Method: Cylindrical specimens of three commercial composites, hybrid, microhybrid and nanohybrid (FiltekP60, FiltekZ250, Filtek Z350XT, respectively) were prepared and stored at 37 C for 24 h. After this period, they were subjected to experimental heat treatments in dry heat at 220°C for10 min. The control group consisted of only light-cured specimens. The degree of conversion was evaluated by Fourier transform infrared spectroscopy – FTIR (n=5). For simulated toothbrushing, the specimens (n=8) were subjected to 30,000 cycles with a load of 200g. Data were statistically analyzed by Student's t test for comparing the degree of conversion between control and heat-treated groups (α=5%).Data from initial and final roughness were analyzed by T test for paired samples (α=5%).
Result: The experimental heat treatment allowed higher conversion, which was statistically significant for the Z350XT composite resin.The simulated toothbrushing increased the superficial roughness of all groups (p≤0.001). For P60 and Z350XT, heat treatment did not influence the increase of surface roughness (p=0.885, p=0.052, respectively). For Z250 specimens, the difference in roughness was statistically lower in heat-treated specimens (p=0.002).
Conclusion: The heat treatment increased the degree of conversion of studied composite resins and influenced the superficial roughness caused by toothbrushing of microhybrid resin, but the same was not observed for the hybrid and nanohybrid ones.