## 3 Discussion  
With the development of micro-anastomosis techniques and the development of microsurgical instruments [6], reconstruction using free flaps on oral and maxillofacial defects is the best prognostic option. In particular, reconstruction of the mandibular region, in which soft and hard tissues are simultaneously depleted, has been performed using osteocutaneous free flaps or using reconstruction plates and soft-tissue free flaps. Reconstruction using a reconstruction plate and soft-tissue free flap has the disadvantage of causing fracture and exposure of the plate in the long term [7; 8]. In the case of an osseous free flap, bone union with existing bone tissue can be achieved within 2-3 months and is maintained in the long term through normal bone remodeling [9]. Therefore, a vascularized free flap that comprises hard and soft tissues is mainly used, and reconstruction using a reconstruction plate is becoming a secondary option. Donor sites containing bone tissue that are mainly used in mandibular reconstruction include the fibula, iliac crest, radial forearm, and scapula. Each donor site differs in the amount of bone available, bone quality and soft tissue, length and thickness of the vascular pedicle, and availability of the two-team approach according to the surgical site. The surgeon has to choose the best flap option for the patient and surgical outcome [10]. The osseous free flap, which has various advantages in the reconstruction of jaw bone defects, has donor site morbidity because it transfers tissues such as hard and soft tissues from the donor site to the defect. The DCIA-based iliac crest flap was first reported in 1979 by [PERSON] [11] and [PERSON] [12]. In 1989, [PERSON] presented a method for reconstructing oral and maxillofacial hard and soft tissue defects using a combination of iliac crest bone and internal oblique muscle. The iliac crest flap has been used for reconstruction of maxillofacial defects because it has good bone quality and sufficient soft tissue [13]. The DCIA-based iliac crest flap has also been reported with various donor site morbidities. [PERSON] [14] and [PERSON] [15] reported herniation through a DCIA donor site. [PERSON] reported gait disturbance after prolonged sitting and one local contour defect in 1 of 15 DCIA flaps. In this paper, we considered the possibility of such gait disturbance and hip contour defects when reconstructing with the DCIA flap [16]. Research on ways to prevent donor site morbidity that may occur in DCIA flaps has also been conducted in various ways. Minimizing the supportive tissue defect in the iliac area using a monocortical DCIA flap while preserving the ASIS can minimize the complications caused by this bone defect [4]. [PERSON] et al. proposed a method to prevent hernia by reconstruction of bone defects using Protack (titanium spiral tacks) and Prolene (polpropylene) mesh [17]. [PERSON] reported a method of restoring a donor site using a 0.4 mm thick titanium sheet [18]. In this report, we proposed reconstruction of the donor site with a 3D-printed titanium implant. This method can alleviate donor complications that may occur in conventional flap reconstruction and can shorten the recovery period. In particular, it is possible to prevent a variety of disorders, such as gait disturbance, loss of hip contour that the patient may feel due to bone defect at the donor site, limitation of mobility, and fracture that may occur at the site weakened by osseous defect. Reconstruction of theiliac bone defect using a 3D-printed patient-specific titanium implant is in accord with the shape of the iliac bone, and we may apply the technique of a surgical guide using computer-assisted surgery. Therefore, the accuracy of the reconstruction is high, which can minimize postoperative complications and shorten the operation time. In addition, the porous structure of titanium implants promotes anchorage with the surrounding bone by improving cell proliferation and mesenchymal stem cell differentiation [19].