1.12 Polymers of Prosthetics

Polymers

Long-chained organic molecules produced by the reaction of many smaller identical molecules called monomers

Denture bases, liners, composites, sealants, temporaries, custom trays, impression materials, adhesives, cements, mouth guards, night guards, and maxillo-facial prostheses

What are uses of polymers in dentistry?

Cross-linked

Which polymer type is the strongest?

True

T/F: Polymer strands are not chemically linked, but rather entangled

More; stronger

The longer the individual polymer chains, the ____ entanglements=the ______ the polymer. The strength, stability, and stiffness of the polymer is generally increased

Highly

When adjacent polymers are joined by _______ charged side chains, the bond is stronger, and the cross-linked polymers are stronger and stiffer

Plasticizing

Large, bulky side groups tend to push the polymer chains apart and reduce the number and effectiveness of entanglements which makes the polymer more flexible, moldable, less rigid, and rubber-like; reduces the number and effectiveness of entanglements

Copolymers

Two different molecules forming the long chain; they enhance the physical properties of the material

Thermoplastic

The ability to be reversibly transformed from a brittle, glassy solid to a softened, moldable plastic by heating beyond a certain temperature

Polymerization

The chemical reaction that links the monomer together to produce a polymer

Addition polymerization and condensation polymerization

What are the two types of polymerization?

1. Initiation

2. Propgation

3. Termination

What are the 3 stages of addition polymerization?

Addition polymerization

What is the most common polymerization in dental materials?

Initiation

The first stage of addition polymerization in which the initiator joins monomer causing a split of double carbon bonds and leave a single carbon bond and a very reactive free radical

Propagation

The second stage of addition polymerization when numerous polymer chains are forming at the same time; the chains get bigger and longer at the same time

Residual monomer

This area of a polymer will alter and affect the stability of the final polymer and is formed because of rapid reaction rate and a fast increase in viscosity

Termination

The final stage of addition polymerization when we few monomers and the viscosity of the acrylic resin increases and we have no free radical

Camphorquinone

What is the initiator for light-cured polymerization?

Condensation polymerization

This polymerization is rarely used in dentistry because the reaction is too slow and it does not produce polymers of a suitable length

• Absorb water

• Do not have as much abrasion resistance or stability as metals or ceramics

• Have a wide range of esthetic possibilities

• Good thermal and electrical insulators

• High coefficient of thermal expansion

• Shrinkage because of volumetric contraction

What are properties of polymers?

Conventional heat and cold-cured

What are two types of prosthetic resins?

Self-curing; greater

Cold-cured prosthetic resins differ from heat-cured in that they are ____ _______. Heat cured resins have ________ strength than cold-cured resins

• Shrinkage caused by excess monomer

• Higher dimensional accuracy in cold-cured

• Heat can cause bubbles in final product

• Low abrasion resistance

• Sufficient thermal stability but can warp if cleaned in hot water

• Fairly acid and base resistant

• Potential irritating and allergenic effect

What are characteristics of prosthetic resins?

Tissue conditioners

Used on irritated or healing tissues, act as a shock absorber, contain polymethylacrylate polymers loaded with plasticizers, such as alcohol, that leach out while material hardens over time. Considered a temporary material

1. Improved adhesion to denture base

2. Lack of clicking sound

3. Oppose natural teeth without abrasion

4. Easy to replace and polish

What are advantages of plastic denture teeth over porcelain denture teeth

Slowly; unreacted monomers

When producing a heat-cured denture, heat should be generated _______ to reduce bubble formation and more residual monomer. The product should be stored in water for 24 hours to dilute _________ _________ and allow for water uptake for an enhanced fit