In vitro degradation of polyurethane orthodontic elastomeric modules

1365-2842

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

summary  The objectives of this study were to investigate the structural characteristics of orthodontic polyurethane elastomeric modules and their changes produced by mechanical and chemical ageing. Three products were tested (Generation II, Dentaurum, Alastic). For each product four groups of modules were studied under the following conditions: as-received (A0); after 3 weeks stretching at 50% elongation in air (B0); after 3 weeks immersion in an ethanol/water solution (3:1 v/v) to induce accelerated ageing (A1); and after 3 weeks immersion in the ethanol/water solution at 50% elongation, as above (B1). The chains and the solution extracts were characterized by micro-MIR FTIR spectroscopy. Specimens of group B0 exhibited changes in peak intensities relative to the control group (A0), attributed to molecular orientation of poly (methylene glycol) soft segments and chain extenders such as butanediol. Moreover, group B0 showed differences in the ω(CH2)b peak at 1364 cm−1, attributed to oxidative degradation of α-methylene groups by formation of ester, carboxylic acid or aldehyde groups due to hydrogen abstraction. Comparison of A1 and B1 groups with the controls (A0, B0) showed no major differences between their respective spectra, apart from the loss of the 1639 cm−1 peak attributed to ethylene NN bis (stearamide) wax. However, comparison of the spectra of the extracts from the elongated modules with the extracts of the controls revealed differences in the concentration of alcohol and alkene groups. The structural changes identified were the same in all the products tested and may indicate degradation mechanisms that could potentially hold intraorally.

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