Vat photopolymerization-printed zirconia veneered with porcelain: Mechanical properties, fatigue properties, and fractographic analysis.

STATEMENT OF PROBLEM: Addition of veneering porcelain to zirconia printed by vat photopolymerization (VPP) is a practical solution to its esthetic issue. Research on the mechanical and fatigue properties of veneered VPP zirconia is lacking.

PURPOSE: The purpose of this in vitro study was to evaluate the mechanical and fatigue properties of VPP-manufactured zirconia veneered with porcelain.

MATERIAL AND

METHODS

Zirconia Ø14×0.5-mm disks were fabricated using stereolithography (SLA), digital light processing (DLP), and computer numerical control (CNC) milling technologies. Veneering ceramic (Ø14×1.0 mm) was applied to the zirconia (n=15). The biaxial flexural strength (BFS) of bilayered specimens was obtained using the biaxial flexure test. Step-stress fatigue test was conducted with 25%-30% of the mean static load as the initial load and a step size of 50 N every 5000 cycles. Scanning electron microscopy was used for fractography. Weibull distribution parameters of BFS and fatigue strength (FS) were analyzed. Statistical analyses were conducted to compare the BFS, FS, and cycles to failure (α=.05).

RESULTS

No significant difference was found in BFS and FS among groups (P>.05). The BFS was 405.9 ±58.7 MPa for SLA, 382.2 ±38.9 MPa for DLP, and 420.1 ±60.7 MPa for CNC. The FS was 290.9 ±57.8 MPa for SLA, 299.6 ±70.1 MPa for DLP, and 297.0 ±52.2 MPa for CNC. Fractography revealed the fracture origin in the zirconia layer and Hertzian cone cracks in the veneer layer. Interlayer delamination of zirconia was observed in the SLA and DLP groups. SLA and DLP zirconia showed larger twist hackles than CNC in fatigue fracture.

CONCLUSIONS

Veneered VPP zirconia had comparable BFS and FS to those of veneered CNC zirconia.