Rehabilitating severely atrophic maxillae, particularly when bone loss and sinus pathologies preclude conventional dental implants, is a complex challenge. Techniques such as all-on-four offer solutions for some patients, but severe resorption may necessitate zygomatic implants. Guided surgery, aided by digital tools, improves implant accuracy and reduces complications. These techniques help avoid sinus or orbital damage and ensure better prosthetic outcomes. A review of clinical studies highlights the precision of bone-supported guides for implant placement and underscores the importance of surgical expertise in reducing complications.
Key points
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Rehabilitation of severely atrophic maxillae presents challenges in modern dentistry, particularly when sinus pathologies and bone atrophy prevent conventional dental implants.
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The all-on-four technique is an alternative for rehabilitation without grafts, but severe bone loss may still require zygomatic implants.
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Digital planning and guided surgery enhance zygomatic implant placement by optimizing surgical outcomes and reducing complications.
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Cone beam computed tomography (CT) with a large field of view and multidetector CT are essential imaging tools for accurate assessment of zygomatic bone anatomy.
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Clinical evidence supports the precision of guided zygomatic implant placement, but surgeon expertise remains critical for handling complications.
Introduction
Rehabilitating severely atrophic maxillae is a real challenge in modern dentistry. Conventional dental implants can sometimes be used to treat these patients. In this technique, implants are evenly distributed across the maxilla, and the prosthesis is designed with a short cantilever. However, certain local or systemic conditions may prevent using this method; for example, sinus pathologies like recurrent or infected sinusitis, or severe bone atrophy where only the palatal cortical bone remains, can limit the possibility of large reconstructions and the implant placement.
Rehabilitation without grafts is an option to consider when large reconstructions are impossible. The all-on-four technique is an example where the jaw is restored using 4 dental implants without grafts, which reduces the time needed for rehabilitation. In this technique, 2 implants are placed vertically in the anterior part of the maxilla, where the bone is denser. The other 2 implants are placed at an angle distally to improve bone contact and avoid anatomic structures like the maxillary sinus. Immediate loading can be applied in this technique if there is a primary stability of 35 N cm.
However, bone resorption can be so severe that it prevents the placement of conventional implants, even when using the all-on-four technique, because there is no bone available in the anterior or posterior areas. In this situation, zygomatic implants can be a reasonable solution for full arch rehabilitation. Understanding the anatomy of the zygomatic bone and its surrounding structures is essential for performing this technique. Proper anatomic knowledge leads to better implant placement, improved mechanical stability of the prosthesis, and fewer sinus or orbital complications, which are frequently reported in the literature.
Digital planning and guided surgery are tools that can help the surgeon avoid complications and optimize surgical outcomes. These tools allow for a detailed study of the patient’s anatomy, virtual 3-dimensional implant placement, and the creation of surgical guides to transfer the digital plan to a physical device.
The precision of this technique can be verified by superimposing the planning with postoperative examinations. This is crucial for reducing complications and improving the quality of the technique. Understanding the accuracy of drilling guides supports better clinical and scientific discussions aimed at reducing inaccuracies. These details will be discussed, providing a step-by-step guide to established techniques along with some easy tips to help readers achieve better results.
Guided surgery to zygomatic implants
Brånemark used panoramic radiographs to plan rehabilitation with zygomatic implants. However, this approach is no longer recommended because it lacks precision. Today, cone beam computed tomography (CBCT) is the most important tool for diagnosis and planning, offering high-resolution and low radiation doses. However, CBCTs with a small field of view (FOV) do not provide a complete view of the zygomatic area. Therefore, it is important to use CBCTs with a large FOV or multidetector CT (MDCT) for a thorough analysis of the anatomic structures. From these tomographic images, it is possible to create stereolithography models for simulated surgeries or to print surgical guides for use during the procedure.
Anatomic variations of the zygoma are critical for the zygoma anatomy-guided approach (ZAGA) protocol, as they help avoid excess volume in prosthetic rehabilitation and include the curvature of the lateral maxillary sinus wall. Once again, CBCT is essential for assessing these anatomic details. This imaging technique provides high precision for evaluating nasal abnormalities that could contraindicate the use of zygomatic implants.
Digital tools, such as tomography images, jaw scans, and computer-aided design and manufacturing (CAD-CAM) software, are used from the planning stage through to the creation of surgical guides. It is important to consider that longer instruments used for placing zygomatic implants can be difficult to control during surgery, which may lead to significant injuries to vital structures.
The use of technology aims to reduce the risk associated with human errors. Zygomatic surgical guides can be either mucosal or bone-supported. However, mucosal-supported guides are less stable, and their position may cause uncertainty during the procedure. The metallic bone-supported guides developed by Chow (2016) are more suitable for the ZAGA technique. These devices guide the initial drill into the alveolar crest and the perforation into the zygomatic bone.
In the digital planning for guided zygomatic implants, a double tomography protocol is used. The first tomography sequence is performed with the patient wearing the upper provisional denture, and the second sequence is performed with the denture alone. The denture must have radiopaque markers for accurate alignment in the software. This protocol helps determine the best implant position relative to the bone structures and the prosthetic rehabilitation. Therefore, the provisional prosthesis must have appropriate dimensions and aesthetics.
The surgical guide consists of 2 parts. The first part is fixed directly to the bone, and the second part is attached to the first one. The first part is used for drilling through the anterior zygoma wall, while the second part guides the drilling into the zygomatic body and the placement of the implant. Although this technique requires extensive bone exposure to fix the guides, the increased precision helps to reduce surgical trauma.
Guided surgery offers additional benefits in cases involving the placement of 4 zygomatic implants (quad zygoma). This tool helps the surgeon identify suitable areas for placing 2 zygomatic implants in the postero-superior zygomatic body, such as the region around the orbital crest. Visualizing this area is challenging, and placing 2 zygomatic implants simultaneously can be difficult. The planning protocol remains the same as for single zygomatic implants.
Even though digital tools offer significant advantages, the surgeon must have expertise and training in freehand implant placement to manage complications or accidents during surgery. Innovative navigation technologies also represent promising advancements in this field. Lastly, it is important to consider the financial investment required for this type of treatment.
Clinical and scientific evidence of the precision and accuracy of guided surgery for zygomatic implants
Bone-supported guides for zygomatic implant placement have shown promising results. However, as previously mentioned, it is necessary to evaluate the precision of this technique by comparing deviations between the planned and actual implant positions. Distortions can occur during the planning process, from image acquisition to surgical orientation, leading to changes in the final implant position. Gallo and colleagues (2019) conducted a study with 19 patients and 59 zygomatic implants. The study reported a 100% implant survival rate during a 6-month follow-up. The qualitative analysis demonstrated a notable alignment between the planned and postoperative implant positions, as verified by superimposition and color maps generated from Standard Triangle Language (STL) files. Although the quantitative analysis showed some angular discrepancies, these were clinically insignificant and did not affect the precision of the procedure. Despite the limitations and the absence of a control group, the authors concluded that guided surgery could achieve a high level of precision and represents a viable alternative to conventional surgery.
The literature reports varying results regarding the accuracy of zygomatic implants placed using guided surgery. Van Steenberghe and colleagues (2003) found a mean difference of 2.0 to 2.5 mm in linear discrepancies and 3° in angular displacements. Grecchi and colleagues (2022) evaluated the accuracy of a new bone-supported guide model by comparing it with the freehand technique for placing zygomatic implants in human cadavers. They placed 40 implants in 10 cadavers, with half placed using the guided method and the other half placed freehand. Postoperative tomography demonstrated high precision with guided surgery across all variables, including linear and angular deviations. These findings support the idea that new concepts in guided surgery, such as metallic bone-supported guides, can enhance clinical outcomes and ensure safer procedures for patients.
The systematic review by Van Assche and colleagues (2012) reported mean deviations of 0.73 mm plus or minus 0.16 at the starting drill site, 0.98 mm plus or minus 0.20 at the apex, and 3.08° plus or minus 0.37 for angular deviations. Another systematic review by Fan and colleagues (2023) compared dynamic computer-assisted surgery (d-CAIS), static CAS (s-CAIS), and the freehand technique, including 14 studies with 511 implants. The review found that both computer-assisted techniques had better precision compared to freehand surgery, with s-CAIS showing slightly better results. Implant survival rates ranged from 98.64% to 100%. Conversely, Xing Gao and colleagues (2021) evaluated the accuracy of digital planning for zygomatic implants by placing 14 implants in 4 patients. They found significant discrepancies in 3-dimensional dimensions when comparing the planned and postoperative implant positions, particularly in the right first molar area, with lengths exceeding 45 mm. All studies underscored the usefulness of digital planning but emphasized the importance of the surgeon’s expertise in performing these procedures and suggested that more robust studies are needed to validate the data.
Proposals for changes to reduce inaccuracies during the execution of the technique in challenging cases
This section will consider the most significant extra- and intrasinusal approaches and propose some guide designs to improve implant positioning and reduce the risk of accidents and complications. For cases with large intrasinusal spaces (ZAGA 0 or 1), guides with windows can assist with antrostomy and the displacement and inspection of the membrane, as illustrated in Figs. 1–4 .
