Residual methyl methacrylate monomer, water sorption, and water solubility of hypoallergenic denture base materials

Abstract 

Statement of problem

Denture base materials have the potential to cause irritation and allergic reaction to the oral mucosa. Water sorption and water solubility of denture base resins affect dimensional behavior and denture stability. A correlation between residual monomer and water sorption exists.

Purpose

This in vitro study compared the amount of residual monomer, quantity of water sorption, and solubility of 4 denture base materials purported to be hypoallergenic with those of a polymethyl methacrylate–based (PMMA) heat-polymerizing acrylic resin.

Material and methods

The denture base resins Sinomer (heat-polymerized, modified methacrylate), Polyan (thermoplastic, modified methacrylate), Promysan (thermoplastic, enterephthalate-based), and Microbase (microwave polymerized, polyurethane-based), which are purported to be hypoallergenic, and Paladon 65 (heat-polymerized, methacrylate, control group) were examined. Specimens of each material were tested for residual methyl methacrylate (MMA) monomer (% wt, n=3), amount of water sorption (μg/mm³, n=5) and water solubility (μg/mm³, n=5), according to ISO 1567:2000. The residual MMA monomer concentrations were determined by gas chromatography (GC). The data were analyzed with 1-way ANOVA and the Bonferroni-Dunn multiple comparisons post hoc analysis for each test variable (α=.05).

Results

Significantly lower residual MMA monomer was shown for Sinomer and Polyan compared to the PMMA control group (0.90 ± 0.20% wt, P<.05). Sinomer contained 0.31% ± 0.00% wt MMA monomer, and Polyan exhibited residual MMA monomer content of 0.44% ± 0.01% wt. Promysan and Microbase did not contain detectable residual MMA. Water sorption of Promysan (16.21 ± 0.96 μg/mm³) was significantly lower than Paladon 65 (23.04 ± 3.13 μg/mm³, P<.0001), whereas water solubility of the hypoallergenic denture base materials (0.34-0.84 ± 0.05-0.09 μg/mm³) was not significantly lower than the PMMA material (0.40 ± 0.06 μg/mm³, P>.05). Except for Sinomer, the tested denture base resins passed the requirements of ISO 1567 regarding residual MMA monomer (<2.2% wt). Sinomer failed to comply with the requirements for residual MMA monomer because the manufacturer claimed that the material did not contain any MMA. The tested denture base materials fulfilled the requirements regarding water sorption (<32 μg/mm³) and solubility (<1.6 μg/mm³).

Conclusion

The tested hypoallergenic denture base materials exhibited significantly lower residual monomer content than PMMA. Promysan and Microbase showed no detectable residual MMA.