Utilizing a Fully Digital Approach for Oral Squamous Cell Carcinoma Treatment and Zygomatic Implant-Based Rehabilitation for Maxillary Defects

Oral squamous cell carcinoma involving the maxilla (OSCCM) is uncommon and comprises approximately 6%–7% of all head and neck malignancies.^1,2  Standard OSCCM treatment requires surgery, often complemented by radiotherapy, chemotherapy, and immunotherapy, tailored to tumor stage and lymph node involvement.³  Complete tumor removal is essential but challenging due to anatomical complexities and limited surgical access with incomplete excision potentially leading to local recurrence and increased patient mortality.^4,5  Aggressive OSCCM treatments result in significant dental and bony structure loss, facial defects, and anatomical changes. En bloc resection for OSCCM can cause maxillary defects, impacting speech, swallowing, nutrition, respiratory health, and facial appearance.⁶  Therefore, accurate tumor excision and reconstruction are vital for effective OSCCM management.

Establishing oronasal separation is crucial for enhancing the quality of life in patients with OSCCM and can be accomplished through vascularized osteomyocutaneous flaps or prosthetic devices.^7,8  However, reconstructive surgery is sometimes contraindicated due to patient health conditions or to prevent additional surgical morbidity. Removable maxillary obturator prostheses are key in restoring oral functions, promoting effective swallowing and speech, supporting orbital contents to avoid enophthalmos and diplopia, and enhancing midfacial contour for improved aesthetics.⁹  These prostheses are a valuable postoperative reconstruction alternative for OSCCM patients. Nonetheless, fabricating an obturator for OSCCM patients presents difficulties, particularly in the absence of stable dentition and due to variable resection boundaries that may include the hard and soft palate, alveolar ridges, and occasionally the nasal floor, affecting prosthesis retention and stability.¹⁰ 

Maxillofacial defect reconstruction after tumor resection is a complex surgical endeavor that demands optimal functional and aesthetic results. Zygomatic implants provide robust retention and support for significant maxillary deficiencies, benefiting from their integration into the zygomatic bone, often less affected by radiation therapy.^11,12  However, the precise placement of these implants is intricate as the absence of clear anatomical landmarks makes the procedure particularly challenging on the defect-affected side due to the extended drill path.¹³ 

Clinicians face the challenge of achieving precise OSCCM resection and restoration with zygomatic implant support. Advances in virtual surgical planning and 3D printing have improved OSCCM treatment, increasing precision and reliability while allowing for tailored patient care.^14,15  This clinical report describes a meticulous subtotal maxillectomy for OSCCM and the application of a zygomatic implant–supported prosthesis, employing digital techniques including 3D reconstruction, computer-guided surgery, and photogrammetry (Icam4D). Additionally, 3D finite element analysis (FEA) is applied to assess the technique’s efficacy and analyze stress patterns around the zygomatic implant.

A 56-year-old male presented with a painful palate ulcer (Figure 1a) at the Department of Oral and Maxillofacial Surgery and was diagnosed with OSCCM (T4aN0M0, stage IVA, American Joint Committee on Cancer) (Figure 1b). Maxillofacial computerized tomography (CT) scans confirmed OSCCM-induced maxillary damage (Figure 1c and d). To improve surgical accuracy and outcomes, the team employed digital approaches, including virtual surgical planning with a 3D skull model and computer-guided surgery, and designed a digital full-mouth removable denture supported by maxillary implants alongside immediate zygomatic implant placement using a digital guide plate. The plan for permanent restoration is set for 6 months postoperation. The study protocol was approved by the hospital’s ethics committee (No. 2020-156-01), and the patient provided informed consent.

Preoperatively, virtual surgical planning was conducted alongside generating a 3D skull model and fabricating a reconstruction plate and computer-guided surgery. A head CT scan was acquired with spiral CT equipment (Siemens Sensation 16, Siemens), and the Digital Imaging and Communications in Medicine–formatted data, sliced at 0.625 mm, was processed in Mimics software (version 20.0, Materialise) to create a patient-specific 3D virtual model (Figure 2a). Maxilla resection margins extended 2 cm from the tumor (Figure 2b). The virtual plan was scrutinized in 3 dimensions for optimal outcomes (Figure 2c through e). Digital scans and photographs captured the maxillofacial anatomy and occlusion (Figure 2f). A 3D simulation of the maxilla resection and zygomatic implant reconstruction was completed. Corresponding computer-guided surgery was designed with osteotomy-aligned slots (Figure 3a through d).

Zygomatic implant FEA models were constructed (Brånemark System zygomatic implant, Nobel Biocare), adhering to manufacturer specifications. The zygomatic implant length, determined by the distance from the residual maxilla to the jugal point (JU) of the zygomatic bone (45–55 mm), led to the selection of suitable 15 (4.5 × 50 mm), 16 (4.5 × 47.5 mm), 25 (4.5 × 52.5 mm), and 26 (4.5 × 47.5 mm) implants, which were modeled and positioned in the skull for optimal bone contact (Figure 4a through f). The apices of the posterior zygomatic implants were placed close to or slightly protruding through the zygomatic bone’s external surface. The prosthesis was designed as a computer-aided design and computer-aided manufacturing milled titanium alloy bar, 10 × 8 mm in size.

All components were integrated into the simulation platform (Ansys Workbench, ANSYS). Engineering data for each material used in the FEA were inputted, assumed homogenous, isotropic, and linearly elastic and were based on the Young modulus and Poisson ratio (Table 1). By threshold processing and image segmentation algorithms, we distinguished between cortical bone (Hounsfield units 700–1500) and cancellous bone (Hounsfield units 100–700). Rigid boundary conditions are imposed at the patient’s occipital foramen magnum to preclude rotational movement of the model. The *CONTACT_AUTOMATIC_SINGLE_SURFACE algorithm was utilized between the prosthesis, zygomatic implants, and zygomatic bone to ensure noninterpenetrating contact among the components. A 150 N occlusal force^16,17  was applied to the superstructure’s palatal surface (Figure 5a through c) with stress distribution visualized using colored contour bands (Figure 5d). Stress was distributed across the zygomatic implants (Figure 5e) and craniofacial structures (Figure 5f), peaking at the implant-abutment connection (100.15–78.05 Mpa, Figure 5g) and minimal at the prosthesis (4.92–3.12 Mpa, Figure 5h). The designed obturator prostheses ensured stability on both zygomatic implants and the remaining maxillary structures.

After the virtual surgical plan was approved, stereo models for reconstruction, maxillary osteotomy, zygomatic implant guidance, and templates were created and converted into STL files for 3D printing using a rapid prototyping machine (Wiiboox, JOC) and clear heat-polymerized acrylic resin (Figure 6a and b). The resulting computer-guided surgery, skull model, and plates were then prepared for sterilization.

The surgery began with maxillary exposure, followed by attaching the maxillary osteotomy guide to facilitate the planned resection (Figure 7a through c). The resection ensured tumor-free soft tissue margins, confirmed by frozen section analysis. A bilateral neck dissection was conducted, and no metastasis was found in the specimens. The zygomatic implant plate was then fixed to the residual maxilla, addressing the defect left by the resection. Zygomatic implants were accurately placed according to the preoperative plan and computer-guided surgery (Figure 7d) with Brånemark System implants installed at positions 15, 16, 25, and 26 (Figure 7e through g), using a 15 N.cm torque. These implants were secured into the zygomatic bone, passing through the maxillary sinus frontal wall with the implant head visible on the buccal side of the sinus wall. Guided bone regeneration (GBR) was used to cover the exposed implant surfaces with cortical bone grafts from Bio-Oss (Geistlisch, Switzerland) on the buccal side of the implants (Figure 7e through h), and a resorbable collagen membrane Bio-Gide (Geistlich, Switzerland) was placed over the surface. The designed digital full-mouth removable denture was not immediately placed during the surgical procedure. The primary reason was the initial instability of the zygomatic implants and, second, to reduce the duration of the surgery and avoid unnecessary stress on the zygomatic implants during the healing process. Post-subtotal maxillectomy and zygomatic implantation, iodoform gauze is utilized for wound compression to mitigate bleeding. The dressing is subsequently excised 1 week postoperatively (Figure 7h). Postoperative cone beam CT (CBCT) analysis indicates that the zygomatic implants are optimally positioned with minimal distances to the orbital floor at 3.61 mm for implant 15 and 2.52 mm for implant 25 (Figure 7i and j). The precise alignment adheres to the preoperative 3D plan, preserving the integrity of the maxillofacial anatomical structures. Six weeks later, the patient received adjuvant radiotherapy (54 Gy in 30 sessions at 1.8 Gy per session) and chemotherapy (Cisplatin 20 mg).

At 6 months postsurgery, the patient exhibited stable vital signs with no evidence of tumor recurrence or metastasis. The intraoral incision has healed satisfactorily, and a modest amount of hyperplastic mucosa is present surrounding the implant site (Figure 8a). Six months after surgery, the patient was examined with a CBCT scan, confirming good osseointegration of the zygomatic implants (Figure 8b and c). A CBCT examination was conducted on the patient, revealing robust osseointegration of the zygomatic implants. Additionally, the imaging demonstrated the presence of neo-ossification within the region of the zygomatic implant GBR, indicative of successful bone regeneration (Figure 8d). A digital impression was subsequently taken using the ICam4D photogrammetry system (Imetric4D Imaging Sàrl) (Figure 8e and f), which involved an intraoral scanner for soft tissue STL data and an external scanner for capturing zygomatic implant position and orientation. This data was merged into digital design software, and a 10 × 8 mm milled titanium alloy bar was crafted to connect with multiunit abutments, following the preoperative plan.

A digital occlusal frame was used to design an integrated upper bracket and wax shape, informed by preoperative jaw position records. The occlusal surface morphology and relationship from the preoperative scan guided adjustments for optimal occlusion and function, aiming for balance articulation, early contact and interference prevention, and proper tooth coverage. The prosthesis design considered principles of complete denture restoration, focusing on balance articulation, reduced posterior tooth size, decreased apex inclination, and deepened occlusal sockets for esthetic coverage of anterior teeth. The denture’s arch was customized to fit the patient’s jaw and implant abutment positions. Trial fitting involved digital preparation of the removable obturator, ensuring proper fit and occlusal efficacy. The fabrication of the zygomatic implant–supported prosthesis was then finalized (Figure 8g and h).

Six months after surgery, a postoperative CT scan confirmed excellent osseointegration of the zygomatic implants, consistent with the initial virtual plans (Figure 8b through d). Over a 3-year follow-up, the patient remained disease-free with no signs of lesion recurrence. After reconstruction, the patient enjoyed clear speech, effective swallowing, and a regular diet (Figure 9a through f). The implants and prosthesis have been stable and complication-free for 3 years postfunctional loading. Postoperative CBCT analysis at the 3-year mark revealed deviation angles of zygomatic implants, which is crucial for evaluating the accuracy of implant positioning. The comparison with the preoperative zygomatic implant guide indicated a maximum deviation of 5.78° for implant 16 and a minimum of 0.69° for implant 25, underscoring the precision of the surgical placement (Figure 10a). Both the patient and surgeons evaluated postoperative esthetics, speech, and masticatory function, noting a near-preoperative midfacial appearance and a 3.5-cm mouth opening range (Figure 10b, Table 2). Serial CBCT scans performed on the day of surgery and at 6 months, 1 year, and 3 years postoperatively demonstrated stable graft integration without notable resorption (Figure 10c). The patient reported high satisfaction with the functional and esthetic results of the prosthesis.

This study shows that digital surgical methods are effective for predictable OSCCM resection, zygomatic implant placement, and prosthetic restoration in postmaxillectomy OSCCM patients, potentially reducing surgical and prosthetic complications.

Restoring oral function in patients with OSCCM is intricate. Negative margin resection in OSCCM is especially challenging, requiring detailed knowledge of the tumor’s extent.^18,19  This study utilized computer-aided planning and rapid prototyping to map the maxillofacial area’s anatomy and pathology accurately, enhancing presurgical planning for precise resection and defect reconstruction while safeguarding critical structures. The choice of postmaxillectomy rehabilitation, influenced by defect size, patient factors, and comorbidities, aims to restore maxillary support, esthetics, and oral function. Common approaches include vascularized bony flaps and dental implants. However, these may not be ideal for older patients or those facing postoperative radiotherapy due to the risk of surgical wound complications.⁷  An implant-retained obturator prosthesis, removable for inspection and management of complications,²⁰  was selected for this case. Therefore, in this case, the treatment choice was a zygomatic implant–supported, full-mouth removable denture as it allowed for the preservation of bilateral zygomatic bones during cancer ablative surgery.

The complex nature of head and neck surgery, particularly in maxillary and midface tumor management, extends beyond disease control to include optimizing reconstruction and rehabilitation strategies.²¹  Traditional maxillectomy techniques, heavily dependent on a surgeon’s expertise, have yielded inconsistent outcomes. Digital surgery has revolutionized this field, allowing for precise virtual planning that can be accurately executed with computer-guided surgery.²²  Preoperative digital models crafted from photocured polyacrylic resins offer significant advantages, enabling comprehensive planning and testing of resection and reconstruction scenarios, ensuring patient safety, and reducing procedural time.^23,24  In the case of OSCCM treatment, virtual planning and 3D printing have increased accuracy and predictability, facilitating patient-specific resection solutions.

En bloc resections for extensive OSCCM often compromise the separation between oroantral and oronasal compartments, creating speech, eating, swallowing, and breathing difficulties.²⁵  Postsurgery, implant-supported prostheses are usually required, but the scarcity of adequate bone for implantation poses a challenge. Surgeons may opt for distant bone structures, such as the zygomatic bone or the palatopterygoid fusion zone, to secure the prosthesis. The zygomatic bone, less likely to be irradiated, offers a favorable anchorage site, especially beneficial when postoperative radiotherapy is anticipated.^10,11,26  Zygomatic implants postmaxillectomy can enhance prosthetic support, and studies have underscored the benefits of prosthodontic rehabilitation after ablative surgery.²⁶  However, the precise placement of zygomatic implants without anatomical guides is complex, particularly when dealing with the long drill path and absence of the maxilla on the defect side. Implants may not be fully seated in hard tissue due to the resection cavities, and incorrect placement could lead to complications, such as uncontrolled bleeding, orbital damage, maxillary sinus perforation, and orbitozygomatic complex fractures.²⁶  Inaccurate implant positioning and angulation may also cause prosthetic misalignment. This study employed 3D reconstruction and surgical guidance to place 4 zygomatic implants immediately after OSCCM resection. In oral implantology, angular deviations of less than 10° are deemed acceptable for achieving osseointegration and functional restoration.²⁷  In this case report, all deviations measured fell within this threshold. To fully leverage the limited residual zygomatic bone and ensure implant stability, we positioned the implant apices close to or slightly beyond the bone’s external surface. This placement aligns with biomechanical principles, optimizing implant anchorage and load bearing by proximity to cortical bone and promoting favorable stress distribution for implant longevity. The 3-year postoperative assessment revealed sustained stability of the zygomatic implants, underscoring the significance of accurate placement in facilitating osseointegration, minimizing complications, and enhancing patient satisfaction. The findings indicate that digital surgical planning improves accuracy and predictability, enabling customized zygomatic implant–supported repair for post-OSCCM resection patients.

This case study utilized 3D FEA to assess the viability of zygomatic implant–supported dentures, specifically by examining stress distribution around the implants to evaluate their capacity to support bite forces.²⁸  Understanding stress and load transfer at the implant-bone interface is crucial for the success of the implants. There is a risk that overloading these implants could fail. Whereas clinical evaluation is necessary to understand the biomechanical behavior of implants, it is not feasible to directly assess every component due to structural complexity, ethical considerations, and the prolonged duration of studies. As it enables the analysis of various complex geometries and implant configurations, FEA is beneficial in these situations.²⁹  In this study, the implant surface was assumed to be fully in contact with the bone with uniform forces and displacements at the interface. The analysis revealed maximum von Mises stresses and total deformation, visualized on a colored scale. Stresses under a 150N force ranged from 14.05 MPa to 35.58 MPa, consistent with previous research.^16,17,29  These stresses were effectively distributed across facial buttresses, prostheses, implants, and dentate skulls. The study concluded that 4 zygomatic implants could support a bite force effectively as demonstrated through FEA. Whereas the FEA provided valuable insights into the biomechanical behavior of the implant-supported prosthesis, it is essential to consider the study’s limitations. The static load application may not capture the full spectrum of functional loads.

Additionally, the assumption of complete osseointegration might reflect something other than the variability observed in clinical practice. The observed stress concentrations at the implant-abutment connection over the implants suggest further studies exploring the long-term effects of such distributions. The postoperative outcomes demonstrate the patient’s enhanced mastication, ability to chew peanuts without difficulty, improved articulation, and the absence of dysphagia during liquid intake, all indicative of optimal prosthetic function. These findings suggest a successful osseointegration with the zygomatic bone and patient adaptation to the prosthesis. This approach exhibits marked superiority over traditional prosthetic augmentation for maxillary reconstruction.

Trismus, xerostomia, and mucositis frequently complicate OSCCM treatments, leading to fibrosis that restricts mouth opening and hinders prosthodontic processes. This difficulty is compounded for dentists taking impressions and patients inserting obturators.³⁰  However, digital impression techniques such as intraoral scanning and photogrammetry, which use photographs for precise measurements, can effectively address these challenges. Photogrammetry is especially beneficial for complex cases involving multiple implants, significant distances between them, and varied angulations. The ICam4D photogrammetry system is renowned for its precision in long-span implant-supported restorations.³¹  It utilizes photographic data to create director vectors to accurately determine the relative positions of scan bodies, which can improve accuracy without the need for picture overlap. This system is operated extraorally, reducing the influence of saliva and blood and limiting mouth opening on precision.³²  In this instance, the combination of intraoral scanning and photogrammetry technology effectively overcame postoperative mouth opening restrictions and achieved successful maxillofacial reconstruction and occlusion.

Our clinical report introduces a groundbreaking protocol for severe maxillary defect rehabilitation post-OSCCM, tackling a complex reconstruction challenge. We’ve optimized zygomatic implant placement for biomechanical success by employing cutting-edge digital surgery and FEA. Icam4D’s precision captured the patient’s anatomy, enabling a customized prosthesis. The patient’s functionality, esthetics, speech, and swallowing satisfaction highlight our method’s effectiveness. This synergy of advanced planning, surgical precision, and biomechanical analysis marks a significant advancement in maxillofacial prosthetics.

This work was supported by grants from the Part 73: China Postdoctoral Science Foundation of China (No. 2023M734255), the Program of State Key Laboratory of Oral and Maxillofacial Reconstruction and Regeneration (No. 2021KB02), and the Youth Training Program of the Second Affiliated Hospital of the Army Medical University (No. 2022YQB048).

There are no conflicts of interest in this study. The participants consented to the study according to the declaration of Helsinki and granted written approval for the publication and use of their photographs in various forms.