The first thing to look at is the density of the sinus. A normal sinus will appear as a low-density homogenous cavity.

The maxillary sinus communicates with the homolateral nasal fossa by means of a natural ostium located posterosuperiorly on the medial surface (Fig. 3.2).

Determining the position and the integrity of the osteomeatal complex is essential when planning SFE procedures.

The mesiobuccal and medial bone walls are the ones most often involved in SFE. An accessory ostium may sometimes be found on the medial wall. When this occurs, it should be identified before any maxillary sinus-elevation procedure is performed, to avoid detaching the mucosa up to this point.

Unfortunately, a small “field of view” (FOV) is often used to visualize only the inferior part of the maxillary sinus and its relation to the remaining bone where implants will be placed. Guidelines suggest that extending the FOV to include the osteomeatal complex may be justified to avoid postoperative complications resulting from a compromised drainage system (Harris et al. 2012). An adequate FOV in CBCT technique should allow precise evaluation of its numerous components, revealing any irregularities in development (e.g., conchae bullosa, septum deviation, or inflammation involving the maxillary sinus ostium) (Fig. 3.2). Respecting the structure of the ostium is essential for a successful SFE.

Septa (Fig. 3.3) are the most frequent anatomic variations within the maxillary sinus. They were first described by Underwood in 1910 and, therefore, have sometimes been referred to as Underwood’s septa (Underwood 1910).

It has been reported that they increase the risk of sinus membrane perforation during SFE. If septa are present on the sinus floor, they can complicate both the inversion of the bone plate and elevation of the sinus membrane. One of the possible complications associated with perforation of the sinus membrane is the development of maxillary sinusitis (Quiney et al. 1990; Ueda and Kaneda 1992; Zimbler et al. 1998).

If septa are encountered on the antral floor, some authors recommend cutting them with a narrow chisel and removing them with a hemostat, so the bone graft can be placed over the entire antral floor without interruption (Boyne and James 1980). Therefore, a modification of the conventional surgical technique is required when septa are present (Betts and Miloro 1994).

Tables 3.3 and 3.4 propose some clinical recommendations related to the height of vertical and horizontal sinus septa.

Three arteries supply blood to the maxillary sinus: the infraorbital artery, the posterior lateral nasal artery, and the posterior superior alveolar artery (PSAA). While their presence should be investigated to avoid hemorrhages during SFE, severe hemorrhages tend to be rare, as the main arteries do not run inside the surgical area.

The progressive atrophy of the alveolar ridge with age and tooth loss results in changes in the blood supply to that area. The maxilla is very densely vascularized in young, dentate individuals. In older, edentulous populations, the number of vessels and vessel diameter decreases, while the tortuosity of the vessels increases (Elian et al. 2005; Ulm et al. 1995; Watzek et al. 1993).

To confirm the radiographic presence of the canal, one must examine the axial and coronal images. In coronal views, the PSAA appears as a circular or oval low-density structure that is fully or partially embedded within the thickness of the lateral wall of the maxillary sinus. It has to be seen along the sinus border while scrolling the axial views (Noujeim et al. 2014).

The radiographic location can be divided in three categories (Fig. 3.4):

The canal can radiographically be identified in over 50 % of examined CT images, equally between the right and left side. The canal is between 1 and 2 cm superior to the alveolar crest (average height = 16.4 mm) (Noujeim et al. 2014). Different studies achieve almost the same results (Elian et al. 2005; Ilgüy et al. 2013).

Table 3.5 proposes recommendations based on some parameters of PSAA.

The Schneiderian (mucous) membrane lines the inner walls of the sinus and in turn is covered by pseudo-stratified columnar ciliated epithelium. Serum-mucosa glands are located in the lamina directly underneath, especially next to the ostium opening. The sinus membrane appears to be the main carrier of bone reformation after SFE, as multiple experimental studies suggested (Troedhan et al. 2012).

Normally, the thickness of the Schneiderian membrane varies from 0.13 to 0.5 mm (Tiziano 2012). However, inflammation or allergic phenomena may cause its thickening, either generally or locally (Fig. 3.5). In such cases, it may be necessary for an ENT to restore the sinus to a physiologic state before SFE can be carried out (see Chap. 4).

Mucosal thickening is the most frequently observed abnormality (66.0 %). It is generally associated with some kind of irritation, such as odontogenic pathology or allergic phenomena. Nonvital posterior maxillary teeth, periodontal abscesses, retained roots, embedded or impacted teeth, extensively carious teeth, and oroantral fistulae could be etiological factors in pathologies of odontogenic origin (Rege et al. 2012).

During osteotomy, the membrane should not be perforated:

Table 3.6 shows the influence of the sinus membrane thickness on SFE.