We performed an 11-year retrospective review of patients who presented to the Department of Oral and Maxillofacial Surgery at Seoul National University Dental Hospital from September 2010 to November 2021 and studied 15 cases with displaced implants in the maxillary sinus. The study protocol complied with the principles of the Declaration of Helsinki and was approved by the Seoul National University Institutional Review Board (S-D20170005). All methods were performed in accordance with the relevant guidelines and regulations. All patients were informed of the surgical procedure with the potential risks and benefits, and an informed consent was obtained to undergo treatment and be included in the study.

Implant migration was identified in 8 male and 7 female patients with an age range of 48–74 years. The patient characteristics, medical histories, clinical and imaging results, and post-removal outcomes were retrospectively assessed. Two patients presented within the first 24 h of displacement, 10 patients presented within the first 8 weeks of implant placement, and 3 patients presented 6 months after loading. All patients had unremarkable medical histories. The patient demographic information is shown in Table 1. Panoramic radiographs, Water’s view, and paranasal sinus (PNS) computed tomography (CT) were used to investigate the anatomical locations of the displaced dental implants. There were 6 cases of implant displacement in the right maxillary sinus (40%) and 9 cases in the left maxillary sinus (60%) (Fig. 1).

The preoperative radiographic evaluation visualizing displaced dental implants on panoramic radiographs, Water’s view, posteroanterior and lateral cephalograms, and computed tomography of the 15 patients included in this study

Four main surgical approaches were used to retrieve the displaced dental implants: (1) crestal approach through the implant insertion site; (2) a CLP through the bony window near the canine fossa; (3) FESS through the nasal cavity for identification and enlarging of the OMU, which is the opening part of the maxillary sinus and ethmoidal sinus; and (4) MESS. All surgeries were carried out by one experienced surgeon. The MESS technique, which involves accessing the maxillary sinus through the lateral window between the canine fossa and the buttress, was developed and refined over time based on the CLP and FESS approaches.

The patients were retrospectively divided into three groups based on the timing of implant displacement: early displacement, late displacement, or delayed displacement (Table 2). The early displacement group included all complications that occurred intraoperatively and were associated with incorrect surgical planning, including placement of implants at sites with inadequate bone height and volume, a lack of surgical experience, overpreparation of the recipient site, applying heavy force during implant insertion, and sinus membrane perforation during the drilling procedure. Late displacement was related to implant displacements that occurred during the follow-up and re-entry procedures and typically occurred within the first 6 months resulting from incorrect surgical technique, constant bone destruction due to an existing alveolar bone infection, osteoporosis, or osteopenia [7, 8]. Delayed displacement was observed in all cases after prosthesis delivery due to changes in paranasal pressure, destruction of the bone around the implant leading to impaired osseointegration, resorption resulting in the incorrect distribution of occlusal forces, and detachment of the implant from the prosthetic retention structure [9].

Antimicrobial prophylaxis was administered using 250 mg cephalosporin, 386 mg ibuprofen arginine, and 95 mg Phazyme taken three times a day for 5 days. All of the procedures were carried out under general or conscious sedation using midazolam. A 2% lidocaine solution with 1:100.000 epinephrine was infiltrated into the buccal sulcus of the affected site. Epinephrine and xylocaine-soaked cotton were applied in an alternating manner to the middle meatus for 10 min before local anesthetic administration. The MESS technique can be performed under local anesthesia for the removal of a displaced dental implant in the maxillary sinus. However, in cases of extensive maxillary sinusitis or more complex procedures, intravenous sedation may be required.

The crestal approach was established by a horizontal incision following the margins of the oroantral communication (if present) and extended distally and mesially with releasing vertical incisions. A full-thickness mucoperiosteal flap was elevated, and the implant was removed from the maxillary sinus using a thin suctioning tip and/or sinus forceps through the implant insertion site (Fig. 2A–D).

The crestal approach for displaced implant removal through the implant insertion site in Case 2. Preoperative intraoral view (A), a full-thickness mucoperiosteal flap (B), displaced implant removal using the suction tip (C), and the removed implant specimen (D)

For the CLP procedure, a crestal incision followed by a full-thickness mucoperiosteal flap was raised with the aim of exposing the anterior-lateral wall extending from the canine to the molar region. A 1.5-cm window was ground into the anterior wall. The Schneiderian membrane (SM) was incised for removal of the displaced dental implant, and the pathologic mucosa was enucleated with a surgical curette. After implant removal, the maxillary sinuses were carefully irrigated and the SM (if present) was sutured using 6–0 Vicryl® (Polyglactin 910; Johnson & Johnson, Somerville, NJ, US). In cases where there was extensive destruction of the maxillary anterior wall, a 6-hole miniplate was used for reconstruction (Fig. 3A–D).

The CLP approach to access the displaced implant and infected bone graft materials in Case 4. Preoperative intraoral view (A). After implant removal, the maxillary sinus was carefully irrigated (B). In cases of extensive destruction in the maxillary anterior wall, a 6-hole miniplate was used for reconstruction (C). Inflamed tissue, infected bone graft material, and the displaced dental implant specimen (D)

The FESS was used in cases of implant displacement in the maxillary sinus with or without paranasal sinusitis symptoms and OMU obstruction, but with no oroantral communications. The endoscopic technique included a partial uncinectomy and enlargement of the maxillary sinus ostium in a middle meatal antrostomy, allowing for easier access to the maxillary sinus and reestablishment of adequate patency to the OMU. Hemostasis was established with diathermy intraoperatively and an anterior nasal tamponade at the end of the surgery (Fig. 4A, B) [3].

Preoperative intraoral view of Case 9 for FESS (A). The removed #16i displaced dental implant specimen (B)

The MESS approach included a vestibular incision followed by the creation of a bony window 10 × 7 mm in size in the anterolateral wall of the maxillary sinus. The bony window was stabilized with a four-hole microplate and partially fixed to minimize the time required for repositioning. The bony window was then separated, and the SM was carefully incised with a scalpel (Fig. 5A–C). Several different (0º, 70º, and 90º) endoscopes were used to inspect the maxillary sinus though the incision (Fig. 6A–C). The inflamed tissue and displaced dental implants were then removed using a thin suctioning tip and/or with sinus forceps. After sinus irrigation, the SM was sutured using 6-0 Vicryl® (Polyglactin 910; Johnson & Johnson, Somerville, NJ, US.). The bony window was repositioned and stabilized using a 4-hole microplate and screws (Fig. 5A–F).

The routine MESS procedure consisted of creating a pre-fixed 10 × 7 mm bony window on the anterolateral wall of the maxillary sinus using a small round bur with a diameter of 0.5 mm, as shown in Case 5 (A). The Schneiderian membrane was incised minimally using a sharp scalpel, followed by endoscopic assessment of the inner surface of the maxillary sinus (B). To approach the implant, a firm and gentle negative suction force was applied through the sinus bony window, while visualization and illumination were obtained from the nasal meatal endoscope (C). After implant removal, the sinus was carefully irrigated with warm saline, and the Schneiderian membrane was re-sutured (D, E). The bony window was repositioned into its original position and was fixed with a four-hole miniplate and pre-drilled screws (F)

Intraoperative endoscopic images of the displaced dental implant. Endoscopic inspection though the nose and osteomeatal unit (A). Endoscopic inspection though the upper maxilla after creating a bony window (B, C)