Qualitative characterization of the composition of dental thermoplastic polymers by pyrolysis GC-MS

The objective of this study was to qualitatively screen the composition of common dental thermoplastic by double-shot pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) combined with evolved gas analysis-mass spectrometry (EGA-MS); and to identify polymer families and potential additives/residual compounds. Ingredient identification is primordial for biocompatibility research and future quantitative analytical research.

Nine commercial dental thermoplastic sheets, including aligners, mouthguards, splints, and bleaching trays, were analyzed. EGA-MS was first performed to obtain thermal decomposition profiles. Subsequently, double-shot Py-GC/MS was performed, involving a thermal desorption (TD) stage to analyze volatile and semi-volatile organic compounds, followed by a flash pyrolysis (FP) stage to characterize the polymer backbones.

EGA-MS and FP revealed diverse polymers, including copolyesters, ethylene vinyl acetate (EVA), styrenics, and polyolefins. Multilayer aligners exhibited profiles consistent with those of methylene diphenyl diisocyanate (MDI)-based polyurethanes and copolyesters containing cyclohexanedimethanol (CHDM) and terephthalic acid (TPA). During the TD stage, low-molecular-weight compounds, such as phenolic antioxidants, aldehyde-based clarifiers, and processing-related residues such as tetrahydrofuran (THF) were tentatively identified. Variations between analytical findings and manufacturer documentation consulted in this study were observed across the tested materials.

This study provided deeper insights into polymers in thermoplastic materials and identified potential additives and residual compounds to target in future quantitative elution studies. Variations between analytical findings and manufacturer declarations highlight potential gaps in current medical device disclosure policies. Double-shot Py-GC/MS provides a robust non-targeted qualitative screening approach for chemical characterization, allowing further biocompatibility assessment and facilitating subsequent targeted quantification of leachates.