P.K. VALLITTU*, (Univ of Turku, Inst of Dent, Dept of Prosthet, Turku, Finland.)
The objective of this investigation was to determine the inhibiting effect of oxygen on polymerization of autopolymerizing polymethylmethacrylate (PMMA) (Palapress Vario, Kulzer, Germany) resin and glass fiber (GF) - PMMA composite. The GF-PMMA composite can be used as reinforcement of a denture. Type of the fibre added into the PMMA was E-glass fibre weave (48 g/m2 , Hexcel, France). Three powder-to-liquid (P/L) ratios of PMMA were tested. The unreinforced samples and the GF-PMMA composite samples (n=5 per group) were polymerized between two glass plates at +55°C in air under an air pressure of 300 kPa (3 Atm). The inhibition depth was measured by a light microscopic technique with polarized light. The inhibition depth was affected by the P/L ratio of the PMMA: the mean inhibition depth of PMMA with the P/L ratio 10:10 was 232.8 µm, while it was 175.4 µm in PMMA with the P/L ratio of 10:8 (p=0.044 by ANOVA). The inhibition depths were higher (up to 249 µm) in the GF-PMMA composite than in the plain PMMA. This was explained by an inadequate impregnation of the GF weave with the PMMA resin. The results of this study emphasize the importance of good impregnation of fibres with PMMA; improper impregnation may lead to the internal oxygen inhibition of the polymerization of the GF-PMMA composite. This cannot be compensated, e.g by polymerizing the composite in water.