Smoother Polish Did Not Mean Stronger Ceramic in CAD/CAM Finishing Study

Edited by Dentaltown staff

Finishing and polishing protocols that produced the smoothest surfaces did not necessarily preserve the greatest flexural strength in CAD/CAM restorative materials, and the effects varied by material, according to a laboratory study published Aug. 11 in Clinical Oral Investigations.

Researchers tested three materials: a nanoceramic resin, a polymer-infiltrated ceramic, and a leucite-reinforced glass-ceramic. They prepared 120 bars measuring 8 by 2 by 1 mm, with 15 specimens per group, and subjected them to four protocols: an unpolished control, bur only, diamond bur followed by diamond-impregnated rubber tips, and diamond bur followed by silica-impregnated rubbers. Half of each group underwent 10,000 thermocycles to simulate aging.

Flexural strength was measured by three-point bending, surface roughness by optical profilometry, and surface characteristics by scanning electron microscopy.

Material composition determined the response. Both finishing protocol and aging significantly affected the polymer-infiltrated ceramic and the glass-ceramic, while only finishing protocol influenced the nanoceramic resin.

The pattern diverged by material. In the polymer-infiltrated ceramic, silica-impregnated rubbers produced the highest strength after aging at 121.8 MPa, while the diamond-impregnated rubber protocol produced the lowest. In the glass-ceramic, the highest values came from the unpolished control at 125.7 MPa and the bur-only group at 114.8 MPa. In the nanoceramic resin, the aged diamond-impregnated group recorded the lowest strength in the study at 112.0 MPa.

Diamond-impregnated rubber tips produced smoother surfaces after bur adjustment, but that smoothness did not translate into mechanical benefit and appeared to compromise the glass-ceramic.

The authors concluded that polishing protocols should be selected according to material composition. All systems performed comparably on the nanoceramic resin, minimal or no polishing better preserved the glass-ceramic, and silica-based systems may be preferable for the polymer-infiltrated ceramic.

Helena Nóbrega Almeida, Francisca Jennifer Duarte de Oliveira, and colleagues, including senior author Rodrigo Othávio de Assunção e Souza, conducted the study.

The work tested standardized bars rather than finished restorations under a single aging protocol, so it describes material behavior rather than clinical performance.

Sources:
Clinical Oral Investigations, “Effect of different finishing/polishing protocols and aging on flexural strength, roughness, and surface characteristics of definitive restorative materials for CAD/CAM,” published online Aug. 11, 2026: link.springer.com/10.1007/s00784-026-07061-w