Jaw reconstruction using an additive-manufacturing titanium artificial bone (AMTAB) has recently attracted considerable attention. The synthesis of a titanium artificial bone is based on three-dimensional computed tomography images acquired before surgery. A histological evaluation of porous AMTAB (pAMTAB) embedded in rat calvarial bone defects was conducted. This study examined three groups: rats implanted with mixed-acid and heat-treated pAMTAB, rats implanted with untreated pAMTAB, and rats with no implant. In both pAMTAB groups, bone defects were created in rat calvarial bones using a 5-mm trephine bar, followed by pAMTAB implantation. The pAMTAB was fixed to the defect using the fitting force of the surrounding bones. The rats were sacrificed at 4, 8, and 16 weeks after implantation, and the skull was dissected. Undecalcified ground slides were prepared and stained with Villanueva Goldner. Compared with the no implant control group, both pAMTAB groups exhibited new bone formation inside the defect, with greater bone formation in the mixed-acid and heat-treated pAMTAB group than in the untreated pAMTAB group, but the difference was not significant. These data suggest that pAMTAB induces bone formation after implantation in bone defects. Bone formation appears to be enhanced by prior mixed-acid and heat-treated pAMTAB.