signup and view all the answers

    What is a notable difference between Type 1 and Type 2 impression compounds?

    <p>Type 1 is used for border molding; Type 2 is for making custom impression trays.</p> Signup and view all the answers

    Which color is commonly associated with high-fusing impression compounds suitable for custom trays?

    <p>Black</p> Signup and view all the answers

    What happens to impression compound when it is heated?

    <p>It softens into a plastic mass.</p> Signup and view all the answers

    What characteristic distinguishes polysulfide impression material?

    <p>One paste is usually dark and the other is white.</p> Signup and view all the answers

    Which of the following describes a disadvantage of using polysulfides?

    <p>It has a long setting time.</p> Signup and view all the answers

    What is the main composition of silicone impression materials?

    <p>Silicone and ethyl silicate.</p> Signup and view all the answers

    Why should silicones be used in thin consistent layers?

    <p>To reduce setting shrinkage.</p> Signup and view all the answers

    What is an advantage of polysulfide impression materials?

    <p>Excellent flow for detail reproduction.</p> Signup and view all the answers

    Which elastomeric impression material is most commonly associated with removable prosthodontics?

    <p>Polysulfides.</p> Signup and view all the answers

    What is a key disadvantage of condensation reaction silicones?

    <p>They exhibit significant setting shrinkage.</p> Signup and view all the answers

    What is an important characteristic of polysulfide impression materials regarding handling?

    <p>They must be poured within half an hour.</p> Signup and view all the answers

    What is the primary purpose of low-fusion impression wax?

    <p>As a corrective liner for final impressions</p> Signup and view all the answers

    Which of the following is true about impression paste?

    <p>It consists of a base and a hardener/catalyst</p> Signup and view all the answers

    Why must low-fusion wax impressions be handled with care?

    <p>They can easily be distorted</p> Signup and view all the answers

    Which impression material is characterized by being rigid when set and not springing over undercuts?

    <p>Impression paste</p> Signup and view all the answers

    What characterizes elastomeric impression materials?

    <p>They polymerize into a rubbery state upon mixing</p> Signup and view all the answers

    In what situation is low-fusion impression wax least accurate?

    <p>In the fabrication of an impression tray</p> Signup and view all the answers

    What is the role of impression paste in denture procedures?

    <p>To reline impressions for complete dentures and RPDs</p> Signup and view all the answers

    What is a significant disadvantage of elastomeric impression materials?

    <p>They are non-reversible and can be used only once</p> Signup and view all the answers

    What is the main disadvantage of impression-type agar?

    <p>It can only be poured one time.</p> Signup and view all the answers

    Which statement accurately describes laboratory duplicating hydrocolloid?

    <p>It can be used repeatedly if properly handled.</p> Signup and view all the answers

    What is the primary use of alginate-type hydrocolloid?

    <p>Making impressions for partial dentures.</p> Signup and view all the answers

    What ingredients are typically used in making alginate impression material?

    <p>Sodium alginate and magnesium oxide.</p> Signup and view all the answers

    What is required to maintain the water balance in laboratory duplicating hydrocolloid?

    <p>Heating it in a stainless steel double boiler.</p> Signup and view all the answers

    What is one of the main purposes of using impression hydrocolloid?

    <p>For making RPD impressions.</p> Signup and view all the answers

    How must impression hydrocolloid be prepared before usage?

    <p>Heated to soften and tempered.</p> Signup and view all the answers

    What happens to impression hydrocolloid after it is used?

    <p>It undergoes dimensional change due to evaporation.</p> Signup and view all the answers

    What is the main purpose of dustless alginates?

    <p>To prevent inhalation of alginate particles</p> Signup and view all the answers

    How does evaporation affect alginate impressions?

    <p>It leads to syneresis in the material</p> Signup and view all the answers

    What should be avoided when disinfecting alginate impressions to maintain dimensional stability?

    <p>Prolonged exposure to aqueous solutions</p> Signup and view all the answers

    What are the effects of imbibition on alginate materials?

    <p>It causes fluid absorption resulting in swelling</p> Signup and view all the answers

    What method is recommended for maintaining alginate impressions before pouring?

    <p>Keeping in a humid environment</p> Signup and view all the answers

    What is a recommended method for disinfecting alginate impressions?

    <p>Applying 0.5% sodium hypochlorite spray</p> Signup and view all the answers

    What should be done if it is not feasible to pour alginate impressions immediately?

    <p>Wrap them in a moistened paper towel</p> Signup and view all the answers

    Why is it important to disinfect alginate impressions?

    <p>To eliminate microorganisms that can cause infection</p> Signup and view all the answers

    What was the primary issue with materials used for dental impressions before the introduction of agar?

    <p>They were not elastic after setting.</p> Signup and view all the answers

    What is considered a key disadvantage of using alginate as an impression material?

    <p>It has dimensional instability.</p> Signup and view all the answers

    Which of the following impression materials was developed after agar and primarily used during World War II?

    <p>Alginate</p> Signup and view all the answers

    What is the purpose of creating a dental impression?

    <p>To fabricate a dental cast.</p> Signup and view all the answers

    Which elastomeric impression material was introduced first in modern dentistry?

    <p>Polysulfide</p> Signup and view all the answers

    Which property is essential for impression materials used in partial denture work?

    <p>Capability to register undercuts.</p> Signup and view all the answers

    What is one of the primary challenges associated with digital dentistry compared to traditional impression materials?

    <p>Lack of accuracy in impressions.</p> Signup and view all the answers

    Why is there still a need for new impression materials despite advancements in technology?

    <p>No impression material is completely accurate.</p> Signup and view all the answers

    What is the primary basic ingredient of polysulfide impression material?

    <p>Polysulfide rubber</p> Signup and view all the answers

    Which of the following is an advantage of using polysulfide impression materials?

    <p>Least rigid and most flexible</p> Signup and view all the answers

    What disadvantage is commonly associated with condensation reaction silicones?

    <p>Significant setting shrinkage</p> Signup and view all the answers

    Which statement about polysulfide impression materials is false?

    <p>They can be mixed with other brands.</p> Signup and view all the answers

    Which of the following cons is associated with using polysulfide impression materials?

    <p>Requires immediate pouring within thirty minutes</p> Signup and view all the answers

    What is the primary benefit of the low viscosity in polysulfide materials?

    <p>Accurate registration of tissues</p> Signup and view all the answers

    What is a significant disadvantage of silicone materials during the impression process?

    <p>They shrink if allowed to sit for too long.</p> Signup and view all the answers

    Which of the following is a characteristic of polyvinylsiloxanes?

    <p>They do not require a uniform thickness for accurate impressions.</p> Signup and view all the answers

    What method typically uses silicone materials during the dental impression process?

    <p>Two-phase impression method</p> Signup and view all the answers

    What is a common challenge faced when using polyvinylsiloxanes?

    <p>Interference from latex materials during polymerization.</p> Signup and view all the answers

    Which characteristic is most closely associated with the odor of polysulfide impression materials?

    <p>Foul smell</p> Signup and view all the answers

    What is the main consequence of exposing gelled hydrocolloid to air or water?

    <p>It alters the dimensions quickly.</p> Signup and view all the answers

    Which of the following best describes the setting reaction of dental alginates?

    <p>It involves a sol to gel transformation in two steps.</p> Signup and view all the answers

    How does the setting reaction of polyvinylsiloxanes occur?

    <p>By reacting hydrosilane-terminated molecules with vinyl end groups.</p> Signup and view all the answers

    What is an advantage of using polyvinylsiloxanes in dental impressions?

    <p>They allow for excellent dimensional stability.</p> Signup and view all the answers

    What is the primary function of the potassium sulfate solution in handling reversible hydrocolloid impressions?

    <p>To fix the surface quality of the cast.</p> Signup and view all the answers

    What is a reason for the short setting time in polyvinylsiloxanes?

    <p>It minimizes the production of hydrogen gas.</p> Signup and view all the answers

    Which factor does NOT affect the setting reaction time of dental alginates?

    <p>Type of gypsum used.</p> Signup and view all the answers

    What characteristic of impression plaster helps in creating an accurate impression?

    <p>It is weak and brittle.</p> Signup and view all the answers

    What is the typical maximum time frame to pour hydrocolloid impressions after setting?

    <p>10 minutes.</p> Signup and view all the answers

    Which factor must be considered when using addition silicone materials?

    <p>The impression area must be dry to ensure accuracy.</p> Signup and view all the answers

    What is a common additive to impression plaster that aids in its removal from casts?

    <p>Cornstarch</p> Signup and view all the answers

    How does the addition of more water during alginate mixing affect the material?

    <p>It decreases viscosity.</p> Signup and view all the answers

    What impact does hydrogen gas production have on impressions made with polyvinylsiloxanes?

    <p>It can cause pitting in the final cast.</p> Signup and view all the answers

    Which impression compound type is generally used for border molding?

    <p>Type 1 - Low fusing</p> Signup and view all the answers

    Which of the following statements about alginate setting times is true?

    <p>Type I alginate hardens faster than Type II.</p> Signup and view all the answers

    What property does high-fusing impression compound exhibit during use?

    <p>Flows at approximately 135 to 140 °F.</p> Signup and view all the answers

    What is an essential characteristic of alginates as mucostatic impression materials?

    <p>They capture soft tissues without compression.</p> Signup and view all the answers

    Which application is NOT a primary use of impression compound?

    <p>Filling cavities</p> Signup and view all the answers

    What is a key advantage of using elastomeric impression materials over other types?

    <p>They possess excellent dimensional stability.</p> Signup and view all the answers

    What is a significant limitation of using impression compound in partial denture work?

    <p>It does not accurately conform to undercuts.</p> Signup and view all the answers

    Which impression material is classified as irreversible?

    <p>Impression plaster</p> Signup and view all the answers

    What is the primary characteristic of Type 2 impression compound?

    <p>It can be softened and reshaped.</p> Signup and view all the answers

    Why must impression plaster be broken into pieces for removal?

    <p>It lacks elasticity and cannot adjust to undercuts.</p> Signup and view all the answers

    Which of the following is NOT a requirement for ideal impression materials?

    <p>Compatibility with dental tools</p> Signup and view all the answers

    Which consistency of impression material is best for capturing fine details in a mucostatic impression?

    <p>Light body</p> Signup and view all the answers

    Which classification of dental impressions includes alginate materials?

    <p>Irreversible impression materials</p> Signup and view all the answers

    What is the primary characteristic of mucocompressive impression materials?

    <p>They exert pressure on the underlying tissues.</p> Signup and view all the answers

    What necropsy material is primarily recommended for secondary impressions?

    <p>Elastomeric putty</p> Signup and view all the answers

    Study Notes

    Introduction to Impression Materials

    • A variety of impression materials are used in dental clinics.
    • Each material has slightly different properties.
    • Complete denture work needs a material that accurately records all denture-bearing areas.
    • Partial denture work has an additional requirement, capable of registering both tooth and soft tissue undercuts.
    • Often, multiple materials are used in sequence to take advantage of their individual properties.

    History of Impression Materials

    • Wax was the sole impression material until the mid-19th century.
    • Gutta-percha and then thermoplastic modeling compound (similar to today's impression compound) emerged.
    • Early materials were rigid and couldn't accurately reproduce undercuts.
    • Agar, a reversible hydrocolloid material from algae, was a significant advancement as it maintained elasticity after setting.
    • Alginate, derived from local algae during World War II, gained popularity due to the unavailability of agar.
    • Elastomeric materials (rubber-based) like polysulfides, condensation silicones, polyethers, and addition silicones followed.
    • Digital dentistry is also becoming increasingly important.

    What is an Impression?

    • An impression is a negative replica of tissues (teeth and surrounding oral structures).
    • Impressions are created to be poured with dental plaster, forming a dental cast.

    What is a Dental Cast?

    • A dental cast is a positive replica of oral tissues.
    • It's a three-dimensional model used for analyzing cases, making prostheses, and creating occlusal splints/mouthguards.

    Ideal Requirements of Impression Materials

    • Sufficient fluidity to capture fine details.
    • Suitable working time (setting time).
    • Sufficient mechanical strength to prevent tearing or deformation during insertion/removal.
    • Sufficient dimensional stability.
    • Compatible with die and cast materials.
    • Safe (non-toxic or non-irritating).
    • Acceptable to patients (pleasant taste, color, and odor).
    • Good keeping qualities.

    Classification of Impression Materials

    According to Behavior After Setting

    • Non-Elastic: Fracture or permanent distortion during removal from undercuts.
      • Plastic impression, impression compound, zinc oxide-eugenol.
    • Elastic: Recovers after removal from undercuts.
      • Hydrocolloids (agar / alginate), elastomers (polysulfide, condensation silicones, addition silicones, polyether).

    According to Setting

    • Chemical reaction: Plaster impression, zinc oxide eugenol.
    • Physical changes: Impression compound, agar.

    According to Use

    • Complete dentures: Plaster impression, zinc oxide-eugenol, impression compound, alginate.
    • Partial dentures: Alginate, elastomers (elastomers).
    • Crowns and bridges: Elastomers.

    Impression Plaster and Soluble Impression Plaster

    • Specifically compounded for use in the mouth.
    • Fast-setting to minimize time in the mouth.
    • Brittle and weak to allow for fracturing and reassembly outside the mouth.
    • Properties are adjusted with added accelerators/retarders and/or color/flavoring.
    • Sometimes made water-soluble for easier removal.

    Impression Compound/Modeling Compound

    • Thermoplastic, rigid, and reversible impression material.
    • Softened by heat, hardened by cooling.
    • Used for preliminary impressions, custom impression trays, modifying stock trays.
    • Limited use in partial denture work due to lack of undercut reproduction.

    Impression Wax

    • Low-fusing impression wax: specially formulated for controlled flow under pressure in the mouth.
    • Used for corrective liners, final impressions or relines for complete dentures and RPDs.
    • Handling in the lab must be careful to avoid distortions.
    • Requires water bath melting and application to impression tray. May not accurately capture details in the impression.

    Impression Paste (Zinc Oxide Eugenol Paste)

    • Supplied as a base and a hardener/catalyst.
    • Mixed in specific proportions to form a paste that is rigid upon setting.
    • Used primarily for corrective lining within immediate denture and RPD work.
    • It can be a liner in sectional impressions.
    • Used in some instances to make the impression fit the cast and mouth.

    Elastomeric Impression Materials

    • These materials are two-part systems: a base and an accelerator paste (sometimes liquid).
    • The mixture polymerizes (or cures) into a rubbery state for irreversible reactions.
    • Primarily used in the production and preparation of crowns and bridges. Also used for:
      • Fixed prosthodontics
      • Corrective liners
      • Complete dentures impressions

    Types of Elastomeric Impression Materials

    • Polysulfides
    • Silicones (condensation reaction silicones)
    • Polyvinylsiloxanes (addition reaction silicones)
    • Polyethers

    Polysulfides

    • The primary ingredient is polysulfide rubber with fillers, pigments, and modifiers.
    • The pastes are usually dark and white for easy identification.
    • Has a unique odour.
    • Low viscosity allows accurate registration of soft and hard tissues.
    • Most often used in removable prosthodontics.

    Silicones

    • The impression material contains silicone and ethyl silicate.
    • Used in a two-phase method (either on the mouth or diagnostic cast).
    • A putty form of the material is first used with a stock tray.
    • A wash impression is made using a lower viscosity silicone material..
    • Lighter in color and translucent.

    Polyvinylsiloxanes

    • Materials are similar to conventional silicones in nature but differ in their chemical structure and reactions.
    • Polymerization shrinkage is well controlled and the material thickness is not critical..
    • Used in a two-stage impression technique.

    Polyethers

    • Base is a polyether compound, accelerator is a sulfonic acid.
    • Laboratory studies show these materials are among the most accurate in the field of elastomers.
    • The materials are stiff when set, making removal from the mouth difficult, especially in cases with significant tooth undercuts.
    • Available in several consistencies (light, medium, and heavy).

    Hydrocolloids

    • Materials elastically deform and return to their initial shape, accurately capturing undercuts.
    • Two basic types: agar and alginate.
      • Agar (reversible)
      • Alginate (irreversible)

    Agar Hydrocolloids (Reversible)

    • Gelatin-like material composed mainly of agar-agar.
    • Mixed with water and heated to soften.
    • Tempered and placed into tray, cooled to form gel.
    • Used for duplicating in labs and for making RPD and fixed prosthodontic impressions.
    • One-time use due to the dimensional change caused by evaporation or drying out.

    Alginate Hydrocolloids (Irreversible)

    • A fine powder that mixes with water.
    • Ingredients include: Sodium/Potassium alginate, plaster materials, magnesium oxide, trisodium phosphate, sodium phosphate and diatomaceous earth.
    • Used as an impression material for partial dentures and also used for immediate dentures and cast duplication.
    • Requires more water for duplication.
    • Materials may be in the form of powder or a sol/paste.

    Setting Reaction of Alginate

    • The setting reaction involves two stages: retardation and gelation reactions.
    • The primary reaction creates calcium sulfate and sodium sulfate, controlling the manipulation time. In the gelation stage, Potassium alginate and Calcium sulfate create calcium alginate gel.

    Types of Alginate Based on Setting Time

    • Type I: Fast set (hardening in 1–2 minutes).
    • Type II: Standard set (hardening in 2–5 minutes).
    • Setting time depends on water temperature and water-to-powder ratio. Higher the water temperature, faster the setting reaction.

    Modified Alginates

    • Dustless alginates are manufactured to prevent inhalation.
    • The particles are coated with glycerin or a similar substance for better handling.
    • Chromatic alginates change color during mixing.

    Alginate Properties

    • Sufficient dimensional stability over time for pouring. Alginate impressions can swell, shrink or change shape over time from water absorption, evaporation of water or expulsion of water.
    • Imbibition is fluid absorption leading to swelling.
    • Syneresis is the expulsion of liquid from the gel.
    • The best pouring time is as soon as possible, or ideally in a humid environment.

    Alginate Disinfection

    • Alginate disinfection must be carried out carefully to avoid material distortion from material swelling.
    • Rinse impressions with tap water to remove any residual moisture before disinfection.
    • Solutions of 0.5 % sodium hypochlorite or 2% glutaraldehyde can be used.

    Advantages and Disadvantages of Impression Materials

    • Detailed information on advantages and disadvantages for each impression material is provided throughout the study notes..

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    Description

    Test your knowledge on the properties and classifications of dental impression materials. Explore different types, their uses, and essential characteristics. This quiz covers fundamental concepts crucial for dental practices.

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