Influence of temperature on the visco-elastic properties of direct and indirect dental composite resins

Objectives The first aim of this study was to determine the visco-elastic properties of two direct (DiamondLite and Grandio) and two indirect (Artglass and Vita Zeta LC) dental composites over a wide range of temperatures, in order to avoid choosing a composite that would undergo sudden changes in its mechanical properties during service. Methods Within this objective the composites were tested immediately after fabrication or after storage at 37 °C, either in air or distilled water for 1 day, 7 or 90 days. During dynamic testing, the elastic modulus (E′), viscous modulus (E″) and loss tangent (tan δ) were determined using a dynamic mechanical analyzer (DMA) over a temperature range from 0 to 200 °C, at an approximate masticatory frequency of 1 Hz. Results Based on their high glass transition temperatures (Tg) and on the fact that materials are basically equilibrated at 37 °C in the mouth and are not thermal conductors, temperature changes from 37 °C are expected to be small and should lead to only modest changes in both moduli. However, composites might improve their initial degree of conversion when exposed to normal mouth temperature and higher temperatures due to the ingestion of hot food and beverages. This event can have positive and negative effects on the restoration, such as greater rigidity and additional micro-leakage, respectively. Significance According to these results it could be said that monitoring the visco-elastic properties of dental composites under conditions that simulate the oral environment seems to be a useful tool to predict their clinical performance as restorative materials.