This study has some limitations. First, the sample size was too small to establish the effectiveness of single best approach. Second, the range of maxillary sinus status between the different groups was not the same. Although further study of a large population is needed to establish definite indications and limitations of each approach, our study offers a comparison between the four approaches, showing that surgical access is comparable.
Migration of dental implant into the maxillary sinus is considered iatrogenic because it mostly happens due to lack of proper planning of the surgical procedures. Varol et al7 and Chappuis et al8 listed some causes of displacement during surgery, including less experienced surgeons, poor primary implant stability, unsuccessful bone regeneration following previous maxillary sinus floor elevation, and implantation without treatment of perforation caused by implant drilling. In particular, poor primary stability causes implant micromovement, which prevents clot formation and revascularization and makes new bone formation more difficult. All of these factors can lead to poor implant fixation and failure to obtain osseointegration, resulting in late implant displacement9,10,11.
Consequently, an implant displaced in the maxillary sinus often result in serious complications such as maxillary sinusitis, nasal obstruction, bony necrosis, foreign body aspiration, and migration into deeper sinus cavities. Therefore, a migrated implant in the maxillary sinus should be removed as early as possible to prevent further risks of worsening symptoms and uneventful sequelae12,13,14. Caldwell Luc surgical approach has been one of the most favorable classical approaches to the maxillary sinus due to its ease of access and visibility. However, several postoperative complications have been reported following a CLA, such as postoperative maxillary cysts (POMC) and a high rate of relapse of sinus symptoms, which were thought to be induced by decreased sinus volume, resulted from the inferior osteotomy15.
On the other hand, intracrestal approach is recommended by many clinicians due to the direct access, rapid recovery of sinus functions, less invasiveness, and flexibility. The crestal approach requires less bone volume removal and less surgical trauma as the bone is less dense and more trabecular than the lateral wall of the maxillary sinus16,17. However, this blind procedure may lead to unsatisfactory results when the material is entrapped in the undercut of the sinus, and often leads to undesirable postoperative depression of the alveolar ridge due to the procedure of enlarging the socket for a suction tube18.
In our study, the intracrestal approach was associated with less pain and less facial swelling compared with CLA. The approach was distant from the infraorbital nerve, the main sensory nerve in the labial gingiva and upper lip, and there were no neuropathy reported in the present study following the intracrestal approach. The Caldwell-Luc approach is the gold standard for access to the maxillary sinus for treatment of various problems, including retrieval of foreign bodies. There are some disadvantages encountered in this approach in the current research include the resulting bone defect of the lateral antral wall and injury of the mucosal branches of infraorbital nerve. Our findings related to the complications related to CLA were in accord of previous studies 19,20,21.
A more serious nerve injury reported in one case associated with upper lateral approach, the facial paresthesia involved both the oral mucosa and the skin on the lateral side of the nose. The upper lateral antrostomy was carried out at the premolar-molar region, the flap extended more superiorly to expose and remove the thick zygomatic bone using round bur might be the possible causes to injure the infra orbital nerve. The time required to remove the implant was 35 minutes and the surgery scored as difficult due to difficulty in removing the bone and this might be the possible cause of the pain and severity of the facial swelling that happened after the surgery.
The localization of the implant inside the sinus is extremely difficult due to the large size of the sinus. The average capacity of the maxillary sinus varies from 9.5 to 20 mL and averages 14.75 mL. The average dimensions are 3.75 cm vertically, 2.5 cm mediolaterally and 2.5 cm antero-posteriorly. The sinus cavity may also extend into the zygoma. Thus, a sinus can usually be filled with 10 to 20 mL of lavage saline22,23,24. Considering the position of the implant in the maxillary sinus, it is often difficult to visualize the implant. In particular, when the implant is located on the superior or posterior aspects. It usually a challenge to remove through the intracrestal or Caldwell Luc approach.
Posterior displacement of the implant is a real challenge due to accessibility. Dryer and Conrad25 reported a case regarding surgical complications related to implants in the pterygomaxillary region. In their report, the dental implant was removed with a CT-guided endoscope transnasally. In current study, two of the implants displaced into the posterior aspect of the maxillary sinus was retrieved by posterior lateral window approach. The surgery took 42 minutes as an average despite the soft bone that existed in this area which removed easily. The longer time taken to remove the implant was attributed to the bleeding from the pterygoid venous plexus. Another challenge in this approach was difficulty to locate the implant as the implant change its position according to patient position. It is worth knowing that this is the only case where the surgery done within the first 24 hours of the displacement.
Immediate or early removal of the displaced implants is indicated to prevent infectious complications due to the contact of the implant with the mucosa of the sinus interior26. However, immediate displacement of the implant deep inside the sinus after sinus lifting with unnoticeable membrane perforation render the implant free and changing positions due to non attachment status of the implant to the sinus membrane. Thus the authors recommend leaving the implant in situ for 2 weeks to allow granulation tissue encapsulation.