## 1 Introduction  
Implant-based dental rehabilitation can be achieved with multiple approaches. The use of conventional implants requires adequate bone height and width in patients. In patients with severe atrophic maxilla (classes V e VI according to the Cavood-Howell classification of edentulous jaw) conventional rehabilitation is not a viable option. In this scenario, [PERSON] et al. [1] proposed positioning zygomatic implants (ZIs) as a reliable technique for maxillary rehabilitation using the resistant zygomatic bone as an anatomical site for anchoring [2]. Various other alternatives are commonly employed in maxillary atrophy, such as sinus floor elevation for bone grafting, free re-vascularized flaps, Le Fort I osteotomy and bone grafts from the iliac crest or other sites [3, 4, 5].  
Different techniques have been proposed for ZI placement, and many authors have contributed to improve and modify [PERSON]'s initial technical proposal [6] in which ZIs were placed within an intrasinusal pathway using a sinus window to elevate and preserve the sinus membrane. Nowadays, the zygomatic anatomy guided approach (ZAGA) proposed by [PERSON] [7] is gaining greater success, in which the surgical technique is customized to the patient's anatomy in relationship to the maxillary sinus. The extrasinusal approach involves placing the implants outside the maxillary sinus without compromising the Schneider's membrane, while the sinus slot technique proposed by [PERSON] et al.  
in 2000 [8] is a technique involving consideration of extrasinusal and intrasinusal positioning [6]. Nowadays, the most used protocol for the edentulous maxilla involves the placement of two zygomatic implants in the premalor area and two to four conventional dental implants in the premaxilla area to provide additional support for a full-arch maxillary prosthesis [9]. Furthermore, the QUAD-ZYGOMA technique describes the use of four ZIs (two for each side) in cases where the premaxilla does not allow the placement of conventional implants [10].  
Regardless of the surgical technique, successful outcomes have been demonstrated. [PERSON] et al. in 2016 showed a cumulative survival rate of 95% at 12 years, with most failures occurring in the first 6 months after surgery [11]. Generally, the level of patient satisfaction was excellent as reported by [PERSON] and colleagues in 2012 [12].  
Even though prosthetic failure is infrequent, ZIs are not free of complications. Maximly sinusitis is reported to be the most common [13; 14; 15] and, together with intraoral soft-tissue infection [2; 7; 15], chronic pain, nerve deficits [13; 16; 17] and oro-antral fistula [18; 19], may reduce implant survival and undermine patient's quality of life.  
While many studies have focused on long-term implant stability, less importance has been dedicated to describing how ZIs can affect maxillary sinuses [20], as well as the management and/or prevention of sinusitis.  
To date, maxillary sinusitis is known to be the most frequent complication after placement of zygomatic implants. However, there are no studies in the literature that focus only on this complication and highlight the modalities of onset, diagnosis, and the principles of treatment. The purpose of this study is to review the literature to assist the surgeon in managing the possible occurrence of post-operative maxillary sinusitis after zygomatic implant placement.