Clinical Application of Three-Dimensional-Printed Magnetic Connection Digital Guides for Precise Segmental Maxillary Osteotomy

Summary

This protocol describes the digital design, three-dimensional (3D) printing, and intraoperative use of magnetically connected, patient-specific osteotomy guides for a three-segment Le Fort I osteotomy to transfer virtual plans accurately and improve segment alignment.

Abstract

This study introduces the design and clinical application of a novel magnetic-connection digital osteotomy guide to enhance the precision and efficiency of segmental maxillary osteotomy. Segmental Le Fort I osteotomy is an essential technique for correcting complex transverse and vertical dental-maxillofacial deformities, yet traditional methods involving manual plaster model surgery are prone to significant errors. To address these challenges, this protocol integrates virtual surgical planning (VSP) using CT scans and specialized modeling software to create a patient-specific, 3D-printed two-part guide system. The primary component is designed to guide the horizontal Le Fort I osteotomy and bilateral premolar extraction lines. Once the maxilla is down-fractured, a secondary segmental guide is connected to the primary component via four embedded neodymium magnets, each measuring 3 mm in diameter and 1.5 mm in thickness. This magnetic connection provides a stable, rapid, and interference-free attachment that allows for precise guidance of palatal and midline osteotomy lines. This protocol demonstrates the clinical application of a modular magnetic guide system for transferring the virtual osteotomy plan in patients with maxillary protrusion and arch width discrepancies. Postoperative color-map analysis showed local surface deviations of approximately 0.5–0.9 mm around the visible osteotomy margins, supporting the preliminary accuracy of osteotomy-region transfer. The modular magnetic design provides staged osteotomy guidance and may reduce the need for repeated adjustments, unnecessary bone removal, and soft-tissue manipulation, which is consistent with vascular-preserving principles, although segment perfusion was not directly assessed. Neodymium magnets are biocompatible, maintain stability after sterilization, and are cost-effective due to their reusability. Despite the potential fragility of current three-dimensional (3D)-printed resin materials, the magnetic connection digital osteotomy guide offers significant clinical value by bridging the gap between virtual planning and surgical execution. This method ensures highly accurate bone removal and positioning, representing a promising advancement for complex orthognathic surgical procedures.

Introduction

Segmental Le Fort I osteotomy is a well-established surgical method for correcting transverse maxillary discrepancies in skeletally mature patients. In a three-segment Le Fort I osteotomy, the maxilla is first mobilized with a Le Fort I osteotomy and then divided into three segments through interdental and palatal osteotomies. This allows the surgeon to reposition the anterior and posterior maxillary segments according to the planned occlusion and transverse correction. Depending on the planned movement of the maxillary segments, this technique can be used for transverse expansion, correction of asymmetric transverse deformity, or reduction of excessive maxillary arch width^1,2. Compared with a one-piece Le Fort I osteotomy, a segmental Le Fort I osteotomy requires additional interdental and palatal osteotomy lines. These additional osteotomies increase the complexity of both virtual surgical planning and intraoperative execution^2,3.

Virtual surgical planning and computer-aided design/computer-aided manufacturing techniques are increasingly used in orthognathic surgery to transfer preoperative plans to the operative field^4,5. Patient-specific osteotomy guides can help transfer planned osteotomy lines to the surgical site and reduce the need for freehand marking^5,6. However, in the three-segment Le Fort I osteotomy, the initial Le Fort I osteotomy, interdental osteotomies, and palatal osteotomy are often performed at different surgical stages³. After maxillary downfracture, the surgical access, visibility, and conditions for guide stabilization are different from those before downfracture. This may make it difficult to use a conventional single-piece guide throughout the entire osteotomy sequence. Therefore, a modular guide that can be used sequentially before and after downfracture, while maintaining a stable relationship between guide components, may be more suitable for this procedure.

This article presents a magnetically connected, patient-specific osteotomy guide system for a three-segment Le Fort I osteotomy. The representative application in this protocol focuses on arch-width reduction in patients with excessive maxillary arch width. The first guide component is used to guide the Le Fort I osteotomy and interdental osteotomies through the bilateral maxillary first premolar extraction sites. After maxillary downfracture, the second guide component is magnetically connected to the first component and is used to guide the palatal osteotomy and planned palatal bone removal. The goal of this method is to provide a reproducible workflow for virtual planning, digital guide design, three-dimensional (3D) printing, magnet assembly, and sequential intraoperative application of the guide system.

Protocol

This study was approved by the institutional review board of Kunming Medical University (approval No. KYKQ2024MEC0087), and written consent forms were completed by all patients.

1. Preparation before guide design

1. Save the patient’s preoperative computed tomography (CT) data in digital imaging and communications in medicine (DICOM) format.
   NOTE: Use thin-slice CT data whenever possible to provide enough image layers for accurate 3D reconstruction. Poor image quality, large slice thickness, or an insufficient number of slices may reduce the accuracy of the reconstructed maxillary model and affect the subsequent virtual osteotomy and guide design. For the representative case, preoperative CT images were acquired with a slice thickness of 0.3 mm.
2. Import the DICOM data into 3D reconstruction software, such as Mimics Research 21.0. Select an appropriate segmentation threshold and reconstruct the maxillofacial skeleton.
   NOTE: The segmentation threshold should preserve important anatomical structures, including the maxilla, tooth roots, nasal floor, and palatal bone, while avoiding distortion of the bone surface caused by an excessively low threshold. In the representative case, the threshold range was set to 226–31743 HU. Check the reconstructed model carefully and remove any obvious artifacts before exporting it.
3. Perform model preprocessing in 3D reconstruction software, including segmentation, smoothing, and removal of unnecessary structures.
   NOTE: If the CT image quality is sufficient, avoid smoothing the reconstructed maxillary model whenever possible. Over-smoothing may change the surface morphology and affect the seating of the bone-supported guide.
4. Import the scanned data of the upper and lower dental plaster models into virtual surgical planning software, such as ProPlan CMF 3.0.
   NOTE: For the representative case, the dental models were scanned using a dental model scanner with an accuracy of less than 10 µm.
5. Register the maxillary and mandibular bone models with the corresponding upper and lower dental scan models to obtain a composite skeletal-dental model.
   1. Use stable tooth surfaces for registration whenever possible. Check the occlusal surface, dental arch, and tooth root position after registration to confirm that the skeletal and dental data are matched correctly.
6. Combine the clinical examination findings, occlusal analysis, and 3D cephalometric analysis to evaluate the maxillary and mandibular deformities.
   NOTE: The purpose of this step is not only to diagnose the deformity, but also to determine whether three-segment Le Fort I osteotomy and arch-width reduction are appropriate for the patient.

2. Virtual surgical planning for three-segment Le Fort I osteotomy

1. Create a virtual surgical plan for a three-segment Le Fort I osteotomy.
   NOTE: In this protocol, the representative case involves arch-width reduction in a patient with excessive maxillary arch width. The same design logic can be modified according to the patient’s segmentation pattern and planned bone removal.
2. Determine the postoperative occlusion before finalizing the maxillary segment positions.
   NOTE: Before formal virtual osteotomy planning, perform model surgery on the dental model. Simulate the osteotomy, reassemble the maxillary segments, and check whether a stable postoperative occlusion can be achieved. Use this step to roughly estimate the bone removal amount and osteotomy position. Determine the final occlusal relationship before designing the definitive osteotomy lines.
3. Design the Le Fort I osteotomy line according to the conventional Le Fort I osteotomy approach. At the same time, perform a virtual bilateral sagittal split ramus osteotomy (BSSRO) on the mandible according to the planned orthognathic surgical design.
   NOTE: Although this protocol focuses on the maxillary osteotomy guide, virtual mandibular osteotomy is needed when bimaxillary surgery is planned. This allows the mandibular distal segment to be moved according to the final occlusion.
4. After virtual Le Fort I osteotomy, create temporary separation lines on the maxilla to divide it into three segments.
   NOTE: In this protocol, the bilateral first premolar regions are included in the planned segmentation and bone removal areas. The first premolars and surrounding alveolar bone are virtually separated together with the maxillary segments, rather than being removed as an independent tooth extraction step.
5. Set the temporary separation lines to approximately 0.01 mm in width.
   NOTE: These temporary lines are only used to divide the virtual maxilla into three segments. They do not represent the final osteotomy width or the final amount of bone removal.
6. Scan the three-segment maxillary dental model, mandibular dental model, and occlusal record obtained from model surgery.
   NOTE: These scanned data represent the stable postoperative occlusion determined by model surgery. Use them as the reference for virtual occlusal registration.
7. Import the scanned model-surgery data into the virtual surgical planning software.
8. Register the virtually segmented maxillary model and the virtually osteotomized mandibular model with the scanned model-surgery occlusion using occlusion registration.
   NOTE: This step transfers the final occlusion from model surgery into the virtual surgical plan. After registration, the tooth positions determine the final position of the three maxillary segments and the mandibular distal segment.
9. Remove the overlapping bone between the repositioned maxillary segments. Keep the matched maxillary segments as the planned postoperative position and size of the three maxillary bone segments.
   NOTE: The overlapping area indicates the bone that must be removed to allow segment assembly per the virtual surgical plan. Check this area in relation to the adjacent tooth roots, nasal floor, and palatal bone. The planned osteotomy and bone removal area should be designed to avoid injury to adjacent tooth roots and should be checked carefully in relation to important anatomical structures, including the nasal floor, piriform aperture, infraorbital region, and palatal bone.
10. Move the three maxillary segments back to their original position after virtual Le Fort I osteotomy. Use the space between the segments as the planned bone-removal region, and perform Boolean subtraction to obtain the STL data for the osteotomy and bone-removal area (Figure 1).
    NOTE: This STL file should be used as the basis for designing the osteotomy slots and the magnetic connecting region of the guide system. During subsequent guide design, the guide base and osteotomy slots should be limited to the necessary exposed bony area and should not be extended unnecessarily toward the tooth roots, nasal floor, infraorbital region, or palatal soft tissue.

3. Design of the magnetically connected osteotomy guide system

NOTE: The design workflow of the first guide component is shown in Figure 2.

1. Export the required models from the virtual surgical planning software, including the skull and maxillary model with the registered upper dentition, the maxilla after virtual Le Fort I osteotomy, the Le Fort I osteotomy line, and the planned maxillary bone removal region.
   ​NOTE: Export all models in the same coordinate system. Do not move, rotate, or realign the models after export, because this may affect the accuracy of the guide design.
2. Import all exported models into 3D design software, such as 3-matic Research 13.0.
3. Crop the skull and maxillary model with the registered upper dentition, and keep only the infraorbital and maxillary regions needed for guide design (Figure 2A).
   NOTE: Cropping the model can reduce the calculation load of the software. Keep enough maxillary bone surface for guide seating, but remove unnecessary skull structures.
4. Apply the Wrap function to the cropped maxillary model (Figure 2B).
   NOTE: Wrapping creates a small clearance between the guide and the bone surface. This clearance helps the guide seat more smoothly during surgery. In the representative case, the clearance generated by wrapping was kept below 1 mm. The clearance should be adjusted according to the guide fit, printing accuracy, and clinical requirements.
5. Use the Mark function to select the base area of the first guide component (Figure 2B).
   NOTE: Select a region slightly larger than the expected final guide margin, and include stable bony areas that may help guide retention. The concavity around the piriform aperture and other irregular bony surfaces can improve the stability of the bone-supported guide. A larger selected area also allows later trimming of the guide edge.
6. Wrap the selected region to generate the initial guide surface (Figure 2C).
   NOTE: This wrapped surface will be used to remove undercuts in the next step.
7. Remove undercuts according to the planned insertion direction of the guide (Figure 2D).
8. Invert the undercut-free surface and thicken it to form the solid base of the first guide component.
9. Trim the edge of the first guide component (Figure 2E).
10. Use the planned maxillary bone removal region to trim the bilateral connecting regions of the first guide component (Figure 3).
    NOTE: The width of each connecting region should match the planned bone removal width in the corresponding first premolar region. Do not narrow this region only to reduce the guide size. Do not extend it excessively, because this may require unnecessary soft-tissue reflection.
11. Import the trimmed first guide component into the virtual surgical planning software.
12. Adjust the range and width of the Le Fort I osteotomy line according to the guide design, create the osteotomy slot for the Le Fort I osteotomy, and add fixation holes on the first guide component for intraoperative fixation with titanium screws (Figure 2F).
    NOTE: The osteotomy slot should be wide enough to allow the saw blade to enter, but not so wide that it loses its guiding effect. In this protocol, the slot width is 1 mm. The fixation holes should be placed in stable bone areas and should not interfere with the osteotomy slot, tooth roots, or planned fixation plates.
13. Use the maxilla after virtual Le Fort I osteotomy as the reference model to design the second guide component.
14. Generate the base of the second guide component using the same method described above, including cropping, wrapping, marking, undercut removal, inversion, and thickening (Figure 4A–E).
15. Trim the edge of the second guide component according to the planned palatal osteotomy and bone removal region.
    NOTE: The width of the second guide component should correspond to the planned bone removal region. This width is determined by the virtual surgical plan and should not be changed without rechecking the plan.
16. Mark the medial connecting area of the first guide component. Generate a surface from the marked area, copy it to a new part, and thicken this copied surface to form the connecting solid of the second guide component (Figure 4F and Figure 5).
    NOTE: The connecting solid of the second guide component should match the connecting region of the first guide component. Both regions should correspond to the planned bone removal width in the bilateral first premolar areas.
17. Merge the trimmed second guide base with the connecting solid to form the final second guide component.

4. Design of the neodymium magnet connection

1. Identify the corresponding connection surfaces on the first and second guide components.
2. Design two magnet grooves on each guide component according to the size of the neodymium magnets.
   NOTE: In this protocol, each groove is designed for a neodymium magnet with a diameter of 3 mm and a thickness of 1.5 mm. The groove size should match the actual magnet size. The paired grooves on the two guide components should be accurately aligned. If the grooves are too shallow, the magnets may protrude and interfere with the guide connection. If the grooves are too deep or misaligned, the magnetic attraction or guide seating may be affected.
3. Use Boolean subtraction or a similar cutting function to create the final magnet grooves on both guide components (Figure 6).

5. 3D printing and magnet assembly

1. Export the final guide design in STL format.
2. 3D print the first and second guide components using biocompatible surgical guide resin.
   NOTE: In this protocol, the guide components were printed using a biocompatible surgical guide resin at a resolution of 5760 × 3600 pixels. The printing material and parameters should be selected according to the printer manufacturer’s instructions and institutional requirements for intraoperative surgical guide fabrication.
3. Remove support structures and complete post-processing according to the manufacturer’s instructions. Clean the guide components using the manufacturer-recommended cleaning agent, dry them, and post-cure each surface in a curing unit. After post-curing, polish the residual support marks on the guide surface.
   NOTE: In the representative case, post-curing was performed for 2 min on each surface. The post-curing time may vary depending on the resin material, printer, and curing unit used. Carefully inspect the osteotomy slots, guide base, and magnet grooves after post-processing. Residual resin or support material in these areas may affect guide seating or magnetic connection. Polishing should be limited to residual support marks and nonfunctional surfaces; the osteotomy slots, guide base, and magnet grooves should not be modified.
4. Embed four neodymium magnets with a diameter of 3 mm and a thickness of 1.5 mm into the reserved grooves.
5. Bond the magnets securely in the grooves.
   NOTE: Confirm the polarity of all magnets again before bonding. In this protocol, the magnets were bonded into the guide grooves using dental resin cement. The resin cement should be applied and polymerized according to the manufacturer’s instructions. After bonding, test whether the two guide components connect smoothly and remain stable. The bonded magnets should also be inspected after sterilization to confirm magnet retention and bonding stability before intraoperative use.
6. Test the completed guide system on the 3D printed maxillary model (Figure 7).
7. Confirm that the first guide component fits the maxillary bone surface without obvious rocking or interference.
8. Connect the second guide component to the first guide component and confirm that the magnetic connection is stable.
   NOTE: If the guide does not seat smoothly, check the guide base, soft-tissue clearance, magnet depth, and connection surface. Minor nonfunctional edges can be trimmed before sterilization, but the osteotomy slots and connecting region related to bone removal should not be modified without rechecking the virtual surgical plan.
9. Sterilize the guide system according to the approved clinical sterilization protocol before surgery.
   NOTE: In this protocol, the assembled guide system was sterilized using low-temperature hydrogen peroxide plasma sterilization before intraoperative use. The sterilization method should be selected according to the resin material, magnet properties, adhesive compatibility, and institutional requirements for intraoperative use. After sterilization, inspect the complete guide-magnet assembly to confirm guide integrity, magnet retention, and stability of the magnetic connection. If magnets are reused in laboratory testing or clinical preparation, reuse should follow institutional sterilization and infection-control rules. Magnets with coating damage, corrosion, or reduced retention should not be reused.

6. Intraoperative application of the guide system

1. Perform the orthognathic surgery under general anesthesia according to the planned surgical procedure.
   NOTE: In the representative case, the surgical procedure included a three-segment Le Fort I osteotomy, bilateral sagittal split ramus osteotomy, and double-step genioplasty.
2. Extract the bilateral maxillary first premolars according to the surgical plan.
3. Expose the maxillary osteotomy area.
4. Place the first guide component on the exposed maxillary bone surface (Figure 8A).
5. Fix the first guide component with titanium screws through the predesigned fixation holes.
6. Perform the Le Fort I osteotomy along the osteotomy slot of the first guide component (Figure 8B).
7. Downfracture the maxilla after completing the Le Fort I osteotomy.
8. After maxillary downfracture, place the second guide component and connect it magnetically to the first guide component (Figure 8C).
   1. Confirm that the second guide component is fully seated and that the magnetic connection is stable before performing the segmental osteotomy.
   2. Because the first guide component remains fixed to the maxilla with titanium screws, stabilize the second component by the predefined magnetic interface and its contact with the exposed palatal bone surface.
   3. Before osteotomy, check that no soft tissue, blood clot, or bone debris is interposed between the guide and the bone surface. Do not force the second component into position if stable seating cannot be achieved.
9. Perform the interdental and palatal osteotomies under the guidance of the second guide component (Figure 8D).
10. Remove the guide system after completing the guided osteotomies, and continue the remaining orthognathic procedures according to the surgical plan.

7. Postoperative accuracy assessment

1. Reconstruct the postoperative maxillofacial model from postoperative CT data using the same 3D reconstruction software used for preoperative reconstruction, and export the reconstructed model in STL format. Use the same segmentation threshold as that used for the preoperative model reconstruction.
   NOTE: In the representative case, the postoperative CT model was reconstructed using the same threshold range as the preoperative model, 226–31743 HU, to maintain consistency between preoperative planning and postoperative accuracy assessment.
2. Import the postoperative model and the preoperative virtual surgical design into 3D data analysis software, such as Geomagic Wrap 2021.
3. Register the postoperative model to the preoperative virtual surgical design using stable, non-operated craniofacial regions as the reference area.
   NOTE: The operated maxillary segments should not be used as the registration reference. The reference area should be selected from stable regions that were not affected by surgery, such as the regions around the nasion (N), infraorbital rim/orbitale (Or), and superior margin of the external auditory canal/porion (Po).
4. After registration, select the region of interest and perform surface deviation analysis between the postoperative model and the preoperative virtual surgical design.
5. Generate a color map to visualize the deviation between the planned and postoperative surfaces. Record the maximum distance, average distance, standard deviation, and RMS estimate provided by the software.
   NOTE: The average distance and RMS estimate should be reported separately, because the average distance may be affected by positive and negative deviations. If available, record the maximum positive and negative deviations separately. In this protocol, the region of interest focuses on the osteotomy region and visible osteotomy margins, rather than the final position of the entire maxillary segments.
6. To assess intraobserver reproducibility, the same trained observer repeated the registration, ROI selection, and deviation analysis after a time interval. Intraclass correlation coefficients were calculated using a two-way mixed-effects model for absolute agreement.

Results

Using this workflow, a patient-specific virtual surgical plan and a magnetically connected osteotomy guide system were completed for three-segment Le Fort I osteotomy. Preoperative CT data and dental model scans were integrated to create a composite skeletal-dental model. In the representative case, virtual planning was performed for arch-width reduction in a patient with excessive maxillary arch width. Bilateral first premolar extraction sites were used as the interdental osteotomy regions, and the palatal osteotomy lin...

Discussion

Three-segment Le Fort I osteotomy is more complex than one-piece Le Fort I osteotomy. In this procedure, the maxilla is not only mobilized but also divided into separate bone segments. After segmentation, each maxillary segment must be repositioned to achieve a stable postoperative occlusion and the planned transverse correction^7,8. Therefore, the accuracy of this procedure depends on two main steps: accurate preoperative planning of the final segment positions a...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
3-matic Research 13.0	Materialise	Version 13.0	Used for digital design of the guide components, including cropping, wrapping, marking, undercut removal, inversion, thickening, trimming, and Boolean operations.
Autoscan-DS-EX pro	SHINING 3D	https://www.shining3ddental.com/solution/ds-ex-pro-lab-sacnner/	3D Scanner; Used to scan the upper and lower dental models and the occlusal record
Calibra Universal dual-cure self-adhesive	Dentsply Sirona	https://www.dentsplysirona.com/en-in/discover/discover-by-brand/calibra-cements/calibra-universal.html	Resin cement; For bonding neodymium magnets into the 3D-printed surgical guide.
CT scanner	Siemens Healthineers, Erlangen, Germany	https://www.siemens-healthineers.com/computed-tomography	64-row/128-slice; Used for three-dimensional reconstruction of the craniofacial/maxillary model.
Edge MAX/Edge E2	RAYSHAPE	https://www.rayshape3d.com/3d-printers/edge-e2/	3D printer; Used to print the first and second guide components.
Geomagic Wrap 2021	3D Systems	Version 2021	Used for postoperative model superimposition and color-map deviation analysis.
Mimics Research 21.0	Materialise	Version 21.0	Used for segmentation, three-dimensional reconstruction, and removal of unnecessary structures.
Neodymium magnets	Purchased from Jinyixin Magnetics	https://jingxin-magnet.com/	3 mm diameter × 1.5 mm  thickness; Embedded into the reserved magnet grooves to connect the first and second guide components.
ProPlan CMF	Materialise	Version 3.0.1	Used for virtual orthognathic surgical planning, including Le Fort I osteotomy, BSSRO planning, segmentation, and occlusal registration.
Resin	RAYSHAPE	SGV2/Model 1 lvory	Used to fabricate the intraoperative magnetically connected osteotomy guide components.
ShapeCure	RAYSHAPE	https://www.rayshape3d.com/post-processing/uv-curing-machine-shapecure/	Curing unit