Surface roughness, gloss and sequential polishing times of various chairside computer aided design/manufacturing restorative materials

OBJECTIVE: To investigate the effect of polishing on surface roughness, gloss and optimum polishing time of various computer aided design/computer aided manufacturing (CAD/CAM) restorative materials and to provide a proper polishing procedure for dental clinicians. METHODS: Five CAD/CAM restorative materials including vita mark Ⅱ (VM), vita enamic (VE), lava ultimate (LU), shofu block HC (SB) and brilliant crios (BC) were selected. Six specimens were prepared for each material. The specimen was fixed on a custom-made polishing apparatus and sequentially polished with Sof-Lex poli-shing disk system including medium disk (with abrasive particle sizes of 10-40 μm), fine disk (with abrasive particle sizes of 3-9 μm) and superfine disk (with abrasive particle sizes of 1-7 μm). Surface roughness (Ra value) and gloss value were measured every 10 seconds until the numerical values were no longer changed. Then the surface roughness, gloss value and polishing time were recorded and the specimen was moved to the next sequence of polishing. Finally, statistical analysis was performed using SPSS 24.0. RESULTS: For all the restorative materials, the Ra values were significantly reduced (P < 0.05) and the gloss values were significantly increased (P < 0.05) after sequentially polishing with Sof-Lex disks. No significant difference was detected among Ra values of all the tested materials (P>0.05) after sequential polishing. The gloss values of LU [(68.1±4.5) GU] and BC [(68.2±5.8) GU] were significantly higher than those of VE [(48.1±8.1) GU] and BC [(53.2±5.8) GU], P < 0.05. To obtain optimal surface smoothness, VM cost the shortest polishing time [40 (30, 55) s] among all the restorative materials (P < 0.05). No significant differences in the total polishing time were observed among VE [140 (135, 145) s], LU [130 (120, 140) s], SB [140 (130, 150) s] and BC [130 (120, 140) s], P>0.05. CONCLUSION: The surface roughness of all CAD/CAM restorative materials were decreased after sequentially polishing with Sof-Lex disk system. To obtain the smoothest surface, different types of restorative materials might need different polishing times using Sof-Lex polishing disk system. For ceramic restorative material VM, we recommend polishing only with medium disk for 40 s. For hybrid restorative material VE and composite restorative material LU, SB and BC, we recommend polishing with medium disk, fine disk and superfine disk in sequence for 130-140 s in total.