Dental Resins and Polymerization Concepts

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Questions and Answers

What is a common cause of internal porosities in denture bases?

Excessive curing time

Overpacking of the resin

Insufficient pressure during packing (correct)

Use of excessive heat during curing

Which method can be used at home to clean dentures?

Professional polishing

Soaking or brushing daily (correct)

Boiling in water

Using toothpaste

What characteristic must an ideal denture cleaner possess?

Nontoxic and easy to remove (correct)

Requires long soaking times

Highly abrasive to remove tough stains

Only effective on organic materials

What is one effect of using tissue conditioners on oral tissues?

They provide a cushioning effect Signup and view all the answers

What type of resins are used to create acrylic resin teeth?

Self-curing acrylic resins Signup and view all the answers

Which of the following can lead to external porosities in denture bases?

Too rapid curing Signup and view all the answers

What is the primary use of synthetic resins in dentistry?

Restorative materials, adhesives, and sealers Signup and view all the answers

What are thermoplastic materials characterized by?

Molded without chemical change and are soluble in organic solvents Signup and view all the answers

What is the definition of monomer?

A low molecular weight compound Signup and view all the answers

Which of the following statements about thermoset materials is true?

They undergo a chemical reaction during molding Signup and view all the answers

What describes a cross-linked polymer?

A high molecular network polymer created by linking polymer chains Signup and view all the answers

What does 'plasticize' mean in the context of synthetic resins?

To soften materials and make them more flexible Signup and view all the answers

Which type of polymer consists of two or more different monomers?

Copolymers Signup and view all the answers

What accurately describes a free radical?

A fragment molecule with an unpaired electron Signup and view all the answers

Which of the following is NOT a characteristic of thermoplastic materials?

They undergo a change in chemical composition when heated Signup and view all the answers

What is the dough forming time according to ADA SPEC.#12?

At least 20 minutes Signup and view all the answers

What indicates that the dough has reached the stiff stage?

It cannot be molded Signup and view all the answers

How long should the assembly be kept in the water bath during the rapid curing method?

1-1.5 hours until it boils Signup and view all the answers

What is the ideal temperature for the slow curing method?

74°C Signup and view all the answers

What is the purpose of placing a polyethylene sheet over the resin during trial closure?

To prevent the adhesion of resin to the lower mold surface Signup and view all the answers

What defines the working time in the curing process?

The time that elapses between stage 2 and beginning of stage 4 Signup and view all the answers

Which of the following describes bench curing?

Flask is kept at room temperature for 30-60 minutes Signup and view all the answers

What is required for the dough to remain moldable according to ADA SPEC.#12?

At least 5 minutes of moldability Signup and view all the answers

What happens during the heating process of the resin?

The resin undergoes polymerization Signup and view all the answers

What should happen during the rapid curing process after boiling?

Remain in the bath for another 30 minutes Signup and view all the answers

What is the first step in the denture base construction process?

Preliminary impression Signup and view all the answers

What is the purpose of using Colorgard in the process?

To prevent the union between investing medium and U&L halves Signup and view all the answers

What is the purpose of applying 2 layers of colorgard during the construction of the denture base?

To prevent the penetration of monomer into the investing medium Signup and view all the answers

During which stage does the mixture become stringy and adhesive?

Sticky Stage Signup and view all the answers

Which technique involves the polymer to monomer ratio of 3 – 3.5:1 by volume?

Compression molding Signup and view all the answers

What happens during the Dough Stage of the polymerization process?

The mass becomes smoother and no longer tacky Signup and view all the answers

Which part of the metal flask is NOT included in the investing process?

Wax pattern Signup and view all the answers

What is the boiling point of the transparent liquid resin used in denture base construction?

100.8°C Signup and view all the answers

What is indicated by the presence of flash after filling the mold?

Excess material has overflowed onto the surrounding area Signup and view all the answers

What is the primary purpose of deflasking in the denture base construction process?

To remove the wax pattern Signup and view all the answers

What is the final shape of the material called after completing the trial closures?

Cohesive Structure Signup and view all the answers

What should be done to soften the wax before removing it from the mold?

Place it in boiling water Signup and view all the answers

What occurs in Stage 4, the Rubbery Stage?

The mass becomes more cohesive due to monomer evaporation Signup and view all the answers

Why is it important to use a vent in the flask?

To allow excess POP to escape Signup and view all the answers

What is the recommended weight ratio of polymer to monomer for the packing of resin?

2 – 2.5:1 Signup and view all the answers

What characterizes the Damp Sand Stage of the polymerization process?

The polymer gradually settles into the monomer Signup and view all the answers

Which step comes immediately after constructing the individual tray for the final impression?

Master/Working cast Signup and view all the answers

What is the role of the monomer in the polymerization process?

To create a plastic mass suitable for molding Signup and view all the answers

What should be done after separating the upper and lower halves of the metal flask?

Remove the wax and prepare the mold space Signup and view all the answers

How many trial closures are done before removing the polyethylene sheet?

Two Signup and view all the answers

Study Notes

Dental Resins/Synthetic Resin

Nonmetallic materials, made by combining organic compounds.
Can be molded into many shapes.
Also known as "plastics," categorized as fibrous, rubber-like, resinous, or hard-rigid.
Composed of polymers, large molecules with high molecular weight, often termed as polymers.

Thermal behavior

Thermoplastic: Softens under heat, becomes liquid at high temperatures, and can be molded without chemical change. Solvable in organic solvents.
Thermoset: Undergoes a chemical reaction during molding, permanently changing its composition. Becomes infusible and insoluble after curing.

Polymerization

Monomer: A single unit molecule.
Polymer: A molecule formed from many monomer units.
Free Radical: A molecular fragment with an unpaired electron.
Cross-linked polymer: A network polymer with high molecular weight, formed by covalent bonds between polymer chains.
Copolymers: Made from two or more monomers.
Plasticize: To soften.

Polymerization Process (Acrylic and Rubber-reinforced Acrylic)

Involves conversion of low molecular weight monomers to high molecular weight polymers.
The process involves adding monomer to polymer to create a plastic mass that can be packed into a mold.

Denture Base Construction

Impression Making:
- Preliminary impression is taken first.
- Study cast is constructed from the preliminary impression.
- An individual tray is made for the final impression.
- Master/working cast is created based on the final impression.
Construction of Denture Base (DB) Wax Pattern:
- 1-2 layers of high fusing pink wax are applied to the master cast.
- Wax is adapted to the master cast and edges are sealed.
Investing: This process uses a metal flask with four parts: base, lower half, upper half, and cover.
- The master cast is placed in the lower half of the flask.
- Powder of Paris (POP) is poured into the lower half and allowed to set.
- Colorgard, a separating medium, is applied to prevent the union between investing medium and the flask parts.
- The upper half of the flask is placed on top of the lower half and filled with POP.
- The filled flask is put in a presser to remove excess POP.
- Colorgard is also applied before investing.
Wax Elimination:
- The flask is placed in boiling water for 5-10 minutes to soften the wax.
- The upper and lower halves of the flask are separated.
- The softened wax is removed, and hot water is poured into the mold space to create a clear space.
- The mold space is cleaned and prepared for packing resin.
Packing of Resin:
- Two methods: Dough-molding technique/Compression molding and Injection-molding technique.
- Dough-molding Technique:
  - Uses polymer and monomer in specific ratios by volume (3-3.5:1) or weight (2-2.5:1).
- Injection-molding Technique:
  - Uses a vent in the flask to attach an outside injector that pushes soft resin into the mold space.

Trial Closure

The polyethylene sheet separates the resin from the lower mold surface to prevent sticking.
Trial closure ensures proper mold filling and eliminates air bubbles.

Curing/Processing

Heating resin to polymerize it.
Two methods: Rapid Curing and Slow Curing.
Rapid Curing
- Uses a water bath to slowly increase the temperature until boiling.
- Allows the assembly to remain in the bath for 1-1.5 hours after boiling.
Slow Curing
- The ideal curing cycle.
- The assembly is placed in a water bath at 74°C for 6-8 hours (often overnight).

Denture Cleaners

Dentures collect deposits like natural teeth: stains, calculus.
Two common removal methods:
- Professional repolishing.
- Soaking or brushing at home.
Ideal denture cleaner requirements:
- Nontoxic, easy to remove and leaves no traces.
- Able to remove organic and inorganic deposits.
- Harmless to denture materials, eyes, skin, and clothing.
- Stable in storage.
- Preferably bactericidal and fungicidal.

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Description

This quiz covers the essential concepts of dental resins and synthetic polymers, including their thermal behavior and classification as thermoplastics and thermosets. Additionally, it explores the process of polymerization, focusing on monomers, polymers, free radicals, and copolymers.