Key points
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When indicated, Zygomatic implants can offer a graftless approach to patients with severely atrophic maxilla.
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The time from surgical intervention to final prosthetic restoration can be shortened with the use of zygomatic implants.
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New guidelines are being developed for the evaluation of the success of zygomatic implants since the parameters for stability and restorability differ from traditional implants.
Introduction
Paired with the promise of “teeth-in-a-day,” zygomatic implants have increased in popularity as a graftless treatment option that can reduce the timeline between the surgical procedure and prosthetic reconstruction, while offering a highly predictable outcome for patients with a severely resorbed maxilla. , However, the placement of these implants requires ample knowledge of the local anatomy and surgical technique in order to optimize treatment outcomes and avoid major complications. Careful planning and open communication between the surgeon, restorative dentist, laboratory technicians, and patient can assist in optimizing the final results.
Recent surgical approaches pay close attention to individual anatomic, physiologic, and prosthetic needs in order to create safer surgical protocols, increase predictability, and consequently, achieve satisfactory long-term results. , Zygomatic implants may offer an answer to the complicated question of how to rehabilitate completely edentulous patients with a severely deficient maxilla. Implant-supported prosthetics can enhance the quality of life of edentulous individuals by improving their function and esthetics and positively affecting the patient’s social life.
Other treatment options for the rehabilitation of the atrophic maxilla with an implant-supported prosthesis include bone augmentation with delayed or immediate placement of endosseous implants, as well as pterygoid plate, “all-on-four,” and short implants. Bone grafting techniques used to satisfy the horizontal and vertical requirements for successful implant placement include sinus augmentation, guided bone regeneration, onlay grafting, interpositional bone grafts, ridge splitting, and distraction osteogenesis. Autogenous bone remains the gold standard for alveolar bone augmentation because of its unique combination of osteoinductive, osteoconductive, and osteogenic properties.
In the severely atrophic maxilla, the use of extensive autogenous bone augmentation may be required in order to allow for a successful treatment outcome. One of the disadvantages of harvesting large amounts of autogenous bone is the addition of distal surgical sites, which can lead to increased operating time and potentially increased surgical morbidity. In addition, the time between bone grafting in severely atrophic sites with autogenous bone grafts and implant placement can range from 4 to 6 months.
Zygomatic implant placement, a graftless technique, provides another modality for patients who have had bone graft failures in the past or for those who are medically complex and cannot tolerate extensive surgical procedures. A position statement by the American College of Prosthodontists stated that “the use of the zygomatic implant in various clinical scenarios with multiple configurations enables the dental team to restore quality of life and gives patients an expedited and predictable option.” The reduction in surgical sites, fewer number of surgical procedures, and the shortening of the timeframe between surgery and final prosthesis delivery are some of the advantages that may lead the surgeon and patient to choose this treatment option. In this article, the authors aim to provide an overview of the indications for zygomatic implants and the local anatomy involved and describe the various techniques used for the placement of these implants.
Background
Brånemark and colleagues , introduced zygomatic implants in 1988 with the initial objective of providing implant-supported prosthetic solutions for patients with severe maxillary atrophy and maxillary defects resulting from trauma or resections. After a decade of clinical studies, zygoma implants were made available to the dental profession ( Fig. 1 ). Changes to the initially proposed surgical approach have rapidly taken place as individual considerations and prosthetic needs have become evident. Currently, various companies offer different variations of zygomatic implants, including Nobel Biocare, Neodent, Noris Medical, Southern Implants, and Implant Swiss. Nobel Biocare Zygomatic implants are available in lengths from 30 to 52.5 mm. Brånemark System Zygoma Implants have a 45° abutment head and can have a TiUnite surface or machined surface. TiUnite is a roughened thickened titanium oxide layer that is highly porous. The machine surface layer implants have an opening in the head, allowing for the use of the regular platform Brånemark System components.
Indications and contraindications
Zygomatic implant placement is indicated for the implant-supported rehabilitation of completely edentulous patients with significant sinus pneumatization and severe posterior alveolar ridge resorption. There is little clinical research demonstrating the success of these implants in partially edentulous patients. Bedrossian described a systematic pretreatment approach for the classification and treatment of the atrophic maxilla. The maxilla is divided into the following 3 zones: zone I (premaxilla), zone II (premolar area), and zone III (molar area) ( Fig. 2 ). The availability of bone in each zone should be assessed by the clinician, typically through the evaluation of a preoperative cone-beam computed tomography (CBCT). Table 1 describes the recommended surgical approaches. These recommendations can assist the surgeon in formulating the surgical treatment plan. Bedrossian and colleagues recommended the placement of zygoma implants when there is less than 2 to 3 mm in zone 2 and zone 3. In the case of an edentulous patient with inadequate bone in all 3 zones, the placement of 4 zygoma implants, also known as Quad Zygomatic Implants, has shown promising results in the literature ( Boxes 1 and 2 ). ,
| Areas of Adequate Bone for Implant Placement | Bedrossian Zones | Surgical Approach |
|---|---|---|
| Premaxilla, premolar, and molar area | Zones 1, 2, and 3 | Traditional endosseous implants |
| Premaxilla and premolar area | Zones 1 and 2 | All-on-four |
| Premaxilla only | Zone 1 | Zygomatic implants plus 2–4 traditional implants |
| Insufficient bone | Four zygomatic implants “quad-zygomas” |
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Prosthetic rehabilitation of patients with extensive defects of the maxilla owing to trauma, congenital defects, or neoplastic disease
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Completely edentulous patients with severe atrophy in zone II and zone III of the maxilla who require implant placement for prosthesis support ( Fig. 3 ):
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Significant sinus pneumatization
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Severe atrophy of the maxillary alveolar ridge
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Patients with history of bone graft failure in the maxilla
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Patients unable to undergo bone grafting procedures because of compromised vasculature or other comorbidities
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Absolute contraindications
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Acute sinus infection
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Maxillary or zygoma pathologic condition
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Underlying uncontrolled or malignant systemic disease
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Relative contraindications
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Chronic infectious sinusitis
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Bisphosphonate use
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Smoking more than 20 cigarettes a day
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Biomechanics
The stability and success of zygomatic implants have been attributed to the “quad-anchoring” of the implant to the maxilla and zygoma bones. When following Professor Brånemark’s technique, the stability of zygomatic implants originates from its engagement at the alveolar crest by the lingual cortex of the alveolus and the cortical floor of the maxillary sinus ( Fig. 4 ). Stabilization at the apex of the implant is provided by the zygomatic bone itself. In a study by Nkenke and colleagues, the bone mineral density, trabecular bone volume, and trabecular bone patterns were assessed in 30 human zygomatic bone specimens. Interestingly, the quantitative computed tomography and histomorphometry analysis revealed the zygomatic bone has an unfavorable microarchitecture for implant placement. However, despite that fact, the study concluded that zygoma implants may achieve long-lasting success, as proven by the literature, when multicortex stabilization is achieved. It was determined that the engagement of the zygomatic implant to cortical bone plays a more significant role in the stability of the implant than contact with larger amounts of trabecular bone.
Various studies have focused on the precise location of stress of these implants during function. When occlusal forces are applied, most of the support comes from the zygoma bone. , More specifically, Freedman and colleagues described the lateral cortex of the zygoma as the main load-bearing area. Ujigawa and colleagues conducted a finite elemental analysis that concluded that the stresses during occlusal load transfer differ in zygomatic implants with or without connected standard implants supporting the superstructure. In Fig. 5 , connected zygoma implants to standard implants, referred to as the combination model, show better stress distribution. In contrast, stress load of implants not combined with standard implants, or the single model, is seen to be partially concentrated at the joint of the fixture abutment. It can also be appreciated that in both models, the midportion of the implant shows higher stresses during bending movements. Bending forces could have adverse effects in the stability and longevity of the implant. The role of the maxillary alveolar support in reducing the maximum stress distribution of zygomatic implants was further studied by Freedman and colleagues. When the 2 zygomatic implants, anchored in the zygomatic bone and maxillary alveolar bone, are connected by a fixed bridge, the occlusal and lateral stresses are reduced compared with models with no alveolar bone support.
These studies prove that with the current techniques, the distribution of forces is better managed by cross-arch stabilization of the zygoma implants with a rigid superstructure to standard implants in the premaxilla. Final prosthesis considerations should include minimizing distal cantilevers, achieving a balanced occlusion, and decreasing the cuspal inclination of prosthetic teeth.
Workflow: anatomically versus prosthetically driven
Multiple approaches have been developed by oral surgeons with the intention to decrease surgical time, decrease patient morbidity, and increase the success of zygomatic implants. The ultimate decision on which approach to use lies at the hands of the operator after a throughout review of the patient’s local and systemic factors. Evaluation of the potential implant site and trajectory of the zygomatic implant via computed tomography is crucial in the planning phase. Special attention is placed on the availability of bone in the zygomatic arch and the residual alveolar crest. The relationship of the proposed zygomatic implant path to the lateral wall of the maxillary sinus and proximity to the orbital rim should be considered. There are 2 proposed surgical approaches: anatomically driven and prosthetically driven. , , The placement of the zygoma implants can be extramaxillary, extrasinus, or intramaxillary.
The zygomatic anatomy-guided approach (ZAGA) was originally proposed by Dr Carlos Aparicio in 2010 ( Fig. 6 ). The investigator studied 200 zygomatic implant sites in 100 patients with a focus on skeletal forms of the zygomatic buttress-alveolar crest complex and developed 5 typical anatomic and implant pathway situations. The proposed classification is outlined in Table 2 . The ZAGA system highlights the anatomic differences among patients and within the same patient bilaterally and can be used during surgical planning.
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