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Technical Discussion: Denture Base Acrylics

Technical Discussion: Denture Base Acrylics

What are the different types of denture base acrylics available? Which
one is best?

L.T. Armstrong, DMD: While there are more than a hundred different brand names and shades of denture acrylics available, they all have the same base chemical composition (7% cross-linked copolymerized methylmethacrylate). The primary differences between them are color and monomer residue left after processing. Methylmethacrylate is a primitive plastic and its primary use is in the making of Plexiglas. When processed, the monomer has shrinkage of 20% by volume. Dental researchers reduced this to a more acceptable 7% by taking several steps. The monomer has a coloring agent added and is processed into polymer(polymethylmethacrylate). It is then ground into a fine powder and mixed in a three to one ratio with monomer. The resulting dough is press packed into a dental appliance mold and cured.

While methods that inject plastic into a closed flask sound as if they will increase accuracy, the technique has its shortcomings. Fluid, poured or injected acrylics use a higher proportion of liquid to power in the initial mix. Depending on how the restoration is cured, there can be a higher ratio of free monomer left in the processed base. Unused or free monomer in the appliance is what causes allergic reactions to acrylic. Vacalon is a solution.

Currently denture allergies are rare, but appear to be on the increase. Like other allergic responses, monomer reactions require a pre-sensitization and are cumulative, generally appearing in the patient’s second or third acrylic appliance. The free
monomer in any dental restoration leaches out over time. The higher proportion of liquid to power in fluid resin or injected materials leaves more free monomer within the processed restoration. The method of curing can reduce the amount of this free monomer, see Vacalon section.

Lucitone 199 and other high impact acrylics have additives, which supposedly increase the yield strength and flexibility of the processed denture.

Which material is “best” depends on individual preference but if I were the patient, either Lucitone 199 or Vacalon would be my choice.

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