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. (A)</p> Signup and view all the answers

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

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

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

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

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

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

What is the disadvantage of using impression plaster?

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

What characteristic should impression plaster possess to fracture cleanly?

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

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

<p>Cornstarch (A)</p> Signup and view all the answers

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

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

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

<p>135 to 140 °F (A)</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. (B)</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. (A)</p> Signup and view all the answers

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

<p>Black (C)</p> Signup and view all the answers

What happens to impression compound when it is heated?

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

What characteristic distinguishes polysulfide impression material?

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

Which of the following describes a disadvantage of using polysulfides?

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

What is the main composition of silicone impression materials?

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

Why should silicones be used in thin consistent layers?

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

What is an advantage of polysulfide impression materials?

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

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

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

What is a key disadvantage of condensation reaction silicones?

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

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

<p>They can easily be distorted (D)</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 (B)</p> Signup and view all the answers

What characterizes elastomeric impression materials?

<p>They polymerize into a rubbery state upon mixing (D)</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 (A)</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 (C)</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 (C)</p> Signup and view all the answers

What is the main disadvantage of impression-type agar?

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

Which statement accurately describes laboratory duplicating hydrocolloid?

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

What is the primary use of alginate-type hydrocolloid?

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

What ingredients are typically used in making alginate impression material?

<p>Sodium alginate and magnesium oxide. (D)</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. (A)</p> Signup and view all the answers

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

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

How must impression hydrocolloid be prepared before usage?

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

What happens to impression hydrocolloid after it is used?

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

What is the main purpose of dustless alginates?

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

How does evaporation affect alginate impressions?

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

What are the effects of imbibition on alginate materials?

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

What method is recommended for maintaining alginate impressions before pouring?

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

What is a recommended method for disinfecting alginate impressions?

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

Why is it important to disinfect alginate impressions?

<p>To eliminate microorganisms that can cause infection (B)</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. (A)</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. (A)</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 (D)</p> Signup and view all the answers

What is the purpose of creating a dental impression?

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

Which elastomeric impression material was introduced first in modern dentistry?

<p>Polysulfide (D)</p> Signup and view all the answers

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

<p>Capability to register undercuts. (B)</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. (B)</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. (C)</p> Signup and view all the answers

What is the primary basic ingredient of polysulfide impression material?

<p>Polysulfide rubber (A)</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 (D)</p> Signup and view all the answers

What disadvantage is commonly associated with condensation reaction silicones?

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

Which statement about polysulfide impression materials is false?

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

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

<p>Accurate registration of tissues (B)</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. (C)</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. (B)</p> Signup and view all the answers

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

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

What is a common challenge faced when using polyvinylsiloxanes?

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

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

<p>Foul smell (C)</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. (C)</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. (C)</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. (A)</p> Signup and view all the answers

What is an advantage of using polyvinylsiloxanes in dental impressions?

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

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

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

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

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

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

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

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

<p>Cornstarch (C)</p> Signup and view all the answers

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

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

Which impression compound type is generally used for border molding?

<p>Type 1 - Low fusing (D)</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. (D)</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. (D)</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. (C)</p> Signup and view all the answers

Which application is NOT a primary use of impression compound?

<p>Filling cavities (B)</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. (A)</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. (C)</p> Signup and view all the answers

Which impression material is classified as irreversible?

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

What is the primary characteristic of Type 2 impression compound?

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

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

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

Which classification of dental impressions includes alginate materials?

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

What is the primary characteristic of mucocompressive impression materials?

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

What necropsy material is primarily recommended for secondary impressions?

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

Flashcards

Dental Impression Materials

Materials used to create a three-dimensional replica of the mouth for dental procedures.

Ideal Impression Material Properties

Properties of impression materials needed for accurate and useful dental models, including fluidity to capture fine details, suitable setting times, strength, dimensional stability, compatibility, safety, and patient acceptance.

Impression Plaster

A rigid, quick-setting dental impression material used for making detailed models of the oral cavity.

Impression Compound

A rigid dental impression material that is used to obtain an impression of the oral cavity.

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Impression Wax

A pliable material used for taking dental impressions, especially for temporary or diagnostic purposes.

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Impression Paste

A broad term for dental impression materials that involve a viscous or semi-solid substance for taking impressions.

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Classification of Impressions (Use)

Dental impressions are categorized by their intended use, such as primary (initial) or secondary (more detailed).

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Setting Reaction Classification

Dental impression materials are classified by their setting mechanism, either reversible (physical) or irreversible (chemical).

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Impression Plaster Properties

Needs to be weak and brittle for clean fracture and have a low setting expansion for accurate impression.

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Impression Compound Uses

Used for preliminary impressions, custom impression trays, and modifying stock trays.

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Low Fusing Impression Compound

A type of impression compound with a lower melting point.

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High Fusing Impression Compound

Type of Impression Compound used to create custom impression trays with a higher melting point.

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Impression Compound Limitations

Doesn't mold around deep grooves (undercuts) well, limiting its use in partial denture work.

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Impression Compound Solubility

Some impression plasters can be made water-soluble to help remove them from casts easily.

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Impression wax properties

Low-fusing impression wax flows under pressure, melts in water, and is used as a corrective liner. It's also used for relines.

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Impression wax handling

Handle impression wax carefully to avoid distortion, using care to not come in contact with the tissue side of impression and periphery. Rinse with room-temperature water (carefully).

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Impression paste composition

Impression paste is a mixture of zinc oxide and eugenol/lauric acid. It's two parts mixed to form a rigid paste that does not spring.

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Impression Paste Uses

Impression paste is primarily used as a corrective material, relines complete and RPD impressions.

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Elastomeric Impression Material

Elastomeric materials are two-part systems (base and accelerator) that polymerize to a rubbery state. They are used for precision impressions (crowns, bridges, implants).

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Elastomeric Material Properties

Elastomeric materials are not reversible and are used only once, important for accuracy in specific dental tasks like crown & bridges.

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Separator for casts

A separator is not required when casting from impression paste or low-fusing wax impressions, however, not used due to inaccuracies in detail from the impression.

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Type 1 stick impression compound use

Type 1 stick impression compound is softened over a flame and placed on the borders of a custom impression tray.

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Polysulfides

A type of elastomeric material; one paste is dark, the other white; has a distinctive odor and low viscosity.

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Silicone Impression Material

Two-part silicone material; shows setting shrinkage; often used with a custom tray for accurate impressions.

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Setting Shrinkage

A reduction in volume during the hardening process of a material.

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Cross-mixing Pastes

Never mix elastomeric pastes from different brands; can cause issues.

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Custom Tray

A tray specifically tailored to a patient's mouth for making impressions.

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Polysulfide Odor

Polysulfide materials have a distinguishing smell.

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Biocompatible

Materials that do not harm living tissues.

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What are hydrocolloids?

They are impression materials used in dentistry to create a replica of the mouth. There are two main types: agar (reversible) and alginate (irreversible).

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What makes agar hydrocolloid special?

It's a reversible material, meaning it can be heated and softened, then cooled and set, multiple times.

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What's the main use of agar hydrocolloid?

It's primarily used for taking impressions for creating RPDs (removable partial dentures) and fixed prosthodontic models.

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Why is a double boiler important for agar?

It ensures the material maintains the correct water balance, crucial for accurate setting.

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What makes alginate different from agar?

It's irreversible, meaning it sets permanently after being mixed with water.

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What's a major advantage of alginate?

It's easy to use, as it's supplied as a powder that simply needs water for mixing and setting.

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What's the main use of alginate?

It's widely used for taking impressions for making partial dentures.

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What's a key disadvantage of alginate?

It's not reusable, meaning only one cast can be poured from the impression.

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Dustless Alginate

Alginate impression material modified to prevent inhalation of particles. The particles are coated with glycol or glycerine to increase their density.

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Chromatic Alginate

Alginate that changes color during mixing to guide the setting time. It helps make sure the impression is ready to take.

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Alginate Impression Stability

Alginate impressions lose accuracy over time due to processes like imbibition (swelling) and syneresis (expulsion of liquid).

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Storing Alginate Impressions

To preserve the shape of an alginate impression, store it in a humid environment, like wrapping it in a damp paper towel.

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Disinfecting Alginate

Alginate impressions must be disinfected to prevent the spread of microorganisms. Use 0.5% sodium hypochlorite spray or 2% glutaraldehyde.

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Excessive Immersion of Alginate

Avoid prolonged soaking of alginate in water as this can lead to swelling and distortion of the impression.

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Alginate Disinfection Steps

  1. Rinse the impression to remove saliva or blood. 2. Disinfect with sodium hypochlorite spray or glutaraldehyde. 3. Rinse again to remove any remaining disinfectant.
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Why Disinfect Alginate?

Disinfection is important as dental materials can transmit microorganisms that can cause infections.

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Dental Impression

A negative replica of teeth and surrounding oral structures, creating a mold for a dental cast.

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Dental Cast

A positive reproduction of teeth and oral tissues, created by pouring dental plaster into a dental impression.

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What makes a good impression material?

It should accurately capture details, remain stable over time, and be easy to handle and use.

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Why were early impression materials problematic?

They became rigid after setting, making it impossible to capture undercuts and detailed oral structures.

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Why is Alginate so Popular?

It's easy to use, affordable, and sets quickly, making it ideal for routine impressions.

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What are Elastomers?

Rubber-like impression materials that provide accurate details and offer better dimensional stability than hydrocolloids.

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What is Setting Shrinkage?

A reduction in size or volume of a material as it hardens or sets. This can affect the accuracy of dental impressions.

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Impression Material Types

Dental impression materials fall into two main categories: rigid and elastic. Rigid materials, like plaster, are good for making detailed copies but don't bend well. Elastic materials, like alginate, can easily capture the shape of the teeth and gums because they can flex.

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Mucostatic vs. Mucocompressive

Mucostatic impression materials, like plaster, create a replica of the mouth without pressing on the tissues. Mucocompressive materials, like compound, compress the tissues slightly for a more accurate impression.

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What is Impression Compound?

Impression compound is a rigid material used for preliminary impressions. It's useful for custom trays and making basic models of the teeth and gums.

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Alginate: Irreversible Hydrocolloid

Alginate is a powder mixed with water to form an elastic material that sets permanently. It's widely used for partial denture impressions.

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Why Disinfect Alginate Impressions?

Disinfecting alginate impressions is crucial to prevent the spread of germs. Use a disinfectant like sodium hypochlorite spray or glutaraldehyde to kill bacteria and viruses.

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Impression Plaster: Rigid Material

Impression plaster is a quick-setting, rigid material used for making impressions of the mouth. Because it's brittle, it needs to be broken apart to be removed, making it less popular for most dental procedures.

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Why Water-Soluble Impression Plaster?

Some impression plasters include cornstarch to make them water-soluble, allowing easy removal from a cast.

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Impression Compound - Reusable?

Impression compound is a thermoplastic, meaning it can be softened and reused for multiple impressions in the same patient.

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Type 1 Stick Impression Compound

Type 1 stick impression compound is softened over a flame and placed on the borders of a custom impression tray to create a precise fit.

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Cross-mixing Elastomeric Pastes

Never mix elastomeric pastes from different brands. It can lead to unpredictable reactions and potentially affect the final impression.

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Advantages of Polysulfides

Polysulfide impression material offers advantages like flexibility, good tear strength, biocompatibility, excellent flow, and hydrophilicity.

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Disadvantages of Polysulfides

Polysulfides have disadvantages including a requirement for a custom tray, long setting time, bad odor, unpleasant taste, and potential staining of clothes.

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Two-Phase Impression Method

A technique where a putty silicone is used to create a custom tray for a second, more detailed impression with a lower viscosity silicone material.

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Silicone Material

A type of dental impression material known for its translucency, subdued odor, and good elastic recovery. It's commonly used for accurate reproduction of teeth and oral structures.

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Setting Shrinkage (Silicone)

A disadvantage of silicone materials where they shrink in size if left to sit for more than 30 minutes before pouring the impression.

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Polyvinylsiloxane

Another type of dental impression material that's similar to silicone but has a controlled polymerization shrinkage. It's used for accurate impressions, even with thin material layers.

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Two-Stage Impression Technique

A method used with polyvinylsiloxanes where the impression is taken in two steps. This allows for greater accuracy and detailed reproduction.

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Setting Reaction (Polyvinylsiloxane)

The chemical reaction that makes polyvinylsiloxane harden. It involves a base paste, an accelerator paste, and a platinum catalyst.

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Hydrogen Gas Production (Polyvinylsiloxane)

A side effect of the setting reaction in polyvinylsiloxane that can lead to pitting in the cast if the impression is poured too quickly.

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Polyvinylsiloxane Advantages

Excellent dimensional stability, good elastic recovery, great accuracy, short setting time, good tear resistance, and compatibility with gypsum.

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Polyvinylsiloxane Disadvantages

Hydrophobic, sulfur interference with polymerization, and hydrogen gas can lead to pitting in the cast.

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Alginate Setting Reaction

Alginate's setting process involves two stages: 1) Retardation reaction, where calcium sulfate reacts with trisodium phosphate, followed by 2) Gelation reaction, where potassium alginate reacts with calcium sulfate to form the calcium alginate gel.

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Alginate Types Based on Setting Time

There are two main types of alginate based on their setting time: Type I (fast set) hardens in 1-2 minutes, while Type II (standard set) takes 2-5 minutes.

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Water Temperature Impact on Alginate Setting

Warmer water speeds up the setting reaction of alginate, while colder water slows it down.

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Water-to-Powder Ratio Impact on Alginate Setting

More powder in the alginate mix leads to a faster hardening reaction.

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Alginate Handling: Mucostatic

Alginate is a mucostatic impression material, meaning it captures the soft tissues without compressing them.

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Alginate Impresion Accuracy

Pouring an alginate impression quickly (within 10 minutes) is crucial for accuracy because it quickly absorbs water or air and changes dimension.

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Alginate's Effect on Gypsum Surfaces

Alginate can cause gypsum surfaces to be soft and chalky. Some alginate brands require fixing with a potassium sulfate solution to improve the cast surface.

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Alginate's Importance in Dentistry

Alginate is a commonly used dental impression material for taking impressions for partial dentures because it's easy to use, affordable, and has a suitable setting time.

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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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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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