Thermal expansion characteristics of light-cured dental resins and resin composites

The thermal expansion characteristics of dental resins prepared by light-curing of Bis-GMA, TEGDMA, UDMA, Bis-EMA(4) or PCDMA dimethacrylate monomers and of commercial light-cured resin composites (Z-100 MP, Filtek Z-250, Sculpt-It and Alert), the organic matrix resin of which is based on different combinations of the above monomers, were studied by thermomechanical analysis (TMA). This study showed the existence of a glass transition temperature at around 35–47°C for the resins and 40–45°C for the composites; then the coefficient of linear thermal expansion (CLTE) was calculated at the temperature intervals 0–60°C, 0-Tg and Tg-60°C. The CLTE values of Bis-GMA, TEGDMA and UDMA resins are similar and lower than those of Bis-EMA (4) and PCDMA resins. The CLTE values of the composites indicated that the major factor that affects the CLTE of a composite is the filler content, but it also seems to be affected by the chemical structure of the matrix resin. TMA on water-saturated samples showed that water desorption takes place during the measurement and that the residual water acts as a plasticizer decreasing the Tg and increasing the CLTE values. Furthermore, TMA on post-heated samples for 1, 3 or 6 h showed, only for the resins, an initial decrease of CLTE and increase of the Tg after 1 h that was not significantly changed after 6 h of heating.