The armamentarium for zygomatic implants includes zygoma retractors, specific drills and burrs, depth gauge, inserting hand tools, prosthetic tools, and multiple angulated abutments from 0° to 60°.
When a guided system is used, the armamentarium also includes the surgical guides, guiding drilling sleeves, and fixing pins and screws.
The surgical approach is dictated by the maxillary bone volume availability and the prosthetic demands upon which the implant layout is chosen.
The extramaxillary approach is prosthetically derived. The emergence profile is located at the alveolar crest and the prosthetic work is easy and intuitive.
Zygomatic implants were first introduced by Brånemark in 1988 as an alternative treatment for patients with extensive defects of the maxilla caused by tumor resections, trauma, and congenital defects. Later, uses for these implants were expanded to other indications, including rehabilitation of completely edentulous patients with severe maxillary atrophy, excessive maxillary sinus pneumatization, and in cases of failed maxillary sinus augmentation procedures. ,
The zygomatic implants are anchored in the zygomatic basal bone, and usually there is no need for additional bone augmentation or grafting in these patients. Different surgical approaches and implant placement techniques and configurations have been proposed, with the reported success rate ranging between 95.8% and 99.9%, all aiming for full-arch maxillary rehabilitation.
Multiple neighboring structures are included in the anatomic geography of the implantation region of zygomatic implants, including the orbit and its content, maxillary artery, pterygoid venous plexus, and skull base. As such, extensive anatomic knowledge alongside a comprehensive 3-dimensional orientation is mandatory when surgically installing these implants.
Contraindications for the use of zygomatic implants are acute sinusitis, zygomatic or maxillary pathologic condition, and an underlying disease deeming the patient unfit for implant surgery. Relative contraindications include heavy smoking, treatment with bisphosphonates or other antiresorptive medications known to cause medication related osteonecrosis of the jaw, and chronic sinusitis.
The purpose of this article is to describe the different surgical approaches and armamentarium for the installation of zygomatic implants.
The original Brånemark technique, the intrasinus technique, uses a 4-cortex anchorage of the zygomatic implant. The zygomatic implant is installed from the palatal aspect of the edentulous alveolar ridge and is directed toward the zygomatic bone, passing through the maxillary sinus. This is intended to give the implant maximal stability by engaging both the maxilla and the zygoma in a bicortical fashion.
However, this installation layout may result in a prosthetic challenge, as the prosthetic emergence profile of the implants tends to be palatal, thus requiring bulky palatal prosthetic rehabilitation, which may lead to patient discomfort ( Fig. 1 A and B). In addition, the intrasinus passage of the implant may be contraindicated in cases of chronic sinusitis.
In an attempt to overcome the prosthetic and anatomic challenges of the intrasinus approach, the extrasinus approach was developed. This prosthetically and anatomically driven approach aims to position the prosthetic emergence profile of the zygomatic implant at the desired occlusal position at the alveolar crest, and to avoid, as much as possible, implant pathway through the maxillary sinus ( Fig. 2 A–C), thus minimizing the risk for postoperative sinusitis.
This approach mandates a one-piece full-arch prosthetic rehabilitation with cross-arch stabilization, in order to maintain a stable and immobile maxillary prosthesis. Because of the position of the implants’ emergence profile at the peak of the alveolar crest, the prosthetic flow for the prosthodontist remains the same as for standard full-arch dental implants.
The surgical approach should also be dictated by the maxillary bone volume availability and the prosthetic demands, which will guide the choice of implant layout and the type and number of implants installed. Anatomic considerations and guidelines are discussed in detail in the preceding article in this text.
Bedrossian divided the maxilla into 3 zones: zone 1 (the premaxilla); zone 2 (the premolar area); and zone 3 (the molar area) ( Fig. 3 , Table 1 ). When graftless implantation with immediate rehabilitation is planned, the bone volume availability in the different zones should dictate the surgical approach and implant layout.
|Available maxillary bone||Surgical implants layout|
|Zones 1, 2, 3||Standard dental implants (axial)|
|Zones 1, 2||4–6 standard dental implants (tilting of the distal implants)|
|Zone 1||2–4 standard dental implants in the premaxilla and 1 zygomatic implant on each side (optional: pterygoid implants for distal support)|
|No bone available||Quad-zygomatic layout: 2 zygomatic implants on each side (optional: pterygoid implants for distal support)|
In cases of adequate bone volume in zones 1 and 2, a choice of 4 to 6 standard implants with tilting of the most distal implants may be favored.
In cases of adequate bone volume only in zone 1, the implant layout includes the use of 2 to 4 axial dental implants placed in the premaxillary region for anterior prosthetic support together with 1 zygomatic implant emerging at the premolar area on each side for posterior prosthetic support ( Fig. 4 A and B).
In cases of severe maxillary atrophy with inadequate bone volume in all 3 zones, 4 zygomatic implants may be used ( Fig. 5 ).
Implant planning and positioning
Proper installation of a zygomatic implant in the correct spatial position requires comprehensive anatomic 3-dimensional understanding and visualization. Inappropriate placement of a zygomatic implant may lead to severe complications, including uncontrolled bleeding, damage to the orbit and its content, damage to the maxillary sinus, and traumatic fractures to the orbital and zygomatic bones.
The surgical procedure should be planned based on a high-resolution maxillary cone beam computed tomography (CBCT; 200–400-μm slices). The scanning protocol should include the full extent of the lateral orbital wall and the temporal process of the zygomatic bone. When the patient has metallic prosthetics or dental implants, high-resolution CBCT (thin slices) may result in metallic artifacts, which may lead to loss of information and inability to use a virtual planning system in order to properly plan the surgery. To some extent, these artifacts may be removed using designated software, but in cases of widespread artifacts, the use of the hospital-based multidetector computed tomography with thicker slices (500 μm) may be advised. For correct prosthetic-derived surgical planning, the scan should be performed with a denture carrying fiducial markers (eg, barium sulfate, gutta percha), or with a prosthodontic setup of the desired prosthetic work ( Fig. 6 ).
Zygomatic implants can be installed freehand or using presurgical virtually planned navigation and guiding systems. A detailed description of guided and navigation techniques for zygomatic implants is presented elsewhere in this text.
When planning the positioning of zygomatic implants, the vertical plane and the horizontal plane must both be taken into consideration.
The vertical plane, or the “up/down” plane, determines the position of the implant apices between the inferolateral border of the orbit cranially and the inferolateral border of the zygomatic complex caudally. This surgical axis is visible, allowing a skilled surgeon to position the implant in a relatively accurate position ( Fig. 7 ).
The horizontal plane, or the “in/out” plane, of the implant vector determines the apical position of the implant between the anterior and posterior surfaces of the zygomatic complex. This plane is somewhat invisible in its nature without wide surgical exposure and is assessed mainly by the surgeon’s personal experience rather than by objective landmarks ( Fig. 8 ). The notch of the zygomatic process is a safe landmark to engage a zygoma retractor for improved visibility and can aid in trajectory guidance to avoid the orbital confines.