Effect of different finishing/polishing protocols and aging on flexural strength, roughness, and surface characteristics of definitive restorative materials for CAD/CAM

Abstract

OBJECTIVE: To evaluate the effect of finishing/polishing and aging on the flexural strength, roughness, and surface characteristics of CAD/CAM restorative materials. MATERIALS AND METHODS: Three CAD/CAM materials were tested: Nanoceramic resin (CR), Polymer-infiltrated ceramic (PIC), and Leucite-reinforced glass-ceramic (LC). A total of 120 bars (8 × 2 × 1 mm; n = 15/group) were prepared and subjected to different finishing/polishing protocols (C: control; B: bur; BD: diamond bur + diamond-impregnated rubber tips; BS: diamond bur + silica-impregnated rubbers) and aging (without/with 10,000 thermocycles). Mini-flexural strength (σ) was assessed by three-point bending. Surface roughness (Sa) was analyzed using optical profilometry, while surface characterization was performed using SEM. Data were analyzed with two-way ANOVA/Tukey's test (α = 0.05) and Weibull analysis. RESULTS: For σ, both finishing/polishing and aging factors significantly affected PIC and LC (p < 0.05), whereas only finishing/polishing influenced CR. In CR, aged CR_BD had the lowest strength (112.0 ± 17.9 MPa). In PIC, aged PIC_BS (121.8 ± 21.4) showed the highest strength, while PIC_BD groups showed the lowest. In LC, the highest values were seen in aged LC_C (125.7 ± 22.9), LC_B (114.75 ± 19.09), and non-aged LC_C (108.11 ± 29.54). Sa was significantly affected by material type and finishing/polishing protocols. CONCLUSIONS: Silica-impregnated rubbers improved the flexural strength of PIC after bur finishing. The BD protocol, producing smoother surfaces, may compromise the flexural strength of LC. In contrast, CR was not significantly affected by the polishing protocol. Moreover, aging negatively impacted PIC strength, and polyurethane rubber tips impregnated with diamond particles produced smoother surfaces after bur adjustments. CLINICAL RELEVANCE: Within the limitations of this in vitro study, polishing protocols should be selected according to material composition, since surface smoothness does not necessarily correlate with improved mechanical performance. For CR, all polishing systems showed comparable performance; for LC, minimal intervention or no polishing better preserved mechanical performance; for PIC, silica-based polishing systems may be preferred.