Effect of CAD/CAM milling protocols on surface topography and mechanical behavior of polycrystalline zirconia

Even though improvements in CAD/CAM technology have allowed the milling protocol to be modified according to specific treatment requirements, it remains unclear how different protocols affect the surface quality and mechanical properties of the final restoration. This study aims to evaluate the effect of the CAD/CAM milling protocol on the topography, flexural strength, and reliability of 3 mol% yttria partially stabilized zirconia (3Y-PSZ).

Disc-shaped specimens (∅12 mm×1.2 mm) were fabricated using three different CAD/CAM dry-milling protocols (n = 20): slow (S), normal (N), and fast (F). Control polished specimens were fabricated by cutting pre-sintered CAD/CAM blocks using a cutting machine and polishing with silicon carbide papers, in wet (P_wet) and dry (P_dry) conditions (n = 20). Surface topography was evaluated using an optical profilometer (n = 3). Specimens were subjected to a piston-on-three-balls flexural strength test using a universal testing machine. Fractographic analysis was performed using optical and scanning electron microscopes. The characteristic flexural strength (σ₀), Weibull modulus (m), and the 90 % confidence intervals (90 % CI) were estimated. XRD was used to identify the tetragonal, cubic, and monoclinic phases.

Distinct topographies were observed for polished and CAD/CAM-milled specimens. Surface roughness parameters (Sa and Sz) followed a decreasing order: F > N > S > P (P_wet and P_dry) There was no difference for σ₀ and m values among the three CAD/CAM milling protocols. P_dry had similar σ₀ and m to CAD/CAM-milled groups, while P_wet resulted in lower values.

Distinct CAM-milling protocols produce apparent differences in the topography of 3Y-PSZ while preserving flexural strength and reliability.