Acrylic Resins for Dentures: Properties and Processing

Why polymethyl methacrylate remains, after decades, the reference material for denture bases, and the processing steps that determine its final quality.

Polymethyl methacrylate (PMMA) has for several decades been the reference material for making removable, complete and partial denture bases, thanks to a combination of properties hard to match with more recent alternatives: good mechanical strength for its intended use, ease of processing and finishing, ability to be repaired if fractured, low cost, and satisfactory aesthetics thanks to its ability to reproduce the pink shade of gingival tissue. Chemically it's a thermoplastic resin obtained by polymerizing methyl methacrylate, available in heat-cured (heat-activated), self-cured (cold, chemically-cured) and, more recently, light-cured formulations.

Traditional processing involves flasking the model with the prosthetic teeth already positioned in wax, followed by replacing the wax with acrylic resin through a pressing process and controlled polymerization in a specific heat cycle. A relevant technical aspect concerns polymerization shrinkage: heat-cured acrylic resin undergoes volumetric reduction during setting that, if not correctly managed with an appropriate pressing and curing protocol, can result in imprecise fit of the denture base to the tissues, with direct consequences for the stability and retention of the finished appliance.

A distinct but equally common use of PMMA concerns making custom trays, built on plaster models obtained from a preliminary alginate impression. Unlike thermoplastic materials, which don't undergo significant dimensional changes on cooling, acrylic resins show continuous volumetric changes in the first 24-48 hours after polymerization: an often underestimated technical detail, which requires waiting this period before using the tray for the final impression, or risking a systematic dimensional error.

In recent years, the digital workflow has also introduced variants of prosthetic acrylic resin designed for CAD/CAM milling and 3D printing: industrially pre-polymerized PMMA discs, with a more homogeneous molecular structure and less residual porosity than traditional flask polymerization, generally offer greater fracture resistance and better color stability over time, although the traditional technique remains widely used, especially for complex complete dentures.

On Oralzon you'll find heat- and self-cured acrylic resins for denture bases and custom trays, along with PMMA discs for digital-workflow CAD/CAM processing.