Unpolymerized surface layer of autopolymerizing polymethyl methacrylate resin

The aim of this study was to determine the thickness of the unpolymerized surface layer of autopolymerizing polymethyl methacrylate (PMMA) resin. Powder: liquid (P/L) ratios of 10:4-10 by weight of the PMMA were tested, and the PMMA resin was polymerized at 55 degrees C either in water or in air under an air pressure of 100 kPa or 300 kPa. Five samples were polymerized for each of the test groups. The thickness of the unpolymerized surface layer, i.e. inhibition depth of PMMA, was measured by a light microscopic technique with polarized light. The inhibition depth of the samples polymerized in air under 100 kPa pressure varied from 39 to 174 microns, and the samples polymerized under 300 kPa pressure had an inhibition depth of 91-391 microns. The P/L ratio and the polymerization pressure had a significant effect on the inhibition depth (P < 0.001). No inhibition layer was observed in the samples polymerized in water. The results suggest that in order to obtain an adequate degree of polymerization on the surface of autopolymerizing PMMA resin, the polymerization process should be carried out in water.