Implant displacement or migration in the maxillary sinus is a rare complication due to infections, failure to plan for surgery, or malpractice. The spread of digital technologies was supposed to reduce the incidence and the lack of diagnosis of this complication, but it is increasingly reported in the literature [11, 12]. An accurate preoperative evaluation to exclude anatomical or pathological contraindications represents the key factor in avoiding postoperative complications in the implant-prosthetic rehabilitation of the maxillary bone [13].

In cases of severe pneumatization of the maxillary sinus and thin residual alveolar bone, wrong positioning of the fixture or inaccurate prosthetic procedures can lead to implant displacement. It can occur more often in patients undergoing simultaneous sinus lift and implant placement, mainly when residual bone height is less than 3–4 mm [14, 15]. According to Galindo et al., differences in the air pressure between the maxillary sinus and nasal cavity and bone remodeling during osteointegration could cause implant displacement in case of inappropriate force application, lack of primary implant stability, unsuitable temporary denture usage, and peri-implantitis [16]. Immediate removal of implants dislocated in the maxillary sinus is strongly recommended. However, when the removal is not contextual, migrations of the fixtures can occur so that management could become complex [17].

This condition is frequently associated with OAF and sinusitis. The fixtures could migrate into ethmoid and sphenoid sinuses, orbit, and anterior cranial fossa. Other complication in implant dentistry includes ingestion or inhalation [11, 18]. Surgical approaches for removing displaced implants are trans-oral and trans-nasal. Some authors describe trans-oral and trans-nasal as two different approaches that can be used alternatively in cases where implant migration occurs [19]. The most relevant results of a literature search on the topic are summarized in Table 2.

The authors reported a retrospective case series of forty patients with dental implant displacement in the maxillary sinus. Seventeen patients sustained implant-associated chronic sinusitis associated in most cases with pain, nasal obstruction, and purulent nasal discharge. Seven patients presented with OAF. In 15 cases, an ostium obstruction was diagnosed. Twenty-five patients underwent trans-oral surgery under local anesthesia. Eleven patients were treated solely via a trans-nasal approach, and four patients with OAF underwent surgery through a combined trans-nasal and trans-oral approach. All patients healed uneventfully without complications. Statistical analysis showed a significant difference in residual bone quantity at the moment of implant retrieval between patients that received cylindrical compared to conical implants. Specifically, the displacement of conical implants almost always occurred with less than 4 mm of residual bone, unlike those cylindrical, which also migrated with more than 4 mm of residual bone. These results could be related to an unfavorable fixture shape for cylindrical implants regarding achieving sufficient primary stability in the maxillary bone. Instead, conical implant geometry could ease the achievement of primary stability in the reduced bone amount [26]. The data analysis also highlighted a higher prevalence in the dislocation of bone level implants compared to tissue level ones in this case series. However, the number of cases examined is relatively low considering the prevalence of posterior maxilla implant-prosthetic rehabilitation. Based on literature findings and authors’ experience, implant migration could occur after surgical or prosthetic errors or infection/inflammation at the implant site. The lack of primary stability due to inadequate implant site preparation or placement in insufficient quantity or quality bone could also be possible. The bone volume was often inadequate to support the implants used in the posterior maxilla. Sinus lift or short implant placement would probably have avoided dislocation in most cases reported.

The Caldwell-Luc approach has not been used in any reported cases, as the medial inferior maxillary sinus antrostomy is not always effective in the functional restoration of the maxillary sinus [27]. Furthermore, it is associated with possible multiple complications, which in some cases require the use of vascularized bone flaps as described by Biglioli and Goisis [28].

Adequate patency of the maxillary sinus ostium is the sine qua non to recover the sinus’s ventilatory function after removing the foreign body [23]. In the case of ostium obstruction, this can be achieved with a minimally invasive procedure such as FESS. Its main advantages are the possibility of examining and treating the nasal cavity and all the paranasal sinuses, possibly involved by the infection starting from the maxillary sinus and enlarging the obstructed maxillary ostium [25].

Several authors have described a trans-nasal approach to treat sinusitis secondary to implant displacement. Matti et al. reported a series of 16 patients among a pure trans-nasal approach was used for dental implant retrieval [21].

As with any surgical procedure, FESS has associated risks and complications. Although infrequent, the most common complications are bleeding and recurrence of the disease (with persistence or worsening of sinus symptoms and facial pain). Severe complications involving the skull base and the orbit are rare (less than 0.1%). Other uncommon risks of FESS include swelling or bruising of the area around the eye, alteration of the sense of smell or taste, and change in the resonance or quality of the voice [29, 30].

In the case of OAF or alveolar infection, FESS alone may not be sufficient in treating chronic sinusitis derived from the dislocated implant and bone infection. In these cases, a combination of FESS and an intraoral approach allows the removal of foreign bodies from the sinuses with a less invasive procedure and closure of the OAF with local flaps [19]. Safadi et al., in their experience of 24 patients treated with endoscopic sinus surgery for dental implant displacement into the maxillary sinus, reported that five patients requested a combined trans-nasal and trans-oral approach because of OAF [25].

In the case of no maxillary ostium obstruction, without signs and symptoms of maxillary sinus mucosa infection, an intraoral approach with implant removal through the pre-existing implant site (or communication in the case of OAF) or after a lateral antrostomy, followed by primary closure of the access flap, may be the treatment of choice [22].

Manor et al. reported a case series of 55 patients with dental implant displacement in the maxillary sinus. In 52 cases, implants were removed through a lateral antrostomy (Caldwell-Luc like approach). Local flaps were used to treat OAF in 46 patients. Manor et al. also reported that older patients showed more cases of sinusitis and OAF and that they required more than one surgery for OAF closure and a longer hospitalization [24]. Ridaura-Ruiz et al. reported 9 cases of implant displaced in the maxillary sinus, all treated with a lateral window approach with primary wound closure because it allows good surgical access, a low rate of complications, and simple surgical technique [20]. Biglioli and Chiapasco also described the removal of 36 dental implants displaced in the maxillary sinus via an intraoral approach consisting of the creation of a bony window pedicled to the maxillary sinus membrane without complications [31].

The trans-oral approach is cost-effective because surgery can be performed under local anesthesia, and patients could be discharged immediately. However, it is not always possible to use this approach, for example, in the case of ostium obstruction [22].

In conclusion, despite the limitations of this study, the flowchart for the choice of surgical treatment presented in this manuscript could be a rational proposal (Fig. 6). The use of conical implants should be preferred in the posterior atrophic maxilla. Immediate removal of the implant from the maxillary sinus is always preferable. Migration of displaced implants and sinus mucosal changes may also occur over a short period, eventually causing secondary sinusitis. Therefore, early surgical removal minimizes sinus inflammation and prevents more invasive procedures. The results presented and recent literature validate that the FESS, trans-oral approach or a combination of these procedures can be used safely to treat complications following the displacement/migration of dental implants in the maxillary sinus. Each procedure presents specific indications that must be carefully evaluated prior to treatment choice in order to optimize intervention outcomes.