Key points

Introduction

Zygomatic implants have emerged as a paradigmatic treatment alternative to bone augmentation procedures, offering a viable solution for implant-supported fixed prosthetic rehabilitation in cases where maxillary bony support is insufficient. Initially designed by Per-Ingvar Brånemark, zygomatic implants enable prosthetic rehabilitation in patients with limited maxillary bone, precluding conventional dental implant placement and rendering traditional denture wear challenging due to inadequate retention and stability (Brånemark ). The placement of dental implants in patients with tumor-related or trauma-related defects, or with vertical and horizontal maxillary deficiencies, is often complicated by extensive pneumatization of the sinus cavities and poor quality and quantity of remaining bone. Recent literature recommends angled implants, with or without single zygomatic implants, to avoid extensive bone grafting procedures. However, the palatal and posterior resorptive pattern of the edentulous maxillae may limit the horizontal bony volume necessary for successful angled endosseous implant placement. Severe maxillary atrophy can result from various factors, including tumor resection, trauma, abnormal anatomy, generalized aggressive periodontitis, genetic disorders, or syndromes. Fabricating a prosthesis with adequate retention and stability for patients with an atrophic edentulous maxilla poses a significant challenge, even for skilled surgeons. Zygomatic implant treatment concepts have evolved as an alternative to bone augmentation procedures, initially conceived for trauma victims or maxillary resection patients with significant structural loss. ^, Most surgeons rely on their experience, anatomic knowledge, and intraoperative landmarks for implant placement without a surgical guide. However, surgical misadventures have led to the acceptance of guided zygomatic implants, which involve presurgical planning using 3-dimensional (3D) imaging and software, followed by the creation of a custom-made surgical guide for precise implant placement. This approach enhances precision, predictability, and efficiency, reducing complications and ensuring optimal outcomes with higher success rates. In the reconstruction of the edentulous maxilla using quadruple zygomatic implants, 2 approaches are considered: the classical intramaxillary protocol (Brånemark ^, ) and the exteriorized approach, also known as the extramaxillary or extrasinus technique (Migliorança and colleagues, 2006; Aparicio and colleagues, 2007). This article provides a comprehensive discussion of the indications, anatomy, and contraindications of guided surgical techniques. The choice between freehand and guided zygomatic implant surgery depends on the surgeon’s experience, case complexity, time constraints, cost, and available technology and resources. Guided surgery offers higher precision and predictability, making it a popular choice in complex cases, while freehand surgery is often employed by highly skilled surgeons who can adapt during the procedure.

Severe maxillary bone loss poses a significant challenge in dental implantology, limiting the feasibility of conventional implant placement. Guided zygomatic implant surgery has revolutionized the management of such cases, allowing for the precise placement of implants anchored in the zygomatic bone. This article aims to explore the evolution, techniques, outcomes, and future prospects of guided zygomatic implant placement.

Planning and preparation

The approach to full-arch rehabilitations is leaning more and more toward digitalization rather than analogue, both during the restorative and surgical phases. The need for a more predictable prosthodontic prognosis has created the need to have implants placed not just in relation to the existing bone proposition but rather in relation to the future restoration to achieve an optimal AP spread and reduce the length of the cantilever as well as the balcony. Due to this and other factors, such as the advancement of 3D printing and selective laser melting (SLM) technology with the ability to have an in-house production has led to the ample advancement of guided surgery, especially in the more challenging clinical cases. While planning such cases, it is important to note that the rehabilitation starts from the end result, meaning that prior to implant placement the lost dentition is virtually recreated in an optimal relation to both esthetic ( Fig. 1 ) and functional parameters ( Fig. 2 ) and only then does the surgeon and prosthodontist decide which implant configuration ( Fig. 3 ) should be chosen for the clinical case. With the improvement of digital diagnostic devices and methods, such as intraoral scanners, facial scanners, DICOM segmentation, digital smile design, photogrammetry, and digital jaw-motion at this time, it is possible to recreate the patient as a virtual 3D avatar ( Fig. 4 ) without the need for several additional visits and countless try-ins, which greatly improves the time-management of such cases for the clinician, the patient, and the dental laboratory. Following the virtual restorative and implant configuration planning, a surgical guide can be designed ( Fig. 5 ) in order to achieve the desired implant position. The inception of photogrammetry technology into the digital full-arch protocols has allowed the planned virtual restoration to be transferred into the oral cavity with great accuracy and a passive fit in comparison to analogue protocols of the past.

Surgical planning around missing dentition is visualized via facial scanning that allows for optimal relation in both esthetic and functional parameters.

Virtual surgical planning not only allows the clinician to understand the patient anatomy but also a better understanding of projected implant placement procedures and techniques.

Implant placement can be visualized and planned to unique patient anatomy, and can offer clinicians the ability to consider the surgical outcomes of different treatment plans without the presence of the patient, and removes margins of human error due to its specificity.

Facial scanning and mapping removes the need for several additional visits and countless try-ins, which greatly improves the time-management of such cases for the clinician, the patient, and the dental laboratory.

Digital models of patient anatomy afford clinicians the ability to avoid miscalculated implant placement as digital renderings can provide hypothetical scenarios of planned implant placement and explore various outcomes in relation to surgical technique and patient anatomy.

Guide design and structure

Static Zygomatic Guides by their nature are a subcategory of bone-supported guides, which means that they are placed directly on the bone after flap elevation. This is crucial to the protocol because statistically bone-supported guides are the most predictable and accurate category of Static Surgical Guides available at the moment of writing this article. It is not recommended to use mucosa-supported, tooth-supported, or hybrid-supported guides for zygomatic surgery due to the lack of accuracy and stability of these types of guides.

The basic zygomatic guide ( Fig. 6 ) consists of the following elements.

• 1.

  Zygomatic bone support

• 2.

  Vomer bone support

• 3.

  Palatal support

• 4.

  Zygoma drill sleeve

• 5.

  Fixture screw support

• 6.

  Additional implant sleeves

This 3D rendering of the basic zygomatic guide relies on zygomatic bone and vomer bone support, palatal support, ensuring 3 support points. It also includes features like a zygoma drill sleeve for drill guidance along with additional implant sleeves dependent on the case performed. Finally, fixture screw support is a key feature of the zygomatic guide, as it stabilizes the apparatus to ensure no movement of the guide takes place during surgery.

During the design of the zygomatic guide, communication between the clinician and the CAD designer/bioengineer is essential. Understanding not just the digital design process, but the anatomy and clinical steps greatly increases the change of a successful surgery. The most important aspect of planning a zygomatic guide is deciding on which topographic sites of the maxilla it is going to be placed. If the patient has an edentulous maxilla, there should hardly be any changes post flap elevation; however, if the patient has to have, for example, tooth extraction or cystectomy performed, this may differ from the initial anatomy visible on the CBCT. While experimenting with guide designs, we have come to differentiate bone structures and stable and unstable, stable meaning that they most likely are not going to be affected after flap elevation and unstable meaning that they are indeed going to affected after flap elevation. An example of a stable bone structure would be the vomer, zygomatic, and palatal bones. These structures remain intact after flap elevation in most cases. An additional example would be the edentulous alveolar ridge. An example of an unstable bone structure would be a postextraction socket, a maxillary defect, or a postimplant removal site. These structures tend to be unpredictable and can greatly differ during surgery from the initial CBCT due to either the quality of the initial data or the clinical approach. In most cases, 3 support points are sufficient for the accurate placement of the zygomatic guide (vomer bone, zygomatic bone, palatal bone). Additionally, the zygomatic guides can also be combined with standard implant sleeves, for example, for guided pterygoid or conventional implant placement with a standard guided surgery kit.

Zygomatic guides should have a very passive fit once placed on the bone, depending on the accuracy of the initial CBCT to STL segmentation. To counter this and ensure that the guide does not move during the osteotomy, it is recommended to stabilize them using osteosynthesis fixture screws ( Fig. 7 ). The positioning of the screws may vary depending on the anatomy of the patient; however, it is advised to always try and place them in stable bone structures, such as the vomer and zygomatic bone as well as the palatal side of the alveolar ridge, for the same reason as listed earlier. Empirical analysis shows that 3 screws should be sufficient to achieve stability of the zygomatic guide without the risk of it moving during the surgery.

Osteosynthesis screws are visualized in a 3D model to depict how they stabilize the surgical guide during surgery. While screw placement location is dependent on patient anatomy, typically 3 screws are sufficient to achieve proper apparatus stability.

The osteotomy and implant site preparation protocol utilizing a Static Zygomatic Guide greatly differentiates from standard guided surgery protocols. It utilizes 2 concepts of guided surgery: the sleeveless concept and the semi-sleeve concept. Elaborating further on this lets to explore the 2 concepts and understand further how they are implemented in static zygomatic guides.

The sleeveless concept is a form of guided surgery design created to bypass the need for a standard titanium or peek sleeve integration into the guide, but rather manufacture the guide with a direct printed sleeve. It is also theorized that by doing so it is possible to decrease the offset between the sleeve and the guided osteotomy drill, therefore, increasing the accuracy of the osteotomy. The semi-sleeve concept is an idea where by dividing the sleeve in 2 you allow better access for the osteotomy drills. Conventionally, it is utilized in the posterior mandible region to allow a vestibular access for the osteotomy drill.

Due to the zygomatic osteotomy protocol requiring the use of longer drills compared with conventional guided implant placement and in most cases the absence of an osteotomy canal as a support element for the drill, the most difficult challenge during guided zygomatic implant placement lies in stabilizing the drills in order to prevent deviation. To combat this, the zygomatic guides are designed as a sleeveless guide with an average offset between the guide and the drill being about 100 microns. Furthermore, the sleeve itself is divided into 2 parts ( Fig. 8 ), one on the base of the alveolar ridge and the other on the surface of the zygomatic bone, hence creating 2 separate semi-sleeves ( Fig. 9 ), which stabilize the long shaft of the drill during implant site preparation.

Drill stability remains a challenge while using longer drills for zygomatic osteotomy placement. To combat this issue, the zygomatic drill sleeve is able to guide the drill in the proper angulation.

This digital model observes the 2 separate semi-sleeves that are designed into the zygoma drill guide.

Materials and methods for manufacturing such static zygomatic guides may vary. A dental technician/bioengineer may opt for the use of 3D printed plastics, 3D printed metals utilizing SLM technology, or a more classic approach using metal casting. 3D printed plastics may work, however, due to the elasticity of the plastics the guide has to be made thicker than it would otherwise be if manufactured out of metal, which may affect the comfort of the clinician during surgery and the visibility of the surgical site. Metal casting may also be used as an effective method of manufacturing; however, due to the precise nature of the procedure, an inaccurate casting technique may cause problems with the seating of the guide on the bone site. At the moment of writing this article, empirical data suggest that the most optimal method of manufacturing static zygomatic guides is SLM utilizing cobalt chromium (CoCr). This is a highly precise manufacturing technique and very cost-efficient due to the price of the CoCr SLM material averaging about one-third of titanium SLM material. CoCr allows the zygomatic guides to be both sturdy and thin at the same time, which greatly decreases the risk of guide fracture or movement during the surgery as well as a decent surgical site visualization. Titanium SLM may also be an effective method to manufacture the static zygomatic guides, however, due to the guide being patient-specific and single-use and offering no real upside to CoCr SLM it might not be cost-efficient.

Guided zygomatic instruments

Due to the specifics of the osteotomy site preparation during guided zygoma implant placement, special surgical kits started to develop as an addition to the conventional zygoma kits, the most prevalent being the EZygoma kit by Noris Medical. However, with innate understanding of the principles of guided zygomatic surgery any conventional zygoma kit can be converted into a guided kit with a few additional instruments and modifications.

A guided zygomatic implant kit typically includes a range of instruments and components specifically designed for the precise placement of zygomatic implants using a guided surgery approach. While the specific contents may vary depending on the manufacturer and the intended surgical technique, a typical guided zygomatic implant kit may include the following components ( Fig. 10 ).

• 1.

  Modified diamond drill

• 2.

  Zygoma bone profiler

• 3.

  Zygoma pilot drills

• 4.

  Pilot sleeve handle

• 5.

  Standard zygomatic drills

• 6.

  Zygoma guided implant driver

A typical zygomatic implant kit is equipped with instruments specifically designed for zygomatic implant placement with a guided approach. The instruments modeled here include a modified diamond drill, a zygoma bone filer, zygoma pilot drills, a pilot sleeve handle, standard zygomatic drills, and a zygoma guided implant driver, respectively.

Depending on the surgical protocol, one may not require every instrument listed, however, in more complex cases it is recommended. Theoretically, it is possible to perform the Digital ZAGA protocol while only utilizing the standard zygomatic kit, depending on the surgical guide design and implant position; however, this may affect the accuracy of the implant placement.

Protocols of guided zygomatic surgery

When comparing guided surgery to conventional implant placement several key differences are notable, mainly the need for additional instruments such as a separate guided surgery kit, the manufacturing of additional devices, that is, surgical guides and different osteotomy tactics and drilling protocols, specifically unique to guided surgery kits. These factors in combination with material ones, such as purchasing of a separate kit and manufacturing fees of surgical guides as well as the time management tend to push away a decent amount of practitioners away from guided surgery and toward free-hand placement. What separates guided zygomatic implant placement protocols is the absence of most of the differences listed earlier. As mentioned in the “Guided Zygomatic Instruments,” any normal zygomatic kit used for conventional free-hand techniques can easily be used while placing zygomatic implants via a surgical guide. With the optional addition of several instruments into the kit, it can be further enhanced; however, this is highly dependent on the goals and philosophy of the operator.

Taking the statement above into account, there are several key differences between the guided protocols for ZAGA-0-1 and ZAGA-2-3-4. As such, we have come to separate guided zygomatic implant placement into 2 protocols: Digital ZAGA-1 (for placement of ZAGA-2-3-4 implants) and Digital ZAGA-2 (for placement of ZAGA-0-1 implants) with a slight guide modification depending on the anatomy of the maxillary sinus in regards to the implant position.