Genioplasty using a simple CAD/CAM (computer-aided design and computer-aided manufacturing) surgical guide
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The present study introduces the design and fabrication of a simple surgical guide with which to perform genioplasty.
A three-dimensional reconstruction of the patient’s cranio-maxilla region was built, with a dentofacial skeletal model, then derived from CT DICOM data. A surgical simulation was performed on the maxilla and mandible, using three-dimensional cephalometry. We then simulated a full genioplasty, in silico, using the three-dimensional (3D) model of the mandible, according to the final surgical treatment plan. The simulation allowed us to design a surgical guide for genioplasty, which was then computer-rendered and 3D-printed. The manufactured surgical device was ultimately used in an actual genioplasty to guide the osteotomy and to move the cut bone segment to the intended location.
We successfully performed the osteotomy, as planned during a genioplasty, using the computer-aided design and computer-aided manufacturing (CAD/CAM) surgical guide that we initially designed and tested using simulated surgery.
The surgical guide that we developed proved to be a simple and practical tool with which to assist the surgeon in accurately cutting and removing bone segments, during a genioplasty surgery, as preoperatively planned during 3D surgical simulations.
KeywordsGenioplasty CAD/CAM Surgical guide
The simulation of orthognathic surgery using three-dimensional (3D) facial skeletal analyses is increasingly popular [1, 2, 3]. The patients’ computed tomography (CT) images can be combined to construct three-dimensional models with which to simulate surgery. These simulations allow us to plan the osteotomy line and predict any movement of the jaw. The surface-data generated is converted into a stereolithography (STL) model, which is computer-rendered and then 3D-printed. These processes follow well-established, computer-aided design and computer-aided manufacturing (CAD/CAM) protocols used for medical devices. The result is a 3D-printed orthognathic surgical guide. The fusion of 3D imaging and ever more powerful CAD/CAM technologies is a powerful new driver in allowing surgeons to design, and create, multiple new surgical devices for use in orthognathic surgeries [1, 4, 5].
Surgical simulations provide the opportunity to derive a more accurate preoperative diagnosis and then plan and simulate surgery. Success at this stage is more likely to lead to the esthetic and functional outcomes desired [6, 7]. For our purposes, several surgical devices can be used to establish the osteotomy line and measure the movement of the chin bone in a genioplasty [4, 6, 7]. In this study, we assessed one method of genioplasty, in which we performed a 3D surgical simulation of a mandibular genioplasty . By simulating the osteotomy on a 3D model, we predicted the movements of the cut chin bone and used these data to 3D-print a surgical guiding device. This device could then be used in an actual genioplasty to guide the osteotomy and move the cut bone segment to the intended location.
Surgical simulation and the manufacture of a surgical guide for advancement genioplasty
Using facial CT data, with slices of less than 1 mm, we reconstructed three-dimensional surfaces using the Mimics software (version 14.0, Materialise, Leuven, Belgium), using the CT data imported in DICOM format (Digital Imaging and Communications in Medicine). The patient’s cranio-maxilla region was reconstructed as a three-dimensional image, and then a model of the dentofacial skeleton was generated using the CT DICOM data. We then performed a surgical simulation on the maxilla and the mandible, using three-dimensional cephalometry; at this point, the final surgical treatment plan was established. A genioplasty simulation was then conducted using the 3D model of the mandible, according to the surgical plan. We could now rehearse, in silico, the osteotomy of the mentum, paying close attention to the positions of the mental nerve, the mental formen, and the margin between the osteotomy line and the anterior teeth root apex. The outcome of this simulation allowed us to make any final adjustments to the position of the osteotomy line.
Advancement genioplasty using a surgical guide
Having completed the surgery simulations, we progressed to actual surgery. The manufactured device was positioned and fitted to the exposed chin bone during surgery. The “fitting process” is guided by the surgical plan, generated in computer simulations of this phase of the surgery. As mentioned, the anteroposterior width of the surgical guide equaled the desired forward movement of the mandible. Then, mini screws, approximately 2–4 mm longer than the width of the device, were used to fix the device into position; screw positioning depended on the method chosen to stabilize the cut chin bone. For central plate positioning, flanking screws must be used, as in the present example. If the metal plate is to be fixed to the left or right, then only one screw must be used, at the center of the surgical guide. In these cases, the surgeon must pay close attention to ensure that the guide does not slip and rotate, while being attached to the chin bone.
Surgical simulation and manufacturing a surgical guide for reduction genioplasty
Reduction genioplasty using a surgical guide
Results and discussion
Recently, there have been several reports of cutting guides used in genioplasty of the mandible [4, 6, 7]. These guides confer several advantages. First, the form and position of the osteotomy line can be adjusted in simulated surgery, which allows the osteotomy line to be preoperatively planned, minimizing the possibility of dental or neural damage. Moreover, using a cutting guide allows the surgeon to adjust the depth when cutting, leading to a non-invasive and stable osteotomy. Cutting guides also make orthognathic surgeries easier by allowing the bone segments to be moved to the planned positions, according to the design of the guide. In a recent multicenter study, the root-mean-square deviation (RMSD) was used to measure the results of orthognathic surgeries using computer-aided surgical simulations (CASS) . Significantly fewer errors were found for genioplasty when surgical guides were used, which led to more favorable surgical outcomes; the largest positional RMSD was 1.0 mm, and the largest orientation RMSD was 2.2°. When a surgical guide was not used, the outcomes varied .
There are also drawbacks to using a cutting guide. These include the extra cost of the design and manufacture of a surgical guide. However, these disadvantages diminish as the technologies in this field improve. Given that CAD/CAM-based orthognathic guides are already in use for the maxilla, additional guide models for use in genioplasty can be designed and manufactured more rapidly and therefore more cheaply. We envisage the use of orthognathic surgical guides to cut, and remove, the jaw. In addition, they could be used in conjunction with jaw positioning guides, to allow the surgeon to determine the amount of jaw displacement, using landmark data. More complex guides could even be designed to both hold maxillary and mandibular bone segments in place and link with cutting guides.
Practically, then, it may be more helpful to perform a simulation surgery and then manufacture guides using a 3D printer. Polley et al. reported various CAD/CAM-based surgical guides for use in orthognathic surgeries . Among these devices, those used in genioplasty required more accurate mandibular dental data, and were more complex to design, compared to the method that we now describe [4, 8]. The usefulness of STL guides may also depend on the surgeons’ expertise, and the type of genioplasty, such as zigzag genioplasty [10, 11, 12].
Currently, preoperative surgical simulations are widely used and confer an array of advantages . The benefits of faster and more accurate operations when using STL-derived surgical guides are clear [6, 9, 14]. However, there is a cost associated with the time, effort, and materials needed to design and manufacture these devices. Surgical guides may be of most use in complex genioplasty, when it is difficult to accurately reproduce the results of a surgical simulation in the actual operation room with small error; in these scenarios, a surgical guide can be hugely beneficial in guiding the surgeon. We believe that this study will be followed by more thorough research on various designs of surgical guides for use in genioplasty. We expect further research on the development and assessment of orthognathic surgical devices, together with iterative improvements in computing power and software that will expand the possibilities for computer-assisted surgeries. Enhanced navigation and precision robotic surgeries will further increase the power of the now well-established CAD/CAM field in orthognathic surgery [15, 16].
Using the surgical guide that we have designed, the surgeon can locate the exact point of the chin bone to be cut and can easily perform the osteotomy and genioplasty, according to the simulation plans. Furthermore, the guide can be used as a wafer, fixing the chin bone and clearing the operating view for surgeons. An additional benefit is that this particular surgical guide is small and easy to design, which reduces the time and cost needed to manufacture the device with a 3D printer.
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