Designing CAD/CAM Surgical Guides for Maxillary Reconstruction Using an In-house Approach

This method can help answer key questions in the head and neck reconstruction field about computer assisted design on the modeling reconstruction of the maxilla. The main advantage of this technique is that CAD and CAM simulations are accessible to everyone. The implications of this technique extended to a reconstructive surgery therapy as these surgeries are typically performed using a free-hand approach.

After selecting the area of bone to be excised, make a large plane and place the plane on the border of the area for removal in the appropriate computer aided design software. Continue to place more planes until the entire area for removal has been surrounded and select the vertices of the planes. Connect the plates by adjusting edges and faces of the planes in the edit mode to surround the area for removal.

Then use a boolean modifier to subtract the receptable solid from the facial bone to generate a shaved facial bone for the maxillary defect model. Boolean modifiers sometimes fail. If this happens, don't panic.

And try again. Next, place a fibula into the maxillary defect area, and mark the fibula with one small green cube eight centimeters distal to the fibular head and one small green cube five centimeters proximal to the lateral malleolus. For the maxilla, place red cubes for the identification of the reconstructed points.

Using a parent setting in the object mode, link the small cubes to the fibula and place more small marker cubes over the areas in the maxillary lesion where reconstruction is necessary to increase the visibility of the necessary reproduction points. If the fibula is displaced from the midline, fit the fibula to the front margin of the alveolar bone and use the previous plane of the midline maxillary osteotomy as a first fibular osteotomy plane. Place a new osteotomy plane where appropriate.

And link this new plane to the fibula as a parent setting. Copy the fibula and two planes of osteotomy as a parent setting in the object mode. And move the copied fibula with the first block area with two cutting planes on both ends to the secondary area where reconstruction is necessary to plan the second fibula block.

Then, add a new plane in the object mode to place the second cutting plate. To design the fibular cutting guide, visualize only the fibula and cutting planes and make each cutting plane smaller so that each plane occupies only half of the area of the fibula cutting section. Unite two end planes to build a solid shape in the object mode and select the vertices of all of the planes to form a solid rectangle.

Use a boolean modifier to subtract the fibula from the rectangle and unite each subtracted solid in the object mode. Place a cube near the subtracted solids and extrude the faces to make pillars. Then unite the pillars to the subtracted solids to generate the fibular cutting guide.

To design the maxillary cutting guide, add the maxillary and zygomatic planes for the original remaining surface after the maxillary removal and extrude the faces to thicken the plane. Use the solidify modifier to solidify the plates in the edit mode and delete the thickened object over the resection planes on both ends of the maxilla to generate the maxillary cutting guide. To generate the fibular segment fixation guide, use cutting planes on both ends to remove the intersecting area between the fibula and the solid construct for each fibular block in the boolean modifier.

Extract half of the superficial surface of each fibular block and unite all of the superficial surfaces in the object mode. Then, use a knife cut to delete any small faces to secure the spaces for the metal plate fittings and use the solidifying modifier to thicken the surfaces. For 3D printing, export the designs of the guides in STL format and print all of the guides and bones.

Then, fit the maxillary cutting guide to the facial bone model and use a saw to cut the facial bone along the cutting plane. Attach the fibular cutting guide to the fibular bone model and cut the bone into pieces. Then, attach the fibular blocks to the fixation guide and use screws and plates to fix the resulting fixation guide complex to the maxillary defect.

Then, fix the fibular segments to the maxilla where the fixation guide does not attach with additional screws and plates and remove the fixation guide. The reconstruction is now complete. The designs for these representative fibular cutting, maxillary cutting, and fibular fixation guides were created and exported in STL format as demonstrated for 3D printing.

The maxillary cutting and fibular cutting guides were then completely fitted to the facial bone and fibular bone models. The models were cut with a saw and the resulting model was fixed with titanium plates and screws. A 3D reconstructed image was then determined by a 3D scanner within an approximately two millimeter deviation.

While attempting this procedure, it's important to remember to check that each object does not interfere with the surrounding tissues and that the vascular pedicles are not compressed or kinked by the printed object and transverse tissues. Using these computer guided surgery approaches, the accuracy of free-handed, reconstructive surgery techniques can be improved.