Comparing the load-bearing capacity of 3D printed and CAD/CAM milled 3Y-TZP bridges after artificial ageing.

OBJECTIVE

To evaluate the load-bearing capacity of 3 mol% yttria-stabilized zirconia (3Y-TZP) four-unit fixed dental prostheses (FDPs) fabricated using four different additive manufacturing (AM) workflows representing three different AM technologies compared with subtractive manufacturing (SM), both in a pristine condition (P) and after dynamic loading combined with hydrothermal ageing (L).

METHODS

Seventy-nine FDPs were produced by AM (stereolithography [aSLA], material jetting [aMJ], digital light processing [aDLP1/aDLP2]) or SM [s1/s2]. All samples were split into groups P and L (5x106 dynamic loading cycles, including 5-55 °C hydrothermal cycling). Loads to failure of surviving (L) and pristine (P) samples were measured. Within L subgroups, two samples each (n = 10) underwent Micro-Computed Tomography scans before and after ageing to evaluate internal defects and defect propagation. Fractography was performed by scanning electron microscopy.

RESULTS

Within group P, aDLP2 (1427N), s1 (1447N), and s2 (1336N) revealed the highest average fracture load, whereas aDLP1 (820N) and aMJ (846N) achieved the lowest loads. Within group L, 12 AM FDPs and 1 SM FDP failed. Among the surviving specimens only, both SM groups (s1: 1811N; s2: 1535N), as well as groups aDLP1 (1138N) and aMJ (1016N), revealed an increase in fracture load compared to pristine samples, whereas aSLA (896N) showed a decrease.

CONCLUSIONS

The tested AM zirconia workflows showed workflow-related processing defects and higher failure rates during dynamic loading/hydrothermal ageing than the subtractive reference workflows. Although mean pristine fracture loads exceeded the reported maximum bite force reference value, premature failures during ageing and the survivor effect limit direct clinical interpretation. Within the limitations of the tested materials, printers, designs, and protocols, current AM workflows for long-span 3Y-TZP FDPs require further optimization, workflow-specific validation, and reliable quality control before routine clinical use can be recommended.