Effect of different mechanical polishing systems on surface properties in indirect restorations

The aim of this in vitro study is to compare the effects of surface treatments applied to two different lithium disilicate ceramic CAD/CAM blocks on the surface roughness and surface gloss values of the materials, and to evaluate their surface topographic morphologies by imaging them at the nanometric and micrometric scales. A total of 192 samples obtained from two different lithium disilicate CAD/CAM block materials, IPS e.max CAD Block and GC Initial LiSi Block, were used in the study. All blocks were prepared in 6 × 13 × 0.5 mm dimensions and 0.5 mm thickness. Each material type was subjected to eight different surface treatments (glazing, milling abrasion, and two different variations [with/without polishing paste] of three different mechanical polishing systems [G&Z Instrumente Set, Panther Set, and OptraGloss Set] applied after abrasion] (n=12). Surface roughness (Ra) was measured using a profilometer and surface gloss (GU) was measured using a glossmeter. Surface topography was examined using atomic force microscopy (AFM), scanning electron microscopy (SEM) and light microscopy. The normality of the data was assessed using the Shapiro–Wilk test in statistical analyses; the Kruskal–Wallis H test was used for parameters that did not follow a normal distribution. The Bonferroni-corrected Dunn test was employed to determine significant differences between groups. The results of the study revealed that the type of material used and the surface treatments applied had a statistically significant effect on the roughness (Ra) and gloss (GU) values of the surfaces (p < 0.05). The milling process, which mimics clinical adaptation, made the ceramic surfaces unacceptably rough and reduced their gloss significantly. At this stage, the roughness values were highest (1.0775 μm Ra) and the gloss values were lowest (3.2250 GU) in the GC Initial Block group. Of the mechanical polishing systems, Panther and OptraGloss achieved high gloss by reducing surface roughness below the clinical threshold, regardless of polishing paste usage. The IPS e.max Block – OptraGloss – Paste combination produced the smoothest (0.0667 μm Ra) and brightest (92.9083 GU) results of the study. While the G&Z instrument set alone was insufficient, the performance of all systems increased statistically significantly when combined with diamond polishing paste, yielding results equivalent to the control group (grinding) (p < 0,05). Qualitative analyses (AFM, SEM and light microscopy) confirmed that the Panther and OptraGloss systems produced smooth, flat topographies, whereas the G&Z application without paste left deep pits on the surface, thereby corroborating the quantitative data. The data obtained indicate that the effectiveness of mechanical polishing depends not only on the system used, but also on the microstructure of the ceramic material. The study demonstrated that the Panther and OptraGloss mechanical polishing systems are effective for lithium disilicate ceramic surfaces in terms of surface roughness and surface gloss. The data obtained indicate that the effectiveness of mechanical polishing depends not only on the system used but also on the microstructure of the lithium disilicate ceramic material. Adding diamond polishing paste as the final step in mechanical polishing systems improved Ra and GU values. In cases where glazing cannot be performed after occlusal adjustments following the cementation of the restoration in the clinic, re-polishing with mechanical polishing systems was found to be effective. Keywords: Gloss; LiSi block; polishing; roughness.