Key points
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Maxillary ablative defects—the Brown classification is the system used most widely to describe maxillary defects; this system also is beneficial in guiding reconstructive techniques and options.
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Zygomatic implants for maxillary rehabilitation—no single approach exists because each patient and condition is unique. One key is to ensure wide exposure of the surgical field due to absent and/or altered native anatomy.
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Prostheses selection and flexibility—prosthetic planning and execution are critical to implant and reconstructive success. Prostheses should be based not only on esthetics and function but also on stability considering the unique surgical field postablative surgery.
Introduction
Reconstruction of maxillary defects following avulsive injuries and ablative surgery presents a challenging task due to the inherent complexity of this region. The aim of reconstructing maxillary defects depends on the classification of the defect, mainly size and location, but also may include complex antral defect repair, dental rehabilitation, and providing orbital and midface support. Frequently, a soft tissue or osteocutaneous free tissue transfer is selected as the optimal option. Microvascular surgery requires a specialty trained surgeon, significant hospital resources, and, most importantly, a patient who is deemed appropriate for complex surgical procedures. Patients with significant comorbidities or lack of appropriate donor sites may be left with limited reconstructive options. The advent of zygomatic implants has allowed for an additional versatile option in rehabilitation of ablative maxillary defects, especially in those patients who are not suitable for advanced surgical reconstruction. Zygomatic implants have become an adaptable option for patients with complex postablative defects to undergo a graftless complete dental rehabilitation of the maxilla in a single procedure.
Indications
Zygomatic implants conventionally have been used when there is insufficient bone volume for traditional endosseous implants. They are ideal for many patients as well because they can shorten treatment time greatly, avoid multiple surgical procedures, and allow for an immediately loaded prosthesis. Zygomatic implants are a proved and reliable modality, with long-term survival of 97.86% found in systematic review. Multiple restoration options are available with zygomatic implants, including obturators, complex maxillofacial prosthetics, and fixed or removable dental prosthesis. The decision depends on prosthetic goals, patient preferences, and the classification of maxillary defects according to Brown. Brown described maxillary defects with respect to vertical and horizontal components ( Fig. 1 ). Based on this classification, defects classes 2 b/c/d are most suitable for zygomatic implant supported dento-facial rehabilitation. Additionally, there has been a report of zygomatic implants used for prosthesis support in class VI defects, which utilizes magnetic retention of a nasal maxillofacial prosthetic device. Another common way to evaluate need for zygomatic implants as well as ideal configuration of implant type is by maxillary zones, commonly zone I anterior, zone II premolar region, and zone III molar. The rehabilitation can be planned based on which configuration of implants are appropriate (ie, axial, angled, or zygomatic). If there is inadequate alveolar bone in only zone I or zone II, axial and angled posterior implants should be used. If only zone I has adequate bone, then a mix of 2 zygomatic implants and 2 axial implants can be considered. Finally, if poor bone exists in all 3 zones, then 4 zygomatic implants should be considered.
Contraindications
Zygomatic implant placement is performed most often under general anesthesia; thus, patients with significant comorbidities who are unable to undergo general anesthesia are not suitable candidates. There are specific contraindications to zygomatic implants. Absolute contraindications include restricted mouth opening, because it does not allow for access of the specialized instrumentation. Active maxillary and/or zygomatic pathologic disease, such as acute sinusitis, osteomyelitis, osteoradionecrosis, or malignancy, also are absolute contraindications. Relative contraindications include chronic sinusitis, but less severe cases can be considered acceptable, as well as a history of bisphosphonate use or radiation therapy. There currently are no definitive studies regarding zygomatic implants and bisphosphonates or radiation. The zygomatic implants’ effect on the delivery of postoperative radiotherapy is important to consider when reconstructing large ablative defects caused by oncologic disease. Many of these patients undergo radiation after implant placement, because it is believed to help avoid osteoradionecrosis when placed prior to radiation therapy. The exact detriment of the zygomatic implants in the radiation field is not known, but available studies suggest a negative impact. , Dental implants cause major problems in radiation therapy treatment planning by causing CT artifact. This results in less accurate delineation of tumor target volumes and adjacent critical structures, causing errors in dose calculation that can have an adverse effect on treatment outcomes. Additionally, having to remove a failing zygomatic implant(s) in an irradiated field also is problematic and leads to the need for further complex reconstruction, now in irradiated tissue. Therefore, at this time, the authors recommend primarily zygomatic implants for the reconstruction of defects following trauma and resection of benign disease. They maybe an option, however, in early-stage malignant disease.
Preoperative planning
If no contraindications to general anesthesia are identified, evaluation for zygomatic implant placement is carried out. A different set of considerations must be kept in mind for patients who are planned for delayed versus immediate zygomatic implant placement following ablation when performing physical examination and assessing preoperative imaging. Patients who underwent ablative procedures previously must demonstrate adequate mouth opening (>35 mm interarch distance) and no evidence of oral pathology or active infection on physical examination. A cone beam computed tomography (CBCT) scan is an adequate modality that can be obtained easily in most oral and maxillofacial surgery offices at the initial consultation appointment. When approaching a patient with existing pathology, an in-depth discussion with the ablative surgeon is warranted. An adequate zygomatic bone stock as well as the extent and type of the anticipated maxillary defect to facilitate planning number and angulation of zygomatic implants must be discussed. Additionally, presence of soft tissue defects requiring reconstruction also should be addressed. Physical examination in the presence of pathologic mass is of little value because placement of zygomatic implants takes place in a drastically different anatomic field. Therefore, as long as a mass is resectable without compromise of the zygomatic bone, a patient can be considered for zygomatic implant. In the event that a patient demonstrates inability to open the mouth, the ablative surgeon should be asked if mandibulotomy for access is planned. Under these circumstances, the presence of preoperative trismus is not a contraindication to zygomatic implant surgery. Patients with existing pathology are likely to have a medical-grade computed tomography (CT) scan already available and should be used for zygomatic implant surgery planning. Optimal implant placement provides for the most ideal prosthetic outcome and is even more critical in a complex ablative case where surgeons are left with deficient or absent maxillary bone and the need to work around a vascularized flap if present. Although not a requirement, virtual surgical planning (VSP) can assist in obtaining ideal placement, especially for less experienced surgeons. VSP allows for a safer and more efficient placement of zygomatic implants into a complex anatomic site. VSP encompasses a variety of modalities. Stereolithic models can be used to help plan ideal angulation and position, and there are many computer software platforms available to help decide implant size, depth, and angulation ( Fig. 2 ). From this planning, custom surgical guides can be fabricated to guide pilot drills intraoperatively. Navigation also has been employed to position the angulation and depth of the zygomatic implants precisely. If navigation and/or surgical guides are not utilized, computer-based planning still is essential to analyze the amount of zygomatic bone present to support implant placement as well as visualization of planned position/angulation of implants.
