This study evaluated the in vivo performance of a novel, 3D-printed personalized temporomandibular joint (TMJ) condylar prosthesis featuring an integrated elastic functional layer (EFL) in a goat model. Conventional rigid metal and ultra-high-molecular-weight polyethylene prostheses often trigger stress shielding and contralateral joint degeneration due to a mechanical mismatch with the native articular disc. To address these limitations, unilateral hemi-TMJ reconstructions were performed on four adult male goats using a custom prosthesis combining a porous Ti6Al4V stem and a 3D-printed UHMWPE/HDPE composite elastic layer. Over a 6-month follow-up, clinical, radiographic, and histological parameters were evaluated. All animals survived without serious complications. Maximum passive mouth opening and lateral excursion ranges successfully returned to levels comparable to preoperative baselines, while masticatory efficiency stabilized after an initial postoperative decline. Hepatic and renal function metrics confirmed the material's systemic biosafety. CT and micro-CT imaging verified stable prosthetic positioning, robust osseointegration, and bone matrix ingrowth into the porous metallic scaffold. Histological analysis revealed the formation of a beneficial "synovial-like" membrane on the elastic substrate surface, which was supported by significantly elevated local expression of the regenerative cytokine TGF-β via ELISA. These findings suggest that the elastic design promotes favorable initial stability, good biocompatibility, and vital functional recovery. The observed synovial metaplasia provides a promising protective mechanism to minimize wear and prevent heterotopic ossification, offering strong preclinical evidence for elastic configurations in advanced TMJ arthroplasty.