Craniomaxillofacial surgery is difficult due to the dangerous structures in the compact and deeply hidden region [1] . In the past, surgery in this area was performed by conventional methods, so-called “free hand”, depending on surgeons’ competence, experience, and 2-dimensional (2-D) imaging. However, in recent years, advanced engineering technology including medical image processing, computer-aided design and computer-aided manufacturing (CAD/CAM), rapid prototyping (RP) known as 3-D printing, and surgical navigation have been widely used in the fields of neuro- [2] , orthopedic- [3] , and otolaryngological surgery [4] . Of these advanced techniques, virtual surgical simulation before the actual surgery progressing from 2-D images to sophisticated 3-D images and surgical navigation providing real-time feedback to the surgeons dramatically improve the quality and efficiency of the actual surgery. However, these computer-assisted surgery techniques are still in their preliminary stages in the field of craniomaxillofacial surgery [5] .

The mandible plays an important role in facial symmetry, occlusion, mastication, and speech functions [6] - [9] . Defects of the mandible caused by tumor, osteomyelitis, or severe trauma affect patients’ quality of life both physiologically and psychologically. Various approaches for mandibular reconstruction, including reconstructive titanium plates, nonvascularized or vascularized bone grafts, and autogenous iliac bone grafts in combination with a ready-made titanium mesh trays, have been tried [10] [11] . The most common approach for mandibular reconstruction today is a vascularized-bone graft from the fibula and iliac crest [6] - [8] . However, the area for resection of the mandible cannot be positioned precisely even with any of the approaches described above, and the complexity of the regional anatomy makes it very difficult to reconstruct the facial contour and recover ideal occlusal function. For example, due to the straight configuration of the fibula, surgical time and the risk of vascular complications are increased. To completely resolve these problems, advanced engineering technology has been used for mandibular resection and reconstruction in the clinic. Preoperative computer design, including pre- bending reconstruction materials combined with intraoperative navigation, provides a more accurate, safer, and less time-consuming method for reconstruction of the mandible compared with conventional methods of flap insertion.

In the present report, computer-assisted mandibular resection with the guidance of real-time navigation and reconstruction using a patient-specific titanium mesh tray and particulate cancellous bone and marrow (PCBM) harvested from bilateral anterior ilia is reported. The combination of surgical simulation with a virtual 3-D model, intraoperative navigation with real-time feedback to the surgeons, and CAD/CAM technique provides a safe and precise method for mandibular reconstruction.

Operations during the clinical course of this case are shown in Figure 3. First, the right mandibular body was opened and exposed, and then the segmental resection of the defective mandible was performed safely and precisely with the guidance of real-time navigation. The resection curve was performed between the third molar posteriorly in the right mandible to the canine anteriorly in the left mandible for full excision of the tumor on a virtual 3-D model, and an accurate match between the operative anatomy and the CT images was achieved within 1.0 mm. Furthermore, unlike rotational reciprocating motion, the cutting action of bone using the Sonopet^Ò was performed finely and sequentially with no grabbing or kicking.

Subsequently, reconstruction of the mandible was undertaken. PCBM was harvested from the lateral edges of bilateral anterior iliac crests. The amount of harvested PCBM was 40.0 g. A patient-specific titanium mesh tray was accurately positioned to the remaining mandibular fragments without difficulty and fixed using several monocortical screws without positional change of the condyle (Figure 3(d)). The PCBM was loaded into the tray and densely condensed to increase graft density. The surgical simulation with the virtual 3-D model and surgical navigation provided safe and precise mandibular reconstruction. Six months postoperatively, both facial contour recovery (Figure 4(a) and Figure 4(b)) and occlusal rehabilitation (Figure 4(c) and Figure 4(d)) were achived, showing excellent new bone formation of the mandible radiologically (Figure 4(e)).

This is the first report describing how computer planning and intraoperative navigation are used for reconstruction of the mandible with a patient-specific titanium mesh tray and PCBM. The proposed protocol incorporated all of the latest technologies and improved the safety and precision of the mandibular reconstruction surgery. It had been generally considered that a navigation system could not be used in mandibular surgery because of the complexities of navigating a mobile structure [5] [8] . However, these limitations were overcome to have a stable registration point using a maxillomandibular splint before CT was performed [8] [12] . This method did not take any additional cost and had no invasive action. Even if an open jaw surgery was required, the intraoperative navigation surgery was possible to undergo with a splint reproducing the same open-jaw position used during the CT scan. In fact, Ohba et al. [13] applied the navigation system to mandibular surgeries through a transoral approach with wearing a divided splint. Since accurate synchronization of the acquired CT data was also achieved for the mandibular body in our case, cutting of mandible bone based on the pre-operative design was successfully and precisely performed under intraoperative navigation guidance. Since the surgical simulation plans could be transferred to the actual surgery intraoperatively with the guidance of real-time navigation, a surgical template with bone cutting guides was not needed in this case.

A 3-D formable titanium mesh and exclusive forming-hand press machine were used to fabricate a patient- specific titanium mesh tray. This method has major advantages over the conventional bending technique with respect to the mechanical strength of the titanium mesh tray, thus preventing titanium mesh fracture. To avoid this serious complication, Yamada et al. [11] reported that combination repair with a titanium reconstruction plate or fabrication of a reinforced titanium mesh tray (e.g. double layered titanium mesh) was necessary for the cases of long-span defect of the mandible. Instead of their materials, a 3-D formable titanium mesh may play critical roles in mandibular reconstruction. Furthermore, mandibular reconstruction using CAD/CAM-mediated trays has advantages of being accurately reproduced and less time-consuming [9] . Therefore, computer-assisted mandibular reconstruction with a CAD/CAM-mediated, patient-specific reconstruction titanium mesh tray becomes a promising method for mandibular reconstruction.

In this case, to achieve satisfactory oral functions, including masticatory performance, mouth opening, and speech, placement of dental implants and prosthodontic rehabilitation are planned as the next step. These sequential treatments are needed for the patient to recover his quality of life, both physiologically and psychologically.

Taken together, integration of preoperative software planning, 3-D surgical simulation combined with intraoperative navigation, and CAD/CAM-mediated patient-specific reconstruction materials improves the surgeons’ ability to tailor mandibular reconstruction to individual patients. In the near future, computer-assisted surgery will become standard in craniomaxillofacial surgery.

No grants were received in relation to this paper.

The authors declare that they have no competing interests.