Zygomatic Implants in the Atrophic Maxilla: Anatomy, Protocols and Complication Management

The severely atrophic posterior maxilla has always represented the most demanding challenge in implant rehabilitation. When bone resorption reaches Cawood and Howell classes V and VI, conventional regenerative techniques — lateral sinus lift with grafting, onlay block grafts, distraction osteogenesis — require biological healing times of six to nine months, involve a second surgical site for harvesting, and show graft resorption rates that in some series exceed thirty per cent at five years.

The zygomatic implant, introduced by Branemark in 1988 for the rehabilitation of oncological patients following maxillectomy, has progressively broadened its indications to become a first-choice option in severe maxillary atrophy. The biomechanical principle is as simple as it is effective: bypass the residual maxillary bone entirely, insufficient in both quality and quantity, and anchor into the zygomatic body — a dense cortical bone of predictable volume and essentially not subject to resorption.

The anatomy of the zygomatic body deserves careful consideration. Usable bone thickness typically ranges between 5 and 8 millimetres in the central portion, with cortical density corresponding to D1-D2 in Misch's classification. Zygomatic implant length ranges from 30 to 55 millimetres: primary anchorage derives almost exclusively from the zygomatic cortex, while passage through the maxillary sinus and alveolar process provides secondary but not negligible stabilisation.

Branemark's original technique involved an intra-sinus path: the implant crosses the maxillary sinus cavity after a lateral bone window has been created. This route presents two documented drawbacks. The first is the palatal emergence of the implant head, which complicates prosthetic design and creates areas difficult to clean at home. The second is direct contact between the implant body and the sinus mucosa, with a risk of chronic sinusitis that some systematic reviews quantify between 3 and 12 per cent at five years.

The extra-sinus approach proposed by Aparicio in 2010 modifies the path, keeping the implant lateral to the sinus wall without entering the cavity. This variant — indicated when the concavity of the antero-lateral maxillary wall is pronounced — reduces palatal emergence, improves hygiene access and lowers the incidence of sinus complications. The choice between the two techniques is not ideological but anatomical: it depends on sinus wall morphology, which can only be assessed with preoperative three-dimensional imaging.

The ZAGA classification (Zygoma Anatomy Guided Approach), also by Aparicio, systematises this decision into five categories based on the relationship between alveolar crest, sinus wall and zygomatic body. ZAGA 0 identifies a flat wall allowing the classic intra-sinus path; ZAGA 4 describes a marked concavity requiring a fully extra-sinus approach. The clinical value of this classification lies in turning an intuitive choice into a reproducible, documentable decision.

Planning requires cone beam computed tomography with an extended field of view, sufficient to include the entire zygomatic-orbital complex. Parameters to assess include zygomatic body volume, cortical thickness, infraorbital nerve position, sinus pneumatisation and — an element often underestimated — the presence of pre-existing sinus pathology, which constitutes a relative contraindication until resolved.

The surgical protocol involves general anaesthesia or deep sedation with local anaesthesia, given the duration of the procedure and the extent of access. A crestal incision with vestibular releasing incisions allows elevation of a full-thickness flap exposing the anterior maxillary wall, infraorbital rim and zygomatic body. Identifying the infraorbital nerve is the first mandatory step: injury produces paraesthesia of the cheek and upper lip, a sensory complication poorly tolerated by patients.

Site preparation proceeds with drills of increasing diameter under abundant irrigation, following an axis running from the alveolar crest to the zygomatic body. Directional control is critical: a deviation of a few degrees at entry is amplified over a length of forty millimetres, risking perforation of the orbit or infratemporal fossa. Stereolithographic surgical guides, now available for zygomatic surgery as well, appreciably reduce this margin of error.

Implant insertion requires controlled torque: values above 50 Newton-centimetres in the zygomatic cortex do not improve stability and may produce microfractures. Adequate primary stability allows immediate loading, which in most contemporary protocols is performed within 24 to 48 hours with a screw-retained provisional prosthesis. This is the most clinically relevant advantage over regenerative techniques: the patient leaves the appointment with a fixed rehabilitation.

Survival rates reported in the literature are high and consistent. The most recent systematic reviews indicate cumulative survival of 96 to 98 per cent at five years and 95 per cent at ten years, values comparable to conventional implantology in native bone. This is remarkable considering that these implants are placed in patients with severe atrophy, that is, in the anatomically least favourable condition.

Complications deserve honest discussion. Sinusitis is the most frequent, with an incidence varying appreciably by technique: series using the extra-sinus approach report values below 5 per cent, while intra-sinus series reach 12 to 15 per cent in longer follow-ups. Management requires collaboration with an ENT specialist and, in refractory cases, may necessitate implant removal.

Orbital complications, though rare, are the most serious. Perforation of the orbital floor during preparation may produce diplopia, enophthalmos or — in extreme cases — injury to orbital contents. Prevention lies entirely in planning and intraoperative directional control: no effective salvage technique exists once perforation has occurred.

Prosthetic management presents specific features the technician must understand. Zygomatic implant emergence is typically more palatal than conventional implants, and the angulation often requires angled abutments or custom-designed screw-retained frameworks. Digital design with intraoral scanning and CAD-CAM workflow has considerably simplified this stage, allowing compensation for divergences that were problematic with analogue techniques.

Home and professional hygiene require dedicated instruction. Palatal emergence creates stagnation areas hard to reach with conventional brushing: interdental brushes of adequate size, oral irrigators and floss with threaders become integral to the maintenance protocol. Recommended professional recall frequency is quarterly in the first year and six-monthly thereafter.

In conclusion, the zygomatic implant represents a documented and predictable solution for severe maxillary atrophy, with high success rates and considerably shorter rehabilitation times than regenerative alternatives. It does, however, require a significant learning curve, dedicated instrumentation and the ability to manage complications involving critical anatomical structures. It is not a technique to improvise: case selection and operator experience remain the principal determinants of outcome.