An integrated orthognathic surgery system for virtual planning and image-guided transfer without intermediate splint

Customized Genioplasty and Advantages of 3D Virtual Planning: An Updated Literature Review

Genioplasty is a surgical technique that modifies the projection of the chin in three dimensions to achieve symmetry and facial harmonization. Virtual 3D planning is increasingly used, supplanting the conventional surgical technique due to the precise and predictable results obtained.The definition of the objective of the study was first carried out using the PICO (Patient, Intervention, Comparison, Outcome) question method. Posteriorly, an updated literature review was carried out in the "PubMed" database using the keywords "Genioplasty and Virtual 3D Planning," obtaining 11 articles for the study with the objective of defining the advantages and disadvantages of performing a virtually planned genioplasty, comparing it with the conventional technique.In the results, it is observed that virtually planned genioplasty presents greater precision, a reduction in surgical time, and a lower rate of complications than the conventional technique. Virtual planning using computer-aided design/computer-aided manufacturing technology presents good reproducibility in the patient with <2 mm variations between what was planned and what was obtained postoperatively, with statistically significant results (p < 0.001).In conclusion, virtually planned genioplasty with customized cutting guides and osteosynthesis plates achieves very precise surgery results with good reproducibility, reducing surgical time, intraoperative complications, and the difficulty of the surgical technique.

V2-Net: An Attention-guided Volumetric Regression Network for Tooth Landmark Localization on CT Images with Metal Artifacts

For virtual surgical planning in orthognathic surgery, marking tooth landmarks on CT images is an important procedure. However, the manual localization procedure of tooth landmarks is time-consuming, labor-intensive, and requires expert knowledge. Also, direct and automatic tooth landmark localization on CT images is difficult because of the lower resolution and metal artifacts of dental images. The purpose of this study was to propose an attention-guided volumetric regression network (V2-Net) for accurate tooth landmark localization on CT images with metal artifacts and lower resolution. V2-Net has an attention-guided network architecture using a coarse-to-fine-attention mechanism that guided the 3D probability distribution of tooth landmark locations within anatomical structures from the coarse V-Net to the fine V-Net for more focus on tooth landmarks. In addition, we combined attention-guided learning and a 3D attention module with optimal Pseudo Huber loss to improve the localization accuracy. Our results show that the proposed method achieves state-of-the-art accuracy of 0.85 ± 0.40 mm in terms of mean radial error, outperforming previous studies. In ablation studies, we observed that the proposed attention-guided learning and a 3D attention module improved the accuracy of tooth landmark localization in CT images of lower resolution and metal artifacts. Furthermore, our method achieved 97.92% in terms of the success detection rate within the clinically accepted accuracy range of 2.0 mm.

A Complete Digital Workflow for Planning, Simulation, and Evaluation in Orthognathic Surgery

The purpose of this study was to develop a complete digital workflow for planning, simulation, and evaluation for orthognathic surgery based on 3D digital natural head position reproduction, a cloud-based collaboration platform, and 3D landmark-based evaluation. We included 24 patients who underwent bimaxillary orthognathic surgery. Surgeons and engineers could share the massive image data immediately and conveniently and collaborate closely in surgical planning and simulation using a cloud-based platform. The digital surgical splint could be optimized for a specific patient before or after the physical fabrication of 3D printing splints through close collaboration. The surgical accuracy was evaluated comprehensively via the translational (linear) and rotational (angular) discrepancies between identical 3D landmarks on the simulation and postoperative computed tomography (CT) models. The means of the absolute linear discrepancy at eight tooth landmarks were 0.61 ± 0.55, 0.86 ± 0.68, and 1.00 ± 0.79 mm in left–right, advance–setback, and impaction–elongation directions, respectively, and 1.67 mm in the root mean square direction. The linear discrepancy in the left–right direction was significantly different from the other two directions as shown by analysis of variance (ANOVA, p < 0.05). The means of the absolute angular discrepancies were 1.43 ± 1.06°, 0.50 ± 0.31°, and 0.58 ± 0.41° in the pitch, roll, and yaw orientations, respectively. The angular discrepancy in the pitch orientation was significantly different from the other two orientations (ANOVA, p < 0.05). The complete digital workflow that we developed for orthognathic patients provides efficient and streamlined procedures for orthognathic surgery and shows high surgical accuracy with efficient image data sharing and close collaboration.

Robot-Assisted Maxillary Positioning in Orthognathic Surgery: A Feasibility and Accuracy Evaluation

Several methods enabling independent repositioning of the maxilla have been introduced to reduce intraoperative errors inherent in the intermediate splint. However, the accuracy is still to be improved and a different approach without time-consuming laboratory process is needed, which can allow perioperative modification of unoptimized maxillary position. The purpose of this study is to assess the feasibility and accuracy of a robot arm combined with intraoperative image-guided navigation in orthognathic surgery. The experiments were performed on 12 full skull phantom models. After Le Fort I osteotomy, the maxillary segment was repositioned to a different target position using a robot arm and image-guided navigation and stabilized. Using the navigation and the postoperative computed tomography (CT) images, the achieved maxillary position was compared with the planned position. Although the maxilla showed mild displacement during the fixation, the mean absolute deviations from the target position were 0.16 mm, 0.18 mm, and 0.20 mm in medio-lateral, antero-posterior, and supero-inferior directions, respectively, in the intraoperative navigation. Compared with the target position using postoperative CT, the achieved maxillary position had a mean absolute deviation of less than 0.5 mm for all dimensions and the mean root mean square deviation was 0.79 mm. The results of this study suggest that the robot arm combined with the intraoperative image-guided navigation may have great potential for surgical plan transfer with the accurate repositioning of the maxilla in the orthognathic surgery.

Effect of computer-assisted design and manufacturing cutting and drilling guides accompanied with pre-bent titanium plates on the correction of skeletal class II malocclusion: a randomized controlled trial

This study was performed to assess the effect of correcting skeletal class II malocclusion based on the application of computer-assisted design and manufacturing (CAD/CAM) cutting and drilling guides accompanied with pre-bent titanium plates. Fifty patients with skeletal class II malocclusion were recruited into this prospective randomized controlled clinical trial and assigned to two groups. Patients underwent bilateral sagittal split ramus osteotomy directed by CAD/CAM cutting and drilling guides accompanied with pre-bent titanium plates (group A) or CAD/CAM splints (group B). Postoperative assessments were performed. Differences between the virtually simulated and postoperative models were measured. Patients in both groups had a satisfactory occlusion and appearance. More accurate repositioning of the proximal segment was found in group A than in group B when comparing linear and angular differences to reference planes; however, no significant difference was revealed for the distal segment. In conclusion, CAD/CAM cutting and drilling guides with pre-bent titanium plates can provide considerable surgical accuracy for the positional control of the proximal segments in bilateral sagittal split ramus osteotomy for the correction of skeletal class II deformities.

Postsurgical changes of mandible based on vertical dimension increase in Skeletal Class III deformities

The aim of this study was to evaluate the postsurgical mandibular changes after surgery based on vertical dimension increase in skeletal Class III deformities. Patients who underwent mandibular setback surgery for skeletal Class III malocclusion correction with surgery-first orthognathic treatment were enrolled in the study. Lateral cephalograms were obtained at initial visit, immediately after surgery, 6 months after surgery, and at post-treatment. Postsurgical change of the mandible based on the vertical dimension increase was estimated using a diagrammatic method before surgery and this amount was compared with the actual amount of mandibular forward movement at 6 months after the surgery, using a paired t-test and Bland-Altman plot. Thirty patients (16 men and 14 women; mean age, 22.6 years) with skeletal Class III deformities had undergone mandibular setback surgery with the surgery-first orthognathic treatment. Immediately after surgery, the mandible setback was 9.4 ± 3.7 mm at pogonion. Six months after surgery, the mandible moved forward at an average of 2.3 ± 1.5 mm which corresponded to the estimated value of 2.2 ± 0.9 mm. The estimated amount of postsurgical movement did not show a statistically significant difference from the actual value on paired t-test (p = 0.349). The Bland-Altman analysis showed that the difference between the two values was within the limits of agreement. The postsurgical changes based on vertical dimension increase in surgery-first orthognathic treatment might be predicted by using a diagrammatic method.

Quantitative Augmented Reality-Assisted Free-Hand Orthognathic Surgery Using Electromagnetic Tracking and Skin-Attached Dynamic Reference

The purpose of this study was to develop a quantitative AR-assisted free-hand orthognathic surgery method using electromagnetic (EM) tracking and skin-attached dynamic reference. The authors proposed a novel, simplified, and convenient workflow for augmented reality (AR)-assisted orthognathic surgery based on optical marker-less tracking, a comfortable display, and a non-invasive, skin-attached dynamic reference frame. The 2 registrations between the physical (EM tracking) and CT image spaces and between the physical and AR camera spaces, essential processes in AR-assisted surgery, were pre-operatively performed using the registration body complex and 3D depth camera. The intraoperative model of the maxillary bone segment (MBS) was superimposed on the real patient image with the simulated goal model on a flat-panel display, and the MBS was freely handled for repositioning with respect to the skin-attached dynamic reference tool (SRT) with quantitative visualization of landmarks of interest using only EM tracking. To evaluate the accuracy of AR-assisted Le Fort I surgery, the MBS of the phantom was simulated and repositioned by 6 translational and three rotational movements. The mean absolute deviations (MADs) between the simulation and post-operative positions of MBS landmarks by the SRT were 0.20, 0.34, 0.29, and 0.55 mm in x- (left lateral, right lateral), y- (setback, advance), and z- (impaction, elongation) directions, and RMS, respectively, while those by the BRT were 0.23, 0.37, 0.30, and 0.60 mm. There were no significant differences between the translation and rotation surgeries or among surgeries in the x-, y-, and z-axes for the SRT. The MADs in the x-, y-, and z-axes exhibited no significant differences between the SRT and BRT. The developed method showed high accuracy and reliability in free-hand orthognathic surgery using EM tracking and skin-attached dynamic reference.

Three-dimensional accuracy of virtual planning in orthognathic surgery

INTRODUCTION

This study aimed to assess the accuracy of virtual surgical planning (VSP) performed by Dolphin Imaging software (version 11.9; Dolphin Imaging and Management Solutions, Chatsworth, Calif).

METHODS

Ten people requiring bimaxillary surgery and genioplasty were followed up prospectively. All patients had preoperative cone-beam computed tomography, plaster models, and photographs allowing for VSP. Interocclusal intermediate surgical splints were produced using a 3-dimensional (3D) printer. Postoperative images were acquired 15 days after surgery using cone-beam computed tomography. ITK-Snap (version 3.6; Cognitica, Philadelphia, Pa) allowed the segmentation of reliable 3D models. Geomagic Qualify 2013 (3D Systems, Rock Hill, SC) and MeshValmet (version 3.0) were used to identify the differences between VSP and actual surgical results through the root mean square values and the 3D translational displacement (3-axes) of the 3D centroid of each model.

RESULTS

Discrepancies between the VSP and the actual result were found at the mandible (P = 0.013) and the chin (P = 0.013) when considering the root mean square values. In addition, 3D centroid differences were found in the transverse and sagittal direction of the right ramus (P = 0.034 and P = 0.005, respectively) and the sagittal aspect of the left ramus (P = 0.025). Considering 2 mm as a threshold of clinical relevance, almost all the bone fragments (maxilla, proximal, and distal mandibular segments) were accurately corrected by surgery, although not in the chin.

CONCLUSIONS

On the basis of the obtained values, it is possible to consider the Dolphin Imaging software as clinically acceptable for performing virtual orthognathic surgical planning.

Real-time augmented model guidance for mandibular proximal segment repositioning in orthognathic surgery, using electromagnetic tracking

It is essential to reposition the mandibular proximal segment (MPS) as close to its original position as possible during orthognathic surgery. Conventional methods cannot pinpoint the exact position of the condyle in the fossa in real time during repositioning. In this study, based on an improved registration method and a separable electromagnetic tracking tool, we developed a real-time, augmented, model-guided method for MPS surgery to reposition the condyle into its original position more accurately. After virtual surgery planning, using a complex maxillomandibular model, the final position of the virtual MPS model was simulated via 3D rotations. The displacements resulting from the MPS simulation were applied to the MPS landmarks to indicate their final postoperative positions. We designed a new registration body with 24 fiducial points for registration, and determined the optimal point group on the registration body through a phantom study. The registration between the patient's CT image and physical spaces was performed preoperatively using the optimal points. We also developed a separable frame for installing the electromagnetic tracking tool on the patient's MPS. During MPS surgery, the electromagnetic tracking tool was repeatedly attached to, and separated from, the MPS using the separable frame. The MPS movement resulting from the surgeon's manipulation was tracked by the electromagnetic tracking system. The augmented condyle model and its landmarks were visualized continuously in real time with respect to the simulated model and landmarks. Our method also provides augmented 3D coronal and sagittal views of the fossa and condyle, to allow the surgeon to examine the 3D condyle-fossa positional relationship more accurately. The root mean square differences between the simulated and intraoperative MPS models, and between the simulated and postoperative CT models, were 1.71 ± 0.63 mm and 1.89 ± 0.22 mm respectively at three condylar landmarks. Thus, the surgeons could perform MPS repositioning conveniently and accurately based on real-time augmented model guidance on the 3D condyle positional relationship with respect to the glenoid fossa, using augmented and simulated models and landmarks.

Autonomous bone reposition around anatomical landmark for robot-assisted orthognathic surgery

The purpose of this study was to develop a new method for enabling a robot to assist a surgeon in repositioning a bone segment to accurately transfer a preoperative virtual plan into the intraoperative phase in orthognathic surgery. We developed a robot system consisting of an arm with six degrees of freedom, a robot motion-controller, and a PC. An end-effector at the end of the robot arm transferred the movements of the robot arm to the patient's jawbone. The registration between the robot and CT image spaces was performed completely preoperatively, and the intraoperative registration could be finished using only position changes of the tracking tools at the robot end-effector and the patient's splint. The phantom's maxillomandibular complex (MMC) connected to the robot's end-effector was repositioned autonomously by the robot movements around an anatomical landmark of interest based on the tool center point (TCP) principle. The robot repositioned the MMC around the TCP of the incisor of the maxilla and the pogonion of the mandible following plans for real orthognathic patients. The accuracy of the robot's repositioning increased when an anatomical landmark for the TCP was close to the registration fiducials. In spite of this influence, we could increase the repositioning accuracy at the landmark by using the landmark itself as the TCP. With its ability to incorporate virtual planning using a CT image and autonomously execute the plan around an anatomical landmark of interest, the robot could help surgeons reposition bones more accurately and dexterously.

Accuracy of virtual surgical planning in two-jaw orthognathic surgery: comparison of planned and actual results

OBJECTIVE

This study aims to evaluate the accuracy of virtual surgical planning in two-jaw orthognathic surgery via quantitative comparison of preoperative planned and postoperative actual skull models.

STUDY DESIGN

Thirty consecutive patients who required two-jaw orthognathic surgery were included. A composite skull model was reconstructed by using Digital Imaging and Communications in Medicine (DICOM) data from spiral computed tomography (CT) and STL (stereolithography) data from surface scanning of the dental arch. LeFort I osteotomy of the maxilla and bilateral sagittal split ramus osteotomy (of the mandible were simulated by using Dolphin Imaging 11.7 Premium (Dolphin Imaging and Management Solutions, Chatsworth, CA). Genioplasty was performed, if indicated. The virtual plan was then transferred to the operation room by using three-dimensional (3-D)-printed surgical templates. Linear and angular differences between virtually simulated and postoperative skull models were evaluated.

RESULTS

The virtual surgical planning was successfully transferred to actual surgery with the help of 3-D-printed surgical templates. All patients were satisfied with the postoperative facial profile and occlusion. The overall mean linear difference was 0.81 mm (0.71 mm for the maxilla and 0.91 mm for the mandible); and the overall mean angular difference was 0.95 degrees.

CONCLUSIONS

Virtual surgical planning and 3-D-printed surgical templates facilitated the diagnosis, treatment planning, and accurate repositioning of bony segments in two-jaw orthognathic surgery.

Virtual skeletal complex model- and landmark-guided orthognathic surgery system

In this study, correction of the maxillofacial deformities was performed by repositioning bone segments to an appropriate location according to the preoperative planning in orthognathic surgery. The surgery was planned using the patient's virtual skeletal models fused with optically scanned three-dimensional dentition. The virtual maxillomandibular complex (MMC) model of the patient's final occlusal relationship was generated by fusion of the maxillary and mandibular models with scanned occlusion. The final position of the MMC was simulated preoperatively by planning and was used as a goal model for guidance. During surgery, the intraoperative registration was finished immediately using only software processing. For accurate repositioning, the intraoperative MMC model was visualized on the monitor with respect to the simulated MMC model, and the intraoperative positions of multiple landmarks were also visualized on the MMC surface model. The deviation errors between the intraoperative and the final positions of each landmark were visualized quantitatively. As a result, the surgeon could easily recognize the three-dimensional deviation of the intraoperative MMC state from the final goal model without manually applying a pointing tool, and could also quickly determine the amount and direction of further MMC movements needed to reach the goal position. The surgeon could also perform various osteotomies and remove bone interference conveniently, as the maxillary tracking tool could be separated from the MMC. The root mean square (RMS) difference between the preoperative planning and the intraoperative guidance was 1.16 ± 0.34 mm immediately after repositioning. After surgery, the RMS differences between the planning and the postoperative computed tomographic model were 1.31 ± 0.28 mm and 1.74 ± 0.73 mm for the maxillary and mandibular landmarks, respectively. Our method provides accurate and flexible guidance for bimaxillary orthognathic surgery based on intraoperative visualization and quantification of deviations for simulated postoperative MMC and landmarks. The guidance using simulated skeletal models and landmarks can complement and improve conventional navigational surgery for bone repositioning in the craniomaxillofacial area.