The Effect of Preheating on the Mechanical and Physical Properties of Various Composite Resins

The present study aimed to evaluate the effect of preheating on the mechanical and physical properties of different resin composites. A total of 72 disc—and 72 bar-shaped specimens were fabricated using four different resin composites: a hybrid composite (Saremco ELS), a bulk-fill composite (Filtek One), a nanofilled composite (TMR-ZFill 10), and a nanohybrid composite (FGM Opallis). For the preheated groups, the composites were heated at 68°C for 5 min using a composite heating device. The materials were placed into the molds in a single increment, and each surface was light-cured for 20 s. After initial surface roughness and microhardness measurements, specimens were kept in distilled water for 45 days. Following water storage, final surface roughness and microhardness measurements were obtained, and flexural strength testing was performed. Preheating significantly increased the flexural strength, microhardness, and surface roughness of the tested resin composites (p < 0.05), although the magnitude of these changes varied among the materials. Filtek One exhibited the highest flexural strength, whereas Saremco ELS showed the highest surface roughness values following preheating. Water storage significantly affected the surface roughness and microhardness scores, irrespective of preheating. To sum up, preheating improved the microhardness and flexural strength of the tested composites; however, its effects were material-dependent.