Which Option to Choose? Zygomatic Implants or Sinus Grafting

There are essentially two applications for the zygomatic implant. The first is the traditional zygoma concept, which involves placement of one zygomatic implant in each posterior quadrant in conjunction with two to four axial implants in the premaxilla. Patients in this group have remaining bone in only the premaxilla area (zone 1) and are missing bone in the bicuspid and molar regions (zones 2 and 3, respectively). The second application is the quad zygoma concept, in which two zygomatic implants are placed in each of the patient's zygoma bones bilaterally. Patients in this category are missing their entire maxillary alveolar bone in all three zones.

For patients who present with either of these maxillary resorption patterns the placement of zygomatic implants and immediate loading with an implant-supported hybrid prosthesis can be easily accomplished in one surgical appointment. The pink portion of the hybrid prosthesis serves as the "prosthetic reconstruction" of the surgical defect. The alternative approach to using the zygoma concept is to graft the maxillary sinus, ie, sinus lift procedure. This procedure addresses only missing bone in the posterior maxilla and not missing bone in the premaxilla. An alternative approach to the quad zygoma concept (in cases of total maxillary alveolar resorption) is the "Bränemark horseshoe" graft using autogenous iliac bone to reconstruct the vertical, horizontal, and posterior resorption of the maxilla. This is a surgical reconstruction of a surgical defect.

Thorough knowledge of bone biology is essential for predictable prognosis when either grafting or using zygomatic implants. Clinicians must understand the remodeling phases of bone, including changes that occur during the anabolic and catabolic stages of bone remodeling.

Grafting procedures were initially developed by oral and maxillofacial surgeons who harvested the patient's iliac bone, considered the gold standard, as a donor graft. A "living" autogenous bone graft has osteogenic, osteoinductive, and osteoconductive properties. Today, these grafting procedures have been largely replaced by the placement of "dead" allograft (human donor) and xenograft (animal donor), which have primarily osteoconductive properties. They require substantial bone turnover before they are resorbed and replaced by mature "living" bone.

The time needed for bone and blood clot maturation to become primary/woven/immature bone (3 months), which is then followed by the first bone "turnover" (during months four, five, and six) into secondary/laminar/mature bone, is considerable. In many cases, allografts resorb before maturation into bone. Xenografts may remain for years because resorption and replacement of xenograft by the host is extremely slow. This slow process is advantageous for supporting the thin buccal plate in an immediate implant procedure in the esthetic zone, but not necessarily when reconstructing the severely resorbed maxilla.

The surgeon's understanding of biomechanical loads placed onto the zygomatic implant and supporting bone during function is critical to the implant's success. Multiple systematic reviews have shown zygomatic implant long-term success rates to be more than 97.5%.¹ This is similar to the long-term success rate reported using axial implants in patients' native bone. However, the success of grafts with delayed implant placements in this severely atrophic group of patients is unclear in the literature. The success rate of alternative graft materials to autogenous bone is poorly reported and difficult to assess. The success of implants placed in these types of graft materials is even less clear in the literature.

The graftless approach using zygomatic implants may be more readily accepted by patients because immediate placement of the implants in one procedure is possible. Shorter treatment time, the elimination of the patient's need to depend on a potentially poor-fitting interim removable prosthesis, and lower cost (when compared to multi-stage grafting procedures) are reasons for favorable treatment acceptance of the graftless approach.

The use of dental implants for the rehabilitation of fully edentulous maxillae, especially atrophic maxillae, has evolved over the past three decades. The paradigm has shifted from a staged approach, including separate and consecutive procedures for bone augmentation, implant installation with a 3- to 6-month osseointegration period, followed by prosthetic restoration, to a minimally invasive and immediate loading approach that aims to enable fixed rehabilitation in as short a time as possible. This shift mandated a modification to the standard implant protocol, eventuating in a change in surgical technique to incorporate navigation and guiding technologies.^2,3

The sinus floor bone graft, which first achieved consensus in dentistry in 1996, was one of the most important clinical advancements since the osseointegrated implant itself. This procedure allowed for the edentulous maxilla, not primarily the mandible, to be treated with implants. Considering the new techniques and methods used today, the sinus graft should not be forgotten.⁴

In 1992, the first published zygomatic implant placement was performed in a patient in whom a sinus graft could not be performed because the maxilla had been removed due to a tumor excision. Two long, standard implants were placed bilaterally into the zygomas to anchor a naso-maxillary prosthesis. At the time, the preferred reconstruction method was to first develop the bone structure to support implants within the maxillary envelope. Since then, the zygomatic implant concept has been steadily refined with increasing utilization and product development.⁵

Because the zygomatic implant method could be used in most any edentulous maxilla, the question is not when to use this implant. Rather, the issues are knowing what is required in a given atrophic condition, what approach is least invasive and within the clinician's skill set, and what is best for the patient long-term.

The threshold for placing a zygomatic implant is based on objective diagnostic criteria any clinician can learn. However, classifications for zygomatic implants, although systematic, do not specify minimum criteria for implant fixation for complete maxillary reconstruction. For example, Aparicio et al's zygoma anatomy guided approach (ZAGA) criteria is an excellent descriptor, but it does not establish absolute criteria for when or when not to place a zygomatic implant.⁶ Likewise, Bedrossian et al divided the maxilla into three regions-the premaxilla, premolar, and molar zones-providing a nonquantitative algorithm for implant placement for so-called graftless maxillary reconstruction.⁷

Quantitative zygomatic use criteria for the edentulous maxilla should include: (1) reduced arch length, ie, less than 45 mm (measured on the spline of the CT occlusal view) between the anterior sinus walls; (2) reduced molar-molar transverse dimension (such as a "micro-maxilla"), ie, less than 30 mm; (3) reduced alveolar height, ie, less than 2 mm; (4) absence of confluence bone at the midline suture (midline bone mass, including nasal crest height, less than 4 mm in height), lateral pyriform rim (bone mass less than 2 mm in width), and pterygoid bone mass at the pterygomaxillary suture (less than 4 mm in height).^8,9

One day, machine learning likely will determine an individualized threshold for a zygomatic implant using CT data input. For now, what the above criteria show is that at some threshold of atrophy and reduced total maxillary dimension (in conjunction with absence of "extra-alveolar" bone mass at the pyriform rim, nasal crest, and pterygoid) the zygomatic bone becomes the necessary final option to fix an implant apically without resorting to sinus floor or vertical alveolar bone grafting.

The complications that may arise from a sinus graft or zygomatic implant are not trivial. Sinus infection in both procedures can be severe. In fact, the elimination of the sinus graft or sinus penetration of implants by placing short or angled implants has been advocated. Trans-alveolar grafting of the sinus floor, as opposed to lateral wall antrostomy, has proven to be much less invasive and is now used routinely. However, the use of the zygomatic implant to avoid sinus grafting is not well established in the literature. Conversely, the use of small anterior sinus grafts to augment paranasal bone volume and avoid the use of zygomatic implants is more commonly suggested. In many respects, sinus grafting is preferred to the use of a zygomatic implant because it is usually more intuitive for clinicians and can be more easily done in most edentulous settings.^10,11

Sinus grafting usually results in a delay in fixed maxillary reconstruction. Although the one-stage technique of implant placement simultaneously with sinus grafting may be used, immediate loading is typically contraindicated unless there are high levels of initial implant stability. Zygomatic implants usually have enough primary stability for immediate loading.

A final consideration is peri-implant disease and health. Both standard and zygomatic implants may develop peri-implant mucositis. Unlike with standard implants, however, peri-implant disease does not influence anchorage at the zygomatic bone for zygomatic implants and does not cause implant failure similarly. Zygomatic implants can develop peri-implant sinus tracts, essentially oral antral fistulae, that are sometimes difficult to treat without implant removal.¹²

Zygomatic implants can also play a role in the anterior maxilla; they can be angled and extended to the anterior maxillary zone, commonly in the canine location. Prosthodontic indications for zygomatic implants are potentially greater than for sinus grafts.

Rehabilitation of patients with maxillary edentulism or failing maxillary dentitions is predictable and highly successful. These patients are commonly restored with a fixed maxillary implant prosthesis, which generally enables them to return to their normal dental lives. This type of treatment is life changing for many patients, restoring their confidence and allowing them to return to normal oral function.

The surgical options to reconstruct the atrophic maxilla involves either a grafting or nongrafting approach. The grafting approach involves bone grafting areas of the maxilla, typically posteriorly with sinus lifts and/or anteriorly with onlay grafting. In the author's practice, the bone source varies from either an allograft material or an autogenous graft, typically harvested locally from the jaws or, if more bone is needed, the tibia region. The nongrafting approach involves the use of zygomatic implants. Posterior zygomatic implants can eliminate the need for sinus lift grafts. In the severely atrophic maxilla, when anterior bone grafting may be needed, the nongrafting approach with the zygomatic implant can again be used. The zygomatic implant can be utilized in combination with traditionally placed dental implants or without them. If a nongrafting approach is to be used in a severely atrophic maxilla, two zygomatic implants may be placed per side. This is called a quad zygoma reconstruction.

Zygomatic implants are typically immediate-loaded with a provisional prosthesis. These implants run along the lateral aspect of the maxilla, engaging the base of the zygomatic process. The placement of zygomatic implants can be performed with the patient under either sedation or a general anesthetic.

There are many advantages to using the zygomatic implant for maxillary reconstruction versus the grafting approach, including the number of surgeries needed. With a zygomatic implant reconstruction, placement of both the implant and a screw-retained fixed provisional implant-supported prosthesis are performed in one surgery. The grafting approach may require two or three surgeries to rehabilitate the maxilla before the provisional prosthesis is placed. Cost also favors the nongrafting zygomatic implant approach because, in addition to fewer surgeries, less material and time are involved. Typical total treatment time of the nongrafting zygomatic implant approach is 6 months from surgery with use of a provisional restoration to the insertion of the definitive restoration. Whereas with the grafting approach the range of time to deliver the provisional restoration can be 7 to 13 months and the definitive restoration can be from 9 to 18 months.

While some may consider the nongrafting zygomatic implant approach a last resort when all other options have been attempted, the author considers it a first-choice solution. Our zygomatic implant success rate is 97% over the past 14 years. Of the more than 120 patients in our practice who have been reconstructed with nongrafted zygomatic implants, nearly half had had failed previous grafting procedures.

Dr. Per-Ingvar Bränemark, who created the zygomatic implant in 1987, called it a valuable addition to reconstruct the edentulous patient. In 2021 it continues to be a treatment method with a high degree of success that should be considered in the management of the atrophic edentulous maxilla.

Edmond Bedrossian, DDS
Professor, Department
of Oral and MaxillofacialSurgery, University of the Pacific, San Francisco, California; Diplomate, American Board of Oral and Maxillofacial Surgery

Ole Jensen, DDS, MS
Clinical Assistant Professor at New York University, University of Michigan, and University of Colorado at Denver; Diplomate, American Board
of Oral and Maxillofacial Surgery

Nardy Casap, DMD, MD
Professor and Chairman, Oral
and Maxillofacial
Surgery Department,
Faculty of Dental Medicine, Hebrew
University-Hadassah, Jerusalem, Israel

Michael Alterman, DMD
Director, Residency Training Program and Outpatient Clinic, Oral and Maxillofacial Surgery Department, Faculty of Dental Medicine, Hebrew University-Hadassah, Jerusalem, Israel

Jay Neugarten, DDS, MD
Associate Clinical Professor, Weill
Cornell Medical
Center, New York,
New York, and Long Island Jewish Medical Center, Manhasset, New York; Private Practice, New York, New York