Roughness profile and surface roughness after toothbrushing and degree of conversion of bulk-fill resins

The aim of this study was to assess roughness profile and surface roughness after simulated toothbrushing cycles, as well as the degree of conversion (DC) of bulk-fill resin composites at different depths. Forty nine composite discs were made from three low-viscosity bulk-fill resins (Filtek Bulk-Fill Flowable/3M Oral Care - FBF, Beautifil- Bulk Flowable/Shofu Inc. - BBF and Surefill SDR Flow/Dentsply Caulk - SDR), three high-viscosity bulk-fill resin composites (Filtek Bulk-Fill Restorative/3M Oral Care - FBR, Beautifil-Bulk Restorative/Shofu Inc. - BBR and Tetric EvoCeram Bulk Fill/Ivoclar Vivadent - TEB) and one conventional composite (Filtek Supreme Ultra/3M Oral Care - FSU) (n=7), using addition silicon molds (2 mm thick x 10 mm diameter). The roughness profile (Rv) and surface roughness (Sa) were analyzed after 30,000 brushing cycles using confocal laser scanning microscopy. Five samples (4 mm thick x 2 mm diameter) were produced per resin composite and light-cured for 20 seconds using a LED-curing unit. After 24 hours at 37oC, DC of samples was evaluated at four depths, using a confocal Raman microscope. The data were analyzed by ANOVA and Tukey post hoc multiple-comparison tests (α = 0.05). The Rv values of FSU were lower than those obtained for BBR and BBF. The toothbrushing significantly decreased the Sa for all composites. The DC was significantly reduced at 4 mm depth. Toothbrushing changed composite surface of all materials, especially for BBR and BBF. Composites were not able to maintain the DC values shown at the top compared with those at the bottom (4 mm depth).