Polymers in Dentures and Prosthodontics

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Questions and Answers

What is a characteristic of cross-linked polymers?

They have a linear structure.

They form covalent bonds in a three-dimensional network. (correct)

They are primarily amorphous.

They are thermoplastic.

Which of the following methods can help reduce polymerization shrinkage?

Using monomers with high shrinkage rates.

Mixing the monomer with an inert material. (correct)

Performing polymerization in a vacuum.

Using low-pressure polymerization.

What does the degree of crystallinity influence in polymers?

The color of the polymer.

The degree of water sorption. (correct)

The thermal conductivity.

The cost of production.

What potential allergic reactions are associated with self-cured acrylic resins?

Reactions to residual monomer and benzoic acid. (B) Signup and view all the answers

Which statement is true regarding thermoplastic glassy polymers mixed with plasticizers?

They reduce the transition temperature from the glassy state to a flexible state. (B) Signup and view all the answers

What is the primary characteristic of polymers?

They consist of repeating structural units leading to high molecular weight. (B) Signup and view all the answers

Which of the following is a use of self-curing acrylic resins in dentistry?

Fabrication of custom trays. (C) Signup and view all the answers

How does an increase in the molecular weight of a polymer affect its mechanical properties?

It enhances mechanical strength, hardness, and stiffness. (C) Signup and view all the answers

What characterizes a linear or branched polymer chain?

It exhibits physical and weak bonds that can break upon heating. (B) Signup and view all the answers

What defines a copolymer?

A polymer formed from two or more different monomers. (D) Signup and view all the answers

What effect does a high temperature (over 74°C) have on heat-cured denture materials?

It causes the evaporation of residual monomer. (B) Signup and view all the answers

Which component is used as a plasticiser in heat-cured denture base polymers?

Dibutyl phthalate (B) Signup and view all the answers

What is the result of the breaking of C=C double bonds during the polymerization process?

It produces a high amount of energy. (B) Signup and view all the answers

Which of the following is NOT an imposed condition for denture base polymers?

Heavy weight for better stability (B) Signup and view all the answers

Which substance is used as an initiator in the polymerization of both heat-cured and self-cured systems?

Benzoyl peroxide (C) Signup and view all the answers

What advantage does the powder-liquid system offer compared to using only the monomer?

Reduced polymerization shrinkage. (C) Signup and view all the answers

Which of the following properties is desirable for denture base polymers?

Radioopacity. (A) Signup and view all the answers

Which component in the self-cured system acts as an accelerator?

Organic amine (A) Signup and view all the answers

Study Notes

Polymers Used for Movable Denture and Provisional Prosthodontics

Acrylic resins are used extensively in dentistry for various applications, including denture bases, denture teeth, and orthodontic retainers.
They are also used for surgical dentures, mouth guards, provisional acrylic partial dentures, and as a veneering material for metal frameworks in acrylic-metal restorations.
Self-curing acrylic resins are used for impression-patterns, functional impressions, relining materials for full dentures, custom trays, and denture base repairs.

Polymer Classification

Denture base materials are classified into heat-cured, autopolymerized, and injection molded acrylics, leading to soft liners and tissue conditioners.
Heat-cured PMMA (polymethyl methacrylate) is a common material.
Other classifications include conventional, high impact, unfilled, reinforced, and carbon fiber reinforced PMMA.
Polymers can also be classified according to the presence of a cross-linked structure and the presence of fillers.
Different variants, like room-temperature vulcanizing (RTV) silicones, are also noteworthy.

Polymer Definitions and Terms

Polymers are materials with high molecular weights, formed through repeating structural units.
Oligomers are short polymers with 2, 3, or 4 repeating units.
Monomers are molecules that form polymers through polymerization (covalent bond formation), often providing the name for the final polymer.
Copolymers involve two or more types of monomers within a polymer.
Degree of polymerization correlates directly with the molecular weight of the polymer.
An increased molecular weight results in higher mechanical strength, hardness, stiffness, and plastic strain strength (but potentially more brittleness).

Spatial Structure of Polymeric Chains

Linear/branched chains have physical, weak bonds broken by heating, making them thermoplastic.
Examples include polystyrene, polyvinyl, and PMMA (polymethyl methacrylate).
Cross-linked chains have covalent bonds, resulting in three-dimensional networks.
They are not thermoplastic.
Examples include bis-GMA, cross-linked PMMA, and impression silicones.
Illustrations of linear, branched, and cross-linked polymers are also provided in the notes..

General Properties of Polymers

The degree of crystallinity influences water sorption, stiffness, and mechanical strength in polymers.
Most polymers have an amorphous structure, exhibiting glassy characteristics.
Water sorption can partially offset polymerization shrinkage.
Thermoplastic glassy polymers, when combined with plasticizers (small molecules), can reduce stiffness and lower the transition temperature between glassy and flexible states.
Volumetric shrinkage values are provided for different acrylic resin types (e.g., acrylic resin without filler: -21%, AR denture bases: -6%, composite resins: -1-2%).
Polymerization shrinkage is the accumulation of internal stresses in a material during polymerization. Methods of reducing this shrinkage include the mixing of monomers with inert materials, powder-liquid mixtures, polymerisation under pressure, and using monomers with low shrinkage.

Polymerization Reaction

Polymerization through addition or condensation reactions is presented.
Polymerization reactions involve monomers undergoing addition or condensation. Examples include PMMA, Bis-GMA, and addition-cured silicones, as well as polyamides, condensation-cured silicones, and polysulphides.
Initiation stages, propagation phases, and termination reactions are explained using chemical diagrams.
Factors influencing polymerization include free radical number, optimal monomer-polymer ratios, homogenous mixtures, and the type and frequency of termination reactions.

Biocompatibility

PMMA generally exhibits good biocompatibility.
Immediate allergic responses can occur due to soluble components, such as residual monomers and benzoic acid, from acrylic resins, especially self-cured ones.
Delayed allergic reactions (e.g., mycotic stomatitis) can also develop over time.
Materials like polycarbonate and polyamides (nylon) serve as alternatives for patients sensitive to components of acrylic resins.
Dental technicians are susceptible to allergic reactions stemming from direct contact with, or inhalation of, methacrylate monomers.

Denture Base Polymers

Denture base polymers must meet several requirements, including natural appearance, high strength and toughness, accurate surface reproduction, absence of odor or toxicity, and resilience to oral fluids and bacterial growth.
Ease of handling, reparability, patient-friendliness in terms of cleaning, low density (for reduced weight), good radioopacity, and affordability are also considered.

Polymer Composition

Acrylic resin composition is detailed (separate tables listing components for heat-cured and self-cured resins)
Powder and liquid components, including PMMA, different initiators, opacifiers, plasticisers, and fillers, are explained.
Additives and colorants like organic pigments are mentioned.

Powder-Liquid System

Working with a powder-liquid system can benefit from attributes like a dough-like consistency and a potential reduction in polymerization shrinkage from the pre-polymerized powder present.
Mixing techniques, including the four stages of mixing, and necessary steps in time, such as doughing time and working time.
Ideal powder-liquid ratios are highlighted for optimal properties.

Heat-Cured Acrylic Resins

Composition of heat-cured acrylic resins are mentioned, including various constituents.
Storage conditions and safety precautions relating to liquid contamination with powder are given.
Polymerization reactions through heat are described, and the importance of controlling heat release during the process is emphasized, to avoid porosities and internal stresses.
Techniques for promoting slow polymerization and avoiding internal stresses are stated. Also factors leading to polymerization mistakes are illustrated.
Properties of heat-cured acrylic resins include porosity from shrinkage and gaseous porosities.
Internal stresses, originating from thermal expansion mismatch during heating and subsequent polymerization shrinkage of the material, leading to crazes and fractures in the denture are highlighted.
The mechanical properties of heat-cured acrylic resins are discussed, including reduced hardness, high abrasion rate, low tensile strength, reduced modulus of elasticity, and low fracture strength. Specific aspects of improving fracture strength with the use of reinforcement fibres.
Physical properties, such as thermal conductivity. coefficient of thermal expansion, water absorption, and solubility in organic solvents are elaborated.

Injection Molded Resins (IMR)

Advantages and disadvantages of IMR, including constant molecular weight and issues related to adhesion, materials' strength concerning crazing, and expensive equipment requirements are highlighted.
Technologies of IMR include melting the polymer powder and injecting it into the mold.
Composition of IM acrylic resins - linear PMMA without cross-linking agents., and technologies for avoiding internal stresses during processing are presented.
Further technologies and compositions of IMR polycarbonate and polyamide resins (nylon) for different denture types are addressed.

Other Polymers

Light-cured acrylic resins (CR) use a composite organic matrix (UDMA and acrylic copolymer) with inorganic filler (like colloidal silica) for specific applications (e.g., complete denture bases).
Other uses of acrylic resins are highlighted, including artificial teeth, temporary crowns, and bridges in metal-acrylic restorations, orthodontic devices, and surgical prosthesis. Resilient acrylic materials may be used as soft liners.

Self-Cured Acrylic Resins

Applications are for denture repairs, temporary crowns, custom trays, impression patterns, cast inlays, and onlays.
Liquid components, such as dimethyl paratoluidine (as an activator) are emphasized.
Properties similar to heat-cured acrylics, but with potential concerns regarding hardness, stiffness, chromatic stability, and residual monomer content are discussed.

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Description

Explore the various polymer materials used in movable dentures and provisional prosthodontics. This quiz covers classifications, applications, and the technological aspects of acrylic resins in dental practices. Test your knowledge on self-curing acrylics and their uses in dental restorations.