Role of Acrylic Resins in Modern Dentistry: A Step-by-Step Guide

Removable Prostheses And Acrylic Resins

Describe acrylic denture base materials in detail.
Answer:

Acrylic denture base materials

These are also known as polymethyl methacrylate resins.

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According to the method of their activation, there are three types of acrylic denture base materials, i.e.

1. Heat activated resins
2. Chemically activated resins
3. Light activated resins.

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1. Heat Activated Resins:

Polymerization Reaction: Polymerization of heat-activated resin is achieved by the application of heat and pressure. The reaction is:

Powder   +    Liquid    +    Heat     →      Polymer    +   Heat
(Polymer)    (Monomer)    (External)     (Reaction)

Advantages Of Heat Activated Resins:

• It has low shrinkage, so it is dimensionally accurate.
• Vertical dimensions do not increase.
• The denture base is homogeneous.’
• Its impact strength is good.

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Disadvantages Of Heat Activated Resins

• The cost of equipment is high.
• Problems are in mold designing
• Crazing resistance is low
• Requirement of special flask.

2. Chemically Activated Acrylic Resin:

• Polymerization Reaction:
  • Polymer (Powder)    +     Monomer (Liquid)     →    Polymer    +    Heat
    (Peroxide initiator)             Amine accelerator           ( Reaction)

Manipulation Of Activated Acrylic Resin: Manipulation of chemically cured acrylic resin is done by following techniques:

• Sprinkle on technique
• Hand-adapting dough technique
• Fluid resin technique
• Compressing molding technique.

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The most commonly used techniques for manipulation of self cure resin is sprinkle-on technique and hand-adapted dough method.

• Sprinkle-on technique:
  • In this technique, both polymer and monomer are added to the cast which consists of a separating medium.
  • In this powder is added to the cast and monomer is added to it till the proper thickness is achieved.
  • The liquid is added to the powder with the help of a dropper.
• Hand-adapted dough technique:
  • In this technique, both the powder and liquid are proportionate and mixed in a porcelain jar.
  • As the mix proceeds to the dough stage, it is placed in between two glass slabs, now it is removed, and is adapted to the cast manually in the desired shape.

3. Light Activated Acrylic Resin:

They are single component system. Light-activated resin is supplied as premixed sheets or ropes packed in light-proof pouches to prevent accidental polymerization.

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Composition of Light Activated Acrylic Resin:

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Technique or Manipulation:

• Fabrication of denture base: As the base material is in the plastic stage, it should be adapted on the master cast. Polymerize it to hard set in the light chamber without teeth to be used as a base plate.
• Completion of denture: Attach the teeth to the base plate by additional material and the anatomy of the polished surface should be made accordingly. As sculpting is complete denture should be placed again in a light chamber for polymerization. As polymerization is overdenture should be fiished and polished.

Mode of Polymerization:

• Here the mode of polymerization is blue light of wavelength 400 to 500 nm.
• So as camphor quinone and organic amine come in contact with blue light of wavelength 400 to 500 nm they generate free radicals.
• This activation of the photoinitiator initiates the polymerization reaction.
• Light curing chamber consists of a rotating table over which the denture is placed so that it is exposed to the uniform intensity of light.

Properties Of Activated Acrylic Resin:

• The impact strength for visible light curing denture material is 13 J/m which is less than other dentures.
• Flexural strength is 80 MPa which is comparable to other resins.
• The hardness of light-activated resin is 18 KHN.

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Advantages Of Activated Acrylic Resin:

• It has less porosity.
• It is light in weight.
• Its fabrication final adjustment should be done in the mouth.
• It does not produce any allergic reaction.
• It is free of methyl methacrylate.
• It is non-toxic.
• It also decreases polymerization shrinkage.

Disadvantages Of  Activated Acrylic Resin:

• It should not be packed, so need artistic skills.
• Its procedure is time-consuming.
• It is very technique sensitive.