Podcast
Questions and Answers
What is one of the primary disadvantages of using modeling compound occlusion rims?
What is one of the primary disadvantages of using modeling compound occlusion rims?
Which is NOT a use of occlusion rims?
Which is NOT a use of occlusion rims?
What material is MOST commonly used for making occlusion rims?
What material is MOST commonly used for making occlusion rims?
Which measurement is typical for the wax dimensions of occlusion rims?
Which measurement is typical for the wax dimensions of occlusion rims?
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During what process is additional stabilization with Zn & Eugenol impression material required?
During what process is additional stabilization with Zn & Eugenol impression material required?
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Which method allows for the preservation of the impression borders?
Which method allows for the preservation of the impression borders?
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What is one disadvantage of using hard base plate wax for trial denture bases?
What is one disadvantage of using hard base plate wax for trial denture bases?
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Which requirement is essential for a record base?
Which requirement is essential for a record base?
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What is an advantage of boxing impressions?
What is an advantage of boxing impressions?
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What material is commonly used for temporary trial denture bases?
What material is commonly used for temporary trial denture bases?
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What type of trial denture base is typically replaced by a permanent trial denture base?
What type of trial denture base is typically replaced by a permanent trial denture base?
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What is a characteristic of a well-fitting occlusion block?
What is a characteristic of a well-fitting occlusion block?
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What facilitates the production of a cast with a predetermined thickness in boxing?
What facilitates the production of a cast with a predetermined thickness in boxing?
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What is the primary purpose of a dental impression?
What is the primary purpose of a dental impression?
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Which material is typically used for making a preliminary impression?
Which material is typically used for making a preliminary impression?
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What distinguishes a master cast from a primary cast?
What distinguishes a master cast from a primary cast?
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Which characteristic is NOT associated with stock trays?
Which characteristic is NOT associated with stock trays?
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What is a key feature of stock trays for dentulous patients?
What is a key feature of stock trays for dentulous patients?
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What are the components of an impression tray?
What are the components of an impression tray?
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Which statement about flanges in trays is accurate?
Which statement about flanges in trays is accurate?
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What material is commonly used for making master casts?
What material is commonly used for making master casts?
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What is a primary advantage of using special trays over stock trays?
What is a primary advantage of using special trays over stock trays?
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What is a characteristic of a wax spacer used in custom trays?
What is a characteristic of a wax spacer used in custom trays?
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What is a disadvantage of using shellac base plates?
What is a disadvantage of using shellac base plates?
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Which technique is also known as the 'Definite pressure impression technique'?
Which technique is also known as the 'Definite pressure impression technique'?
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Which of the following is an advantage of swaged tin in denture construction?
Which of the following is an advantage of swaged tin in denture construction?
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What is the purpose of the perforations in a perforated special tray?
What is the purpose of the perforations in a perforated special tray?
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Which statement about acrylic resin special trays is correct?
Which statement about acrylic resin special trays is correct?
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What advantage does auto polymerizing resin provide over shellac bases?
What advantage does auto polymerizing resin provide over shellac bases?
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What is the focus of the muco-static impression technique?
What is the focus of the muco-static impression technique?
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What is a significant disadvantage of using permanent trial denture bases?
What is a significant disadvantage of using permanent trial denture bases?
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Which material is typically used for the bases of permanent trial dentures?
Which material is typically used for the bases of permanent trial dentures?
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How does the wax shim assist during the impression process?
How does the wax shim assist during the impression process?
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What is emphasized in the selective pressure impression technique?
What is emphasized in the selective pressure impression technique?
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What is one advantage of heat cured acrylic resin in denture construction?
What is one advantage of heat cured acrylic resin in denture construction?
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What is a key advantage of metal bases in dentures?
What is a key advantage of metal bases in dentures?
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What is a disadvantage of using heat cured acrylic resin?
What is a disadvantage of using heat cured acrylic resin?
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Study Notes
Impression Tray
- A device used to hold, confine, and control impression material while making an impression.
Dental Impression
- A copy of the form of the teeth and supporting structures.
Cast
- A reproduction of the tissues.
Types of Impressions
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Preliminary impression: Records the overall dimensions of the arch.
- Uses: Stock trays and impression compound or alginate.
- Resulting cast: Study (primary) cast.
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Secondary impression: Records fine details of the arch.
- Uses: Special trays and plaster, Zno & E, or rubber base impression material.
- Resulting cast: Master cast
Components of an Impression Tray
- Handle: Facilitates holding and manipulating the tray.
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Body: Main part of the tray that holds impression material.
- Floor: The bottom surface that conforms to the arch.
- Flanges: The vertical extensions that surround the arch.
Types of Impression Trays
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Stock Trays: Ready-made trays available in different sizes, forms, and materials.
- Materials: Metal (aluminum or stainless steel) and plastic.
- Types: Perforated or non-perforated.
- Fit: Should conform to the shape and contour of the residual ridge, providing 4-6 mm of space for impression material.
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Special Trays (Custom or Individual Trays): Individually fabricated trays designed for a specific patient.
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Advantages:
- Accurate fit to the dental arches.
- Reduced bulk of impression material, minimizing dimensional changes.
- Less impression material required.
- Increased comfort for the patient.
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Advantages:
Stock Tray Components
- Body: Consists of a floor and flanges. The shape varies depending on the patient's dentition - dentulous, edentulous, or partially edentulous.
- Handle: The shape and length of the handle differ for dentulous, edentulous, and partially edentulous patients.
Classification of Stock Trays
- Material of construction: Metal (aluminum or stainless steel) or plastic.
- Impression material: Perforated, non-perforated, or water-cooled.
- Size: Small, medium, large, or numbered sizes (e.g., 1, 2, 3).
Uses of a Study Cast
- Analyze ridge shape, palatal vault, denture bearing area, undercut areas, relief areas, posterior palatal seal area, sharp bony edges, sulcus depth, inter-arch relations, and space.
- Construct special trays.
Special Trays Fabrication
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Materials:
- Self-cure acrylic resin.
- Shellac baseplate.
- Swaged metal.
Advantages of Acrylic Resin Special Trays
- Easy to construct.
- More rigid than shellac trays.
- Accommodates thermoplastic border tracing material.
- Easily trimmed.
Wax Spacer or Wax Shim
- Used in minimal pressure impression technique.
- 2-3 mm thickness.
- Contains tissue stops (perforations) - typically two in the canine and two in the molar region.
Advantages of a Spacer
- Provides even thickness for impression material, ensuring consistent dimensional change.
- Facilitates accurate assembly of fractured plaster impressions.
Impression Technique Types
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Muco-static impression technique (Minimal pressure impression technique): Records impression at rest.
- Trays: Perforated with spacer.
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Muco-compressive impression technique (Definite pressure impression technique): Records impression under biting force.
- Trays: Non-perforated, without spacer.
-
Selective pressure impression technique: Uses selective pressure for specific areas of the arch.
- Trays: Non-perforated with separating medium.
Boxing of Impressions
- Building vertical walls around the impression periphery.
-
Methods:
- Wax bead boxing method.
- Plaster and pumice boxing method.
Advantages of Boxing
- Preserves impression borders.
- Uniform thickness of the base.
- Reduces air bubbles in the cast.
- Conserves time and material.
Occlusion Blocks
- Consist of occlusion rims attached to trial denture bases.
Trial Denture Base
- Known as a base plate or record base.
- Directly adapted to the master cast.
Uses of Trial Denture Base
- Carries occlusion rims for jaw relation recording.
- Supports teeth during the try-in stage.
- Evaluates the accuracy of the final impression.
Requirements of Trial Denture Base
- Rigid for load bearing.
- Accurate adaptation to the master cast.
- Easy to construct and fully extended.
- Relieved from undercuts.
- Even thickness.
- Smooth, rounded edges.
- Dimensional stability.
Types of Trial Denture Bases
- Temporary trial denture base: Replaced by a permanent trial denture base (PTDB).
- Permanent trial denture base: Forms the base of the final denture.
Materials for Temporary Trial Denture Bases
- Hard base plate wax.
- Shellac base plate.
- Cold-curing acrylic resin.
- Light-cured acrylic resin.
- Swaged tin.
Hard Base Plate Wax
- Advantages: Easy, rapid, and thin application to provide space for teeth.
- Disadvantages: Lack of dimensional stability.
Shellac Base Plates
- Thermoplastic plates adapted by heat softening.
- Advantages: Controlled uniform thickness for limited inter-arch space cases.
- Disadvantages: Lack of rigidity, unsuitable for patients with strong biting force.
Swaged Tin
- Three layers of tin gauge 5 are swaged over a master cast die, forming a rigid, accurate, and dimensionally stable base.
Autopolymerizing Resin (Cold-Cure Acrylic Resin Denture Base, Tray Type)
- Commonly used for trial denture bases.
-
Advantages over Shellac Bases:
- Close and accurate fit to the cast.
- Dimensional stability in the mouth.
- High strength for biting pressure.
Permanent Trial Denture Bases
- Serve as the bases of the final denture.
- Provide a clear idea about extension, retention, and stability of the final denture.
- Disadvantages: Additional shrinkage during second processing to attach teeth.
Materials for Permanent Trial Denture Bases
- Heat-cured acrylic resin.
- Metal bases (cast gold, chromium-nickel alloy, chromium-cobalt alloy).
Heat-Cured Acrylic Resin
-
Advantages:
- Strong and rigid.
- Controlled thickness during waxing.
- Minimal dimensional changes.
- Becomes part of the final denture.
- Minimal finishing and polishing.
-
Disadvantages:
- Time-consuming.
- Requires mounting casts.
- Potential for warpage during tooth attachment.
Metal Bases
-
Advantages:
- No acrylic warpage.
- Strong.
- Accurate.
- Reduced tissue change under the base.
- Hygienic due to less porosity.
- Good thermal conductivity.
- Less deformation during function.
-
Disadvantages:
- Expensive.
- Difficult to reline.
- Time-consuming.
Stabilization of Recording Bases
- Can be achieved by relining with zinc oxide eugenol impression material after adapting tin foil to the master cast.
Occlusion Rims (Record Rim)
- Typically made of pink modeling wax.
-
Uses:
- Registration of jaw relationships.
- Tooth selection.
- Tooth setup.
- Lip and cheek support.
- Accurate try-in.
Types of Occlusion Rims
- Wax occlusion rims (Most common).
- Modeling compound occlusion rims (For graphic tracing method).
- Plaster and pumice rims (For functional chew-in technique).
Modeling Compound Occlusion Rims
-
Disadvantages:
- Longer trimming and adjusting time.
- Residual pigment can remain in the final denture.
Plaster and Pumice Rims
- Used for recording mandibular movements using the functional generating path technique.
Wax Rim Dimensions
- Buccal and lingual thickness: 6-8 mm.
- Occlusal surface width: 8-10 mm.
- Anterior height: 20-22 mm.
- Posterior height: 16-18 mm.
- Bevel: 45 degrees.
- Posterior palatal seal area: 2/3 retromolar pad.
- Retromolar pad thickness: 8-10 mm.
- Anterior thickness: 6 mm.
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Description
This quiz explores the concept of dental impressions, including the types and functions of impression trays. Learn about the components of impression trays and how they are used to create accurate reproductions of dental arches. Test your knowledge and understanding of these essential dental tools.
