Although the use of oral implants in the oral rehabilitation of edentulous patients is widely accepted, serious medical complications related to implant surgery are a social problem [1]. The serious complications include intra- or postoperative bleeding, hematoma formation, varying degrees of neurosensory alteration, maxillary sinusitis, displacement/migration of the implant into the maxillary sinus, and so on [2,3,4]. Although the number of complications after implant surgery in the edentulous jaw is decreasing in Japan, maxillary-sinus-related complications (MSRCs) (both maxillary sinusitis and displacement or migration of the implant into the maxillary sinus) have remained the highest after implant surgery since 2012 (Figure 1) [5,6,7]. The approach for the latter is thought to be relatively easy when the surgeon uses functional endoscopic sinus surgery (FESS) and/or an oral approach (OA) technique [4]. Therefore, ear, nose, and throat (ENT) specialists and dentists should take particular care to prevent maxillary sinusitis after implant surgery.

The possible causes of chronic maxillary sinusitis after dental implantation caused by surgeons include sinus penetration by the implant (Figure 2), perforation of the Schneiderian membrane during the sinus lift, and so on [3]. However, maxillary sinusitis rarely occurs after sinus penetration by implant or perforation of the Schneiderian membrane during a sinus lift, because the implant body or bone graft is sterilized and clean [8]. Therefore, it is not clear whether sinus penetration by the implant or perforation of the Schneiderian membrane during a sinus lift is a possible factor predisposing the patient to maxillary sinusitis after dental implantation.

In order to prevent this complication, we need to identify possible causal factors prior to implant surgery and eliminate these factors before surgery. In this study, we highlight the main possible causal and risk factors for postoperative complications after implant surgery with or without sinus augmentation of the maxilla molar region to achieve optimal treatment outcomes and reduce complications. In particular, we need to keep in mind anatomical variations, which can cause the impairment of maxillary sinus drainage, in addition to maxillary sinus pathologies. Furthermore, we propose a new paradigm for personalized medicine for patients with a maxillary edentulous jaw through ENT and dentist cooperation.

The common maxillary sinus pathologies that can be identified on coronal CT images of the paranasal sinus at our institution are shown in Figure 5. These pathologies are classified into three pathologies: those that need treatment, those that do not need treatment, and those that are not candidates for maxillary implantation. A normal maxillary sinus, retention cyst or solitary polyp, and mucosal thickening in the maxillary sinus do not need treatment before maxillary implantation (Figure 5A–C), whereas preoperative sinusitis needs treatment because it is a cause of the development of postoperative maxillary sinusitis (Figure 5D–F) [17]. Patients with a postoperative maxillary cyst also need treatment (Figure 5G). Patients with eosinophilic chronic rhinosinusitis are not suitable for maxillary implantation (Figure 5H).

As shown in Section 3 [20,21,29], previous personalized medicine for patients with a maxillary edentulous jaw by ENT specialist and dentist cooperation was selected according to the maxillary sinus pathologies. Some clinicians pointed out that some anatomic variants such as Haller cells, a deviated nasal septum, concha bullosa, and paradoxical curvature can be risk factors of maxillary sinusitis after maxillary implantation, even if the maxillary sinus is normal before the maxillary implantation [14,15]. Therefore, when these anatomical risk factors are discovered before maxillary implantation, conservative or surgical prevention is recommended [30]. However, when personalized medicine is chosen according to maxillary sinus pathologies, we have serious concerns about the possibility of overlooking high-risk patients with such anatomic variants whose maxillary sinus is normal, as shown in Figure 4 and Figure 5A. Rhinosinusitis tends to result from any anatomic variations that can cause stenosis of maxillary drainage pathways [11,12,13]. Therefore, personalized medicine for patients with a maxillary edentulous jaw by ENT and dentist cooperation should be chosen according to both anatomical variations and maxillary sinus pathologies. Here, we propose an evaluation and management protocol based on sinonasal CT findings (Figure 6). When there is a normal lesion, small retention cyst, small solitary polyp, or mucosal thickening that is less than one-third to one-half of the maxillary sinus height in the maxillary sinus, the patients can receive a maxillary implant with or without revision of the anatomical variations. Patients with acute and/or chronic rhinosinusitis, benign tumor, or POMC can receive a maxillary implant with or without revision of the anatomical variations after recovery from these illnesses. Patients with refractory disorders such as ECRS and malignant tumors are not suitable for maxillary implantation with sinus elevation; as an alternative, other prostheses such as dentures, implant-supported overdentures, and the sinus slot technique may be candidates as an alternative method [31]. Under this new paradigm, there is no patient with chronic rhinosinusitis who might need FESS after maxillary implantation at our institution (unpublished data).

This study has some limitations. The first limitation is the small number of participants under this new paradigm at our institution. The number is less than the eighty-four that was previously reported by Chen et al. [21]. We think the reason for this is that the number of patients planning to attend the dental clinic in order to receive maxillary implantation has decreased during the COVID-19 pandemic. The second limitation is deficient comparison with the traditional paradigm. Therefore, we are conducting further research into whether the clinical outcome under this new proposal is superior to that under the traditional paradigm by increasing the number of participants under this new paradigm.

Before the COVID-19 pandemic, ENT specialists tended to use both nasal endoscopy and sinonasal CT for these anatomic variations [12,21,30]. However, during the COVID-19 pandemic, it was recommended that nasal endoscopy not be used except in emergencies, because a nasal endoscopy examination may carry the risk of possible droplet infection [32]. Therefore, we recommend that ENT specialists evaluate both anatomic variations and maxillary pathologies using paranasal CT during the COVID-19 pandemic because paranasal CT findings correspond to those of a nasal endoscopy [13]. Promising alternative diagnostic evaluations for pathologies in the maxillary sinus are low-dose cone-beam CT and dental magnetic resonance imaging (MRI) using the black-bone MRI sequence [33,34]. Because anatomic variations that can cause stenosis of maxillary drainage pathways in addition to maxillary sinus pathologies should be evaluated, the imaging range should involve the natural ostium of the maxillary sinus.

ENT specialists do not recommend treatment for mucosal thickening less than one-third to one-half of the maxillary sinus height [20,21]. However, some dentists reported that mucosal thickening of more than 5 mm is associated with an increased risk of sinus outflow obstruction [35,36]. Carmeli et al. reported that mucosal thickening of <5 (11.1%), <10 (36.2%), and >10 mm (74.3%) was associated with the obstruction of the maxillary natural ostium (p < 0.0001) [35]. Shanbhag et al. found that the obstruction was associated with mucosal thickening of 2–5 (6.7%), 5–10 (24%), and >10 mm (35.3%, p < 0.001) [36]. Therefore, there are many cases in which the natural ostium is patent even when mucosal thickening is greater than 5 mm. We think that mucosal thickening greater than 5 mm does not matter when the natural ostium is patent because the ventilation and drainage of the maxillary sinus are performed through the natural ostium [30]. Dentists should pay attention to the status of the natural ostium. Patients with ECRS have a contraindication for maxillary implantation even if mucosal thickening is less than 5 mm. Therefore, we should judge whether patients are suitable for maxillary implantation according not only to mucosal thickening, but also to the patency of the natural ostium.

We showed that aberrant anatomical factors are predisposing risk factors for postoperative complications of the maxillary sinus. The paradigm for personalized medicine for patients with a maxillary edentulous jaw by ENT specialist and dentist cooperation is shifting from the assessment of maxillary sinus pathologies alone to including the assessment of anatomic variations, which can cause the impairment of maxillary sinus drainage in addition to maxillary sinus pathologies. Precise risk assessments are required, and further work is essential to verify whether the clinical outcome under this new proposal is superior to that under the traditional paradigm in order to provide more clinical relevance to this new proposal.

We thank all the members of the Department of Oral Radiology and Diagnosis, Ohu University School of Dentistry, Koriyama, Japan, for their support.

Conceptualization, Y.B. and K.T.; writing—original draft preparation, Y.B. and K.T.; writing—review and editing, Y.B., Y.K. and K.T. All authors have read and agreed to the published version of the manuscript.

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The authors declare no conflict of interest.

This research received no external funding.