## 4 Discussion
The literature to date does not specifically report on the status of the region of the osteo-meatal complex (COM) and the middle meatus. Particularly, there is a lack of the following information:  
1. Alterations of the natural ostium of the maxillary sinus. 2. Presence of the accessory ostium, which could modify the physiological drainage capacity from the maxillary sinus as well as (in the case of surgical treatment) modify the approach to setting up at typical antrostomy. 3. Alteration of the middle meatus with consequent difficulty of sinus drainage due to a paradoxical curvature of the middle turbinate or its preumatization with a concha bullosa, which, in both cases, would drastically reduce the space of the middle meatus resulting in the condition of dysfunctional. The above should be taken into account and considered as further correlated risk factors for sinusitis onset after ZI positioning [35; 46; 47]. Preserving the sinus membrane is still debated, and no evidence in literature could be found to establish a strict protocol to follow for implant zygomatic surgery. However, damage of the maxillary mucosa due to a protruding implant is not the leading cause in developing sinusitis and not linked to a shorten survival rate of ZI [24; 48]. Nevertheless it may be advisable to avoid oroantral communication during zygomatic implant placement. [PERSON] et al. [14] suggested an extrasinusal procedure, in which a retained bone window is made up and used as a shield to preserve the attached sinus membrane intact before positioning the implant. Avoiding the breach of the membrane by the extrasinusal position of the ZI leads to positive results and perfect osteointegration. [PERSON] et al. in 2001 [49] explained this by the absence of mobility of these implants, avoiding irritation of the sinus mucosa and/or obstruction of the meatal complex. However, seven patients needed partial (one patient) or complete (six patients) ZI removal to relieve symptoms of sinusitis. Many factors were associated with the onset of sinusitis, from a blockage of the maxillary ostium [50] to the poor osseointegration of the implants in the posterior palatal region undermining prosthetic stability [18] or the creation of a direct link for the passage of bacteria from the oral cavity into the maxillary sinus [15]. In addition, trauma involved in the placement of zygomatic implants can cause a maxillary hemosinus which, by slowing down the epithelial and mucociliary activity in the sinus, can contribute to the onset of sinusitis [51]. In the literature reviewed there was no definite and clear evidence about the relationship between maxillary sinusitis and the technique used for ZI positioning. The great majority of surgeons seems to prefer the extrasinusal approach (765 ZIs with an extrasinusal approach compared to 107 ZIs with an intrasinusal approach), but a detailed analysis of an increase in complications in terms of sinusitis of one technique compared to the other was not possible. It emerged that there are episodes of sinusitis even in cases of extrasinusal implants placement. In this case, therefore, one possible goal might be to evaluate, both from a clinical and radiological point of view, the timing of the onset of sinusitis to assess the pathogenesis of sinusitis. It may be possible to find reactive sinusitis six months after the surgery [52] specifically related to surgical procedures. In this regard, it could be interesting to investigate, in the case of the extra-sinusal technique, where the onset of sinusitis is not immediately correlated to the surgical maneuvers, the timing of the FESS treatment. In the cases analyzed in this review, regardless of the surgical technique used the treatment of sinusitis was approached with administration of antibiotic therapy in most cases. This needs further study, since antibiotic therapy alone may resolve the acute condition but not completely resolve the pathology of the sinus. However, no univocal treatment protocol emerged.