Dental Materials for Denture Bases

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Questions and Answers

What is a characteristic of the material mentioned that affects its use in denture bases?

Low residual monomer content

High solubility (correct)

High biocompatibility

Excellent color stability

Which of the following is a disadvantage of using this material for denture bases?

Excellent mechanical properties

High residual monomer (correct)

Rapid polymerization

Low creep rate

How long does polymerization take for the material described?

1-2 hours

Over 2 hours

30-45 minutes (correct)

15-20 minutes

What is a drawback related to the mechanical properties of the material?

Compromised mechanical properties Signup and view all the answers

Which of the following statements is true about the creep rates of the material?

Higher creep rates are favorable Signup and view all the answers

Which materials can be used for mechanical reinforcement of modified acrylic resins?

Glass and carbon fibers Signup and view all the answers

What types of inserts can be used to reinforce modified acrylic materials?

Metal wires and plates Signup and view all the answers

Which of the following is NOT a method of reinforcing acrylic resins?

Using water-based adhesives Signup and view all the answers

What is the primary purpose of using fibers in modified acrylic materials?

To improve mechanical strength Signup and view all the answers

Which of the following fibers is commonly used for reinforcing acrylic materials?

Carbon fibers Signup and view all the answers

What is a significant disadvantage of heat-cured resins in comparison to chemically-cured resins?

Higher percentage of volumetric contraction Signup and view all the answers

What type of materials are used in the compression moulding technique for creating denture bases?

Heat-activated denture base resins Signup and view all the answers

Which statement best describes the advantages of heat-cured resins over chemically-cured resins?

Heat-cured resins provide stronger mechanical properties. Signup and view all the answers

Which statement accurately describes a step in the compression moulding technique?

Resins are shaped by applying heat and pressure simultaneously. Signup and view all the answers

In terms of curing methods, how do heat-cured and chemically-cured resins fundamentally differ?

Heat-cured resins undergo a thermal curing process. Signup and view all the answers

What factor primarily limits the use of heat-cured resins despite their advantages?

Volumetric contraction upon curing Signup and view all the answers

Which process is primarily involved in the creation of denture bases using the compression moulding technique?

Shaping under heat and pressure Signup and view all the answers

What is a potential advantage of using heat-activated denture base resins in compression moulding?

They often cure faster than other types of resins. Signup and view all the answers

Which of the following is a benefit of chemically-cured resins compared to heat-cured resins?

Lower volumetric contraction Signup and view all the answers

What is NOT a characteristic of the compression moulding technique for denture bases?

It involves a one-step process of shaping resins. Signup and view all the answers

What is one primary cause of high processing stresses in compression moulding?

Polymerization shrinkage Signup and view all the answers

Which component's thermal characteristics contribute to the processing stresses in compression moulding?

Gypsum Signup and view all the answers

What percentage by volume does polymerization shrinkage represent in compression moulding?

7% Signup and view all the answers

In addition to polymerization shrinkage, which other factor contributes to high processing stresses in compression moulding?

Thermal shrinkage as the resin cools Signup and view all the answers

How does the difference in thermal contraction between materials relate to processing stresses in compression moulding?

It causes high processing stresses. Signup and view all the answers

What is the recommended pressure when ejecting the mold from the flask?

Minimum pressure Signup and view all the answers

What is the purpose of allowing the flasks to bench cool?

To facilitate easier removal of the mold Signup and view all the answers

Which tool is suggested for removing the flask lid?

Buffalo knife Signup and view all the answers

What should be done first after ejecting the mold from the flask?

Allow the flasks to bench cool Signup and view all the answers

What technique is used to remove the lid from the flask?

Wedging an instrument in the notch Signup and view all the answers

Study Notes

Prosthetic Dentistry - Study Notes

Prosthodontics: The branch of dentistry dealing with the restoration and replacement of missing teeth and oral structures.
Topics Covered: Flasking, denture base materials, packing procedures, and curing cycles.
Clinical and Laboratory Steps: A process involving primary impressions, record bases, jaw relations, and teeth setting. Secondary impressions, mounting, wax-up, and try-in procedures follow
Flasking: The process of investing a cast and a waxed denture in a flask to create a sectional mold for the acrylic resin denture base. The last step in denture construction.
Flasking Materials: Metal cases or sectional metal flasks used in investing procedures, using artificial stone or plaster of Paris.
Flask Components: Lids, upper and lower components (shaped depending on top or bottom), and a knockout disc. The lid and components have ID numbers.
Flasking Techniques:
- Compression moulding (most common)
- Injection moulding
- Polymerization via microwave energy
- Fluid resin technique
- Light-activated denture base resins
Flasking Process:
- Placing the cast in flasks (maxillary parallel to base, mandibular inclined from back to front). Maintaining a 3-6 mm space between teeth and flask. Reducing cast base if needed.
- Lubricating casts with petroleum jelly. Preparing the flask with petroleum jelly.
- Investing the lower half of the flask with plaster. Positioning the cast to allow excess plaster to surround it.
- Trimming off excess plaster to leave the cast clear of the flask lip.
- Applying separating medium (like petroleum jelly or tinfoil substitute) to the plastered surfaces.
Wax Elimination: Dentures are placed in boiling water for 4-6 minutes to soften the wax, and then residual wax is removed with a stream of boiling water.
Mold Formation: After trimming, a sectional mold is manufactured.
Denture Base Materials: Must meet specific mechanical and chemical requirements. These materials usually have minimum requirements since they are definitive restorations, not temporary, and need to be rigid, resistant to fracture, and maintain their structure over time.
Heat-Activated Denture Base Materials: Composition is important as it impacts various properties during the process. Examples of components include PMMA beads, initiator (peroxide), monomers, and pigments.
Heat-Cured PMMA: Features favorable working characteristics, acceptable aesthetics, and physical/mechanical properties. However, it undergoes water absorption, has low thermal conductivity, may deform under load, and doesn't always bond well with non-acrylic teeth. Possible water absorption during and after manufacturing can create colonization by candida.
Other Types of Base Materials: Injection molding, chemically activated resins, microwave-activated polymers, and modified acrylic materials.
Polymerization Cycles: Steps for the final stage of denture processing involving controlled heating. Two cycles exist: long cycle with a constant temperature of 74°C for 8 hours or more followed by a brief boil, and a short cycle 74°C for 2 hours followed by 1 hour of boiling.
Bench Cooling: Procedure to cool down the flasks after packing.
Deflasking the Dentures: Process to remove the prosthetic from the flasks after the polymerization process. Using tools and sometimes a spring clamp.
Internal Porosity: Internal air bubbles that can occur due to high temperatures, unreacted monomer, and poor thermal control during the polymerization process.
Important Considerations: Safety and precautions related to monomers like allergic reactions are important.

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Description

Test your knowledge on the characteristics and properties of materials used in denture bases. This quiz covers polymerization, mechanical reinforcement, and the advantages and disadvantages of different acrylic resins. Perfect for students studying dental materials or oral health.