This paper presents the application of additively manufactured (3D-printed) shape-optimized core fillers in composite sandwich structures, demonstrated on a full-scale aircraft landing gear component. The study compares conventional foam cores with 3D-printed honeycomb structures and evaluates their performance through three-point bending tests. Furthermore, the integration of complex-shaped fillers into a composite landing gear structure is described. The results highlight the advantages of additive manufacturing in terms of geometric accuracy, functional integration, and manufacturability. The solution has been implemented in a production aircraft, confirming its practical applicability.