Analysis of Surface Roughness, Fracture Toughness, and Weibull Characteristics of Different Framework-Veneer Dental Ceramic Assemblies after Grinding, Polishing, and Glazing

PURPOSE To compare the surface roughness and biaxial flexural strength of dental ceramics obtained after chairside surface modification by mechanical polishing procedures, versus laboratory reglazing. MATERIALS AND METHODS Discs (16 × 1.5 ± 1.6 mm) (N = 90) of various framework-veneering combinations were fabricated: D/FC: lithium disilicate/feldspathic ceramic; Z/AL: zirconium dioxide/aluminous ceramic; N/FC: noble alloy/feldspathic ceramic; N/FF: noble alloy feldspathic with fluorapatite; B/FC: base alloy/feldspathic ceramic; B/FF: base alloy/feldspathic ceramic with fluorapatite. In each group 10 specimens were ground using a diamond bur (46 μm) and five were polished with silicone-reinforced disc polishers (25 μm). Surface roughness (Ra) was measured using contact profilometry. After thermocycling in artificial saliva (6000 cycles, 5 to 55 ± 5°C), biaxial flexural strength was measured using "piston-on-three ball" test. The data (N) were analyzed using one-way ANOVA, Bonferroni, and Tukey's posthoc tests. Weibull distribution values were calculated. RESULTS Surface roughness was significantly higher in the ground group only (p < 0.0001). Mean fracture toughness was significantly lower for chipping (RK: 287, HS: 22, ISO: 1099 MPa) than for total fracture (p < 0.05), (RK: 841, HS:64, ISO: 3222 MPa). For chipping, Weibull distribution presented the highest shape value (m) for D/FC (3.82-5.07) and for total fracture for B/FC (3.69-4.6). CONCLUSION Chairside surface polishing restored veneer ceramic roughness and mechanical strength to the level of glazing. Feldspathic ceramic with fluorapatite presented better polishing results than conventional feldspathic ceramic did. Ceramic fused to metal was more resistant than lithium disilicate or zirconium dioxide framework-veneer assemblies. Lithium disilicate framework veneered with feldspathic ceramic presented more durability against chipping. CLINICAL IMPLICATIONS After chairside occlusal modifications in the surfaces of cemented all-ceramic or fused-to-metal FDPs, mechanical polishing procedures should always be carried out