Large segmental mandibular defects remain difficult to reconstruct, and patient-specific biodegradable scaffolds produced by additive manufacturing may offer an alternative to permanent alloplastic implants. This exploratory study evaluated three 3D-printed poly(DL-lactide) (PDLLA)-based implant configurations in a periosteum-preserving minipig mandibular defect model: PDLLA, PDLLA containing 10 wt% strontium-modified hydroxyapatite microparticles (PDLLA + SrHAp-P), and a biphasic PDLLA-shell/SrHAp-core implant (PDLLA/SrHAp-C). Twelve adult minipigs received patient-specific implants and titanium reconstruction plates (n = 4 per group). Bone formation was monitored by digital volume tomography and sequential fluorochrome labeling for 6 months; one animal per group underwent non-terminal follow-up to 14 months. Complications occurred in 11 of 12 animals and included dehiscence, abscess or fistula formation, implant swelling, screw loosening, and fracture or displacement of the SrHAp core. Bone bridging was radiographically observed in all animals by 6 months, including an animal in which the implant had been removed prematurely, indicating a major contribution of the preserved periosteum and host tissues. New bone formed mainly around, rather than within, the implants. Implant-associated bone ingrowth was observed only in the biphasic group, but was not a uniform finding and fibrous encapsulation was frequent. The 3 animals followed to 14 months showed continued consolidation without terminal sacrifice. These findings identify degradation-associated tissue reactions, dimensional instability, soft-tissue coverage, and construct mechanics as major limitations of large PDLLA-based mandibular implants. The biphasic architecture showed a potentially favorable local osteointegration pattern, but the small sample size and high complication rate preclude claims of efficacy or superiority. Further optimization of polymer content, ceramic architecture, porosity, mechanical stability, and soft-tissue management is required before additional translational studies.