Zygomatic Implants in Severe Maxillary Atrophy: Surgical Technique, Indications and Complications

Zygomatic implants (ZI) are an unconventional surgical solution for cases of severe maxillary atrophy where remaining bone volume doesn't allow placing standard implants even combined with bone augmentation techniques. Introduced by Brånemark in 1988 as an alternative to iliac graft bone reconstruction for oncology patients undergoing maxillectomy, ZIs have been progressively adopted also in patients with non-oncological atrophy — congenitally deficient maxillary bone, long-term edentulous patients with severe crestal resorption, or as an alternative to bilateral sinus lift in patients with a high surgical risk profile. The biomechanical rationale of ZIs is transferring occlusal load from the atrophic maxillary skeleton to the zygoma — the malar bone — through a 30-52 mm implant crossing the maxillary tuberosity, the maxillary sinus, and anchoring in the zygomatic process of the malar bone with 5-7 mm of bone engagement.

The anatomy of the zygomatic pathway is the parameter governing surgical planning and candidate patient classification. Aparicio's classification (ZAGA, Zygoma Anatomy-Guided Approach, 2011) identifies five zygomatic pathway morphologies (ZAGA 0-4) based on the relationship between maxillary alveolar crest position and the anterolateral maxillary sinus wall. In ZAGA 0 morphology (full alveolar crest, vertical sinus wall), the implant path is fully intraoral; in ZAGA 4 morphology (severe crestal atrophy with a large sinus), the implant emerges from the most apical part of the atrophic crest and runs partly extrasinus, in a submucosal position on the anterior sinus wall — the technical variant with the lowest sinus impact but with implant exposure under the buccal mucosa. CBCT planning with preoperative measurement of the optimal path and three-dimensional simulation (coDiagnostiX® or Simplant® software with dedicated ZI modules) are prerequisites for safe zygomatic surgery.

Brånemark's classic surgical technique for ZI placement involves: opening a wide flap with access to the lateral sinus wall, osteotomy of the sinus window, visual landmark of the zygomatic-malar process, insertion of the pilot bur with manual guidance along the predetermined path, widening with sequential zygoma burs up to the final diameter (3.5-4 mm), placement of the ZI with an apical cup anchoring in the zygomatic process. The risk of orbital penetration — from deviation off the planned trajectory — requires direct visualization of the path through the sinus window and palpatory checking of bur position on the infraorbital side. The ZAGA technique (extrasinus for ZAGA 3-4 morphologies) avoids opening the sinus window, reducing sinus surgical trauma but requiring a specific learning curve.

ZI complications documented in the literature are divided into immediate (rare) and late. The most common late complication is zygomatic-implant-associated sinusitis, reported with a variable incidence of 2.5% to 25% across case series, with a systematic study by Aparicio et al. (2014) documenting radiographic sinusitis in 29% and symptomatic sinusitis in 10% of 194 ZIs followed for 5 years. The proposed mechanism is altered sinus mucociliary drainage caused by the implant crossing the sinus cavity, and, in intrasinus techniques, biofilm proliferation on the implant surface inside the sinus. Management requires ENT consultation and targeted antibiotic therapy; in refractory cases, functional endoscopic sinus surgery (FESS) is indicated to restore drainage. Persistent oro-antral communication through the placement site is another documented late complication, managed surgically.

Long-term zygomatic implant survival rates are documented in systematic reviews of growing quality. Davo et al.'s meta-analysis (Clin Oral Implants Res, 2018) on 2,161 zygomatic implants with an average follow-up of 5.9 years reported cumulative survival of 96.7% (95% CI 95.9-97.5%) — an excellent figure considering the complexity of the cases treated. Prosthetic outcomes in terms of patient satisfaction (VAS scales) and chewing function are reported as very favorable in prospective series, with significant quality-of-life improvement compared to the pre-treatment condition. The "competing" alternative represented by short implants (4-6 mm) — which over the last ten years have shown survival rates comparable to standard implants in sites with limited bone — has narrowed ZI indications to severe grade IV-V Cawood-Howell atrophy, making ZIs an elite solution for selected cases.

Planning the prosthetic restoration on zygomatic implants follows its own principles determined by the palatal/paramedian position of implant emergence and the anterior angulation of ZIs relative to standard anterior implants. The restoration is invariably fixed and immediately loaded within the first 24-48 hours, both for functional reasons (patients with severe maxillary atrophy have often endured prolonged periods with removable dentures and compromised chewing function) and biological ones (immobilizing ZIs through a rigid prosthetic bar reduces micromovement of each implant during healing). Restoration design must carefully manage posterior cantilever extension — forces transmitted to ZIs by prolonged distal cantilevers amplify at the zygomatic fulcrum, with a risk of overload in areas already anatomically critical.