Maxillary atrophy following partial edentulism can impede treatment using conventional osseointegrated implants. Originally, zygomatic implants were developed to treat patients with atrophic maxilla or total edentulism [1-3], they were also used as an alternative treatment for hemimaxillectomized patients [4]. To treat partially atrophied maxillae, clinicians can use zygomatic implants alone or in combination with other implants [5]. This approach to treatment can reduce the morbidity and time associated with rehabilitation.

Rehabilitation of atrophic maxilla using osseointegrated implants is a challenge for oral and maxillofacial surgeons. Reduction of the alveolar bone compromises the stability of primary implants. Despite the successes of sinus grafts, bone loss [6] around implants, comorbidities, and the long duration of treatment are problems to consider [7].

Zygomatic implants are a good alternative to bone grafts; they provide early or immediate function for patients, are safe and predictable, and reduce the duration, morbidity, and cost of atrophic maxilla treatment [8]. Zygomatic implants are rarely indicated in cases of full arch rehabilitation. Nonetheless, they have been widely used as an anchorage for prostheses in patients undergoing hemi maxillary ablative surgeries. To ensure stability and oronasal separation, rehabilitative prostheses generally require anchors in cases of partially resected maxillae [9-11].

In this paper, we reported the cases of five patients with hemimaxilla who were treated using unilateral zygomatic implants. The implants were all installed at a position similar to those used in edentulous patients, providing a favorable anchorage for the prosthesis abutments and showing that the mathematical data provided by the analyses is reproducible. Therefore, the unilateral use of zygomatic implants is a viable alternative to sinus augmentation to treat atrophic maxilla.

In this series, five patients with posterior class V and VI maxillary alveolar bone atrophy, as described by Cawood and Howell [12], were selected. The patients had an average age of 57.3 years (range: 43–72 years). Three of the patients had unilateral edentulism, while two had bilateral posterior edentulism. All patients had a history of failed graft procedures, and one had used a subperiostal implant for 10 years. This implant had been removed 1 year prior to the zygomatic implant surgery, and the patient displayed intense fibrous tissue within the posterior maxillary soft tissues. One of the patients presented an oro-sinusal fistula that had been closed by the senior author one year prior to the zygomatic surgery (Figure 1 and Table 1).

Figure 1: Oro-sinusal fistula closed by the senior author one year prior to the zygomatic surgery.

Table 1: One of the patients presented an oro-sinusal fistula that had been closed by the senior author one year prior to the zygomatic surgery.

Patients were anesthetized by endovenous sedation using midazolam and dormonid [13]. All zygomatic implants were inserted via the extra maxillary route (Figure 2). The zygomatic bone was approached by making an incision in the jugal mucosa and creating a tunnel from the alveolar crest into the body of the zygomatic bone. The drilling sequence was conducted in accordance with the manufacturer’s instructions, and the zygomatic implants were installed using a manual key. All implants were inserted with a minimum of 55 N (Figures 3 and 4).

Figure 2: External access to the maxillary sinus.

Figure 3: Insertion of zygomatic implant.

Figure 4: Unilateral zygomatic implant.

All patients were treated using a fixed-bridge prosthesis. In three patients, osseointegration was observed within 4 months. In one patient, bilateral alveolar atrophy occurred, and an immediate loading protocol was adopted. In all patients, rigid, bridged-tree prostheses were used. Among these, five zygomatic implants were connected to conventional implants. In one patient, the zygomatic implant was connected to a tooth through a mobile connector (Figures 5-10).

Figure 5: Zygomatic implant connection.

Figure 6: Bar proof.

Figure 7: Implant and prosthesis connection.

Figure 8: Occlusal view.

Figure 9: An implant attached to the tooth by means of a fixed prosthesis.

Figure 10: All implants were positioned on the alveolar crest and were in a good position for prosthetic rehabilitation.

The average follow-up period was 36 months (range: 4–52 months). Patients underwent panoramic radiography 1 week and 4 months after the initial surgery, and then on a yearly basis. After 1 year, all the implants were submitted to a 6-monthly follow-up control protocol. At the time this report was submitted, all the implants remained functional, with proper occlusal balance. No signs of peri-implantitis were observed, and no clinical infection or exudates occurred. The maxillary sinus remained clean in all cases, with no signs of sinusitis. One patient required early revision of the torque of the prosthetic screw 5 months after the prosthesis installation. However, the patient only returned for semestral follow-ups subsequently.

The zygomatic implant surgery offers an interesting alternative for moderately to severely reabsorbed rehabilitation of the maxilla. The zygomatic bone is a solid for anchoring the implant and later for placement of a fixed prosthesis [14].

In this regard, the zygomatic implant has shown excellent results, with a high survival rate during treatment. Indeed, several studies have confirmed that zygomatic implants are an excellent alternative treatment in patients with atrophic maxilla. For instance, Yade [10] reported an 86% success rate among 43 zygomatic implants installed in severely atrophic maxillae, and Malevez [11] reported a survival rate of 100% after 36 months when immediate loading was not used. In a 2009 clinical retrospective analysis involving a follow-up that ranged from 9 months to 5 years, Balshi et al. [12] showed a 96% survival rate among zygomatic implants that had been immediately loaded. Our report points to a survival rate of 99.5% for follow-up of up to 48 months, which is in accordance with other published studies [15-19].

On a related note, Chrcanovic [13] reviewed the various techniques used to place zygomatic implants, as well as the types of maxillary reabsorption that are associated with each method. He concluded that the outward technique is less invasive and faster, and that it is thus the most suitable method in the treatment of maxillae that present a higher rate of reabsorption and have large sinus cavities. The slot technique [20,21], which was used in the present cases, permits a minimally invasive approach, reducing swelling and soft tissue changes around the abutments. In the present study, we employed an extra sinus implant and used a minimally invasive approach to all zygomatic implants. In this way, we achieved a good prosthodontic position, as well as healthy soft tissues around the implants.

Among the complications we reported maxillary sinusitis [15], implant loss [22] and orosinusal communication [23-25]. As an alternative to reduce the risk of maxillary sinusitis, we propose the externalized technique developed by Malavez, where we avoid implantation of the implant inside the maxillary sinus, reducing the chance of sinusitis. [11,17].

The zygomatic implant, unlike conventional implants, tends to cause an imbalance in axial occlusal forces. To stabilize these forces, an implant on the opposite site is required; this cancels the torsion forces and prevents micromovements, which destabilize the implant. Indeed, the opposite implant is fundamental to balancing the maxillary arch, reducing micromovements, and ensuring implant longevity [26,27]. Despite the success of rehabilitation using a combination of zygomatic implants and contralateral implants, no studies have yet shown that treatment is unfeasible without these techniques.

Furthermore, titanium intraoral implants can provide additional restraint and prevent excessive mechanical stress exerted by anchoring elements in the residual maxilla. In this regard, a finite element analysis revealed that the success of these implants is directly related to the biomechanical stability of the bone. That is, if the load distribution is concentrated, the bone will regenerate; if it is not, bone reabsorption will occur. It follows that stress is distributed throughout the body of the implant, suggesting that it provides good stabilization without causing bone defects at its base. The studies mentioned all focused on full-arch rehabilitation. However, these constructs have also been used for hemi-arch treatment, suggesting that rehabilitation is feasible without opposite side implants [28].

Within the proposed in this study, the most complicated is to plan a mechanic that supports a unilateral implant without the force dissipated on this one is factor of loss of the implant early. Thus, we propose the use of the externalized technique associated with the prosthesis connected to another implant or dental element canceling out the forces of mastication, such as shearing.

The present report shows the feasibility of zygomatic implants in the treatment of partial maxillary edentulism. Despite the good results achieved in this report, more case studies involving a larger number of patients, as well as clinical trials comparing zygomatic implants with bone augmentation, will be necessary to provide more information about this treatment approach.