The Concept of Prosthetically Guided Maxillofacial and Implant Surgery for Maxillary Reconstruction

The surgical treatment of maxillary tumors in the oral cavity and sinus typically requires a partial or fully extended maxillectomy; the use of virtual planning to restore lost tissues has become popular in reconstructive surgery.¹  A few studies have partially investigated the correlation between the positions of the free graft and oral implants for fixed dental prostheses. Computer-aided design/computer-aided manufacturing (CAD/CAM) technology has recently opened new frontiers in maxillofacial bone reconstruction, improving the precision of this treatment technique and increasing the success of functional and esthetic outcomes.^2–5  Its direct application to maxillofacial reconstruction consists of elaborating computerized tomography (CT) data to produce and project a virtual surgical plan, to preoperatively manufacture a customized reconstructive bone plate with the appropriate shape and morphology, and to determine the best position of the fibula free flap to accommodate the final prosthesis.^6,7  A new methodology for restoring large defects in the maxillofacial region with subsequent intraoral discrepancies between the maxillary arches is proposed using an example case in which the maxillectomy, reconstruction with a fibula free flap and titanium plate, and oral rehabilitation were carried out using CAD-CAM technology.

A 15-year-old boy with recurrent benign odontogenic myxoma of the left upper maxilla was scheduled to undergo full maxillary resection and reconstruction using a fibula free flap (Figure 1a and b). The protocol involved 5 steps: surgical planning of the bony resections; CAD and rapid prototyping of cutting guides; titanium mesh and bone plate; maxillofacial surgery; oral implant surgery; and prosthetic rehabilitation. The protocol was approved by the S. Orsola Hospital Ethical Committee in September 2011 (approval no. 57/2011/O/Disp). Written informed consent was obtained.

Planning began with a high-resolution CT scan of the patient's craniofacial skeleton and soft tissue. The surgeon analyzed the DICOM-format data using the CMF software (version 6.0; Materialise, Leuven, Belgium) to plan the surgery, determining the anatomical volume to be removed, and designing the fibula free flap for the maxillary reconstruction (Figure 1c).

The customized surgical guides for the cuts were designed first. Then the guide for the fibula was designed using the vascular peduncle as a reference for its positioning on the bone. The third component was the customized reconstructive bone plate that supported the fibula free flap. Thus, virtual positioning of the fibula on the frontal plane aligned to the roots of the residual natural teeth was performed in the horizontal plane for the best future implant positioning (Figure 2).

The cutting guide and bone plate were prepared for laser sintering with the Magics software (version 16.02; Materialise) and a rapid prototyping machine (Eosint P100 Formiga; Electro Optical Systems GmbH, Munich, Germany). The surgical guide was made from polyamide material (biocompatible-certified and autoclavable).

Under general anesthesia the upper maxilla was accessed through a left Weber–Ferguson incision extended laterally along the subciliary rim, and the tumor was delimited. The cutting guide was introduced into the field; it was fixed inferiorly to the alveolar bone, superiorly to the nasal bone, and laterally to the zygomatic arch, leaving the proposed surgical margins free for cutting. These 3 points of fixation allowed correct positioning and engagement of the cutting guide for resection in safe tissues. The cutting guide was fixed with titanium screws, and a piezosurgical instrument was used to create the osteotomies. The cutting guide was removed and the maxilla was resected, with the orbital floor and palatal osteotomies completed manually. A cutting guide was used for segmentation of the fibula free flap. The reconstructive bone plate was introduced and fixed using the same holes with which the maxillary guide had been fixed to ensure its correct 3D location. The reconstructive plate supported the fibula free flap in the correct position and precisely restored the patient's original midfacial contour, as virtually projected (Figure 3). Antibiotic, analgesic, and cortisonic terapy was performed and no complications occured during the postoperatory period. A provisional removable prosthesis was constructed for immediately restoring the esthetics. At the 8-month follow-up, 4 implants were inserted in the fibula free flap (2 implants: 4.0 × 15 mm; 2 implants: 4.0 × 13-mm RD, RBM self-tapping threaded implant, Restore RD external prosthetic connection, Keystone, Burlington, Mass). A 2-stage surgery was used and the uncovering was carried out after 4 months. No complication occurred during the healing period (Figure 4). After 1 month of healing, a digital impression and an occlusal registration were made using specific custom-made scan abutments and the LAVA-COS (3M, Seefeld, Munich, Germany) intraoral scanner. The project of the fixed implant-supported prosthesis was carried out using the Trios software (3Shape Dental System, Copenhagen, Denmark; Figure 5). To fill the volume defect of the maxilla, restored with the fibula free flap, it was necessary to project a Toronto (screw-retained) bridge. To reduce the costs, a cobalt–chromium metal framework and presintered composite teeth (SR Vivodent PE, Ivoclar, Schaan, Liechtenstein) were used. The cobalt–chrome framework was manufactured by rapid prototyping using a milling machine (MICRON HSM 400U LP, AgieCharmilles, Geneva, Switzerland) and clinically tried-in and tested using radiographs, for documenting the passive engagement of the framework on the implant platforms. The dental technician mounted the composite teeth on a physical articulator, and completed the prosthesis using the resin prototyped models obtained with the virtual impression and mounted in the physical articulator. For this purpose, specifically projected landmarks in the prototyped models were used for positioning the models in the articulator with the correct interarch centric relation as in the virtual environment (Figure 6). The framework passive fit was tested using the Sheffield test. This resulted in a visual and radiographic absence of a gap between the implant platform and the prototyped framework. These tests (try-in, radiographs, and Sheffield test) suggest absence of inaccuracies in the prototyped framework and of potential tensile strenghts on implants. Occlusal and interproximal points of contact clinical results were as projected virtually: 1 centric occlusion for each tooth and the correct interproximal contact were registered (Figure 7). The Toronto bridge connecting screws were tightened at 32 N, and the prosthesis was delivered.

The introduction of virtual surgery has changed perspectives in maxillofacial surgery, especially when a large part of the maxilla or mandible is involved in tumor removal.^8–12  The new concept of prosthetically guided maxillofacial and implant surgery (PGMS) is the main outcome of this technological advance. In PGMS, the position of the fibula free flap is oriented according to the final prosthetic needs, with a virtual design projecting the precise position of oral implants inserted 8 months after surgery.^13–17  The young age of the patient was taken into consideration during the projection phase, considering that the facial skeletal growth was not completed.¹⁸  Over the 3-year follow-up period intraoral and extraoral photographs and CT scans were acquired demostrating stable functional and esthetic results (Figure 8).

When a large part of the maxilla (total left and partial right maxillectomy) plus the orbital floor and anterior zygomatic arch are ablated for cancer removal, as in the present case, the guiding concept for prosthetic rehabilitation is the same as used for edentulous patients. The implants may be placed in a different position with respect to the roots of the natural teeth, but they must be functional. The implants were positioned correctly according to the following principles: (1) in the frontal and lateral planes of the maxilla, the position of the fibula free flap provided continuity with the healthy alveolar bone; and (2) in the horizontal plane, the buccopalatal position of the implant platform corresponded with the masticatory antagonist arch (Figure 9). The expansion of this protocol will include routinely intraoperative navigation to ensure that the guide and plate positions coincide with the planned virtual surgery.^19–20  PGMS is a viable method to reproduce the correct anatomy of the maxillary arches in relation to the prosthetic needs of rehabilitation. Moreover, the protocol presented in this paper offers some adjunctive benefits, such as time and cost saving, ideal esthetic facial contouring (orbital floor and zygomatic profile), and preoperative try-in of the prototyped resin model. Potential drawbacks of this technique include the adjunctive cost of design and prototyping, even if the cost of a standard bone plate is avoided. Further investigations are necessary to compare the tolerance and mechanical properties of the customized reconstructive titanium plate with those of commercially available plates that are used currently in reconstructive surgery.

The authors would like to thank Dr Andrea Sandi for his valuable work in the CAD and rapid prototyping of the surgical guide and bone plate.