9.1 Introduction

We are working in the era of the fourth industrial revolution, which includes three-dimensional (3D) computer simulation, computer-aided design–computer-aided manufacturing technology, 3D printing technology, artificial intelligence, augmented reality, virtual reality, and navigation. Some doctors may believe that these technologies are mostly used in industry; however, 3D technology is already a reality in medicine.

Craniofacial surgeons, in particular, are pioneers in the clinical application of these technologies, with 3D computer simulations, computer modelling, and 3D printing technology having been applied since the late 1990s. Since the 2000s, the rapid prototype model has been commonly used in craniofacial surgical planning. Since the 2010s, 3D printing technology has become a daily routine in many craniofacial practices [1–4] (Fig. 9.1).

Do you use a navigation system when you drive? I do, most of the time. Of course, without using a navigation system, I could arrive at my destination (Fig. 9.2). However, using such a system makes me more comfortable while driving. I believe that the adoption of the new 3D technologies will allow us, in a manner analogous to our automobile navigation systems, to reach our desired destination quickly, precisely, and reproducibly. This is the role of 3D simulation and 3D printing technology in medicine.

In orthognathic surgery, the traditional dental model setup is a typical example of presurgical simulation, and the occlusal splint or wafer provides a very good example of a surgical guide that connects the simulation with the real surgery.

Now that orthodontists and maxillofacial surgeons have used these simulation processes for a long time, they can adopt the brand-new 3D technologies more easily, in my opinion.

Simulation-guided orthognathic surgery (SGOS) is the process of using 3D patient data to create a stepwise guide for making an accurate diagnosis, creating 3D cephalometric measurements, virtually planning the surgical steps, and predicting the consequences of these steps on the dentoskeletal complex and soft tissue envelope.

I adopted 3D simulation and 3D printing technology for orthognathic surgeries in 2012. Prior to that, even without 3D simulation and 3D printing, orthognathic surgeries were successfully performed, in my practice. However, the adoption of these 3D technologies has allowed me to prepare for the surgery more intensively, more precisely perform operations, and more objectively evaluate the surgical outcomes.

Several reports have recently aimed to establish the basics of this domain. Thus, the broad lines of the technique (starting with data acquisition and passing through segmentation, surgical step simulation, and plan-transport template designs) are now widely accepted [4–6]. Furthermore, the development of simulation software has allowed prediction of soft tissue responses and provided the aesthetic standards for different populations (aesthetic-centered virtual planning) [7–9]. Studies on the efficacy of using virtual surgical planning (VSP) reported higher osteotomy and repositioning accuracies and greater timesaving during the planning and surgical stages than conventional methods [10–13].

As expected, the increased popularity of these techniques has drawn attention to measuring outcome accuracies and comparing them with conventional methods, as well as comparing different techniques [14–16]. However, measuring SGOS accuracy has two considerations. The first is the applicability of comparing VSP to real surgery, as VSP should be measured as a separate entity with its own controlling factors, regardless of its utility in planning the accuracy of surgical techniques (Fig. 9.1). The second is that the absolute difference between measurements mainly depends on large travel distances. Therefore, another method for detecting the accuracy of small movement achievements should be used to investigate the factors affecting VSP applicability accurately. For the understanding of the readers, I introduce how to apply the 3D computer simulation and patient-specific 3D printing technology to the orthognathic surgery. Then I will share my outcomes of my investigation related to simulation guided orthognathic surgery.

9.2 Methods [17, 18]

9.2.1 Data Acquisition

Two forms of data are acquired before the simulation process: (1) radiographic data from cone-beam computed tomography (CT; 1-mm thick) are obtained in a Digital Imaging and Communications in Medicine (DICOM) file and (2) a 3D file of the external facial appearance, created using a special 3D scanner (Morpheus 3D; Dental Solution MDS, Seoul, South Korea) designed to acquire a rich 3D file that is used in the simulation process (soft tissue 3D file) (Fig. 9.3).

Subsequently, the two sets of data are introduced to the simulation and aligned using a semiautomatic process. In cases where dental landmarks are unclear, an additional data file containing scanned dental arches is merged with the skeletal 3D file. We use two types of software during the study: the Mimics program (version 19, Materialise-NV, Leuven, Belgium) is mainly used for bone segmentation and cephalometric analyses and the Morpheus 3D program (Dental Solution MDS, Seoul, South Korea) is used for soft tissue simulation; both are used in VSP.

9.2.2 Virtual Surgical Planning

Using the simulation tools, the planned osteotomies are performed for both jawbones, including the Le Forte 1 osteotomy in the maxilla and the bilateral sagittal split osteotomy and genioplasty in the mandible. Afterward, the bone segments are moved, in a scaled manner, relative to the XYZ axes. These movements are performed under the guidance of the orthodontic plan, which was previously introduced into the software, and the average aesthetic measurements of the Korean population, which are integrated into the program database in the form of reference anthropometric measurements (Fig. 9.4).

9.2.3 Template Design and Manufacture

The surgical templates are designed as intermediate and final wafers, along with repositioning guides (Fig. 9.5). The designs are made using 3matic (version 11, Materialise-NV) and are based on the simulation results. Subsequently, the templates are 3D printed, using liquid-based techniques (stereolithography), to prepare them for intraoperative use.

9.2.4 Surgical Intervention

These templates undergo preoperative, low-temperature plasma sterilization to avoid any risk of deformation. After the LeFort I osteotomy has been performed, the intermediate wafer and maxillary repositioning template are used to guide the maxillary movement in 3D patterns. Similarly, after mandibular osteotomies, the final wafer and mandibular repositioning template are used for mandibular repositioning (Fig. 9.6).

9.3 Postoperative Analysis

I introduce one of my investigations regarding the postoperative analysis in the clinical application of 3D technology to orthognathic surgery [18]. This retrospective study included patients with dentofacial deformities who underwent 3D simulation-guided two-jaw surgeries between June 2015 and February 2017 in the Plastic Surgery Department of Asan Medical Center (Seoul, South Korea). The study inclusion criteria required the patients to be ≥16 years old, undergo two-jaw orthognathic surgery with 3D VSP guidance, and using digitally designed plan-transporting templates. After excluding patients with previous orthognathic surgeries, 35 participants were included. 3D CT data was combined with 3D camera data (Fig. 9.7).

CT was performed within the first 3 postoperative weeks; the DICOM file was uploaded into the simulation software to create the early postoperative 3D model.

9.3.1 Measurement Protocol (Fig. 9.8)

The preoperative, post-simulation, and postoperative 3D models undergo similar measurements by recording certain point positions, including, the upper canine, right upper canine, left upper molar 1, right upper molar 1, left upper incisor-anterior nasal spine (ANS), ANS-posterior nasal spine (PNS) positions for the maxilla, and the lower molar 1, right-lower molar 1, left B-point-pogonion positions for the mandible. These points are measured relative to 3 fixed planes (Frankfort horizontal, coronal, and sagittal planes) that are perpendicular to each other at the Sella point. Subsequently, the travel distances are calculated as positional differences for each point, relative to the XYZ axes. This was done by the planned travel distances (Tp) being used to represent the movement from the preoperative to post-simulation positions and the actual travel distances (Ta) being represented by the preoperative to early postoperative positions (Fig. 9.1). Each point is measured twice, and the mean of both measurements is approximated to the nearest 0.01-mm value.

To calculate the applicability, we measure the absolute difference between Ta and Tp to determine the absolute misapplication index (abMAI) and two other equations used to determine the relative MAI (rMAI):

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