Polishing effects and wear performance of chairside CAD/CAM materials

To investigate the surface roughness of CAD/CAM materials immediately after milling and after different chairside and labside polishing procedures. A two-body wear test was performed to compare the different wear characteristics of the materials and the corresponding antagonists.

Specimens (n = 12 per series) from different CAD/CAM materials (three composites: Lava Ultimate, Cerasmart, BRILLIANT Crios; one hybrid ceramic: VITA Enamic; three ceramics: Celtra Duo, VITA Suprinity, IPS Emax.CAD) were polished according to the manufacturer's instructions. The effect of different polishing procedures was investigated by comparing surface roughness (R_a, R_max) after labside polishing and after chairside polishing. Wear behavior (mean, volume, and maximum wear) of specimens and antagonists as well as changes in surface roughness were determined in a pin-on-block wear test. Statistical analysis was performed with a one-way analysis of variance (ANOVA)/Bonferroni multiple-comparison post hoc test and a multifactorial ANOVA/Tukey's significant difference post hoc test (α = 0.05). SEM micrographs were used for the qualitative evaluation of surfaces and wear traces.

After chairside high-gloss polishing, ceramics and composites exhibited R_a values between 0.08 and 0.10 μm and between 0.11 and 0.13 μm, respectively. After labside high-gloss polishing, values varied between 0.02 and 0.09 μm for ceramics and between 0.06 and 0.16 μm for resin composites. No significant differences were found between labside and chairside pre- and high-gloss polishing. For the ceramics, lower mean wear depths (between - 132.2 ± 19.9 and - 137.0 ± 19.0 μm) were identified compared to the resin composites (which exhibited wear depths between - 159.1 ± 19.4 and - 176.3 ± 23.9 μm). For maximum wear depth and volume, a different ranking of the materials was found. Antagonistic wear varied between 12.0 ± 6.4% and 30.6 ± 9.9% and was higher for the ceramic materials and Lava Ultimate. For all materials, a smoothing between 0.20 and 2.70 μm (R_a) was identified after wear simulation.

Chairside polishing is as effective as labside polishing, although surfaces were directly adjusted (roughened) only before the chairside polishing. Wear was lowest for ceramics, followed by the resin-infiltrated material and the resin composites.

Polishing after milling or adjustment is essential to guaranteeing optimal clinical performance. Chairside polishing after adjustment leads to comparably smooth surfaces as labside polishing after milling and grinding. Ceramics are expected to exhibit lower wear than resin composites under clinical conditions.