Background
Skeletal malocclusion affects oral health and is highly associated with dental trauma and masticatory difficulties as secondary effects of parafunction and teeth crowding [
1]. Orthognathic surgery (OGS) is used to resolve imbalances involved in the craniofacial structure and skeletal malocclusion, thereby improving the oral and facial function and aesthetics of the patient. The efforts of both orthodontists and surgeons can dramatically improve the quality of life of patients experiencing functional and aesthetic discomfort. However, jaw misplacement by a surgeon during OGS is difficult for an orthodontist to revise after the operation. During traditional bimaxillary OGS, the maxilla is first moved, and the mandible is relocated relative to the maxilla. Therefore, it is most important to move the maxilla to a planned position during OGS. Efforts to achieve such outcomes include freehand relocation [
2] and the use of an internal reference point, which are currently applied by several surgeons. However, external reference points are the most accurate method to use during LeFort I osteotomy [
3]. In recent years, the progress in OGS has mainly resulted from the use of a virtual surgery plan (VSP) to accurately reposition the bone segments [
4]. There are problems associated with conventional OGS and several reasons why VSPs are favored. An analysis of dentofacial deformity is based on the information obtained through several preoperative examinations. Once the analysis is completed, subsequent surgical planning is initiated using a visual treatment objective (VTO), which determines where each component should be positioned in relation to the fixed reference structure (skull base) and another. When the VTO involves the movement of only a single jaw, either the maxilla or mandible, a simple hinge articulator is sufficient for mock surgery. However, when the VTO involves the movement of both jaws, a semi-adjustable articulator is used as these articulators can better reproduce the centric relation (CR) and centric occlusion within an acceptable anatomical average. The most difficult aspect in performing model surgery is in the repositioning of the maxillary cast during bimaxillary surgery [
5]. After the mock surgery is performed according to the surgical plan, two surgical occlusal splints (an intermediate splint (IMS) and a final splint) are made for bimaxillary surgery. Occlusal splints (or wafers) locate the dental arches in any preplanned relationships and eliminate unreliable intraoperative guesswork [
6]. As the first step in simulating a bimaxillary surgery, a face-bow transfer procedure is required to transfer the maxilla to a semi-adjustable articulator. However, it is impossible to transfer the patient’s maxillary dentition to the articulator and accurately reproduce the patient’s anatomy [
7‐
10]. In addition, it is difficult to achieve complete three-dimensional (3D) movement in a model surgery in cases of patients with severe facial anomalies, even though the face-bow is used to correctly reproduce the patient’s actual maxillary position in the articulator. During the model surgery, the upper arm of the semi-adjustable articular is used as a reference for moving the maxillary cast. However, the most common technique for repositioning the maxilla in the operating room is the use of an external reference point with the help of the IMS. Therefore, the substantive reference for repositioning the maxilla is the mandible. In most cases, OGS requiring maxillary movement is performed under general anesthesia. Some researchers have reported that the position of the mandible deviates from its normal position under general anesthesia [
11,
12]. Even if a face-bow transfer is performed well enough to accurately reflect the anatomy of the patient, the model surgery is performed well, and the IMS is made perfectly, errors may occur when the surgeon uses the mandible as a reference and repositions the maxilla using only the IMS. Therefore, considerable time is required to determine the desired position of the maxilla when conventional bimaxillary surgery is planned. Recently, computer-aided surgical simulation (CASS) and device manufacturing using computer-aided design (CAD) and computer-aided manufacturing (CAM) technologies have attracted attention for precise OGS [
13,
14]. Herein, we performed a VS using FaceGide® (MegaGen Co., Daegu, Korea), a CASS program, instead of a model surgery and face-bow transfer in preparation for OGS. In addition, patient-customized miniplates (PCMs) were used instead of the IMS. The purpose of this study was to evaluate the surgical accuracy and long-term stability of maxillary repositioning using the FaceGide® system by comparing cone beam computed tomography (CBCT) images over time.
Discussion
In this study, we report virtual surgical simulation with FaceGide® incorporating PCGs (including drilling holes for screws), PCMs and a customized final splint. In our series, the surgical transfer of the VSP by FaceGide® showed good accuracy, and the final position of the maxilla measured at the points associated with the root of the tooth (bone surface) was 0.94 ± 0.17 mm from the mean value. The ANS, PNS, and A point may show large differences between Tv and T1 because they are the sites of bone removal during the actual operation. However, the error was still approximately 1.01 ± 0.3 mm, even when these points were included.
With the introduction of CBCT, which reduces the hardware costs and radiation doses, 3D imaging can be used as a standard tool for diagnosis and treatment planning [
16]. Although it is possible to obtain much information from this 3D diagnostic method, the IMS is generally used in conventional bimaxillary OGS. Increased use of the IMS can cause postoperative problems because the inherent thickness of the splint may result in a degree of autorotation after the splint’s removal [
17]. Additionally, Perez et al. reported that the temporomandibular joint (TMJ) is not a discrete ball-and-socket joint. The mandibular condyle rotates and translates within the TMJ [
18]. Therefore, repositioning the maxilla in relation to the position of the mandible may have several limitations. The mandible and maxilla can be fixed together with an IMS during OGS, but a certain amount of space can develop as a result of the mobility of the mandibular condyle. Therefore, the maxilla cannot be precisely positioned relative to the base of the skull using only an IMS, and the surgeon must take time to adjust it manually. In addition, inaccuracy of the IMS can arise from the model surgery stage. Model surgery depends on the accurate recording of the occlusion in the retruded position and the face-bow transfer to the articulator. These recordings both have inherent inaccuracy. Baily et al. measured the angulation of the occlusal plane to the Frankfort plane on a Hanau articulator and compared this with lateral cephalograms; they found a mean difference of 5 degrees, which corresponded to 70% of the error during the face-bow transfer [
19]. Ellis et al. reported that the average case had an inaccuracy of almost 7 degrees in the angulation of the occlusal plane [
20]. The accuracy of the 3D position of the upper first molar was highly variable using four different Hanau face-bows [
21]. When using a conventional articulator for OGS, it is essential that the angle between the occlusal plane and the Frankfort horizontal plane for the patient is the same as the angle between the occlusal plane and the upper member of the articulator on the maxillary model. OGS using the FaceGide® system can reduce errors related to mock surgery because it does not use such an articulator during preoperative preparation.
The surgical method presented in this study using the FaceGide® system is not necessary for all patients with craniofacial deformity. Rustemeyer et al. reported that a 2D cephalometric analysis and a 3D mock operation are sufficient for accurate planning and will ensure good results for experienced surgeons [
22]. We agree with this opinion, and if the patient has no facial asymmetry or requires only single-jaw surgery, conventional OGS can produce good results. However, if major 3D movements are indicated, including changes to the transverse occlusal plane or major rotation of the jaws, a navigation system should be chosen for complex 3D planning and controlling the position of the maxilla during surgery [
23]. Most of the patients in this study had facial asymmetry. Therefore, the use of the FaceGide® system was recommended for surgery, and complex 3D movement of the jaws was performed. Our method of OGS using the FaceGide® system is very original, albeit not new. The principle of the FaceGide® system that we present is based on the combination of previously mentioned processes and is associated with predrilling determined by a reverse approach [
24]. In a study by Xia et al., the final state was made into a medical replica after the VS, and the ready-made plates were bent according to the outline of this replica. During the actual operation, drilling for screw insertion was performed using the navigation system [
24]. Use of the FaceGide® system is the same as the reverse approach of that reported by Xia et al., but customized miniplates and corresponding osteotomy guides (including drilling guides) are used. Similar processes involving predrilling and positioning osteotomy guides or prebent plates in OGS have been reported [
25‐
28].
Ellis reported that the average accuracy of maxillary positioning in the horizontal plane deviated 2 mm from what was planned when external references were used, whereas the vertical accuracy ranged from 0.5 to 1 mm [
29]. Jacobson et al. reported that a 2-mm or greater discrepancy was noted for 20 to 30% of 46 patients who underwent LeFort I osteotomy [
30]. With the development of CAD and CAM, VSPs and 3D-printed navigation templates have been proposed as alternatives to conventional model surgery [
31]. Sun et al. performed a clinical study using an orthognathic surgical template made from a 3D printer and VSP and reported that the mean vertical, lateral, and anteroposterior errors in the anterior maxillary region were 0.57 mm, 0.35 mm, and 0.5 mm, respectively [
32]. Although our study shows a higher error than that of Sun et al.’s study, the difference may have been due to the use of different measurement methods, and our error was smaller than that reported in previous studies [
29,
30] that used conventional methods. During the entire process, errors in surface rendering, data integration (merging dentition and CBCT data), and setting 3D coordinates in the virtual space or during guide, surgical splint and miniplate fabrication (3D printing or milling process) are related to accuracy. Accuracy can be improved with the use of a systemic process during surgical planning and preparation. Zinser et al. reported that the mean vertical, lateral, and anteroposterior errors compared with the anterior maxillary region were 0.23 mm, 0.04 mm, and 0.09 mm, respectively, and that the vertical, lateral, and anteroposterior errors compared with the posterior maxillary region were 0.15 mm, 0.04 mm, and 0.1 mm, respectively [
33]. Our results are not comparable because we did not use the same measurement approach that was used by Zinser et al. However, in our study, the differences between the VS and the actual surgery were 0.26 mm, 0.47 mm, and 1.11 mm in the anterior maxillary region (incisor tip, #13 cusp tip and #23 cusp tip) and 0.02 mm, 1.6 mm, and 0.6 mm in the posterior maxillary region (#16 cusp tip, #26 cusp tip and PNS).
We are aware that this study may have limitations. The small number of patients in this retrospective study limits the ability to draw definite conclusions. One reason for the small sample size was the utilization of strict inclusion and exclusion criteria, which resulted in the exclusion of the majority of patients who underwent OGS in the department during the study period. However, image analysis using 3D comparison programs is highly reproducible and can yield significant results even with a small number of cases. There were some trial and error in the operation using the FaceGide® system. There were no significant differences between ΔTv and ΔT0, but in some cases, the Y coordinate value of the PNS was somewhat different from that of the other sites. Therefore, even when the operation is performed using this system, more attention should be paid when the posterior part of the maxilla is moved. In three patients, the maxilla was unstable after fixation, so the ready-made miniplates were added for reinforcement. In some cases in which the surgeon was unfamiliar with the newly developed system, wide-diameter screws were used because of a widening of the holes after drilling. However, this problem could be solved by drilling with a small-diameter round burr and self-drilling screws. PCGs with an arm that originates from the cusp of the teeth can also confirm the accuracy of the bone contact (Fig.
2). Minor mispositioning of the PCGs is impossible to detect by the naked eye and can result in erroneous cuts. Therefore, this type of PCG is believed to be more accurate than a bone-only supported guide because it is supported by both the bone surface and the cusp of the teeth, but further research regarding its accuracy is needed. The accuracy of OGS using CASS is influenced by reproduction of the VS in the actual surgery. Individual errors can originate from internal sources, including the CBCT image quality, file conversion process, computer design software, and interactions between mechanical components, and external sources, such as the adaption of the osteotomy guide, customized plate, and splints and the surgeon’s experience. The accumulation of such errors produces the total deviation between the planned and postoperative outcomes. However, this study demonstrates the suitable accuracy and stability of OGS using the FaceGide® system.
The facial surgery protocol using FaceGide® has advantages similar to those of other CASS systems. Digital diagnosis and VS data files can be transmitted to the surgeon and orthodontists for final adjustments [
33]. Such exchanges have the advantage of allowing the creation of an interdisciplinary platform that centralizes the technical and surgical domains of expertise and produces financial and operative efficiency, all within a digital environment [
31]. Because the site of the bone screw insertion is designed to avoid the root of the tooth, it is unlikely that root damage will occur when conventional methods are used. Some clinicians may claim that using CASS can expose the patient to increased radiation [
34]. However, it can eliminate the need for additional radiographic examinations, which is indicated when there are doubts about the final surgical position. It is well known that the radiation dose of most CBCT systems used to acquire DICOM data is considered minimal [
35]. There have been reports of the use of one piece of customized plate in the maxilla that have claimed accuracy [
36‐
38]. However, the amount of titanium used in one-piece plates is greater than the amount of titanium used in conventional maxillary fixation methods. Hosoki et al. reported that the detailed mechanism of action of allergy and hypersensitivity to metallic materials is not known but is related to the total exposure to specific metallic ions [
39]. In this study, four customized L-shaped miniplates were used, and they remained stable for more than one year without any bone changes. An excessive amount of titanium can cause a foreign body reaction. The volume of titanium used in our study is equal to or less than the volume of titanium used in the conventional fixation method of LeFort I osteotomy. Although not reported in this study, the PCMs were removed in three patients one year after surgery and did not cause clinical problems. Future studies involving PCM removal will be conducted. Unlike conventional surgery, the use of PCGs in our study allowed us to remove the necessary amount of bone, thereby increasing contact between bone segments. Our method was less invasive than conventional methods, and the patients recovered rapidly and were able to return quickly to normal life.