Dental light-cured nanocomposites based on a dimethacrylate matrix: Thermal degradation and isoconversional kinetic analysis in N2 atmosphere

• Characterization of commercial dimethacrylate-matrix dental nanocomposites using TG.
• Degradation of the dental nanocomposites occurs in three stages.
• The chemical structure of the polymeric matrix is the major factor defining thermal endurance.

The thermal degradation of five commercial dental nanocomposites, based on a dimethacrylate matrix, was studied using thermogravimetric analysis in order to retrieve information on the structure of the macromolecular network formed. Grandio, Protofill-nano, Filtek™ Supreme XT Body, Tetric® EvoCeram and Filtek™ Supreme XT Translucent were tested under four different heating rates up to 700 °C in an inert (N2) atmosphere. The data provided thus were sufficient not only for a complete record of the decomposition steps in each case, but also for performing a kinetic analysis based on isoconversional methods. The variation of the activation energy as a function of the extent of degradation was estimated using an integral and a differential method. It resulted that the heating endurance of a composite is mainly a matter of the constituents building its polymeric matrix as well as its relative amount. The nature of the inorganic filler little affects the degradation in overall. From the isoconversional analysis at least two degradation steps were revealed depending on the type and the amount of dimethacrylate monomers used. Defect structures formed in the polymeric network during polymerisation resulted in lower initial activation energy values.

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